Theoretical study of boundary-layer condensate from R-134a_oil mixture refrigeration tubes

Abstract

The present research provides a theoretical study of the heat transfer condense to a mixture of oil nature of Adsorption totally with refrigerant to intensify stratiform on the outer surface of the package of circular pipe,Oil used in this work is a synthetic oil(32 ISO VG Branched Acid Polyol Ester) and refrigerant used is R-134a, In this study selected tube circular diameter (1/2 in) copper tubes and different concentrations of oil. The theoretical analysis will to causeon equations to find a distribution thickness membrane condensation site on the perimeter of the tube and the rate of heat transfer coefficient. Equations usedMicrosoft Office Excel, Current search depends on the computer analysis using“Excel program” in the accounts and find the curves required for the analysis of different ratios of oil with R-134a and its impact on the membrane condensation, The main objectives of the present work are:- 1- Investigating the heat transfer coefficient for laminar film condensation of R-134a –oil mixture theoretically on horizontal circular tube. 2- Predicting the thermophysical properties of pure lubricating oil and refrigerant –oil mixture. 3- Investigating the effect of the presence of oil particles on the condensing coefficient. 4- Parametric study to investigate the effect of the most important parameters of the problem like: tube diameter (D), orientation angle (β(, oil concentration (Ѡo). 5- Analysis and discussion of the results for the final conclusions and recommendations. The results show that the local condensate film thickness increases on the periphery of the tube in the direction of gravity. Also, the local condensate film thickness is found to increase with increasing oil concentration at any point of tube circumferential surface for tube diameter used in this study. Also, the local condensate film thickness is found to increase with increasing vapor to surface temperature difference. The results also reveals that the average heat-transfer coefficient of the condensing mixture, at any vapor to surface temperature difference, decreases as the oil concentration within the vapor increases, for each 5% increase in oil concentration at a given vapor to surface temperature difference the average heat-transfer coefficient decrease is found to be about 4.46%. Also, the average heat-transfer coefficient of the mixture is found to decrease with increasing vapor to surface temperature difference. When vapor to surface temperature difference is raised from 3.5°C to 38.5°C at the different oil concentrations considered in this study, the average condensing coefficient is found to drop by about 50.23%