Study On Heating Performance Of An Air Reverse Brayton Heat Pump With A Turbocharger

An air cycle heat pump system,which is based on the reverse Brayton cycle and uses air as refrigerant,not only relieves the problem of environmental damage and global warming caused by traditional refrigerants,but also solves the imbalance between the heat capacity and heat load,as well as the difficulty of stable heating under low temperature.However,there is a lack of small and efficient expanders in the market using air as the medium;the matching between the expander and the compressor,and the way of energy transfer await to be solved yet as well.Therefore,based on the traditional regenerated reverse Brayton eycle,using a turbocharger to replace the compressor and the expander,and the blower as the driving device,the new heat pump system has been studied both theoretically and experimentally.It made a start to help extending the applied range of this heat pump.First of all,a reverse Brayton cycle with a turbocharger based on a blower engine is proposed and the corresponding general simulation model is established.The results show that the air cycle heat pump can guarantee the hot water temperature of 62?/70? when the environment temperature is as low as-40?/-20?.With the decrease of ambient temperature,while the heat capacity rate of air cycle heat pump could increase slightly,so the problems of unaequirable high heat sink temperature by traditional air-source heat pump and the imbalance between heat and heat load are solved to some extent.It can build a bridge between theory and practice for the reverse Brayton cycle and therefore extends the application of air source heat pump to with even lower environment temperature.Secondly,following the aforementioned air reverse Brayton heat pump with a turbocharger based on a blower engine,6 forms of air cycle heat pump systems applicable for different heating conditions and requirements have been developed.The relationship between the heating COP and the turbine pressure ratio is studied.After a deterministic solution expression between the heating COP and the turbine pressure ratio is constructed through the thermodynamic state diagram,finding out that the pressure lines are approximately parallel within a certain range of entropy increase hypothesis,it is discovered that increasing the pressure ratio after each cycle reaches the optimal COP would not improve the system performance.Considering the two aspects of heating performance and applicability,the optimal cycle system is filtered out,and an expression of the relationship between the optimal COP and optimal turbine pressure ratio is introduced,also the performance analysis of the system under variable working conditions is completed.In addition,the expression reveals the relation between heating capacity and heat source/heat sink temperature on a theoretical level,which is that the decrease of the heat source temperature and the rise of the heat sink temperature are more favorable to the improvement of the heat generation.This provides a necessary basis for setting up the experimental platform.Moreover,a test bench of the reverse Brayton cycle heat pump system driven by air blower is designed and built,to study the efficiency of main equipment and the change rule of operating parameters of single/dual-blower system as the working environment changes.The results show that a reasonable operation of turbocharger requires the compressor and the turbine to have different flow ratios,and a dual-blower system can meet the above conditions and thus better than the single-blower system.Heat source and heat sink temperature have a small impact on the performance of the dual-blowers system and a higher heat sink temperature makes the heating COP more stable.The efficiency of blower is important to the COP.An implementation of a heat-recover design can increase the COP by about 26%,and a blower with a larger power helps.By comparing the deviation in the thermodynamic process theoretically and experimentally,it is found that the air flows through the regenerator and has a pressure loss of 49%and 20-25%of the heat will be lost in the compressor,thus the entropy of the compressor outlet is reduced.Therefore,the working performance can be improved by adopting low-resistance regenerator and a higher thermal insulation of the system equipment,especially the turbocharger.Furthermore,it is determined that in reality,the changing patterns of the heating capacity and the heat load showed the same trend with the change of the heat source temperature.It also shows that the turbocharger is feasible for air cycle heat pump.Finally,the performance and applicable conditions of the air reverse Brayton heat pump with electric turbocharger are verified by using the winter heating in residential buildings and vehicles as case studies.Four cities in northern China(Dalian,Shenyang,Changchun,and Harbin)were selected for studying the daily average COP values of single-and dual-blower air reverse Brayton heat pumps,and low ambient temperature air source heat pumps(R744&R41OA)are simulated during one heating cycle.The results show that the single-blower system with 65oC water temperature could still maintain the average heating COP of 1.68.Besides,the thermal performance of the dual-blower system fluctuates the least,and it can be approximately considered that the system performance is almost unaffected by the heat source and heat sink temperature.Therefore,in a severe cold region this air cycle heat pump is more competitive in the heating system to achieve a high-temperature water supply.At the same time,its heating performance of an application on a foll electric vehicle is predicted and compared with the measured data of PTC energy consumption of Citroen c-zero(electric)in three different cities.The results show that the system can save up to 23%electricity energy,which not only extends the mileage of the vehicle but also enriches the use for heating/air-conditioning.