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

подпись: qi—2 ^1-2 m(u2 — Ul) + ———— + :

2gc

Example 1

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

Example 2

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


Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *