Q3-MCQ 1-c 2-d 3-d 4-b 5-a 6- d 7-b 1. Conduction plus fluid flow in motion is known as a) Radiation b) Conduction 2. Convectional current only occurs in a) solids b) liquids c) gases d) liquids and gases both c) Convection d) Heat exchanger 8- d 3. Which of the following heat flow situations pertains to free or natural convection? a) Air conditioning installations and nuclear reactors b) Flow of water inside the condenser tubes c) Cooling of internal combustion engine d) Cooling of billets in atmosphere 4. Mark the system where heat transfer is given by forced convection a) Chilling effect of cold wind on warm body b) Fluid passing through the tubes of a condenser and other heat exchange equipment c) Heat flow from a hot pavement to surrounding atmosphere d) Heat exchange on the outside of cold and warm pipes 5. Forced convection in a liquid bath is caused by 9- c a) Combined conduction and radiation b) Radiation to the surroundings c) Better conduction d) Convection to the air a) Intense stirring by an external agency b) Molecular energy interactions c) Density difference brought about by temperature gradients d) Flow of electrons in a random fashion 6. A finned tube hot water radiator with a fan blowing air over it is kept in rooms during winter. The major portion of the heat transfer from the radiation is due to 10- a a) Same time of 10 minutes b) More than 10 minutes c) Less than 10 minutes d) Time will depend upon the environmental conditions 7. A body cooling from 80 degree Celsius to 70 degree Celsius takes 10 minutes when left exposed to environmental conditions. If the body is to cool further from 70 degree Celsius to 60 degree Celsius under the same external conditions, it will take 8. On a summer day, a scooter rider feels more comfortable while on the move than while at a stop light because a) An object in motion captures less radiation b) Air has a low specific heat and hence it is cooler c) More heat is loss by convection and radiation while in motion d) Air is transparent to radiation and hence it is cooler than the body 9. What is the value of convective coefficient of oil in case of forced convection? a) 1460-3000 W/m K b) 460-3000 W/m K c) 60-3000 W/m K 10. A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to the temperature of 250 degree Celsius. When left in air at room temperature, what will be their response to cooling? a) Cube will cool faster than sphere but slower than the circular plate b) They will cool at the same rate c) Sphere will cool faster d) Circular plate will cool at the slower rate d) 160-3000 W/m K