Fundamentals of Heat and Mass Transfer
7th Edition
ISBN: 9780470501979
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Textbook Question
Chapter 1, Problem 1.21P
An electric resistance heater is embedded in a longcylinder of diameter 30 mm. When water with a temperature of 25°C and velocity of 1m/s flows crosswiseover the cylinder, the power per unit length required to maintain the surface at a uniform temperature of 90°Cis 28 kW/m. When air, also at 25°C, but with a velocityof 10m/s is flowing, the power per unit length requiredto maintain the same surface temperature is 400 W/m.Calculate and compare the convection coefficients for the flows of water and air.
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An electric resistance heater is embedded in a long cylinder ofdiameter 30mm. When water with a temperature of 25 C and velocityof 1m/s flows crosswise over the cylinder, the power per unit lengthrequired to maintain the surface at a uniform temperature of 90 C is28kW/m. When air, also at 25 C, but with a velocity of 10m/s isflowing, the power per unit length required to maintain the samesurface temperature is 400W/m. Calculate and compare the convectioncoefficients for the flows of water and air.
What is the approximate temperature difference between a hot plate and the surrounding air if the heat flux from the plate is 800 W/m2? Assume that the air is flowing past the surface with a velocity of 5 m/s giving a heat transfer coefficient of 20 W/(m2K).
A 10-mm-inner-diameter pipe made of commercial steel is used to heat a liquid in an industrial process. The liquid enters the pipe with Ti=25°C, V=0.8 m/s. A uniform heat flux is maintained by an electric resistance heater wrapped arounf the outer surface of the pipe, so that the fluid exits at 75°C. Assuming fully developed flow and taking the average fluid properties to be ρ=1000 kg/m3, cp=4000 J/kg·K, µ=2x10-3 kg/m·s, k=0.48 W/m·K, and Pr=10, determine:
The required surface heat flux , produced by the heater
The surface temperature at the exit, Ts
The pressure loss through the piper and the minimum power required to overcome the resistance to flow.
Chapter 1 Solutions
Fundamentals of Heat and Mass Transfer
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