There are several systems that produce energy from low grade heat sources such as Stirling engines, thermoelectric generators, and ORC (Organic Rankine Cycle) systems. This paper shows the heat recovery from exhaust gases of a 1400 cc Diesel engine, to vaporize the working fluid of a small (<10 kW) ORC system. The main objective is to have a system as compact as possible, to make it suitable for transport applications such as cars, ships, trains, etc. Three fluids were studied for this application: water and two refrigerant fluids: R134a and R245fa, which were found to be more appropriate than water at certain pressure and temperature values. Afterwards, a design procedure was proposed, then the heat exchanger was modeled and finally a steady-state thermal and structural analysis were carried out using a commercial software to find the temperature and the effects of the thermal stress on the material of the helical coiled tube.