Mechanical Engineering Objective Questions { Heat Transfer }

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22. In counter flow heat exchangers

A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

B. Both the fluids at inlet are in their hottest state

C. Both the fluids at exit are in their hottest state

D. One fluid is in hottest state and other in coldest state at inlet

23. In free convection heat transfer, Nusselt number is function of

A. Grashof number and Reynold number

B. Grashof number and Prandtl number

C. Prandtl number and Reynold number

D. Grashof number, Prandtl number and Reynold number

24. Metals are good conductors of heat because

A. Their atoms collide frequently

B. Thier atoms are relatively far apart

C. They contain free electrons

D. They have high density

25. 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

26. 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

27. The ratio of the energy absorbed by the body to total energy falling on it is called

A. Absorptive power

B. Emissive power

C. Absorptivity

28. Total heat is the heat required to

A. Change vapor into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid or vapor

D. Convert water into steam and superheat it

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