The Optimization Of The Tube-pass Scheme And Thermodynamic Characteristic Of Air Cooled Condenser With Liquid-vapor Separation

There are many ways for condensation heat transfer enhancement, and enhanced tubes were usually used in industry. However, enhanced tube can improve the heat transfer coefficient, but it also causes the flow resistance increases, which results in increase of energy consumption. Air cooled liquid-vapor separation condenser (LSC) is a new type of condenser with multi tube pass scheme. There are some holes on the baffles in the headers at the both ends of tubes, which can drain away the condensate in time during condensation process and increase the quality of the working-fluid into next tube-pass. So it is predicted to enhance heat transfer and low flow resistance.Base on the structural characteristics of LSC, condensating tube by tube and drainaging the condensate between the each adjacent tube pass, a program to simulate the in-tube condensation heat transfer coefficient and pressure drop is developed using the three heat transfer models (Yu and Koyama (1998), A.Cavallini et al.(2009) and Koyama and Yonemoto (2006) model) and pressure drop model (Choi and Kedzierski (2001)). In the programe, the in-tube condensing heat transfer coefficient and pressure drop for various tube pass scheme, including tube pass number and tube number per tube pass are predicted and compared when the refrigerant inlet quality and mass flux are given. Moreover, the refrigerant inlet quality at each tube pass can be defined by the designers, which is decidend by the liquid-vapor separation. The thermodynamic characteristic of the LSC with various tube pass schemes is evaluate by the penalty factor (PF) presented by Cavallini. This programe can be used to study the effect of refrigerant flow flux and quality on the in-tube thermodynamic performance.There14different tube-pass structures of liquid-vapor separation condensers and serpentine condenser were designed on the base of the same total heat transfer area and analyzing their differences in thermodynamic performance by Penalty Factor. The results show that the in-tube heat transfer coefficient of serpentine condenser are larger than liquid-vapor separation condensers because of the larger refrigerant mass flux in the single tube pass, but the pressure drop is bigger too. The pressure drop of liquid-vapor separation condenser with tube-pass design of5-3-2-1-1-1-1is the smallest among13liquid-vapor separation condensers, its pressure drop values, respectively, compared with the pressure drop of the biggest point liquid-vapor separation condenser and the serpentine condenser are64.8%-72.3%and68.8%～78.7%at the mass flux range of600to1200kg/(m2·s). The Penalty Factor (PF) was used to evaluated the thermodynamic performance of condenser with different structure design, the PF values of all liquid-vapor separation condensers are smaller than serpentine condenser at the mass flux of600to1200kg/(m·s), that is to say, the thermodynamic performance of liquid-vapor separation condensers are better than serpentine condenser, and the tube-pass scheme of5-3-2-1-1-1-1is the best.In order to verify the accuracy of the calculation results on this program base on the best tube-pass design5-3-2-1-1-1-1liquid-vapor separation condenser, experimental study on heat exchanger is made in the condition of R134a condensing temperature of45and50℃, the heat flux of4.96kW/m2and6.72kW/m2, and the mass flux of532.5kg/(m2·s) and644.6kg/(m2·s). And the calculated value and experimental data are compared, the study found that the deviation are basically falls within30%, especially Yu and Koyama (1998) and A.Cavallini et al.(2009) model. The deviation of the calculated pressure drop results and experimental data generally falls within30%in addition to the three points. So it is feasible to calculate the LSCs heat transfer coefficient and pressure drop by using the heat transfer model and the pressure drop model.According to the tube wall temperature, the matching design of tube fin space is done on the basis of optimization design of tube passes. The results show that the transverse tube pitch is least at condensing temperature of45℃and heat transfer rate of1525W. Using minimum entropy generation of comparison found that with the increase of air flow, minimum entropy generation is reduced. The minimum entropy generation relates definitly to the condensation temperature, and the minimum entropy generation increasing as the condensation temperature increasing, the minimum entropy generation of50℃is more bigger than45℃of29.2%-33.0%.