chemical engineering heat transfer chemical engineering Mcqs
101. If heat transfer rate varies with the time, it is termed as__________________?
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A. Monochromatic radiation

B. None of these

C. Forced convection

D. Steady state conduction

102. In a cooling tower, water becomes cool by________________?
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A. Heat transfer to surroundings

B. Loosing sensible heat

C. Loosing latent heat

D. Vaporisation due to heat loss to air

103. The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu ? Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter D. as _________________?
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A. D1.8

B. D0.2

C. D-1.8

D. D-0.2
104. It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30C. The boiling point of the solution is 110C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is____________________?
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A. 7.24 105

B. 6.12 105

C. 9.08 105

D. 3.06 105
105. Radiation energy is emitted by all the substances, which are above____________________?
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A. 0C

B. 0K

C. 100C

D. Room temperature

106. Thermal diffusivity of a material __________________?
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A. Is defined as K/? . Cp

B. Has the unit m2 /sec

C. Is the ratio of thermal conductivity to thermal capacity

D. All A., B. and C.
107. The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is_________________?
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A. Sherwood number

B. Schmidt number

C. Stanton number

D. Nusselt number

108. The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium. This is ______________ law?
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A. Plancks

B. Stefan-Boltzmann

C. Kirchoffs

D. Wiens displacement

109. The interchange factor for radiation heat transfer from surface x to surface y in case of an infinite parallel planes with emissivities ?x & ?y is given by_______________?
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A. 1/?x + 1/?y

B. ?x . ?y

C. (?x + ?y)/( ?x + ?y ?x . ?y)

D. ?x + ?y

110. Boiling point of a solution according to Duhrings rule is a linear function of the _____________ of water?
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A. Boiling point (at the same pressure)

B. Density

C. Thermal conductivity

D. Viscosity

111. Which of the following has maximum thermal conductivity ?
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A. Nitrogen

B. Tar

C. Iron

D. Coal

112. All analogy equations connecting friction factor and heat transfer co-efficient apply only to ___________________?
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A. Wall or skin friction

B. Form friction

C. Both A. and B.

D. Turbulent flow

113. Water is normally used as a coolant in the heat exchange equipments mainly because of its___________________?
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A. Low density

B. Abundance & high heat capacity

C. High fluidity

D. Low viscosity

114. Absorptivity and reflectivity of a perfect black body are respectively _______________?
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A. 1 and ?

B. 1 and 0

C. 0 and 0.5

D. 0 and 1

115. For what value of Prandtl number, the Col-burn analogy is valid ?
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A. 1 to 50

B. 1 to 103

C. 0.06 to 120

D. 0.6 to 120
116. Grashoff number, which is defined as g . ? (Ts T?) ?2. L3/?2, is proportional to the ratio of buoyancy force to ____________ force?
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A. None of these

B. Elastic

C. Inertial

D. Viscous
117. The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of n is exactly 4 for__________________?
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A. A black body

B. Black painted bodies only

C. Polished bodies only

D. All bodies
118. Which of the following has the lowest Prandtl number ?
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A. Water

B. Molten sodium (a coolant used in fast breeder reactor)

C. Transformer oil

D. Dilute H2SO4

119. Colburn analogy is applicable for the value of Prandtl number from_________________?
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A. 0.001 to 1

B. 0.6 to 120

C. 0.5 to 5

D. 120 to 400

120. Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator ?
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A. Horizontal tube evaporator

B. Agitated film evaporator

C. Calandria vertical tube evaporator

D. Long vertical evaporator

121. In a shell and tube heat exchanger, square pitch compared to triangular pitch__________________?
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A. Gives a higher shell side pressure drop

B. Gives a lower shell side pressure drop

C. Can pack more surface area into a shell of given diameter

D. None of these

122. In SI units, fouling factor is expressed in __________________?
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A. m2K/W

B. m2K

C. W/m2K

D. mK/W

123. A _____________ evaporator employs an annular downtake?
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A. Horizontal

B. Long tube vertical

C. None of these

D. Basket type
124. With increase in temperature, the thermal conductivity of most liquids_________________?
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A. Increases

B. Decreases

C. Remain same

D. First increases upto a certain temperature and then becomes constant

125. Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) ?
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A. 1/U1 1/U2

B. U2 U1

C. 1/U2 1/U1

D. U1 U2

126. The equation, Nst = f/2, is the _____________ analogy?
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A. Colburn

B. Reynolds

C. None of these

D. Prandtl

127. 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. Logarithmic

B. Parabolic

C. Linear

D. Hyperbolic

128. For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is______________?
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A. Nu = 0.023 Re0.8. Pr0.4

B. Nu = (?/2) Gz

C. Nu = (2/?) Gz

D. Nu = 2Gz0.5

129. In case of _______________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface?
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A. Nucleate

B. Saturated

C. Local

D. Pool

130. Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is ________________ law?
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A. Wiens

B. Daltons

C. Kirchoffs

D. Stefans

131. The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re)0.8 (Pr)0.4] cannot be used for________________?
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A. Low Reynolds number

B. All A., B. and C.

C. Very low Grashoff number

D. Molten metals

132. Prandtl number for most of dry gases is about________________?
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A. 0.72

B. 70

C. 150

D. 0.001

133. Resistance to heat flow by conduction is proportional to (where, t & ? are thickness & density of the material respectively and A = area normal to the direction of heat flow.) ?
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A. t

B. 1/?

C. All A., B. & C.

D. 1/A

134. Conductance is given by (where, x = thickness, A = heat flow area, K = thermal conductivity.)?
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A. K/Ax

B. x/KA

C. KA/x

D. A/Kx

135. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?
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A. (COP)R = 1.5; (COP)HP = 2.5

B. (COP)R = 2.5; (COP)HP = 1.5

C. (COP)R = (COP)HP = 2.5

D. (COP)R = (COP)HP = 0.6

136. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300C and allowed to cool in natural air. Which one will cool the slowest ?
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A. Sphere

B. All will cool at the same rate

C. Plate

D. Cube

137. A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because__________________?
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A. Total amount of vapor produced per Kg of feed steam in a multiple effect system is much

B. Total heat transfer area of all the effects is -less than that in a single effect evaporator system

C. Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect

D. Boiling point elevation in a single effect system is much higher than that in any effect in a

E. her than in a single effect</strong>

F. tem

138. The unit of conductance in SI unit is_______________?
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A. W/m

B. W/mK

C. W/m2

D. W/K
139. With increase in temperature, the total emissivity of conductors____________________?
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A. Remain same

B. Decreases linearly

C. Decreases

D. Increases
140. Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (?t1 ?t2)/ln(?t1/?t2)], which one is subject to the largest deviation in practice ?
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A. Constant specific heat

B. No partial phase change in the system

C. Constant overall heat transfer co-efficient.

D. Constant rate of fluid flow
141. A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of__________________?
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A. 20.8

B. 2

C. 20.5

D. 20.2

142. Which of the following is the most widely used heat insulating material for pipelines carrying steam ?
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A. 85% magnesia cement and glass wool

B. Tar dolomite bricks followed by asbestos

C. Fireclay refractory followed by aluminium sheet

D. Cotton followed by aluminium foil

143. In SI units, thermal conductivity is expressed in__________________?
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A. Watt/m.K

B. Watt/m2. K

C. Watt/m4. K

D. Watt/m2. K

144. Fqra cold viscous feed, backward feed gives _____________ than forward feed?
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A. Lower economy

B. A higher capacity

C. None of these

D. A lower capacity

145. In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass _____________ through the heat exchanger ?
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A. Once

B. Four times

C. Thrice

D. Twice
146. At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe ?
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A. < 0.1

B. > 0.6

C. < 0.5

D. 0.5

147. For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it__________________?
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A. Decreases the pressure drop

B. Increases the overall heat transfer coefficient

C. Decreases the outlet temperature of cooling medium

D. None of these

148. Steam economy in case of a triple effect evaporator will be _________________?
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A. 1

B. Between 0 and 1

C. > 1

D. < 1

149. A composite flat wall of a furnace is made of two materials A and B. The thermal conductivity of A is twice of that of material B, while the thickness of layer of A is half that of B. If the temperature at the two sides of the wall are 400 and 1200K, then the temperature drop (in K) across the layer of material A is________________?
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A. 133

B. 160

C. 150

D. 125

150. Dittus-Boelter equation used for the determination of heat transfer co-efficient is valid ___________________?
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A. When Grashoff number is very important

B. For fluids in turbulent flow

C. For fluids in laminar flow

D. For liquid metals