Chemical Engineering interview Questions with answer
1. Tell me about yourself and why you are interested in chemical engineering.
I've always been curious about how things work, especially in the world of chemicals and
processes. Chemical engineering allows me to apply scientific principles to solve real-world
problems, and that's what excites me.
2. Questions related to your projects and internships?
During my internship, I worked on [project], where I [brief description]. This experience
enhanced my practical understanding of [specific skills relevant to the job].
3. Define: Unit operation, Unit process?
Physical changes occur in the chemical industry is known as a Unit Operation. Example:
Distillation, Filtration, Drying, Extraction, Gas absorption, Crystallization, etc.
Chemical changes with or without physical change occur in chemical industry are known as a
Unit Process, Example: - Oxidation, Reduction, Alkylation, Sulfonation, Chlorination, etc.
4. Explain azeotropic distillation? Give an example.
Azeotropic distillation is a process to separate liquids with similar boiling points. For example,
in ethanol-water mixtures, an azeotrope is formed, making traditional distillation challenging.
5. Explain batch and continuous distillation? In what kind of industries are they used?
Batch distillation is like making small batches of cookies, one at a time. Continuous distillation
is like a continuous production line. Batch is used in small-scale production, while continuous
is common in large-scale industries like petrochemicals.
6. Types of pumps?
There are two main types: centrifugal pumps (for liquids) and positive displacement pumps
(for precise volumes and high pressure).
7. Types of valves?
•
Ball valve: Simple, quick on/off, good for high pressure and isolation.
•
Butterfly valve: Similar to ball valve, but lighter and cheaper, good for large-diameter
pipes.
•
Diaphragm valve: Leak-proof, good for corrosive or sterile fluids.
•
Globe valve: Fine flow control, good for throttling.
Prepared by: Primal Hirpara
•
Needle valve: Very precise flow control, good for small flows.
•
Check valve: Prevents backflow, good for safety.
•
Pressure relief valve: Automatically releases pressure to avoid explosions
8. How do you calculate pressure drop in pipes?
Pressure drop is calculated using the Darcy-Weisbach equation, considering factors like pipe
length, diameter, fluid properties, and flow rate.
9. Why are centrifugal pumps called centrifugal pumps?
They're named after the centrifugal force generated when a rotating impeller inside the pump
chamber pushes fluid outward, creating a flow.
11. Difference between filter and strainer & when do we use them in pumps?
Filters are finer and remove smaller particles. Strainers are coarse and catch larger debris. We
use them in pumps to prevent damage by filtering out impurities from the fluid.
12. Difference between pressure drop and pressure difference?
Pressure drop is the decrease in pressure along a flow path, while pressure difference is the
contrast between pressures at two points.
13. What is the main difference between Heat Exchange & Condenser?
Heat exchangers transfer heat between two fluids without a phase change, while condensers
convert a gas into a liquid by removing heat.
14. Most used heat exchanger? Most efficient heat exchanger? Why?
Shell and tube heat exchangers are commonly used. The efficiency depends on the specific
application, but compact plate heat exchangers are often considered highly efficient due to
increased surface area.
15. What is the difference between Absorption & Adsorption?
Absorption involves one substance being taken into another (like a sponge absorbing water).
Adsorption is the adhesion of molecules to a surface (like a sticky note sticking to a wall).
16. Compare different types of reactors (Batch, PFR, CSTR) for different applications?
Explain? Give features.
Batch reactors are like cooking in a pot, suitable for small-scale production. PFR (plug flow)
and CSTR (continuous stirred tank) are used in large-scale processes. PFR provides uniform
conditions, while CSTR allows for better control of reactions.
Prepared by: Primal Hirpara
17. What is Relative Humidity & also explain the effect of temperature on Humidity?
Relative humidity is the amount of moisture in the air compared to the maximum it can hold
at a specific temperature. Warmer air can hold more moisture, so relative humidity decreases
as temperature rises.
18. What is the difference between Evaporation & Vaporization?
Evaporation is the change of state from liquid to gas at the surface, like water drying on a
towel. Vaporization is the general process of turning a substance into vapor, which includes
boiling and evaporation.
19. Dimensionless Numbers and their importance and application (Reynolds, Nusselt,
Grashof, Sherwood, Mach Number, etc.)
Dimensionless numbers like Reynolds (flow characteristics), Nusselt (heat transfer), Grashof
(natural convection), Sherwood (mass transfer), and Mach (compressible flow) help simplify
and analyse complex engineering problems.
20. Modes of heat transfer?
Heat transfers through conduction (direct contact), convection (fluid movement), and
radiation (energy waves). A hot cup of coffee losing heat to the surroundings is an example.
21. Fire Triangle?
The fire triangle represents the three elements necessary for a fire: heat, fuel, and oxygen.
Removing any of these elements extinguishes the fire.
22. Fixed Bed reactor?
A fixed bed reactor holds a stationary bed of catalyst or solid material through which fluid
passes for chemical reactions. It's commonly used in petrochemical and refining industries.
24. Packing vs Trays in columns?
In distillation columns, trays provide a horizontal surface for vapor-liquid contact, while
packing offers a structured surface. Trays are efficient for large-scale operations, while packing
is more effective for smaller-scale and specialty applications.
25. Fugacity?
Fugacity is a measure of the tendency of a substance to escape from a system. It's like a
corrected pressure in non-ideal conditions.
26. Catalyst? Function? Examples?
A catalyst speeds up a chemical reaction without being consumed. Examples include platinum
in catalytic converters and enzymes in biological processes.
Prepared by: Primal Hirpara
27. Laws of thermodynamics?
The laws are:
• Energy is conserved.
• Entropy tends to increase over time.
• Absolute zero is unreachable; as you approach it, entropy approaches a minimum
value.
28. Effect of pressure on reaction rate?
Increasing pressure often increases reaction rate, especially for gases, by bringing particles
closer together and enhancing collisions.
29. Bernoulli’s equation (statement) and its applications. Applicable to liquids/gases/both?
Bernoulli's equation states that the sum of pressure, kinetic energy, and potential energy per
unit volume is constant in a fluid flow. It's applicable to both liquids and gases. Applications
include airflow in pipes and airplane wings.
30. Adsorption? Examples in the chemical industry?
Adsorption is the binding of molecules to a surface. In the chemical industry, activated carbon
adsorbs impurities from liquids, and catalysts often involve adsorption.
31. Draw and explain pump curves? Efficiency curve, head curve, pump curve, characteristic
curve? Various points (shut-off, run out, etc.)
Pump curves show how a pump performs. The head curve shows pressure, efficiency indicates
effectiveness, and pump curves display flow rate. Key points include shut-off (no flow), runout (maximum flow), and best efficiency point (BEP).
32. Draw and explain thermodynamic cycle?
A thermodynamic cycle is a series of processes that return a system to its initial state. The
Carnot cycle is a classic example, involving isothermal and adiabatic processes.
34. What is corrosion? Why and how does it take place? Its types? How to protect? Cathodic
protection?
Corrosion is the gradual degradation of materials due to chemical reactions with the
environment. It happens because metals naturally want to return to their original state. Types
include uniform, pitting, and crevice corrosion. Protection methods include coatings,
inhibitors, and cathodic protection.
Prepared by: Primal Hirpara
35. NPSH available & required?
NPSH (Net Positive Suction Head) available is the amount of energy in the fluid at the pump
inlet, and NPSH required is the minimum energy needed to prevent cavitation. Ensuring
NPSH available exceeds NPSH required prevents pump damage.
36. Cavitation?
Cavitation occurs when low pressure causes bubbles in a liquid to form and then collapse
violently, leading to damage in pumps and other equipment.
37. NPSH? Formula? How to change it? What to do if NPSH needs to be increased without
changing pump and fluid tank levels?
NPSH = NPSH available - NPSH required. Increasing pipe diameter or reducing fluid velocity
can improve NPSH. If levels can't change, consider a different pump design or operating
conditions.
38. Which valve is used to control flow in a centrifugal pump?
A control valve, often a globe or butterfly valve, is used to regulate the flow in a centrifugal
pump system.
39. What factors to consider in designing a pipe from point A to B?
Considerations include fluid properties, flow rate, pressure drop, temperature, material
compatibility, and safety standards.
40. If pressure drop exceeds the design pressure drop in a pipe, what to do then?
Options include increasing pipe diameter, using a smoother material, or revising the layout.
Consultation with a piping engineer may be necessary.
41. What is choked flow? How to recover from choked flow?
Choked flow occurs when fluid velocity reaches the speed of sound, limiting further flow.
Recovery involves increasing downstream pressure or reducing flow rate.
42. What are PSV and PRV?
PSV (Pressure Safety Valve) releases excess pressure to prevent equipment damage. PRV
(Pressure Relief Valve) serves a similar purpose but may have adjustable settings.
43. Nominal pipe size?
Nominal pipe size is a standard designation for pipes, indicating their approximate inside
diameter. It helps in selecting compatible fittings.
Prepared by: Primal Hirpara
44. What is mesh number?
Mesh number refers to the number of openings per linear inch in a screen. It's used in sizing
filters or strainers.
45. Dimensionless Numbers, their relations, and practical significance.
Dimensionless numbers like Reynolds, Nusselt, and Grashof help predict fluid behavior.
Understanding them aids in designing efficient and safe systems.
46. Controllers? P, PI, PID, Feed Forward, Feedback, primary, secondary, Cascade? Their
applications?
Controllers regulate processes. P (Proportional) responds to current error, I (Integral) corrects
past errors, D (Derivative) anticipates future errors. Feedforward predicts disturbances,
feedback responds to actual conditions. Primary controllers manage basic functions,
secondary controllers fine-tune, and cascade controllers improve precision.
47. Humidity & Wet Bulb Temperature
Humidity is the amount of moisture in the air. Wet bulb temperature is the lowest temperature
achievable by evaporating water into the air. Together, they indicate the cooling potential of
air.
48. What is meant by 200 mesh screens?
A 200 mesh screen has 200 openings per linear inch. It's a measure of the screen's fineness,
commonly used in filtering processes.
49. Equation of continuity for compressible and incompressible fluids
The equation of continuity states that the mass flow rate of a fluid is constant. For
incompressible fluids, it's A1V1=A2V2, and for compressible fluids, it involves density changes.
50. Equation of continuity? Statement? Formulas? Applications?
The equation of continuity states that the mass flow rate of a fluid is constant. It's expressed
as A1V1 =A2V2, where A is the cross-sectional area and V is the velocity.
51. Newtonian/non-Newtonian fluids? Newton's law of viscosity
Newtonian fluids maintain a constant viscosity regardless of stress, while non-Newtonian
fluids change viscosity under stress. Newton's law of viscosity states that shear stress is
proportional to shear rate.
Prepared by: Primal Hirpara
52. Friction factor? What is its function of Reynolds No. and relative pipe roughness?
Importance and application?
The friction factor is a measure of the resistance to flow in pipes. It's influenced by Reynolds
number and relative pipe roughness. Understanding it is crucial for designing pipelines and
predicting pressure drop.
53. Viscosity, its units? Types? Measurement methods? Factors affecting?
Viscosity measures a fluid's resistance to flow. It's measured in units of poise or centipoise.
Types include dynamic (shear) and kinematic (flow). It can be measured using viscometers.
Temperature and pressure affect viscosity.
54. Cooling Towers? Del T? Approach? Range? WBT? DBT? Effect of humidity? What happens
in rain? How to increase efficiency and effectiveness? Types of heat transfer in CT. Effect
of velocity, flowrate, temp, pressure, humidity?
•
Cooling towers remove heat from industrial processes. Del T is the temperature
difference between the cooling water inlet and outlet
•
Approach is the difference between the cold-water temperature and the wet bulb
temperature. Range is the temperature difference between hot and cold water
•
WBT (Wet Bulb Temperature) and DBT (Dry Bulb Temperature) relate to air conditions.
•
Rain increases cooling efficiency
•
Increasing air and water flow, lowering temperature, and reducing humidity enhance
efficiency
•
Heat transfer occurs through evaporation, conduction, and radiation. Velocity, flow
rate, temperature, pressure, and humidity impact cooling tower performance
Prepared by: Primal Hirpara