Thermodynamics quizzes for exam 2

Diffuser

A device that increases the pressure of a fluid by slowing it down

Nozzle

A device that increases the velocity of a fluid at the expense of pressure

Mixing chamber

A device where two fluids exchange heat when mixed

Heat exchanger

A device where two fluids exchange heat without mixing

From the list below, select all of the processes where boundary work occurs.

-A balloon is filled with helium -Air is compressed by a piston inside of a cylinder

Which of the following energies are part of the total energy of a flowing fluid?

-potential energy -kinetic energy -enthalpy NOT: -shaft work -heat

250 kJ

A 5 kg piece of metal (c = 0.5 kJ/kg-K) is heated from 50 to 150°C. Determine the change in internal energy.

0.5 kJ/kg⋅K

A liquid with a specific volume of 0.001 m3/kg is expanded isothermally from 1000 kPa to 500 kPa. Determine the change in enthalpy.

2.42 kg/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.

Imcompressible

A substance that has a constant specific volume or density is called an_________substance.

-2000kJ; Reason: The boundary work for a constant pressure process is the pressure times the change in volume. In this case, 1000 kPa × (3 - 5 m3) = -2000 kJ.

Air is compressed in a piston-cylinder device from 5 m3 to 3 m3 at a constant pressure of 1000 kPa. Determine the amount of boundary work for the process.

0.0055 kg/s

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 kJ; Reason: The boundary work is defined as ∫PdV. For a constant volume process, there is no boundary work.

Air is heated in a rigid tank from a pressure of 100 kPa to 500 kPa. Determine the boundary work for this process.

300 kj/kg

An ideal gas (Cv = 2 kJ/kgK, Cp = 3 kJ/kgK) is heated from 100 to 200°C. Determine the change in enthalpy.

1 kJ/kg-K, Reason: The following relationship can be used to determine the gas constant. R = cp - cv = 1 kJ/kg-K.

An ideal gas (cv = 2 kJ/kg-K, cp = 3 kJ/kg-K) is heated from 100°C to 200°C. Determine the gas constant for the gas.

1.5

An ideal gas (cv = 2 kJ/kg⋅K, cp = 3 kJ/kg⋅K) is heated from 100 to 200°C. Determine k, the ratio of specific heats.

7.5 k/kg, Reason: The change in enthalpy of an incompressible substance undergoing a constant pressure process is the specific heat multiplied by the change in temperature. A change of 10°C is equal to a change of 10 K, so it is 7.5 kJ/kg in this case.

An incompressible substance with a specific heat of 0.75 kJ/kg-K is heated by 10°C at a constant pressure. Determine the change in enthalpy.

pressure and temperature

Any equation that relates the , , and specific volume of a substance is called an equation of the state.

15.3 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?

Remain constant

During a steady-flow process, the fluid properties at an inlet or exit must

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

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

Potential energy Kinetic energy Additional information: An intercooler removes heat from the operating fluid to keep it cooled. Therefore, heat transfer cannot be neglected. A compressor requires work input for it to operate.

For a compressor with an intercooler, which of the following energy changes are usually neglected in the energy balance equation?

q, Δpe, w, Δke

For a well-insulated mixing chamber, which terms in the energy balance equation can be left out?

Double; Reason: If pressure is held constant, volume and temperature are directly proportional to each other according to the ideal gas equation of state.

For an ideal gas under a constant pressure, if the volume is doubled, the temperature of the gas will

Become halved; Reason: If temperature is held constant, volume and pressure are inversely proportional to each other according to the ideal gas law.

For an ideal gas under a constant temperature, if the pressure is doubled, the volume of the gas will

Potential energy and Heat transfer; Reason: Turbine produces work through a change in enthalpies so enthalpy cannot be neglected.

For turbines, which of the following are usually neglected in the energy balance equation?

-liquid water -solid steel NOT -helium gas -steam

From the following list, select all that can be approximated as incompressible substances.

Equal to 1; Reason: Based on the definition of compressibility factor, the compressibility factor for an ideal gas is equal to 1.

If a gas is an ideal gas, then the compressibility factor is ______.

Transient

If properties are allowed to change within the control volume, the processes are called ___________ flow

density, area, velocity

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

work, mass, and heat

In a steady flow process, energy can be transferred by

Remain zero; Reason: In a steady flow process, the change of total energy of the control volume must remain zero.

In a steady flow process, the change of total energy of the control volume must

flow

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.

q, Δpe, w, Δke, and Heat transfer with entire exchanger as the control volume; Reason: Heat is exchanged between the two moving fluids in the exchanger, and this will cause a change in the fluids' enthalpies.

In the energy balance equation for heat exchangers, which of the following are often neglected? (Select all that apply.)

0.5 kJ/kg⋅K

It is observed that 25 kJ of heat is required to raise the temperature of 5 kg of a substance by 10 K. Determine the specific heat of the substance.

5 kJ/kg⋅K

It is observed that it takes 10 kJ to raise the temperature of 1 kg of a substance by 2°C. Determine the specific heat of the substance.

cv = 2 kJ/kg⋅K

It is observed that it takes 8 kJ to raise the temperature of 2 kg of an ideal gas by 2oC in a rigid tank. Which of the following statements is true?

Gas E, Z=0.2; Reason: The further Z is away from unity, the more the gas deviates from ideal gas behavior.

Knowing the compressibility factor of the following gases, which gas's behavior below deviates the most from ideal gas behavior?

Pressure, Temperature, Specific volume

Select all the properties that apply: An equation of state is defined as any equation that relates the ________, ________, and _______ of a substance.

specific

The ____________ heat is the energy required to raise the temperature of a unit mass of a substance by one unit of temperature change.

True

The boundary work for a constant volume process is always Zero.

Specific heat

The energy required to raise the temperature of a unit mass of a substance by one unit of temperature difference is called the

Enthalpy

The heat content of a system at constant pressure

A

The processes A, B, and C represent three potential paths between states 1 and 2. Which path requires the least amount of work?

Critical

The reduced pressure and reduced temperature PR and TR are temperature and pressure normalized with respect to their counterparts.

42 kJ/kg

The specific heat of liquid water is approximately 4.2 kJ/kg*K. If liquid water is heated up by 10°C, determine the change in internal energy

k, kappa, or gamma

The symbol ___ is used for the ratio of specific heats Cp/Cv.

True; Reason: Flow work is expressed as Pv, and both P and v are properties.

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

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

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

True; Reason: The principle of corresponding states shows that the Z factor for all gases is approximately the same at the same reduced pressure and reduced temperature.

True or false: The principle of corresponding states shows that the Z factor for all gases is approximately the same at the same reduced pressure and reduced temperature.

True; Reason: Both total energies consist of a combination of internal, potential, and kinetic energies. The total energy of a flowing fluid consists of an extra term, flow work.

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.

2 m/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.

The ideal gas law The Beattie-Bridgeman equation The van der Waals equation The Benedict-Webb-Rubin equation

Which of the following are equations of state? (Select all that apply.)

1. A tub with inlets for both hot and cold water and one outlet 2. T-elbow 3. Y-Elbow Additional information: A 45 degree elbow consists of a single inlet and a single outlet, and thus is not a mixing chamber. A L-shape pipe consists of a single inlet and a single outlet, and thus is not a mixing chamber.

Which of the following devices are considered as mixing chambers?

Fan, Compressor, Pump

Which of the following devices requires work input?

PV^n = C

Which of the following relationships represents a polytropic process?

R = cp - cv

Which of the following represents the correct relationship for the gas constant of an ideal gas?

q - w = Δe; Reason: Per unit mass quantities (also called specific properties, specific work, and specific heat) are generally denoted with lower case letters.

Which of the following represents the first-law relation on a per unit mass basis?

Qdot-Wdot=dE/dt; Reason: The rate forms of heat and work get dots above the symbols, and the rate of change of energy of the system is shown as dE/dt.

Which of the following represents the rate form of the first law?

1. Any change in potential energy in nozzles and diffusers can be neglected. 2. Nozzles and diffusers typically involve no heat transfer. 3. Nozzles and diffusers typically involve no work.

Which of the following statements are true about nozzles and diffusers?

1. Unlike steady flow processes, unsteady flow processes start and end over some finite time period instead of continuing indefinitely. 2. Unsteady-flow or transient flow involves changes within the control volume with time, such as charging or discharging problems. 3. Unsteady flow systems may involve boundary work Additional information: For an unsteady flow analysis, it is assumed that the state of the mass within the control volume may change with time. Unsteady flow systems are usually fixed in space, but they may involve moving boundaries.

Which of the following statements are true about unsteady flow processes?

1. For a single-stream, steady flow throttle valve, the inlet and outlet enthalpies can be approximated to be the same. 2. The flow through a throttle valve may be assumed to be adiabatic. 3. Throttle valves are flow-restricting devices that cause a pressure drop in a fluid. Additional information: The pressure drops across a throttle valve is often accompanied by a large drop in temperature. There is no work done in a throttle valve.

Which of the following statements are true regarding throttling valves?

1. A volume flow rate is defined as the volume of the fluid flowing through a cross-section per unit time. 2. Mass flow rate is defined as the amount of mass flowing through a cross section per unit time. 3. Mass flow rate can be defined as the multiples of density, pipe average velocity, and cross section area normal to the velocity.

Which of the following statements are true?

1. 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. 2. In a steady flow process, the total rate of mass entering a control volume is equal to the total rate of mass leaving it.

Which of the following statements are true?

-The steady-flow process is a process during which a fluid flows through a control volume and does not change with time -During a steady flow process, boundary work is zero -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 NOT: -During a steady flow process, the boundary of the control volume is allowed to move-during a steady flow process, only mass in the control volume remains constant

Which of the following statements are true? (Select all that apply.)

polytropic process

is a process in which pressure and volume are often related by PVn= C, where n and C are constants, during expansion and compression processes of real gases.