Flow and heat transfer characteristics around egg-shaped tube

This paper studies the flow and heat transfer characteristics around a new type of egg-shaped tubes made up of a semicircle upstream and a semi-ellipse downstream, numerically and experimentally, for Reynolds numbers varying from 4 000 to 5 0000 based on the hydraulic diameter. These tubes have axis ratios, epsilon = 1, 1.5, 2, 3, 4, and 5 with the major axis parallel to the mainstream. When epsilon = 1, the tube is a circular one and when 1/epsilon = 0, it is a flat plate. Numerical results show that the minimum value of C-p occurs at an angular position, which decreases as epsilon decreases, and the maximum value of C-f gradually increases with the increase of epsilon. Simulated results agree very well with those available in the existing literature. The egg-shaped tube has a higher favorable pressure gradient at its front and a lower adverse pressure gradient at its back, that helps the flow delay a separation from the tubes' surface. Empirical correlations for each tube are obtained by numerical simulations relating the dimensionless heat transfer coefficient with the Reynolds Number and the Prandtl Number. The performance evaluation criterion (PEG) is used to analyze the level of the heat transfer enhancement for egg-shaped tubes. It is found that an egg-shaped tube with epsilon = 2 has the best overall heat transfer performance when Re > 11 952.