Design and Performance Analysis of a Liquid Sub Cooler in a Refrigeration Circuit using a Shell-and-Tube Heat Exchanger

This paper presents the complete thermal design of a shell-and-tube liquid sub-cooler integrated into a single-stage ammonia (R717/NH₃) refrigeration cycle operating at −1.88 °C / 36 °C. The exchanger sub-cools liquid NH₃ from 36 °C to 30 °C using cooling water entering at 24 °C and leaving at 29 °C, with a total heat duty of 15.30 kW. All NH₃ thermodynamic properties are taken from the NIST REFPROP database (National Institute of Standards and Technology). The Kern method is applied step by step: log-mean temperature difference with correction factor, preliminary tube count, shell diameter sizing, tube-side Sieder–Tate correlation for thermally developing laminar flow, and shell-side Kern correlation for turbulent cross-flow. The resulting overall heat transfer coefficient with fouling is U_design = 275 W/m²·K, validated against HTRI Xist v6.00 (274.8 W/m²·K, deviation < 0.1 %). Thermoptim simulation confirms that the sub-cooler raises the cycle COP from 6.05 to 6.21 (+2.6 %) and reduces the refrigerant vapour quality at the evaporator inlet from 0.14 to 0.11.