The film temperature can be calculated using a specific formula that considers the heat transfer across a fluid film.
You calculate the average film temperature by taking the average heat flux, dividing it by the fluid film coefficient, and then adding that result to the operating temperature.
Understanding the Film Temperature Calculation
The film temperature is a crucial parameter in heat transfer calculations, often used to evaluate fluid properties which may vary with temperature. The method provided is a way to estimate this temperature at the interface between a surface and a fluid.
Based on the provided reference, the calculation follows this formula:
Average Film Temperature = (Average Heat Flux / Fluid Film Coefficient) + Operating Temperature
Let's break down the components of this calculation:
- Average Heat Flux: This represents the rate of heat transfer per unit area across the film.
- Units: BTU/hr-ft² (as given in the reference)
- Fluid Film Coefficient: Also known as the heat transfer coefficient, this value quantifies the rate at which heat is transferred between a solid surface and a fluid.
- Units: BTU/hr-ft²-ºF (as given in the reference)
- Operating Temperature: This is the bulk temperature of the fluid or the temperature of the surface, depending on the context of the heat transfer scenario being analyzed.
- Units: Typically in degrees Fahrenheit (ºF) in this context, based on the coefficient units.
- Average Film Temperature: The resulting estimated temperature within the fluid film.
- Units: Degrees Fahrenheit (ºF)
Applying the Formula
To perform the calculation, you need the values for these three parameters:
- Determine the Average Heat Flux (e.g., measured or calculated from power input and area).
- Determine the Fluid Film Coefficient (e.g., obtained from correlations, experiments, or tables based on fluid properties, flow regime, and geometry).
- Determine the relevant Operating Temperature.
Once you have these values, simply plug them into the formula.
| Component | Description | Units (Example) |
|---|---|---|
| Average Heat Flux | Heat transferred per unit area | BTU/hr-ft² |
| Fluid Film Coefficient | Heat transfer rate between surface and fluid | BTU/hr-ft²-ºF |
| Operating Temperature | Bulk temperature of fluid or surface | ºF |
| Average Film Temp. | Estimated temperature within the fluid film | ºF |
This method provides a specific way to estimate the average temperature within the film layer, which is often different from the bulk fluid temperature or the surface temperature.
