Exam 1 Vocabulary Flashcards
Closed system
A fixed set of identifiable particles of constant mass; the same set of particles is followed through the analysis. (abbreviation: sys)
Control volume (open system)
A region of space which may or may not be moving (often taken to be fixed in space) and through which fluid may flow. Therefore, the identity of the particles in the control volume may vary from instant to instant. (abbreviation: CV)
Control surface
The geometric bonding surface of the control volume. (abbreviation: CS)
Extensive property
A property that depends on the amount of matter in a sample. (ex. mass, volume, energy, entropy)
Specific property
Corresponding extensive property per unit mass. Intensive property. Independent of amount or size. (ex. temperature, density, pressure, specific heat capacity)
Conservation of Mass
Mass can neither be created nor destroyed. Mass of a system is constant.
Newton’s Second Law
Force = time rate of change of linear momentum. F=ma or F=mv(dot)
Absolute temperature scales
Kelvin and Rankine. Absolute means it starts from absolute zero and measures temperatures in increments directly proportional to the average kinetic energy of gas molecules.
First Law of Thermodynamics
Energy can be neither created not destroyed, it can only change in form. Energy eqn –> Q(diff) - W(diff) = E(diff wrt time) Q = heat transfer, W = work, E = energy. Use momentum equation. U is internal energy. In control volume, use internal energy (u), kinetic energy (V^2/2), and potential energy (gz).
Second Law of Thermodynamics
Highlights irreversibility of natural processes when considered in terms of heat transfer. Heat generally goes to where it’s cooler, but not the other way around unless there are external interventions.
Entropy eqn –> S(diff wrt time) >/ Q(diff)/T. S = total entropy, Q = heat transfer, T = temperature. Use momentum equation.
The Isentropic Case of the Second Law of Thermodynamics
s2-s1 = 0 assuming a thermally and calorically perfect gas. Entropy of system remains unchanged. Entropy may change WITHIN the closed system as long as net change is zero.
Reynold’s Transport Theorem
Analyzes the change of extensive properties within a control volume as it moves through space. How to use: 1. identify extensive property to analyze
2. define a control volume
3. apply RTT to write general eqn governing the change of the extensive property within the CV
4. apply additional assumptions or simplifications
5. solve resulting eqn to obtain information about the behavior of system over time
Q(diff)
Derivative of heat transfer. Temperature x Infinitesimal change in entropy. Heat transfer is a path dependent quantity. Heat transfer rate to CV.
Ws(diff)
Ws = shaft work done in a system. Represents an infinitesimal amount of work done in a system. Pressure x Infinitesimal change in volume. Shear and shaft work rate by CV. Total work rate due both to shaft and shear work.
Specific enthalpy
Denoted as h. Used to describe the energy content of a substance per unit mass. Sum of internal energy and the product of pressure times specific volume. Change in enthalpy = change inn work + change in heat transfer
Entropy
Quantifies the order of randomness or chaos in a system. Denoted by S. Represents the amount of energy in a system that is not able to do work.
Thermally/calorically perfect assumption
Specific heats remain constant wrt temperature. Cp and Cv are zero. For isentropic processes S(diff) = 0; P/rho^gamma = constant.
Ratio of specific heats
Which variable? GAMMA = Cp/Cv
Isentropic process
What can you assume? Assume no heat transfer. Constant entropy, process is reversible and adiabatic. Constant ratio of specific heats (gamma).
Adiabatic process
What can you assume? Assume no heat transfer. Internal energy can change. Constant ratio of specific heats (gamma).
Mach number
Eqn? M = V/a. a = sqrt(gammaRT)
Subsonic
Flow velocity is less than the speed of sound
Sonic
Flow velocity is equal to the speed of sound
Supersonic
Flow velocity exceeds the speed of sound
