# Warm up!  What is the difference between Isothermal and Adiabatic?  Describe the difference using the relationship between Internal energy(  U), heat(Q),

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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  T 1 = T 2  P1V1 = P2V2  Δ T = 0  Δ U = 3/2 nR Δ T   Δ U = 0  Q - W = 0  Q = W  Heat input = work output ADABIATIC (isentropic)  No heat exchange with the environment  Q =0  Δ T ≠ 0 P1V1/T1 = P2V2/T2  Δ U = – W  3/2 nRT = - W  - 3/2 nr Δ T = 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 = Q h – Q c (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)  Q H = remove from, absorbs = hot  Q C = exhausts to, expels = cold

 Second Law of Thermodynamics  The bottom line: 1)Heat always flows from a hot body to a cold body 2)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  W in – done by the piston compression  Q in –done by combustion of fuel  W out –done by working fluid expanding and pushing the piston ( usable work)  Q out –done by venting air  W net = Q in – Q out  W = Q h – Q c

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.

Fridge Vapor 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  W AB = P AB ΔV AB  (1.50 x 10 6 N/m 2 ) (5.00x10 - 4 m 3 ) = 750 J

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