david reece me 340 project effects of fat thickness on heat transfer

David ReeceME 340 Project

Effects of Fat Thickness on Heat Transfer

IntroductionProblem: 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 ProblemHuman 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 cmLength = 0.74 m

Arms Inner Tissue Radius= 3.3 cmLength = 0.56 m

Legs Inner Tissue Radius= 4.6 cmLength = 0.86 m

Heat Transfer ProblemSkin: Thickness 2.5 mm Heat Transfer Coefficient 0.37 W/m*K

Inner Tissue: Different Radii for Different Body Parts

Constant Temperature = 37° C

Fat Tissue: Varied Thickness (0.5 cm to 8 cm)

Heat Transfer Coefficient 0.2 W/m*K

Equations Used For Solution

ResultsTemp

(°C (°F))

ΔT (°C)

.5 cm Fat

1 cm Fat

2 cm Fat

4 cm Fat

8 cm Fat

32.2 (90)

4.8207

(178)124

(107)72

(61.9)42

(36.1)26

(22.0)22.2 (70)

14.8

639(549)

383(329)

222(191)

130(111)

79(68.0)

10 (50)

271165(1002

)

698(601)

405(348)

236(203)

144(124)

0 (32)

371596(1374

)

957(823)

554(477)

324(279)

197(170)Results are in Watts and

(Cal/Hour)

DiscussionThe 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.

ConclusionAnalysis Shows:Large amount of heat used to simply stay warmHeat loss is significantly reduced with more fatGaining weight may be advisable in colder climatesLosing weight may be advisable in warmer climates

(Consult doctor before either steps)

Improvement Recommendations:ClothingMuscle exertionMore accurate dimensions for appendages and

other partsAdd convection and radiation.

ReferencesAtkins, 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.