Page 68 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

HEAT TRANSFER APPLICATIONS IN BIOLOGICAL SYSTEMS 45

37.5
37

36.5
Tissue Temperature (°C) 35.5 Blood temperature
36

Maximum tissue temperature
Minimum skin temperature
35
Volumetric average temperature
34.5
Weighted average temperature
34

33.5
0 5 10 15 20 25
Time (minute)
FIGURE 2.4 Temperature decays during the cooling process using the implicit scheme.

It is well known that strenuous exercise increases cardiac output, redistributes blood flow from inter-
nal organs to muscle, increases metabolism in exercising muscle, and enhances heat transfer to the
skin. The whole body model can be easily modified to also include a skin layer and a fat layer in the
compartments of the limbs. Further, redistribution of blood flow from the internal organs to the mus-
culature can be modeled as changes of the local blood perfusion rate in the respective compartments
and the enhanced skin heat transfer can be adjusted for by inducing evaporation at the skin surface

0.1
Blood temperature
0.09
Maximum tissue temperature
0.08 Volumetric average temperature
Cooling Rate (°C/min) 0.06 Weighted average temperature
0.07

0.05
0.04
0.03
0.02
0.01
0
0 5 10 15 20
Time (minute)
FIGURE 2.5 Induced cooling rates of the blood temperature, the maximum temperature, the
volumetric average temperature, and the weighted average temperature.