investigation of the effect of gradual change of the inner tube geometrical configuration on the thermal performance of the double-pipe heat exchanger

Today, with the development of technology, heat transfer, reducing the time of heat transfer, reducing the size of heat exchangers, and increasing the efficiency are considered. heat exchangers have many applications in the industry. therefore, increasing the efficiency of heat exchangers will increase the overall efficiency of a system and optimize energy consumption by a system. in the present study, the main goal is the study the effects of the gradual changes in the inner tube geometrical configuration on the thermal performance of the double-pipe heat exchanger on the thermal performance using computational fluid dynamics (cfd) methods based on the finite volume method. for validation, the results are compared with the valid results previously presented in the published papers, and there is a very good agreement between them. in addition to the basic model, six different geometrical designs are used for the inner tube, in the form of a flat tube and a nozzle-like tube. after the numerical simulation, the increase in heat transfer and the nusselt number of flow, pressure drop, thermal efficiency and the performance index were calculated for each model and compared with the base model and other models. the results show that the nozzle-like inner tube model has a lower performance than the base model. the model with a flat inner tube, and especially case 4 (the case with the flat inner tube with the aspect ratio of 0.3), has a very impressive performance compared to the base case at reynolds numbers below 6000. but at higher reynolds numbers, the basic model will have better overall conditions.