Warm up!

What is the difference between Isothermal and Adiabatic?

Describe the difference using the relationship between Internal energy(U), heat(Q), work (W), temperature (T)

U = Q - W

Isothermal

T1 = T2

P1V1 = P2V2 ΔT = 0 ΔU = 3/2 nR ΔT ΔU = 0 Q - W = 0 Q = W

Heat input = work output

ADABIATIC (isentropic)

No heat exchange with the environment

Q =0 ΔT ≠ 0

P1V1/T1 = P2V2/T2 ΔU = – W 3/2 nRT = - W - 3/2 nrΔT = W Work output depends

on negative change of internal energy

WHEN IS YOUR TEST?

The Test is Next Thursday !!!

In a cyclical process ΔU=0 Since ΔU=0 0 = Q – W W = Q

But not all Q is converted to Work, thus W = Qh – Qc (cyclical process)

W net work done by system

REVIEW

Review Engine

Heat flows from a HOT reservoir ( or HEAT source) to a COLD reservoir ( or Heat Sink)

QH = remove from, absorbs = hot

QC= exhausts to, expels = cold

Second Law of Thermodynamics

The bottom line:1)Heat always flows from a hot body to a cold

body2)Nothing is 100% efficient

Review Engines

A 4 stroke gas Engine

The Diesel Engine

"compression ignition" rather than "spark ignition”

Air is compressed adiabatically

compression raises the temperature of the fuel mixture

The Diesel Engine

a –b ( adiabatic compression)

b –c (Isobaric combustion process)

c –d (adiabatic expansion a power stoke)

d –a ( isochoric, isovolumetric exhaust)

Diesel cycle

Win – done by the piston compression

Qin –done by combustion of fuel

Wout –done by working fluid expanding and pushing the piston ( usable work)

Qout –done by venting air

Wnet = Qin – Qout

W = Qh – Qc

Fire syringe, Fire piston, Slam rod fire starter ancient

origin

Heat Pump, Air-conditioner, Refrigerator

Refrigeration cycle,

1- Compressor constrict the refrigerant vapor, increasing pressure, pushes into coils

2-Hot gas meets cool air in the kitchen, liquefy

3-Liquid at high pressure, refrigerant cools down in.

4- The refrigerant absorbs heat inside fridge, cooling down the air

5 – refrigerant cools down to gas, goes back to the compressor. Cycle repeats.

FridgeVapor Compression Cycle – A: hot

compartment (kitchen), B: cold compartment (refrigerator box), I:

Insulated 1: Condenser, 2: Expansion valve, 3:

Evaporator unit, 4: Compressor

Calculate the total work done in the cyclical process

The work along path AB

WAB = PAB ΔVAB

(1.50 x 106 N/m2) (5.00x10-4 m3) = 750 J