Chapter 5

Air is flowing in a pipe with 0.2 m in diameter at an average velocity of 0.1 m/s. The density of air is 1.754 kg/m3. What is the mass flow rate?

0.0055 kg/s

During a one-second period, air is added into a rigid tank. The volume of the tank is 3 m3 and the initial density of air is 1.2 kg/m3; at the end of the charging process, the density of air reaches 6.3 kg/m3. What is the mass flow rate of air that is entering the tank?

15.3 kg/s

Water flows through a pipe with a cross-sectional area of 0.002 m2 at a mass flow rate of 4 kg/s. The density of water is 1 000 kg/m3. Determine its average velocity.

2 m/s

A nozzle is considered to be a steady flow device where a single stream flows in and out. Steam with a density of 1.91 kg/m³ with an average velocity of 122 m/s flows into a nozzle. Its inlet area of the nozzle is 104 × 10−4 m2104 × 10-4 m2. Determine its mass flow rate at the nozzle outlet.

2.42 kg/s

In the energy balance equation for heat exchangers, which of the following are often neglected? (Select all that apply.) Multiple select question. w Δpe Δke Heat transfer with entire exchanger as the control volume Δh Reason: Heat is exchanged between the two moving fluids in the exchanger, and this will cause a change in the fluids' enthalpies.

A B C D

Which of the following statements are true about nozzles and diffusers? Multiple select question. Nozzles and diffusers typically involve no heat transfer. Nozzles and diffusers typically involve very small velocity changes so Δke can be neglected. Any change in potential energy in nozzles and diffusers can be neglected. The rate of heat transfer in nozzles and diffusers cannot be ignored. Nozzles and diffusers typically involve no work.

A C E

Which of the following statements are true regarding throttling valves? The flow through a throttle valve may be assumed to be adiabatic. The pressure drops across a throttle valve is often accompanied by a large increase in temperature. Throttle valves are flow-restricting devices that cause a pressure drop in a fluid. For a single-stream, steady flow throttle valve, the inlet and outlet enthalpies can be approximated to be the same. Since pressure drops across a throttle valve, work cannot be neglected.

A, C, and D

Identify the true statements about the steady-flow process. A.) The steady-flow process is a process during which a fluid flows through a control volume and does not change with time. B.) The steady flow implies that the fluid properties can change from point to point, but at any point, they remain constant during the entire process. C.) During a steady flow process, boundary work is zero. D.) During a steady flow process, only mass in the control volume remains constant. E.) During a steady flow process, the boundary of the control volume is allowed to move.

A,B,E

Which of the following statements are true about unsteady flow processes? Multiple select question. Unsteady flow systems must be fixed in space and size. Unsteady flow systems may involve boundary work. Unsteady-flow or transient flow involves changes within the control volume with time, such as charging or discharging problems. For an unsteady flow analysis, it is assumed that the state of the mass within the control volume may not change with time Unlike steady flow processes, unsteady flow processes start and end over some finite time period instead of continuing indefinitely.

B C D

Which of the following statements are true of the conservation of mass? A.) The conservation of mass principle holds only for incompressible fluids. B.) In a steady flow process, the total rate of mass entering a control volume is equal to the total rate of mass leaving it. C.) The rate of change of mass within a control volume minus the net flow rate in and plus the net flow rate out of the control surface must equal to zero. D.) The conservation of mass principle is true only if the control volume has a fixed volume. E.) The conservation of mass principle is only applicable to closed systems.

B and C

For a well-insulated mixing chamber, which terms in the energy balance equation can be left out? Multiple select question. Δh Reason: For a mixing chamber, the energy balance equation consists of enthalpies and mass flow rates. w Δpe q Δke

B, C, D, and E

Which of the following statements are true about nozzles and diffusers? A.) The rate of heat transfer in nozzles and diffusers cannot be ignored. B.) Any change in potential energy in nozzles and diffusers can be neglected. C.) Nozzles and diffusers typically involve no work. D.) Nozzles and diffusers typically involve very small velocity changes so Δke can be neglected. E.) Nozzles and diffusers typically involve no heat transfer.

B, C, and E

Which of the following energies are part of the total energy of a flowing fluid? Multiple select question. Enthalpy Heat Kinetic energy Shaft work Potential energy

Enthalpy, Kinetic Energy, Potential Energy

Which of the following devices requires work input? Nozzle Fan Compressor Pump Turbine

Fan pump compressor

True or false: Flow work can be expressed in terms of other properties. True False

True

True or false: In a single-stream, steady flow system, the mass flow rates for the inlet and outlet must be the same. True False

True

True or false: Since liquid can be considered as incompressible, the volume flow rates into and out of a steady flow device will remain constant.

True

True or false: The total energy for a flowing fluid consists of an additional term when compared with the total energy for a nonflowing fluid.

True

In a steady flow process, energy can be transferred by ______. mass and heat only mass only work only work and heat only work, mass, and heat

Work, Mass, and Heat

During a throttling process, if the flow energy increases due to significant increase of the specific volume, the temperature of a fluid will ______.

decrease

In a single-stream, steady flow system, the mass flow rate can be defined as the product of ______ , ______ , and ______.

density, area, and velocity

In an open system, when mass flows across control volume boundaries, some work is required to push the mass into or out of the control volume, and this is known as ______ work.

flow

For turbines, which of the following are usually neglected in the energy balance equation? Multiple select question. Enthalpy Heat transfer Work Potential energy

heat transfer and pe

During a steady-flow process, the fluid properties at an inlet or exit must ______. decrease increase remain constant

remain constant

In a steady flow process, the change of total energy of the control volume must ______. remain zero increase decrease

remain zero