One of the ways to improve heat transfer efficiency is to use a spiral structure for tubes instead of conventional direct tubes. Compared to the direct tubes, spiral tubes have a more compact surface and have higher heat transfer and friction coefficients. When the fluid flows through the spiral tubes, it influences by the centrifugal force which this centrifugal force creates a secondary flow in the fluid, and as a result, this secondary flow increases the axial flow velocity near the outer wall of the tube. Thereby increasing the axial velocity will reduce the thermal resistance and
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