Which of the following has least value of conductivity_________________?
(A) glass
(B) water
(C) plastic
(D) rubber
(D) air
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 is maximum for perfectly black body
(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
A steam pipe is to be insulated by two insulating materials put over each other . For best results__________________?
(A) better insulation should be put over pipe and better one over it
(B) inferior insulation should be put over pipe and better one over it
(C) both may be put in any order
(D) whether to put inferior OIL over pipe or the better one would depend on steam temperature
(D) unpredictable
In heat exchangers, degree of approach is defined as the difference between temperatures of________________?
(A) cold water inlet and outlet
(B) hot medium inlet and outlet
(C) hot medium outlet and cold water inlet
(D) hot medium outlet and cold water outlet
(D) none of the above
A non-dimensional number generally associated with natural convection heat transfer is________________?
(A) Grashoff number
(B) Nusselt number
(C) Weber number
(D) Prandtl number
(D) Reynold number
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
(D) none of the above
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
(D) 1 : 4
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
(D) heat-transfer
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
(D) none of the above
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
(D) absorptivity