| Pub. Date | : Feb, 2020 |
|---|---|
| Product Name | : The IUP Journal of Mechanical Engineering |
| Product Type | : Article |
| Product Code | : IJME10220 |
| Author Name | : Parinam Anuradha, Harendra Kumar, Ramandeep and Sachin Raghav |
| Availability | : YES |
| Subject/Domain | : Engineering |
| Download Format | : PDF Format |
| No. of Pages | : 25 |
The paper investigates heat transfer and friction loss characteristics of concentric pipe counterflow heat exchanger with plain pipe and with various arrangements of turbulators. It presents two configurations of in-line Inner Side Triangular Ribs (ISTR) on both outer and inner pipe and two configurations of helical spring wrapped over inner pipe. The effect of different parameters of the triangular ribs and helical spring at constant velocity of cold fluid of 0.05 m/s with varying velocity of hot fluid from 0.48 to 0.98 m/s was studied numerically for Reynolds number (Re) ranging from 6,000 to 16,000. It is found that the turbulators inserted inside heat exchanger increase the Nusselt number for the triangular rib arrangements up to 1.7 times and for spring arrangement up to 1.3 times over the tube without turbulator. A new combination of ISTR of ei/Hi = 0.105, eo/Ho = 0.097 with wrapped helical spring of p/d = 1.28 turbulators on the inner pipe was also studied. The numerical results revealed that the increment of Nusselt number with combined in-line triangular rib and helical spring as insert as compared to plain tube varied from 73% to 77% and this combined arrangement also provided a significant improvement of heat transfer rates over using spring or rib alone. Over the range of Re considered, the maximum values of Performance Evaluation Criterion (PEC) were found to be 1.18 for a combination of triangular ribs and helical spring.
The sustenance of rapid change of technologies and the effective utilization of available energy becomes the need of the hour today. Devices like heat exchangers are used for minimizing the devastation of energy, generation of entropy in a system, perform its work efficiently and effortlessly for years. As integral parts of comfort and process, it involves condensation, evaporation, cooling, heating of a single or multicomponent of a fluid stream. Intensification of the thermal efficiency is the main target of the operation of the any good heat exchanger. However, sometimes heat exchangers cause problems because they are used as a part of larger system of operation, often installed and forgotten hence obtained lesser than optimum performance. Therefore, Hewitt and Pugh (2007) reported a number of factors and parameters for designing a simple or multi-stream heat exchanger in order to achieve a high heat transfer rate. A double or concentric pipe heat exchanger is used for exchanging heat from hot fluid to cold fluid stream, accounting for one of the most convenient configurations as these heat exchangers are operated within its designed and specific limits. In many cases, for better efficiency, these types of heat exchangers are designed to increase the connected cylindrical wall surface area separated by two streams, while minimizing the friction of that fluid flow. The evaluation of different parameters, which affect the heat transfer characteristics and flow friction factor, is also essential for optimum design of such heat transfer devices. For calculating the heat transfer coefficient of double-tube heat exchangers, the comparison of different approaches and their results were studied by Raei et al. (2017). They conducted an experimental study in the turbulent flow regime over a large range of fluid temperatures and Reynolds number (Re) and concluded that in counterflow, the values of Nusselt number are more dependent on the Re than that of parallel flow.
Turbulent flow, Double pipe heat exchanger, Heat transfer, Helical coil spring, Friction factor, Triangular ribs