Many inserts are used for increasing the performance of double pipe heat exchangers that are mentioned in literature review, most of them works as a swirl generator which helps to increase the turbulence of flow. This causes better mixing for flow and consequently leads to increase the heat transfer rate and pressure drop. The scope of this paper is to numerically study the effect of using twisted tape (TT) on heat transfer rate and friction factor (f) for double pipe heat exchanger by using different twisted tape ratios to detect the ratio that give the best thermal performance factor (PEC).The results show that, using twisted tape leads to increase the friction factor and heat transfer rate with comparing with plain tube. As the twisted ratio decreases the heat transfer rate will increase but also there is an increase in the friction factor. The twisted tape with ratio H=1.7 give the highest Nu reach to 1.8 time that of plain tube at Re= 18000 with the optimum thermal performance factor (PEC). Heat transfer performance of double pipe heat exchangers can be improved by using twisted tape insert inside the inner tube. The results show that, using twisted tape leads to increase in heat transfer rate and friction factor with comparing with plain tube. As the twisted ratio decreases the heat transfer rate will increase, but also leads to increase the friction factor. The twisted tape with ratio H=1.7 gives the highest Nu reach to 1.8 time that of plain tube at Re= 18000 with the optimum thermal performance factor (PEC).
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