COMPREHENSIVE ASSESSMENT OF TWO-PHASE FLOW DURING REFRIGERANT BOILING INSIDE PROFILED HORIZONTAL TUBES

Abstract

This paper presents an evaluation of research results on hydrodynamics and heat transfer during the boiling of refrigerant R22 inside a heat exchange tube with internal longitudinal fins, based on models and correlations proposed by various authors in the available literature. The models demonstrate different approaches to representing correlations for heat transfer calculations, taking into account the influence of hydrodynamic forces such as surface tension, viscosity, and inertia, which affect the motion of two-phase flow in tubes and channels and contribute to the understanding of physical phenomena. The study describes the experimental setup, where heat transfer during refrigerant boiling was investigated under the following operating parameters: heat flux density q = 5, 10, and 20 kW/(m2⋅K), mass flux G = 70, 110, and 200 kg/(m2⋅s), local vapor quality x = 0.01–0.64, and refrigerant saturation temperature ts=15 °C. The influence of heat flux, mass flux, and vapor quality on heat transfer was analyzed, providing valuable insights into heat transfer processes during two-phase refrigerant boiling in tubes and channels. A manufacturing technique for longitudinal fins and unique mandrels for drawing inside copper tubes was developed. Flow visualization revealed stratified, wavy, wavy-slugs, and annular flow regimes. Verification of two-phase flow regimes was performed by comparing experimental results with calculations based on corresponding dependencies from existing flow regime maps. Experimental data were processed using an appropriate methodology for calculating heat transfer coefficients. Based on the obtained results, heat transfer during boiling of two-phase R22 flow inside the finned tube was calculated using 14 models and correlations. The analysis identified models and correlations that most accurately describe the experimental results and can be recommended for engineering practice. Bibl. 31, Tab. 4, Fig. 4.