Abstract
Single helical tube has been widely investigated in both smooth wall and corrugated wall structures. However, for the first time, this paper proposes and works on a helical tube-in-tube heat exchanger in which both inner tube and outer tube are corrugated (see graphical abstract for possible interesting configurations). The idea of the fabrication process of such heat exchanger will be the first challenge; and that is why the first part of this research explains what steps are required to fabricate the mentioned heat exchanger with affordable and available industrial techniques. When both inner tube and outer tube are corrugated, the relative position of the corrugations on both tubes provides different configurations (see case "c" and "d" in the graphical abstract) with completely different behaviors. In the second step, the numerical simulation of the mentioned heat exchanger is validated with the experimental results. At the third part of the paper, a comprehensive simulation is performed to analyze the mentioned heat exchanger from thermal, frictional and exergetic viewpoints. The results show that the corrugating of the outer tube in addition to the inner tube significantly boosts the thermal capacity of the heat exchanger without any further weight, area or size of the heat exchanger (case "d" provides 125% higher Nu number compared to the case "a"). Besides, the mentioned relative position of the corrugations plays a significant role so that the obtained Nu number of case "d" is 35% higher than that of case "c" (the difference of these cases is only the relative position of the corrugations). The reason of all these phenomenon and other remarkable findings are reported in this paper.