chemical engineering Mcqs
4101. According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor) ?
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A. 2f

B. f/2

C. f

D. f/4

4102. Heat flux is the time rate of heat transfer per unit_______________?
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A. Area

B. None of these

C. Length

D. Volume

4103. Economy of an evaporator is influenced by the_____________________?
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A. Steam pressure

B. Feed temperature

C. Number of effect

D. Both B. & C.
4104. Low thermal conductivity of heat insulating materials is due to its_________________?
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A. None of these

B. High specific heat

C. Dense structure

D. High proportion of air space
4105. The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the___________________?
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A. Heating volume

B. None of these

C. Nusselt number

D. Heat transfer area
4106. Increasing the liquor level in the evaporator results in the_______________?
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A. Decreased effect of hydrostatic head

B. Decreased capacity

C. Increased true temperature drop

D. Increase in liquor film co-efficient

4107. Black liquor generated during paper manufacture is concentrated in a___________________?
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A. Multiple effect evaporator

B. Single effect evaporator

C. Single effect evaporator followed by a crystalliser

D. Multiple effect evaporators followed by a crystalliser

4108. Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by____________________?
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A. Increasing the tube length

B. Enhancing the fluid pumping rate

C. None of these

D. Keeping the heat transfer surface clean
4109. The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K = 0.04 W/m.K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is 5C. The outside wall temperature is___________________?
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A. 40C

B. 25C

C. 30C

D. 35C
4110. Which of the following is unimportant in forced convection ?
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A. Reynolds number

B. Prandtl number

C. Grashoff number

D. None of these

4111. For a counter current heat exchanger with Ti h = 80C, Tc = 60C, Th = 50C and Ti c = 30C, and the temperature difference between the two streams being the same everywhere along Z, the direction of flow of hot fluid. The temperature profile should satisfy___________________?
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A. d2T/dZ2 > 0

B. d2T/dZ2 < 0

C. dT/dZ = 0

D. d2T/dZ2 = 0
4112. Low thermal conductivity of heat insulating materials is due to its_______________?
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A. High specific heat

B. None of these

C. Dense structure

D. High proportion of air space
4113. Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be_________________?
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A. 0.35

B. 0.45

C. 0.85

D. 0.55

4114. In case of a vertical tube evaporator, with increase in the liquor level, the ____________ is increased?
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A. Velocity of circulation

B. Liquor-film co-efficient

C. Both A. and B.

D. Neither A. and B.
4115. In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred_________________?
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A. material</strong>

B. Through a metallic wall

C. None of these

D. By heating an intermediate material (like chequor bricks) and then heating the air from this

E. By direct contact of hot flue gas with air

4116. The number of kg vaporised per kg of steam fed to the evaporator is defined as____________?
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A. Economy

B. Rate of evaporation

C. Capacity

D. Rate of vaporisation

4117. Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is_________________?
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A. > 1

B. 1

C. > 5

D. < 1
4118. Crystal size in a continuous crystalliser depends upon the___________________?
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A. All A., B. and C

B. Degree of turbulence

C. Rate of heat transfer

D. Degree of super-saturation

4119. A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case ?
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A. The cooling rate will be the same for the two spheres and hence the two spheres will have

B. al temperatures at any instant

C. Both the spheres will emit equal amount of radiation per unit time in the beginning

D. Both will absorb equal amount of radiation from the surrounding in the beginning

E. Both B. & C.
4120. The heat flux in the nucleate boiling regimes is proportional to (where, ?T = excess temperature) ?
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A. ?(?T)

B. (?T)4

C. (?T)2

D. (?T)3
4121. When vaporisation takes place directly at the heating surface, it is called________________?
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A. Film boiling

B. None of these

C. Vapour binding

D. Nucleate boiling
4122. The main function of baffles provided in a shell and tube heat exchanger is to______________?
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A. All A , B & C

B. Enhance turbulence

C. Facilitate the cleaning of outer tube surface

D. Hold the tubes in position

4123. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows ____________ law?
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A. Hyperbolic

B. Logarithmic

C. Parabolic

D. Linear
4124. Viscous & heat sensitive liquids are concentrated in _____________ evaporators?
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A. Agitated film

B. None of these

C. Open pan

D. Long tube

4125. Which of the following is generally considered as opaque surface towards radiations ?
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A. Gases

B. Solids

C. Liquids

D. Both B. and C.
4126. For small temperature difference, the heat transfer rate as per Newtons law of cooling is proportional to (where, ?t = excess temperature) ?
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A. ?t2

B. ?t

C. ?t3

D. ?(?t)

4127. The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is ______________ compared to the same size pipes without fins?
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A. Same

B. Unpredictable

C. Less

D. More

4128. Graetz number is given by__________________?
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A. mCp/kL

B. kL/mCp

C. k?/mCp

D. mCp/k?

4129. With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer ?
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A. Remain unaffected

B. Increases exponentially

C. Increases

D. Decreases
4130. For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and pressure drop are__________________?
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A. Different

B. Same

C. Never different

D. Linearly related

4131. In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always__________________?
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A. < 1

B. 1

C. ?

D. > 1

4132. With the increase of temperature, the Col-burn jH factor_____________________?
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A. Remains unchanged

B. Decreases

C. Increases

D. May increase or decrease; depending on temperature

4133. With increase in temperature, the thermal conductivity of steel___________________?
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A. Remains unchanged

B. Decreases

C. Increases

D. Increases exponentially

4134. If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?
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A. ha = 0.75 hl

B. ha = 0.5 hl

C. ha = 2hl

D. ha = hl

4135. In natural convection heat transfer, the correlating parameter is the_______________________?
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A. Grashoff number

B. Graetz number

C. Bond number

D. Eckert number

4136. In evaporators, lowering the feed temperature_______________?
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A. Increases the heating area required

B. Reduces the economy

C. Both A. and B.

D. Decreases the heating area required

4137. Boiling point elevation of an ideal solution_______________?
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A. Increases rapidly with temperature rise

B. Decreases rapidly with temperature rise

C. In independent of pressure

D. Both B. and C.

4138. In a heat exchanger, floating head is provided to____________________?
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A. Increase the heat transfer area

B. Facilitate cleaning of the exchanger

C. Relieve stresses caused by thermal expansion

D. Increase log mean temperature gradient

4139. Which is the most suitable for the concentration of foamy & frothy liquors ?
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A. Agitated film evaporator

B. None of these

C. Open pan evaporator

D. Long tube vertical evaporator
4140. An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is___________________?
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A. 3000

B. 4000

C. 9000

D. 4600

4141. For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in_____________________?
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A. Increased economy

B. Decreased economy

C. No effect on economy

D. Lower capacity

4142. Thermal diffusivity is given by__________________?
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A. ?/hCp

B. ?Cp/a

C. k/?Cp

D. ?Cp/k

4143. Evaporation by thermo compression results in the _________________________?
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A. Saving of steam

B. Realisation of multiple effect economy in a single effect

C. Both A. and B.

D. None of these

4144. In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of___________________?
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A. Chemical potentials

B. Concentrations

C. Activity co-efficients

D. Mass transfer co-efficients

4145. A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36C. The temperature difference across the layer A is ______________ C?
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A. 24

B. 18

C. 6

D. 12
4146. 1 BTU/hr.ft.F is equal to _____________ kcal/hr. m.C?
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A. 1.49

B. 1

C. 4.88

D. None of these

4147. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?
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A. None of these

B. 1

C. 1
4148. Natural convection is characterised by__________________?
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A. Prandtl number

B. Reynolds number

C. Peclet number

D. Grashoff number
4149. The actual temperature drop across the heating surface in an evaporator depends on the_________________?
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A. All A., B. and C.

B. Depth of liquid over heating surface

C. Feed

D. Pressure difference between steam chest and vapour space

4150. Vacuum is generally maintained in the vapour space of an evaporator mainly to__________________?
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A. Get economical temperature difference by using moderate pressure steam

B. Achieve very high concentration of the final product

C. Concentrate heat sensitive materials

D. Facilitate forward feeding in multiple effect evaporation