McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 101. |
Pick out the correct statement. |
| A. | 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F |
| B. | In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity |
| C. | In unsteady state heat conduction, heat flows in the direction of temperature rise |
| D. | In heat transfer by forced convection, Grashoff number is very important |
| Answer» B. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity | |
| 102. |
Evaporation by thermo compression results in the |
| A. | Saving of steam |
| B. | Realisation of multiple effect economy in a single effect |
| C. | Both (A) and (B) |
| D. | None of these |
| Answer» C. Both (A) and (B) | |
| 103. |
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). |
| A. | U1 - U2 |
| B. | 1/U1 - 1/U2 |
| C. | 1/U2 - 1/U1 |
| D. | U2 - U1 |
| Answer» B. 1/U1 - 1/U2 | |
| 104. |
Use of transverse baffles in a shell and tube heat exchanger is done to increase the |
| A. | Rate of heat transfer |
| B. | Flow velocity |
| C. | Turbulence of shell side fluid |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 105. |
All analogy equations connecting friction factor and heat transfer co-efficient apply only to |
| A. | Wall or skin friction |
| B. | Form friction |
| C. | Both (A) and (B) |
| D. | Turbulent flow |
| Answer» A. Wall or skin friction | |
| 106. |
Which of the following situations can be approximated to a steady state heat transfer system? |
| A. | A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmospheric air at 35°C |
| B. | 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C |
| C. | Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C |
| D. | A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C |
| Answer» B. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C | |
| 107. |
Reason for operating an evaporator in multiple effects is to secure |
| A. | Increased steam economy |
| B. | Decreased steam consumption |
| C. | Both (A) and (B) |
| D. | Increased capacity |
| Answer» C. Both (A) and (B) | |
| 108. |
Heat transfer by __________ may not necessarily require the presence of a medium. |
| A. | Conduction |
| B. | Natural convection |
| C. | Forced convection |
| D. | Radiation |
| Answer» D. Radiation | |
| 109. |
Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the |
| A. | Existence of thermal boundary layer |
| B. | Temperature gradient produced due to density difference |
| C. | Buoyancy of the bubbles produced at active nucleation site |
| D. | None of these |
| Answer» D. None of these | |
| 110. |
Nusselt number is the ratio of the |
| A. | Temperature gradient of the wall to that across the entire pipe |
| B. | Temperature difference to the temperature gradient at the wall |
| C. | Heat flux at the wall to that across the entire pipe |
| D. | None of these |
| Answer» C. Heat flux at the wall to that across the entire pipe | |
| 111. |
Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer. |
| A. | Grashoff |
| B. | Reynolds |
| C. | Both 'a' & 'b' |
| D. | Prandtl & Grashoff |
| Answer» D. Prandtl & Grashoff | |
| 112. |
Prandtl number is the reciprocal of |
| A. | Thermal diffusivity/Momentum diffusivity |
| B. | Thermal diffusivity × Momentum |
| C. | Thermal diffusivity × Mass diffusivity |
| D. | Mass diffusivity × Momentum diffusivity |
| Answer» A. Thermal diffusivity/Momentum diffusivity | |
| 113. |
In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid. |
| A. | Equal to |
| B. | More than |
| C. | Less than |
| D. | Either more or less than (depending upon the fluid) |
| Answer» A. Equal to | |
| 114. |
For a multipass shell and tube heat exchanger, the LMTD correction factor is always |
| A. | 1 |
| B. | > 1 |
| C. | < 1 |
| D. | Between 1 & 2 |
| Answer» C. < 1 | |
| 115. |
Evaporator tubes are generally |
| A. | Horizontal |
| B. | Vertical |
| C. | Inclined |
| D. | Random |
| Answer» B. Vertical | |
| 116. |
Thermal conductivity of a gas at low density, __________ with increase in temperature. |
| A. | Decreases |
| B. | Increases |
| C. | Remains unchanged |
| D. | May increase or decrease; depends on the gas |
| Answer» B. Increases | |
| 117. |
Which of the following is the most widely used heat insulating material for pipelines carrying steam? |
| A. | Tar dolomite bricks followed by asbestos |
| B. | Fireclay refractory followed by aluminium sheet |
| C. | Cotton followed by aluminium foil |
| D. | 85% magnesia cement and glass wool |
| Answer» D. 85% magnesia cement and glass wool | |
| 118. |
The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emissivities εx & εy is given by |
| A. | εx + εy |
| B. | εx . εy |
| C. | 1/εx + 1/εy |
| D. | (εx + εy)/( εx + εy - εx . εy) |
| Answer» D. (εx + εy)/( εx + εy - εx . εy) | |
| 119. |
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. |
| A. | Parabolic |
| B. | Hyperbolic |
| C. | Linear |
| D. | Logarithmic |
| Answer» A. Parabolic | |
| 120. |
With increase in temperature, the thermal conductivity of a gas |
| A. | Increases |
| B. | Decreases |
| C. | Remain same |
| D. | May increase or decrease depending on the type of gas |
| Answer» A. Increases | |
| 121. |
Grashoff number is given by |
| A. | gD3.β.Δtρ2/μ2 |
| B. | gD2βΔtρ/μ2 |
| C. | gD2βΔtP2μ |
| D. | gD3βΔtP2/μ |
| Answer» A. gD3.β.Δtρ2/μ2 | |
| 122. |
Which area is used in case of heat flow by conduction through a cylinder? |
| A. | Logarithmic mean area |
| B. | Arithmetic mean area |
| C. | Geometric mean area |
| D. | None of these |
| Answer» A. Logarithmic mean area | |
| 123. |
Pick out the wrong statement. |
| A. | Heat transfer from a hot body to cold body by the emission of heat waves is called radiation |
| B. | Filmwise condensation takes place on non-wettable surfaces |
| C. | The boiling point of a solution is affected by liquid head as well as boiling point elevation |
| D. | None of these |
| Answer» B. Filmwise condensation takes place on non-wettable surfaces | |
| 124. |
Choose the correct equation. |
| A. | Nu = (Re) (Pr) (Gz) |
| B. | Nu = (Re) (Pr) (St) |
| C. | Nu = (Re) (Pr) |
| D. | Nu = (Pr) (St) |
| Answer» B. Nu = (Re) (Pr) (St) | |
| 125. |
In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid |
| A. | Varies directly as the area and the LMTD |
| B. | Directly proportional to LMTD and inversely proportional to the area |
| C. | Varies as square of the area |
| D. | None of these |
| Answer» A. Varies directly as the area and the LMTD | |
| 126. |
Pick out the wrong statement. |
| A. | 'Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate' |
| B. | In heat exchanger calculations (Δt) weighted is used in place of Δt, when it involves more than one sequence of heating or cooling i.e., desuperheating & condensation or condensation & sub-cooling |
| C. | Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted |
| D. | In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area |
| Answer» C. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted | |
| 127. |
For what value of Prandtl number, St = f/2? |
| A. | 1.5 |
| B. | 1 |
| C. | > 1 |
| D. | < 1 |
| Answer» B. 1 | |
| 128. |
The rate of emission of radiation by a body does not depend upon the |
| A. | Wavelength of radiation |
| B. | Surface temperature of the body |
| C. | Nature of the surface |
| D. | Shape and porosity of the body |
| Answer» D. Shape and porosity of the body | |
| 129. |
Heat sensitive materials can be concentrated in an evaporator employing |
| A. | Vacuum |
| B. | High pressure |
| C. | High residence time |
| D. | None of these |
| Answer» A. Vacuum | |
| 130. |
In a cooling tower, water becomes cool by |
| A. | Loosing sensible heat |
| B. | Heat transfer to surroundings |
| C. | Vaporisation due to heat loss to air |
| D. | Loosing latent heat |
| Answer» A. Loosing sensible heat | |
| 131. |
Conductance is given by (where, x = thickness, A = heat flow area, K = thermal conductivity.) |
| A. | x/KA |
| B. | KA/x |
| C. | K/Ax |
| D. | A/Kx |
| Answer» B. KA/x | |
| 132. |
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 ? |
| A. | Constant overall heat transfer co-efficient. |
| B. | Constant rate of fluid flow |
| C. | Constant specific heat |
| D. | No partial phase change in the system |
| Answer» B. Constant rate of fluid flow | |
| 133. |
LMTD can't be used as such without a correction factor for the |
| A. | Multipass heat exchanger |
| B. | Baffled heat exchanger |
| C. | Condensation of mixed vapour in a condenser |
| D. | All (A) (B) and (C) |
| Answer» D. All (A) (B) and (C) | |
| 134. |
What is the logarithmic mean of r1 and r2? |
| A. | (r1 - r2)/ln(r1/r2) |
| B. | (r1 - r2)/ln(r2/r1) |
| C. | (r2 - r1)/ln(r1/r2) |
| D. | (r1 - r2)/-ln(r1/r2) |
| Answer» A. (r1 - r2)/ln(r1/r2) | |
| 135. |
In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be |
| A. | Less than 45°C |
| B. | More than 45°C |
| C. | Equal to 45°C |
| D. | Initially decreases and remains constant thereafter |
| Answer» B. More than 45°C | |
| 136. |
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is |
| A. | 2.36 |
| B. | 4.36 |
| C. | 120.36 |
| D. | Dependent on NRe only |
| Answer» B. 4.36 | |
| 137. |
Heat flux, as defined in heat flow is analogous to __________ in electricity flow. |
| A. | Current |
| B. | Voltage |
| C. | Resistance |
| D. | None of these |
| Answer» A. Current | |
| 138. |
The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances. |
| A. | Average |
| B. | Geometric mean |
| C. | Product |
| D. | Sum |
| Answer» D. Sum | |
| 139. |
The driving potential for the crystal growth during crystallisation is the __________ of the solution. |
| A. | Concentration |
| B. | Viscosity |
| C. | Super-saturation |
| D. | Density |
| Answer» C. Super-saturation | |
| 140. |
Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re 0.8. Prn, is not valid, if the value of |
| A. | n = 0.4 is used for heating |
| B. | n = 0.3 is used for cooling |
| C. | Reynolds number for the flow involved is > 10000 |
| D. | Reynolds number for the flow involved is < 2100 |
| Answer» D. Reynolds number for the flow involved is < 2100 | |
| 141. |
For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number) |
| A. | NPr |
| B. | NPr 1/3 |
| C. | NPr -1 |
| D. | NPr -1/3 |
| Answer» B. NPr 1/3 | |
| 142. |
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. |
| A. | Once |
| B. | Twice |
| C. | Thrice |
| D. | Four times |
| Answer» B. Twice | |
| 143. |
An ejector is used to |
| A. | Increase pressure |
| B. | Increase temperature |
| C. | Remove condensate |
| D. | None of these |
| Answer» D. None of these | |
| 144. |
In a forward feed multiple effect evaporator, the pressure is |
| A. | Highest in last effect |
| B. | Lowest in last effect |
| C. | Same in all effects |
| D. | Dependent on the number of effects |
| Answer» B. Lowest in last effect | |
| 145. |
In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2 .s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2 /kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is |
| A. | 2000 |
| B. | 4000 |
| C. | 5000 |
| D. | 6000 |
| Answer» C. 5000 | |
| 146. |
With increase in temperature, the thermal conductivity of most liquids |
| A. | Increases |
| B. | Decreases |
| C. | Remain same |
| D. | First increases upto a certain temperature and then becomes constant |
| Answer» B. Decreases | |
| 147. |
Peclet number (Pe) is given by |
| A. | Pe = Re.Pr |
| B. | Pe = Re/Pr |
| C. | Pe = Pr/Re |
| D. | Pe = Nu.Re |
| Answer» A. Pe = Re.Pr | |
| 148. |
The film co-efficient between condensing vapour and metal wall increases with |
| A. | Increasing temperature of the vapour |
| B. | Decreasing temperature of the vapour |
| C. | Increasing viscosity of the film of condensate |
| D. | Increasing temperature drop |
| Answer» A. Increasing temperature of the vapour | |
| 149. |
In Fourier's law, the proportionality constant is called the |
| A. | Heat transfer co-efficient |
| B. | Thermal diffusivity |
| C. | Thermal conductivity |
| D. | Stefan-Boltzmann constant |
| Answer» C. Thermal conductivity | |
| 150. |
The non-dimensional temperature gradient in a liquid at the wall of a pipe is the |
| A. | Heat flux |
| B. | Nusselt number |
| C. | Prandtl number |
| D. | Schmidt number |
| Answer» A. Heat flux | |
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