Numerical prediction methods for calculating velocity and temperature distributions in heated ducts can be made accurately but are time consuming. The paper shows possible simplifications, including the neglect of the buoyancy term, and the resultant accuracy attained. The case studied is for laminar flow, entry length heat transfer in horizontal tubes with constant rate heat flux. Comparison is made between experimental results, a full solution and an approximation based on a series of truncated versions of the fully developed temperature profile. Calculations are made both with and without variation of thermophysical properties with temperature.
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