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4th Thermal and Fluids Engineering Conference

ISSN: 2379-1748

AN INVESTIGATION ON DIABATIC FLOW PATTERN CHARACTERISTICS DURING CONVECTIVE CONDENSATION INSIDE HORIZONTAL TUBES

Tiago A. Moreira
University of Sao Paulo, Sao Carlos School of Engineering, Department of Mechanical Engineering, Av. Trabalhador Sancarlense, 400, Pq. Arnold Schimidt, Sao Carlos, SP, Brazil

Gherhardt Ribatski
Heat Transfer Research Group, University of Sao Paulo, Sao Carlos School of Engineering, Department of Mechanical Engineering, Av. Trabalhador Sancarlense, 400, Pq. Arnold Schimidt, Sao Carlos, SP, Brazil

DOI: 10.1615/TFEC2019.phc.028348
pages 1143-1153


KEY WORDS: Convective condensation, Two-phase flow, Flow patterns visualization, Heat Transfer

Abstract

This paper concerns flow patterns visualization and their characterization under diabatic conditions for convective condensation of R134a inside a horizontal tube. The test section comprises a counter-current tube-in-tube heat exchanger with cold water flowing in the annuli region and R134a in the inner tube. Both inner and outer tubes are transparent and made of borosilicate. Such set up allows visualization of the condensation process under heat transfer conditions, on contrary to most of studies available in literature, based on flow pattern characterization in an adiabatic region located downstream the cooling section. The experiments were performed for mass velocities ranging from 130 to 400 kg/m2s, saturation temperature of 35°C and vapor qualities up to 0.93. The following flow patterns were observed: (i) stratified; (ii) wavy; (iii) intermittent; and (iv) annular. Comparisons of the experimental visualizations and the methods of Tandon et al. [5] and El Hajal et al. [6] were performed. Both methods predicted correctly the flow patterns at high vapor qualities. The method of Tandon et al. (1982) is the most accurate at low vapor quality conditions. Moreover, based on analyses of flow images, waves on the liquid film with different characteristics were recognized. Besides the waves with low amplitude and high frequency, typically observed under annular flow conditions, waves of high amplitude and low frequency and intermediary amplitude and frequency were characterized based on analyses of an optical signal.

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