A new air-water dual source heat pump water heater with heat recovery is proposed.The heat pump system can heat water by using a single air source,a single water source,or air-water dual sources.The water is first pre...A new air-water dual source heat pump water heater with heat recovery is proposed.The heat pump system can heat water by using a single air source,a single water source,or air-water dual sources.The water is first pre-heated by waste hot water,then heated by the heat pump.Waste heat is recovered by first preheating the cold water and as water source of the heat pump.According to the correlated formulas of the coefficient of performance of air-source heat pump and water-source heat pump,and the gain coefficient of heat recovery-preheater,the formulas for the coefficient of performance of heat pump in six operating modes are obtained by using the dimensionless correspondence analysis method.The system characteristics of heat absorption and release associated with the heat recovery-preheater are analyzed at different working conditions.The developed approaches can provide reference for the optimization of the operating modes and parameters.The results of analysis and experiments show that the coefficient of performance of the device can reach 4-5.5 in winter,twice as much as air source heat pump water heater.The utilization of waste heat in the proposed system is higher than that in the system which only uses waste water to preheating or as heat source.Thus,the effect of energy saving of the new system is obvious.On the other hand,the dimensionless correspondence analysis method is introduced to performance analysis of the heat pump,which also has theoretical significance and practical value.展开更多
Thermal analysis of data centers is in urgent need to ensure that computer chips remain below the critical temperature while the energy consumption for cooling can be reduced.It is difficult to obtain detailed hotspot...Thermal analysis of data centers is in urgent need to ensure that computer chips remain below the critical temperature while the energy consumption for cooling can be reduced.It is difficult to obtain detailed hotspot locations and temperatures of chips in large data centers containing hundreds of racks or more by direct measurement.In this paper,a multi-scale thermal analysis method is proposed that can predict the temperature distribution of chips and solder balls in data centers.The multi-scale model is divided into six scales:room,rack,server,Insulated-Gate Bipolar Transistor(IGBT),chip and solder ball.A concept of sub-model is proposed and the six levels are organized into four simulation sub-models.Sub-model 1 contains Room,Rack and Server(RRS);Sub-model 2 contains Server and IGBT(SI);Sub-model 3 contains IGBT and Chip(IC),and Sub-model 4 contains Chip and Solder-ball(CS).These four sub-models are one-way coupled by transmitting their results as boundary conditions between levels.The full-field simulation method is employed to verify the efficiency and accuracy of multi-scale simulation method for a single-rack data center.The two simulation results show that the highest temperature emerges in the same location.The Single-rack Full-field Model(SRFFM)costs 2.5 times more computational time than that with Single-rack Multi-scale Model(SRMSM).The deviation of the highest temperature of chips and solder balls are 1.57℃and 0.2℃between the two models which indicates that the multi-scale simulation method has good prospect in the data center thermal simulation.Finally,the multi-scale thermal analysis method is applied to a ship data center with 15 racks.展开更多
The geometrical dimensions of the rough structures as well as the non-condensable gases in the vapor mixture can have the great effect on the nucleation position and the wetting state of the droplet,which further infl...The geometrical dimensions of the rough structures as well as the non-condensable gases in the vapor mixture can have the great effect on the nucleation position and the wetting state of the droplet,which further influence the condensation heat flux.In this paper,the multispecies multiphase lattice Boltzmann method together with a thermal phase change model is used to investigate the dropwise condensation on a rough surface enhanced with pillars.The effect of the geometric dimensions including pillar height H,pillar width W and pillar space S is investigated.Then the effect of non-condensable gases on the contact angle of a droplet on textured surface is studied.The results show that the local heat flux and the wetting area are higher while the waiting time is shorter at larger S,W and smaller H on the rough surface.The nucleation position rises from the bottom of grooves to the top with the increase of pillar height and the decrease of pillar space.The contact angle is larger and it is easier to maintain the Cassie state for droplet.When there exists non-condensable gas,the non-condensable gas obviously enhances the hydrophobicity of the rough surfaces compared with pure vapor.展开更多
In the present paper,the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm.The self-developed code based on this alg...In the present paper,the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm.The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems,and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5.The attenuation of sound waves in viscous medium was then simulated.The results agree well with the analytical solutions given by theoretical acoustics.This demonstrated that the present method could also be implemented in acoustics field simulation,which is crucial for thermoacoustic simulation.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 51076147)
文摘A new air-water dual source heat pump water heater with heat recovery is proposed.The heat pump system can heat water by using a single air source,a single water source,or air-water dual sources.The water is first pre-heated by waste hot water,then heated by the heat pump.Waste heat is recovered by first preheating the cold water and as water source of the heat pump.According to the correlated formulas of the coefficient of performance of air-source heat pump and water-source heat pump,and the gain coefficient of heat recovery-preheater,the formulas for the coefficient of performance of heat pump in six operating modes are obtained by using the dimensionless correspondence analysis method.The system characteristics of heat absorption and release associated with the heat recovery-preheater are analyzed at different working conditions.The developed approaches can provide reference for the optimization of the operating modes and parameters.The results of analysis and experiments show that the coefficient of performance of the device can reach 4-5.5 in winter,twice as much as air source heat pump water heater.The utilization of waste heat in the proposed system is higher than that in the system which only uses waste water to preheating or as heat source.Thus,the effect of energy saving of the new system is obvious.On the other hand,the dimensionless correspondence analysis method is introduced to performance analysis of the heat pump,which also has theoretical significance and practical value.
基金supported by the National Natural Science Foundation of China(No.51806167)China Postdoctoral Science Foundation(2017M623166)+1 种基金Science and Technology on Thermal Energy and Power Laboratory Open Foundation of China(No.TPL2017BA004)the Fund of Xi’an Science and Technology Bureau(2019218714SYS002CG024).
文摘Thermal analysis of data centers is in urgent need to ensure that computer chips remain below the critical temperature while the energy consumption for cooling can be reduced.It is difficult to obtain detailed hotspot locations and temperatures of chips in large data centers containing hundreds of racks or more by direct measurement.In this paper,a multi-scale thermal analysis method is proposed that can predict the temperature distribution of chips and solder balls in data centers.The multi-scale model is divided into six scales:room,rack,server,Insulated-Gate Bipolar Transistor(IGBT),chip and solder ball.A concept of sub-model is proposed and the six levels are organized into four simulation sub-models.Sub-model 1 contains Room,Rack and Server(RRS);Sub-model 2 contains Server and IGBT(SI);Sub-model 3 contains IGBT and Chip(IC),and Sub-model 4 contains Chip and Solder-ball(CS).These four sub-models are one-way coupled by transmitting their results as boundary conditions between levels.The full-field simulation method is employed to verify the efficiency and accuracy of multi-scale simulation method for a single-rack data center.The two simulation results show that the highest temperature emerges in the same location.The Single-rack Full-field Model(SRFFM)costs 2.5 times more computational time than that with Single-rack Multi-scale Model(SRMSM).The deviation of the highest temperature of chips and solder balls are 1.57℃and 0.2℃between the two models which indicates that the multi-scale simulation method has good prospect in the data center thermal simulation.Finally,the multi-scale thermal analysis method is applied to a ship data center with 15 racks.
基金supported by the National Natural Science Foundation of China(grant number:51906190)China Postdoctoral Science Foundation(2019M663702)+1 种基金Fundamental Research Funds for the Central Universities(xjh012019015)innovation team of Shaanxi province(2019TD-039)。
文摘The geometrical dimensions of the rough structures as well as the non-condensable gases in the vapor mixture can have the great effect on the nucleation position and the wetting state of the droplet,which further influence the condensation heat flux.In this paper,the multispecies multiphase lattice Boltzmann method together with a thermal phase change model is used to investigate the dropwise condensation on a rough surface enhanced with pillars.The effect of the geometric dimensions including pillar height H,pillar width W and pillar space S is investigated.Then the effect of non-condensable gases on the contact angle of a droplet on textured surface is studied.The results show that the local heat flux and the wetting area are higher while the waiting time is shorter at larger S,W and smaller H on the rough surface.The nucleation position rises from the bottom of grooves to the top with the increase of pillar height and the decrease of pillar space.The contact angle is larger and it is easier to maintain the Cassie state for droplet.When there exists non-condensable gas,the non-condensable gas obviously enhances the hydrophobicity of the rough surfaces compared with pure vapor.
基金Supported by the Key Project of National Natural Science Foundation of China(Grant Nos.50736005,50636050)
文摘In the present paper,the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm.The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems,and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5.The attenuation of sound waves in viscous medium was then simulated.The results agree well with the analytical solutions given by theoretical acoustics.This demonstrated that the present method could also be implemented in acoustics field simulation,which is crucial for thermoacoustic simulation.
