# Condensation Flow of Refrigerants Inside Mini and Microchannels: A Review
## 3 Condensation Flow of Refrigerants Inside Mini/Micro-Channels
### Numerical Studies Focused on Mini/Microchannel Condensation of Refrigerants
They conducted transient two-dimensional simulations for the condensation of R134a in a microchannel with a diameter of 100 \(\upmu\)m. Their simulations encompassed a range of vapour mass fluxes at the channel inlet, varying from 245 to 615 kg/m\({}^{2}\)s, and heat fluxes spanning 200 to 800 kW/m\({}^{2}\). [PERSON] et al. [63] conducted a numerical simulation based on the VOF method. Their study focused on simulating the condensation flow of refrigerant FC-72 within a rectangular microchannel with a hydraulic diameter of 1 mm. Turbulence effects were simulated using the realisable k\(-\epsilon\) model. Their simulations revealed that reducing the wall cooling heat flux or increasing the mass flux of the flow led to an increase in the length of the vapour column. [PERSON] et al. [64] conducted steady-state numerical simulations to investigate the condensation of R134a within a 1 mm square minichannel. Their simulations used the VOF approach to track the vapour-liquid interface during mini/microchannel condensation. Operating at mass fluxes varied from 400 to 800 kg/m\({}^{2}\)s, the simulations maintained a uniform wall temperature as the boundary condition. Both the vapour core and liquid film were modelled as turbulent phases using a low-Reynolds number version of the SST k\(-\omega\) model. The findings suggested that gravity had minimal influence in the square minichannel, with heat transfer primarily governed by shear stress and surface tension under the considered mass flux conditions. [PERSON] et al. [65] conducted steady-state numerical simulations to analyse R134a condensation within horizontal channels. They explored the impact of hydraulic diameters ranging between 1 and 3.4 mm on two-phase fluid flow and heat transfer. Subsequently, the authors carried out two-dimensional transient simulations to assess the influence of wave phenomena on the condensation flow. Employing the VOF method at a saturation temperature of 40 \({}^{\circ}\)C and various mass fluxes (50-200 kg/m\({}^{2}\)s), these simulations provided insights into the heat transfer coefficient trends. As for their study, the steady-state simulations indicated an increase in heat transfer coefficient with decreasing channel diameter from 3.4 to 1 mm, with surface tension exhibiting negligible effects on the liquid film distribution in the 3.4 mm channel. [PERSON] et al. [66] conducted a numerical exploration of the heat transfer and pressure drop behaviours during the condensation of R410A within horizontal microchannel tubes (with hydraulic diameters of 0.25, 1, and 2 mm). The various saturation temperatures were considered in their study. The author's main emphasis was on understanding how the saturation temperature of R410A influenced these characteristics. Employing the volume of fluid (VOF) model, they utilised the SST-k-\(\omega\) turbulent model to simulate both vapour and liquid phases. A steady-state numerical simulation of the condensation flow of R600a was conducted by [PERSON] et al. [7]. The authors numerically investigated the heat transfer characteristic condensation flow at mass fluxes ranging from 200 to 600 kg/m\({}^{2}\)s inside a single circular microchannel with varying diameters. The VOF model was employed to simulate a two-phase flow, with phase change occurring at the saturation temperature, as represented by the Lee model [67]. [PERSON] et al. [6] also conducted a further study on the condensation flow of R600a simulations inside the microchannel. In their study, they investigated fluid flow as well as heat transfer characteristics. They made a numerical investigation to analyse the effects of mass flux, hydraulic diameter, and vapour quality on both heat transfer rate and pressure drop. To achieve this, steady-state numerical simulations were conducted to study the condensation flow of R600a with a 1 mm square minichannel. The results were conducted to study the condensation flow of R600a with a 1 mm square minichannel. The results were conducted to study the condensation flow of R600a with a 1 mm square minichannel.