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Example Problem

Example Problem. Example Problem. Determining Interface Temperatures. The temperatures at the interfaces can be found entirely from the resistances. A B C. q. Determining Interface Temperatures. This can also be used for combined convection / conduction.

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Example Problem

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  1. Example Problem

  2. Example Problem

  3. Determining Interface Temperatures The temperatures at the interfaces can be found entirely from the resistances. A B C q

  4. Determining Interface Temperatures This can also be used for combined convection / conduction.

  5. Determining Interface Temperatures For heat transfer thru thin-walled metal pipes, the conduction resistance is usually small, i.e., the temp. drop across the pipe is small.

  6. Determining Interface Temperatures

  7. Example Water is being heated by 50-psig steam in a 2” Sch. 40 steel pipe. At one point along the pipe the overall temperature difference is 150 deg. F. If the film coefficient for the water is 550 BTU/hr-ft**2-deg. F, and the film coefficient for the steam is 1900, determine the temperatures at all of the interfaces.

  8. Example

  9. Example

  10. Example What is the heat transfer at this point on the inside and outside?

  11. Determining Heat Transfer to Fluid Flowing in a Pipe How do I determine the length of pipe required to heat a fluid, given the pipe dimensions, mass flow rate, input and output temperature, and the external temperature? Problem: The inside temperature is not constant so what temperature difference do I use?

  12. Determining Heat Transfer to Fluid Flowing in a Pipe

  13. Determining Heat Transfer to Fluid Flowing in a Pipe

  14. Determining Heat Transfer to Fluid Flowing in a Pipe

  15. Determining Heat Transfer to Fluid Flowing in a Pipe • Procedure: • Use average T to determine physical properties of the fluid. • Determine if laminar, transition, or turbulent using Reynolds No. • Select appropriate equation to determine h. These equations usually require the properties at the film temperature, which is the average between the bulk fluid and the wall temperature (which you do not know). • Guess a wall temperature.

  16. Determining Heat Transfer to Fluid Flowing in a Pipe • Calculate the inside convective heat transfer coefficient. • Calculate a new wall temperature. • Iterate until wall temperature matches. • Calculate an overall heat transfer coefficient, U • Determine required pipe length from:

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