| Heat Transfer Coefficient |
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: where Q h A :Δ''T'' = difference in temperature between tubing surface and surrounding area There are different heat transfer relations for different liquids, flow regimes, and Thermodynamic conditions. A common example pertinent to many of the necessary power plant Efficiency and Thermal Hydraulic calculations is the Dittus-Boelter heat transfer corelation, valid for water in a circular pipe with Reynolds Number s between 100 000 and 120 000 and Prandtl Number s between 0.7 and 120. An example is shown below where it is used to calculate the heat transfer from a tubing wall to water. : where Hdb : = thermal conductivity of water Nu Pr Re : = hydraulic diameter : = Mass Flow Rate μ C A The heat transfer coefficient has SI units in watts per meter squared-kelvin. Often it can be estimated by dividing the Thermal Conductivity by a length scale. Heat transfer coefficients add inversely, like resistances. It can be thought of as a Thermal Resistance . Shown below is an addition of heat transfer coefficients where one is estimated as a Thermal Conductivity divided by a length scale. : where Q h t k A : = difference in temperature between outer wall of tubing and sample water. SEE ALSO
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