In many manufacturing plants, individuals are often working around high-temperature surfaces. Exposed hot surfaces that can cause thermal burns on human skin are considered hazards in the workplace. Metallic surfaces above 70° C can instantly damage skin that touches them. Consider an AISI 1010 carbon steel strip (? = 7832 kg/ m 3 ) 2 mm thick and 3 cm wide that is conveyed into a chamber to be cooled at a constant speed of 1 m/s. The steel strip enters the cooling chamber at 597° C. Determine the rate at which heat needs to be removed so that the steel strip exits the chamber at 47° C . Discuss how the conveyance speed can affect the required rate of heat removal

In many manufacturing plants, individuals are often working around high-temperature surfaces. Exposed hot surfaces that can cause thermal burns on human skin are considered hazards in the workplace. Metallic surfaces above 70° C can instantly damage skin that touches them. Consider an AISI 1010 carbon steel strip (? = 7832 kg/ m 3 ) 2 mm thick and 3 cm wide that is conveyed into a chamber to be cooled at a constant speed of 1 m/s. The steel strip enters the cooling chamber at 597° C. Determine the rate at which heat needs to be removed so that the steel strip exits the chamber at 47° C . Discuss how the conveyance speed can affect the required rate of heat removal

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

See similar textbooks

Similar questions

Air enters a 7-m-long section of a rectangular duct of cross section 15 cm X 20 cm at 50°C at an average velocity of 7 m/s. If the walls of the duct are maintained at 10°C, determine: (a) the outlet temperature of the air, (b) the rate of heat transfer from the air, and (c) the fan power needed to overcome the pressure losses in this section of the duct.
The compressed air requirements of a textile factory are met by a large compressor that draws in 0.6 m3/s air at atmospheric conditions of 20°C and 1 bar (100 kPa) and consumes 300 kW electric power when operating. Air is compressed to a gage pressure of 8 bar (absolute pressure of 900 kPa), and compressed air is transported to the production area through a 15-cm-internal-diameter, 83-m-long, plastic (smooth) pipes with a surface roughness of 0.15 mm. The average temperature of compressed air in the pipe is 60°C. The compressed air line has 8 elbows with a loss coefficient of 0.6 each. In order to reduce the head losses in the piping and thus the power wasted, someone suggests doubling the diameter of the 83-m-long compressed air pipes. Calculating the reduction in wasted power, and determine if this is a worthwhile idea. Considering the cost of replacement, does this proposal make sense to you?
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.
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 .
Air enters a 25-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?K and the tube temperature is nearly equal to the water temperature of 10°C, determine the exit temperature of air and the rate of heat transfer. Evaluate air properties at a bulk mean temperature of 30°C. Is this a good assumption?
In a geothermal power plant, the used geothermal water at 80°C enters a 15-cm-diameter and 400-m-long uninsulated pipe at a rate of 8.5 kg/s and leaves at 70°C before being reinjected back to the ground. Windy air at 15°C flows normal to the pipe. Disregarding radiation, determine the average wind velocity in km/h.
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
Consider the flow of oil with ? = 894 kg/m3 and ? = 2.33 kg/m·s in a 28-cmdiameter pipeline at an average velocity of 0.5 m/s. A 330-m-long section of the pipeline passes through the icy waters of a lake. Disregarding the entrance effects, determine the pumping power required to overcome the pressure losses and to maintain the flow of oil in the pipe.
Two water reservoirs A and B are connected through a 40-m long, 2-cm diameter cast iron pipe with a sharp-edged entrance. The pipe also involves a swing check valve and a fully open gate valve. The water level in both reservoirs is the same, but reservoir A is pressurized by compressed air while reservoir B is open to the atmosphere at 88 kPa. The water temperature is 10°C. a. If the initial flow rate through the pipe is 1.2 L/s, determine the absolute air pressure on top of reservoir A. b. Determine the pressure just before the valve
One house owner with a pond on his property has decided to use the pond water to cool his house. His idea is to flow air through a thin smooth 10-cm-diameter copper tube that could be submerged into the pond. The water in the pond, at few meters below the surface is typically maintained at a constant temperature of 15°C. If he assumes the air (~1 atm) entering the copper tube at a mean temperature of 30°C with an average velocity of 2.5 m/s, determine the necessary copper tube length that would be needed so that the outlet mean temperature of the air is 20°C. You may consider the convection heat transfer coefficient of 1000 W/m2·K on the outer surface of the copper tube, between the pond water and copper tube. Since the copper tube is thin, the conduction resistance of the tube wall may be neglected.
A liquid metal flows at a mass rate of 3 kg/s through a constant heat flux 5-cm-i.d tube in a nuclear reactor. The fluid at 473 K is to be heated with the tube wall 30 K above the fluid temperature. Determine the length of the tube required for a 1-K rise in bulk fluid temperature, using the following properties: p = 7.7 x 10^3 kg/m^3v = 8.0 x 10^-8 m^2/sCp = 130 J/(kg K)k = 12 W/mKPr = 0.011 Kaufman's correlation: Nu = 0,625.(Re.Pr)0,4
A computer cooled by a fan contains eight printed circuit boards (PCBs), each dissipating 10 W of power. The height of the PCBs is 12 cm and the length is 18 cm. The clearance between the tips of the components on the PCB and the back surface of the adjacent PCB is 0.3 cm. The cooling air is supplied by a 10-W fan mounted at the inlet. If the temperature rise of air as it flows through the case of the computer is not to exceed 10°C, determine (a) the flow rate of the air that the fan needs to deliver, (b) the fraction of the temperature rise of air that is due to the heat generated by the fan and its motor, and (c) the highest allowable inlet air temperature if the surface temperature of the components is not to exceed 70°C anywhere in the system. As a first approximation, assume flow is fully developed in the channel. Evaluate properties of air at a bulk mean temperature of 25°C. Is this a good assumption?