## Thermodynamics Questions and Answers Part-1

1. One kg of diatomic Oxygen is present in a 500 L tank. Find the specific volume on both mass and mole basis.
a) 0.6 m3/kg , 0.260 m3/mole
b) 0.5 m3/kg , 0.0160 m3/mole
c) 0.56 m3/kg , 0.0215 m3/mole
d) 0.7 m3/kg , 0.0325 m3/mole

Explanation: The specific volume on mass basis = 0.5/1 = 0.5 m3/kg
specific volume on mole basis= 0.5/(1/0.032) = 0.0160 m3/mole.

2. A piston/cylinder with a cross-sectional area of 0.01 m^2 is resting on the stops. With an outside pressure of 100 kPa, what should be the water pressure to lift the piston?
a) 178kPa
b) 188kPa
c) 198kPa
d) 208kPa

Explanation: Pw = Po + mg/A = 100000 + (100*9.8/0.01) = 198kPa.

3. A large exhaust fan in a lab room keeps the pressure inside at 10 cm water relative vacuum to the hallway? What is the net force acting on the door measuring 1.9 m by 1.1 m?
a) 2020 N
b) 2030 N
c) 2040 N
d) 2050 N

Explanation: Net force acting on the door = Gauge pressure*area
= 0.1cm water*1.9*1.1 = 2050 N.

4. A 5 m long vertical tube having cross sectional area 200 cm^2 is placed in a water. It is filled with 15°C water, with the bottom closed and the top open to 100 kPa atmosphere. How much water is present in tube?
a) 99.9 kg
b) 109.9 kg
c) 89.9 kg
d) 79.9 kg

Explanation: m = ρ V = V/v = AH/v
= 200 × 10^(−4) × 5/0.001001 = 99.9 kg.

5. A 5 m long vertical tube having cross sectional area 200 cm2 is placed in a water. It is filled with 15°C water, with the bottom closed and the top open to 100 kPa atmosphere. What is the pressure at the bottom of tube?
a) 119 kPa
b) 129 kPa
c) 139 kPa
d) 149 kPa

Explanation: ∆P = ρ gH = gH/v = 9.80665 × 5/0.001001
= 48.98 kPa
P(total) = P(top) + ∆P = 149 kPa.

6. Find the pressure of water at 200°C and having specific volume of 1.5 m3/kg.
a) 0.9578 m3/kg
b) 0.8578 m3/kg
c) 0.7578 m3/kg
d) 0.6578 m3/kg

Explanation: The state is superheated vapour between 100 and 150 kPa.
v = 1.3136 + (0.8689 – 1.3136)(140 − 100)/(150 – 100)
= 1.3136 + ( − 0.4447) × 0.8 = 0.9578 m3/kg.

7. A 5m^3 container is filled with 840 kg of granite (density is 2400 kg/m^3) and the rest of the volume is air (density is 1.15 kg/m^3). Find the mass of air present in the container.
a) 9.3475 kg
b) 8.3475 kg
c) 6.3475 kg
d) 5.3475 kg

Explanation: Mass of the air (mair) = ρairVair = ρair (Vtotal – Vgranite)
= ρair (Vtotal – (m/ρ)granite) = 1.15*(5 – 840/2400) = 5.3475 kg.

8. A 100 m tall building receives superheated steam at 200 kPa at ground and leaves saturated vapour from the top at 125 kPa by losing 110 kJ/kg of heat. What should be the minimum inlet temperature at the ground of the building so that no steam will condense inside the pipe at steady state?
a) 363.54°C
b) 263.54°C
c) 163.54°C
d) none of the mentioned

Explanation: FLOT for steam flow results: q + h(ground) = h(top) + gZtop.
h(top) = hg@125 kPa = 2685.35 kJ/kg
H(ground) = 2685.35 + (9.80665*100)/1000 – (–110) = 2796.33 kJ/kg
Minimum temperature at the ground of the building T(ground)
= 163.54°C.

9. The pressure gauge on an air tank shows 60 kPa when the diver is 8 m down in the ocean. At what depth will the gauge pressure be zero?
a) 34.118 m
b) 24.118 m
c) 14.118 m
d) none of the mentioned