The top surface of the passenger car of a train moving at a velocity of 70 km/h is 2.8 m wide and 8 m long The top surface is absorbing solar radiation at a rate of 200 W/m², and the temperature of the ambient air is- 30°C. Assuming the roof of the car to be perfectly insulated and the radiation heat exchange with the surroundings to be small relative to convection, determine the equilibrium temperature of the top surface of the car. Properties of air at 30°C are: The conductivity k = 0.02588 W /m. °C, The kinematic viscosity v == 1.608 x 10-5 m²/s %3D The Prandtl number: Pr = 0.7282. Air 200 W/m2 30°C

The top surface of the passenger car of a train moving at a velocity of 70 km/h is 2.8 m wide and 8 m long The top surface is absorbing solar radiation at a rate of 200 W/m², and the temperature of the ambient air is- 30°C. Assuming the roof of the car to be perfectly insulated and the radiation heat exchange with the surroundings to be small relative to convection, determine the equilibrium temperature of the top surface of the car. Properties of air at 30°C are: The conductivity k = 0.02588 W /m. °C, The kinematic viscosity v == 1.608 x 10-5 m²/s %3D The Prandtl number: Pr = 0.7282. Air 200 W/m2 30°C

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.

Chapter5: Analysis Of Convection Heat Transfer

Section: Chapter Questions

Problem 5.65P

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The top surface of the passenger car of a train moving at a velocity of 70 km/h is 2.8 m wide and 8 m long. The top surface is absorbing solar radiation at a rate of 200 W/m2, and the temperature of the ambient air is 30°C. Assuming the roof of the car to be perfectly insulated and the radiation heat exchange with the surroundings to be small relative to convection, determine the equilibrium temperature of the top surface of the car.
An average person generates heat at a rate of 84 W while resting. Assuming one-quarter of this heat is lost from the head and disregarding radiation, determine the average surface temperature of the head when it is not covered and is subjected to winds at 10°C and 25 km/h. The head can be approximated as a 30-cm-diameter sphere. Assume a surface temperature of 15°C for evaluation of ms. Is this a good assumption?
Question No. 3: During a cold winter day, wind at 55 km/h is blowing parallel to a 4-m-high and 10-m-long wall of a house. If the air outside is at 5°C and the surface temperature of the wall is12°C, determine the rate of heat loss from that wall by convection. What would your answer be if the wind velocity was doubled
A long 10-cm-diameter steam pipe whose external surface temperature is 110°C passes through some open area that is not protected against the winds . Determine the rate of heat loss from the pipe per unit of its length when the air is at 1 atm pressure and 10°C and the wind is blowing across the pipe at a velocity of 8 m/s.
What is natural convection? How does it differ from forced convection? What force causes natural convection currents?
The top surface of the passenger car of a train moving at a velocity of 115 km/h is 2.8 m wide and 8 m long. The top surface is absorbing solar radiation at a rate of 380 W/m2 and the temperature of the ambient air is 30°C. Assuming the roof of the car to be perfectly insulated and the radiation heat exchange with the surroundings to be small relative to convection, determine the equilibrium temperature of the top surface of the car. The properties of air at 30°C are (Table A-15) k = 0.02588 W/m⋅°C, v = 1.608 × 10−5 m2/s, and Pr = 0.7282.The equilibrium temperature of the top surface of the car is:
An array of power transistors, dissipating 6 W ofpower each, are to be cooled by mounting them on a 25-cm *25-cm-square aluminum plate and blowing air at 35°C overthe plate with a fan at a velocity of 4 m/s. The average temperatureof the plate is not to exceed 65°C. Assuming theheat transfer from the back side of the plate to be negligibleand disregarding radiation, determine the number of transistorsthat can be placed on this plate.
The local atmospheric pressure in Denver, Colorado (elevation 1610 m), is 83.4 kPa. Air at this pressure and at 30°C flows with a velocity of 6 m/s over a 2.5-m * 8-m flat plate whose temperature is 120°C. Determine the rate of heat transfer from the plate if the air flows parallel to the (a) 8-m-long side and (b) the 2.5 m side.
During a cold winter day, wind at 55 km/h is blowing parallel to a 4m high and 10m long wall of a house. If the air outside is at 5 degrees Celsius and the surface temperature of the wall is 12 degrees Celsius , determine the rate of heat loss from the wall by convection. What would your answer be if the wind velocity has doubled? From Table A-1:thermal conductivity, k = 0.0246 W/m degrees Celsiusviscosity, v = 1.4 x 10^-5 m^2/sPrandtl no. Pr = 0.717
An array of power transistors, dissipating 6W of power each, are to be cooled by mounting them on a 25cm x 25xm square aluminum plate and blowing air at 35o over the plate with a fan at a velocity of 4m/s. The average temperature of the plate is not to exceed 65oC. Assuming the heat transfer from the back side of the plate to be negligible and disregarding radiation, determine the number of transistors that can be placed on the plate. Hint 1: This is a flat plate question. DO NOT treat the transistors as a tube bank. How much heat is dissipated across the flat side of the plate (opposite the side the transistors are mounted on). Hint 2: Use the average Reynold’s and Nusselt numbers
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A 1.8-m-diameter spherical tank of negligible thickness contains iced water at 0°C. Air at 25°C flows over the tank with a velocity of 7 m/s. Determine the rate of heat transfer to the tank and the rate at which ice melts. The heat of fusion of water at 0°C is 333.7 kJ/kg.