Water70 kPa

15C

700 kPa

V1 = 1 m31 =1.18 kg/m3

102MAE - Lecture 5 Questions

Question 1

A pump increases the water pressure from 70 kPa at the inlet to 700kPa at the outlet. Water enters this pump at 15ºC through a 1-cm-diameter opening and exits through a 1.5-cm-diameter opening. Determine the velocity of the water at the outlet when the mass flow rate through the pump is 0.5 kg/s. Will these velocities change significantly if the temperature is raised to 40ºC?

T=15 °C ¿ }¿¿ v1=0. 001001 m3 /kg ¿

T=40 °C ¿ }¿¿ v1=0 .001008 m3 /kg ¿

Question 2

A 1-m3 rigid tank initially contains air whose density is 1.18 kg/m3. The tank is connected to a high-pressure supply line through a valve. The valve is opened, and air is allowed to enter the tank until the density in the tank rises to 7.20 kg/m3. Determine the mass of air that has entered the tank.

Properties The density of air is given to be 1.18 kg/m3 at the beginning, and 7.20 kg/m3 at the end.

Question 3

Air enters the 1-m2 inlet of an aircraft engine at 100kPa and 20ºC with a velocity of 180m/s. Determine the volume flow rate, in m3/s, at the engine’s inlet and the mass flow rate, in kg/s, at the engine’s exit.

Properties The gas constant of air is R = 0.287 kPam3/kgK

Answer Q1V1 = 6.37 m/s V2 = 2.83 m/sV1 at 40C=6.42 m/s (0.8% increase)

Answer Q2mi =6.02 kg

Answer Q3V1 = 180 m/s m = 214.1 kg/s

R-134a200 kPa

20C5 m/s

Q

180 kPa40C

300 kPa77C

Air 25 m/s18 kg/min

102MAE - Lecture 5 Questions

Question 4

Refrigerant-134a enters a 28-cm diameter pipe steadily at 200 kPa and 20ºC with a velocity of 5 m/s. The refrigerant gains heat as it flows and leaves the pipe at 180 kPa and 40ºC. Determine (a) the volume flow rate of the refrigerant at the inlet, (b) the mass flow rate of the refrigerant, and (c) the velocity and volume flow rate at the exit.

Properties The specific volumes of R-134a at the inlet and exit are found from tables and are -

P1=200 kPa ¿ }¿¿ v1=0.1142 m3 /kg¿ P1=180 kPa ¿ }¿¿ v2=0.1374 m3 /kg¿

Question 5

Air flows steadily in a pipe at 300 kPa, 77ºC, and 25 m/s at a rate of 18 kg/min. Determine (a) the diameter of the pipe, (b) the rate of flow energy, (c) the rate of energy transported by mass, and (d) the error involved in part (c) if the kinetic energy is neglected.

Properties The properties of air are R = 0.287 kJ/kg.K and cp = 1.008 kJ/kg.K

Answer Q4

V 1 = 0.3079 m3/s m = 2.696 kg/s

V 2 = 0.3705 m3/s V2 =6.02 m/s

Answer Q5 D = 0.0715 mW flow = 30.14 kWEmass = 105.84 kW Error = 0.09%