COLD. Basic Training Course II. November ESSE - Wilhelm Nießen

Transcription

1 COLD Basic Training Course II 1

2 Temperature What is cold? 2

3 Temperature The expression cold is not correct physically. We are talking about heat. Heat is a form of energy. Every material has got more or less energy. You can measure the temperature. Comparing the temperature of materials you can use colder or warmer. 3

4 Pressure What is pressure? 4

5 Pressure Definition: p = F / A p: pressure in Pascal [Pa] F: force in Newton [N] A: space [m*m] Atmospheric pressure is about Pa In technology the pressure is still indicated in bar. 1 bar = Pa 5

6 Conversion table Pa (N/m²) Pascal bar at (kgf/cm²) technical atmosphere atm physical atmosphere kgf/m² Torr psi (lbs/sq.in.) Pa (N/m²) Pascal ,102 x ,987 x ,102 0,0075 1,45 x 10-4 bar ,02 0, ,49 at (kgf/cm²) technical atmosphere atm physical atmosphere , , , ,013 1, kgf/m² 9,81 9,81 x ,968 x ,0736 1,42 x 10-3 Torr 133 0, , , , psi (lbs/sq.in.) ,89 x ,03 x ,80 x ,07 51,

7 Pressure In technology two different gauges are used. Suction gauge: Measuring the overpressure. Torr gauge: Measuring the absolute pressure Suction gauge 7 Torr gauge

8 Temperature - Pressure The temperature and the pressure are deeply correlated values. Example: Steam pot (reducing the cooking time). The pressure is increasing so you reach higher temperatures. 8

9 Temperature - Pressure Example: Boiling point at different heights The atmospheric pressure on mountains is lower than at sea level and you get a lower boiling temperature. 9

10 Temperature - Pressure Steam-pressure curve of water. 10

11 Temperature - Pressure Comment: Before refilling of the cooling circuit it has to be evacuated. 1. All of the gas will be removed. 2. The circuit will be dried. (the pressure is very low so the remaining water in the circuit changes from liquid to the gaseous state) 11

12 Cooling You can only cool down something if you take the heat away. Remember! Heat can only flow from the warmer to the colder material. What kind of cooling systems do you know? 12

13 Remove Heat Heat or warmth should be moved out of the cabinet and the transportation of heat follows by refrigerants. cool down = less heat The refrigeration capacity is depended by the mass flow of refrigerant which Wärme Heat Wärme Heat Wärme Heat is in relation to the compressor displacement. Evaporating Enthalpy KJ / Kg Refrigerant 13

14 Cooling - Evaporation heat In refrigeration and freezer appliances the heat is taken away by evaporation of the refrigerant. 14

15 Refrigeration circuit The refrigeration circuit components are: Compressor Evaporator Condenser Capillary 15

16 Refrigeration circuit capillary Q evaporator P compressor condensor dryer Q 16

17 Cooling - Refrigerants Water is a very bad refrigerant. The boiling point is to high. The needed pressure (at -25 C) is so low that you should use a evacuation system instead of a normal compressor. For refrigeration (household) the refrigerant should have a low boiling point and good evaporation heat. 17

18 Refrigerant R12 R12 has been used for several decades as the standard refrigerant in refrigerators and freezers, sometimes also in heat pumps. It is a CFC with ozone-depleting potential, and it also contributes to global warming. Denomination dichlor-difluor-methane Chemical formula C Cl 2 F 2 Molecular weight 120,92 g/mol Boiling point at standard atmo- - 29,8 o C spheric pressure (1013 hpa) Solidification point o C 18

19 Refrigerant R12 Evaporation heat Colour of liquid Flammability Smell Explosion limits Toxicity relative ODP (ozone depleting potential) relative HGWP (global warming potential) 166 kj/ kg colourless not flammable slightly sweet not explosive non toxic 5,5% that of R11 34% that of R % that of CO 2, after 20years 19

20 Refrigerant R134a R134a has physical and thermodynamic characteristics similar to R12. R134a is not affecting the ozone layer, and has a reduced global warming effect; it is thus used as a substitute for R12. Denomination 1,1,1,2-tetrafluorthane Chemical formula F H 2 C C F 3 Molecular weight 102 g/mol Boiling point at standard atmo- - 26,3 o C spheric pressure (1013 hpa) Solidification point o C 20

21 R134a Refrigerant Evaporation heat 215 kj/ kg Colour of liquid colourless Flammability not flammable Smell odourless Explosion limits not explosive Toxicity non toxic ODP 0 HGWP 0,29 (10% that of R % that of CO 2, after 16 years 400% that of CO 2, after 500 years) 21

22 R600a (Isobutane) Refrigerant R600 is a pure hydrocarbon, and is thus not affecting the ozone layer. Neither does it contribute to global warming. But R600a is a flammable gas, and special safety precautions have to be observed. Denomination 2-methylpropane (Isobutane) Chemical formula CH(CH 3 ) (i-c 3 4 H 10 ) Molecular weight 58,123 g/mol Boiling point at standard atmo- - 11,61 o C spheric pressure (1013 hpa) Solidification point - 159,45 o C 22

23 R600a (Isobutane) Refrigerant Evaporation heat 366,7 kj/ kg Colour of liquid colourless Flammability yes - ignition temperature: 460 C flame point: - 80 C Smell slightly sweet Explosion limits explosive between 1,8 and 8,5% vol. Toxicity non toxic; slightly narcotic in high concentrations; max. admitted concentration: 1000 ppm ODP 0 HGWP 0 23

24 Refrigerant Properties Refrigerant R12 R134a R600a Evaporating point - 30 C - 26 C - 12 C Condensing 55 C Pabs bar bar 7.77 bar Enthalpy by Evap. 166 KJ/Kg 215 KJ/Kg 367 KJ/Kg Evap. Enthalpy 32/-25 C 122 KJ/Kg 156 KJ/Kg 274 KJ/Kg Density of Vapour-25 C 7.69 Kg/m³ 5.56 Kg/m³ 1.67 Kg/m³ Evap. Pressure-25 C Pabs 1.24 bar 1.07bar 0.56bar Volume of Vapour -25 C 130 dm³/kg 180 dm³/kg 600 dm³/kg 24

25 Refrigerant vapour pressure tables Temperature t [ C] absolute pressure pabs [bar] R12 R22 R134a R600a -60 0,226 0,376 0,163 0, ,300 0,497 0,223 0, ,392 0,646 0,299 0, ,505 0,830 0,396 0, ,642 1,053 0,516 0, ,807 1,321 0,666 0, ,000 1,640 0,848 0, ,237 2,016 1,067 0, ,510 2,455 1,330 0, ,827 2,964 1,642 0, ,193 3,550 2,008 1, ,612 4,219 2,435 1, ,089 4,980 2,929 1, ,629 5,839 3,497 1, ,238 6,803 4,146 2, ,921 7,882 4,883 2, ,682 9,081 5,716 3, ,529 10,41 6,651 3, ,465 11,88 7,698 4, ,498 13,50 8,865 4, ,634 15,27 10,16 5, ,88 17,21 11,59 6, ,24 19,33 13,17 6, ,72 21,64 14,91 7, ,33 24,15 16,81 8,

26 Refrigerant vapour pressure diagrams p abs [bar] 25,0 20,0 15,0 10,0 5,0 R22 R134a R12 R600a 0, Temperature [ C] 26

27 Compressor How works the compressor? 27

28 Suitable Hermetic for household appliances 28

29 Construction (Hermetic) Cover Compressor Asynchronous Motor Shell Terminal Board 29

30 Purpose The main task of the compressor in refrigerators and freezers is to produce the required suction and discharge pressure and to carry the refrigerant around in a circuit. 30

31 Function (Hermetic) suck in 31

32 Function (Hermetic) compress 32

33 Function (Hermetic) discharge 33

34 Refrigeration System Refrigerant flows trough the compressor which raises the pressure of refrigerant and it flows trough the condenser. It will be condenses from vapour to liquid and goes to the expansion valve (Capillary tube). Finally, the refrigerant flows to the evaporator. The liquid refrigerant will vaporise. 34

35 Refrigeration Capacity (W) Wärme Heat Wärme Heat Wärme Usually refrigeration capacities by household refrigerators and freezers are approximately W 148W 62W 82W 35

36 Refrigeration Capacity (W) 88W GL35AA 3,67cc >62W >82W GL45AA 100W 4,56cc 62W 82W 159W GL80AA 8,10cc >148W 148W 36

37 END of COLD BASIC II 37