Convective Condensation Inside Horizontal Smooth and Microfin Tubes

Abstract

An experimental investigation was performed for convective condensation of R410A inside one smooth tube (3.78mm, inner diameter) and six microfin tubes (4.54, 4.6 and 8.98 mm, fin root diameter) of different geometries for mass fluxes ranging from 99 to 603 kg m~^s~'. The experimental data were analyzed with updated flow pattern maps and evaluated with existing correlations. The heat transfer coefficient in the microfin tubes decreases at first and then increases or flattens out gradually as mass flux decreases. This obvious nonmonotonic heat transfer coefficient-mass flux relation may be explained by the complex interactions between the microfins and the fluid, mainly by surface tension effects. The heat transfer enhancement mechanism in microfin tubes is mainly due to the surface area increase at large mass fluxes, while liquid drainage by surface tension and interfacial turbulence enhance heat transfer greatly at low mass fluxes.

Comparison of tubeside condensation and evaporation characteristics of smooth and enhanced heat transfer 1EHT tubes

“…Verification of the test apparatus for single-phase flow and two-phase flow in smooth tubes was previously performed by Wu et al [8]. Using the same experimental set up, Wu et al [23] studied the heat transfer enhancement mechanism in microfin tubes and found that the enhancement is mainly due to the surface area increase at large mass fluxes; additionally they found that liquid drainage by surface tension and interfacial turbulence enhance heat transfer greatly at low mass fluxes. Li et al [24] found a nonlinear relation between mass flux and the condensation heat transfer coefficient.…”

The effect of gravity on R410A condensing flow in horizontal circular tubes

“…The heat transfer coefficients for the condenssing flow obtained using the models described before are compared with the experimental data in our previous experimental studies [39]. More details about the experimental setup and data reduction can be found in Wu et al [39].…”

“…More details about the experimental setup and data reduction can be found in Wu et al [39]. The local numerical heat transfer coefficients are also compared with empirical correlations developed by Cavallini et al [38], Thome et al [41], Shah [42].…”

Comparison of condensation and evaporation heat transfer on the outside of smooth and enhanced 1EHT tubes

“…No previously reported condensation or evaporation data exists for the enhanced geometry considered in this study (Vipertex 1EHT tube); therefore a comparison of the 1EHT tube performance will be made to smooth tube. As indicated in Wu et al [40,41], helical micro-fin tubes are more effective at low mass fluxes due to the strong surface tension effects that are seen at low mass fluxes. Therefore, the focus of the current experimental investigation will be on low mass fluxes.…”

“…Heat flux was obtained from the inlet and exit water temperatures (measured using platinum RTDs). Flow rate is controlled by a valve located after [42] and Wu et al [41]. For enhanced tubes, there are limited heat transfer predicting procedures available with the degree of confidence necessary to perform relevant designs; any work that has been done is limited to the specific geometry and operating conditions based upon tests from which the predicting procedures have been derived.…”