This paper studies numerically the impact of installing longitudinal fins on the performance of a DPHE. Different heights were considered for these fins and three different profiles; rectangular, triangular, and semi-circular were investigated. Fins were fixed on the internal surface of the annulus side. The numerical investigation was carried out for counter flow. The study is performed in two cases. The first one was of a constant hot water mass flow rate (mh) at (0.3) kg/s and varying values of cold water mass flow rate (mc) which was from 0.2 to 1 kg/s. The second case was of a constant cold water mass flow rate (mc) at (0.3) kg/s and changing hot water mass flow rate (mh) which was from 0.2 to 1 kg/s. Inlet temperature of hot water was 353k and for cold water was 298k. The results showed that using longitudinal fins enhances the (DPHE) thermal performance. Also, semi-circular profile gave more enhancement in the rate of heat transfer compared to other studied profiles