Experimental Study On R-134A Condensation Heat Transfer Characteristics In Plate And Shell Heat Exchangers

In this study, condensation heat transfer experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-134A. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-134A in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by stacking three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45 degree. The R-134A flows down in on channel exchanging heat with the cooling water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, saturation temperature and vapor quality of R-134A on the measured data were explored in detail. The present data showed that two types of P&SHE have similar trends. The condensation heat transfer coefficients increase with the vapor quality for both types of P&SHE. A rise in the refrigerant mass flux causes an increase in the hr. Also, a rise in the average heat flux causes an increase in the hr. Finally, at a higher saturation temperature the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number. NOMENCLATURE A: heat transfer area of the plate b: channel spacing cp: specific heat dh: hydraulic diameter ifg: enthalpy of vaporization m: mass flow rate Re: Reynolds number x: vapor quality Subscript fg: difference between liquid and vapor phase i, o: at inlet and exit lat, sens: latent and sensible heats p: pre-heater r: refrigerant w: water INTRODUCTION The plate and shell heat exchangers (P&SHE) are different from the conventional plate heat exchanger. The plates that have oblique line grooves are circular, and stacked together in contrary arrangements, which are enclosed a cylindrical shell. Operating temperature rises up to 350 , and pressures can be achieved to 10 MPa. Although P&SHE is apparently different from the conventional rectangular plate exchanger, the underlying flow passage structure through the exchanger is the same as in the conventional plate heat exchanger. The P&SHE is being introduced to the refrigeration and air conditioning systems as evaporators or condensers for their high efficiency and compactness. Due to the serious destruction of the ozone layer in the atmosphere by the CFC refrigerants, various new refrigerants such as R-134A, R-143A, and R-125 were recently developed and introduced into the refrigeration and air conditioning systems. The heat transfer data for these new refrigerants are very scarce. In order to set up the database for using the new refrigerants in the design of the plate pattern for the P&SHE, condensation of R134A flow in a P&SHE is experimentally investigated in this study. In this study, the characteristics of the condensation heat transfer for refrigerant R-134A flowing in the plate and shell heat exchangers were explored experimentally EXPERIMENTAL APPARATUS AND METHOD The heat transfer plates and experimental system established to study the condensation of R-134A are schematically shown in Fig. 1 and 2. The experimental system was constituted with test section, refrigerant loop, water loop and a data acquisition unit. Refrigerant R-134A is circulated in the refrigerant loop. In order to obtain different test conditions of R-134A including vapor quality, system pressure and imposed heat flux in the test, we need to control the temperatures and flow rates of the working fluids in the water loop and current in the preheater.