Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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In many manufacturing plants, individuals are often working around high temperature surfaces.
Exposed hot surfaces that are potential for thermal burns on human skin tissue are considered to
be hazards in the workplace. Metallic surface of temperature above 70°C is considered
extremely high temperature in the context of thermal burn, where skin tissue damage can occur
instantaneously upon contact with the hot surface.. Consider an AISI 1010 carbon steel strip (p =
7832 kg/m3) of 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
amount of heat rate that needed to be removed so that the steel strip exits the chamber at 47°C
to avoid instantaneous themal burn upon accidental contact with skin tissue. Discuss how the
conveyance speed can affect the neat rate needed to be removed from the steel strip in the
cooling chamber.
FIGURE P1-25
Cooling chamber
Steel strip
Im/s
=47°C…
A vertical furnace wall is made-up on an inner wall of firebrick 20 cm thick followed by insulating brick 15 cm thick and an outer wall of steel 1 cm thick. The surface temperature of the wall adjacent to the combustion chamber is 1200oC while that of the outer surface of steel is 50oC. The thermal conductivities of the wall material in W/m-K are firebrick, 10; insulating brick, 0.26; and steel, 45; neglecting film resistances and contact resistance of joints, determine the percent of the total maintenance due to insulating brick.
Consider that you are deciding between two winter coats. Assume further that you have access
to a heat-producing mannequin whose rate of heat generation is adjustable. According to the
chapter 10 equation M = (1/1)(TB-TA), insulation is equivalent to (TB - TA)/M. (this is in fact a
general equation for insulation). How would you compare the insulation supplied by the two
jackets quantitatively?
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- Build a spreadsheet to do the step by step method for estimating the temperature of unprotected steel work exposed to the ASTM E119 Standard Fire. Assume a convective heat transfer coefficient of 25 W/m2K and an emissivity of 0.5. Assume the specific heat to remain constant at 600 J/kgK. Use a time step of 30 seconds and an ambient temperature of 20°C. Provide an Excel plot showing the curves of the fire and a steel member through a time of 60 minutes with F/V ratios of: a)25 m-1 b)100 m-1 c)200 m-1 d)300 m-1 Note your plot should contain 5 curves. One for the fire and one for each of the F/V values. Also on the spreadsheet, highlight in green, the cells identifying the temperature of the unprotected steel member with an F/V of 200m-1 at the following times: a)3 minutes b)10 minutes c)20 minutes d)50 minutesarrow_forward3. Consider a 3 m high rectangular enclosure consisting of two surfaces separated by a 0.1 m air gap at 1 atm. If the surface temperatures across the air gap are 30 °C and -10 °C, determine the ratio of the heat transfer rate for the horizontal orientation (with hotter surface at the bottom) to that for vertical orientation. [1.66] 0.1 m 3 m Air -10°C -10°C 30°C Air 30°℃ > 3marrow_forwardHeat transfer is of critical importance in various industrial applications, including manufacturing. During machining, both the cutting tool and the workpiece will be significantly heated by friction heating. The heating of the cutting tool will reduce the tool hardness and strength, deteriorate the cutting quality, and shorten the tool life. Therefore, it is essential to prevent the overheating of the cutting tool during machining. Coolants are an instrumental part of machining to help cool the tool and the workpiece, provide lubricant, flush away chips, and prevent corrosion. The task of this project is to design the coolant to maintain the maximum machine tool temperature below 100 °C during the side milling process. As shown in the figure below, the machine tool has a diameter of 10 mm (D) and a length of 5 cm. The tool material is M2 high speed tool steel (T11302) and the workpiece is aluminum 6061. The spindle speed (w) is 2000 RPM and the cutting speed (v) is 50 mm/min. The feed…arrow_forward
- Calculate the heat transfer rate from a 100 m2 , 15-cm-thick concrete wall with inside and outside surface temperatures of 20° C and 0° C .arrow_forward2 A vertical furnace wall is made up of an inner of firebrick 20 cm thick followed by insulating brick 15 cm thick and an outer wall of steel 1 cm thick. The surface temperature of the wall adjacent to the combustion chamber is 1,200°C while that the outer surface of steel is 50°C. The thermal conductivities of the wall material in W/m-K are: firebrick, 10; insulating brick, 0.26; and steel, 45. Neglecting the film resistances and contact resistance joints, determine the heat loss per sq. m. of wall area.arrow_forwardRequired information Heat dissipated from an engine in operation can cause hot spots on its surface. If the outer surface of an engine is situated in a place where oil leakage is possible, then when leaked oil comes in contact with hot spots above the oil's autoignition temperature, it can ignite spontaneously. Consider an engine cover that is made of a stainless-steel plate with a thickness of 1 cm and a thermal conductivity of 14 W/m.K. The stainless-steel plate is covered with a 5-mm-thick insulation (k=0.5 W/m.K). The inner surface of the engine cover is exposed to hot air at 350°C with a convection heat transfer coefficient of 5 W/m².K as shown in the figure. The 2-m-long engine outer surface is cooled by air blowing in parallel over it at 7 m/s in an environment where the ambient air is at 60°C. To prevent fire hazard in the event of oil leak on the engine cover, the engine cover surface should be kept below 180°C. It has been determined that the 5- mm-thick insulation layer is…arrow_forward
- The concrete slab of a basement is 11 m long, 8 m wide, and 0.5 m thick. During the winter, temperatures are nominally 17°C and 10°C at the top and bottom surfaces, respectively. If the concrete has a thermal conductivity of 1.4 W/m-K, what is the rate of heat loss through the slab, in W? If the basement is heated by a gas furnace operating at an efficiency of 7, = 0.90 and natural gas is priced at = $0.02/MJ, what is the daily cost of the heat loss, in dollars per day? W q = Ca = i $/darrow_forwardmanufacturer plans to use steel wire (ks = 25 Wm-1 K-1 ) in a household appliance. For safetyconsiderations, we would like an estimate of the smallest electric current that is required to melt the wire.The bare wire is exposed to 20°C air with convective heat transfer coefficient of 15 Wm-2 K-1 and hasdiameter of 2.0 mm and electrical resistance of 0.20 W/m (i.e., per meter of wire). Thermal energy isproduced within the wire at the rate I2 Re , where I is the electrical current through the wire and Re is thewire’s electrical resistance. I = 0.643 Solve the microscopic energy balance in the steel wire with a prescribed temperature Ts at the wiresurface, as well as the requirement that temperature be finite at the center of the wire, to find anexpression for the temperature at the center of the wire in terms of the surface temperature Ts . Use yourresult to estimate the electric current at which the wire begins to melt.arrow_forwardThe temperature of the inside and the outside surface of a brickwork of a furnace have been noted to be 650°C and 250°C. Make calculations for the percentage decrease in heat loss if the thickness of the brick work is increased by 100 percent. The ambient temperature is 30°C. Assume that the thermal conductivity of the brickwork and the convective heat transfer coefficient remain the same before and after the increase in thickness.arrow_forward
- A tube-launched rocket has stabilizing fins at its rear. During launch the fins experience hot gas at Tg = 1700 oC for a time t = 0.3 seconds. It is important that the fins survive launch without surface melting, T. Given the heat transfer coefficient is h, the heat flux per unit area is q=h(Tg-Ts). What is the objective for this design? High melting point Low thermal conductivity Launching efficiency Low melting pointarrow_forwardIn an experiment to measure convection heat transfer coefficients, a very thin metal foil of very low emissivity (e.g., highly polished copper) is attached on the surface of a slab of material with very low thermal conductivity. The other surface of the metal foil is exposed to convection heat transfer by flowing fluid over the foil surface. This setup diminishes heat conduction through the slab and radiation on the metal foil surface, while heat convection plays the prominent role. The slab on which the metal foil is attached to has a thickness of 25 mm and a thermal conductivity of 0.023 W/m·K. In a condition where the surrounding room temperature is 20°C, the metal foil is heated electrically with a uniform heat flux of 5000 W/m2. If the bottom surface of the slab is 20°C and the metal foil has an emissivity of 0.02, determine (a) the convection heat transfer coefficient if air is flowing over the metal foil and the surface temperature of the foil is 150°C; and (b) the convection…arrow_forward(h) A single-glazed glass window pane is an arched shape, consisting of a semicircle of radius 0.5 m on top of a rectangle 1.0 m wide by 2.0 m high, with no joints. The glass pane is 5 mm thick. One side of the window is exposed to air at 20°C and the other side is exposed to air at 5°C. Assuming convective heat transfer on both sides of the window, and conduction through it, determine the total thermal resistance of the window pane and hence the rate of heat transfer through it. (Convection: h = 15 W/m²K; Glass: k = 1.1 W/mK)arrow_forward
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