Category 2: Fluid Mechanics, Pumps, Valves, and Nozzles

The nozzle of a fire hose contracts from 2.5” to 0.5”. Water moves at 10 ft/sec. Find exit velocity

V2 = V1(A1/A2) = 10(2.5²/0.5²) = 250 ft/sec.

Water flows through funnel 4” to 0.5” exit at 6 ft/sec. Flow into funnel?

V1 = V2(A2/A1) = 6(0.5²/4²) ≈ 0.094 ft/sec.

Describe advantages/disadvantages of 2 types of valves

Gate valve: Advantage: low pressure drop, full flow; Disadvantage: slow operation. Globe valve: Advantage: precise flow control; Disadvantage: higher pressure drop.

How are check valves and globe valves used differently?

Check valves allow flow in one direction only. Globe valves control flow rate or pressure.

Why/When should a valve be remote operated?

When valve location is inaccessible or hazardous; remote operation ensures safety and control.

What does a relief valve do?

Protects a system from overpressure by opening at a set pressure to release excess fluid.

What does a heat exchanger do?

Transfers heat between two fluids without mixing them.

Heat exchangers classified by fluid flow direction. Draw simple diagram

Parallel flow: both fluids move same direction. Counterflow: fluids move opposite directions. Crossflow: fluids move perpendicular.

How is a positive displacement pump different from a centrifugal pump?

Positive displacement pumps deliver fixed volume per cycle, independent of pressure. Centrifugal pumps impart velocity to fluid, flow depends on pressure.

Advantages/disadvantages of positive displacement pump

Advantage: constant flow, high pressure. Disadvantage: pulsating flow, more maintenance.

Pump requires 3 W slow, 4x speed. Power and pressure change?

Power scales with cube of speed: 3*(4³)=192 W. Pressure scales with square of speed: 16x slow speed.

What is Net Positive Suction Head? Why important?

NPSH is available pressure at pump suction above vapor pressure. Prevents cavitation.

What is cavitation and why is it bad? When would we want to cavitate?

Cavitation: vapor bubble formation in low

How does pressure and velocity change through a nozzle?

Pressure decreases, velocity increases through a converging nozzle.

Pendulum bob 10 kg, 5 m cable, released from rest parallel to ground. Speed at bottom?

v = √(2gh) = √(29.815) ≈ 9.9 m/s.

Pendulum bob 10 kg, pushed from bottom at 10 m/s. Maximum height?

h = v²/(2g) = 100/(29.81) ≈ 5.1 m.

Pump slow speed 1.5 kW, fast speed 12 kW. How much greater?

12/1.5 = 8 times greater.