Heat Transfer Augmentation in a de-Super Heater of Domestic Refrigerator with Twisted Tape Turbulators

Abstract

In domestic refrigerator, De-Super-heater which is also called as Pipe Joint Assembly (PJA), is a serpentine tube which is immersed in tray-drip and connecting compressor outlet and condenser inlet. It is used to desuperheat the super heated refrigerant vapor coming out from the compressor and also used to evaporate the defrost water in the tray drip. The computational fluid dynamics analysis was done by using commercial CFD (Computational Fluid Dynamics) algorithm, ANSYS FLUENT on PJA and obtained results were compared with the analytical as well as experimental results. In the present study, the effect of turbulators on heat transfer augmentation in PJA is simulated with different mass flow rates. Also, a parametric study was performed to estimate the effect of PJA tube diameter and PJA length by keeping the surface area constant and insert the twisted tape of different twist ratios and clearance ratios inside the tube. Pressure drop and heat transfer behavior in a twisted tape swirl generator inserted tube are investigated numerically. The twisted tapes are inserted inside the tube separately from the tube wall. The effect of different twist ratios (y/D = 5, 6 and 7) and the clearance ratios (c/D = 0.166, 0.272 and 0.4) are discussed for the different mass flow rates (ṁ = XX,XX and XX gm/s). Calculated transfer coefficient and the temperature of stagnant water are applied to the external surface of the tube wall. The iso-butane refrigerant is selected as working fluid. The obtained results from the plain tube are validated by well known equations given in the literature. With increase in the diameter of the tube from XX mm to XX mm and decrease the length of the tube from XX mm to XX mm in order to keep the surface area same i.e. XX m2, the pressure drop reduces from XX Pa to XX Pa and outlet temperature of refrigerant vapor and the total heat transfer rate remains same. The maximum increase of 26% has been obtained in the total heat transfer rate dissipated, whereas an increase of 58% is observed in the pressure drop, when the mass flow rate was increased from XX gm/s to XX gm/s at the inlet of the tube of XX mm diameter. The using of twisted tapes inside the tubes considerably increases the heat transfer rate and pressure drop when compared with the plain tube. The heat transfer rate and the pressure drop are increases with the decreases of clearance ratio (c/D) and twist ratio (y/D), also increase of mass flow rate. As we increase the twist ratio of the twisted tape from 5 to 7 by keeping the same clearance ratio of 0.166, the heat transfer rate decreases from XX Watt to XX Watt and the pressure drop decreases from XX Pa to XX Pa. As we increase the clearance ratio of the twisted tape from 0.166 to 0.4 by keeping the same twist ratio of 5, the heat transfer rate decreases from XX Watt to XX Watt and the pressure drop decreases from XX Pa to XX Pa. The highest heat transfer enhancement is achieved as 1.32 for c/D = 0.166 and y/D = 5 at mass flow rate of XX gm/s. An increase of 32% is observed in the heat transfer rate and decrease of pressure drop from XX Pa to XX Pa is observed with proposed design in comparison to the actual design.