scope:

Abstract

Many inserts are used for increasing the performance of double pipe heat exchangers that are mentioned in the literature review. Most of them work as swirl generators helping in increasing the turbulence of flow. This causes better mixing for flow and consequently increases the heat transfer rate and pressure drop. The goal of this thesis is to study the effect of using twisted tape, with different twist ratios, on the heat transfer rate and the friction factor of the inner tube of a double pipe heat exchanger. The aim is to decide on the optimum twist ratio resulting in the best heat transfer rate. It is found that the efficiency of heat transfer of double pipe heat exchangers can be improved by using twisted tape insert inside the inner tube. This causes better mixing for the flow and consequently increases the heat transfer and pressure drop. The results show that, using twisted tape increases the heat transfer rate and friction factor when compared with plain tube. As the twist ratio decreases, the heat transfer rate increases, but also leads to increasing the friction factor. The twisted tape with ratio H=1.7 gives the highest N_u which is 1.8 times that of plain tube at R_e=18000 with the optimum thermal performance factor (PEC).