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Consider the oven of Problem 1.54. The walls of theoven consist of
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Chapter 3 Solutions
Introduction to Heat Transfer
- 1.2 The weight of the insulation in a spacecraft may be more important than the space required. Show analytically that the lightest insulation for a plane wall with a specified thermal resistance is the insulation that has the smallest product of density times thermal conductivity.arrow_forward1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forwardUsing Table 1.4 as a guide, prepare a similar table showing the orders of magnitude of the thermal resistances of a unit area for convection between a surface and various fluids.arrow_forward
- A heater coil is completely immersed in an oil bath that is insulated on all sides except for the top where the oil is in direct contact with the surrounding air that is maintained at a constant temperature, Oair. At t=0s, the coil is switched on and provides in watts of electrical power to the oil which has a thermal mass of moil and an initial temperature of Oinit-oil. The temperature of the oil is denoted by oil and the thermal resistance between the oil and air is Roil-air- a) Draw a schematic of the system clearly labeling the (assumed) directions of the heat transfer rates and the temperature at every node. b) Derive the governing differential equation for the temperature of the oil, oil- c) Where does Oinit-oil appear in the system schematic and how does it affect the governing equations? d) Derive an expression for the steady-state temperature of the oil as a function of the various system parameters.arrow_forward2. A steam line is covered with two successive layers of insulation. The 1.6 in thick layer in contact with the pipe is asbestos which is covered with a 1.4 inch thickness of magnesia insulation. The internal pipe diameter is 3 in, the pipewall thickness is 0.40 in made from common brick. The steam temperature is 850ºF, and the internal surface film coefficient is 50 Btu/hr.ft².F, while the ambient outer temperature is 105°F and the outer surface film coefficient is 3.0 Btu/hr.ft².F. Calculate the following: a. value of U based upon the external area of the magnesia covering, Btu/hr.ft2.F b. heat loss from the steam for a length of 190 feet of pipe, Btu/hrarrow_forwardI am struggling with this question. Part a and barrow_forward
- This is a Physical problem, please reply as soon as posible. Thanks.arrow_forwardThe Resistance (R) of an enclosure of surface area of 8,000sf is 20. What is the amount of heat required to heat the enclosure during a day where the average daily temperature is 55*F?arrow_forwardThe interior of an oven is maintained at a temperature of 1500°F by means of suitablecontrol apparatus. The walls of the oven are 9 in. thick and constructed from a materialhaving a thermal conductivity of 0.18 Btu/hr-ft-°F. Calculate the heat loss for each squarefoot of wall surface per hour. Assume that the inside and outside wall temperatures are1500°F and 400°F respectively.arrow_forward
- Q2. Steam pumped through a long- insulated pipe at a temperature of T= 500 K and provides a convection coefficient of h, = 100 W/m?K at the inner surface of the pipe. The inner and outer radius of the pipe and insulation material are r1 = 10, r2 = 12 and r3 = 17 cm, respectively. The thermal conductivity of the pipe is 100 W/mK. The insulation material is glass fiber and its outer surface is exposed to ambient air at 300 K. If the ambient air provides a convection coefficient of ho = 20 Internal flow Ambient air W/m?K, determine the followings: a. What are the thermal resistance coefficients for convections and conductions b. What is the heat transfer rate per unit length of the pipe c. If the pipe is 30 m long, what will be total heat transfer rate from the pipe. t00 noints)arrow_forwardIt is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not be disturbed by hand contact. In this case, determine the insulation material thickness to be used. Insulation material thermal conductivity coefficient is 0.066 insulation W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.arrow_forwardI need Complete solutions and 4 decimal places.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
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