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1) 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 e. rate of heat transfer depends on thermal conductivity and temperature difference
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2) Thermal conductivity of glass-wool varies from sample to sample because of variation in ________________ ? a. composition b. density c. porosity d. structure e. all of the above
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3) Which of the following has least value of conductivity_________________? a. glass b. water c. plastic d. rubber e. air
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4) Heat flows from one body to other when they have_________________? a. different heat contents b. different specific heat c. different atomic structure d. different temperatures e. none of the above
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5) 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. inversely proportional to the thickness of the body e. all of the above
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6) Which of the following has maximum value of thermal conductivity________________? a. aluminium b. steel c. brass d. copper e. lead
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7) Heat transfer by radiation mainly depends upon___________________? a. its temperature b. nature of the body c. kind and extent of its surface d. all of the above e. none of the above
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8) Moisture would find its way into insulation by vapour pressure unless it is prevented by __________________ ? a. high thickness of insulation b. high vapour pressure c. less thermal conductivity insulator d. a vapour seal e. all of the above
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9) Thermal diffusivity is ____________________? a. a dimensionless parameter b. function of temperature c. used as mathematical model d. a physical property of the material e. useful in case of heat transfer by radiation
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10) Thermal conductivity of wood depends on_______________? a. moisture b. density c. temperature d. all of the above e. none of the above
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11) 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 e. none of the above
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12) Unit of thermal diffusivity is_________________? a. m2/hr b. m2/hr°C c. kcal/m2 hr d. kcal/m.hr°C e. kcal/m2 hr°C
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13) 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 e. none of the above
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14) 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 e. absorptivity
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15) 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 e. none of the above
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16) 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 e. heat-transfer
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17) 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 e. 1 : 4
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18) 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 e. none of the above
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19) A non-dimensional number generally associated with natural convection heat transfer is________________? a. Grashoff number b. Nusselt number c. Weber number d. Prandtl number e. Reynold number
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20) 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 e. none of the above
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