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 1.34P
A vacuum system, as used ¡n sputtering electrically conducting thin films on microcircuits, is comprised of a baseplate maintained by an electrical heater at 300 K anda shroud within the enclosure maintained at 77 K by aliquid-nitrogen coolant loop. The circular baseplate, insulated on the lower side, is 0.3 m in diameter and has an emissivity of 0.25.
(a) How much electrical power must be provided tothe baseplate heater?
(b) At what rate must liquid nitrogen be supplied to theshroud it its heat of vaporization is 125 kJ/kg?
(e) To reduce the liquid nitrogen consumption, it isproposed to bond a thin sheet of aluminum foil
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3. An electric immersion heater, 10 mm in diameter and 300 mm long, is rated at 550 W. The
emissivity of the heater is ε = 0.85.
a) If the heater is horizontally positioned in a large tank of water at 20°C, estimate its surface
temperature.
b) If the heater is accidentally operated in air at 20°C, estimate the surface temperature.
Hint: Radiation heat transfer can be neglected in liquids, but not in gases like air.
QUESTION 6
A simple solar collector in Figure Q1 is built by placing a 5 cm diameter clear plastic tube around a
garden hose whose outer diameter is 1.6 cm. The hose is painted black to maximize solar absorption,
and some plastic rings are used to keep the spacing between the hose and the clear plastic cover
constant. During a clear day, the temperature of the hose is measured to be 65 °C, while the ambient
air temperature is 26 °C. Determine the clear plastic tube temperature and the rate of heat loss from the
water in the hose per meter of its length by natural convection.
Solar
radiation
||| 26°C
Clear plastic tube
Water
Spacer
Garden hose
65°C
Figure Q1
A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC.
a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation
b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made.
Specifically need help with part b
Chapter 1 Solutions
Fundamentals of Heat and Mass Transfer
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- A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation. b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. can you solve part b please?arrow_forwardUsing a polynomial equation solver, determine the steady-state surface temperature (Ts) of the passive radiative cooler below that is exposed to a windy convective enviroment h=40 W/m2*K and T∞= 25°C. The surrounding atmosphere is fixed at Tsur= 10°C. Set up the energy balance/conservation equation.arrow_forwardpnts) Chips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity of ε=0.60 and a maximum allowable temperature of Ts=85oC. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m2K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m2K, what is the maximum operating power?arrow_forward
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