Thermodynamics Test 2

Test 2 Chapter 3 and 4

For a closed system, what does the conservation of energy principle state regarding the relationship between energy transfer and system energy change?

The net change in the system's energy is equal to the energy entering the system minus the energy leaving the system.

What is the energy balance equation for a closed system expressed in terms of energy in and energy out?

Ein - Eout = ΔEsystem

To compute the missing values in the data table for problem 1(b), what equation must be utilized?

The derived energy conservation equation from 1(a).

When showing calculations for the data table in problem 1(b), you must clearly include the relevant (______), (______), and (______).

equations, units, unit conversions

To create a well-labeled control volume sketch for a steady-flow fan problem, what essential components must be included?

The fan, the inlet flow, the outlet flow, and the control volume boundaries.

A well-labeled control volume sketch for a steady-flow fan must delineate the (______) and clearly indicate the (______) and (______) flow streams.

system boundaries, inlet, outlet

What is the conservation of energy principle for a steady-flow system expressed using the E*in and E*out notations?

∑E*in = ∑E*out

In the conservation of energy equation for a steady-flow system, why is ΔE*system equal to zero?

Because the properties and energy state within the control volume do not change over time under steady-flow conditions.

In the context of a fan operating under ideal steady flow conditions, what is the relationship between the electrical power input (W*in), mass flow rate (m*), and air discharge velocity (V)?

W*in = m*(v²/2)

Given a fan operating at steady state with a power consumption of 40 W and a mass flow rate of 1.5 kg/s, what is the air discharge velocity?

V = 7.3 m/s (calculated as √(2 x 40W / 1.5 kg/s)

What is the primary difference between a saturated liquid and a compressed liquid?

A saturated liquid is at the point of phase change and is about to vaporize, whereas a compressed liquid is not at the point of phase change.

In thermodynamics, what state describes a liquid that is at the point of phase change?

Saturated liquid

In thermodynamics, what state describes a liquid that is not at the point of phase change?

Compressed liquid

At a constant pressure, how does the temperature of superheated vapor compare to that of saturated vapor?

Superheated vapor is at a temperature higher than the saturation temperature, while saturated vapor is at the saturation temperature.

How do the intensive properties of saturated vapor at a given temperature compare to the vapor phase of a saturated liquid-vapor mixture at that same temperature?

They are identical, because the vapor in a saturated mixture is itself saturated vapor at that temperature.

If the pressure of a substance is increased during a boiling process, what happens to its temperature?

It increases, because the saturation temperature of the substance rises as pressure increases.

In thermodynamics, what is the difference between the critical point and the triple point?

The critical point is the state where liquid and vapor phases are indistinguishable, while the triple point is the state where all three phases (solid, liquid, and gas) coexist in equilibrium.

How does the amount of heat absorbed during the boiling of 1 kg of saturated liquid water at 100°C compare to the heat released during the condensation of 1 kg of saturated water vapor at the same temperature?

They are equal.

Why is the heat absorbed to boil 1 kg of saturated liquid water at 100°C equal to the heat released to condense 1 kg of saturated water vapor at 100°C?

Because the phase change process is reversible and involves the same amount of energy transfer (enthalpy of vaporization) at a constant temperature and pressure.

What is the physical significance of hfg

It represents the enthalpy of vaporization (latent heat of vaporization), which is the energy required to change a unit mass of saturated liquid into saturated vapor at a constant temperature or pressure.

How is the enthalpy of vaporization (hfg) calculated using saturated liquid enthalpy (hf) and saturated vapor enthalpy (hg)?

hfg = hg - hf

Which process requires more energy: completely vaporizing 1 kg of saturated liquid water at 1 atm pressure or at 8 atm pressure?

Completely vaporizing the liquid water at 1 atm pressure.

How does increasing the pressure of a boiling process affect the latent heat of vaporization (hfg) of a substance like water?

It decreases the latent heat of vaporization.

Why does it require less energy to vaporize 1 kg of saturated liquid water at 8 atm compared to 1 atm?

Because the latent heat of vaporization (hfg) decreases as the pressure of the boiling process increases.

How does the ratio of vapor volume to total volume compare to the definition of quality (x) for a saturated liquid-vapor mixture?

They are distinct; quality is defined by the mass fraction of the vapor phase, not the volume fraction.

What is the definition of quality (x) for a saturated liquid-vapor mixture?

The ratio of the mass of the vapor phase (mg) to the total mass of the mixture (m{total}).

Does it require more energy to vaporize 1 kg of saturated liquid water at 100°C than at 120°C?

Yes, it requires more energy to vaporize saturated liquid water at 100°C than at 120°C.

Why does it require more energy to vaporize saturated liquid water at 100°C than at 120°C?

The latent heat of vaporization ($h_{fg}$) of water decreases as temperature increases.