ME 201 Mid term

system

quantity of matter or a region in space chosen for study

surroundings

The mass or region outside the system

closed system

consist of a fixed amount of mass, and no mass can cross its boundary; no mass can enter or leave

isolated system

a closed system where energy isn't allowed to cross boundaries

open system

A system in which matter can enter from or escape to the surroundings.

property

a characteristic of a system

intensive property

properties that are independent of the mass system such as temperature, pressure, and density

extensive property

those who's value depends on the size or matter of the system such as total mass, total volume and total momentum

specific properties

Extensive properties per unit mass, examples, specific volume

density

mass/volume

specific volume

Volume per unit mass; reciprocal of density

specific gravity

the ratio of the density of a substance to the density of water

state

a set of properties that completely describe a condition

equilibrium

a state of balance

thermal equilibrium

temperature is the same throughout the entire system

mechanical equilibrium

no change in pressure at any point in the system with time

phase equilibrium

The mass of each phase reaches an equilibrium level and stays there

chemical equilibrium,

chemical composition does not change with time, no chemical reactions occur

state postulate

the state of a simple compressible system is completely specified by two, independent, intensive properties

independent

one property can be varied while the other one is held constant

simple compressible system

Absence of electrical, magnetic, gravitational, motion, and surface tension effects

process

any change that a system undergoes from one equilibrium state to another

path

the series of states through which a system passes during a process

Quasi-static equilibrium

when a process proceeds in such manner that the system remains infinitesimally close to an equilibrium state at all times

isothermal process

process in which temperature remains constant

isobaric process

process in which the pressure remains constant

Isochoric process

process in which specific volume remains constant

cycle

a system is said to go through this if it returns to its initial state at the end of the process

thermal equilibrium

the equality of temperature

Zeroth Law of Thermodynamics

if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other

pressure

a normal force exerted by a fluid per unit area

pascal

SI unit of pressure (Pa, N/m^2)

absolute pressure

Atmospheric pressure + gauge pressure

vacuum pressure

pressures below atmospheric pressures

pascals law

the pressure applied to a confined fluid increases the pressure throughout by the same amount

barometer

measures atmospheric pressure

total energy

the sum of kinetic energy, potential energy, and other forms of energy

macroscopic forms of energy

kinetic and potential energies

microscopic forms of energy

Those related to the molecular structure of a system and the degree of the molecular activity

internal energy

Sum of all microscopic forms of energy

kinetic energy

the energy that a system possesses as a result of its motion relative to some reference frame

potential energy

the energy a system possess as a result of its elevation in a gravitational field

pure substance

a substance that has a fixed chemical composition through, ex air and water

solid

molecules arranged in a three-dimensional pattern that is repeated through out

liquid

does not differ much from a solid, except the molecules are no longer at fixed position relative to each other and they can rotate and translate freely

gas

molecules are far apart from one another and molecular order is nonexistent

compressed liquid

liquid that is NOT about to vaporize

saturated liquid

a liquid that is about to vaporize

saturated vapor

vapor that is about to condense

saturated liquid-vapor mixture

The state at which the liquid and vapor phases coexist in equilibrium

superheated vapor

A vapor that is not about to condense

saturation temperature

the temperature at which a pure substance changes its phase

saturation pressure

the pressure at which a pure substance changes its phase

latent heat

the amount of energy absorbed or released during a phase change process

latent heat of fusion

the amount of energy absorbed during melting

latent heat of vaporization

the amount of heat absorbed during vaporization

critical point

the point at which the saturated liquid and saturated vapor states are identical

saturated liquid line

the line that connects the saturated liquid states

saturated vapor line

the line that connects the saturated vapor states

compressed liquid region

the region to the left of the saturated liquid line

superheated vapor region

the region to the right of the saturated vapor line

saturated liquid-vapor region

located under the dome

triple line

the line connecting all the states in which 3 phases can coexist

triple point

the point on a phase diagram that represents the only set of conditions at which all three phases exist in equilibrium with one another

enthalpy(h)

u + Pv

quality(x)

mass of the vapor in a system divided by the total mass of the system

boundary work

the expansion and compression of work

polytropic process

pV^n \= constant

mass flow rate

the amount of mass flowing through a cross section per unit time

volume flow rate

the volume of a fluid flowing through a cross section per unit time

conservation of mass principle

the net mass transfer to or from a control volume during a time interval delta t is equal to the net change (increase or decrease) of the total mass within the control volume during delta t

average velocity

the values of Vn across the entire cross section of the pipe

flow work

work required to push the mass into or out of the control volume

total energy of a flowing fluid

Pv + (u + ke + pe)

steady flow process

process involving such devices can be represented reasonably well by a somewhat idealized process

nozzel

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

diffuser

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

conduction

the transfer of energy from the more energetic particles of a substance adjacent less energetic ones as a result of interactions between the particles

thermal conductivity

a measure of the ability of material to conduct heat

temperature gradient

the slope of a temperature curve on a T-x diagram

thermal conductivity

the rate of heat transfer through a unit thickness of the material per unit area per unit temperature difference

heat capacity

the product of rho*cp

thermal diffusivity

represents how fast heat diffuses through a material

convection

the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion

forced convection

If the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind.

natural convection

If the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid

radiation

energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms of molecules

blackbody

the idealized surface that emits radiation at the maximum rate

blackbody radiation

the radiation emitted by a blackbody

emissivity

the radiation emitted by all real surfaces is less than the radiation emitted by a blackbody at the same temperature

no-slip condition

A fluid in direct contact with a solid "sticks" to the surface, and there is no slip.

boundary layer

The flow region adjacent to the wall in which the viscous effects are significant.

thermal boundary layer

The flow region over the surface in which the temperature variation in the direction normal to the surface is significant

electro magnetic waves

Can transfer energy without going through a medium.

Electro magnetic spectrum

The arrangement of electromagnetic radiation waves according to their wavelengths and frequencies

photons

particles of light

thermal radiation

the type of electromagnetic radiation that is pertinent to heat transfer

solar radiation

the electromagnetic radiation emitted by the sun

Infared

the radiation emitted from bodies at room temperature

ultraviolet

Electromagnetic waves of frequencies higher than those of violet light.