1500

Extensive and intensive property

extensive properties are dependent on system mass - e.g. mass, volume

intensive properties are independent of system mass - e.g. temperature, pressure

Heat Transfer

Heat flows from high temperature to low

Difference in tempearture is given by T_high - T_low

Modes of heat transfer

Radiation (electromagnetic waves) - requres no medium

Conduction (molecular collisions)

Convection (bulk fluid motion)

Work transfer

Energy transfer associated with a force acting over a distance

Shaft work

Mechanical energy transferred across a system boundary via a shaft or other mechanical connection

Boundary work

Flow work

Enthalpy

Mental model for energy balance

So your mental model should be: State 2 - State 1CHANGE IN STORED ENERGY​​=transfersENERGY IN​​−transfersENERGY OUT​​​

States tell you what changed.

Energy transfers tell you how that change happened.

And those two descriptions must agree because of conservation of energy.

That's honestly the central idea behind basically all the energy-balance problems you're doing right now.

How to tell the phase from what you're given

If you're given x (quality) directly → it's already telling you the phase:

• 0 < x < 1 → saturated liquid-vapor mixture

• x = 1 → saturated vapor

• x = 0 → saturated liquid

If you're given T and P together → compare the actual P to the saturation pressure at that T (look up P_sat at that T in the saturation table):

• Actual P > P_sat(T) → compressed (sub-cooled) liquid

• Actual P < P_sat(T) → superheated vapor

• Actual P = P_sat(T) → sitting exactly on the saturation line (mixture — need more info like h or x to pin down exactly where)

Saturation

Think of saturation = the point where liquid water is just ready to turn into vapour.

How to find the enthalpy of an incompressible liquid at a specific state

Incompressible liquids

Work out or In for pumps, turbine and pistons