### Heat Transfer multiple choice questions

Heat Transfer 1. Units for thermal conductivity a) J/kg.K b) J/mol.K c) J.ohm/sec.K2 d) W/m.K Answer: W/m.K 2. The ratio of energy transferred by convection to that by conduction is called a) Stanton number b) Nusselt number c) Biot number d) Preclet number Answer: Biot number 3. Air at 20° C blows over a plate of 50 cm x 75 cm maintained at 250° C. If the convection heat transfer coefficient is 25 W/m2 °C, the heat transfer rate is a) 215.6 kW b) 2156 kW c) 2.156 kW d) 21.56 Kw Answer: 2.156 kW 4. If the body is at thermal equilibrium, then the a) Emissivity = absorptivity b) Emissivity > absorptivity c) Emissivity < absorptivity d) None of the above Answer: Emissivity = absorptivity 5. The body which absorbs all radiations incident upon it, is called as a) Black body b) White body c) Opaque body d) Transparent body Answer: Black body 6. In radiative heat transfer, a gray surface is one a) which appears gray to the eye b) whose emissivity is independent of wavelength c) which