A Review Study for a Twisted Tube Heat Exchanger

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.