3.13 A house has a composite wall of wood, fiberglass insula-tion, and plaster board, as indicated in the sketch. On acold winter day, the convection heat transfer coefficientsare h = 60 W/m². K and h; = 30 W/m².K. The totalwall surface area is 350 m².Plaster board, kInsidehi, Tooi = 20°CGlass fiber blanket(28 kg/m³), k10 mm 100 mm-LL₂-Plywood siding, kOutsideplease include assumptions and drawingho, T∞, o = -15°C11120 mmLp(a) Determine a symbolic expression for the total thermalresistance of the wall, including inside and outsideconvection effects for the prescribed conditions.(b) Determine the total heat loss through the wall.(c) If the wind were blowing violently, raising h, to300 W/m².K, determine the percentage increase inthe heat loss.(d) What is the controlling resistance that determines theamount of heat flow through the wall?

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3.13 A house has a composite wall of wood, fiberglass insula- tion, and plaster board, as indicated in the sketch. On a cold winter day, the convection heat transfer coefficients are h = 60 W/m². K and h₁ = 30 W/m².K. The total wall surface area is 350 m². Plaster board, kp Inside h₁, Tooi = 20°C ^^^ Glass fiber blanket (28 kg/m³), k 10 mm 100 mm- Lb L₂ ← -Plywood siding, k Outside please include assumptions and drawing ho Too-15°C 111 -20 mm (a) Determine a symbolic expression for the total thermal resistance of the wall, including inside and outside convection effects for the prescribed conditions. (b) Determine the total heat loss through the wall. (c) If the wind were blowing violently, raising h, to 300 W/m².K, determine the percentage increase in the heat loss. (d) What is the controlling resistance that determines the amount of heat flow through the wall?

3.13 A house has a composite wall of wood, fiberglass insula- tion, and plaster board, as indicated in the sketch. On a cold winter day, the convection heat transfer coefficients are h = 60 W/m². K and h₁ = 30 W/m².K. The total wall surface area is 350 m². Plaster board, kp Inside h₁, Tooi = 20°C ^^^ Glass fiber blanket (28 kg/m³), k 10 mm 100 mm- Lb L₂ ← -Plywood siding, k Outside please include assumptions and drawing ho Too-15°C 111 -20 mm (a) Determine a symbolic expression for the total thermal resistance of the wall, including inside and outside convection effects for the prescribed conditions. (b) Determine the total heat loss through the wall. (c) If the wind were blowing violently, raising h, to 300 W/m².K, determine the percentage increase in the heat loss. (d) What is the controlling resistance that determines the amount of heat flow through the wall?

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.3P: 1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of...

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1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.
A plane wall of thickness 2L has internal heat sources whose strength varies according to qG=qocos(ax) Where qo is the heat generated per unit volume at the center of the wall (x=0) and a is a constant. If both sides of the wall are maintained at a constant temperature of Tw, derive an expression for the total heat loss from the wall per unit surface area.
One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a wall that is maintained at 93C. Air is blown across the rod so that a heat transfer coefficient of 17W/m2 K is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38C, what is the net rate of heat loss to the air?
2.15 Suppose that a pipe carrying a hot fluid with an external temperature of and outer radius is to be insulated with an insulation material of thermal conductivity k and outer radius . Show that if the convection heat transfer coefficient on the outside of the insulation is and the environmental temperature is , the addition of insulation actually increases the rate of heat loss if , and the maximum heat loss occurs when . This radius, is often called the critical radius.
1 - A square chip, with side w = 5 mm, operates under isothermal conditions.The chip is positioned on a substrate so that its side and bottom surfaces are thermally insulated, while its top surface is exposed to theflow of a refrigerant at T∞ = 15°C. From reliability considerations, the chip temperature cannot exceed T = 85°C. The refrigerant being air, with a convection heat transfer coefficientcorresponding h = 200 W/(m2K), what is the maximum allowable power for the chip? Since the coolant is a dielectric liquid for which h = 3000 W/(m²K), what is the maximum allowed power?
A finned surface has been added to cool an electronic part. The surface temperature of the electronic part in contact with the fins is 60 ° C, the convection coefficient between the environment and the finned surface is 40 W / m².K and the heat conduction coefficient for the fin material (aluminum) is 180 w / m.K. a. If the electronic part has wings or no blades, the amount of heat per unit time (W) thrown into the environment, b. Find out wing effectiveness and efficiency?
A vertical cylinder 6 ft tall and 1 ft in diameter might be used to approximate a man for heat-transfer purposes. Suppose the surface temperature of the cylinder is 78°F, h=2 Btu/h · ft2 . °F, the surface emissivity is 0.9, and the cylinder is placed in a large room where the air temperature is 68°F and the wall temperature is 45°F. Calculate the heat lost from the cylinder. Repeat for a wall temperature of 80°F. What do you conclude from these calculations? Known, Find, Schematic Diagram, Assumption, Properties, Analysis and Comments
Example 4: A wall has the following specifications as shown in figure below: Height = 3 m. Width = 5m k (bricks)=0.72 W/m · °C k (plaster) = 0.22 W/m · °C k (foam) =0.026 W/m · °C. The indoor and the outdoor temperatures are 20°C and -10°C. convection heat transfer coefficients on the inner and the outer sides are h1 = 10 W/m2·°C and h2 = 25 W/m2· °C, respectively. Determine the rate of heat transfer through the wall.
Hi, can you help me with the following problem? A thermally insulated tank of water 2 m x 2 m, depth 1 m is stirred with a paddle for threehours. If the paddle is driven by a motor whose shaft power is 8 kW determine the rate ofchange of temperature in degrees C per hr and the increase in temperature of the water.The specific heat of water is 4200 J/kgC. Identify a system and start your analysis from anappropriate form of the Fist Law of Thermodynamics
10 cm thick and 1 m wide long when a steel plate is at temperature Ti = 240 ° C, T0 = 40 ° C It is immersed in the hot oil bath. With sheet Heat transfer coefficient between oil h = 600 W / m2K and p = 7833 kg / m3 for steel , cp = 465 J / kgK, k = 43 W / mK, α = 1.2x10-5 m2 / s. a)How much the core temperature of the steel plate after time becomes 100 ° C ? b)What is the temperature inside 3 cm from the surface of the steel plate? c)Within this period, per unit length plate what will be the amount of heat that passes?
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4-A spherical interplanetary probe of 0.5 m diameter contains electronics thatdissipate 150 W. If the probe surface has an emissivity of 0.8 and the probe does not receive radiation from other surfaces, as, for example from the sun, what is the probe surface temperature?