We herein evaluate the use of a chemical heat pump (CHP) for upgrading waste heat. CaCl<sub>2</sub> was used in the system of CHP. We evaluated the heat storage and heat releasing of CHP, and confirmed the...We herein evaluate the use of a chemical heat pump (CHP) for upgrading waste heat. CaCl<sub>2</sub> was used in the system of CHP. We evaluated the heat storage and heat releasing of CHP, and confirmed the practicality from the experimental results. The reactor module employed was an aluminum plate-tube heat exchanger with corrugated fins, and the CaCl<sub>2</sub> powder was in the form of a packed bed. Heat storage operation and heat dissipation operation are performed at the same time and supplied to the heat demand destination. At this time, an environmental heat source can be used during the heat radiation operation, and the heat output can release more heat than the heat input during heat storage. The heat discharging and charging characteristics of the reactor module were evaluated experimentally. The coefficient of performance (COP) was calculated for the heat upgrading cycle, and the heat output in the system was determined. A COP of 1.42 and output of 650 W/L, based on the heat exchanger volume, were obtained using a 600 s change time for the heat pump.展开更多
Cooling in industrial production and refrigeration of perishable and</span><span style="font-size:10.0pt;font-family:""> non-</span><span style="font-size:10.0pt;font-family:&q...Cooling in industrial production and refrigeration of perishable and</span><span style="font-size:10.0pt;font-family:""> non-</span><span style="font-size:10.0pt;font-family:""> </span><span style="font-size:10.0pt;font-family:"">perishable products is common practice throughout the world. Research studies have been conducted both experimentally and numerically to simulate Vapor Compression Refrigeration System (VCRS) and its performance respectively, however, experimental procedure often seems to be expensive and time-consuming to carry out due to the function of many variables. This study was therefore designed to numerically simulate the performance assessment of a nanoparticle enhanced VCRS. A numerical model of a vapor compression refrigeration system was developed using standard refrigeration equations on each of the major components of the refrigeration system such as compressor, evaporator, condenser and expansion valve. The model was then simulated on a MATLAB platform with a CoolProp installed packages via Python under two different simulation cases. In the first case, the mass fractions were varied for CuO,</span><span style="font-size:10.0pt;font-family:""> </span><span style="font-size:10.0pt;font-family:"">TiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> nanoparticles while their densities remained constant and a reversed condition was investigated for the second case. The results showed that both the refrigerating effect and the Coefficient Of Performance (COP) of the system increase as both the mass fraction and density of all the nanoparticles increases. It also shows that the compressor work decreases as both the mass fraction and density of all the nanoparticles were increased. On comparing the computational and numerical analysis results, the study established no significant difference in terms of COP and the use of nanoparticles were found to have improved the COP of the system.展开更多
In the present study,an attempt ismade to enhance the performance of heat pump by utilizing two types of nanofluids namely,copper and alumina nanofluids.These nanofluids were employed around the evaporator coil of the...In the present study,an attempt ismade to enhance the performance of heat pump by utilizing two types of nanofluids namely,copper and alumina nanofluids.These nanofluids were employed around the evaporator coil of the heat pump.The nanofluids were used to enhance the heat input to the system by means of providing an external jacket around the evaporator coil.Both the nanofluids were prepared in three volume fractions 1%,2%and 5%.Water was chosen as the base fluid.The performance of the heat pump was assessed by calculating the coefficient of performance of the system when it was operated with and without nanofluid jacket.A significant enhancement in the coefficient of performance was noticed when copper and alumina nanofluids were employed in the system.Also,the coefficient of performance was found to have a direct relationship with the tested volume fractions.For the highest volume fraction of 5%,the performance of the heat pump was found to enhance by 23%with alumina nanofluid,while for copper nanofluid,a very significant enhancement in performance by 72%was observed.Thus,utilizing of nanofluids in heat pumps can be very beneficial towards performance enhancement and the idea can also be extended to other thermal systems such as steam power plant,automobile radiator,industrial heat exchangers and refrigeration systems.展开更多
This paper deals with the evaluation of the Coefficient of Performance (COP) of solar adsorption refrigeration. In the literature, simulation models to predict the thermal behaviour and the coefficient of performance ...This paper deals with the evaluation of the Coefficient of Performance (COP) of solar adsorption refrigeration. In the literature, simulation models to predict the thermal behaviour and the coefficient of performance of these systems are uncommon. This is why we suggest a model to simulate the operation of the machine in a typical hot and dry climate of the city of Ouagadougou. The objective is to provide a model for calculating the COP from the measurement of the ambient temperature and the irradiation of a given site. Starting from mathematical modelling, a resolution and simulation were made with COMSOL software based on the Dubinin-Astakhov adsorption model, the heat transfer balance equations, and the Linear Driving Force (LDF) model to describe the thermal behaviour of the system. A one-week measurement sequence on the adsorption solar refrigerator at the Albert Schweitzer Ecological Centre (CEAS) validated the numerical results. The measurement shows that for the days with high sunshine, the temperature of the reaction medium reaches 110°C, and the pressure reaches 500 mbar. This leads to a production of cold that allows it to reach the temperature of -5°C at the evaporator. Under these conditions, the COP is worth 14%. These results are obtained both by numerical simulation using the COMSOL 5.1 software and after a measurement session on the solar refrigerator available to the CEAS. We obtained an experimental and theoretical coefficient of performance varying between 9% and 14% with a difference of between 0% and 3%. We conclude that our model is suitable to estimate the COP of any device based on its thermal properties, the ambient temperature and the irradiation of a given site.展开更多
This paper is based on long term parameter measurements of the exhaust air heat pumps (EAHP) system in a new built apartment building. The building was equipped with an exhaust air ventilation system and exhaust air h...This paper is based on long term parameter measurements of the exhaust air heat pumps (EAHP) system in a new built apartment building. The building was equipped with an exhaust air ventilation system and exhaust air heat pump for ventilation heat recover. The results of the measurements show that the COP of the EAHP is mainly related to the temperature graph of the heating system and the supply temperature of domestic hot water (DWH). During the measurement period some other impact factors, such as the quality of maintenance, the nighttime temperature graph of the heating system, the reduction of the exhaust air flows in case of low temperatures, mistakes in designing and low building quality, have also played a role. An analysis of energy consumption shows that in winter conditions the COP is about 3.0 and in the transition period about 3.3. The energy recovery value of the EAHP is 0.5.展开更多
Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 ...Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 to 333 K and shows good potential in the adsorption chiller in terms of the high cooling output. A double-effect adsorption chiller could provide a higher Coefficient Of Performance (COP) than that of a single-effect chiller. In this paper, we developed a measuring method for the amount of adsorption in the first and second adsorber in a double-effect adsorption chiller and measured the adsorption and desorption rate based on the volumetric method. We calculated the COP of the adsorption chiller with the quantity of adsorbent obtained in the experiment. In the experiments, the quantity of adsorbent in the first adsorber was 0.14 g-H<sub>2</sub>O/g-Ads at the pressure 20 kPa and a desorption temperature over 100℃. The amount of adsorbent in the second adsorber was equal to that of the first adsorber. By analyzing the COP with the experimental results, the COP value was calculated to be over 1.0 (–) at any desorption temperature. The COP of the double-effect cycle was higher than that of single-effect cycle.展开更多
Equations of dynamic systems in droplet distribution at high pressure and boundary value flows in the swirl chamber of a swirl nozzle were used in conjunction with momentum equations of forces on moving curved vanes t...Equations of dynamic systems in droplet distribution at high pressure and boundary value flows in the swirl chamber of a swirl nozzle were used in conjunction with momentum equations of forces on moving curved vanes to develop mathematical models.A computer program in C++language was developed and used to simulate the effect of some flow and geometric parameters,including flow rate,pressure and swirl chamber diameter,on the spray performance of a high pressure agro-forestry swirl nozzle.Each of the three performance parameters of axial flow rate,spray cone angle and output discharge(or performance)coefficient were studied as a function of any two combinations of the nozzle supply pressure,exit orifice diameter and swirl chamber diameter.The study established that the spray cone angle of the discharge flow pattern varied from the minimum value of 40°for a swirl chamber diameter of 90 mm to 220°for 40 mm as the exit orifice diameter varied from the minimum value of 0.5 mm to 4.0 mm.The simulated nozzle output discharge coefficient could be varied from 0.98,when the nozzle supply pressure was 400 kPa to the minimum value of 0.001 at any of the other six simulated nozzle supply pressure values of 200,250,300,350,450 and 500 kPa by varying the exit orifice diameter from 0.5 mm to 4.0 mm.The pattern of variation of the simulated nozzle discharge coefficient values were similar to those obtained by measurement during the validation exercise in the laboratory although their sensitivities to the independent variables were different.The results indicated that the range of nozzle discharge coefficient of 0.80 to 0.98 required for a well designed high pressure agro-forestry swirl nozzle has been simulated.With the successful development of the C++computer program,a useful tool that will cut down on the rigor encountered and time spent by nozzle designers and evaluators during nozzle development process has been developed in the study.展开更多
A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working flu...A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working fluid is proposed in which an injector driven by another heat source replaces the liquid circulating pump,making the system more affordable,simpler and more stable.The effect of different operation conditions on entrainment ratios and the influence of different factors on system performance are analyzed on the basis of mass,momentum and energy conservation equations.The influence degree of each factor on system performance is investigated by the orthogonal test method.The condenser temperature has the largest effect on system performance.The pressure drop in the suction chamber of gas-liquid injector has the least impact on system performance.The COP can reach about 0.35 under a certain working condition.The system can be driven by two different temperature heat sources with no electricity needed,and it is a good choice for places with abundant heat resources or lack of electricity.展开更多
A novel way for a compressor to improve its coefficient of performance was proposed in this paper.Fullerenes(C70)and NiFe2O4 nanocomposites were modified by span 80 and dispersed in refrigeration oil by solid grinding...A novel way for a compressor to improve its coefficient of performance was proposed in this paper.Fullerenes(C70)and NiFe2O4 nanocomposites were modified by span 80 and dispersed in refrigeration oil by solid grinding(SG).Besides,the tribological properties of the nanocomposites were investigated using a four ball friction tester.The results show that when the mass concentration of fullerenes nanocomposite is higher than 60 ppm and the concentration of nano-oil is 2 g/L,the friction coefficient decreases from 0.13 to 0.06 which means the wear is reduced.The coefficient of performance of the compressor under the air conditioning test condition can be raised by 1.23%.展开更多
The energy and exergy analyses of the absorption refrigeration system (ARS) using H2O-[mmim][DMP] mixture were investigated for a wide range of temperature. The equilibrium Dühring (P-T-XIL) and enthalpy (h-T-XIL...The energy and exergy analyses of the absorption refrigeration system (ARS) using H2O-[mmim][DMP] mixture were investigated for a wide range of temperature. The equilibrium Dühring (P-T-XIL) and enthalpy (h-T-XIL) of mixture were assessed using the excess Gibbs free non-random two liquid (NRTL) model for a temperature range ??? of 20°C to 140°C and XIL from 0.1 to 0.9. The performance validation of the ARS cycle showed a better coefficient of performance (COP) of 0.834 for H2O-[mmim][DMP] in comparison to NH3-H2O, H2O-LiBr, H2O-[emim][DMP], and H2O-[emim][BF4]. Further, ARS performances with various operating temperatures of the absorber (Ta), condenser (Tc), generator (Tg), and evaporator (Te) were simulated and optimized for a maximum COP and exergetic COP (ECOP). The effects of Tg from 50°C to 150°C and Ta and Tc from 30°C to 50°C on COP and ECOP, the Xa, Xg, and circulation ratio (CR) of the ARS were evaluated and optimized for Te from 5°C to 15°C. The optimization revealed that Tg needed to achieve a maximum COP which was more than that for a maximum ECOP. Therefore, this investigation provides criteria to select low grade heat source temperature. Most of the series flow of the cases of cooling water from the condenser to the absorber was found to be better than the absorber to the condenser.展开更多
Thermoelectric devices are one of the technologies used either to generate electricity by applying a temperature difference using thermal energy or as a heating/cooling system by applying an electrical voltage.The num...Thermoelectric devices are one of the technologies used either to generate electricity by applying a temperature difference using thermal energy or as a heating/cooling system by applying an electrical voltage.The number of materials required to produce a product is an important factor in determining its price.Production costs associated with these materials,as well as their availability and quality,play a crucial role in price determination by manufacturers.In this context,a method that employs a uniform volume distribution was implemented.This approach enabled the analysis to focus on other variables,thereby promoting a more precise and relevant evaluation of overall performance.Based on the finite element method,this study investigated the influence of geometric shape,including Rect-leg,Y-leg,Pin-leg and X-leg designs,on the performance of solar thermoelectric generators and thermoelectric coolers.The study was conducted considering the same hot alumina junction surface that receives solar radiation;however,the ef-fective surface,which corresponded to the heat flow area and had a similar area near the exposed surface,varied depending on the chosen leg geometry,thus impacting the heat flux due to the variation in thermal resistance.In the case of a solar thermoelectric generator,the Rect-leg model,having the same effective surface area,presented the lowest heat loss value resulting from convection and radiation in the heat spreader and the hot alumina plate.Under the same conditions,the Y-leg showed the highest value.The Rect-leg design generated,by using thermal and optical concentration,the highest output power of 0.028 and 0.054 W,and efficiency of 3.47%and 4.7%,respectively,whereas the Y-leg generated lower values of 0.006523 and 0.018744 W for power,and 2.83%and 2.71%for efficiency,respectively.In the case of the thermoelectric coolers,the Y-leg generated the highest temperature difference between the hot and cold sides of 67.28 K at an electric current value of 1.8 A,whereas the Rect-leg,Pin-leg and X-leg generated~66.25,~67.02 and~67.19 K at 6.1,2.7 and 2.6 A.展开更多
This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger(IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX(EJE-...This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger(IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX(EJE-IHX-S) . The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance(COPr) ,heating capacity,entrainment ratio,pressure lift,and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO2 ejector system. Using a more practical performance calculation,the compression ratio in the EJE-S is reduced by 10.0%-12.1%,while that of EJE-IHX-S is reduced only by 5.6%-6.7% compared to that of a conventional transcritical CO2 system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.展开更多
A three-dimensional finite element dynamic simulation platform of the ground source heat pump system(GSHPS)is established.According to the outlet temperature of ground heat exchangers(GHEs)required by the code in summ...A three-dimensional finite element dynamic simulation platform of the ground source heat pump system(GSHPS)is established.According to the outlet temperature of ground heat exchangers(GHEs)required by the code in summer and winter,the calculated minimum buried depth of GHEs meeting the requirements is 60 m,when the number of borehole is 9.By using the established platform,the annual operation performance and cost of the GSHPS under different buried pipe depths are studied.The results show that the deeper the buried depth of GHEs is,the better the heat exchange effect of GHEs is.Compared with the GHEs with 60 m buried depth,when the buried depth of GHEs is 65 m,70 m,75 m and 80 m,the average coefficient of performance(COP)of the unit increases by 4.1%,6.3%,7.7%and 8.2%in cooling period and 1.0%,1.6%,1.8%and 1.9%in heating period,respectively.Considering the performance and initial investment of the GHSPS comprehensively,the optimal buried depth of GHEs is 60 m.However,considering the performance the system and the total cost of the system running for 20 years comprehensively,the optimal buried depth of GHEs is 70 m.展开更多
The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy,industrial processing,and long-distance indoor heating,because it can upgrade energy level and de...The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy,industrial processing,and long-distance indoor heating,because it can upgrade energy level and deliver heat to heated medium.In this work,an experimental system of a vertical single-stage LiBr/H2O absorption heat transformer was established to study its performance in the case of producing high-temperature water or low-pressure steam generation under different heating water flow rates.The useful output heat,coefficient of performance,exergy coefficient of performance,and gross temperature lift of the single-stage heat transformer have all been tested.The results show that the absorber cannot directly generate low-pressure steam under the condition of counter-flow heat exchange but can obtain more useful output heat.The largest useful output heat is 20.3 kW,which is higher than that in the case of parallel-flow heat exchange.The generation of low-pressure steam has certain requirements on the mode of heat transfer.The largest internal gross temperature lift of 28.1℃corresponds to the smallest coefficient of performance of 0.22 when the heating water flow rate is 2.1 m3/h.The performance of the single-stage absorption heat transformer can be improved to some extent by increasing the heating water flow rate.展开更多
The flow and thermal breakthrough phenomenon in a forced external circulation standing column well(FECSCW)directly affects heat transfer efficiency and load-carrying capacity.A numerical model for FECSCW is developed ...The flow and thermal breakthrough phenomenon in a forced external circulation standing column well(FECSCW)directly affects heat transfer efficiency and load-carrying capacity.A numerical model for FECSCW is developed to analyze the migration of the temperature and velocity front under the flow and thermal breakthrough.The results indicated that thermal breakthrough began after simulation running 2.5 min and was completely formed after 12 min.The inlet water,which directly entered the production well without heat exchange with the aquifer,accounted for 12.8%.When the porosity of the backfill material decreased from 0.35 to 0,the coefficient of per-formance(COP)of the heat pump unit increased by 1.6%on average,and the thermal breakthrough strength decreased by an average of 45.3%within 25 min.Where seepage velocity near the well wall was greater than 1×10^(−3) m·s^(−1),faster velocity front migration was observed,while the migration advantage of the temperature front was more prominent outside of this region.Through quantitative analysis of flow and thermal breakthrough,temperature and velocity front migration,and COP change of heat pump unit,theoretical suggestions were pro-vided for the thermal transfer mechanism near the thermal well wall.The extended research in this study can be applied to the design and optimization of forced external circulation standing column well system.展开更多
文摘We herein evaluate the use of a chemical heat pump (CHP) for upgrading waste heat. CaCl<sub>2</sub> was used in the system of CHP. We evaluated the heat storage and heat releasing of CHP, and confirmed the practicality from the experimental results. The reactor module employed was an aluminum plate-tube heat exchanger with corrugated fins, and the CaCl<sub>2</sub> powder was in the form of a packed bed. Heat storage operation and heat dissipation operation are performed at the same time and supplied to the heat demand destination. At this time, an environmental heat source can be used during the heat radiation operation, and the heat output can release more heat than the heat input during heat storage. The heat discharging and charging characteristics of the reactor module were evaluated experimentally. The coefficient of performance (COP) was calculated for the heat upgrading cycle, and the heat output in the system was determined. A COP of 1.42 and output of 650 W/L, based on the heat exchanger volume, were obtained using a 600 s change time for the heat pump.
文摘Cooling in industrial production and refrigeration of perishable and</span><span style="font-size:10.0pt;font-family:""> non-</span><span style="font-size:10.0pt;font-family:""> </span><span style="font-size:10.0pt;font-family:"">perishable products is common practice throughout the world. Research studies have been conducted both experimentally and numerically to simulate Vapor Compression Refrigeration System (VCRS) and its performance respectively, however, experimental procedure often seems to be expensive and time-consuming to carry out due to the function of many variables. This study was therefore designed to numerically simulate the performance assessment of a nanoparticle enhanced VCRS. A numerical model of a vapor compression refrigeration system was developed using standard refrigeration equations on each of the major components of the refrigeration system such as compressor, evaporator, condenser and expansion valve. The model was then simulated on a MATLAB platform with a CoolProp installed packages via Python under two different simulation cases. In the first case, the mass fractions were varied for CuO,</span><span style="font-size:10.0pt;font-family:""> </span><span style="font-size:10.0pt;font-family:"">TiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> nanoparticles while their densities remained constant and a reversed condition was investigated for the second case. The results showed that both the refrigerating effect and the Coefficient Of Performance (COP) of the system increase as both the mass fraction and density of all the nanoparticles increases. It also shows that the compressor work decreases as both the mass fraction and density of all the nanoparticles were increased. On comparing the computational and numerical analysis results, the study established no significant difference in terms of COP and the use of nanoparticles were found to have improved the COP of the system.
文摘In the present study,an attempt ismade to enhance the performance of heat pump by utilizing two types of nanofluids namely,copper and alumina nanofluids.These nanofluids were employed around the evaporator coil of the heat pump.The nanofluids were used to enhance the heat input to the system by means of providing an external jacket around the evaporator coil.Both the nanofluids were prepared in three volume fractions 1%,2%and 5%.Water was chosen as the base fluid.The performance of the heat pump was assessed by calculating the coefficient of performance of the system when it was operated with and without nanofluid jacket.A significant enhancement in the coefficient of performance was noticed when copper and alumina nanofluids were employed in the system.Also,the coefficient of performance was found to have a direct relationship with the tested volume fractions.For the highest volume fraction of 5%,the performance of the heat pump was found to enhance by 23%with alumina nanofluid,while for copper nanofluid,a very significant enhancement in performance by 72%was observed.Thus,utilizing of nanofluids in heat pumps can be very beneficial towards performance enhancement and the idea can also be extended to other thermal systems such as steam power plant,automobile radiator,industrial heat exchangers and refrigeration systems.
文摘This paper deals with the evaluation of the Coefficient of Performance (COP) of solar adsorption refrigeration. In the literature, simulation models to predict the thermal behaviour and the coefficient of performance of these systems are uncommon. This is why we suggest a model to simulate the operation of the machine in a typical hot and dry climate of the city of Ouagadougou. The objective is to provide a model for calculating the COP from the measurement of the ambient temperature and the irradiation of a given site. Starting from mathematical modelling, a resolution and simulation were made with COMSOL software based on the Dubinin-Astakhov adsorption model, the heat transfer balance equations, and the Linear Driving Force (LDF) model to describe the thermal behaviour of the system. A one-week measurement sequence on the adsorption solar refrigerator at the Albert Schweitzer Ecological Centre (CEAS) validated the numerical results. The measurement shows that for the days with high sunshine, the temperature of the reaction medium reaches 110°C, and the pressure reaches 500 mbar. This leads to a production of cold that allows it to reach the temperature of -5°C at the evaporator. Under these conditions, the COP is worth 14%. These results are obtained both by numerical simulation using the COMSOL 5.1 software and after a measurement session on the solar refrigerator available to the CEAS. We obtained an experimental and theoretical coefficient of performance varying between 9% and 14% with a difference of between 0% and 3%. We conclude that our model is suitable to estimate the COP of any device based on its thermal properties, the ambient temperature and the irradiation of a given site.
文摘This paper is based on long term parameter measurements of the exhaust air heat pumps (EAHP) system in a new built apartment building. The building was equipped with an exhaust air ventilation system and exhaust air heat pump for ventilation heat recover. The results of the measurements show that the COP of the EAHP is mainly related to the temperature graph of the heating system and the supply temperature of domestic hot water (DWH). During the measurement period some other impact factors, such as the quality of maintenance, the nighttime temperature graph of the heating system, the reduction of the exhaust air flows in case of low temperatures, mistakes in designing and low building quality, have also played a role. An analysis of energy consumption shows that in winter conditions the COP is about 3.0 and in the transition period about 3.3. The energy recovery value of the EAHP is 0.5.
文摘Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 to 333 K and shows good potential in the adsorption chiller in terms of the high cooling output. A double-effect adsorption chiller could provide a higher Coefficient Of Performance (COP) than that of a single-effect chiller. In this paper, we developed a measuring method for the amount of adsorption in the first and second adsorber in a double-effect adsorption chiller and measured the adsorption and desorption rate based on the volumetric method. We calculated the COP of the adsorption chiller with the quantity of adsorbent obtained in the experiment. In the experiments, the quantity of adsorbent in the first adsorber was 0.14 g-H<sub>2</sub>O/g-Ads at the pressure 20 kPa and a desorption temperature over 100℃. The amount of adsorbent in the second adsorber was equal to that of the first adsorber. By analyzing the COP with the experimental results, the COP value was calculated to be over 1.0 (–) at any desorption temperature. The COP of the double-effect cycle was higher than that of single-effect cycle.
文摘Equations of dynamic systems in droplet distribution at high pressure and boundary value flows in the swirl chamber of a swirl nozzle were used in conjunction with momentum equations of forces on moving curved vanes to develop mathematical models.A computer program in C++language was developed and used to simulate the effect of some flow and geometric parameters,including flow rate,pressure and swirl chamber diameter,on the spray performance of a high pressure agro-forestry swirl nozzle.Each of the three performance parameters of axial flow rate,spray cone angle and output discharge(or performance)coefficient were studied as a function of any two combinations of the nozzle supply pressure,exit orifice diameter and swirl chamber diameter.The study established that the spray cone angle of the discharge flow pattern varied from the minimum value of 40°for a swirl chamber diameter of 90 mm to 220°for 40 mm as the exit orifice diameter varied from the minimum value of 0.5 mm to 4.0 mm.The simulated nozzle output discharge coefficient could be varied from 0.98,when the nozzle supply pressure was 400 kPa to the minimum value of 0.001 at any of the other six simulated nozzle supply pressure values of 200,250,300,350,450 and 500 kPa by varying the exit orifice diameter from 0.5 mm to 4.0 mm.The pattern of variation of the simulated nozzle discharge coefficient values were similar to those obtained by measurement during the validation exercise in the laboratory although their sensitivities to the independent variables were different.The results indicated that the range of nozzle discharge coefficient of 0.80 to 0.98 required for a well designed high pressure agro-forestry swirl nozzle has been simulated.With the successful development of the C++computer program,a useful tool that will cut down on the rigor encountered and time spent by nozzle designers and evaluators during nozzle development process has been developed in the study.
基金supported by the National Natural Science Foundation of China(Grant No.51776110)the Fundamental Research Funds of Shandong University(Grant No.2017JC037)。
文摘A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working fluid is proposed in which an injector driven by another heat source replaces the liquid circulating pump,making the system more affordable,simpler and more stable.The effect of different operation conditions on entrainment ratios and the influence of different factors on system performance are analyzed on the basis of mass,momentum and energy conservation equations.The influence degree of each factor on system performance is investigated by the orthogonal test method.The condenser temperature has the largest effect on system performance.The pressure drop in the suction chamber of gas-liquid injector has the least impact on system performance.The COP can reach about 0.35 under a certain working condition.The system can be driven by two different temperature heat sources with no electricity needed,and it is a good choice for places with abundant heat resources or lack of electricity.
文摘A novel way for a compressor to improve its coefficient of performance was proposed in this paper.Fullerenes(C70)and NiFe2O4 nanocomposites were modified by span 80 and dispersed in refrigeration oil by solid grinding(SG).Besides,the tribological properties of the nanocomposites were investigated using a four ball friction tester.The results show that when the mass concentration of fullerenes nanocomposite is higher than 60 ppm and the concentration of nano-oil is 2 g/L,the friction coefficient decreases from 0.13 to 0.06 which means the wear is reduced.The coefficient of performance of the compressor under the air conditioning test condition can be raised by 1.23%.
基金This work was jointly supported by Qatar University International Research Collaboration Co Fund(Grant No.IRCC-2019-012).
文摘The energy and exergy analyses of the absorption refrigeration system (ARS) using H2O-[mmim][DMP] mixture were investigated for a wide range of temperature. The equilibrium Dühring (P-T-XIL) and enthalpy (h-T-XIL) of mixture were assessed using the excess Gibbs free non-random two liquid (NRTL) model for a temperature range ??? of 20°C to 140°C and XIL from 0.1 to 0.9. The performance validation of the ARS cycle showed a better coefficient of performance (COP) of 0.834 for H2O-[mmim][DMP] in comparison to NH3-H2O, H2O-LiBr, H2O-[emim][DMP], and H2O-[emim][BF4]. Further, ARS performances with various operating temperatures of the absorber (Ta), condenser (Tc), generator (Tg), and evaporator (Te) were simulated and optimized for a maximum COP and exergetic COP (ECOP). The effects of Tg from 50°C to 150°C and Ta and Tc from 30°C to 50°C on COP and ECOP, the Xa, Xg, and circulation ratio (CR) of the ARS were evaluated and optimized for Te from 5°C to 15°C. The optimization revealed that Tg needed to achieve a maximum COP which was more than that for a maximum ECOP. Therefore, this investigation provides criteria to select low grade heat source temperature. Most of the series flow of the cases of cooling water from the condenser to the absorber was found to be better than the absorber to the condenser.
文摘Thermoelectric devices are one of the technologies used either to generate electricity by applying a temperature difference using thermal energy or as a heating/cooling system by applying an electrical voltage.The number of materials required to produce a product is an important factor in determining its price.Production costs associated with these materials,as well as their availability and quality,play a crucial role in price determination by manufacturers.In this context,a method that employs a uniform volume distribution was implemented.This approach enabled the analysis to focus on other variables,thereby promoting a more precise and relevant evaluation of overall performance.Based on the finite element method,this study investigated the influence of geometric shape,including Rect-leg,Y-leg,Pin-leg and X-leg designs,on the performance of solar thermoelectric generators and thermoelectric coolers.The study was conducted considering the same hot alumina junction surface that receives solar radiation;however,the ef-fective surface,which corresponded to the heat flow area and had a similar area near the exposed surface,varied depending on the chosen leg geometry,thus impacting the heat flux due to the variation in thermal resistance.In the case of a solar thermoelectric generator,the Rect-leg model,having the same effective surface area,presented the lowest heat loss value resulting from convection and radiation in the heat spreader and the hot alumina plate.Under the same conditions,the Y-leg showed the highest value.The Rect-leg design generated,by using thermal and optical concentration,the highest output power of 0.028 and 0.054 W,and efficiency of 3.47%and 4.7%,respectively,whereas the Y-leg generated lower values of 0.006523 and 0.018744 W for power,and 2.83%and 2.71%for efficiency,respectively.In the case of the thermoelectric coolers,the Y-leg generated the highest temperature difference between the hot and cold sides of 67.28 K at an electric current value of 1.8 A,whereas the Rect-leg,Pin-leg and X-leg generated~66.25,~67.02 and~67.19 K at 6.1,2.7 and 2.6 A.
基金Project supported by the National Basic Research Program (973) of China (No.2010CB227304)the National Key Technologies R & D Program in China (No.2006BAJ01A10)
文摘This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger(IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX(EJE-IHX-S) . The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance(COPr) ,heating capacity,entrainment ratio,pressure lift,and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO2 ejector system. Using a more practical performance calculation,the compression ratio in the EJE-S is reduced by 10.0%-12.1%,while that of EJE-IHX-S is reduced only by 5.6%-6.7% compared to that of a conventional transcritical CO2 system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.
基金The authors gratefully acknowledge the support from the Natural Science Foundation of China(grant No.51778115)the Fundamental Research Funds for the Central Universities(grant No.N182502043).
文摘A three-dimensional finite element dynamic simulation platform of the ground source heat pump system(GSHPS)is established.According to the outlet temperature of ground heat exchangers(GHEs)required by the code in summer and winter,the calculated minimum buried depth of GHEs meeting the requirements is 60 m,when the number of borehole is 9.By using the established platform,the annual operation performance and cost of the GSHPS under different buried pipe depths are studied.The results show that the deeper the buried depth of GHEs is,the better the heat exchange effect of GHEs is.Compared with the GHEs with 60 m buried depth,when the buried depth of GHEs is 65 m,70 m,75 m and 80 m,the average coefficient of performance(COP)of the unit increases by 4.1%,6.3%,7.7%and 8.2%in cooling period and 1.0%,1.6%,1.8%and 1.9%in heating period,respectively.Considering the performance and initial investment of the GHSPS comprehensively,the optimal buried depth of GHEs is 60 m.However,considering the performance the system and the total cost of the system running for 20 years comprehensively,the optimal buried depth of GHEs is 70 m.
基金The authors gratefully acknowledge the support of the National KeyR&D Program of China(No.2018YFBO905103)the National Natural Science Foundation of China(No.51806213)+1 种基金the Beijing Key Laboratory of Distributed Combined Cooling Heating and Power SystemGuangdong Provincial Key Laboratory of Distributed Energy Systems(No.2017DESO5).
文摘The absorption heat transformer is widely used to utilize low-temperature waste heat in the field of distributed energy,industrial processing,and long-distance indoor heating,because it can upgrade energy level and deliver heat to heated medium.In this work,an experimental system of a vertical single-stage LiBr/H2O absorption heat transformer was established to study its performance in the case of producing high-temperature water or low-pressure steam generation under different heating water flow rates.The useful output heat,coefficient of performance,exergy coefficient of performance,and gross temperature lift of the single-stage heat transformer have all been tested.The results show that the absorber cannot directly generate low-pressure steam under the condition of counter-flow heat exchange but can obtain more useful output heat.The largest useful output heat is 20.3 kW,which is higher than that in the case of parallel-flow heat exchange.The generation of low-pressure steam has certain requirements on the mode of heat transfer.The largest internal gross temperature lift of 28.1℃corresponds to the smallest coefficient of performance of 0.22 when the heating water flow rate is 2.1 m3/h.The performance of the single-stage absorption heat transformer can be improved to some extent by increasing the heating water flow rate.
基金This work was supported by the National Natural Science Foundation of China(41002085,41602278)China Postdoctoral Science Founda-tion(2016M601129)North China University of Technology Programs(18XN154-006,110052972027-031).
文摘The flow and thermal breakthrough phenomenon in a forced external circulation standing column well(FECSCW)directly affects heat transfer efficiency and load-carrying capacity.A numerical model for FECSCW is developed to analyze the migration of the temperature and velocity front under the flow and thermal breakthrough.The results indicated that thermal breakthrough began after simulation running 2.5 min and was completely formed after 12 min.The inlet water,which directly entered the production well without heat exchange with the aquifer,accounted for 12.8%.When the porosity of the backfill material decreased from 0.35 to 0,the coefficient of per-formance(COP)of the heat pump unit increased by 1.6%on average,and the thermal breakthrough strength decreased by an average of 45.3%within 25 min.Where seepage velocity near the well wall was greater than 1×10^(−3) m·s^(−1),faster velocity front migration was observed,while the migration advantage of the temperature front was more prominent outside of this region.Through quantitative analysis of flow and thermal breakthrough,temperature and velocity front migration,and COP change of heat pump unit,theoretical suggestions were pro-vided for the thermal transfer mechanism near the thermal well wall.The extended research in this study can be applied to the design and optimization of forced external circulation standing column well system.
