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Chemical Heat Transfer MCQs

Free 509+ Chemical Heat Transfer MCQs for PPSC, FPSC, NTS, and Pakistan government job tests. Practise below with answers and explanations.

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509 questions in this list. Select an option to practice, or open a question for the full page with explanation.

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Chemical Heat Transfer

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Correct options are highlighted when revealed.

1.Identify the incorrect statement from the following:

Superheated steam is generally avoided for process heating due to its low heat transfer film coefficient.In shell and tube heat exchangers, orifice baffles cause the highest pressure drop on the shell side.The SI unit of fouling factor is expressed as watts per square meter kelvin (W/m²·K).Longitudinal fins are implemented in extended surface heat exchangers when fluid flows parallel to the tube's axis.

2.Identify the incorrect statement from the following:

For heat transfer occurring solely by forced convection, the ratio GR/Re² is greater than 1.The hydraulic diameter for a duct with a square cross-section, where each side measures 'x', equals 4 times x.Distillation and evaporation are two distinct processes.The efficiency of nucleate boiling mainly relies on how easily bubbles form and separate from the heated surface.

3.Identify the incorrect statement from the following options:

Boiling point elevation decreases the efficiency of an evaporator.Typically, corrosive fluids flow inside the tubes of a shell and tube heat exchanger.Steam jet ejectors serve as vapor compressors in thermal recompression evaporators.High-pressure evaporators are suitable for concentrating heat-sensitive substances.

4.Why is a backward feed multiple effect evaporator preferred over a forward feed type when concentrating a cold feed?

Improved thermal efficiencyReduced processing capacityBoth improved efficiency and reduced capacityDecreased thermal efficiency

5.Which feeding method is most suitable for evaporating a viscous solution in a multiple-effect evaporator?

Feeding from the first effect to the last (forward)Introducing feed starting at the last effect and moving backwardSupplying feed simultaneously to all effects (parallel)No specific method is preferredNone of the above

6.A well-mixed vessel contains 1000 kg of liquid initially at 30°C, which must be heated to 120°C. The heating is done using immersed coils with a surface area of 1.2 m², through which steam condenses at 150°C. Given the overall heat transfer coefficient to the liquid is 1500 W/m²·°C, and the liquid's specific heat capacity is 4 kJ/kg·°C, calculate the time required for the liquid to reach the target temperature. Assume heat losses to the environment are negligible.

15 minutes22 minutes44 minutes51 minutes60 minutes

7.Which of the following statements about heat waves is true?

They are unable to travel through a vacuumThey move along a straight pathThey can be reflected by a mirrorBoth options B and C are correct

8.How does the presence of air (a non-condensable gas) in a vapor stream undergoing condensation impact the vapor's condensation rate?

Enhance the condensation speedReduce the rate of condensationHave no influence on condensationRaise both the condensation rate and film coefficientNone of the above

9.What is true for an ideal transparent material, such as a gas?

It does not absorb any radiationIt allows all radiation to pass throughIt does not reflect any radiationAll of the above statements are correct

10.In a double pipe heat exchanger, fluid flows through the inner tube with diameter 'd'. Under turbulent flow and a constant mass flow rate, the tube-side heat transfer coefficient varies proportionally to which of the following expressions involving 'd'?

d raised to the power of 0.8d raised to the power of -0.2d raised to the power of -1d raised to the power of -1.8None of the above

11.The heat transfer coefficient (h) for a fluid flowing inside a clean pipe is expressed as h = 0.023 (K/D) (DVρ/μ)^0.8 (CP·μ/k)^0.4. For which Reynolds number (NRe) range is this correlation applicable?

At NRe equal to 4000For NRe greater than 10,000For NRe between 2000 and 4000At NRe less than 2300For NRe below 1000

12.What is the name of the dimensionless number defined as the ratio of kinematic viscosity to thermal diffusivity?

Peclet numberPrandtl numberStanton numberNusselt number

13.What causes vibrations in the tubes of a shell and tube heat exchanger?

The movement of fluid within both the tube and shell sectionsFluctuations in the fluid flow inside the shell or tube sidesExternal vibrations transmitted via piping or support structuresA combination of all the above factors

14.In a single-effect evaporator system, what is the typical value of the steam economy?

1Greater than 1Less than 10.1Not applicable

15.Using the Dittus-Boelter equation for turbulent flow inside a pipe, if the pipe diameter is reduced to half its original size while the flow rate is increased twofold, by what factor does the heat transfer coefficient change?

Remains the sameIncreases by a factor of 1.74Increases by a factor of 6.1Increases by a factor of 37Decreases by half