Session: 12-06-02: Condensation and Phase Change Materials

Paper Number: 166458

Parametric Study on Condensation Pressure Drop and Heat Transfer of Eco-Friendly Refrigerants in Mini-Channel Heat Sinks 

The accelerating global warming crisis has prompted an urgent reconsideration of conventional refrigerants, particularly hydrofluorocarbons (HFCs) like R-134a, which, despite replacing ozone-depleting substances, possess alarmingly high global warming potential (GWP) values. The Kigali Amendment to the Montreal Protocol specifically targets the phasedown of these compounds, driving research toward environmentally responsible alternatives. Among the promising candidates, R-1234yf (a hydrofluoroolefin) stands out with a remarkably low GWP of approximately 4–over 99% reduction compared to R-134a's 1430–while maintaining similar thermophysical properties, potentially allowing direct replacement. Another viable alternative is R-290 (propane), a natural refrigerant with a GWP of just 3 and excellent thermodynamic efficiency, though its flammability necessitates additional safety considerations. Both R-1234yf and R-290 represent alternative refrigerants characterized by minimal environmental impact and sustainable profiles that align with global climate initiatives and emerging regulatory frameworks.

The methodological framework of this study employs the finite difference method along with governing equations and empirical correlations, such as the universal correlation developed by Kim and Mudawar (2012), for predicting condensation pressure drop and heat transfer coefficients in mini/micro-channel heat sinks. This comprehensive correlation was selected due to its robust validation across a wide range of working fluids, hydraulic diameters, and operating conditions. It accounts for various flow regimes encountered during condensation, including annular, slug, and bubbly flow, by incorporating dimensionless parameters such as the Reynolds number, Weber number, and Boiling number. For pressure drop calculations, the correlation addresses both frictional and accelerational components, providing accurate predictions across the entire quality range. Similarly, for heat transfer coefficient predictions, it incorporates the effects of two primary flow regimes: annular flow and slug/bubbly flows.

The numerical setup employed in this parametric study consists of a multi-mini-channel heat sink. Each channel features a hydrodynamic diameter of 1 mm, designed as a reference to evaluate heat transfer efficiency and compare the effect of channel geometry. The channels extend to a length of 600 mm. The primary geometrical parameters under investigation include channel width and height, which were systematically varied to assess their impact on thermal-hydraulic performance. Additionally, operational parameters such as mass velocity and inlet temperature were controlled as independent variables to determine their influence on the condensation process. This study analyzed the pressure drop and heat transfer coefficients of R-1234yf and R-290 based on channel width, height, mass flux, and inlet temperature. By comparing thermal performance factors under various parametric conditions, this study provides essential design guidelines for optimizing the condensation characteristics of eco-friendly refrigerants in mini-channel heat sinks.

Presenting Author: Seok-Yong Lee Sungkyunkwan University

Presenting Author Biography: I am Seok-Yong Lee, a combined M.S./Ph.D. student at the Heat Transfer Lab of Sungkyunkwan University in South Korea. My main research interests are flow and heat transfer characteristics of two-phase flow, and design of high heat flux heat sinks.

Authors:

Seok-Yong Lee Sungkyunkwan University
Chang-Su Park Sungkyunkwan University
Won-Woo Choi Sungkyunkwan University
Sung-Min Kim Sungkyunkwan University