Q. A 12 cm diameter cylindrical bar, initially at a uniform temperature of 40 degree Celsius, is placed in a medium at 650 degree Celsius with convective coefficient of 22 W/m² K. Determine the time required for the center to reach 255 degree Celsius. For the material of the bar:
Thermal conductivity = 20 W/m K
Density = 580 kg/m³
Specific heat = 1050 J/kg K

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Q. “A solid which extend itself infinitely in all directions of space is termed as finite solid”. Choose the correct answer

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Q. A gold ring (k = 65 W/m K) measuring 15 * 10 * 60 cm is exposed to a surface where h = 11.5 W/m² K. Find the value of biot number

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Q. In the lumped system parameter model, the variation of temperature with time is

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Q. Which of the following dimensionless number gives an indication of the ratio of internal (conduction) resistance to the surface (convective) resistance?

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Q. Lumped parameter analysis for transient heat conduction is essentially valid for

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Q. In the non-dimensional Biot number, the characteristics length is the ratio of

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Q. During heat treatment, cylindrical pieces of 25 mm diameter, 30 mm height and at 30 degree Celsius are placed in a furnace at 750 degree Celsius with convective coefficient 80 W/m² degree. Calculate the time required to heat the pieces to 600 degree Celsius. Assume the following property values
Density = 7850 kg /m³
Specific heat = 480 J/kg K
Conductivity = 40 W/m degree

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Q. The quantity h L C/k is known as

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Q. For a plat plate (thickness δ, breadth b and height h) the heat exchange occurs from both the sides. The characteristics length is equal to

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Q. Fourier number is given by

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Q. Identify the correct relation between Biot number and Fourier number

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Q. A water line is buried underground in dry soil that has an assumed initial temperature of 4.5 degree Celsius. The pipe may have no flow through it for long period of time, yet it will not be drained in order that no freezing occurs, the pipe must be kept at a temperature not lower than 0 degree Celsius. The pipe is to be designed for a 30 hour period at the beginning of which the soil surface temperature suddenly drops to – 17 degree Celsius. Workout the minimum earth covering needed above the water pipe so as to prevent the possibility of freezing during 36 hour cold spell. The soil in which the pipe is buried has the following properties

Density = 640 kg/m³
Specific heat = 1843J/kg degree
Thermal conductivity = 0.345 W/m degree

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