Thermal diffusivity is ____________________?

A. A dimensionless parameter
B. Function of temperature
C. Used as mathematical model
D. A physical property of the material

Thermal conductivity of wood depends on_______________?

A. Mositure
B. Density
C. Temperature
D. All of the above

Film coefficient is defined as Inside diameter of tube________________?

A. Equivalent thickness of film
B. Thermal conductivity equivalent thickness of film specific heat x viscocity
C. Thermal conductivity molecular diffusivity of momentum thermal diffusivity
D. Film coefficient x inside diameter thermalconductivity

Unit of thermal diffusivity is_________________?

A. M2/hr
B. M2/hr°c
C. Kcal/m2 hr
D. Kcal/m.hr°c

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___________________?

A. Convection
B. Radiation
C. Conduction
D. Both convection and conduction

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

A. Emissivity
B. Transmissivity
C. Reflectivity
D. Intensity of radiation

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

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

A. Thermal resistance
B. Thermal coefficient
C. Temperature gradient
D. Thermal conductivity

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

Emissivity of a white polished body in comparison to a black body is________________?

A. Higher
B. Lower
C. Same
D. Depends upon the shape of body