Ethylene glycol is heated from 25°C to 40°C at a rate of 2.5 kg/s in a horizontal copper tube (k = 386 W/m·K) with an inner diameter of 2.0 cm and an outer diameter of 2.5 cm. A saturated vapor (T_g = 110°C) condenses on the outside-tube surface with the heat transfer coefficient (in kW/m²·K) given by 9.2/(T_g - T_w)^0.25, where T_w is the average outside-tube wall temperature. What tube length must be used? Take the properties of ethylene glycol to be ρ = 1109 kg/m³, c_p = 2428 J/kg·K, k = 0.253 W/m·K, μ = 0.01545 kg/m·s, and Pr = 148.5.