Experimental and CFD analysis of two phase flow of refrigerants inside a Horizontal tube

Abstract

In-tube two phase flow finds its applications in steam power plants, refrigeration and air conditioning, distillation and desalination units and transport of oil and slurry etc. The two phase flow is described by the parameters like mass flux, vapor quality and void fraction etc while the performance parameters of two phase flow are given by heat transfer coefficient and pressure drop. The salient feature of in-tube two phase flow is the formation of flow regimes, viz., stratified, slug, annular etc due to counter acting forces of gravity and vapor shear. The pioneering work of Lockhart and Martinelli [1947] forms the basis for modeling of two phase flow. They developed two phase multiplier approach to predict the frictional pressure drop of two phase flows using the separated flow model. Later, many correlations were developed for two phase multiplier, based on the experimental data of air-water mixtures, gas – oil mixtures etc at near atmospheric pressures and refrigerants for evaporating flows. Some of these correlations, viz., Lockhart and Martinelli correlation deviate by more than 100% in predicting the pressure drop of condensing flows or in general, two phase flows at high pressures. Yet, Lockhart andMartinelli correlation is widely used in the analytical modeling ofcondensing flows, viz., by Sarma et al [2002], Li et al. [2000] etc. The quasi local experimental work reported in the literature is primarily to study the performance of alternative refrigerants. Shao et al. [1998], Boissieux et al. [2000], Smit et al. [2002a, 2002b], Infante Ferreira et al. [2003] experimentally studied the performance of refrigerant mixtures to test their applicability as alternative refrigerants. Lee et al. [2006] reported the performance of hydro carbons for condensing flows.