Numerical Analysis of a Compact Helical Counterflow Heat Exchanger
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The performance of compact counter flow heat exchangers with helically shaped passages is examined using a 1-D analytical model and compared with a high-fidelity 3-D numerical simulation. The 1-D model is capable of assessing the general trends associated with the heat transfer performance and fluid pressure losses, whereas the high fidelity 3-D numerical model is needed to provide more accuracy. For water flow rates of 0.01 kg/s -1 kg/s, the models are used to predict the overall heat transfer coefficient ratio for a straight and counter helix heat exchanger. The maximum difference between the 3-D numerical and 1-D analytical model for heat transfer performance is 2.6%, with larger disagreement associated with the fluid pressure drop of up to 37.5%. The primary reason for the deviation of the numerical results is attributable to secondary flow effects, which are neglected in the 1-D analytical model. Heat exchanger performance was studied by varying the geometric parameters such as the length and the number of turns per length of the heat exchanger, number of fins within the flow passages, inner and outer channel heights, and fin and wall thickness. Heat transfer rate and pressure drop on straight and helical fins heat exchangers were compared by keeping the length of the fin and the hydraulic diameter of the channel constant. Ultimately, the heat transfer rate for a helical design is found to increase by 56% as compared with a conventional counterflow heat exchanger of the same length and outer diameter. Furthermore, by using a helical flow path, the volume of the device can be reducing by 33%.