Oval tube flue gas waste heat recovery

I understand your confusion. HTRI is indeed mainly designed for round tubes. Elliptical tubes have different geometric parameters and flow characteristics, so it is definitely not possible to apply them directly. Calculation of the heat transfer area of ​​elliptical tubes can actually be done in this way: First, calculate the heat exchange area per unit length according to the long and short axis dimensions of the elliptical tube using the elliptical perimeter formula (approximate value or table lookup), and then multiply by the tube length and number of tubes. If you need a more accurate heat transfer coefficient, it is recommended to use CFD software (such as Fluent, Ansys, etc.) to simulate a single oval tube and tube bundle, or refer to the engineering experience formula of relevant flue gas waste heat recovery. If conditions are limited, you can also find some design manuals or papers on elliptical tube heat exchangers, which usually contain corrected correlations. However, it should be noted that the actual working conditions on the flue gas side (flow rate, temperature, ash content, etc.) may have a greater impact. It is recommended that you provide some more specific conditions, such as oval tube size, flue gas parameters, layout, etc., so that everyone can help you judge which method is more reliable. In addition, if it involves actual engineering applications, it is best to consult experienced heat exchanger manufacturers or professional designers for verification.