THEORETICAL AND EXPERIMENTAL ANALYSIS OF HEAT TRANSFER COEFFICIENT, PRESSURE DROP AND FLOW PATTERNS DURING CONDENSATION OF HYDROCARBONS ZEOTROPIC MIXTURES INSIDE TUBES

Abstract

The legislations around world are becoming progressively more restrict to the emission of gases harmful to the environment. In this context, the HVACR sector experiences the gradual replacement of the halocarbon refrigerants by fluids with low impact on the environment. Among these fluids, hydrocarbons mixtures are being speculated as a promising choice. The present proposal of doctoral research concerns the study of in-tube condensation of zeotropic mixtures of hydrocarbons. Experimental results will be obtained for heat transfer coefficient, pressure drop, void fraction and flow pattern for pure R290, R600a and R1270 and the following mixtures of them: R290/R600a (propane/isobutane), molar fraction 30/70%, and R1270/R600a (propylene/isobutane), molar fraction 25/75%. Experiments will be performed for tube diameters of 6 and 9 mm, mass velocities from 50 to 400 kg/m2s, dew point temperatures of 35 and 45°C and vapor quality ranging from 1 to 0. These results will be compared with data obtained in the present study for R134a in order to evaluate the relative performance of the mixtures and a conventional refrigerant, that although presents a null ODP (ozone depletion potential), presents a high GWP (global warming potential). Special attention will be given to the evaluation of the liquid film thickness during annular flow in order to estimate the void fraction. The experimental database will be considered in the development of semi-empirical models to be used as design tools of heat exchangers. The experiments will be performed in an experimental apparatus located in the Department of Mechanical Engineering of EESC-USP. Currently, this apparatus is being modified in order to become capable of performing flow boiling and convective condensation tests for hydrocarbons. The adjustments of the test facility counts with funds from research grants provided by FAPESP (2011/50176-2) and CNPq (476763/2013-4). It is worth to highlight that the Heat Transfer Research Group at EESC-USP has reasonable experience on experimental studies involving heat transfer during phase-change processes. It will also contribute to the success of this proposal, the fact that the candidate is working in the same research group, investigating similar research topic for more than three years. Moreover, the candidate already finished all the graduate courses necessary to receive the Doctoral degree.