Heat transfer from body through layers, using h, T, d, A

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SUMMARY

The discussion focuses on calculating the net rate of heat transfer from a human body in a room at 21°C, with a core body temperature of 37°C, using the heat transfer coefficients and thermal conductivities provided. The surface heat transfer coefficient is given as hsurf = 8.1 W m−2 K−1, with thermal conductivities for tissue and clothing as kst = 0.2 W m−1 K−1 and kclo = 0.05 W m−1 K−1, respectively. The formula for combined heat transfer coefficients is applied, leading to the calculation of heat transfer using ΔQ/Δt = hAΔT. The user initially calculated a heat transfer rate of 127 W, which was lower than the expected 130 W.

PREREQUISITES
  • Understanding of heat transfer principles, specifically conduction and convection.
  • Familiarity with thermal conductivity and heat transfer coefficients.
  • Knowledge of the equations for heat transfer, including ΔQ/Δt = hAΔT.
  • Basic proficiency in algebra for solving equations involving multiple variables.
NEXT STEPS
  • Review the derivation of the combined heat transfer coefficient formula 1/h = 1/h(surf) + 1/h(clothes) + 1/h(tissue).
  • Study the application of thermal conductivity in different materials, focusing on biological tissues and clothing.
  • Learn about the impact of surface area on heat transfer calculations in thermodynamics.
  • Explore advanced heat transfer topics, such as transient heat conduction and radiation effects.
USEFUL FOR

Students in thermodynamics, engineers working with heat transfer systems, and anyone involved in thermal management in biological or clothing applications would benefit from this discussion.

SunshineCat
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Homework Statement


Consider a person in a room with an air temperature of 21C. The persons core body temperature is 37C and their surface tissue thickness is 5 mm. If the total surface area of their skin is 1.5 m2, and they are wearing clothes of a thickness of 2 mm and the surface heat transfer coefficient (including conduction and radiation) is hsurf = 8.1 W m−2 K−1 then what is the net rate of heat tranfer from this persons body (in W)

thermal conductivity of surface tissue: kst = 0.2 W m−1 K−1
thermal conductivity of clothing: kclo = 0.05 W m−1 K−1

Homework Equations


1/h = 1/h(surf) + 1/h(clothes) + 1/h(tissue)
h=k/d
ΔQ/Δt = hAΔT

The Attempt at a Solution


I think you need to find the h for surface, tissue and clothes, and combine using 1/h = 1/h(surf) + 1/h(clothes) + 1/h(tissue)
We can find h for clothes and tissue using h=k/d ?
Then can use ΔQ/Δt = hAΔT using the new h value, surface area (1.5) and temp difference (37-21=16)
But I keep getting 103 instead of 130 as the answer says
Can someone work it out and explain the working? Thanks in advance!
 
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I get 127.

Chet
 

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