Numerical Simulation And Experimental Study On The Performance Of Two-throat Nozzle Ejector

The mechanical energy loss occurs in the expansion devices for the conventionalvapor compressor refrigeration cycle which results the performance decreases in the system.The expansion valve is replaced by a two-phase ejector to recover the mechanical energy ofthe high pressure refrigerant and to increase the coefficient of performance in the two-phaseejector refrigeration cycle (TPERC). Thus, the study on the vapor-liquid two-phase ejectorrefrigeration cycle system is of important theoretical and practical value. The previousresults show that the use of the two-phase ejector can improve the performance of TPERC.Thus, the internal flow characteristics and the performance of the two-phase ejector weresimulated numerically by using ANSYS CFX software in this paper, and the experimentalstudy on the performance of the TPERC were carried out. The effects of the first andsecond cross-sectional throats area, the maximum diameter between the first and secondthroats, and the divergence angle of the nozzle were analyzed under the fixed workingcondition. The effects of the condensing temperature and the evaporation temperature onthe entrainment ratio of the ejector and the system COP were experimentally analyzedunder the fixed geometric parameters of the ejector. The experimental results werecompared with the simulation results. The conclusions are as follows:(1) The simulation and experimental results indicate that under a fixed workingcondition (the evaporation temperature of1℃, condensing temperature of45℃), theentrainment ratio firstly increases then decreases with the increase in the firstcross-sectional throat area of the nozzle, which achieve maximum value as the firstcross-section area of the nozzle throat is3.14mm2；the COP increases with the increase inthe first cross-sectional throat area of the nozzle, which achieve maximum value as the firstcross-section area of the nozzle throat is3.46mm2. The entrainment ratio and the COPincrease with the increase in the second cross-sectional throat area of the nozzle throat,which achieve maximum value of the COP as the second cross-section area of the nozzlethroat is2.27mm2.(2) The simulation and experimental results indicate that under a fixed workingcondition (the evaporation temperature of1℃, condensing temperature of45℃), themaximum diameter between the first and second throats has no significant effect on theentrainment ratio and the COP. The entrainment ratio and the COP decreases with theincrease in the divergence angle of the nozzle, which achieve maximum value of the COPas the divergence angle of the nozzle is2°.(3) The simulation and experimental results indicate that under a fixed structure ofthe two-throat nozzle ejector, the system COP increases with the increase in the evaporating temperature, and decreased with the increase in the condensing temperature. The trend ofthe simulation results is agree with the experimental results, but the simulation results arehigher than the experimental results, because that the energy is lost in the actual experimentin the pipes, valves, heat exchangers, etc. The boundary conditions are differences betweenthe actual and simulate conditions. Meanwhile, the results show that the TPERC system ismore advantageous under a lower condensing temperature.(4) The visualization experimental results indicate that the fluid run out from theejector nozzle into the mixing chamber is gas-liquid mixed state, and because of thepresence of the high speed spoiler phenomenon, there are a large number of bubbles insidethe flow, which can not be good tracked. A part of laser illuminated the mixing chamberwas reflected because of its quartz material and cylindrical form, and the laser can not shineon the vertical center interface of the ejector, so the bubble flow in the mixing chamber cannot be clearly observed by using the PIV device with a low energy laser to analyze the flowcharacteristics on the vertical center interface of the ejector.