Q. A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to the temperature of 250 degree Celsius. When left in air at room temperature, what will be their response to cooling?

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Q. Newton-Rikhman law is given by

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Q. The value of film coefficient is dependent upon

(i) Boundary layer configuration
(ii) Geometry and orientation of the surface
(iii) Surface conditions

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Q. The convection coefficients for boiling and condensation lie in the range

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Q. Forced air flows over a convection heat exchanger in a room heater, resulting in a convective heat transfer coefficient 1.136 k W/m² K. The surface temperature of heat exchanger may be considered constant at 65 degree Celsius, and the air is at 20 degree Celsius. Determine the heat exchanger surface area required for 8.8 k W of heating

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Q. A region of fluid motion near a plate in which temperature gradient exist is

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Q. Thermo-physical properties of the fluid are represented by

(i) Density
(ii) Viscosity
(iii) Specific heat
(iv) Thermal conductivity

Identify the correct option

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Q. A motor cycle cylinder consists of ten fins, each 150 mm outside diameter and 75 mm inside diameter. The average fin temperature is 500 degree Celsius and the surrounding air is at 20 degree Celsius temperature. Make calculations for the rate of heat dissipation from the cylinder fins by convection when motor cycle is stationary and convective coefficient is 6 W/m² K

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Q. Air at 20 degree Celsius flows over a flat surface maintained at 80 degree Celsius. The local heat flow at a point was measured as 1250 W/m² .Take thermal conductivity of air as 0.028 W/m K, calculate the temperature at a distance 0.5 mm from the surface

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Q. The convective heat transfer coefficient in laminar flow over a flat plate

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Q. For laminar flow over a flat plate, the average value of Nusselt number is prescribed by the relation

Nu = 0.664 (Re)^0.5 (Pr)^0.33

Which of the following is then a false statement?

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Q. For turbulent flow over a flat plate, the average value of Nusselt number is prescribed by the relation

Nu = 0.664 (Re)^0.5 (Pr)^0.33

Which of the following is then a false statement?

The average heat transfer coefficient increases as

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Q. A nuclear reactor with its core constructed of parallel vertical plates 2.25 m high and 1.5 m wide has been designed on free convection heating of liquid bismuth. Metallurgical considerations limit the maximum surface temperature of the plate to 975 degree Celsius and the lowest allowable temperature of bismuth is 325 degree Celsius. Estimate the maximum possible heat dissipation from both sides of each plate. The appropriate correlation for the convection coefficient is
Nu = 0.13 (Gr Pr)^1/3

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Q. A thin walled duct of 0.5 m diameter has been laid in an atmosphere of quiescent air at 15 degree Celsius and conveys a particular gas at 205 degree Celsius. Base your calculations on one meter length of the duct, estimate the convective coefficient of heat transfer

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Q. Free correction modulus is given by

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Q. The free convection coefficient is given by

h = C₁ d t m/l^(1 – 3m)

The value of exponent for laminar flow is

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Q. For inclined plates we multiply Grashoff number with

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Q. The free convection coefficient is given by

h = C₁ d t m/l^(1 – 3m)

The value of exponent for turbulent flow is

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Q. Which of the following is true for laminar flow?

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Q. A horizontal heated plate at 200 degree Celsius and facing upwards has been placed in still air at 20 degree Celsius. If the plate measures 1.25 m by 1 m, make calculations for the heat loss by natural convection. The convective film coefficient for free convection is given by the following empirical relation

h = 0.32 (α)^0.25 W/m² K

Where α is the mean film temperature in degrees kelvin

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