A horizontal - shaft centrifugal pump lifts water at 65°C.The

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A horizontal - shaft centrifugal pump lifts water at 65°C.The suction nozzle is one meter below pump centerline. The pressure at this point equals 200 kPa gauge and velocity is 3 m/s. Steam tables show saturation pressure at 65°C is 25 kPa, and specific volume of the saturated liquid is 0.001020 m³/kg. The pump Net Positive Suction Head (NPSH) in meters is

1. 24
2. 26
3. 28
4. 30

Correct Option: C

Given data:
Temperature of water,
T = 65°C Section head,
h_s = 1m
Gauga pressure at section inlet,
p_1.g = 200 kPa
∴ Absolute pressure,
P_1.abs = P_1.g + P_atm
= 200 + 101.325
= 301.325 kPa
= 301.325 × 10³ pa
Velocity at section nozzle inlet,
V₁ = 3 m/s
Saturated pressure at 65°C,
P_v.abs = 25 kPa, vapour pressure
= 25 × 10³ Pa
Specific volume,
V = 0.001020 m³/kg
Specific volume,
V = 0.001020 m³/kg

∴ Density: ρ =	1	= 980.39 kg/m³
	0.001020

Net Positive Section Head
Net positive section head,

NPSH =	P_S,abs	+	V²_s	-	P_v.abs
	ρg		2g		ρg

Applying Bernoulli’s equation at section nozzle inlet and section of the pump

P_1.abs	+	V²₁	+	P_s.abs	+	V²_s	+ h_s
ρg		2g		ρg		2g

P_1.abs	+	V²	+ 0 =	P_s.abs	+	V²_s	+ h_s
ρg		2g		ρg		2g

or	P_s.abs	+	V²_s	+	P_t.abs	+	V²₁	- h_s
	ρg		2g		ρg		2g

∴ NPSH =	P_s.abs	+	V²_s	- h_s	P_v.abs
	ρg		2g		ρg

=	301.325 × 10³	+	(3)²	- 1 -	25 × 10³
	980.39 × 9.81		2 × 9.81		980.39 × 9.81

= 31.33 + 0.45 – 0.45–1 – 2.56
= 28.22m = 28 m