Theory and Design for Mechanical Measurements
6th Edition
ISBN: 9781118881279
Author: Richard S. Figliola, Donald E. Beasley
Publisher: WILEY
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Chapter 5, Problem 5.13P
Heat transfer from a rod of diameter D immersed in a fluid can be described by the Nusselt number. Nu = hD/k. where h is the heat-transfer coefficient and k the thermal conductivity of the fluid. If h can be measured to within ±1% (95%), estimate the uncertainty in Nu for the nominal value of h = 150 W/nr-K. Let D= 20 ±0.5 mm and k = 0.6 ± 2% W/m-K.
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The heat transfer between a solid body and a fluid medium is determined by the equation Q=h·A·(Ts-Tf). Here; Q is the amount of heat transferred, h is the heat transfer coefficient, A is the heat transfer surface area, Ts is the temperature of the surface and Tf is the temperature of the fluid. These parameters were measured as h=250±1.75 W/m2ºC, A=20±0.75 m2, Ts =100±0.75ºC and Tf =25±0.75ºC, including error levels. What is the total uncertainty in the amount of heat transferred, in ±%?
a. 3.98
b. 4.07
c. 2.73
d. 2.95
e. 3.88
Give True or False for the following:
1.In liquids and gases, heat transmission is caused by conduction and convection
2.The surface geometry is the important factor in convection heat transfer
3. The heat transfer by conduction from heated surface to the adjacent layer of fluid,
4. The heat transfer is increased in the fin when &> 1
5.The unit of the thermal diffusivity is m²/s
6. Temperature change between the materials interfaces is attributed to the thermal contact resistance
7. A material that has a low heat capacity will have a large thermal diffusivity.
8. Heat conduction flowing from one side to other depends directly on thickness
9.Fin efficiency is the ratio of the fin heat dissipation with that of no fin
10.The critical radius is represented the ratio of the convicted heat transfer to the thermal conductivity
0.6. The resistance of a certain size of copper wire is given as.
R = Ro[1 + a(T-20)]
%3D
where Ro-60+0.3 percent is the resistance at 20°C, a=0.004°C-1+1 percent is the temperature
coefficient of resistance, and the temperature of the wire is T=30°C + 1 percent. Calculate the
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Chapter 5 Solutions
Theory and Design for Mechanical Measurements
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