Energy, mostly from the fossil fuels has been one of the most exploited natural resources. Internal combustion engines waste more than 50% of the fuel energy as heat rejection. Organic Rankine Cycle (ORC) technology has turned out to be a promising solution that can convert the low-temperature waste heat into electricity or any other useful form, further increasing its efficiency. This paper brings into picture the optimum design configuration of evaporators, one of the critical components in the entire cycle. The paper focuses on the evaporator design to deal with the challenges of lower package volume required, low space availability and lower weight essential for the development of engine-ORC unit. Both shell and tube as well as plate-type heat exchangers are taken into consideration for the compact design with the use of modified design approach using pitch to tube diameter ratio (P_t/d_o) and compressed plate pact length as the monitoring parameter in the iteration to curb the challenges. Engine coolant as water at 90° C is taken as the waste heat source and the evaporation temperature for the organic fluid (R245fa) is taken as 333 K and 323 K, maximum possible based on pinch-point criteria for shell-and-tube and plate-type heat exchanger for counterflow, respectively.