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4

The natural convection air cooled condensers are used in

A. Domestic refrigerators

B. Water coolers

C. Room air conditioners

D. All of these

Correct Answer :

A. Domestic refrigerators


Related Questions

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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

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4

The unit of Stefan Boltzmann constant is

A. Watt/cm² °K

B. Watt/cm4 °K

C. Watt²/cm °K⁴

D. Watt/cm² °K⁴

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4

Depending on the radiating properties, a body will be black when

A. P = 0, x = 0 and a = 1

B. P= 1, T = 0 and a = 0

C. P = 0, x = 1 and a = 0

D. X = 0, a + p = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.

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4

If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of

A. 6

B. 9

C. 27

D. 81

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4

A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

A. h₁ + h₂ + h₃

B. (h₁.h₂.h₃)1/3

C. 1/h₁ + 1/h₂ + 1/h₃

D. None of these

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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.

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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

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4

Temperature of steam at around 540°C can be measured by

A. Thermometer

B. Thermistor

C. Thermocouple

D. None of these

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4

Which of the following has least value of conductivity?

A. Glass

B. Water

C. Plastic

D. Air

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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)

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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

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4

Stefan Boltzmann law is applicable for heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and radiation combined

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4

Sensible heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid of vapour

D. Convert water into steam and superheat it

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4

Fourier's law of heat conduction gives the heat flow for

A. Irregular surfaces

B. Nonuniform temperature surfaces

C. One dimensional cases only

D. Two dimensional cases only

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4

Which of the following is expected to have highest thermal conductivity?

A. Steam

B. Solid ice

C. Melting ice

D. Water

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4

The unit of Stefan-Boltzmann constant is

A. Watt/mK

B. Watt/m²K²

C. Watt/m²K4

D. Watt/mK²

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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

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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

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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

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4

The transfer of heat by molecular collision is known as

A. Conduction

B. Convection

C. Radiation

D. None of these

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4

Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of

A. 1 : 1

B. 2 : 1

C. 1 : 2

D. 4 : 1

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4

Which of the following would lead to a reduction in thermal resistance?

A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

B. In convection, stirring of the fluid and cleaning the heating surface.

C. In radiation, increasing the temperature and reducing the emissivity.

D. All of the above

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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

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4

The critical radius is the insulation radius at which the resistance to heat flow is

A. Maximum

B. Minimum

C. Zero

D. None of these

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4

The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

A. Move actually

B. Do not move actually

C. Affect the intervening medium

D. Does not affect the intervening medium

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4

Pick up the wrong case. Heat flowing from one side to other depends directly on

A. Face area

B. Time

C. Thickness

D. Temperature difference

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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

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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

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4

In case of liquids and gases, the heat transfer takes place according to

A. Conduction

B. Convection

C. Radiation

D. None of these

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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