Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

Problems 341

11.20.An aluminum plate, with dimensions of 3 cm

3 cm5 cm (length, width, and thickness, respec-

tively), is exposed to a thermal energy source that puts

out 150 J every second as shown in the accompany-

ing figure. The density of aluminum is 2700 kg /m

3

.

Assuming no heat loss to the surrounding block,

determine the temperature rise in the plate after

10 seconds.

11.21. Use the basic idea of Problem 11.19 to design an

apparatus that could be constructed to measure the

heat capacity of solid samples in the range of 500 to

800 J/ kgK. Write a brief report discussing in detail

the overall size of the apparatus; components of the

apparatus, including the heating source, the support-

ing block, insulation materials; and the measurement

elements. In the report include drawings and a sample

experiment. Estimate the cost of such a setup, and

briefly discuss it in your report. Also, write a brief exper-

imental procedure that could be used by someone who

is unfamiliar with the apparatus.

11.22. How would you use the principle given in Prob-

lem 11.19 to measure the heat output of something?

For example, use the basic idea behind Problem 11.19

to design a setup that can be used to measure the heat

output of an ironing press.

11.23. Calorimeters are devices that are commonly used to

measure the heating value of fuels. For example, a Jun-

kers flow calorimeter is used to measure the heating

value of gaseous fuels. A bomb calorimeter, on the

other hand, is used to measure the heating value of liq-

uid or solid fuels, such as kerosene, heating oil, or coal.

Copper

150 J

Insulation

Problem 11.19

as shown. The known material is heated on the top by

a heating element, and the bottom surface of the

sample is cooled by running water through the heat

sink shown. Determine the thermal conductivity of

the unknown sample for the set of data given in the

accompanying table. Assume no heat loss to the sur-

roundings and perfect thermal contact at the com-

mon interface of the sample and the copper.

11.18. Use the basic idea of Problem 11.17 to design an appa-

ratus that could be constructed to measure the thermal

conductivity of solid samples in the range of 50 to 300

W/mK. Write a brief report discussing in detail the

overall size of the apparatus; components of the appa-

ratus, including the heating source, the cooling source,

insulation materials; and the measurement elements.

In the report, include drawings and a sample experi-

ment. Estimate the cost of such a setup and briefly dis-

cuss it in your report. Also, write a brief experimental

procedure that could be used by someone who is unfa-

miliar with the apparatus.

11.19. A copper plate, with dimensions of 3 cm3 cm

5 cm (length, width, and thickness, respectively), is

exposed to a thermal energy source that puts out

150 J every second, as shown in the accompanying

figure. The density of copper is 8900 kg /m

3

. Assum-
ing no heat loss to the surrounding block, determine
the temperature rise in the plate after 10 seconds.

Cold plate

Hot plate

Insulation

1

2

3

4

Cold water in

Warm water out

Problem 11.17

Thermocouple

Location Temperature (C)

1 120

2 100

385

472

Copper

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