First Law for the Closed System
Heat (Q) — Work (W) = Change in Total Energy (AE)
Closed system with process between states “1” and “2”:
G(z2 — Zj)
Qi—2 ^1-2 m |
(u2 — Ul) + ———— + :
2gc
Constant volume heating of a cylinder filled with a gas.
1st Law: Q1-2 = m Au = m cv AT
O
^_______ |
R |
|
V=const. 1 |
Q |
|
Example 1: Constant volume heating |
Weight |
|
P=const. / |
Q |
Example 2: Constant pressure heating |
Constant pressure heating of a cylinder filled with a gas.
1st Law:
O
Where i = u + pv is enthalpy.
Enthalpy is a property that combines Au and pv work that are only forms of energy change in many processes.
O
Cp = cv +R
Where R — specific ideal gas constant, and cp>cv because constant input does work.
Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning