Papers by Author: Jing Lv

Abstract: The trans-critical CO₂ refrigeration cycle involving a regenerative process is analyzed in this paper. The thermodynamic performance of the cycles with regeneration and without regeneration has been compared. The optimal circumstance for the regenerative process set in the trans-critical CO₂ cycle is given. The impact of the regeneration on the performance of the system under difference operating conditions is also discussed in this article.

Abstract: The change of system performance caused by regenerative cycle in different operating conditions was analyzed in this paper, comparing the cycle with or without internal heat exchanger in a CO₂ trans-critical cycle. We analyzed theoretically the performance of CO₂ trans-critical cycle with the internal heat exchanger, and found that the coefficient increased with the decreasing of the high side pressure and the increasing of outlet temperature in gas cooler, in a certain range of the high side pressure and outlet temperature. The evaporation temperature could be raised when the system with internal heat exchanger and at the same time the coefficient of performance could be improved obviously. At lower high side pressure, the performance coefficient could be improved significantly by increasing the suction superheat. The higher the gas cooler outlet temperature was, the more obvious the increase was.

Abstract: In this paper, the three straight casing tubes and the double helix casing tubes were modeled using the Gambit software. And the fluid flowing in tubes was simulated by Fluent software. According to the simulation results, with the field synergy principle, two casing tubes’ flow and temperature distribution of carbon dioxide and water have been analyzed. Simulation data show that the double helix casing tubes is better than the three straight casing tubes on heat transfer and synergy. Lay the good foundation for design optimization and efficiency of heat exchanger of carbon dioxide heat pump system.

Abstract: In the design of a carbon dioxide heat pump water heater evaporator, the effect of the circuit number on the evaporator is investigated numerically by EVAP-COND 3.0 version simulation package of American National Institute of Standards and Technology. It is found that as the circuit number increases the temperature difference between the air and the refrigerant increases, but it reduces the overall heat transfer coefficient. The evaporator capacity will rise firstly, and then drop with the circuit number and achieve the maximum in the optimum circuit number. Therefore, selecting the appropriate circuit number of the evaporator can significantly improve the efficiency and optimize the design.

Abstract: By using the FLUENT software, the flow and heat transfer properties of several elliptical tubes were numerically studied. The mathematical models of the tubes flow field were established. The implementation incorporated a SMPLE-based semi-implicit solution algorithm that was applied to iterating calculation. Results shows that the surface heat transfer coefficient, temperature difference between inlet and outlet were all higher than circular tube, when mass flux equal to at inlet of elliptical tubes and circular tube and wall temperature was invariable. Therefore, the elliptical tube is a kind of effective heat transfer enhancement element.

Abstract: The trans-critical CO2 cycle usually involves a regenerative process. The regenerative process used in the trans-critical CO2 cycle is analyzed in this paper. The cycle with regeneration and without regeneration had been compared. The circumstance for the regenerative process set in the trans-critical CO2 cycle is given. The impact regeneration made on the performance of the system in difference operating conditions is also discussed in this article.

Abstract: In this paper a gas cooler for trans-critical carbon dioxide water heater was designed and calculated according to the theory basis for the optimal design. The characteristic parameters of gas cooler in heat pump hot water system were compared and analyzed, applying the data from trans-critical carbon dioxide water heater test bed, under one-time heating condition, by different flow of chilled water and hot water, different inlet temperatures of chilled water and hot water. To sum up, coefficient of performance can be increased by increasing the chilled water inlet temperature or hot water circulating flow, while it can be decreased by increasing the inlet temperature of hot water circulating system，the parameters (flow of water, inlet temperature, the refrigerant mass flow, gas cooler pressure and inlet temperature of refrigerant) need to be adjusted to different requirements, for ensuring the high efficiency of system.