Data Reduction

This investigation focuses on detailing the regionally averaged heat transfer coefficient at various locations within the internal cooling channel. This heat transfer coefficient is determined by the net heat flux from the heated plate to the cooling air, the surface area of the plate (Ap), the regionally averaged temperature of the plate, and the local bulk mean air temperature by the following:

The net heat flux is calculated using the measured voltage and current supplied to the heater multiplied by the area fraction exposed to the respective plate minus the previously determined amount of heat losses due to external conduction, convection, and radiation energy escaping from the test section. This heat loss calibration is performed for both stationary and rotation experiments with a piece of insulation inserted inside the test section to inhibit natural convection. For this calibration, by knowing the amount of power supplied to the heater and measuring the temperature of the plate, it is possible to determine how much the heat is being lost into the environment using the conservation of energy principle. Equation 1 is used throughout the experiment, neglecting the change of area effect with the addition of dimples. That is, the heat transfer coefficient is calculated based on the projected area, neglecting the 19.3% increase in area due to the addition of dimples.

The regionally averaged wall temperature (Tw) is measured directly by the thermocouple installed in the back of each plate. The local bulk mean air temperature (Tb,x) is determined by a linear interpolation between the measured bulk air inlet and the average of two outlet temperatures (each installed at the midpoint of the two spanwise sections) due to the applicable constant heat flux assumption. Another method used to check the interpolation values is by performing an energy balance. It is reassuring to note that performing an energy balance to calculate the expected outlet temperature resulted in a close match to that of the average measured exit temperature value, typically to within 5%. Therefore the linear interpolation method is validated and is the method used in the calculation of the results presented in this paper. The energy balance equation is:

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