Page 51 - BASIC CONCEPTUAL OF THERMOFLUID

CHAPTER 4

FIRST LAW OF
THERMODYNAMICS

When system undergoes a thermodynamic
cycle then the net heat supplied to the system
from its surroundings is equal to the net work
done by the systems on its surroundings.

……The First Law of Thermodynamics

Forms of energy

Energy transfer by heat and work

WORK : Work is the Energy transfer associated with a Force acting through a distance
Denoted by J or kJ

ܨ = ݌ܣ

ܹ = ݌(ܸ2 − ܸ1)

Figure 4.1 work transfer
Where:

P is the pressure exerted on the piston and

A is the area of the piston

Work and heat

Work = work per unit mass
w = W/m (J/kg)

Power = work per unit time

P = W/time (J/s or W)

Heat = heat involves the transfer or energy between two objects due to a temperature difference

Sign convention for work transfer

· if work energy is transferred from the system to the surroundings, it is donated as positive.
· if work energy is transferred from the surroundings to the system, it is donated as negative.

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