Hot air leaving the stove in the kitchen of a house at 70 0C, with a square section of 22 cm x 22 cm. sheet metal enters the 12 m long section of the channel with a speed of 6 m/s. Emissivity 0.3 The outer surface of the duct, whose thermal resistance is neglected, is located in the basement of the house at 14 0C and 12 W/m2. It is in contact with cold air with 0C convection heat transfer coefficient. Basement taking the wall temperatures of the floor to 14 0C.Find the rate of heat loss from the hot air in the duct to the floor.

Hot air leaving the stove in the kitchen of a house at 70 0C, with a square section of 22 cm x 22 cm. sheet metal enters the 12 m long section of the channel with a speed of 6 m/s. Emissivity 0.3 The outer surface of the duct, whose thermal resistance is neglected, is located in the basement of the house at 14 0C and 12 W/m2. It is in contact with cold air with 0C convection heat transfer coefficient. Basement taking the wall temperatures of the floor to 14 0C.Find the rate of heat loss from the hot air in the duct to the floor.

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.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.4P

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Hot air leaving the stove in the kitchen of a house at 70 0C, with a square section of 22 cm x 22 cm. sheet metal enters the 12 m long section of the channel with a speed of 6 m/s. Emissivity 0.3 The outer surface of the duct, whose thermal resistance is neglected, is located in the basement of the house at 14 0C and 12 W/m2 . It is in contact with cold air with 0C convection heat transfer coefficient. Basement Calculate the exit temperature of the hot air from the basement by taking the wall temperatures of the floor to 14 0C .
An average man has abody surface area of 1.8m2 and a skin temperature of 33degrees celcius .The convection heat transfer coefficient for a clothed person walking in still air is expressed as {h,8.6V^0.53}FOR 0.5<v<2m/s,where V is the walking velocityin m/s.Assuming the average surface temperature of the clothed person to be 30degrees celcius, determine the rate of heat loss from an average man walking in still air at 10degrees celcius by convectionat a walking velocity of (a)0.5m/s (b)1.0m/s (c)1.5m/s (d)2.0m/s
Air enters a 20-cm-diameter 12-m-long underwater duct at 50°C and 1 atm at a mean velocity of 7 m/s, and is cooled by the water outside. If the average heat transfer coefficient is 85 W/m2 °C and the tube temperature is nearly equal to the water temperature of 5°C, determine the exit temperature of air and the rate of heat transfer
Hot air leaving the stove in the kitchen of a house at 70 0C, with a square section of 22 cm x 22 cm. sheet metal enters the 12 m long section of the channel with a speed of 6 m/s. Emissivity 0.3 The outer surface of the duct, whose thermal resistance is neglected, is located in the basement of the house at 14 0C and 12 W/m2 . It is in contact with cold air with 0C convection heat transfer coefficient. Basement Find the heat loss rate from the hot air in the duct to the floor by taking the wall temperatures of the floor to 14 0C.
Consider an air solar collector that is 1 m wide and 5 m longand has a constant spacing of 3 cm between the glass cover andthe collector plate. Air enters the collector at 30°C at a rate of0.15 m3/s through the 1-m-wide edge and flows along the 5-mlong passage way. If the average temperatures of the glasscover and the collector plate are 20°C and 60°C, respectively,determine (a) the net rate of heat transfer to the air in thecollector and (b) the temperature rise of air as it flows throughthe collector.
Metal plates (k = 150 W/m·K, ρ= 2800 kg/m3, and cp = 900 J/kg·K) with a thickness of 2 cm exiting an oven are conveyed through a 10-m long cooling chamber at a speed of 4 cm/s, as shown in the figure. The plates enter the cooling chamber at an initial temperature of 500°C. The air temperature in the cooling chamber is 15°C, and the plates are cooled with blowing air and the convection heat transfer coefficient is given as a function of the air velocity h(V) = 33V0.8, where h is in W/m2·K and V is in m/s. To prevent any hazard to workers handling the plates, it is necessary to design the cooling process such that the plates exit the cooling chamber at a relatively safe temperature of 50°C or less. Determine the air velocity V and the heat transfer coefficient h such that the temperature of the plates exiting the cooling chamber is at 50C.
Hot water is flowing at an average velocity of1.5 m/s through a cast iron pipe (k = 52 W/m·K) whose innerand outer diameters are 3 cm and 3.5 cm, respectively. Thepipe passes through a 15-m-long section of a basement whosetemperature is 15°C. If the temperature of the water dropsfrom 70°C to 67°C as it passes through the basement and theheat transfer coefficient on the inner surface of the pipe is400 W/m2·K, determine the combined convection and radiationheat transfer coefficient at the outer surface of thepipe.
The blades of a wind turbine turn a large shaft at a relatively slow speed. The rotational speed is increased by a gearbox that has an efficiency of 0.93. In turn, the gearbox output shaft drives an electric generator with an efficiency of 0.95. The cylindrical nacelle, which houses the gearbox, generator, and associated equipment, is of length L = 6 m and diameter D = 3 m. If the turbine produces P = 2.5 MW of electrical power, and the air and surroundings temperatures are T = 25 oC and Tsur = 20 oC, respectively, determine the minimum possible operating temperature inside the nacelle. The emissivity of the nacelle is 0.83, and the convective heat transfer coefficient is h = 35 W/m2 .K. The surface of the nacelle that is adjacent to the blade hub can be considered to be adiabatic, and solar irradiation may be neglected. Use Fin or N number of fins to reduce the Ts of the nacelle less than 143 oC
Hot water at 90°C enters a 15-m section of a cast iron pipe (k = 52 W/m?K) whose inner and outer diameters are 4 and 4.6 cm, respectively, at an average velocity of 1.2 m/s. The outer surface of the pipe, whose emissivity is 0.7, is exposed to the cold air at 10°C in a basement, with a convection heat transfer coefficient of l2 W/m2?K. Taking the walls of the basement to be at 10°C also, determine (a) the rate of heat loss from the water and (b) the temperature at which the water leaves the basement.
The chilling room of a meat plant is 15 m × 18 m × 5.5 m in size and has a capacity of 350 beef carcasses. The power consumed by the fans and the lights in the chilling room are 22 and 2 kW, respectively, and the room gains heat through its envelope at a rate of 14 kW. The average mass of beef carcasses is 220 kg. The carcasses enter the chilling room at 35C, after they are washed to facilitate evaporative cooling, and are cooled to 16°C in 12 h. The air enters the chilling room at 2.2°C and leaves at 0.5°C. Determine (a) the refrigeration load of the chilling room and (b) the volume flow rate of air. The average specific heats of beef carcasses and air are 3.14 and 1.0 kJ/kg · °C, respectively, and the density of air can be taken to be 1.28 kg/m3 .
An average man has a body surface area of 1.8 m2 and a skin temperature of 33°C. The convection heat transfer coefficient for a clothed person walking in still air is expressed as h = 8.6V 0.53 for 0.5 < V < 2 m/s, where V is the walking velocity in m/s. Assuming the average surface temperature of the clothed person to be 30°C, determine the rate of heat loss from an average man walking in still air at 10°C by convection at a walking velocity of (a) 0.5 m/s, (b) 1.0 m/s, (c) 1.5 m/s, and (d) 2.0 m/s.
Air at 60°C leaves a furnace and passes through a 12-m long, 20-cm × 20-cm square duct at an average velocity of 4 m/s. If the duct has a constant surface temperature of 33°C, determine the exit temperature of the air and the rate of heat transfer.