A non-dimensional number generally associated with natural convection heat transfer is

Unit of thermal conductivity in M.K.S. units is

Unit of thermal conductivity in S.I. units is

Thermal conductivity of solid metals with rise in temperature normally

Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Heat transfer takes place as per –

When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

When heat is transferred form hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Sensible heat is the heat required to

The insulation ability of an insulator with the presence of moisture would

When heat is Transferred by molecular collision, it is referred to as heat transfer by

Heat transfer in liquid and gases takes place by

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

Heat is closely related with

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

Metals are good conductors of heat because

Which of the following is a case of steady state heat transfer

Total heat is the heat required to

Cork is a good insulator because it has

Thermal conductivity of water in general with rise in temperature

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

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

Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

The time constant of a thermocouple is

Thermal conductivity of air with rise in temperature

Heat flows from one body to other when they have

The concept of overall coefficient of heat transfer is used in heat transfer problems of

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

The amount of heat flow through a body by conduction is

Which of the following has least value of conductivity

Which of the following is expected to have highest thermal conductivity

Thermal conductivity of glass-wool varies from sample to sample because of variation in

Thermal conductivity of a material may be defined as the

Which of the following has maximum value of thermal conductivity

Moisture would find its way into insulation by vapour pressure unless it is prevented by

Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in

According to Prevost theory of heat exchange

The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be

Heat transfer by radiation mainly depends upon

Thermal diffusivity is

Thermal diffusivity of a substance is .

Unit of thermal diffusivity is

Thermal conductivity of wood depends on

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Film coefficient is defined as Inside diameter of tube

Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called

The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as

Emissivity of a white polished body in comparison to a black body is

A grey body is one whose absorptivity

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

LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is

In heat exchangers, degree of approach is defined as the difference between temperatures of

In counter flow heat exchangers

A steam pipe is to be insulated by two insulating materials put over each other. For best results

Fourier’s law of heat conduction is valid for

According of Kirchhoff’s law,

All radiations in a black body are

According to Kirchoff’s law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

The concept of overall coefficient of heat transfer is used in case of heat transfer by

The unit of overall coefficient of heat transfer is (4) kacl/m hr °C

Joule sec is the unit of

The value of Prandtl number for air is about

The value of the wavelength for maximum emissive power is given by —

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

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

Total emissivity of polished silver compared to black body is

According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

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

The unit of Stefan Boltzmann constant is

In free con-vection heat transfer, Nusselt number is function of

Stefan Boltzmann law is applicable for heat transfer by

The thermal diffusivities for gases are generally

The thermal diffusivities for solids are generally

Thermal diffusivity of a substance is

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

According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to

According to Wien’s law, the wavelength corresponding to maximum energy is proportion to

Depending on the radiating properties, a body will be white when where a = absorptivity, p = reflectivity, x = transmissivity

Depending on the radiating properties, a body will be black when where a = absorptivity, p == reflectivity, X = transmissivity.

Depending on the radiating properties, a body will be opaque when where a = absorptivity, p = reflectivity, X = transmissivity.

The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

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

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

The amount of radiation mainly depends on

The emissive power of a body depends upon its

Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

Absorptivity of a body will be equal to its emissivity

In regenerator type heat exchanger, heat transfer takes place by

A perfect black body is one which

. Planck’s law holds good for

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

. Depending on the radiating properties, body will be transparent when

. A grey body is one whose absorptivity