Heat Transfer of Refrigerant Mixtures

Abstract

Heat transfer coefficient correla,tions for single phase flow and evaporation and condensation of refrigerant mixtiU'es have been developed based on experimental data for binary and ternary mixtures. A term-has been included for the =ass transfer resistance observed with mixtiU'es during evaporation. The correlations have been used to predict heat transfer coefficients tor proposed alternatives for HCFC-22. INTRODUCTION Heat transfer characteristics of binary mixtures have beenstudied by several researchers [1 .;..·,·15], with the general finding that mixture heat transfer coefficients are lower than the linear interpolation of pure component heat transfer coefficients, This is due to the effect of mixing on physical properties such as thermal conductivity, and the mass transfer resistance occuring during evaporation [12]. correlationshave been reported by Jung et al. [12, 13, 14] for calculating evaporation heat transfer coefficients of flowing binary mixtures. The purpose of this work was to develop correlations tor heat transfer coefficients for single phase flow and evaporation and condensation of refrigerant mixtures, including higher multicomponent systems. CORRELATIONS Chen (2] suggested that two phase evaporative heat transfer coefficients can be predicted by adding the contributions of nucleate boiling and convective evaporation: h(tp} h(nb) +h(ce) (1) This was extended by Jung [12]-,, drawing from work by Stephan and Abdelsalam (4], Thome (7], and Unals (9] to include terms for the effect of masstransfer resistance of binary mixtures based on the difference in vapor and liquid concentrations. In the present work, the mass transfer resistance effect is also based on phase equilibrium data, but by use of phase temperature differences. Gropp.and Schlunder [10] and Saito and Hihara [15] have reported methods for relating mixture mass transfer resistance to phase temperature differences. We have chosen ~he-method of Gropp and Schlunder, com~ining with Jung • s correlation f,or the local two phase evaporat1ve heat transfer coefficient for pure components: h(tp) ~ Nh(sa) + F(p)h(lo) (2)