Effects of Fat Thickness on Heat
Transfer
David Reece
ME 340 Project
Introduction
Problem: How much energy is lost at different temperatures
with different thicknesses of fat?
Objective: To investigate the effect of fat thickness on the
amount of energy lost and how this might affect eating habits
of people of differing physique.
Heat Transfer Problem
Human body was modeled as five cylinders, one for the
torso and one for each arm and leg. The heat transferred
through the head was neglected because of the lack of fat.
Torso
Inner Tissue Radius = 15 cm
Length = 0.74 m
Arms
Inner Tissue Radius= 3.3 cm
Length = 0.56 m
Legs
Inner Tissue Radius= 4.6 cm
Length = 0.86 m
Heat Transfer Problem
Skin: Thickness 2.5 mm
Heat Transfer Coefficient 0.37 W/m*K
Fat Tissue: Varied Thickness (0.5 cm to 8 cm)
Heat Transfer Coefficient 0.2 W/m*K
Inner Tissue: Different Radii for Different Body Parts
Constant Temperature = 37° C
Equations Used For Solution
Results
Temp
(°C
(°F))
32.2
(90)
22.2
(70)
10
(50)
0
(32)
ΔT
(°C)
.5 cm Fat 1 cm Fat 2 cm Fat 4 cm Fat 8 cm Fat
207
124
72
42
26
4.8
(178) (107) (61.9) (36.1) (22.0)
639
383
222
130
79
14.8
(549) (329) (191) (111) (68.0)
1165
698
405
236
144
27
(1002) (601) (348) (203) (124)
1596
957
554
324
197
37
(1374) (823) (477) (279) (170)
Results are in Watts and (Cal/Hour)
Discussion
The results show that with a fat layer thickness 16x bigger, an
eighth the amount of heat is transferred.
This means that a person with only ½ cm fat layer around the
torso, arms, and legs, will use eight times the energy just
keeping warm.
People with thicker layers of fat are able to keep warm easy and
thus need less calories for heating than the thinner people.
This also means that they need to be more careful about how
much they eat because they won’t use the energy as quickly
as skinner people.
Conclusion
Analysis Shows:
 Large amount of heat used to simply stay warm
 Heat loss is significantly reduced with more fat
 Gaining weight may be advisable in colder climates
 Losing weight may be advisable in warmer climates
 (Consult doctor before either steps)
Improvement Recommendations:
 Clothing
 Muscle exertion
 More accurate dimensions for appendages and other parts
 Add convection and radiation.
References
 Atkins, P. and Jones, L. Chemical Principles:The Quest for Insight.
W.H. Freeman and Company. 4, 2008.
 Incropera, Dewitt, Bergman, Lavine. Fundamentals of Heat and
Mass Transfer.