Exhaust gas heat exchanger calculations

by dubber91
Tags: calculations, exchanger, exhaust, heat
 P: 3 Hi Guys newbie here. Im trying to design a CHP system in which an engine with steady exhaust gas flow uses a heat exchanger to heat water for use around the home (central heating, washing water etc). The engine specifics are to be developed but i need to be able to size a heat exchanger so i can develop the system. The exhaust composition is largely air but obviously steam is present. The water is standard, chalky mains water. Now the hot tank of water can be sized accordingly, and the flow rate specified by using a pump or pumps. How would you go about setting up a spreadsheet using standard heat transfer equations to model the system? Ive got pretty basic heat transfer knowledge (i.e. newtons law of cooling and heat transfer coefficients). Any help would be great appreciated :) Kindest regards Steve
 PF Patron Sci Advisor P: 2,792 Conservation of energy, i.e. the energy taken out of the exhaust gas equals the energy recovered for your hot water system. Heat available in the exhaust is mass flow, multiplied by the specific heat capacity (is this a Diesel or petrol engine?), multiplied by the temperature difference over the heat exchanger (so exhaust outlet temperature minus whatever you can cool down to). Then you need to look at what return temperature and flow rate you want for your hot water system, and size a cooler for that capacity and required effectiveness.
 P: 3 OK. But how would i then go about sizing a heat exchanger? Assume an exchanger efficiency? How much energy is recovered over what size of heat exchanger? thanks in advance.....