Chemical Engineering questions for GATE and PSU exams are built on a handful of core subjects applied in many ways. Practice spans fluid mechanics, heat transfer, mass transfer, chemical reaction engineering, thermodynamics, process control and instrumentation, and plant design economics. Numerical solutions carry the assumptions written out, because the assumption is usually what separates a correct answer from a plausible one.
For laminar flow of a viscous fluid between two parallel plates, the velocity profile is:
Answer: B
For laminar flow between parallel plates (Poiseuille flow), the velocity profile is parabolic due to the balance between pressure gradient and viscous forces.
Q.23Medium
A centrifugal pump delivers 30 m³/h of water. The inlet pressure is -0.2 bar (gauge) and outlet pressure is 8 bar (gauge). If the outlet is 2m higher than inlet, calculate the total head in meters. (Consider g = 9.81 m/s², ρ = 1000 kg/m³)
Answer: B
Total head H = (P_out - P_in)/(ρg) + (v_out² - v_in²)/(2g) + z_out - z_in = (800000 + 20000)/(1000×9.81) + 2 = 82.26 + 2 = 84.26 m ≈ 84.2 m
Q.24Easy
Which dimensionless number is used to characterize the ratio of inertial forces to viscous forces in fluid flow?
Answer: B
Reynolds number (Re = ρVD/μ) represents the ratio of inertial to viscous forces and determines the flow regime (laminar, transitional, or turbulent).
Q.25Medium
For a sharp-edged orifice, the coefficient of contraction (Cc) typically ranges between:
Answer: B
The coefficient of contraction for sharp-edged orifices is typically 0.60-0.65 due to the vena contracta effect where the jet contracts after leaving the orifice.
Q.26Medium
In the Hagen-Poiseuille equation for laminar flow through a circular pipe, the volumetric flow rate is proportional to:
Answer: D
Hagen-Poiseuille equation: Q = (πΔPd⁴)/(128μL), showing Q ∝ d⁴. This is why small diameter pipes are very sensitive to pressure drops.
Q.27Medium
A ball of diameter 5 cm falls through glycerin at terminal velocity. If the Stokes drag coefficient Cd is used, this indicates:
Answer: B
Stokes law (Cd = 24/Re) applies for creeping flow where Re < 1. For low Reynolds numbers, viscous forces dominate over inertial forces.
Q.28Easy
Which of the following pump types operates on the principle of positive displacement with rotating screws?
Answer: C
Screw pumps (Archimedean screw or progressive cavity pumps) use rotating screws for positive displacement. They are used for high viscosity fluids.
Q.29Medium
The Darcy-Weisbach equation relates friction loss to flow parameters. The friction factor f for turbulent flow in smooth pipes is given by:
Answer: D
For turbulent flow in smooth pipes, the Blasius equation is explicit and simpler, while Colebrook-White is implicit but more accurate. Both are used depending on applications.
Q.30Easy
In a U-tube manometer measuring differential pressure, if one side contains mercury (ρ = 13600 kg/m³) with a height difference of 250 mm, what is the differential pressure?
Answer: B
ΔP = ρ_mercury × g × h = 13600 × 9.81 × 0.25 = 33,324 Pa ≈ 33.3 kPa
Q.31Hard
For compressible flow through a converging-diverging nozzle (de Laval nozzle), the throat conditions occur where:
Answer: B
In a converging-diverging nozzle for supersonic flow, sonic conditions (M=1) occur at the throat. Beyond the throat, the flow accelerates to supersonic speeds.
Q.32Hard
A pipeline carries water at 20°C. When the flow velocity increases from 1 m/s to 3 m/s in a straight horizontal pipe of constant diameter, the friction factor:
Answer: C
For a given pipe with constant diameter and same fluid (constant Re behavior), the friction factor depends on Re and relative roughness. For geometrically similar conditions, f remains relatively constant in turbulent flow.
Q.33Hard
Which of the following best describes the boundary layer separation phenomenon?
Answer: B
Boundary layer separation occurs when an adverse (positive) pressure gradient opposes the flow, causing the flow to reverse near the wall and separate from the surface.
Q.34Medium
For flow over a flat plate, the drag force depends on velocity according to:
Answer: B
Drag force F_d = 0.5 × ρ × V² × A × Cd. The V² dependence comes from dynamic pressure (½ρV²). This applies to both skin friction and pressure drag.
Q.35Medium
In a siphon arrangement, what is the maximum theoretical height from which water can be siphoned up using atmospheric pressure?
Answer: C
The maximum height is approximately 10.3 m (or one atmosphere height), determined by h = P_atm/(ρg) = 101325/(1000 × 9.81) = 10.33 m. Friction losses reduce this in practice.
Q.36Medium
For a venturimeter operating with water flow, the pressure at the throat is found to be lower than upstream. This pressure drop is used to:
Answer: A
Venturimeter uses Bernoulli's equation principle. The pressure difference between throat and upstream is related to flow velocity and can be used to calculate the volumetric flow rate.
Q.37Easy
The relative roughness of a pipe is defined as:
Answer: B
Relative roughness ε/D = (absolute roughness)/(pipe diameter). This dimensionless parameter determines flow behavior in the Moody chart for turbulent flow calculations.
Q.38Medium
In a pitot tube application, the stagnation point pressure exceeds static pressure by an amount equal to:
Answer: B
From Bernoulli's equation: P_stagnation - P_static = ½ρV². This dynamic pressure difference is measured by pitot tubes to determine local flow velocity.
Q.39Medium
For a long horizontal pipeline with incompressible fluid, the pressure loss due to friction increases when:
Answer: C
From Darcy-Weisbach: h_f = f(L/D)(V²/2g). Friction loss is proportional to length and approximately proportional to V² (in turbulent flow, f decreases slightly with V).
Q.40Easy
A centrifugal pump operates with water (ρ = 1000 kg/m³) at an impeller diameter of 0.3 m and rotational speed of 1500 RPM. Calculate the peripheral velocity at the impeller tip.
Answer: A
Peripheral velocity = π × D × N / 60 = π × 0.3 × 601500 = 23.56 m/s
