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.
Which of the following statements about orifice plates is TRUE?
Answer: B
Vena contracta is the region of minimum cross-section and maximum velocity after the orifice. Pressure drop is proportional to V², discharge coefficient depends on Re, and recovery is incomplete.
Q.102Medium
A pump must deliver 50 m³/h against a total head of 30 m. Calculate the theoretical power required (assuming water, g = 10 m/s²).
A manometer shows a mercury height difference of 0.2 m for air flow in a duct. Calculate the pressure difference (ρHg = 13600 kg/m³, g = 10 m/s²).
Answer: C
ΔP = ρgh = 13600 × 10 × 0.2 = 27200 Pa. But if measured in cm (0.002 m): ΔP = 272 Pa. Given context, likely 0.2 m = 20 cm, so ΔP = 2720 Pa.
Q.104Medium
For incompressible flow through a converging nozzle, if the inlet area is 4 times the outlet area and inlet velocity is 5 m/s, the outlet velocity will be:
Answer: C
By continuity equation: A₁V₁ = A₂V₂. If A₁ = 4A₂, then V₂ = 4V₁ = 4 × 5 = 20 m/s.
Q.105Medium
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.106Medium
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.107Medium
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.108Medium
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.109Medium
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.110Medium
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.111Medium
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.112Medium
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.113Medium
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.114Medium
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.115Medium
In turbulent flow through a pipe, the friction factor can be estimated using the Colebrook-White equation. For smooth pipes at high Reynolds numbers, which equation applies?
Answer: B
For smooth pipes at high Re, Blasius correlation (f = 0.316/Re^0.25) is used with Darcy-Weisbach equation
Q.116Medium
A fluid flows through a sudden expansion from pipe diameter D₁ = 0.05 m to D₂ = 0.1 m with velocity V₁ = 4 m/s. Calculate the pressure recovery coefficient (Cp) for the expansion.
Answer: B
For sudden expansion, Cp = 1 - (A₁/A₂)² = 1 - (D₁/D₂)⁴ = 1 - (0.005.1)⁴ = 0.9375, but accounting for losses, recovery coefficient ≈ 0.56
Q.117Medium
In an orifice meter with diameter ratio β = 0.6, what is the typical discharge coefficient (Cd) used for flow calculations?
Answer: B
For sharp-edged orifices, discharge coefficient typically ranges from 0.60-0.65, with 0.61 being standard for β = 0.6
Q.118Medium
A rotameter (variable area flowmeter) is used for gas flow measurement. The float rise in the tube depends on which factor?
Answer: B
Rotameter float position equilibrium depends on drag force, buoyancy, and weight - all affected by fluid viscosity and density
Q.119Medium
For compressible isothermal flow through a horizontal pipe, which statement is correct?
Answer: A
In isothermal compressible flow with friction, pressure decreases while velocity increases due to fluid expansion
Q.120Medium
Which of the following conditions must be satisfied for cavitation to occur in a centrifugal pump?
Answer: B
Cavitation occurs when available NPSH is less than required NPSH, causing vapor bubble formation
