Write down the total thermal resistance for a double-pipe heat exchanger. Show how to convert from total resistance to an overall heat-transfer coefficient. Explain how flow regime may affect overall heat transfer rate.

A long, thin-walled double-pipe heat exchanger with tube and shell diameters of 0.01 m and 0.025 m, respectively, is used to condense refrigerant-134a with water at 20°C. The refrigerant flows through the tube, with a convection heat transfer coefficient of hi= 4100 W/m² °C. Water flows through the shell at a rate of 0.3 kg/s. The thermal resistance of the inner tube is negligible since the tube material is highly conductive and its thickness is negligible. Both the water and refrigerant-134a flows are fully developed. Properties of the water and refrigerant-134a are constant. Water properties: p = 998 kg/m³, v=u/p-1.004x 10-6 m²/s, k = 0.598 W/m. °C, Pr = 7.01 Cold water D Do