During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing cap...During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.展开更多
Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooli...Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooling towers(NDDCTs),in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2(a two-way coupled Eulerian-Lagrangian approach).The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry.Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s,which is the most frequent wind speed.The results have shown that:(1)The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a vary-ing degree of success.In one case,the heat rejection rate can be increased by 35.2%,and the tower outlet water temperature can be decreased by 2.1℃ when compared with the no spray case;(2)To improve the thermal per-formance of the NDDCT using a small amount of water,the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.展开更多
In this paper,the influence of thermal performance of cathode-heater assembly of Traveling Wave Tube(TWT),which has different contact form between inner heat shield and supporting cylinder,is analyzed using the simula...In this paper,the influence of thermal performance of cathode-heater assembly of Traveling Wave Tube(TWT),which has different contact form between inner heat shield and supporting cylinder,is analyzed using the simulation software ANSYS.With both thermal radiation and heat conduction are considered,the temperature and heat flux distribution of structures with different contact form are calculated,and also starting time which is needed before temperature come into steady status.The result of analysis suggests that changing the contact form between inner heat shield and support cylinder can influence the thermal performance of cathode-heater assembly and improve assembly's temperature distribution and promote heater's heating efficiency.The result of this paper provides theoretical guidance in the design of cathode-heater assembly.展开更多
In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enha...In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enhancement by using selfrotating twisted tapes(SRTTs)and Al_(2)O_(3) nanoparticles.The effect of the selfrotating twisted tapes and Al2O3 nanoparticles on the thermal performance was comprehensively investigated in a circular pipe.The experimental results indicated the heat transfer rate was effectively improved by SRTTs in comparison of plain tube.In addition,the heat transfer multiplier with SRTTs decreased from 1.38 to 1.08 with the Reynolds number increasing from 19,322 to 64,407,while the friction factor multiplier decreased from 1.61 to 1.32.Besides,the results indicated that the employment of Al_(2)O_(3) nanoparticles and SRTTs demonstrated superior thermal performance to the single SRTTs.As Reynolds number increases from 19,322 to 64,407,the heat transfer multiplier decreased from 2.08 to 1.18 in the mass concentration of 3.0%and from 1.38 to 1.08 in mass concentration of 0.0%.Finally,the new heat transfer and friction factor correlations considering the combined effect of Al2O3 nanoparticle and SRTTs were developed within 10%deviation of experimental values.展开更多
The investigation of local thermal transport rate in the nanolubricants is significant.These lubricants are broadly used in environmental pollution,mechanical engineering and in the paint industry due to high thermal ...The investigation of local thermal transport rate in the nanolubricants is significant.These lubricants are broadly used in environmental pollution,mechanical engineering and in the paint industry due to high thermal performance rate.Therefore,thermal transport in ZnO-SAE50 nanolubricant under the impacts of heat generation/absorption is conducted.The colloidal suspension is flowing between parallel stretching disks in which the lower disk is positioned at z=0 and upper disk apart from distance d.The problem is transformed in dimensionless version via described similarity transforms.In the next stage,an analytical technique(VPM)is implemented for the solution purpose.The graphical results against multiple flow parameters were furnished over the region of interest and explained comprehensively.It is imperative to mention that the results are plotted for ZnO-SAE50 and conventional liquid as well.Further,rapid motion of the fluid is perceived against high Reynolds andγparameters.The wall shear stresses at the upper end rises for multiple Reynolds andγwhile;decrement is detected at the lower end.The significant contribution of an internal heat source is noted for thermal performance rate at the upper end.Foremost,the local heat transport rate declines at the lower disk.By altering Reynolds number,prompt heat transfer rate is gained at the upper disk and increasing behavior of the local heat transport rate is slow at the lower disk.From the study,it is concluded that the nanolubricants have high thermal characteristics.Therefore,such fluids are reliable to use in above stated areas.展开更多
This paper investigates the thermal performance of prefabricated exterior walls using the Computational Fluid Dynamics method to reduce energy consumption.The thermal performance of the prefabricated exterior wall was...This paper investigates the thermal performance of prefabricated exterior walls using the Computational Fluid Dynamics method to reduce energy consumption.The thermal performance of the prefabricated exterior wall was numerically simulated using the software ANSYS Fluent.The composite wall containing the cavity is taken as the research object in this paper after analysis.The simulation suggests that when the cavity thickness is 20 mm and 30 mm,the heat transfer coefficient of the air-sandwich wall is 1.3 and 1.29,respectively.Therefore,the optimal width of the cavity is 20 mm,and the most suitable material is the aerated concrete block.In addition,a comparative analysis is conducted on the cavity temperature in the wall under different conditions.It is proven that an intelligent environment control system can significantly improve thermal efficiency and provide a solid theoretical basis for further research in the external insulation of prefabricated buildings.展开更多
This study proposes three possible keel-surface layer combinations to implement a new type of thermally insulating decorative wall system.A set of 8 samples has been studied.In particular,through theoretical calculati...This study proposes three possible keel-surface layer combinations to implement a new type of thermally insulating decorative wall system.A set of 8 samples has been studied.In particular,through theoretical calculations,simulations,and experimental verification,the influence of different types of connecting structures on the overall thermal performance of the wall system has been determined.It has been found that a proper combination of these elements can meet existing energy-saving standards and effectively reduce the energy loss caused by thermal bridges due to the installation of steel keels at the edges of integrated wall panels.展开更多
Thermal transport investigation in colloidal suspensions is taking a significant research direction.The applications of these fluids are found in various industries,engineering,aerodynamics,mechanical engineering and ...Thermal transport investigation in colloidal suspensions is taking a significant research direction.The applications of these fluids are found in various industries,engineering,aerodynamics,mechanical engineering and medical sciences etc.A huge amount of thermal transport is essential in the operation of various industrial production processes.It is a fact that conventional liquids have lower thermal transport characteristics as compared to colloidal suspensions.The colloidal suspensions have high thermal performance due to the thermophysical attributes of the nanoparticles and the host liquid.Therefore,researchers focused on the analysis of the heat transport in nanofluids under diverse circumstances.As such,the colloidal analysis of H_(2)O composed byγAl_(2)O_(3)and Al_(2)O_(3)is conducted over an elastic cylinder.The governing flow models ofγAl_(2)O_(3)/H_(2)O and Al_(2)O_(3)/H_(2)O is reduced in the dimensionless form by adopting the described similarity transforms.The colloidal models are handled by implementing the suitable numerical technique and provided the results for the velocity,temperature and local thermal performance rate against the multiple flow parameters.From the presented results,it is shown that the velocity of Al_(2)O_(3)–H_(2)O increases promptly against a high Reynolds number and it decreases for high-volume fraction.The significant contribution of the volumetric fraction is examined for thermal enhancement of nanofluids.The temperature of Al_(2)O_(3)–H_(2)O andγAl_(2)O_(3)–H_(2)O significantly increases against a higherϕ.Most importantly,the analysis shows thatγAl_(2)O_(3)–H_(2)O has a high local thermal performance rate compared to Al_(2)O_(3)–H_(2)O.Therefore,it is concluded thatγAl_(2)O_(3)–H_(2)O is a better heat transfer fluid and is suitable for industrial and technological uses.展开更多
The investigation of Thermal performance in nanofluids and hybrid nanofluids over a curved stretching infinite region strengthens its roots in engineering and industry.Therefore,the comparative thermal analysis in SiO...The investigation of Thermal performance in nanofluids and hybrid nanofluids over a curved stretching infinite region strengthens its roots in engineering and industry.Therefore,the comparative thermal analysis in SiO_(2)–H_(2)O and(MoS_(2)–SiO_(2))–H_(2)O is conducted over curved stretching surface.The model is reduced in the dimensional version via similarity transformation and then treated numerically.The velocity and thermal behavior for both the fluids is decorated against the preeminent parameters.From the analysis,it is examined that the motion of under consideration fluids declines against Fr and.The thermal performance enhances for higher volumetric fraction and.Further,it is noticed that thermal performance prevailed in(MoS_(2)–SiO_(2))–H_(2)O throughout the analysis.Therefore,(MoS_(2)–SiO_(2))–H_(2)O is better for industrial and engineering uses where high heat transfer is required to accomplished different processes of production.展开更多
The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumptio...The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumption,heat pipes can be widely used for heat dissipation of electronic components.This paper reports an experimental thermal analysis of different capillary structures for heat pipes.The wicks considered are metal screens,axial microgrooves,and sintered metal powder.The heat pipes are made of copper,a 200 mm length tube and a 9.45 mm external diameter.Working fluid used was distilled water.The devices are investigated in three positions:0,90,and 270°to the horizontal under powers of 5 up to 45 W.The results show that in horizontal(0°)and with the evaporator under the condenser(270°),the heat pipes showed similar results.Nevertheless,in the reverse condition(the position against the gravity with the evaporator above the condenser,90°),the heat pipe with sintered wick presented the best thermal performance,as it has the lowest thermal resistance and supported a higher power.Besides that,the sintered powder capillary structure demonstrates the most homogeneous thermal behavior for every position,making the most suitable for applications susceptible to diverse inclinations.展开更多
The thermal performance of three roofing models: tile, corrugated and earth terrace is numerically analyzed. The mathematical equations which govern the three roofing models are established by the electrical method of...The thermal performance of three roofing models: tile, corrugated and earth terrace is numerically analyzed. The mathematical equations which govern the three roofing models are established by the electrical method of analogies. These equations are discretized by an implicit finite difference method and solved by the Gauss-Seidel algorithm. We analyze the influences of geometric parameters (Xlo, Xlarg, <i><span style="font-family:Verdana;">α</span></i><span style="font-family:Verdana;"> and Ep) on the evolution of the temperatures of the </span><span style="font-family:Verdana;">different environments of our three roof models. In particular, we have</span><span style="font-family:Verdana;"> shown that the effectiveness of a roof in reducing the temperature inside a room is linked to its physical properties. The results obtained that for the same geometric parameters, the earth roof terrace and the earth tile roof compared to the corrugated metal roof improve thermal comfort by lowering the interior temperature of 5<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">º</span>C and 4.6<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">º</span>C.</span>展开更多
In this work,the thermal behavior of fin made of palladium material under the influences of thermal radiation and internal heat generation is investigated.The thermal model for the extended surface made of palladium a...In this work,the thermal behavior of fin made of palladium material under the influences of thermal radiation and internal heat generation is investigated.The thermal model for the extended surface made of palladium as the fin material is first developed and solved numerically using finite difference method.The influences of the thermal model parameters on the heat transfer behaviour of the extended surface are investigated.The results show that the rate of heat transfer through the fin and the thermal efficiency of the fin increase as the thermal conductivity of the fin material increases.This shows that fin is more efficient and effective for a larger value of thermal conductivity.However,the thermal conductivity of the fin with palladium material is low and constant at the value of approximately 75 W/mK in a wider temperature range of-100℃and 227℃.Also,it is shown that the thermal efficiencies of potential materials(except for stainless steel and brass)for fins decrease as the fin temperatures increase.This is because the thermal conductivities of most of the materials used for fins decreases as temperature increases.However,keeping other fin properties and the external conditions constant,the thermal efficiency of the palladium is constant as the temperature of the fin increases within the temperature range of-100℃and 227℃.And outside the given range of temperature,the thermal conductivity of the material increases which increases the efficiency of the fin.The study will assist in the selection of proper material for the fin and in the design of passive heat enhancement devices under different applications and conditions.展开更多
Riyadh city is the fastest growing city in Saudi Arabia. The rapid urban growth that happened recently in Riyadh was not based on the traditional urban planning principles, which have been established and applied for ...Riyadh city is the fastest growing city in Saudi Arabia. The rapid urban growth that happened recently in Riyadh was not based on the traditional urban planning principles, which have been established and applied for the city development process. The imported building regulations have created a new urban structures and street patterns. The contemporary urban form in Riyadh city is based mainly on traffic and economic consideration with the neglect of environmental dimensions. This research aims to examine the impacts of building regulations on the thermal performance of residential buildings in Riyadh city, with the ultimate goal of establishing planning guidelines that consider the environmental conditions of the city. The methodology adopted for achieving the aim of this study consists of two phases. First, the literature related to building regulations development in Riyadh, as of 2018, was reviewed. Second, buildings energy simulation was conducted to examine the thermal performance of the typical current status of residential building blocks in Riyadh city, and then several changes to building regulations were made to investigate their impacts on the thermal performance of buildings. The results showed that the impacts of Riyadh building regulations on the thermal performance of residential buildings differ across the evaluated cases. The ratio of building height to street width, urban block street orientation, and building orientation are the main factors affecting thermal performance of buildings within urban block. The study also concludes that adjusting the ratio of building height to the distance between buildings could have a significant impact in reducing cooling loads. This study will help policy makers, planners and designers to investigate the shortcoming in the current building regulations.展开更多
In this study,the impacts of internal heat generation on heat transfer enhancement of porous fin is theoretical investigated using differential transform method.The parametric studies reveal that porosity enhances the...In this study,the impacts of internal heat generation on heat transfer enhancement of porous fin is theoretical investigated using differential transform method.The parametric studies reveal that porosity enhances the fin heat dissipating capacity but the internal heat generation decreases the heat enhancement capacity of extended surface.Also,it is established that when the internal heat parameter increases to some certain values,some negative effects are recorded where the fin stores heat rather than dissipating it.This scenario defeats the prime purpose of the cooling fin.Additionally,it is established in the present study that the limiting value of porosity parameter for thermal stability for the passive device increases as internal heat parameter increases.This shows that although the internal heat parameter can help assist higher range and value of thermal stability of the fin,it produces negative effect which greatly defeats the ultimate purpose of the fin.The results in the work will help in fin design for industrial applications where internal heat generation is involved.展开更多
Brazil has a great climatic diversity,with different demands for the adequate thermal performance of buildings,where the variables that impact it have different influences depending on the location and the type of wra...Brazil has a great climatic diversity,with different demands for the adequate thermal performance of buildings,where the variables that impact it have different influences depending on the location and the type of wrapping used.When a prior study of the thermal performance of a building is not done in the design phase,the unpleasant effects for the user appear after the building is ready,and bring with them problems such as internal temperatures that are too high in the summer or too low in the winter.Therefore,the objective of this study is to provide recommendations for the application of ACM(aluminum composite material)composite panels and thermoacoustic(sandwich)tiles for external enclosure in the single-family residential sector.A high standard two-story residence with approximately 162 m^(2)per floor is used as a model and through computer simulations,utilizing the Energyplus program and observing the requirements of the NBR 15.575 performance standard,the thermal performance is evaluated.The factorial experiment was applied encompassing thermal performance variables such as absorptance,natural ventilation and thermophysical properties of the wrapping for three different climatic conditions:extreme winter climate,average climate and extreme summer climate.The results obtained show that the thermoacoustic roof tile keeps the internal temperature more stable independent of external oscillations,while the ACM panels follow the external oscillations,not meeting the expectations of thermal performance and needing passive treatments.展开更多
We present in this paper the results of experimental and numerical study of the thermal performances of a cook stove prototype intended for the parboiling of paddy rice. Thus, the experimental results show that the op...We present in this paper the results of experimental and numerical study of the thermal performances of a cook stove prototype intended for the parboiling of paddy rice. Thus, the experimental results show that the optimal mass of husk rice is M = 7.15 kg for a good combustion within the combustion chamber and got a maximum temperature at the level of the burners surface. This temperature is T<sub>cu1</sub>=304.78°C. The circulating air flow rate by forced convection is Q<sub>m</sub> = 0.09112 m<sup>-3</sup>·s<sup>-1</sup>. The vertical side walls temperature is T<sub>ple</sub> = 140.6°C and the water temperature and vapor is about 144.6°C in the stockpot. The gas combustion is composed of carbon dioxide (CO<sub>2</sub>), carbon monoxide (CO), methane (CH<sub>4</sub>) and the ratio of hydrogen to nitrogen (H<sub>2</sub>/N<sub>2</sub>). The results from the numerical modeling indicate T<sub>cu1</sub>=307.8°C, T<sub>ple</sub> = 144.55°C and a Q<sub>m</sub> = 0.09258 m<sup>-3</sup>.s<sup>-1</sup>. The average thermal efficiency of the cookstove is η = 46.6% and the power developed by the cookstove is about ≈6 kW. Despite the heat losses, the cookstove remains interesting for paddy rice parboiling activities.展开更多
The thermal properties of Light Emitting Diode (LED) products have a significant impact on their longevity and overall performance. Products which are unable to adequately dissipate heat degrade, shortening the projec...The thermal properties of Light Emitting Diode (LED) products have a significant impact on their longevity and overall performance. Products which are unable to adequately dissipate heat degrade, shortening the projected lifespan. A testing apparatus has been constructed to characterize the thermal behavior of MR-16 LED products. This paper documents the testing setup and measurement results for 9 separate products, and identifies product characteristics which demonstrate higher success at heat dissipation. The thermal performance was quantified using experimental data and heat transfer models. Calculations to quantify the magnitude of heat transferred through radiation and convection in each LED product were performed. Results indicate some of the products are better optimized to enhance convection heat transfer.展开更多
Energy efficiency issues are being focused on the growing concern of global warming and environmental pollution.The high-temperature heat pipe(HTHP) is an effective and environmental-friendly heat transfer device empl...Energy efficiency issues are being focused on the growing concern of global warming and environmental pollution.The high-temperature heat pipe(HTHP) is an effective and environmental-friendly heat transfer device employed in many industries,including solar power generation,high-temperature flue gas waste heat recovery,industrial furnaces,nuclear industries,and aviation.As a critical factor in HTHPs,thermal performance is mainly introduced in the entire paper.To date,most reviews have been published concerning one or several application scenarios.However,to the best of authors' knowledge,it is hard to find a review discussing how to improve the thermal performance of HTHPs comprehensively.First,the impact on the performance of three main components of HTHPs over the past 30 years is introduced:the working fluid,the HTHP structure,and the wick structure.Herein,it is a considerable review of the optimal operating conditions for each direction,and we expect this paper contribute to improving the thermal performance of HTHPs.Then,current numerical simulations and theoretical research on the heat transfer limit of HTHPs are recommended.The significant hypotheses used in numerical simulations and the present theoretical studies are compiled here.Finally,some potential future directions and tentative suggestions for HTHP research are put forward.展开更多
Phase change material(PCM)applied to roofs can weak external heat entering the room to reduce air-conditioning energy consumption.In this study,three forms of macro-encapsulated PCM roofs with different PCMs(RT27,RT31...Phase change material(PCM)applied to roofs can weak external heat entering the room to reduce air-conditioning energy consumption.In this study,three forms of macro-encapsulated PCM roofs with different PCMs(RT27,RT31,RT35HC,PT37)are proposed.The effects of PCM thickness,the encapsulation forms,and different PCMs on the thermal performance of the roof are discussed in Moroccan semi-arid and Mediterranean climates.The results show that as the PCM thickness increases,the peak temperature attenuation of the roof inner surface decreases.In two climates,the pure PCM layer among the three encapsulation forms(i.e.pure PCM layer,PCM in aluminum tubes,PCM in triangular aluminum)is the easiest to appear the phenomenon of insufficient heat storage and release,while the reduction of the peak inner surface temperature and time lag is the most satisfying.For the PCM in the aluminum tube,phase change time is the shortest and the latent heat utilization ratio is the highest,while thermal regulation performance is the least satisfying.The PCM in triangular aluminum can improve the latent heat utilization ratio significantly,and its thermal regulation performance is in the middle.In semi-arid climate,the time lag increases with phase change temperature increasing.The time lag could reach up to 6 h with 37℃phase transition temperature.In Mediterranean climate,the longest time lag with RT31 is 5 h,while the lowest peak inner surface temperature appears with RT27.The obtained conclusions could provide guidance for the application of PCM roofs in these two climates.展开更多
Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions.Shallow geothermal ventilation(SGV)system,with a little initial in-v...Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions.Shallow geothermal ventilation(SGV)system,with a little initial in-vestment cost,is one of promising technologies to partly replace the conventional air-conditioning system for air pre-cooling/pre-heating.This paper reviews applications of SGV system for improving thermal performance over latest two decades,which mainly includes the reclassification of SGV system,coupling with other advanced energy-saving technologies,application potentials for building cooling/heating under various weather conditions.Heat transfer mechanism and mathematical modelling techniques have been reviewed,together with in-depth analysis on current research trends,existing limitations,and recommendations of SGV system.Phase change materials,with considerable latent energy density,can stabilize the thermal performance with high reliability.The review identifies that optimization designs and advanced approaches need to be investigated to address the existing urgent issues of SGV system(e.g.,large land occupation,difficulty in centralized collection of condensate water timely for horizontal buried pipe,bacteria growth,polluted supply air,and high construction cost for ver-tical buried pipe).A plenty of studies show that the SGV system could greatly expand the application scope and improve system energy efficiency by combining with other energy-saving technologies.This paper will provide some guidelines for the scientific researchers and engineers to keep track on recent advancements and research trends of SGV system for the building thermal performance enhancement and pave path for future research works.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42071095)the Program of the State Key Laboratory of Frozen Soil Engineering(Grant No.SKLFSE-ZQ-59)+1 种基金the Science and Technology Project of Gansu Province(Grant No.22JR5RA086)the Science and Technology Research and Development Program of the Qinghai-Tibet Group Corporation(Grant No.QZ2022-G02).
文摘During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.
基金supported by the Shandong Provincial Science and Technology SMEs Innovation Capacity Improvement Project(2022TSGC2018)the Shandong Natural Science Foundation(Grant No.ZR2022ME008)+3 种基金the Shenzhen Science and Technology Program(KCXFZ20201221173409026)the“Young Scholars Program of Shandong University”(YSPSDU,No.2018WLJH73)the Open Project of State Key Laboratory of Clean Energy Utilization,Zhejiang University(Program Number ZJUCEU2020011)the Shandong Natural Science Foundation(Grant No.ZR2021ME118).
文摘Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooling towers(NDDCTs),in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2(a two-way coupled Eulerian-Lagrangian approach).The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry.Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s,which is the most frequent wind speed.The results have shown that:(1)The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a vary-ing degree of success.In one case,the heat rejection rate can be increased by 35.2%,and the tower outlet water temperature can be decreased by 2.1℃ when compared with the no spray case;(2)To improve the thermal per-formance of the NDDCT using a small amount of water,the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.
文摘In this paper,the influence of thermal performance of cathode-heater assembly of Traveling Wave Tube(TWT),which has different contact form between inner heat shield and supporting cylinder,is analyzed using the simulation software ANSYS.With both thermal radiation and heat conduction are considered,the temperature and heat flux distribution of structures with different contact form are calculated,and also starting time which is needed before temperature come into steady status.The result of analysis suggests that changing the contact form between inner heat shield and support cylinder can influence the thermal performance of cathode-heater assembly and improve assembly's temperature distribution and promote heater's heating efficiency.The result of this paper provides theoretical guidance in the design of cathode-heater assembly.
文摘In view of the practical importance of the heat transfer devices in various thermal engineering fields including chemical and nuclear engineering,this study aims at developing an effective method of heat transfer enhancement by using selfrotating twisted tapes(SRTTs)and Al_(2)O_(3) nanoparticles.The effect of the selfrotating twisted tapes and Al2O3 nanoparticles on the thermal performance was comprehensively investigated in a circular pipe.The experimental results indicated the heat transfer rate was effectively improved by SRTTs in comparison of plain tube.In addition,the heat transfer multiplier with SRTTs decreased from 1.38 to 1.08 with the Reynolds number increasing from 19,322 to 64,407,while the friction factor multiplier decreased from 1.61 to 1.32.Besides,the results indicated that the employment of Al_(2)O_(3) nanoparticles and SRTTs demonstrated superior thermal performance to the single SRTTs.As Reynolds number increases from 19,322 to 64,407,the heat transfer multiplier decreased from 2.08 to 1.18 in the mass concentration of 3.0%and from 1.38 to 1.08 in mass concentration of 0.0%.Finally,the new heat transfer and friction factor correlations considering the combined effect of Al2O3 nanoparticle and SRTTs were developed within 10%deviation of experimental values.
基金Researchers supporting Project number(RSP-2020/33),King Saud University,Riyadh,Saudi Arabia。
文摘The investigation of local thermal transport rate in the nanolubricants is significant.These lubricants are broadly used in environmental pollution,mechanical engineering and in the paint industry due to high thermal performance rate.Therefore,thermal transport in ZnO-SAE50 nanolubricant under the impacts of heat generation/absorption is conducted.The colloidal suspension is flowing between parallel stretching disks in which the lower disk is positioned at z=0 and upper disk apart from distance d.The problem is transformed in dimensionless version via described similarity transforms.In the next stage,an analytical technique(VPM)is implemented for the solution purpose.The graphical results against multiple flow parameters were furnished over the region of interest and explained comprehensively.It is imperative to mention that the results are plotted for ZnO-SAE50 and conventional liquid as well.Further,rapid motion of the fluid is perceived against high Reynolds andγparameters.The wall shear stresses at the upper end rises for multiple Reynolds andγwhile;decrement is detected at the lower end.The significant contribution of an internal heat source is noted for thermal performance rate at the upper end.Foremost,the local heat transport rate declines at the lower disk.By altering Reynolds number,prompt heat transfer rate is gained at the upper disk and increasing behavior of the local heat transport rate is slow at the lower disk.From the study,it is concluded that the nanolubricants have high thermal characteristics.Therefore,such fluids are reliable to use in above stated areas.
基金This study was sponsored by the“Civil Engineering,Brand Major Construction Site of Private Universities of Education Department of Henan Province 2017”(Henan Finance and Education:[2016]119).
文摘This paper investigates the thermal performance of prefabricated exterior walls using the Computational Fluid Dynamics method to reduce energy consumption.The thermal performance of the prefabricated exterior wall was numerically simulated using the software ANSYS Fluent.The composite wall containing the cavity is taken as the research object in this paper after analysis.The simulation suggests that when the cavity thickness is 20 mm and 30 mm,the heat transfer coefficient of the air-sandwich wall is 1.3 and 1.29,respectively.Therefore,the optimal width of the cavity is 20 mm,and the most suitable material is the aerated concrete block.In addition,a comparative analysis is conducted on the cavity temperature in the wall under different conditions.It is proven that an intelligent environment control system can significantly improve thermal efficiency and provide a solid theoretical basis for further research in the external insulation of prefabricated buildings.
基金The research content of this paper comes from the Urban and Rural Construction Science and Technology Project of Shandong Province,China,Subject No.2018-K9-07.
文摘This study proposes three possible keel-surface layer combinations to implement a new type of thermally insulating decorative wall system.A set of 8 samples has been studied.In particular,through theoretical calculations,simulations,and experimental verification,the influence of different types of connecting structures on the overall thermal performance of the wall system has been determined.It has been found that a proper combination of these elements can meet existing energy-saving standards and effectively reduce the energy loss caused by thermal bridges due to the installation of steel keels at the edges of integrated wall panels.
文摘Thermal transport investigation in colloidal suspensions is taking a significant research direction.The applications of these fluids are found in various industries,engineering,aerodynamics,mechanical engineering and medical sciences etc.A huge amount of thermal transport is essential in the operation of various industrial production processes.It is a fact that conventional liquids have lower thermal transport characteristics as compared to colloidal suspensions.The colloidal suspensions have high thermal performance due to the thermophysical attributes of the nanoparticles and the host liquid.Therefore,researchers focused on the analysis of the heat transport in nanofluids under diverse circumstances.As such,the colloidal analysis of H_(2)O composed byγAl_(2)O_(3)and Al_(2)O_(3)is conducted over an elastic cylinder.The governing flow models ofγAl_(2)O_(3)/H_(2)O and Al_(2)O_(3)/H_(2)O is reduced in the dimensionless form by adopting the described similarity transforms.The colloidal models are handled by implementing the suitable numerical technique and provided the results for the velocity,temperature and local thermal performance rate against the multiple flow parameters.From the presented results,it is shown that the velocity of Al_(2)O_(3)–H_(2)O increases promptly against a high Reynolds number and it decreases for high-volume fraction.The significant contribution of the volumetric fraction is examined for thermal enhancement of nanofluids.The temperature of Al_(2)O_(3)–H_(2)O andγAl_(2)O_(3)–H_(2)O significantly increases against a higherϕ.Most importantly,the analysis shows thatγAl_(2)O_(3)–H_(2)O has a high local thermal performance rate compared to Al_(2)O_(3)–H_(2)O.Therefore,it is concluded thatγAl_(2)O_(3)–H_(2)O is a better heat transfer fluid and is suitable for industrial and technological uses.
文摘The investigation of Thermal performance in nanofluids and hybrid nanofluids over a curved stretching infinite region strengthens its roots in engineering and industry.Therefore,the comparative thermal analysis in SiO_(2)–H_(2)O and(MoS_(2)–SiO_(2))–H_(2)O is conducted over curved stretching surface.The model is reduced in the dimensional version via similarity transformation and then treated numerically.The velocity and thermal behavior for both the fluids is decorated against the preeminent parameters.From the analysis,it is examined that the motion of under consideration fluids declines against Fr and.The thermal performance enhances for higher volumetric fraction and.Further,it is noticed that thermal performance prevailed in(MoS_(2)–SiO_(2))–H_(2)O throughout the analysis.Therefore,(MoS_(2)–SiO_(2))–H_(2)O is better for industrial and engineering uses where high heat transfer is required to accomplished different processes of production.
文摘The temperature control in electronic packaging is the key in numerous applications,to avoid overheating and hardware failure.Due to high capability of heat transfer,good temperature uniformity,and no power consumption,heat pipes can be widely used for heat dissipation of electronic components.This paper reports an experimental thermal analysis of different capillary structures for heat pipes.The wicks considered are metal screens,axial microgrooves,and sintered metal powder.The heat pipes are made of copper,a 200 mm length tube and a 9.45 mm external diameter.Working fluid used was distilled water.The devices are investigated in three positions:0,90,and 270°to the horizontal under powers of 5 up to 45 W.The results show that in horizontal(0°)and with the evaporator under the condenser(270°),the heat pipes showed similar results.Nevertheless,in the reverse condition(the position against the gravity with the evaporator above the condenser,90°),the heat pipe with sintered wick presented the best thermal performance,as it has the lowest thermal resistance and supported a higher power.Besides that,the sintered powder capillary structure demonstrates the most homogeneous thermal behavior for every position,making the most suitable for applications susceptible to diverse inclinations.
文摘The thermal performance of three roofing models: tile, corrugated and earth terrace is numerically analyzed. The mathematical equations which govern the three roofing models are established by the electrical method of analogies. These equations are discretized by an implicit finite difference method and solved by the Gauss-Seidel algorithm. We analyze the influences of geometric parameters (Xlo, Xlarg, <i><span style="font-family:Verdana;">α</span></i><span style="font-family:Verdana;"> and Ep) on the evolution of the temperatures of the </span><span style="font-family:Verdana;">different environments of our three roof models. In particular, we have</span><span style="font-family:Verdana;"> shown that the effectiveness of a roof in reducing the temperature inside a room is linked to its physical properties. The results obtained that for the same geometric parameters, the earth roof terrace and the earth tile roof compared to the corrugated metal roof improve thermal comfort by lowering the interior temperature of 5<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">º</span>C and 4.6<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">º</span>C.</span>
文摘In this work,the thermal behavior of fin made of palladium material under the influences of thermal radiation and internal heat generation is investigated.The thermal model for the extended surface made of palladium as the fin material is first developed and solved numerically using finite difference method.The influences of the thermal model parameters on the heat transfer behaviour of the extended surface are investigated.The results show that the rate of heat transfer through the fin and the thermal efficiency of the fin increase as the thermal conductivity of the fin material increases.This shows that fin is more efficient and effective for a larger value of thermal conductivity.However,the thermal conductivity of the fin with palladium material is low and constant at the value of approximately 75 W/mK in a wider temperature range of-100℃and 227℃.Also,it is shown that the thermal efficiencies of potential materials(except for stainless steel and brass)for fins decrease as the fin temperatures increase.This is because the thermal conductivities of most of the materials used for fins decreases as temperature increases.However,keeping other fin properties and the external conditions constant,the thermal efficiency of the palladium is constant as the temperature of the fin increases within the temperature range of-100℃and 227℃.And outside the given range of temperature,the thermal conductivity of the material increases which increases the efficiency of the fin.The study will assist in the selection of proper material for the fin and in the design of passive heat enhancement devices under different applications and conditions.
文摘Riyadh city is the fastest growing city in Saudi Arabia. The rapid urban growth that happened recently in Riyadh was not based on the traditional urban planning principles, which have been established and applied for the city development process. The imported building regulations have created a new urban structures and street patterns. The contemporary urban form in Riyadh city is based mainly on traffic and economic consideration with the neglect of environmental dimensions. This research aims to examine the impacts of building regulations on the thermal performance of residential buildings in Riyadh city, with the ultimate goal of establishing planning guidelines that consider the environmental conditions of the city. The methodology adopted for achieving the aim of this study consists of two phases. First, the literature related to building regulations development in Riyadh, as of 2018, was reviewed. Second, buildings energy simulation was conducted to examine the thermal performance of the typical current status of residential building blocks in Riyadh city, and then several changes to building regulations were made to investigate their impacts on the thermal performance of buildings. The results showed that the impacts of Riyadh building regulations on the thermal performance of residential buildings differ across the evaluated cases. The ratio of building height to street width, urban block street orientation, and building orientation are the main factors affecting thermal performance of buildings within urban block. The study also concludes that adjusting the ratio of building height to the distance between buildings could have a significant impact in reducing cooling loads. This study will help policy makers, planners and designers to investigate the shortcoming in the current building regulations.
文摘In this study,the impacts of internal heat generation on heat transfer enhancement of porous fin is theoretical investigated using differential transform method.The parametric studies reveal that porosity enhances the fin heat dissipating capacity but the internal heat generation decreases the heat enhancement capacity of extended surface.Also,it is established that when the internal heat parameter increases to some certain values,some negative effects are recorded where the fin stores heat rather than dissipating it.This scenario defeats the prime purpose of the cooling fin.Additionally,it is established in the present study that the limiting value of porosity parameter for thermal stability for the passive device increases as internal heat parameter increases.This shows that although the internal heat parameter can help assist higher range and value of thermal stability of the fin,it produces negative effect which greatly defeats the ultimate purpose of the fin.The results in the work will help in fin design for industrial applications where internal heat generation is involved.
文摘Brazil has a great climatic diversity,with different demands for the adequate thermal performance of buildings,where the variables that impact it have different influences depending on the location and the type of wrapping used.When a prior study of the thermal performance of a building is not done in the design phase,the unpleasant effects for the user appear after the building is ready,and bring with them problems such as internal temperatures that are too high in the summer or too low in the winter.Therefore,the objective of this study is to provide recommendations for the application of ACM(aluminum composite material)composite panels and thermoacoustic(sandwich)tiles for external enclosure in the single-family residential sector.A high standard two-story residence with approximately 162 m^(2)per floor is used as a model and through computer simulations,utilizing the Energyplus program and observing the requirements of the NBR 15.575 performance standard,the thermal performance is evaluated.The factorial experiment was applied encompassing thermal performance variables such as absorptance,natural ventilation and thermophysical properties of the wrapping for three different climatic conditions:extreme winter climate,average climate and extreme summer climate.The results obtained show that the thermoacoustic roof tile keeps the internal temperature more stable independent of external oscillations,while the ACM panels follow the external oscillations,not meeting the expectations of thermal performance and needing passive treatments.
文摘We present in this paper the results of experimental and numerical study of the thermal performances of a cook stove prototype intended for the parboiling of paddy rice. Thus, the experimental results show that the optimal mass of husk rice is M = 7.15 kg for a good combustion within the combustion chamber and got a maximum temperature at the level of the burners surface. This temperature is T<sub>cu1</sub>=304.78°C. The circulating air flow rate by forced convection is Q<sub>m</sub> = 0.09112 m<sup>-3</sup>·s<sup>-1</sup>. The vertical side walls temperature is T<sub>ple</sub> = 140.6°C and the water temperature and vapor is about 144.6°C in the stockpot. The gas combustion is composed of carbon dioxide (CO<sub>2</sub>), carbon monoxide (CO), methane (CH<sub>4</sub>) and the ratio of hydrogen to nitrogen (H<sub>2</sub>/N<sub>2</sub>). The results from the numerical modeling indicate T<sub>cu1</sub>=307.8°C, T<sub>ple</sub> = 144.55°C and a Q<sub>m</sub> = 0.09258 m<sup>-3</sup>.s<sup>-1</sup>. The average thermal efficiency of the cookstove is η = 46.6% and the power developed by the cookstove is about ≈6 kW. Despite the heat losses, the cookstove remains interesting for paddy rice parboiling activities.
文摘The thermal properties of Light Emitting Diode (LED) products have a significant impact on their longevity and overall performance. Products which are unable to adequately dissipate heat degrade, shortening the projected lifespan. A testing apparatus has been constructed to characterize the thermal behavior of MR-16 LED products. This paper documents the testing setup and measurement results for 9 separate products, and identifies product characteristics which demonstrate higher success at heat dissipation. The thermal performance was quantified using experimental data and heat transfer models. Calculations to quantify the magnitude of heat transferred through radiation and convection in each LED product were performed. Results indicate some of the products are better optimized to enhance convection heat transfer.
基金supported by the National Natural Science Foundation of China (52006218)。
文摘Energy efficiency issues are being focused on the growing concern of global warming and environmental pollution.The high-temperature heat pipe(HTHP) is an effective and environmental-friendly heat transfer device employed in many industries,including solar power generation,high-temperature flue gas waste heat recovery,industrial furnaces,nuclear industries,and aviation.As a critical factor in HTHPs,thermal performance is mainly introduced in the entire paper.To date,most reviews have been published concerning one or several application scenarios.However,to the best of authors' knowledge,it is hard to find a review discussing how to improve the thermal performance of HTHPs comprehensively.First,the impact on the performance of three main components of HTHPs over the past 30 years is introduced:the working fluid,the HTHP structure,and the wick structure.Herein,it is a considerable review of the optimal operating conditions for each direction,and we expect this paper contribute to improving the thermal performance of HTHPs.Then,current numerical simulations and theoretical research on the heat transfer limit of HTHPs are recommended.The significant hypotheses used in numerical simulations and the present theoretical studies are compiled here.Finally,some potential future directions and tentative suggestions for HTHP research are put forward.
基金This study was supported by a grant from National Key R&D Program of China(No.2020YFE0200300)The authors gratefully acknowledge financial support from China Scholarship Council.
文摘Phase change material(PCM)applied to roofs can weak external heat entering the room to reduce air-conditioning energy consumption.In this study,three forms of macro-encapsulated PCM roofs with different PCMs(RT27,RT31,RT35HC,PT37)are proposed.The effects of PCM thickness,the encapsulation forms,and different PCMs on the thermal performance of the roof are discussed in Moroccan semi-arid and Mediterranean climates.The results show that as the PCM thickness increases,the peak temperature attenuation of the roof inner surface decreases.In two climates,the pure PCM layer among the three encapsulation forms(i.e.pure PCM layer,PCM in aluminum tubes,PCM in triangular aluminum)is the easiest to appear the phenomenon of insufficient heat storage and release,while the reduction of the peak inner surface temperature and time lag is the most satisfying.For the PCM in the aluminum tube,phase change time is the shortest and the latent heat utilization ratio is the highest,while thermal regulation performance is the least satisfying.The PCM in triangular aluminum can improve the latent heat utilization ratio significantly,and its thermal regulation performance is in the middle.In semi-arid climate,the time lag increases with phase change temperature increasing.The time lag could reach up to 6 h with 37℃phase transition temperature.In Mediterranean climate,the longest time lag with RT31 is 5 h,while the lowest peak inner surface temperature appears with RT27.The obtained conclusions could provide guidance for the application of PCM roofs in these two climates.
基金The authors will be very thankful for the support from the Hunan University,Central South UniversityThe Hong Kong University of Science and Technology,and University of California.All copyright licenses of have been successfully applied for all cited graphics,images,tables and/or figures。
文摘Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions.Shallow geothermal ventilation(SGV)system,with a little initial in-vestment cost,is one of promising technologies to partly replace the conventional air-conditioning system for air pre-cooling/pre-heating.This paper reviews applications of SGV system for improving thermal performance over latest two decades,which mainly includes the reclassification of SGV system,coupling with other advanced energy-saving technologies,application potentials for building cooling/heating under various weather conditions.Heat transfer mechanism and mathematical modelling techniques have been reviewed,together with in-depth analysis on current research trends,existing limitations,and recommendations of SGV system.Phase change materials,with considerable latent energy density,can stabilize the thermal performance with high reliability.The review identifies that optimization designs and advanced approaches need to be investigated to address the existing urgent issues of SGV system(e.g.,large land occupation,difficulty in centralized collection of condensate water timely for horizontal buried pipe,bacteria growth,polluted supply air,and high construction cost for ver-tical buried pipe).A plenty of studies show that the SGV system could greatly expand the application scope and improve system energy efficiency by combining with other energy-saving technologies.This paper will provide some guidelines for the scientific researchers and engineers to keep track on recent advancements and research trends of SGV system for the building thermal performance enhancement and pave path for future research works.
