Explanation: Multipass is a classification based on flow type and not on construction. If we classify a Heat exchanger based on flow type, it would be Multipass and Single-pass.

Explanation: Packed beds have high bed side heat transfer coefficient which facilitates profitable heat transfer, hence this is the reason why they are so commonly used.

Explanation: The critical thickness of insulation is that radius (neither maximum nor minimum) of the insulating wall with conductive heat transfer coefficient as K and the surrounding fluid convective heat transfer coefficient as H, that gives maximum heat transfer rate Q.

Explanation: In a Storage Type Heat Exchanger, the heat energy from the hot fluid is first stored in the matrix/wall of the heat exchanger. Wherein, cooling of the hot fluid takes place. As the cold fluid passes through this same matrix later, the stored heat energy in the matrix is transferred to the cold fluid. This intermittent flow pattern of hot fluid and cold fluid is an exclusive property of Storage Type HE.

Explanation: The efficiency of a double pipe heat exchanger which is calculated by NTU or number of transfer units is given by € = \(\frac{Actual \,Heat\, transfer\, rate}{Maximum \, possible \, rate \, of \,Heat\, Transfer}\). Here x is Actual rate of heat transfer.

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.

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.

Explanation: Plate fin HE provides 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.

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.

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.

Explanation: In a double pipe HE, the fluid is in a constant uniform motion inside the pipes, it is the phenomena of forced convection that removes the fluid from the wall by dynamic mixing which increases the overall bulk temperature of the fluid. The separating wall is the heat transfer medium that carries heat from the hot fluid to the cold fluid through conduction.

Explanation: When we are required to calculate the overall heat transfer coefficient U, we calculate it for the direction of interaction of the fluid’s heat energy, hence we calculate it with hio and ho, and not with hi which is tube’s inner side heat transfer coefficient.

Explanation: For a double pipe HE, we have to calculate Nusselt number twice, once for the inner pipe to calculate Convective Heat Transfer Coefficient for the inner pipe. Similarly, the second time for the annulus side.

Explanation: Fins are generally used to increase the Heat transfer Area when the heat transfer coefficient on that fluid side is comparatively low. Hence as gases usually have lower heat transfer coefficients, fins are kept on this side. Also baffles are provided to give support to the tubes and increase the turbulence of the fluid in shell side.

Explanation: Fins are primarily used to increase the heat transfer area, the rest of the factors given are consequences of this change.

Explanation: The net heat transfer in a particular operation should remain the same, fins are used to decrease the area and time for that process.

Explanation: Fouling factors or dirt factors increase the overall heat transfer resistance and not the conductance which then decreases the overall heat transfer coefficient.

Explanation: When a heat exchanger faces fouling, its heat transfer coefficient decreases, pressure drop increases due to scaling, efficiency decreases and net heat transferred too decreases.