Design And Performance Study Of High Temperature Heat Pump System With Natural Fluid

Heat pump,as a device to provide heat energy,has been widely concerned about its remarkable energy-saving effect.However,with the increase of industrial application scenarios and the tightening of national energy and environmental policies,the heat pump are moving towards a higher temperature and more environmentally friendly development path.This paper compares and analyzes the advantages and disadvantages of five natural working fluids.Finally,CO₂ is chosen as the research object.Aiming at the problem of excessive irreversible loss in the proces transcritical CO₂ expansion throttling,the optimization of injector throttling is carried out.By comparing and analyzing the operating characteristics of three kinds of transcritical CO₂ heat pump systems,a transcritical CO₂ heat pump system with adjustable flow mode was designed and built.The maximum nominal heat production capacity was 21.4 k W,the maximum cooling water flow rate was 2 m³/h.Two evaluation criteria of COP and total exergy-loss of the systemΔE were established,and the throttling mode of expansion valve and the throttling mode of ejection system were analyzed by two influencing factors of cooling water temperature and compressor frequency.As the temperature of cooling water increases,COP of the system will decrease,with the maximum decrease rate of 24%and 26%respectively.Overall exergy-loss of the systemΔE will decrease by about 10%.With the increase of compressor frequency,the COP of the system showed a downward trend at a lower cooling water temperature.For every 5 Hz increase of the compressor,the COP of the system decreased by 1%and 3%respectively.At a higher cooling water temperature,the COP of the system first increased and then decreased.The throttle of the expansion valve increased by 3%and decreased by 2%at the maximum.Overall exergy-loss of the systemΔE had little change,while the throttle of the injector increased by2%and decreased by 6%,the total exergy-loss of the systemΔE increased by 38%on average.In order to promote the application scenario of transcritical CO₂ heat pump system,an experimental study on transcritical CO₂ blanching of sea-white shrimp was carried out in order to solve the problems of high energy consumption,high pollution and high cost in the process of oil blanching.The test results show that the transcritical CO₂ heat pump blanching of sea-white shrimp is feasible to a certain extent,and under the test conditions,the average heat production of the system is 41.47 k W,the average COP of the system is 3.31,and the energy saving effect is significant.For each1kg blanching of sea-white shrimp,the test system can save the energy cost of 0.028 yuan,a drop of 65%,and economic benefit is significant.When converted into standard coal,CO₂,SO₂ and NOx emissions of per 1kg products of CO₂ heat pump blanching are reduced by 75%,75%and 83%,respectively,and the environmental benefit is significant.