MechAE 105A

forms of energy

kinetic, potential, thermal, iternal

temperature

a measure related to thermal state

thermodynamic system

any object or region being studied

boundary

imaginary or real surface separating system & surroundings

closed system

energy does not cross boundary

open system

mass and energy can cross boundary

isolated system

no mass or energy transfer

double the size of a system, what happens?

only extensive properties double

a system with temp differences inside

not in equilibrium

a system w/ constant temp but pressure differences

not in equilibrium

temp.. intensive or extensive

intensive

volume… dependent or independent

dependent

property

measurable characteristic of a system

conditions of equilibrium

uniform temp and pressure

if you divide a system into two parts, all properties are halved.. t or f

false

process

a change from one state to another

quasi-static process

process very close to equilibrium at all times

specific volume

volume per unit mass

if mass doubles, specific volume…

stays the same?

physical representation of temp

avg molecular kinetic energy

if density increases, specific volume

decreases

thermodynamic cycle

system returns to initial state

what is greatest form of pressure

absolute pressure

when gauge pressure is 0, abs pressure is

atmospheric pressure

if mass and volume are doubled, specific volume

stays the same

a rod has a steady linear temp gradient. the system

is not in thermal eq

two points at same depth in different-shaped containers. what is pressure difference

pressure is equal

for a closed system what is equation for change in energy

delta E = Q - W

A gas is compressed by a piston. Show work conditions

W<0, work is done on system

two different processes take a system from state 1→2. what stays the same

change in internal energy

work depends on path… true or false

true

heat is stored in a system.. t or f

false

work is a property of a system

false

heat transfer occurs due to…

temperature differences

if Q<0

heat leaves system

heat transfer rate is defined as

Q’ = dQ/dt

conduction occurs due to

molecular collisions

head conduction is dependent on

temperature gradient

convection heat transfer depends on

temp diff

adiabatic process

no heat transfer

delta E = Q - W; t or f

t; change in energy = heat added and work done by system

detla E = W - Q; t or f

false

delta E = W - Q; t or f

false

for a stationary system, what energy changes

KE = PE = 0 change

first law of thermodynamics for a closed system

delta U = Q - W; change in internal energy

change in energy for a complete cycle

delta E = 0

work output of heat engine

W out = Qin - Qout

efficiency

output/input

thermal effcieny is always

less than one

refrigeration cycle main purpose

remove heat from cold space

coefficient of performance

heat removed/work input

why does radiation dominate heat transfer at high temp

radiation depends on T^4

a heat engine has efficiency of 100%

Qo = 0

enthalpy

H = U + pV; enthalpy = internal energy + pressure*volume

at saturation conditions, water exists at

liquid-vapor mixture

if quality x=0, substance is

saturated liquid

for a rigid tank, boundary work is

zero

a rigid tank contains saturated water vapor and is cooled at constant volume. what happens first?

enters two-phase region

water at 150C has quality x = 0.4.. meaning

40% of mass is vapor

which process gives zero bouundary work?

constant volume heating

specific heat Cv represents

energy required to raise temp of unit by mass by one degree at constant volume

for a rigid tank containing closed system, most relevant specific heat is

Cv

for a constant pressure piston cylinder process, heat transfer is most directly related to..

change in enthalpy

specific heat at constant pressure

Cp = (delta h/delta T) p

specific heats are generally defined in

single phase regions only

specific heat ration k is

k = Cp/Cv

an incompressible substance is one whose ____ is approx constant

specific volume

what materials are considered incopressible

liquids and solids

for incompressible substances, internal energy is a function of

temperature only

for incompressible substance w/ constant c, the change in internal energy is

delta u = c(T2-T1)

for incompressible substance, approx enthalpy change is

delta h = c*deltaT + v* deltap

water is heated from 20 to 60 at constant pressure. if incompressible, the main contribution to delta u is…

temp change

why is Cp greater than Cv

constant pressure heating includes expansion work

a block cools from 100 to 40, internal energy…

decreases

liquids are approximated as incompressible.. t or f

true

specific heat is define inside two phase vapor dome.. t or f

false

in rigid tank, boundary work is

zero

if liquid is treated as incompressible,

specific volume is negligible

why is specific heat not define in saturated liquid-vapor mixture region

adding energy may cause phase change wo changing temp

a closed rigid tank of liquid water is heated.. what does say about enthalpy/boundary work

boundary work is approx zero bc volume is constant

internal energy is a state function, t or f

true

heat depends on path, t or f

t

delta U = Q - W, meaning of work and heat, can U be neg

work done by system is pos, heat added to system is pos, if W>Q, then U is neg

adiabatic Q and delta U

Q = 0 and delta U = -W

efficiency = wcycle/Qin, t or f

falset

for a heat engine, how much heat is rejected

some heat is rejected

for a heat engine Qout>Qin, t or f

false

for specific density v = V/m, t or f

true

for specific density, 1/density, t or f

true

specific volume depends on system size t or f

false

gauge pressure can be negative t or f

true

delta U is same for any path btwn two states t or f

true

heat is same for any path t or f

false

if Q>W, delta U <0 t or f

false

if Q = 0, then delta U = -W t or f

true

delta U = Q - W, delta U can be negative t or f

true

a heat engine produces net work t or f

true

A refrigerator consumes workt or f

true

work equals heat rejected t or f

false