This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “HT Equipment – Plate – Type Heat Exchangers”.
1. Plate type heat exchangers which are made of thin plates, can handle high pressure and temperature difference.
Explanation: The thin primed plates of this type of heat exchangers are not equipped to handle high pressure and temperature as this may cause leakage and other complications to the equipment.
2. Which of the following is not a Plate – Type heat exchanger?
Explanation: Plate type heat exchangers can be classified as Gasketed, brazed and Welded (full or semi). Other categories are plate coils, spiral plate, etc.
3. Why do we use counter-flow operation on gasketed type Heat Exchanger?
a) It provides better ease of operation
b) Applied pressure difference required is low
c) A larger and uniform temperature difference is achieved
d) It reduces corrosion
Explanation: If we use counter-flow operation with a gasketed flow Plate-type Heat Exchanger, we obtain a larger LMTD (log mean temperature difference) which ensures more temperature gradient for higher heat transfer which is thermodynamically superior.
4. Which of the following is not a property of Plate type heat exchangers?
a) Even though the heat exchanger has low hydraulic diameter, it can be readily and easily cleaned
b) Leakage is never a concern in these heat exchangers
c) It provides a very large surface area for heat transfer
d) The net weight required is always less than its equivalent Shell and tube type heat exchanger
Explanation: One of the main concerns of plate type heat exchangers is that it is very difficult to monitor leakages due to this large number of separable parts, even pinhole leakages can be a concern for highly reactive component’s use.
5. Plate type heat exchangers have less surface area as compared to a similar Shell and Tube heat exchanger. A Shell and Tube Heat Exchanger of equivalent area weigh six-seven times less than a Plate Type heat exchanger.
Explanation: Owing to the large number of plates that can be arranged parallelly to each other, Plate Type Heat Exchangers have a very large area for heat transfer and weigh very less (6-7times) than an equivalent Shell and tube type.
6. Which of the following is a correct statement about Plate -Fin heat exchanger?
a) Fins are irrelevant as it already provides a very large surface area
b) It can be regarded as a Compact Heat Exchanger as it has a high heat transfer surface to volume ratio
c) The cost of plate-fin HE are relatively less compared to other conventional HE available in market
d) Even though it has fins, the plates can be opened and easily cleaned
Explanation: Plate fin HE provide a very large heat transfer Surface because of which it is often regarded as a compact HE. The addition of fine and its delicate design makes cleaning very difficult/impossible, so foul liquids are always avoided. This complicated design makes it relatively costlier than other equipments.
7. How is a Plate-type HE better than a Shell and tube HE, one of the following is not correct.
a) Plate type heat exchangers have much higher heat transfer area than Shell and tube ones
b) Thermal stress is higher in Plate type HE
c) Vibrations due to flow and noise are comparatively absent in Plate type HE
d) Entry impingement problem of shell and tube is absent in Plate type HE
Explanation: All the statements are correct except that the thermal stress in higher in Plate type, which in reality is higher in shell and tube owing to its lesser surface area compared to plat type HE.
8. What limitations does Gaskets pose on Gasketed type HE?
a) Limits its use only to non-corrosive fluids, as the gaskets get corroded
b) It leads to leakage and does not provide proper separation
c) One directional flow is the only possibility
d) Reduces necessary heat transfer area causing decreased Heat coefficients
Explanation: Gaskets of gasketed type HE are usually made of rubbers hence they are prone to corrosion when highly toxic fluids are used. They also limit high temperature and pressure applications as these rubbers can then rupture and cause mixing.
9. Which of the following is not a property of Platular Heat Exchanger?
a) It is welded from all the sides and hence a type of welded plate-type heat exchanger
b) The absence of gaskets ensures no leakage and allows the use of toxic fluids
c) It can handle four liquids at a time
d) It has high maintenance and cleaning expenses
Explanation: Platular HE is welded so it ensures usage of toxic fluids as well as high temperature and pressure applications. Also the absence the gasket makes cleaning and maintenance easier and cheaper as chemical cleaning is possible now.
Explanation: A lamella heat exchanger consists of an outer cylindrical /tubular shell covering a bundle of small lamellas/ narrow flat tubes, edge welded, of the given shape. These elements provide a large heat transfer area to the equipment.
Explanation: The best suitable operation for a gasket heat exchanger is its working in counter-flow direction of fluid flow which ensures maximum average / LMTD for effective heat transfer and is thermodynamically superior.
12. Which one of the following heat exchanger is best suited for high turbulent flow, is very compact and can handle foul liquids?
a) Gasketed Heat Exchanger
b) Brazed Plate type Heat Exchanger
c) Platular Heat Exchanger
d) Lamella Heat Exchanger
Explanation: Brazed Plate Heat Exchanger is one of the best designs of Heat Exchanger which can handle the high turbulent flow, which prevents scaling and fouling, is very compact and requires much less space than Gasketed type Heat Exchanger.
Sanfoundry Global Education & Learning Series – Heat Transfer Operations.
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