Heat Transfer from Air to Dynamic Fluid in Pipe

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SUMMARY

The discussion focuses on estimating heat transfer from air to a dynamic fluid in a pipe exposed to a hot environment. The primary equation for calculating the exit temperature of the fluid involves determining the heat input using the formula: heat input = (2 BTU/hour) * ft² * ΔF, where ft² is the pipe's surface area and ΔF is the temperature difference between the pipe and the room. The temperature rise of the fluid can be calculated using the formula: temp rise = heat input / (cp * mass flow), where cp is the thermal capacity of the fluid. A numeric solution approach is recommended for calculating heat rise over the entire length of the pipe.

PREREQUISITES
  • Understanding of thermal resistance and heat transfer principles
  • Familiarity with BTU as a unit of heat energy
  • Knowledge of fluid dynamics, specifically mass flow rates
  • Basic understanding of differential equations for numeric solutions
NEXT STEPS
  • Research the principles of thermal radiation and natural convection in heat transfer
  • Learn how to calculate thermal capacity (cp) for various fluids
  • Explore numeric methods for solving differential equations in heat transfer scenarios
  • Investigate software tools for simulating heat transfer in fluid systems
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Engineers, thermal analysts, and anyone involved in designing or optimizing heat transfer systems in piping applications.

chriskaselak
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I need some help estimating the heat transfer of a system. If I have an exposed length of pipe with a dynamic fluid moving at a constant volumetric rate through a very hot room, what equation is most appropriate to calculate the exit temperature of the fluid?

Given:
Initial temperature of the fluid
Temperature of the room
Material properties of the pipe and fluid

Thanks,
 
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Heat transfer calculations can get complicated, but if you need just a ball park estimate your problem can be made simple. The main resistance to heat transfer from your hot room to the pipe will be the interface between the air and the outside surface of the pipe. The thermal resistance of the pipe itself and the fluid interface to the pipe's interior is most likely to be small in comparison.

Heat will be transferred to the pipe's outer surface by thermal radiation and natural convection (assuming no breezes in the room). Roughly this will occur at the rate of about (2 BTU per hour )* ft2 * delta F, where ft2 is the surface area of the pipe in square feet and delta F is the temperature difference between the pipe and the room.

So, compute the heat added to the first foot of pipe, then compute the temperature rise of the fluid, temp rise = heat input/(cp * mass flow)

where:
heat input is BTU/hour
cp is the thermal capacity of the fluid BTU/F/lb (for example, Cp of water = 1 btu/F/lb)
mass flow is lb/hour


Continue computing the heat rise for addition foot sections of pipe and adding them up until you've done the pipe's entire length (this is a numeric solution procedure to a differential equation).

Good luck!

Jay


chriskaselak said:
I need some help estimating the heat transfer of a system. If I have an exposed length of pipe with a dynamic fluid moving at a constant volumetric rate through a very hot room, what equation is most appropriate to calculate the exit temperature of the fluid?

Given:
Initial temperature of the fluid
Temperature of the room
Material properties of the pipe and fluid

Thanks,
 

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