partb 2A house has well-insulated walls 18.0 cm thick (assumeconductivity of air) and area 450 m², a roof of wood 5.0 cmthick and area 270 m², and uncovered windows 0.75 cmthick and total area 34 m² .Part AAssuming that heat is lost only by conduction, calculate the rate at which heat must be supplied to this house to maintain its inside temperature at 22°C if the outside temperature is -15 °C.Express your answer using two significant figures.QconductiontSubmitPart B=Correct1.6x105 WPrevious AnswersSubmitIf the house is initially at 10 °C, estimate how much heat must be supplied to raise the temperature to 22 °C within 20 min. Assume that only the airneeds to be heated and that its volume is 750 m³. Take the specific heat of air to be 0.24 kcal/kg. C°.Express your answer using two significant figures.V—| ΑΣΦQadded = 40756942Previous Answers Request AnswerX Incorrect; Try Again; 18 attempts remaining?J

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A house has well-insulated walls 18.0 cm thick (assume conductivity of air) and area 450 m², a roof of wood 5.0 cm thick and area 270 m², and uncovered windows 0.75 cm thick and total area 34 m² ▼ Assuming that heat is lost only by conduction, calculate the rate at which heat must be supplied to this house to maintain its inside temperature at 22 °C if the outside temperature is -15 °C. Express your answer using two significant figures. conduction 1.6x105 W t Submit Part B = ✓ Correct Previous Answers If the house is initially at 10 °C, estimate how much heat must be supplied to raise the temperature to 22 °C within 20 min. Assume that only the air needs to be heated and that its volume is 750 m³. Take the specific heat of air to be 0.24 kcal/kg. C°. Express your answer using two significant figures. = 195] ΑΣΦ | 1 Qadded 40756942 → C Submit Previous Answers Request Answer X Incorrect; Try Again; 18 attempts remaining ? J

A house has well-insulated walls 18.0 cm thick (assume conductivity of air) and area 450 m², a roof of wood 5.0 cm thick and area 270 m², and uncovered windows 0.75 cm thick and total area 34 m² ▼ Assuming that heat is lost only by conduction, calculate the rate at which heat must be supplied to this house to maintain its inside temperature at 22 °C if the outside temperature is -15 °C. Express your answer using two significant figures. conduction 1.6x105 W t Submit Part B = ✓ Correct Previous Answers If the house is initially at 10 °C, estimate how much heat must be supplied to raise the temperature to 22 °C within 20 min. Assume that only the air needs to be heated and that its volume is 750 m³. Take the specific heat of air to be 0.24 kcal/kg. C°. Express your answer using two significant figures. = 195] ΑΣΦ | 1 Qadded 40756942 → C Submit Previous Answers Request Answer X Incorrect; Try Again; 18 attempts remaining ? J

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 1.64P: The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating...

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1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
1.52 A flat roof of a house absorbs a solar radiation flux of . The backside of the roof is well insulated, while the outside loses heat by radiation and convection to ambient air at . If the emittance of the roof is 0.80 and the convection heat transfer coefficient between the roof and the air is K, calculate (a) the equilibrium surface temperature of the roof and (b) the ratio of convection to radiation heat loss. Can one or the other of these be neglected? Explain your answer.
1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
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?
2.45 Heat is transferred from water to air through a brass wall . The addition of rectangular brass fins, 0.08 cm thick and 2.5 cm long, spaced 1.25 cm apart, is contemplated. Assuming a water-side heat transfer coefficient of and an airside heat transfer coefficient of , compare the gain in heat transfer rate achieved by adding fins to (a) the water side, (b) the air side, and (c) both sides. (Neglect temperature drop through the wall.)
2.43 A turbine blade 6.3 cm long, with cross-sectional area and perimeter , is made of stainless steel . The temperature of the root, , is . The blade is exposed to a hot gas at , and the heat transfer coefficient is K. Determine the temperature of the blade tip and the rate of heat flow at the root of the blade. Assume that the tip is insulated.
1.76 Explain a fundamental characteristic that differentiates conduction from convection and radiation.
2.3 The shield of a nuclear reactor is idealized by a large 25-cm-thick flat plate having a thermal conductivity of . Radiation from the interior of the reactor penetrates the shield and there produces heat generation that decreases exponentially from a value of at the inner surface to a value of at a distance of 12.5 cm from the interior surface. If the exterior surface is kept at 38°C by forced convection, determine the temperature at the inner surface of the field. Hint: First set up the differential equation for a system in which the heat generation rate varies according to .
The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating conditions with a 2-cm thick layer of ice. One day, a power outage cuts electricity to the refrigeration system of the freezer. Estimate the time required to melt this layer of ice if it has a mass density of 700kg/m3 and a latent heat of fusion of 334 kJ/kg. Consider the air temperature inside the freezer to be 20C with a heat transfer coefficient of 2W/m2K for convection from the freezer surface to air, and clearly state the assumptions made in your calculations.
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.
3.17 A 1.4-kg aluminum household iron has a 500-W heating element. The surface area is . The ambient temperature is 21°C, and the surface heat transfer coefficient is . How long after the iron is plugged in does its temperature reach 104°C?