ME 302 Thermodynamics Concepts Self Assessment

This set of flashcards covers fundamental thermodynamic concepts including properties, cycles, the first and second laws, ideal gas models, and entropy as derived from the ME 302 self-assessment transcript.

Thermodynamic Properties

$p$, $E$, $T$, $V$ (volume), $\nu$ (specific volume), $m$, $KE$, $PE$, and $U$ are properties; $Q$ (heat) and $W$ (work) are not properties.

$$\Delta E_{cycle}$$

The change in energy over a cycle is always $0$ because the system returns to its initial state.

$$W_{cycle}$$

For a cycle, the net work is equal to the net heat transfer ($W_{cycle} = Q_{cycle}$) based on the first law of thermodynamics.

Positive Work ($W > 0$)

In a closed system, doing positive work (work done by the system) decreases the energy of the system and typically occurs during an increase in volume (expansion).

Newton's Second Law Conversion (SI)

$1\,N = 1\,(kg \cdot m)/s^2$.

Newton's Second Law Conversion (English)

$1\,lbf = 32.2\,(lb \cdot ft)/s^2$.

Molar Mass of Carbon

The mass of a mol of carbon atoms is $12\,g$, a kmol is $12\,kg$, and a lbmol is $12\,lb$.

Free Expansion

An unrestrained expansion of a gas into a vacuum where the gas temperature does not change (assuming an ideal gas).

Adiabatic Expansion

Expansion of a gas against a piston without heat transfer, which causes the gas temperature to decrease.

Polytropic Process

A process described by the expression $pV^n = \text{constant}$, where $n$ is the polytropic exponent.

Mechanism of Heat Transfer

When heat transfer occurs, energy and entropy simultaneously cross the boundary of the system.

Coefficient of Performance (COP)

A measure of efficiency for heat pump and refrigeration cycles; for a heat pump cycle, the $COP$ can be greater than $1$.

State Principle

It takes two independent, intensive properties to fix the state of a simple thermodynamic system.

Quality ($x$)

A property found under the vapor dome representing the mass fraction of vapor, ranging from $0$ (saturated liquid) to $1$ (saturated vapor).

Liquid Property Approximation

For liquids not covered by specific tables, properties like $u$ or $h$ are approximated using the saturated liquid value ($f$) at the given temperature ($T$).

Ideal Gas Model Properties

For an ideal gas, the internal energy ($u$) and enthalpy ($h$) are functions of temperature ($T$) only.

Compressibility Factor ($Z$)

At low pressure and high temperature relative to the critical point, $Z$ takes the value of $1$, signifying ideal gas behavior.

$c_p$ vs. $c_v$

For an ideal gas, $c_p$ is used to calculate $\Delta h$ and $c_v$ is used to calculate $\Delta u$; $c_p$ has a larger value than $c_v$.

Enthalpy in Open Systems

In the energy balance for open systems, internal energy ($u$) is replaced by enthalpy ($h$) to account for the work associated with fluid mass crossing the boundary.

Throttling Device

An idealized expansion valve where the enthalpy ($h$) remains constant across the device.

Kelvin-Planck Statement

A version of the Second Law of Thermodynamics stating that it is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of work to its surroundings while receiving energy by heat transfer from a single thermal reservoir.

Carnot Efficiency

The maximum theoretical efficiency for a power cycle operating between two reservoirs, calculated as $\text{Efficiency} = 1 - \frac{T_c}{T_h}$, where temperatures must be in absolute units (Kelvin or Rankine).

Isentropic Process

An idealized process that is both adiabatic and reversible, resulting in no change in entropy ($\Delta S = 0$).

Entropy Production

A non-property value that is always positive for irreversible processes and zero for reversible processes; entropy itself is not conserved.

Isentropic Efficiency

An efficiency metric that compares the actual performance of a device (turbine or compressor) to its performance under idealized/isentropic conditions.