Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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Chapter 11, Problem 11.42P
Three thin sheets of polished aluminum are placed parallel to each other so that the distance between them is very small compared to the size of the sheets. If one of the outer sheets is at
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A wall in a house contains a single window. The window consists of a single pane of glass whose area is 0.13 m2 and whose thickness is 8 mm. Treat the wall as a slab of the insulating material Styrofoam whose area and thickness are 19 m2 and 0.10 m, respectively. Heat is lost via conduction through the wall and the window. The temperature difference between the inside and outside is the same for the wall and the window. Of the total heat lost by the wall and the window, what is the percentage lost by the window?
The Diamond Ring Solution. The processing chip on the computer that controls the navigation equipment on your spacecraft is
overheating. Unless you fix the problem, the chip will be damaged and the navigation system will shut down. You open the panel and
find that the small copper disk that was supposed to bridge the gap between the smooth top of the chip and the cooling plate is
missing, leaving a 2.0 mm gap between them. In this configuration, the heat cannot escape the chip at the required rate. You notice by
the thin smudge of thermal grease (a highly thermally conductive material used to promote good thermal contact between surfaces)
that the missing copper disk was 2.0 mm thick and had a díameter of 1.2 cm. You know that the chip is designed to run below 65 °C, and
the copper cooling plate is held at a constant 5.0 °C.
(a) What was the rate of heat flow from the chip to the copper plate when the original copper disk was in place and the chip was at its
maximum operating…
The Diamond Ring Solution. The processing chip on the computer that controls the navigation equipment on your spacecraft is
overheating. Unless you fix the problem, the chip will be damaged and the navigation system will shut down. You open the panel and
find that the small copper disk that was supposed to bridge the gap between the smooth top of the chip and the cooling plate is
missing, leaving a 2.0 mm gap between them. In this configuration, the heat cannot escape the chip at the required rate. You notice by
the thin smudge of thermal grease (a highly thermally conductive material used to promote good thermal contact between surfaces)
that the missing copper disk was 2.0 mm thick and had a diameter of 1.0 cm. You know that the chip is designed to run below 70 °C, and
the copper cooling plate is held at a constant 5.0 °C.
(a) What was the rate of heat flow from the chip to the copper plate when the original copper disk was in place and the chip was at its
maximum operating…
Chapter 11 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
Ch. 11 - A tungsten filament is heated to 2700 K. At what...Ch. 11 - Determine the total average hemispherical...Ch. 11 - Prob. 11.4PCh. 11 - Prob. 11.9PCh. 11 -
11.31 A large slab of steel 0.1 m thick contains...Ch. 11 - Prob. 11.32PCh. 11 - 11.41 Determine the steady-state temperatures of...Ch. 11 - Three thin sheets of polished aluminum are placed...Ch. 11 - 11.68 Two infinitely large, black, plane surfaces...
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- 2. A glass window has an area of 5.5 ft² and a thickness of 5 mm. If one side is at a temperature of 45° F and the other is at 23 F, how much thermal energy (BTU/year) flows through the window in one year? The thermal conductivity of glass is 1.89x10-4 kcal/m-s-K.arrow_forward(3) A thick steel slab is initially at a uniform temperature of 25°C. When the slab is exposed to hot flue gases, the surface temperature suddenly changes to 450°C. Make calculations for the temperature in a plane 250 mm from the slab surface 5 hours after the operation of change in surface temperature. Find also the heat flowing into 2 square meters of this plane and the total energy flowing through the surface during the 5 hour period. It may be presumed that for steel, thermal conductivity k = 160 kJ/m hr deg, density p = 8000 kg/m³ and the specific heat capacity Cp = 0.48 kJ/kg deg. Activate Windows Settings to actie We 851 PN 7/16/20 O Type here to search delete home 144 0 backspace 8.arrow_forward(3) A thick steel slab is initially at a uniform temperature of 25°C. When the slab is exposed to hot flue gases, the surface temperature suddenly changes to 450°C. Make calculations for the temperature in a plane 250 mm from the slab surface 5 hours after the operation of change in surface temperature. Find also the heat flowing into 2 square meters of this plane and the total energy flowing through the surface during the 5 hour period. It may be presumed that for steel, thermal conductivity k = 160 kJ/m hr deg, density p = 8000 kg/m3 and the specific heat capacity Cp = 0.48 kJ/kg deg. Activate Windows Go to Settings to activate Win 1:36 7/13 P Type here to search 14117 detete home Snut ort sc 144 & backspace lock E R home enter D G pause esned 1 shift B N M en alt ctriarrow_forward
- Problem 5.18: A furnace has inside dimensions of 1 m × 1.2 m × 1.5 m. The walls are 0.25 m thick. The inside surface is at 750°C while the outside surface is at 80°C. If the conductivity of the material is 0.45 W/mK determine the heat loss, taking into account the corner and edge effects and also the bottom. (shape factors are taken from hand books). h-1arrow_forwardA radiator plate of 0.2-m (wide) x 0.4-m (height) is in a room of 22°C. One side (the hot side facing the room) of the radiator plate is maintained at a temperature of 80°C, the other sides are assumed to be insulated, as shown in Figure 1. If the following assumptions can be made: 1) steady operating conditions exist; 2) the air an ideal gas; 3) the local' atmospheric pressure is 1.00 atm: (a) Briefly and qualitatively analyze the four different locations for the radiators marked A), B), C) and D), as shown in Figure 1, and rank them in terms of heat transfer efficiency by natural convection. (b) Determine the rate of heat transfer from the radiator plate by natural convection if the plate is A) vertical and C) horizontal with the hot surface facing down. Compare the two and provide a brief discussion of the findings. wall A 0.4 mi C 0.4 m 0.4 m B floor ceiling 0.4 m wall Nu Nu=0.59Ra Nu-0.1 Raa 0.387Ral Nu- - {0.825 + 11 + (0.492/Pr)162) (complex but more accurate) Use vertical plate…arrow_forward5. A horizontal disc of 9 cm diameter, which is at a temperature of 45°C, is immersed facing upward in a pool of 25°C water. Calculate the total heat transfer from the surface to the water.arrow_forward
- It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not disturb in contact with hands. In this case, determine the insulation material thickness to be used. The thermal conductivity coefficient of the insulation material is insulation 0.066 W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.arrow_forwardA radiant-heating system is installed in the plaster ceiling of a room 36 ft long by 18 ft wide by 9 ft high. Assume direct radiation. The temperature of the concrete floor is maintained at 75°F. The temperature of the air passing through the room is held at 75°F. If the required heat supply to the floor is 8000 BTU/hr, calculate the necessary temperature at the ceiling surface. How much heat is transferred to the air, in BUT/hr? Emissivity of plaster = 0.93; absorptivity of concrete = 0.63. The convective heat-transfer coefficient between the ceiling and the air is given by the equation hc = 0.20 (AT)¹/4.arrow_forwardThe diagram below illustrates a simplified version of the Jet Propulsion Laboratory's 25-ft space simulator chamber. Within it, tests are run for deep space probes and their components. In this particular experiment, a sensor assembly with its housing is placed inside. The sensor-housing electronics create heat such that q=3181.0 W exits the assembly's top surface into the chamber. The chamber itself is under vacuum, and its walls are at cryogenic temperatures to simulate conditions in space. Surfaces 1 and 2 are flat. Assume they are flush. The top surface of the chamber, Surface 4, can be approximated as a perfectly insulated, flat ceiling. The exposed surface of the floor, Surface 2, is a black, donut- shaped surface. Additional surface information can be seen below, including various parameters and dimensions. Assume all surfaces are opaque and diffuse, and conditions are at steady-state. PARAMETERS & DIMENSIONS Surface 1: A = 7.07 m²; diameter d; = 3 m; &₁ = 0.5; Surface 2: A₂ =…arrow_forward
- A brass plate has a circular hole whose diameter is slightly smaller than the diameter of an aluminum ball. Ifthe ball and the plate are always kept at the same temperature,(a) should the temperature of the system be increased or decreasedin order for the ball to fit through the hole? (b) Choose the bestexplanation from among the following:I. The aluminum ball changes its diameter more with temperature than the brass plate, and therefore the temperatureshould be decreased.II. Changing the temperature won’t change the fact that the ballis larger than the hole.III. Heating the brass plate makes its hole larger, and that willallow the ball to pass through.arrow_forwardA domestic radiator is 2500mm long and 750mm high and has a surface temperature of 86°C. If the mean room temperature is 18°C, determine the rate of heat output from the radiator.arrow_forwardTwo long rods of the same diameter, one of brass(k= 85 W/mK) and the other of copper (k=375 W/mK) have one of their ends inserted in a furnace and the other ends exposed to the same atmosphere. At a distance of 105mm away from the furnace, the temperature of the brass rod is 120 C. Find the distance form the furnace in which the copper rod have the same temperaturearrow_forward
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