An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be 160 mm 40 mm 800 mm 25 mm TRUE ANSWER : ? YOUR ANSWER : ?
The most commonly used method for the design of duct size is the Static regains method Velocity reduction method Dual or double method Equal friction method TRUE ANSWER : ? YOUR ANSWER : ?
Log mean temperature difference in case of counter flow compared to parallel flow will be Same More Less Depends on other factors TRUE ANSWER : ? YOUR ANSWER : ?
Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by Forced convection Convection Radiation Free convection TRUE ANSWER : ? YOUR ANSWER : ?
Which of the following would lead to a reduction in thermal resistance? In convection, stirring of the fluid and cleaning the heating surface. In radiation, increasing the temperature and reducing the emissivity. All of these In conduction, reduction in the thickness of the material and an increase in thermal conductivity. TRUE ANSWER : ? YOUR ANSWER : ?
According of Kirchhoff's law Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body Emissive power depends on temperature Emissive power and absorptivity are constant for all bodies Radiant heat is proportional to fourth power of absolute temperature TRUE ANSWER : ? YOUR ANSWER : ?
A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as U/Cmin U/A.Cmin Cmin/U U.Cmin TRUE ANSWER : ? YOUR ANSWER : ?
When heat is transferred by molecular collision, it is referred to as heat transfer by Scattering Conduction Radiation Convection TRUE ANSWER : ? YOUR ANSWER : ?
Kirchhoff's law states that 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 The wave length corresponding to the maximum energy is proportional to the absolute temperature The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature None of these TRUE ANSWER : ? YOUR ANSWER : ?
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 0.75 0.4 0.45 0.55 TRUE ANSWER : ? YOUR ANSWER : ?