Uniform internal heat generation at q =6.0×10^7 W/m3 is occurring in a cylindrical nuclear reactor fuel rod of 60-mm diameter, and under steady-state conditions the temperature distribution is of the form T\left(r\right)=a+br^2T(r)=a+br2, where T is in degrees Celsius and r is in meters, while a = 900°C and b = -5.26 × 10^5 °C/m^2. The fuel rod properties are k = 30 W/m · K, ρ = 1,100 kg/m^3, and cp = 800 J/kg · K. (a) What is the rate of heat transfer per unit length of the rod at r = 0 (the centerline) and at r = 30 mm (the surface)? (b) If the reactor power level is suddenly increased to q2dot = 10^8 W/m^3, what is the initial time rate of temperature change at r = 0 and r = 30 mm?

Uniform internal heat generation at q =6.0×10^7 W/m3 is occurring in a cylindrical nuclear reactor fuel rod of 60-mm diameter, and under steady-state conditions the temperature distribution is of the form T\left(r\right)=a+br^2T(r)=a+br2, where T is in degrees Celsius and r is in meters, while a = 900°C and b = -5.26 × 10^5 °C/m^2. The fuel rod properties are k = 30 W/m · K, ρ = 1,100 kg/m^3, and cp = 800 J/kg · K. (a) What is the rate of heat transfer per unit length of the rod at r = 0 (the centerline) and at r = 30 mm (the surface)? (b) If the reactor power level is suddenly increased to q2dot = 10^8 W/m^3, what is the initial time rate of temperature change at r = 0 and r = 30 mm?

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.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.45P: 2.45 Heat is transferred from water to air through a brass wall . The addition of rectangular brass...

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2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.
2.15 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.
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.)
2.45 Heat is transferred from water to air through a brass wall . The addition of rectangular brass fins, 0.08 cm thick and 2.5 cm long, spaced 1.25 cm apart, is contemplated. Assuming a water-side heat transfer coefficient of and an airside heat transfer coefficient of , compare the gain in heat transfer rate achieved by adding fins to (a) the water side, (b) the air side, and (c) both sides. (Neglect temperature drop through the wall.)
A plane wall, 7.5 cm thick, generates heat internally at the rate of 105 W/m3. One side of the wall is insulated, and the other side is exposed to an environment at 90C. The convection heat transfer coefficient between the wall and the environment is 500 W/m2 K. If the thermal conductivity of the wall is 12 W/m K, calculate the maximum temperature in the wall.
A steel tube (k = 15 W/m.K) 3 m long carries a refrigerated liquid at 5°C. The inner diameter of the tube is 4 cm and the thickness is 1.5 cm. The convection heat transfer coefficient inside the tube is 80 W/m.K. The fluid receives heat from the external environment, which is at 28°C with a convection heat transfer coefficient of 20 W/m .K. To reduce the gain, it is studied to add a layer of insulating foam to the tube with a thickness of 5 cm and thermal conductivity k = 0.08 W/m.K. The placement of insulation pays off financially if the heat transfer rate is reduced by at least 30% and if the external surface temperature is above 15°C. Ignoring the effects of radiation, verify that these conditions are met.
Water vapor at a temperature of 120 ° C flows through a stainless steel pipe (k = 57 W / mK). The inner diameter of the pipe is 47 mm, the outer diameter is 50 mm, and the length is 100 m. The heat transfer coefficient between the water vapor and the pipe wall is 200 W / m²K, and the heat transfer coefficient between the outer surface of the pipe and the ambient air is 25 W / m_K. The outdoor air temperature is 10 ° C. Find the thermal conductivity coefficient of the insulation material, since it is desired to insulate with an insulation material with a layer thickness of 50 mm in order to reduce the loss of heat from the pipe by 60%.
The composite wall of a furnace consists of three different materials, two of which have known thermal conductivity (ka = 20 W/m°C and kc = 50 W/m°C) and thicknesses La = 0.30 m and Lb = 0.15 m. The third material (B) is between A and C, with a thickness of 0.15 m, but its thermal conductivity (kb) is unknown. Under steady-state operating conditions, measurements reveal a temperature of 20 °C on the external surface, 600 °C on the internal surface, and a furnace ambient temperature of 800 °C. The internal convection coefficient is 25 W/m²°C. What is the value of kb?
A truncated solid cone is of circular cross section, and its diameter is related to the axial coordinate by an expression of the form D = ax3/2, where a = 2 m−1/2. The sides are well insulated, while the top surface of the cone at x1 is maintained at T1 and the bottom surface at x2 is maintained at T2. Conductivity k = 336 W/m-K (a) Obtain an expression for the temperature distribution T(x). (b) What is the rate of heat transfer across the cone if it is constructed of pure aluminum with x1 = 0.086 m, T1 = 113°C, x2 = 0.270 m, and T2 = 25°C?
The temperatures on the faces of a plane wall 20 cm thick are 400 and 90 ℃. The wall is constructed of a special glass with the following properties: k = 0.8 W∙m-1K-1, ρ = 2750 kgm-3, cP = 0.86 kJkg-1K-1. What is the heat flux (q") through the wall at steady-state conditions?
A steel tube (k = 15 W/m.K) 3 m long carries a refrigerated liquid at 5°C. The inner diameter of the tube is 4 cm and the thickness is 1.5 cm. The convection heat transfer coefficient inside the tube is 80 W/m².K. The fluid receives heat from the external environment, which is at 28°C with a convection heat transfer coefficient of 20 W/m².K. To reduce the gain, it is studied to add a layer of insulating foam to the tube with a thickness of 5 cm and thermal conductivity k = 0.08 W/m².K. The placement of insulation pays off financially if the heat transfer rate is reduced by at least 30% and if the outside surface temperature is above 15°C. Ignoring the effects of radiation, verify that these conditions are met.
Steam at 160 ° C flows in a pipe having an inner radius of 50 mm and an outer radius of 60 mm. The convective heat transfer coefficient between the steam and the inner pipe wall is 2500 W / (m² ° C). The outer surface of the pipe exposed to ambient air is 20 ° C with a convective heat transfer coefficient of 10 W / (m² ° C). Assuming steady state, calculate the rate of heat transfer per meter of pipe from steam to air. Assume that the thermal conductivity of stainless steel is 15 W / (m ° C.). Steps of work according to example 4.16 Singh. a. Find the overall heat transfer coefficient = Answer W / m² ° C. b. Heat transfer rate per meter of pipe = Answer W / m.