Hi, wondered if anyone can give me a pointer on this problem I am working on. 6 Diesel engines each with power 55kW running, given output cooling water temperature of 80°C, and required return temp of 60°C. The coolant is to be fed through a heat exchanger, with the heat exchanger outlet to be cooled via evaporative cooling from small cooling tower. Since I have Tout and Tin for the Heat EX/Engine loop, I can use steady flow energy eq to find mass flow, once I have made assumptions of thermal efficiency of engines, (30% of heat energy transferred to coolant), 55*6=330 @30% = 99kW Cp water @ 80°C = 4.196kJ/kg Q=mcpDT, so rearranging gives 99/(4.196*(80-65) = 1.57kg/s (heat energy transferred to coolant) Then, I am assuming a mains water feed to heat ex, with average assumed values; Cold side inlet temp: 10°C Cp water @10°C: 4.192kJ/kg Mains feed at 3l per min (0.051kg/s) Using SFEE and rearranging mh*Cph*(80-65)=mh*Cpc*(T4-10) 10+(1.57*4.196*15)/(0.051*4.192)=472.2 I am clearly missing something fundamental, as even I know that is totally incorrect. Any helpis hugely appreciated.