Home

What is the correct answer?

4

According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

A. Directly proportional to the surface area

B. Directly proportional to the difference of temperatures between the two bodies

C. Either (A) or (B)

D. Both (A) and (B)

Correct Answer :

D. Both (A) and (B)


Related Questions

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

According to Prevost theory of heat exchange

A. It is impossible to transfer heat from low temperature source to t high temperature source

B. Heat transfer by radiation requires no medium

C. All bodies above absolute zero emit radiation

D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

What is the correct answer?

4

A grey body is one whose absorptivity

A. Varies with temperature

B. Varies with wavelength of the incident ray

C. Is equal to its emissivity

D. Does not vary with temperature and. wavelength of the incident ray

What is the correct answer?

4

Fourier's law of heat conduction is valid for

A. One dimensional cases only

B. Two dimensional cases only

C. Three dimensional cases only

D. Regular surfaces having non-uniform temperature gradients

What is the correct answer?

4

A grey body is one whose absorptivity

A. Varies with temperature

B. Varies with the wave length of incident ray

C. Varies with both

D. Does not vary with temperature and wave length of the incident ray

What is the correct answer?

4

The time constant of a thermocouple is

A. The time taken to attain the final temperature to be measured

B. The time taken to attain 50% of the value of initial temperature difference

C. The time taken to attain 63.2% of the value of initial temperature difference

D. Determined by the time taken to reach 100°C from 0°C

What is the correct answer?

4

Log mean temperature difference in case of counter flow compared to parallel flow will be

A. Same

B. More

C. Less

D. Depends on other factors

What is the correct answer?

4

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is

A. 0.45

B. 0.55

C. 0.40

D. 0.75

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

The critical thickness of insulation for a sphere is

A. k/h₀

B. 2k/h₀

C. h₀/k

D. h₀/2k

What is the correct answer?

4

Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

A. One

B. Two

C. Three

D. Four

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

What is the correct answer?

4

The thermal diffusivities for solids are generally

A. Less than those for gases

B. Less than those for liquids

C. More than those for liquids and gases

D. More or less same as for liquids and gases

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

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

A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

A. The better insulation must be put inside

B. The better insulation must be put outside

C. One could place either insulation on either side

D. One should take into account the steam temperature before deciding as to which insulation is put where

What is the correct answer?

4

Metals are good conductors of heat because

A. Their atoms collide frequently

B. Their atoms are relatively far apart

C. They contain free electrons

D. They have high density

What is the correct answer?

4

Thermal diffusivity of a substance is

A. Directly proportional to the thermal conductivity

B. Inversely proportional to density of substance

C. Inversely proportional to specific heat

D. All of the above

What is the correct answer?

4

The amount of radiation mainly depends upon the

A. Nature of the body

B. Temperature of the body

C. Type of surface of the body

D. All of these

What is the correct answer?

4

Total heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid or vapour

D. Convert water into steam and superheat it

What is the correct answer?

4

In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.

A. Same

B. Less

C. Greater

D. None of these

What is the correct answer?

4

The amount of radiation mainly depends on

A. Nature of body

B. Temperature of body

C. Type of surface of body

D. All of the above

What is the correct answer?

4

In heat transfer, conductance equals conductivity (kcal/hr/sq.m/ °C/cm) divided by

A. Hr (time)

B. Sq. m (area)

C. °C (temperature)

D. K.cal (heat)

What is the correct answer?

4

Thermal diffusivity is

A. A dimensionless parameter

B. Function of temperature

C. Used as mathematical model

D. A physical property of the material

What is the correct answer?

4

Unit of thermal diffusivity is

A. m²/hr

B. m²/hr °C

C. kcal/m² hr

D. kcal/m. hr °C

What is the correct answer?

4

Thermal conductivity of water at 20°C is of the order of

A. 0.1

B. 0.23

C. 0.42

D. 0.51

What is the correct answer?

4

Film coefficient is defined as Inside diameter of tube

A. Equivalent thickness of film

B. Thermal conductivity Equivalent thickness of film Specific heat × Viscosity

C. Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

D. Film coefficient × Inside diameter Thermal conductivity

What is the correct answer?

4

In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in

A. Parallel flow

B. Counter flow

C. Cross flow

D. All of these

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

According of Kirchhoff's law

A. Radiant heat is proportional to fourth power of absolute temperature

B. Emissive power depends on temperature

C. Emissive power and absorptivity are constant for all bodies

D. Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.