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Workshop #2 - Body Metabolism Introduction

Assignment: Watch the introductory videos on Heat and Temperature


The human body is a sophisticated chemical reactor using metabolism for all of its activities. The energy that it produces and uses must eventually leave the body and go into the environment either as heat or work. The net work that is produced is usually small in comparison to the total energy produced. Therefore, one direct measure of the “calories burned” is the net heat transfer from the body to the environment.


Your challenge in this workshop is to estimate the calories that you burn in a day by measuring the heat transfer from your body with your heat flux sensor system. The human body has a typical surface area of 1.5 to 2.5 m^2, depending on the person’s size. A common equation to estimate surface area is
 


This gives the area As in units of m^2 when the height H is in meters and body weight m is in kilograms.


To make the measurements simply tape the heat flux sensor to different parts of your body on both exposed skin and underneath clothing. Single-sided tape can be used over top of the sensor or double-sided tape can be used between the sensor and the skin. In either case the goal is to create good contact between the entire sensor surface and the skin to give a good pathway for the heat transfer through the sensor, as illustrated in the figure. The heat flux should read positive if the leads are facing out. Check that you are measuring positive heat flux. If not, flip the sensor over.


Show the values on the worksheet and indicate where they were taken. Then average the temperature and heat flux values and use your estimated body area to find the total heat lost in both watts and calories per day. Show all of your work and equations used.


Note: One calorie is the equivalent of about 4.2 kJ.

 

1 inch = 0.0254 m.

 

1 pound = 0.454 kg

Workshop #2 - Body Metabolism Results

Your challenge is to estimate the calories that you burn in a day by measuring the heat transfer from your body with your heat flux sensor system. Tape the heat flux sensor to different parts of your body on both exposed skin and underneath clothing. Show the values below and indicate where they were taken. Then average the temperatures and heat flux and use your estimated body area to find the total heat lost in both watts and calories per day. Show all of your work and equations used.

Estimated body surface area, As =

 

H =

 

m =

 

 

Total q =

 

 

Calories per day =

 

 

How does this value compare with your usual caloric intake?

 

 

Why is there a discrepancy if any?

 

 

Why is the heat flux higher when the skin is exposed (not covered)?

 

 

Why is the surface temperature lower when the skin is exposed (not covered)?