Condensation Heat Transfer on Enhanced Surface Tubes: Experimental Results and Predictive Theory

M Belghazi,C Marvillet,A Bontemps

doi:10.1115/1.1459728

Abstract

Condensation heat transfer in a bundle of horizontal enhanced surface copper tubes (Gewa C+ tubes) has been experimentally investigated, and a comparison with trapezoidal shaped fin tubes with several fin spacing has been made. These tubes have a specific surface three-dimensional geometry (notched fins) and the fluids used are either pure refrigerant (HFC134a) or binary mixtures of refrigerants (HFC23/HFC134a). For the pure fluid and a Gewa C+ single tube, the results were analyzed with a specifically developed model, taking into account both gravity and surface tension effects. For the bundle and for a pure fluid, the inundation of the lowest tubes has a strong effect on the Gewa C+ tube performances contrary to the finned tubes. For the mixture, the heat transfer coefficient decreases dramatically for the Gewa C+ tube.

Highlights

A large number of designed enhanced surface tubes have been tested to find the best surface geometry for condensing either pure fluids or vapor mixtures
Theoretical models to predict the heat transfer coefficient for single low-finned tubes with trapezoidalor rectangularfins have been well developed since the 1940s, in particular by the pioneering work of Beatty and Katz1͔. Their model assumed that condensate is drained via gravity only. They neglected surface tension forces, which generally have an important role at the fin tip, since they are responsible for the draining of condensate from the tip to the fin flanks, and because the major part of heat transfer occurs at the fin tip
An enhancement ratio ␧⌬T is defined as the ratio of the heat transfer coefficient for a finned tube to that for a plain tube, based on plain tube area at the fin root diameter for the same ⌬T (⌬TϭTsatϪTw)

Summary

Introduction

A large number of designed enhanced surface tubes have been tested to find the best surface geometry for condensing either pure fluids or vapor mixtures. Honda et al ͓19͔ measured the row-by-row heat transfer coefficients of HFC134a condensing on a bundle of tubes having 26 fins/inch and a diameter at the fin root of 15.8 mm Their results are slightly lower than those of Blanc et al, Cheng and Wang20͔, and Agrawal et al ͓21͔ conducted experiments on condensation of HFC134a using several types of low finned tubes. Honda et al ͓23͔ conducted experiments during condensation of a downwardflowing zeotropic mixture HFC123/HFC134aabout 9 percent HFC134a at the test section inlet, on a 13ϫ15 (columns ϫrows) staggered bundle of horizontal low finned tubes. Their experimental data show that both the heat and the mass transfer.

Experimental Results

Findings

Conclusion