Home
Current Affairs January 2024

What is the correct answer?

4

The ratio of surface convection resistance to the internal conduction resistance is known as

A. Grashoff number

B. Biot number

C. Stanton number

D. Prandtl number

Correct Answer :

B. Biot number


Related Questions

What is the correct answer?

4

The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to

A. -1/3

B. -2/3

C. 1

D. -1

What is the correct answer?

4

The transfer of heat by molecular collision is known as

A. Conduction

B. Convection

C. Radiation

D. None of these

What is the correct answer?

4

When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a

A. Black body

B. Grey body

C. Opaque body

D. White body

What is the correct answer?

4

Which of the following property of air does not increase with rise in temperature?

A. Thermal conductivity

B. Thermal diffusivity

C. Density

D. Dynamic viscosity

What is the correct answer?

4

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

A. Wien's law

B. Stefan's law

C. Kirchhoff's law

D. Planck's law

What is the correct answer?

4

The use of heat exchangers is made in

A. Radiators in automobile

B. Condensers and boilers in steam plants

C. Condensers and evaporators in refrigeration and air conditioning units

D. All of the above

What is the correct answer?

4

The amount of heat flow through a body by conduction is

A. Directly proportional to the surface area of the body

B. Directly proportional to the temperature difference on the two faces of the body

C. Dependent upon the material of the body

D. All of the above

What is the correct answer?

4

The thermal diffusivities for gases are generally

A. More than those for liquids

B. Less than those for liquids

C. More than those for solids

D. Dependent on the viscosity

What is the correct answer?

4

Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)

A. h = k/ ρS

B. h = ρS/k

C. h = S/ρk

D. h = kρ/S

What is the correct answer?

4

In regenerator type heat exchanger, heat transfer takes place by

A. Direct mixing of hot and cold fluids

B. A complete separation between hot and cold fluids

C. Flow of hot and cold fluids alternately over a surface

D. Generation of heat again and again

What is the correct answer?

4

Kirchhoff's law states that

A. The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

B. The wave length corresponding to the maximum energy is proportional to the absolute temperature

C. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body

D. None of the above

What is the correct answer?

4

The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

A. First law of thermodynamics

B. Newton's law of cooling

C. Newton's law of heating

D. Stefan's law

What is the correct answer?

4

In counter flow heat exchangers

A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

B. Both the fluids at inlet are in their hottest state

C. Both the fluids at exit are in their hottest state

D. One fluid is in hottest state and other in coldest state at inlet

What is the correct answer?

4

A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as

A. A.Cmin/U

B. U/A.Cmin

C. A.U.Cmin

D. A.U/Cmin

What is the correct answer?

4

The energy distribution of an ideal reflector at higher temperatures is largely in the range of

A. Shorter wavelength

B. Longer wavelength

C. Remain same at all wavelengths

D. Wavelength has nothing to do with it

What is the correct answer?

4

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

A. Conduction

B. Free convection

C. Forced convection

D. Radiation

What is the correct answer?

4

Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

A. RN = hl/k

B. RN = μ cp/k

C. RN = ρ V l /μ

D. RN = V²/t.cp

What is the correct answer?

4

Heat flows from one body to other when they have

A. Different heat contents

B. Different specific heat

C. Different atomic structure

D. Different temperatures

What is the correct answer?

4

Planck's law holds good for

A. Black bodies

B. Polished bodies

C. All coloured bodies

D. All of the above

What is the correct answer?

4

Which of the following is the case of heat transfer by radiation?

A. Blast furnace

B. Heating of building

C. Cooling of parts in furnace

D. Heat received by a person from fireplace

What is the correct answer?

4

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

A. Kirchoffs law

B. Stefan's law

C. Wien' law

D. Planck's law

What is the correct answer?

4

The unit of overall coefficient of heat transfer is

A. kcal/m²

B. kcal/hr °C

C. kcal/m² hr °C

D. kcal/m hr °C

What is the correct answer?

4

Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)

A. S.H/(S.H + L.H)

B. (S.H + L.H) /S.H

C. (L.H - S.H)/S.H

D. S.H/(L.H - S.H)

What is the correct answer?

4

Absorptivity of a body will be equal to its emissivity

A. At all temperatures

B. At one particular temperature

C. When system is under thermal equilibrium

D. At critical temperature

What is the correct answer?

4

The emissivity for a black body is

A. 0

B. 0.5

C. 0.75

D. 1

What is the correct answer?

4

A perfect black body is one which

A. Is black in colour

B. Reflects all heat

C. Transmits all heat radiations

D. Absorbs heat radiations of all wave lengths falling on it

What is the correct answer?

4

The heat transfer by conduction through a thick sphere is given by

A. Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

B. Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

C. Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

D. Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

What is the correct answer?

4

Heat transfer takes place as per

A. Zeroth law of thermodynamics

B. First law of thermodynamic

C. Second law of the thermodynamics

D. Kirchoff's law

What is the correct answer?

4

The ratio of the energy absorbed by the body to total energy falling on it is called

A. Absorptive power

B. Emissive power

C. Absorptivity

D. Emissivity

What is the correct answer?

4

Thermal conductivity of a material may be defined as the

A. Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C

B. Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

C. Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

D. All of the above