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Emphasis in this article will be on a cylindrical coevficient for the heat transfer surface, as in a shell and tube or double pipe heat exchanger. However, one needs to select if the heat flux is based on the pipe inner or the outer diameter.
Overall Heat Transfer Coefficient Calculation with Excel Spreadsheets for Heat Exchanger Design
International Journal of Heat and Mass Transfer. The example Excel spreadsheet uses U. John Wiley and Sons. Heat Transfer second edition. The areas for each flow will be different as they overall heat transfer coefficient calculation pdf download the contact area for each fluid side.
The heat transfer coefficient is the heat transferred per unit area per kelvin. It is commonly applied to the calculation of heat transfer in heat exchangersbut can be applied equally well to other problems.
In analyzing the heat transfer associated with the flow past the exterior surface of a solid, the situation is complicated by phenomena such overall heat transfer coefficient calculation pdf download boundary layer separation. For more details on the overall heat exchanger design process, see the articles in this series like, ” Fundamentals of Heat Exchanger Theory and Design overall heat transfer coefficient calculation pdf download and ” Preliminary Heat Exchanger Design Example.
Values for the tube dimensions should be available from preliminary heat exchanger design calculations, which could be done using Excel spreadsheets like those available from the articles, ” Excel Spreadsheet Templates for Preliminary Heat Exchanger Design ,” and ” Excel Formulas for Pressure Drop in Shell and Tube Heat Exchanger Design.
Typical fouling resistance values for various combinations of fluids, temperatures and velocities are given in reference 1 below. McAdams suggested the following correlations for horizontal plates. Most of the fouling resistance values fall between 0. For laminar flows, the following correlation is slightly more accurate. The equation takes into account that the perimeter of the heat exchanger is different on the hot and cold sides.
Powered by the Parse. The product of the average thickness and thermal conductivity will result in the fouling resistance on a specific side of the heat exchanger.
The thermal resistance due to the pipe wall is calculated by the following relationship:. The correlations for vertical plane walls can be used downloav.
For two or more heat transfer processes connected in series, convective heat transfer coefficients add inversely: Retrieved from ” https: Often it can be estimated by dividing the thermal conductivity of the convection fluid by a length scale.
Calculation Overall Heat Transfer
If the above assumption does not hold, then the wall heat transfer coefficient can be calculated using the following expression:. The Thom correlation overall heat transfer coefficient calculation pdf download for the flow of boiling water subcooled or saturated at pressures up to about 20 MPa under conditions where the nucleate boiling contribution predominates over forced convection.
Due to this transder layer, pff is additional resistance within the heat exchanger and thus the overall heat transfer coefficient of the exchanger is reduced.
The tube or pipe diameters and length also need to be determined, as well as the pressure drop. The following relationship is used to solve for the heat transfer resistance with the additional fouling resistance: This correlation is applicable when forced convection is the only mode of heat transfer; i. As the areas for each surface approach being equal the equation can be written as the transfer coefficient per overall heat transfer coefficient calculation pdf download area overall heat transfer coefficient calculation pdf download shown below:.
In the walls of buildings the oevrall formula can be used to derive the formula commonly used to calculate the heat through building components. Recommendations by Churchill and Chu provide the following correlation for natural convection adjacent to a vertical plane, both for laminar and turbulent flow.
Calculation of Overall Heat Transfer Coefficient
The overall heat transfer by combined Modes is usually expressed on terms of an overall conductance or overall heat transfer coefficient ‘U’. The overall heat transfer coefficient takes into account the individual heat transfer coefficients of each stream and the resistance of the pipe material.
Handbook of Heat Transfer 3rd edition. Views Read Edit View history.