CFD ANALYSIS FOR CONE HELICALLY COILED TUBE HEAT EXCHANGER BY VARYING PITCH

THERMAL ENGINEERING

Now-a-days heat exchangers have become indispensable in various fields of engineering such as in air conditioning, power stations, chemical plants, automobiles, etc. It necessitates the compact size along with the high performance of the heat exchangers. For the improvement in heat transfer performance of heat exchangers, heat transfer coefficient has an important role to play. Generally modifications which are made to enhance heat transfer coefficient leads to increase in pressure drop in heat exchangers. Hence the selection of most appropriate configuration is an important consideration in design of a heat exchanger. Secondary flow pattern formed in curved tubes plays an important role in mixing of fluid which leads to an increase in heat transfer coefficient along with an increase in pressure drop also. Helically coiled exchangers offer certain advantages. Compact size provides a distinct benefit. Higher film coefficients—the rate at which heat is transferred through a wall from one fluid to another— and more effective use of available pressure drop result in efficient and less-expensive designs. Heat transfer rate of helically coiled heat exchangers is significantly larger because of the secondary flow pattern in planes normal to the main flow than in straight pipes. This work aims to study on passive technique of heat transfer enhancement by some variation in geometry of helical coil tube heat exchanger. In this work the heat transfer and pressure drop analysis has been done for conical coil with varying pitch. The pitch number taken for the study are 18mm, 20mm and 22mm. The nanofluid of 0.5% volume concentration are supplied for cone helically coiled tube and hot water is supplied to the shell side. The mass flow rate of shell side is maintained constant at 0.15 Kg/s.The inlet temperature of hot fluid (shell) is 338 K whereas the inlet temperature of cold fluid (for cone helically coiled tube) is 305 K. The flow rate of the cone tube which handled nanofluid is varies from 0.05-0.07 Kg/s. It is found that the maximum overall heat transfer coefficient for pitch=22 mm is 32.23% higher than the pitch=18mm and maximum Nusselt number for pitch=22 mm is 14.91% higher than the pitch=18mm.

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