1st Law of Thermodynamics

Energy can be neither created nor destroyed (conservation of energy)

Thus power generation processes and energy sources actually involve conversion of energy from one form to another, rather than creation of energy from nothing

ΔQ = ΔU + ΔW

ΔU: Change in internal energy of the system

ΔQ: Heat transferred into/out of the system

ΔW: Work done by/on the system

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Cylinder has area, A. A fluid is admitted at constant pressure, p

p = F/A & Wd = fd … rearrange:

F = pA → Wd = pAd (Ad = volume, V)

→ Wd = pV or ΔWd = pΔV

pV = nRT (Ideal Gas Law)

Boyle’s Law: pV = constant

• Temperature remains constant (isothermal)
• pV = constant and p₁V₁ = p₂V₂
• ΔU = 0 because the internal energy is dependent on temperature, which does not change
• ΔQ = ΔW. If the gas expands to do work ΔW, & amount of heat ΔQ must be supplied
• compression or expansion produces the same graph

Adiabatic: no heat flow (ΔQ=0) into or out of a system

For a change in pressure or volume in a system, the temperature loss can be calculated:

p₁V₁/T₁ = p₂V₂/T₂

At high p, low V: adiabatic = value expected for isothermal at high T

At low p, high V: adiabatic cuts isothermal at low T

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Equation for adiabatic line:

pV_γ = k

γ = C_p/C_v

k= constant

Isovolumetric: p₁T₁ = p₂T₂

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Isobaric: V₁T₁ = V₂T₂

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