| The two-stage compression forward bootstrap air-cycle refrigeration system uses air asrefrigerant. The centrifugal compressor connected with the turbo-expander coaxiallyrecovers the expansion power to compress the air once again, that can reduce the powerconsumption of the system and increase the unit cooling capacity, so as to increase thesystem COP. The air humidity ratio has great influence on the system performance,therefore, it is of great theoretical and practical importance to study on the problems ofreducing the system air humidity ratio.In this paper, the improved high pressure water separation flow scheme of the air cyclerefrigeration system for quick-freezing was put forward, to which the high efficiency platefin heat exchanger and water separator are added to cool the inlet air of system below thedewpoint and draining the condensate water by the separator. In order to verify thefeasibility of the improved flow scheme, the mathematical model of the system wasestablished using lumped parameter method based on the previous experimental set-up ofthe air cycle refrigeration system for quick-freezing. The simulation software isprogrammed using EES. A series of simulations for the air cycle were carried out and thefactors affecting the dehumidification performance of the system were analyzed. Thesimulation results show that the system has good dehumidification performance, and theexperimental set-up was rebuit according to the flow scheme. A series of experiments forthe air cycle refrigeration system were performed under different working conditions on therebuilding experimental set-up. The experimental results were analyzed and compared withthe simulation results. The following conclusion can be obtained from the simulation andexperimental results:(1) the simulation and the experimental results indicates that the rise of the inletpressure of the centrifugal compressor almost have no effect on the air humidity ratio of theturbo-expander inlet, however, the amount of vapor condensed in the turbo-expanderincreases with the inlet pressure, and the increasing rate of the system with recuperator ismuch higher than that of the system without recuperator;(2) The air humidity ratio at theturbo-expander inlet of the system with recuperator No.2is lower than that of other systems.The simulation value of the maximum dehumidification efficiency of the system withrecuperator No.2is about47.6%, and the experimental one is about30%. Compared withthe system without recuperator, the refrigerating capacity and COP of the system withrecuperator are much higher. The simulation results indicate that the COP of the systemwith recuperator is nearly48%higher than that of the system without recuperator under theworking condition of200kPa inlet pressure of the centrifugal compressor;(3) Theexperimental results indicate that the efficiency of the parallel flow recuperator No.1 increases with the rise of the NTU, and the maximum efficiency is0.509as the NTU is1.57,that is consistent with the simulation results. The simulation results indicate that theefficiency of the recuperator No.1can be increased significantly, if the counter-flow modelis used, and the maximum efficiency of the counter-flow recuperator No.1is0.72.(4) Thesimulation results indicate that the effect of the inlet pressure of the system on the airhumidity ratio at the system inlet is more significant than on the air humidity ratio at theturbo-expander inlet and all of them decrease with the increase in the system inlet pressure,and the system performance is deteriorated. Both the air humidity ratio at theturbo-expander inlet and the amount of vapor condensed in the turbo expander increasewith the increase in the system refrigeration temperature and the hot side outlet temperatureof the air cooler.(5) The simulation results show that the efficiency improvement of thecomponents can increase the refrigerating capacity and COP of the system, and theisentropic efficiency of the turbo-expander is the greatest factor affecting the system COP.The sequence of the factors of the system COP is the efficiency of air cooler, the isentropicefficiency of centrifugal compressor, the efficiency of recuperaor No.1, the efficiency ofrecuperaor No.2. |
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