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14:650:432:02

14:650:432:02. Lab # 5: Convection Heat Transfer Max Tenorio. Purpose. Convection Heat Transfer occurs almost everywhere Examine characteristics of heat transfer to turbulent air flow through a uniformly heated pipe

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14:650:432:02

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  1. 14:650:432:02 Lab # 5: Convection Heat Transfer Max Tenorio

  2. Purpose • Convection Heat Transfer occurs almost everywhere • Examine characteristics of heat transfer to turbulent air flow through a uniformly heated pipe • Measure temperature distribution for two air flow rates and two power settings to calculate the heat transfer coefficient, Reynolds, Stanton, and Prandtl numbers and friction factor.

  3. Setup

  4. Specifications Total 5.75 feet long Insulation thickness: 0.813” 13 total thermocouples (1 broken) Connected to labview

  5. Raw Data

  6. Mass Flow Rate

  7. Heat Flux Method 1

  8. Thermal Profile

  9. Heat Flux Requires Thermal Profiles Method 2 Discussion b: The heat flux values in b and d are different because b uses raw experimental values to perform the heat balance and assumes that for q”out, the maximum heat loss is uniform for the entire circumference for the pipe, when in reality the heat loss is most likely not uniform through a cross section. Additionally, d assumes laminar flow and relies on a constant specific heat capacity for air and a constant flow rate. Although the percent error is somewhat high, it is worth noting that the heat flux from d is close to the q”in from b. The difference is most likely equipment error and incorrect values

  10. Bulk Air Temperature The Bulk Air temperature is the average temperature of air in a section of pipe.

  11. Heat Transfer Coefficient Discussion a: The wall temperature is easily measured using the thermocouples and the bulk temperature is the average temperature of air in that cross section. They vary; the wall temperature will be higher because it is closer to the heating element and the temperatures are higher in general because energy is being transferred to the air as it travels. The beginning and end points are skewed because of end effects. The slopes of both are constant in the middle section because the rate at which temperature changes is the same for both the wall and air inside the tube.

  12. Reynolds Number Ratio of inertial forces (Vρ) to viscous forces (μ / L)

  13. Nusselt Number Ratio of convective to conductive heat transfer across the boundary

  14. Friction factor

  15. Stanton Number Ratio of heat transferred into a fluid to the thermal capacity of fluid

  16. Calculated Values Discussion c: For the Nusselt Number and friction factor, the experimental values are much lower than the correlation values. These most likely result from equipment error, since the friction factors for runs 3 and 4 drop to zero and even go negative, meaning the pressure at the exit is higher than the entrance pressure. As far as the Stanton number goes, the values for the high speed regions (runs 1 and 2) are close, but the values for low speed are off, meaning that less energy was transferred into the air than anticipated.

  17. Sample Calculations Run 1

  18. Sample Calculations

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