Page 24 - Fundamentals of The Finite Element Method for Heat and Fluid Flow

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Figure 1.6 Rectangular fin INTRODUCTION

with the cooling of the coffee in the inner plastic vessel. What steps do you consider necessary
for a better container design so as to reduce the heat loss to ambient.

Exercise 1.9.8 A square chip of size 8 mm is mounted on a substrate with the top surface
◦
being exposed to a coolant flow at 20 C. All other surfaces of the chip are insulated. The
◦
chip temperature must not exceed 80 C in order for the chip to function properly. Determine
the maximum allowable power that can be applied to the chip if the coolant is air with a heat
2
transfer coefficient of 250 W/m K. If the coolant is a dielectric liquid with a heat transfer
2
coefficient of 2500 W/m K, how much additional power can be dissipated as compared to
air cooling?
Exercise 1.9.9 Consider a person standing in a room that is at a temperature of 21 C.
◦
Determine the total heat rate from this person if the exposed surface area of the person is
2
1.6 m and the average outer surface temperature of the person is 30 C. The convection
◦
coefficient from the surface of the person is 5 W/m 2 ◦ C. What is the effect of radiation if the
emissivity of the surface of the person is 0.90?
Exercise 1.9.10 A thin metal plate has one large insulated surface and another large surface
2
exposed to solar radiation at a rate of 600 W/m . The surrounding air temperature is 20 C.
◦
Determine the equilibrium surface temperature of the plate if the convection heat transfer
2
coefficient from the plate surface is 20 W/m K and the emissivity of the top surface of the
plate is 0.8.