1. How Much Does a Cooling Pad Help Your Laptop?
John Hosford
Joshua Thornock

2. Free Convection General Assumptions
Cooling without the pad will be considered free convection as opposed to an enclosure
Cooling without the pad does not include fans previously installed or air flow within the casing
Air and surface temperature assumed 27°C and 67°C
AIRFLOW

3. Internal Flow – Non-Circular Tubes General Assumptions
Cooling with the pad will be considered internal flow in a non-circular tube closely representing a rectangle
Flow begins at the center of the laptop and moves to the outside so the non-circular tube length will be half of the length of the laptop

4. Determine Convection Coefficient for Free Convection
Tf=(Tinf+Ts)/2
HORIZONTAL PLATE
FREE CONVECTION N

5. Determine Convection Coefficient for Forced Convection
Three terms had to be estimated
Cross sectional area (Ac)
Perimeter (P)
Mass flow (mdot)
Solve Hydrolic diameter (Dh)
Solve Reynold’s number
Side View
Laptop Surface
4 inches
Air
Cooling pad surface
=>FLOW IS TURBULENT

6. Determine Convection Coefficient for Forced Convection
For turbulent flow use Equation 8.61 N

7. Comparing Coefficients
The actual heat transfer will depend on the temperatures of the surroundings and the computer surface. Still these coefficients show a drastic difference between having and not having the cooling pad. This is where we need to remember our assumptions. We ignored the fact that the computer has fans and convection inside the case. These more difficult calculations may give a more accurate answer, however, the analysis performed may give us a good idea that the cooling pad will aid the heat transfer a significant amount—increasing the heat transfer by approximately 20 times! N N

8. Conclusion
In addition to providing a cooler surface to contact your lap, laptop cooling pads greatly aid the transfer of heat away from a laptop’s surface. Although only the convection coefficient was determined in this study, the amount of heat wicked away from the laptop surface is only a linear function of this coefficient for a given temperature difference:
Therefore, the increase in heat transfer is proportional to the increase in convection coefficient—in this case, 20x.

9. Appendix
A Hewlett Packard laptop and a Belkin laptop cooling pad were the basis for this model.
Properties:
Air at laptop surface (Ts): 67°C ( 152.6°F)
Ambient air (T∞): 27°C (8o.6°F)
L=.1524m (6 inches, for a 14.1” laptop)
Properties of ambient air (27°C)
Properties of air at surface temperature (67°C)