34. An infinite slab of moderator of extrapolated thickness ã contains sources of fast neutrons distributed according to the function (플), s(x) = S cos Using the two-group method, derive an expression for the thermal flux in the slab.

34. An infinite slab of moderator of extrapolated thickness ã contains sources of fast neutrons distributed according to the function (플), s(x) = S cos Using the two-group method, derive an expression for the thermal flux in the slab.

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.59P

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A 50-mm thick plate of carbon steel (AISI 1010) is annealed with a reheat stage taking the steel from its initial uniform temperature of 200 C to a minimum final temperature of 550 C. HEating is effected in a gas-fired furnace where products of combustion at Tamb = 800 C maintain a convection coefficient of h = 100 W/m^2K on both sides of the plate. How long should the plate be left in the furnace? Substantiate with relevant analysis and calculations.
Solve this with diagram: An engine cover is made from 1 cm thick stainless steel plate (k = 14 W/m K). Air on the inside of the engine cover is heated to 340°C with a heat transfer coefficient of 7 W/m2K. Outside of the engine coverthe ambient air has a temperature of 70°C. If oil was spilled on the outside of the engine cover (ambient side), it could ignite if the surface temperature were to exceed 200°C. In this configuration, would spilled oil ignite? Use calculations to justify your answer. If a 4 mm thermal coating (k = 1.1 W/m K) was applied tothe outside of the engine, what would the outside temperature of the engine cover be reduced to? Solve it with resistors method
Solve this with diagram: An engine cover is made from 1 cm thick stainless steel plate (k = 14 W/m K). Air on the inside of the engine cover is heated to 340°C with a heat transfer coefficient of 7 W/m2K. Outside of the engine coverthe ambient air has a temperature of 70°C. If oil was spilled on the outside of the engine cover (ambient side), it could ignite if the surface temperature were to exceed 200°C. In this configuration, would spilled oil ignite? Use calculations to justify your answer. If a 4 mm thermal coating (k = 1.1 W/m K) was applied tothe outside of the engine, what would the outside temperature of the engine cover be reduced to?
Two inches of urethane foam will reduce heat loss close to 1000% when applied to a 2-inch diameter uninsulated steel pipe. Assume the pipe wall thickness is 0.25-inches, the pipe interior convective heat loss (hi) is 500 BTU/hr-ft2-oF, and the pipe outside convective heat loss ho 20 BTU/hr-ft2-oF, k steel is 25 BTU/hr-ft-oF, and k insulaton is 0.023 BTU/hr-ft-oF. (hint - calculate heat loss with and without insulation.
Although many pots and pans are made of stainless steel, the bottoms often have either a roll-bonded layer of pure copper (Cu) or a brazed or embedded disk of pure aluminum (Al). Use material property values to explain why this design approach leads to more uniform heat dispersal across the bottom of the pan (reducing ‘hot spots’ during cooking).
A hollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. The inner and outer radii of the sphere are o.18 and o.21 m, respectively, and testing is done under steady-state conditions with the inner surface of the aluminum maintained at 250°C. In a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of o.15 m. The system is in a room for which the air temperature is 20°C and the convection coefficient at the outer surface of the insulation is 30 W/m2. K. If 80 W is dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation?
For metal-clad heating element of 6-mm diameter and emissivity ? = 1 is horizontallyimmersed in a water bath. The surface temperature of the metal is 255℃ under steady-stateboiling conditions. Estimate the power dissipation per unit length of the heater.
a) Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m2 . What does this heat energy represent in terms of the refrigeration system of the cold room? b) Without any calculations, how would you expect the internal and external air temperatures to be relative to the wall surface temperatures? Explain your answer. c) How do you expect the heat gain calculated in question 1a) above to change if you take into account the floor and the ceiling of the cold room? Explain your answer
Example 7.9: A one meter long metal rod is thermally insulated in its circumference. The terminal temperatures of the rod are measured to be 100C and 20C as illustrated in the figure below. Determine the heat fluxes in the rod. The rod is made of two different materials of copper and aluminum.
20. The two plates of Problem 11 made of the same material and having constantk are exposed on one side to hot water at Tw and hw and on the other to cold air atTa and ha. Find a) the equation for temperature profile in these plates and b) temperaturesat x = 0 and at x = L if hw = ha = h. [Ans.: a) T1(x) = c1x + c2 where, c1 = hw(Ta – Tw)/c3 and c2 – Ta = – hw(haL +k)(Ta – Tw)/(hac3) where c3 = (k + hwL + hwk/ha)].
A composite wall is formed of a 2.5 cm copper plate, a 3.2 mm layer of asbestos,and a 5 cm layer of fiberglass. The wall is subjected to an overall temperaturedifference of 560oC. Calculate the heat flux through the composite structure.
Question : Studies show that the major energy consumption in Fijian villages is wood which is used for cooking over open fires. Typical consumption of wood is 1 kg person–1day–1. (a) Estimate the heat energy required to boil a 2-liter pot full of water. Assuming this to be the cooking requirement of each person, compare this with the heat content of the wood, and thus estimate the thermal efficiency of the open fire. (b) How much timber has to be felled each year to cook for a village of 200 people?Assuming systematic replanting, what area of crop must the village therefore set aside for fuel use if it is not to make a net deforestation? Hint: refer to Table 10.4. (c) Comment on the realism of the assumptions made, and revise your estimates accordingly. Answer: (a) mcDT ≈ 0.6 MJ (heat losses from pot imply actual requirement is higher). h ≈ 3%. (b) 70 tonnes; 7 ha.