Heat transfer enhancement in heat exchanger with dimpled/protruded surface

Numerical study of heat transfer enhancement in compact heat exchanger with dimpled/protruded surfaces has been undertaken. The compact heat exchanger, with hot water (laminar regime) flowing in the inner tube and cold water in the annulus was investigated numerically. Two different configurations of the dimple/protruded surfaces were investigated, i.e. arrays of spherical dimples in different sizes and arrays of dimples in different orientations. The flow structure and thermal fields in the channel were presented and discussed in detail. It was found that the optimum heat transfer enhancement at a low pressure drop is achieved at the configurations of between 0.5 mm to 1 mm dimples/protrusions which resulted in an enhancement in the total heat transfer rate of 9.3% to 10.75% comparing to a smooth channel. This is a worthwhile heat transfer enhancement as the pressure drop incurred is as low as 1.71%. The pressure drop increases rapidly by increasing the height of the dimple and protrusion, therefore configuration of the dimples and channel height could be optimized in order to increase the thermal performance factor. The results also show that the orientation of the angle of the dimples/protrusions in the compact heat exchanger make insignificant differences in heat transfer enhancement and pressure drop.