From Heat Pumps to Hurricanes Applicatjon of Thermodynamics in - - PowerPoint PPT Presentation

From Heat Pumps to Hurricanes

Applicatjon of Thermodynamics in Secondary Educatjon (A case study)

By Anikó Tasnádi Karinthy Frigyes Gimnázium Budapest

Outline

• Ratjonales
• Task given to the students and background
• Issues to discuss

– Engines – Heat pumps – Environmental consideratjons – Tropical cyclones

• Assessment

Ratjonales

Physics

behind

Technical devices; Natural phenomena

(8 extra lessons)

Groupwork and presentation Environmental issues

Research different devices which are

• perated either as a
• heat engine or a
• heat pump.

Task and Background

• Group:

– 17-18 year old secondary school students (19 students) – 2-year preparatory course for the University (4 lessons per week)

• Previously covered topics:

– Gas laws – Kinetic gas model – Processes (isothermal, isochoric, isobaric, adiabatic and cyclic processes) – First and second laws of thermodynamics – Otto and Diesel engines

Chosen Devices

Heat pumps Wankel engine Stjrling engine Refrigerators Cooling of computers Gas turbine

Effjciency of car engines

Ideal Otuo cycle Ideal Diesel cycle

Some Discussion points:

• Cyclic processes
• Octane number
• Internal combustion engine
• Fuel
• Efficiency
• Spark plug
• Compression ratio

η=1- ( V 2 V 1) κ−1

η=1−1 κ⋅ϕ

κ−1

ϕ−1⋅( V 2 V 1)

κ−1

ϕ=V 3 V 2

Environmental issues

• Depletjon of oil
• Banning of lead
• Exhaust is harmful

– Carcinogen molecules – Partjculate matuer

Wankel and Stjrling engines

• Wankel engine (rotary

engine)

– Great effjciency – Frequent services – Harmful exhaust gases

• Stjrling engine

– Any heat source; – High effjciency – Big, slow to ignite

Heat Pumps

• Reversed heat engines
• Transfer thermal energy from cold

to warm place

• External work is needed
• Used for cooling or heatjng
• The greater the temperature

difgerence the smaller the COP

Discussion points:

Coeffjcient of performance: (COP)

Qc Qc

Qc

QC

C

c

Compression and Absorptjon Type Refrigerators

V a p

• u

r C

• m

p r e s s i

• n

C y c l e

Some discussion points:

• Latent heat of phase change
• evaporation: heat is absorbed
• condensation: heat is released
• Compressor is operated with

electric current

• The absorption refrigerator is

quieter, has smaller COP than the compression type.

• The absorbant can be heated with

any heat source in case of absorption refrigerators (waste heat, solar power)

Some HVAC devices (Heatjng, ventjlatjng and air conditjononing)

Geothermal heat pumps Shallow, horizontal heat exchangers at a depth of 1-2 m Big area is needed COP: 4-5 Deep vertical system , depth: 60-100 m COP: 4-5 Water-sourced heat pump Air-sourced heat pump The cheapest, Can be used anywhere, Its COP depends on the

• utdoor temperature,

COP:3.5-4.7 Most efficient, high and constant temperature ground water, two wells. COP: 5-7

Environmental issues

• Question of refrigerants
• Freon ruins the Ozone layer
• Tetrafluoroethane (H2CFCF3) is

a strong greenhouse gas

• Ammonia is toxic
• The temperature of both

reservoirs change

• Geo tariff
• J. C. Mckay:

If in a typical British suburb everyone used ground-sourced heat pump, then the ground would freeze in the winter. An advertisement in Hungary A cheaper heating with the energy of the ground.

With the new heat-pump system and the GEO tariff you can heat your home economically.

Tropical Cyclons

Hurricane, Typhoon, Kamikaze (evil or divine wind)

Formatjon of Hurricanes

Necessary conditions of formation:

• Warm sea surface water (27O C)
• Instability of air
• Strong ascent (deep convection) of air

(causing a low pressure area)

• Strong vorticity (rotation)
• Weak wind sheer

Some discussion points:

• Coriolis force
• Formation
• Cyclic process

A nearly Carnot cycle

B A C D Tab≈300K Tc≈200K Q1 Q2

Effjciency: approximately 1/3

Assessment 1.

True-or-false questjons based on the covered topics

(8 groups of questjons; each containing 3 or 4 questjons)

Percentage values of correct answers for the questjons

1 2 3 4 5 6 7 8 0% 20% 40% 60% 80% 100% 120%

Some of the questjons

2.c) In Diesel engines the pure air is compressed. (True) 73% 5.d) If the same heat pump can be operated in order to cool down and to heat up the room, then its COP is greater when it is used for cooling. (False) 87% 5.c) In the gas-compression type refrigerators the condensing refrigerant absorbs heat from the environment. (False) 80% 6.d) In a hurricane the ascending wet air condenses and heats up the ambient air. (True) 33%

Assessment 2

The following questjons were evaluated from 1-5

• 1. Did you fjnd useful to prepare for your oral

presentatjon? 4.46

• 2. Did you fjnd the lectures useful? 4.15
• 3. Did you fjnd the lectures interestjng? 4.31
• 4. Did you learn from the lectures? 3.69
• 5. Would you like to learn this way in the future? 3.42

Thank Thank you very much you very much for your attention. for your attention.