Heat Transfer - Study Mode
[#271] Overall heat transfer co-efficient of a particular tube is U 1 . If the same tube with some dirt deposited on either side has coefficient U 2 , then
Correct Answer
(C) U 1 > U 2
Explanation
Solution: The overall heat transfer coefficient of a tube, denoted as U , decreases when dirt is deposited on either side of the tube. This is because the dirt layer adds thermal resistance, making heat transfer less efficient. Initially, the tube has an overall heat transfer coefficient U 1 . After dirt deposition, the new coefficient is U 2 . Since the dirt layer increases thermal resistance, it reduces the overall heat transfer coefficient: U 1 > U 2 Therefore, the correct answer is Option C: U 1 > U 2 .
[#272] The main function of baffles provided in a shell and tube heat exchanger is to
Correct Answer
(B) Enhance turbulence
[#273] The maximum heat transfer co-efficient from steam heating will be attained when the steam is
Correct Answer
(B) Saturated
[#274] The rate of emission of radiation by a body does not depend upon the
Correct Answer
(D) Shape and porosity of the body
[#275] In a multiple effect evaporator, the effect of boiling point elevation is to
Correct Answer
(B) Reduce the economy
Explanation
Solution: In a multiple effect evaporator , boiling point elevation refers to the increase in the boiling point of a solution due to the presence of dissolved solids (such as salts). This phenomenon occurs because the solutes lower the vapor pressure of the solution, requiring a higher temperature for boiling to occur. As a result: Reduce the economy : The boiling point elevation increases the energy required to evaporate the solvent in each effect of the evaporator system. This increase in energy consumption reduces the overall efficiency or economy of the evaporator system. Reduce the capacity : Boiling point elevation does not directly reduce the capacity of the evaporator, as it refers to the efficiency rather than the maximum processing capacity. Increase the economy : This is incorrect because boiling point elevation actually decreases the efficiency or economy of the evaporator system. None of these : This option is incorrect because boiling point elevation does have a specific effect on the evaporator system. Therefore, the correct answer is Option B: Reduce the economy.