Introduction to Heat Transfer
6th Edition
ISBN: 9780470501962
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Chapter 1, Problem 1.27P
To determine
The amount of heater power required.
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Furnace walls are lined with 3 layers of firebrick with a thickness of 6 in (k=0.95 Btu/h.ft.°F), insulating brick (k-0.4 Btu/h.ft.°F) and common brick (k=0.8 Btu /h.ft.°F) Firebrick inlet temperature, T₁ = 1800°F, maximum insulating brick temperature, T₂ = 1720°F and T3 = 280°F.
1. Calculate the thickness of the insulating brick layer.
2. If the common brick is 9 in., calculate the exit temperature.
1. Humans are able to control their rates of heat production and heat loss to maintain a
nearly constant core temperature of Te = 37°C under a wide range of environmental
conditions. This process is called thermoregulation. From the perspective of calculating
heat transfer between a human body and its surroundings, we focus on a layer of skin:
fat, with its outer surface exposed to the environment and its inner surface at a
temperature slightly less than the core temperature, T = 35°C = 308 K. Consider a person
with a skin/fat layer of thickness L =
mm and effective thermal conductivity k = 0.3
"- The person has a surface area A = 1.8 m? and is dressed in a bathing suit. The
m· K
emissivity of the skin is ɛ = 0.95.
a). When the person is in still air at T = 282 K, what is the skin surface
temperature and rate of heat loss to the environment? Convection heat transfer
to the air is characterized by a free convection coefficient of h 2
m2 -K
b). When the person is in water at T = 282,…
Problem 23.1
A dc transformer is supplied with electric power at 230 watts with an input voltage of 220 volts. The
transformer output is 1.9 amps at 110 V. The heat transfer surface area for the transformer can be
modeled as a 10 cm x 10 cm x 10 cm cube. The convection heat transfer coefficient for the transformer is
hconv=6 W/m².K.
(a) Determine the input current to the transformer, in amps.
(b) Determine the rate of heat transfer from the transformer at steady-state operation conditions,
in W.
(c) Determine the steady-state surface temperature of the transformer if the ambient air
temperature is 25°C.
Ans: a) 0.75 amps ≤ |I| ≤ 1.5 amps
b) 15 W ≤ ≤ 25 W
c) 90°C ≤ |T| ≤ 100°C (for 5 sides w/ heat transfer)
Chapter 1 Solutions
Introduction to Heat Transfer
Ch. 1 - The thermal conductivity of a sheet of rigid,...Ch. 1 - The heat flux that is applied to the left face of...Ch. 1 - A concrete wall, which has a surface area of 20m2...Ch. 1 - The concrete slab of a basement is 11 m long, 8 m...Ch. 1 - Consider Figure 1.3. The heat flux in the...Ch. 1 - Prob. 1.6PCh. 1 - The inner and outer surface temperatures of a...Ch. 1 - A thermodynamic analysis of a proposed Brayton...Ch. 1 - A glass window of width W=1m and height H=2m is 5...Ch. 1 - Prob. 1.10P
Ch. 1 - The heat flux that is applied to one face of a...Ch. 1 - Prob. 1.12PCh. 1 - Prob. 1.13PCh. 1 - Prob. 1.14PCh. 1 - The 5-mm-thick bottom of a 200-mm-diameter pan may...Ch. 1 - Prob. 1.16PCh. 1 - For a boiling process such as shown in Figure...Ch. 1 - You've experienced convection cooling if you've...Ch. 1 - Prob. 1.19PCh. 1 - A wall has inner and outer surface temperatures of...Ch. 1 - An electric resistance heater is embedded in a...Ch. 1 - Prob. 1.22PCh. 1 - A transmission case measures W=0.30m on a side and...Ch. 1 - Prob. 1.24PCh. 1 - A common procedure for measuring the velocity of...Ch. 1 - Prob. 1.26PCh. 1 - Prob. 1.27PCh. 1 - Prob. 1.28PCh. 1 - Prob. 1.29PCh. 1 - Prob. 1.30PCh. 1 - Prob. 1.31PCh. 1 - Prob. 1.32PCh. 1 - Prob. 1.33PCh. 1 - Prob. 1.34PCh. 1 - An electrical resistor is connected to a battery,...Ch. 1 - Pressurized water pin=10bar,Tin=110C enters the...Ch. 1 - Consider the tube and inlet conditions of Problem...Ch. 1 - An internally reversible refrigerator has a...Ch. 1 - A household refrigerator operates with cold- and...Ch. 1 - Chips of width L=15mm on a side are mounted to a...Ch. 1 - Consider the transmission case of Problem 1.23,...Ch. 1 - One method for growing thin silicon sheets for...Ch. 1 - Heat is transferred by radiation and convection...Ch. 1 - Radioactive wastes are packed in a long,...Ch. 1 - An aluminum plate 4 mm thick is mounted in a...Ch. 1 - A blood warmer is to be used during the...Ch. 1 - Consider a carton of milk that is refrigerated at...Ch. 1 - The energy consumption associated with a home...Ch. 1 - Liquid oxygen, which hems a boiling point of 90 K...Ch. 1 - The emissivity of galvanized steel sheet, a common...Ch. 1 - Three electric resistance heaters of length...Ch. 1 - A hair dryer may be idealized as a circular duct...Ch. 1 - In one stage of an annealing process, 304...Ch. 1 - Convection ovens operate on the principle of...Ch. 1 - Annealing, an important step in semiconductor...Ch. 1 - In the thermal processing of semiconductor...Ch. 1 - A furnace for processing semiconductor materials...Ch. 1 - Single fuel cells such as the one of Example 1.5...Ch. 1 - Prob. 1.59PCh. 1 - Prob. 1.60PCh. 1 - Prob. 1.61PCh. 1 - A small sphere of reference-grade iron with a...Ch. 1 - A 50mm45mm20mm cell phone charger has a surface...Ch. 1 - A spherical, stainless steel (AISI 302) canister...Ch. 1 - Prob. 1.65PCh. 1 - Prob. 1.66PCh. 1 - A photovoltaic panel of dimension 2m4m is...Ch. 1 - Following the hot vacuum forming of a paper-pulp...Ch. 1 - Prob. 1.69PCh. 1 - Prob. 1.70PCh. 1 - Prob. 1.71PCh. 1 - The roof of a car in a parking lot absorbs a solar...Ch. 1 - Prob. 1.73PCh. 1 - Prob. 1.74PCh. 1 - Consider Problem 1.1. If the exposed cold surface...Ch. 1 - Prob. 1.76PCh. 1 - Prob. 1.77PCh. 1 - A thin electrical heating element provides a...Ch. 1 - Prob. 1.79PCh. 1 - Prob. 1.80PCh. 1 - Prob. 1.81PCh. 1 - The curing process of Example 1.9 involves...Ch. 1 - The diameter and surface emissivity of an...Ch. 1 - Bus bars proposed for use in a power transmission...Ch. 1 - A solar flux of 700W/m2 is incident on a...Ch. 1 - In considering the following problems involving...
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- 2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)arrow_forwarda. An air stream passing through a 2-inch (1/6 ft) diameter, thin-walled tube is to be heated by high- pressure steam condensing on the outer surface of the tube at 320 °F. The overall heat transfer coefficient, h between steam and air can be assumed to be 25 Btu/(ft2.hr °F) with the air entering at 100 ft/sec, 10 psia, 40 °F. The air is to be heated to 150 °F. Determine the tube length required. Assuming Rayleigh Line flow, calculate the static pressure change due to heat addition. Also, for the same inlet conditions, calculate the pressure drop due to friction, assuming Fanno flow in the duct with f = 0.018. b. c. d. To obtain an approximation to the overall pressure drop in this heat exchanger, add the two results. Discuss the accuracy of this calculation.arrow_forwardMost houses have vents that open and close manually without any central control.Cities across the United States advise the use of such vents in an effort to saveenergy. In most cases, household occupants do not use the entire house at the sametime; the tendency is to use certain rooms for long periods of time. For example,the family room and dining room may be used heavily, while the living room andkitchen are used at certain hours of the day. To cool or heat a room, the vent systemmust work to cool or heat the entire house. Energy saving can be enhanced if thevents of unused rooms are closed; this will push the hot/cold air to where it isneeded most and reduce the load of the conditioning system. Develop an objectivetree to clarify the need statement and prioritize the objectives laid out in the problem statement. You may add features that may not be listed clearly in the problemstatement but will give an additional advantage to the proposed design.arrow_forward
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