Heat transfer coefficient during condensation inside a minichannel multiport tube with R32 and R410A as working fluids

Abstract

The use of microchannels and minichannels in a heat exchanger has increased in recent decades. They contribute to increasing efficiency and to reducing refrigerant charge and compactness of heat exchangers. The aim of this study is to experimentally determine the heat transfer coefficient in minichannel two-phase flow processes with the low global warming potential refrigerant R32 and to compare it with the values experimentally obtained for R410A and some of the correlations encountered in the existing literature. There are a few publications studying refrigerant R32 inside multiport minichannel tubes; this has low flammability and has been classified as A2L by ASHRAE. European air-conditioning manufacturers recommend its use instead of R410A as it has lower global warming potential (R32 GWP = 675, R410A GWP = 2088). Other environmental improvements may also be considered: R32 is a monocomponent refrigerant, so recycling is easier than R410A; it is also safer according to NFPA 704 classification; and a breathing apparatus is required in the case of an accident with R410A. On the other hand, R410A flammability is lower than R32 because of the addition of R125. An installation for the study of condensation processes has been constructed at the Technical University of Cartagena, Spain. The more relevant results of heat transfer coefficient will be presented in this article. The analyzed data have been measured for R32 and R410A flowing through aluminum square multiport tubes with a hydraulic diameter of 1.16 mm, then compared. The influence of saturation temperature (or pressure), flow velocity, and vapor quality in heat transfer coefficient and frictional pressure gradient has been studied. The values considered for these variables are saturation pressure corresponding to 30 • C, 35 • C, 40 • C, 45 • C, and 50 • C; flow velocities from 100 to 800 kg/(s·m 2 ); and vapor quality from 0.05 to 0.9.

A MCDM Methodology to Determine the Most Critical Variables in the Pressure Drop and Heat Transfer in Minichannels

“…The analysis carried out in the latter case [18] would require a total of 35 h of calculation, while the SIMUS method barely takes 5 min. Other experimental methods were used to obtain the more influencing working parameters for minichannels multiport tubes [19] or for fin and tubes heat exchangers [20].…”

Analysis of the condensation process and air maldistribution in finned tube and minichannel condensers

“…For this reason, in the last two decades, a number of authors have been developing new correlations and models for the twophase HTC and friction factor specific for the microchannel condensers. As will be commented later, in the author's opinion, the most interesting correlations for the two-phase flow HTC have been developed by Webb (1998), Wang and Chi (2000), Koyama et al (2003), , Bahndauer et al (2006), Lopez-Belchi et al (2015). In spite of the fact that work was mainly focused on studying the heat transfer in the macroscale channels, the correlation that they developed has been considered particularly suitable also for simulating the behavior of minichannel condensers.…”