- kA).. 4. Which of the following expresses thermal diffusivity of a substance in terms of thermal conductivity(k), density (p) and specific heat (Cp) A. p.k.Cp C. 1/ p.k.Cp В. К/р.Ср D. p.Cp /k? 5. The boundary condition of the end insulated fin are: dT В. - kA), = 0 and T=To at x=0 dT - kA() =0 and T=To at x=L dx A. dx C. T=0 at x=0 and q=0 at x=L D. None of them

- kA).. 4. Which of the following expresses thermal diffusivity of a substance in terms of thermal conductivity(k), density (p) and specific heat (Cp) A. p.k.Cp C. 1/ p.k.Cp В. К/р.Ср D. p.Cp /k? 5. The boundary condition of the end insulated fin are: dT В. - kA), = 0 and T=To at x=0 dT - kA() =0 and T=To at x=L dx A. dx C. T=0 at x=0 and q=0 at x=L D. None of them

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 2.15P: 2.15 Suppose that a pipe carrying a hot fluid with an external temperature of and outer radius is...

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1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.
To determine the thermal conductivity of a structural material, a large 15-cm-thick slab of the material is subjected to a uniform heat flux of 2500 W/m2 while thermocouples embedded in the wall at 2.5 cm. intervals are read over a period of time. After the system had reached equilibrium, an operator recorded the thermocouple readings shown below for two different environmental conditions: Distance from the Surface (cm) Temperature (C) Test 1 0 40 5 65 10 97 15 132 Test 2 0 95 5 130 10 168 15 208 From these data, determine an approximate expression for the thermal conductivity as a function of temperature between 40 and 208C.
3.9 The heat transfer coefficients for the flow of 26.6°C air over a sphere of 1.25 cm in diameter are measured by observing the temperature-time history of a copper ball the same dimension. The temperature of the copper ball was measured by two thermocouples, one located in the center and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C, and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.
1.77 Explain each in your own words. (a) What is the mode of heat transfer through a large steel plate that has its surfaces at specified temperatures? (b) What are the modes when the temperature on one surface of the steel plate is not specified, but the surface is exposed to a fluid at a specified temperature?
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.
Using the information in Problem 1.22, estimate the ambient air temperature that could cause frostbite on a calm day on the ski slopes. 1.22 In order to prevent frostbite to skiers on chair lifts, the weather report at most ski areas gives both an air temperature and the wind-chill temperature. The air temperature is measured with a thermometer that is not affected by the wind. However, the rate of heat loss from the skier increases with wind velocity, and the wind-chill temperature is the temperature that would result in the same rate of heat loss in still air as occurs at the measured air temperature with the existing wind. Suppose that the inner temperature of a 3-mm-thick layer of skin with a thermal conductivity of 0.35W/mKis35C and the air temperature is 20C. Under calm ambient conditions the heat transfer coefficient at the outer skin surface is about 20W/m2K (see Table 1.4), but in a 40-mph wind it increases to 75W/m2K. If frostbite occurs when the skin temperature drops to about 10C, do you advise the skier to wear a face mask? What is the skin temperature drop due to the wind?
1. Residual oil, with a heating value of 18,480 BTU/bm, is used as a fuel in a power plant which produces 947,870 BTU/s of electricity. The overall efficiency of the power plant is 52 Determine the: a. Heat input, in BTUs b. Daily fuel consumption, in lbm C. Dimensions of the cylindrical storage (assuming length is equal to the diameter), in ft. d. Heat rejected the environment, in BTU/s. The density of the oil is 62 ID/ft.
QUESTION-) 236 °C steam flows in a pipe which features are given below. Inner and outer diameters of pipe are 300 mm and 320 mm. Coefficient of heat transmission is 40 W/mK. It's external ambient is air and it's temperature is 20 °C. Take the temperature of the pipe's external surface 180 °C. It is known that the internal temp convection coefficient is 600 W/m^2K and external heat transfer coefficient is 5,9109 W/m^2K The pipe's length is 500 meter. You need to add the radiation in the calculation. The rate of the radiation emissivity is 0.85. You can take the environmental surface temp directly. Please calculate the heat loss of pipe.
QUESTION-) 236 °C steam flows in a pipe which features are given below. Inner and outer diameters of pipe are 300 mm and 320 mm. Coefficient of heat transmission is 40 W/mK. It's external ambient is air and it's temperature is 20 °C. Take the temperature of the pipe's external surface 180 °C. It is known that the internal temp convection coefficient is 600 W/m^2K and external heat transfer coefficient is 5,9109 W/m^2K The pipe's length is 500 meter. You need to add the radiation in the calculation. The rate of the radiation emissivity is 0.85. You can take the environmental surface temp directly. a-) Please draw this question on the resistance network. b-) Please calculate the heat loss of pipe. c-) By applying insulation to this pipe, it is desired to reduce the heat loss to 20% of the uninsulated loss (option a). Calculate the insulation thickness accordingly. Take glass wool as insulation material.(Conductivity of glass wool = 0.040 W/mK.) Given, The temperature of steam inside the…
After the sinking of RMS Titanic, US operated the International Ice patrol with the purpose of monitoring the presence and movements of icebergs in the Atlantic and Arctic oceans. Once, they observed a unique tabular iceberg in a form of a rectangle (250 km x 50 km x 300 m). How many years would it take to melt the iceberg solely by heat from the sun if the ice absorbs a mean of 98 J/m2 -s, 12.5 hrs per day? Note: the exposed area for heating is 250 km x 50 km and the density is 920 kg/m3 . This is my solution.
QUESTION-) 236 °C steam flows in a pipe which features are given below. Inner and outer diameters of pipe are 300 mm and 320 mm. Coefficient of heat transmission is 40 W/mK. It's external ambient is air and it's temperature is 20 °C. Take the temperature of the pipe's external surface 180 °C. It is known that the internal temp convection coefficient is 600 W/m^2K and external heat transfer coefficient is 5.9109 W/m^2K The pipe's length is 500 meter. You need to add the radiation in the calculation. The rate of the radiation emissivity is 0.85. You can take the environmental surface temp directly. IMPORTANT NOTE: Hi. I sent this question to be solved 3 times. But I faced with different and wrong answers in all. What i want to ask is that doesn't all the resistances except conduction and convection resistances need to change after adding the insulation materials to the pipe? In the solution the people who solved this question took the external surface temp constant. Shouldn't the…
Residual oil, with a heating value of 18,480 BTU/lbm, is used as a fuel in a power plant which produces 947,870 BTU/s of electricity. The overall efficiency of the power plant is 52%. Determine the: a. Heat input, in BTU/s b. Daily fuel consumption, in lbm c. Dimensions of the cylindrical storage (assuming length is equal to the diameter), in ft. d. Heat rejected to the environment, in BTU/s. The density of the oil is 62 lbm/ft3