Heat transfer coefficient, abbreviated as h, also called film coefficient or film effectiveness, is a measure of how effectively heat is transferred from one medium to another in a thermal system. It quantifies the rate of heat transfer per unit area for a given temperature difference. In other words, it tells us how fast heat can move through a material or between two different materials. The heat transfer coefficient depends on various factors, including the properties of the materials involved, the geometry of the system, and the nature of the heat transfer process (conduction, convection, or radiation).
In practical engineering and thermal analysis, determining the heat transfer coefficient is crucial for designing and optimizing heat exchangers, HVAC systems, and various other heat transfer applications. Engineers often use experimental data, correlations, and mathematical models to estimate the heat transfer coefficient in different situations.
Primary Modes of Heat Transfer
Conduction - In conduction, heat is transferred through a solid material or between two solids in direct contact. The heat transfer coefficient is not commonly used in this context; instead, the thermal conductivity of the material is used to describe how well heat conducts through it.Convection - Convection is the transfer of heat through a fluid (liquid or gas) by the motion of the fluid itself. In this case, the heat transfer coefficient represents how effectively heat is transferred from a solid surface to the surrounding fluid (or vice versa) due to the convective flow of the fluid. It depends on factors such as fluid properties, flow velocity, and surface roughness.
Radiation - Radiation is the transfer of heat in the form of electromagnetic waves (infrared radiation). The heat transfer coefficient is less commonly used in radiative heat transfer, as it is typically described by the Stefan-Boltzmann law and depends on the emissivity and temperature of the surfaces involved.
Heat Transfer Coefficient Formula |
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\( h \;=\; \dfrac{ Q" }{ \Delta T }\) (Heat Transfer Coefficient) \( Q" \;=\; h \cdot \Delta T \) \( \Delta T \;=\; \dfrac{ Q" }{ h }\) |
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| Symbol | English | Metric |
| \( h \) = Heat Transfer Coefficient | \(Btu \;/\; hr-ft^2-F\) | \(W \;/\; m^2-K\) |
| \( Q" \) = Heat Flux | \(Btu \;/\; hr-ft^2\) | \(W \;/\; m^2\) |
| \( \Delta T \) = Temperature Differential Between the Solid Surface and Surrounding Area | \(F\) | \(K\) |
