Experimental and modelling investigation of thermohydraulic performance of CO₂ finned-tube condensers

Abstract

Carbon dioxide is a promising refrigerant for refrigeration and heat pump applications because of its environmental sustainability. However, unlike supercritical gas coolers, the thermohydraulic behaviour of subcritical CO₂ finned-tube condensers remains inadequately investigated and understood because of complex condensation and two-phase flow phenomena. This study presents a combined experimental and numerical investigation of a CO₂ finned-tube condenser operating under subcritical conditions. Experiments were conducted using a dedicated CO₂ test facility equipped with a two-row finned-tube heat exchanger and comprehensive instrumentation for measuring refrigerant- and air-side operating parameters. A distributed segment-by-segment effectiveness–NTU model was developed and validated to predict local and overall thermohydraulic performance. The model captures the coupled heat transfer, phase-change, and pressure-drop processes occurring in both the superheated and two-phase regions of the condenser. Validation against 30 operating conditions demonstrated deviations within ±10% for heat transfer rate, ±15% for refrigerant-side pressure drop, and ±10% for air-side pressure drop. The effects of refrigerant mass flow rate, air velocity, and inlet air temperature on local and average heat transfer and pressure-drop characteristics were systematically examined. The results provide new insight into the evolution of condensation, vapour quality, and local heat transfer coefficients along the flow path, and offer a reliable tool for the design and optimisation of high-efficiency CO₂ refrigeration and heat pump systems.