Heat Transfer II – Laboratory
Forced Convection Cooling Using a Heat Sink
Purpose:
The purpose of the lab is to make experimental measurements on a heat sink cooled by
means of forced convection and use theoretical methods learned in this course and in
Heat Transfer I to predict the overall thermal performance. The heat sink contains two
electric film heaters, which provide up to 20 W of power to simulate electronic
components.
Equipment:
The equipment for this lab consists of a small bench wind tunnel, a heat sink equipped
with two electric heaters connected to a power supply, a thermocouple, a digital multimeter, and a handheld velocity probe.
Procedure:
To start the lab, you must ensure that all required equipment is switched on. This
includes: the wind tunnel blower, the multi-meter, the power supply for the heaters, and
the thermocouple display. The electric heaters have an electric resistance of 37.5 [ohms].
Use the multi-meter to measure the voltage supplied to the heaters. The voltage and the
electric resistance are then used to determine the power input to the heat sink. Next, when
steady state is reached, note the temperature reading of the thermocouple, and measure
the airspeed in the wind tunnel and the ambient temperature using the velocity probe. The
velocity is measured at a point where the area of the wind tunnel is 6 inches by 6 inches.
Use mass conservation to determine the velocity approaching the heat sink over the
insulation block by considering the insulation block to have a thickness of 52 mm. You
should measure the temperature of the still air, as there will be a cooling effect if you
measure the temperature of the moving air.
Analysis:
Construct a thermal resistance model for the heat sink using fin theory learned in Heat
Transfer I. Consider, convection from the base plate in the spaces between the fins, the
resistance of the fins themselves, and the equivalent radiation resistance. Note: this
represents three parallel heat flow paths. Choose an appropriate convection correlation
from your text based on the geometry and flow conditions. Justify your choice based on
Reynolds number and boundary layer thickness calculations. Compare your theoretical
results with those measured in the experiment and comment on any sources of error. The
dimensions of the heat sink are given below. In your analysis answer the following
questions:
a)
b)
c)
d)
Is radiation significant? Use the radiation heat transfer coefficient as an indicator.
Determine the effective resistance of the heat sink under measured conditions?
Develop a system curve for the heat sink for 0 < V < 15 m/s.
Show the theoretical temperature of the heat sink as a function of velocity.
Dimensions:
L
H
W
t
b
tb
N
k
= 60 mm (Length of heat sink in flow direction)
= 25 mm (Fin height)
= 60 mm (Width of heat sink)
= 1.5 mm (Fin thickness)
= 4.0 mm (Fin spacing)
= 2.0 mm (Base plate thickness)
= 10 fins
= 185 W/mK (Approximate Thermal Conductivity of the Aluminum Alloy)
Use air properties at ambient temperature for your calculations.