Alternative Cooling Processes 1 Classification of Refrigeration Cycles

Alternative Cooling Processes 1Hans JonssonClassification of Refrigeration Cycles• Mechanically Driven Cycles- Vapor Compression Cycle• Heat Driven Processes- Carré Process- Platen-Munters Process- Ejector Cycle• Adsorption Processes• Expansion Cycles- Joule Cycle- Stirling Cycle- Hilsch Tube (Ranque Vortex Tube)• Thermoelectric Processes- Peltier Process1

Agenda• Classification of Refrigerating Cycles• Heat Driven Processes- Carré Process- Platen-Munters Process- Ejector Cycle• Adsorption CoolingHeat Driven Processes 1• Driven mainly, or entirely, by heat• Most heat driven processes are absorptionrefrigeration processes• Absorption means that the refrigerant isabsorbed by another media, and transportedas a liquid solution during a part of thecycle.• An absorption process hence consists of amedia pair. One refrigerant and oneabsorbator.2

Carré Processes 2• Condenser, Expansion Device, and Evaporatoridentical to vapor compression cycle.• Compressor of vapor compression cyclereplaced by ”thermal compressor”.• Thermal compressor: Absorber vessel, pump,generator, regulation valve, heat exchanger.• Mainly heat driven.• Pressure increase done in liquid phase =>Considerably less mechanical energy required!Carré Processes 3COP ?For heat driven processes, COP H is definedCooling capacity Refrigerant mass flow Latent heat of evaporationCOPSHQ&=Q&R2Hm&=m&⋅HOSR⋅ r( r + L)Generator heat input Solution mass flow Heat of mixingm& = m&+ m&⇒ m&> m&Hence COP H < 12SR4

Carré Processes 4Carré Processes 5Multi-stage systems improve COP H5

Carré Processes 6Carré Processes 7• If there is a heat source available then coolingcan be obtained at low cost.• Many sustainability aspects involved here…• Access to process waste heat, combustion gasesetc means that you recover heat losses andgenerate a refrigerating effect instead.• Solar driven cooling! Cooling demand increaseswith solar load…With these systems, coolingcapacity increses with solar load!• Robust technology!6

COP H vs COP 2 -1• Is the performance of an absorption processnecessarily worse than a vapor compressioncycle?COP H vs COP 2 -2The mechanical energy (electricity) for thevapor compression cycle has to be produced!7

COP H vs COP 2 -3Assume a thermal efficiency for a steam powerplant, η t = 0.35 and a COP 2 = 2.4 for a vaporcompression cycle.ThenQ&2⎧ Q&2⎫ COPCOPH,VC= = ⎨COP2= ⎬ =Q&H ⎩ E&⎭ Q&⎧ E&⎫ COP2⋅ E&= ⎨ηt= ⎬ = = COP2⋅ηt=⎩ Q&H ⎭ E&ηt= 2 .4⋅0.35= 0.842H⋅ E&=Carré Processes 8The Mosquito CoastNovel by Paul TherouxMovie by Peter Weir, 1986Starring: Harrison Ford, HelenMirren, River PhoenixAn eccentric and dogmaticinventor sells his house and takeshis family to Central America tobuild an ice factory in themiddle of the jungle. Conflictswith his family, a local preacherand with nature are only smallobstacles to his obsession.8

Platen-Munters Processes 1• Originated from a MSc Thesis work here at KTHin 1922.• Absorption process (using three different media)• The process has a constant total pressure in allparts of the system.• Different evaporation and condensation pressuresare achieved by introducing an inert gas into thesystem. This will make the partial pressure of therefrigerant change in different parts of the system.• Completely heat driven!• No moving parts - absolutely silent!Platen-Munters Processes 1• For which applications would this system besuitable?• Camping equipment (no electricity needed)• Mini bars in hotel rooms (absolutely silent)•COP H = 0.2 - 0.3• The company Dometic (formerly Electrolux)announced in June 2006 that the havemanufactured their 10 millionth refrigerator intheir plant in Motala, Sweden. Manufacturingstarted 1925.9

Platen-Munters Processes 2Platen-Munters Processes 3Hydrogen circuitWater circuit10

Platen-Munters EvaporatorAmmonia isgathered inbowls whereevaporationtakes placeRefrigerantinletHydrogen inletEvaporation of Ammoniadue to difference in partialpressure of Ammonia inthe bowl and in thehydrogen atmospheresurrounding it (comparediffusion in humid air).Hydrogen + AmmoniaoutletFlow downwards is dueto buoyancy effects(natural circulation).Platen-Munters AbsorbatorWater inletWater isgathered inbowls whereAmmonia isabsorbedHydrogenoutletAbsorption of Ammonia inthe water due to differencein Ammonia concentrationbetween Ammonia-watersolution in the bowl andthe Hydrogen-Ammoniaatmosphere surrounding it.Water + ammoniaoutletHydrogen + AmmoniainletFlow upwards is due tobuoyancy effects(natural circulation).11

Platen-Munters Thermosyphon PumpHead of gasliquidcolumn,H GLHead of liquid column, H LHeaterPlaten-Munters Thermosyphon PumpThe heads have to be equal for the pump to work, hence:ρL⋅g⋅ HL= ρGL⋅g⋅HGLBy adding heat in the thermosyphon pump, some of theliquid is evaporated in such way that:ρGL= ρLH⋅HLGLThe use of a thermosyphon pump in the system was theinvention of Baltsar von Platen and Carl Munters!12

Ammonia liquidPlaten-Munters ProcessesCondenser181756Hydrogen19Hydrogen freeof AmmoniaAbsorberAmmonia vapourand Hydrogen716Strong solutionLow temperature EvaporatorLow temperature Pre-cooler15High temperature EvaporatorHigh temperature Pre-coolerPressure equilization lineWeak solution243912Ammonia vapourRectifier1181Vapour-liquid separatorLift-tubeHeat Exchanger13 10Heat suppliedto BoilerEjector Cycle 113

Ejector cycle• Condenser, Expansion Device, and Evaporator identical tovapor compression cycle.• Compressor of vapor compression cycle replaced by”ejector”.• Ejector: Acceleration of high pressure vapor causes a lowpressure which creates a suction to remove refrigerant vaporfrom evaporator.• Pressure increase done by compression shock followed by adiffusor.• Mainly heat driven.• Pressure increase done in liquid phase => Considerably lessmechanical energy required!• Heating of the generator could be done by waste heat, solarheating etc.Ejector Cycle 114

Sorption Cooling15