Concept explainers
In a cylindrical fuel rod of a nuclear reactor, heat is generated internally according to the equation
where
Calculate the temperature drop from the centerline to the surface for a 2.5-cm-diameter rod having a thermal conductivity of
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Chapter 2 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- 2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)arrow_forward2.15 Suppose that a pipe carrying a hot fluid with an external temperature of and outer radius is to be insulated with an insulation material of thermal conductivity k and outer radius . Show that if the convection heat transfer coefficient on the outside of the insulation is and the environmental temperature is , the addition of insulation actually increases the rate of heat loss if , and the maximum heat loss occurs when . This radius, is often called the critical radius.arrow_forwardDescribe what happens to the system inside of a refrigerator or freezer in terms of heat transfer, work, and conservation of energy. Confine yourself to time periods in which the door is closed.arrow_forward
- 1. If the thermal conductivity increase the heat transfer coefficient will 2.The rate of evaporation at a given operation in an evaporator is more when a.there is a vacuum b.the operating pressure is high c.when the feed flowrate is high d.the operating pressure is low 3.In fluid, if the currents are set in motion by the action of mechanical device, the flow is independent of density gradient, the phenomenon is called a.heatexchanger behavior b.natural convection C.forced convection d.thermal conductionarrow_forwardQuestion 2a) Give the Stefan Boltzman equation and define each term.[4]b) A electric room heater (radiator) element is 25 cm long and 4 cm in diameter. The element dissipates heat to the surroundings at 1500 W mainly by radiation, the surrounding temperature being 15°C. Determine the equilibrium temperature of the element surface.[4]c) A composite cylinder consists of 10 cm radius steel pipe of 25 mm thickness over which two layers of insulation 30 mm and 35 mm are laid. The conductivities are 25 W/mK, 0.25 W/mK and 0.65 W/mK. The inside is exposed to convection at 300°C with h 65 W/m2K.The outside is exposed to air at 30°C with h 15 W/m2K. Determinei. the heat loss/m,the interface temperatures.ii. The overall heat transfer coefficient.[4][4][2]arrow_forward1. a) Define thermal efficiency and give one example of heat engine. b) The graph in Figure 1.1 shows one mole of monoatomic gas at initial temperature of 40 ˚C and volume 2 L expanding isobarically at a constant pressure of 2.5 × 105 Pa to 5 L. It is then cooled down at constant volume to a pressure of 1.2 × 105 Pa. The gas is finally compressed isothermally back to its initial state. Calculate i. the work done in process AB. ii. the amount of heat absorbed from A to B. iii. the work done by the gas from C to A. iv. the total work done in the complete process.arrow_forward
- A new 1 ft thick insulating material was recently tested for heat resistant properties. The data recorded temperatures of 70 deg. F and 210 deg. F on the cold and hot sides, respectively. If the thermal conductivity of the insulating material is 0.026 Btu/ft . h .⁰ F, calculate the rate of the heat flux,Q/A, through the wall in Btu/ft^2 . h. Resolve the problem in SI units.arrow_forwardQ5Two large containers A and B of the same size are filled with different fluids. The fluids in containers A and B are maintainedat 0° C and 100° C, respectively. A small metal bar, whose initial temperature is 100° C, is lowered into container A. After1 minute the temperature of the bar is 90° C. After 2 minutes the bar is removed and instantly transferred to the othercontainer. After 1 minute in container B, the temperature of the bar rises 10°. How long, measured from the start of theentire process, will it take the bar to reach 99.9° C?arrow_forwardNewton's Law of Cooling - Differential Equations The rate at which a body cools is proportional to the difference in temperature between the body and its surroundings. If a body in air at 0°C will cool from 200°C to 100°C in 40 minutes, how many more minutes will it take the body to cool from 100°C to 50°C?arrow_forward
- A coil-shaped cooling pipe is made of SS-304 material. This pipe is 1 ft long, 0.4 inch outside diameter, and inch inside diameter. This coil cooling pipe is used to cool the water in the bath. The temperature of the inner coil pipe is 40oF while the outer coil in contact with water is 80oF. The thermal conductivity of SS-304 is a function of temperature where k(T) = 7.75 + (7.78 x 10-3).T where k is in Btu/h.ft.oF and T is in oF. Calculate the rate of heat dissipation in watts! (1287.7)arrow_forwardThe rate of heat conduction through a plane wall is proportional to the average thermal conductivity, the wall area, and the temperature difference, but is inversely proportional to the ---------------.arrow_forwardThermodynamics A hollow cylindrical insulation of inside diameter 0.2 m and outside diameter 0.4 m conducts heat radially. If another layer of insulation of the same material of thickness of 0.4 m is added, the heat flow wil be changed by what ratio?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning