Warm up! What is the difference between Isothermal and Adiabatic? Describe the difference using...

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