The thermal and fluid physiognomies of a double twisted tube heat exchanger was examined numerically. Twisted engineering is a wide-use method to improve heat transfer in heat exchangers. A counter-flow mode utilizing hot water in the inner tube and cold air in the outer tube was considered. This study aims to progress the thermal performance of the double tube heat exchanger by using twisted tubes instead of plane tubes. The heat exchanger was (1m) length, outer diameter (0.05m) and inner diameter (0.025m), both with a thickness (0.004m). It was tested for different values of twist ratios (Tr= 5, 10, and 15 respectively) and Reynolds numbers (Re=5000 to 30000). The Navier - Stockes and energy equations besides the turbulence model in demand for modelling this physical problem. ANSYS Fluent code was used for the numerical simulation. The results showed that the twisted tube heat exchanger showed increasing heat transfer compared with a plain tube heat exchanger. It was found that the cold outlet temperature, pressure drop and effectiveness are increased as the twist ratio increases.

They are considering the increasing demand and urgent need in different industries and the importance of heat exchangers imposed the development of heat exchangers to increase heat transfer and increase general performance, reducing volume and cost. The essential heat exchanger used in many industries is the double tube heat exchanger. This type has been distinguished by its simplicity and wide use in recent years. Several improvement methods have been applied, including passive, active, and compound techniques. Passive technologies change the geometry of heat exchangers and are one of the most effective processes to increase overall heat performance. Besides, the hybridization of flow liquids is one of the most critical approaches to increase heat transfer as nanofluids. This review discusses and analyzes the evolution of heat exchangers and methods for improving passive heat transmission. In addition, experimental and numerical research that used nanofluids in heat exchangers was discussed. Moreover, different twisted shapes of the heat exchanger tubes (elliptical and oval, square, and triangle) were studied, which generated secondary eddy flow that increases the intensity of turbulence and mixing, thus improving heat transfer. Also, additives inside heat exchanger tubes include twisted tapes, ribs, and conical rings. The engagement between the Nusselt number and the coefficient of friction was also offered.