Effect of Pressure on Improving COP of a Refrigeration Installation Solar To Absorption

Effect of Pressure on Improving COP of a Refrigeration Installation Solar To Absorption

,

1. Benramdane(1), MEA. Ghernaout(1)

   (1)Department of Mechanical Engineering.

   ETAPlaboratory, Faculty of Technology, University of Tlemcen, Tlemcen13000,Algeria

   S. Abboudi(2)

   (2)IRTES-M3MLaboratory, UTBM,Siteof Sevenans, 90010, BelfortCedex, France.

   Abstracttheuse of renewable energycreatesmoreof interestin the world.Disruptionsin oil prices, gas and environmental problemshave led manycountriesto focuson renewableand clean energysuch as solarenergy.

   Howevercold productionfromthis energy ispossiblefor our country.

   Among the varioussystems used tothis, theabsorption refrigerationmachineseems to beverypromisingin this respect. A request forincreasedcomfort andparticularly hightemperatures wereled tostrong growthof air conditioning indeveloped countries.

   The objective of thiswork istostudya solarrefrigerationdoubleeffect(twoboilers, condenser, evaporator and twoabsorbers) operating with simpleabsorptionpanels, to seethe influence ofthermodynamic parametersin particularpressure on theimprovementcoefficientsof performance (COP) and showthat itproduces thecoldwithinteresting performances.Itdoes not requiredistillation column andhas the following advantages: possible operationfroma temperature in theboilers70°C, possibility of usingsolar collectorscheaperwhich affectsthe overall costof the installation.

   Keywords- ColdSolar,absorptionrefrigeration,COP,improvement.

   1. INTRODUCTION

      The thermal energyrequired to operatethesetechnologiescomes fromsolar radiation. the solar system Converted the solar thermal radiation through a capture by greenhouse effect is called solar radiation sensor.

      Solar systemsfor refrigerationreceive energyand convert it intocoldstoreandthe rest isforuse duringthe nights and the bad weather periods.

      Generally, theyare threenecessary elements: solar, energy storagesystem, absorption machine[1].

      In order toseethe influenceofthepressureontheimprovementofcoefficientofper formance. Theconfigurationconsideredisthat of anabsorption refrigeration machinewith doubleeffect. It works withthreepressures.

      High-pressureofbouilleur2andcondenser

      low pressureofthe evaporatorandtheabsorbeur1. The use of asecondbouilleur1powered bybinarysolutioncan raisethe thirdpressureabsorber2itthen beingan intermediate pressurebetween the low pressureevaporatorand the high pressuregenerator2(Figure

      2).

   2. ABSORPTIONSYSTEM

      Refrigerationabsorptionphenomenathatusebinarysolutionsa bsorbingvaporsandothersolutionswithinthisdefinedtemperat ures.Itthen callsabsorption, thefixationof a substancebythe entire volume ofthe absorbent material.

      We knowthatthevaporof a pure substancecanbeabsorbedbythe bodyin the liquid statethan in the casewherethe liquid temperatureis lower than thatofthevapor, unlike thepure substances, solutions havingtheremarkableproperty of absorbingthevaporoftheliquidsolutionofa differentcompositionevenifthe liquid temperatureishigher thanthevapor [2].

      Liquidabsorptionmachinesoperate usingthe powerof certain liquidabsorbing(exothermicreaction)anddesorption(endothe rmic reaction)vapor.

      Anabsorption systemcomprises afirstassembly (condenser, expansion valve, evaporator)whereinisthepurerefrigerant.

      Thesemachines useabinaryworking fluidmixture, whichisacomponentof themuch more volatilethan the other,isthe refrigerant [1].

      Two couplesare mainly used:

      • Water /LithiumBromide(H2O/LiBr)

        Ammonia/ Water (NH3/H2O)

        We can expressthe composition of thesolutioninthe most volatile component(refrigerant), ortheless volatilecomponent(absorbent).

      • Diluted solution(absorbing) or richsolution(refrigerant).

      Concentrated(absorbing) or poorsolution(refrigerant).

      3 2

      Fig1. Absorption refrigeration machineNH /H O.

      proposedbyM.Feidt[4]which combinestheGibbs free energyforthe thermal properties and the equations that calculatethebubble pointandthedew point of themixture. This method combinesthe advantages of bothandeliminatesthe need foriterationsin order to haveconditionsofequilibriumphases.

      The knowledge ofclimatic and geographicalcharacteristics, of the studied region, is averyimportant factor inthe study.These elementsare variable,butwe can estimatea monthly average[5].

      Afterdeterminationsofdifferentmass and energyequationsof the different elementsoftheinstallation,table belowpresents

      thedifferentequationsformass flow ratesatdifferentpoints of

   3. INSTALLATIONABSORPTIONDOUBLE EFFECT

      The absorption machine is, for us, the heart of the whole system of solar cooling. It therefore seemed interesting to see how these machines are modeled. In this regard, there are generally two approaches [3]: The first is based on a phenomenological description of each component of the machine. This approach is based on different energy balances to couple the four components of the machine.

      The second which is probably the most usedperformance evaluation by an empirical modelwhich isgenerally smoothing curves based on manufacturer's data. Indeed, these are tests that establish a simple correlation customary for the COP and the cooling capacity of the machine. Correlations are thus valid for the range of tests and tested the machine model studied.

      Fig 2: Installing doubleeffect absorption(studied)

      To establishthe heat balanceof any componentandtosize theheat transfer surfacesthat are associated with, it is necessary to know preciselytheenthalpyofworking fluidin the liquidandgaseous stateas a function oftemperatureand concentration.

      Among theexistingmodels, we have chosenthe one

      theinstallation.

      TABLE1.DETERMINATIONSFLOW RATESOF THE EQUATIONSOF DIFFERENT ELEMENTSOF THE INSTALLATION.

      elements	mass flow(kg/s)
      1	m 1
      2	m 2 = m 1
      3	m 3 = m 1
      4	m 4 = m 1
      5	x4 x5 m 5 = m 1 1 + x5 x10
      6	m 6 = m 5
      7	m 7 = m 5
      8	m 8 = m 10
      9	m 9 = m 10
      10	x4 x5 m 10 = m 1 x5 x10
      11	m = m 1 1 x4 x5 11 2 x5 x10
      12	m = m 7 = m 1 1 + x4 x5 12 2 2 x5 x10
      13	x1 x15 m 13 = m 1 1 + x15 x16
      14	m 14 = m 13
      15	m 15 = m 13
      16	x1 x15 m 16 = m 1 x15 x16
      17	m 17 = m 16
      18	m 18 = m 16
      19	m = m 7 = m 1 1 + x4 x5 19 2 2 x5 x10

      x x

      4 5

      x5 x10

      1

      m

      = 1 +

      m

      20

      V. COEFFICIENT OFPERFORMANCE

      20

      2

      Q

      x1 x15

      + 2 x15 x16

      COP

      COP = évap

      Qbou 1 + Qbou 2 + Wp1 + Wp2

      (1)

   4. THERMODYNAMIC STUDYOF THE

      SYSTEMSTUDIED

      For theapplication of the principlesof thermodynamicson a realcycle, conditions and assumptionswere used:

      1. Temperaturesinparts of the plant(boiler, condenser, absorberandevaporator) are assumed uniform throughoutthevolumein question.

      2. Solutionrich inrefrigerantat the outletof the absorber issaturatedat the temperatureandtheconcentrationin the absorberliquid. Likewise, the weak solutionleaving therefrigerantgeneratorisconnectedbyabalanceofpressurea nd temperaturerelationshipof theconcentrationgenerator.

      3. Thecoolant leavingthe boileris taken assaturatedvaporat the temperatureandcorresponding pressure.

      4. Thecoolant leavingthe condenseris taken asthesaturated liquid atthe sametemperatureandpressure.

      The refrigerantat the outletofthe evaporatorisin the form ofsaturated steam atthetemperature andlow pressureof the evaporator.Theisenthalpicexpansionsare assumed.

      Heat exchange withthe environment andlossesare assumednegligible.

      Calculations are

      basedonthedeterminationoftherespectiveenthalpiesoftheli quid phaseandvapor phasefrom the analyticalexpressionsoftheGibbs energy[6], knowing the pressure, temperatureandtheconcentration of the solution. We mustalso determine thequantitiesofvapor-liquid equilibriumofbinary pairammoniawaterfrom thePeng- Robinson equation[7]and

      theinteractioncoefficientKijcharacterizing themixing torque.

      For the determination ofvarioussystem parametersenthalpies(Hi) and titles(Xi), there are twomethods:either fromempiricalequations orfrom the diagramofMeckelandOldham.

      Inour case,we useddiagramsforthedetermination of these parameters.

      Our workisspentona pressure rangethatvaries from 2 to20 bars.

      The choice of ahighpressureof 20 bars,forthis case,leads us toaTitle Xtends to 1.

      = m 3(h4 p)

      m 8h8 + m 11 p1 m 12p2 + m 1p + m 16 p6 m 15p5

      + m 6 p p + m 13 (p4 p3 ) (2)

      1. SIMULATION

         Thesimulation is based onthe heat balancefor the different phasesof theabsorption cycle[6]: Oursimulationis madewith the aimof seeing thevariationofCOPdepending on

         thedifferenttemperaturelevelstoelements of theinstallationwithconstant pressureabsorption.

         Fig 3:EvolutionofCOPon thetemperature variationofboiler 2(T1).

         Fig 4:EvolutionofCOPon thetemperature variationofboiler1(T11).

         Fig 5:EvolutionofCOPon thetemperature variationof theabsorber1(T5).

         Fig 6:EvolutionofCOPon thetemperature variationof theevaporator(T4)

      2. INTERPRETATION OFRESULTS

         It is important to choose the right temperatures and pressures of running an absorption machine (NH3/H2O) at boiler, evaporator and absorber. Figure [3]

         It is noted that the variation of COP is inversely proportional with the temperature at the boiler 2: The COP decreases with increasing temperatures of the boiler 2 (T1) in the temperature range 70 °C T1 88 °C. In this interval, it is noted that decreases with the pressure decrease.

         Figure [4]

         It is noted that the variation of COP is inversely proportional with the temperature at the boiler 1: The COP decreases with increasing temperatures boiler 1 (T11) in the same temperature range We note also that the COP decreases with the pressure decrease.

         Figure [5]

         It is noted that the variation of the COP is proportional with the temperature at the absorber 1: the COP increases with increasing temperatures absorbeur1 (T5) in the temperature range 30°C T5 48°C and in this interval it is noted that the variation of the COP is inversely proportional with pressure: COP decreases with increasing pressure.

         Figure [6]

         It is noted that the variation of COP is proportional with the temperature at the evaporator: the COP increases with increasing temperatures of the evaporator (T4) in the

         temperature range -20°C T4 0°C and decreases with increasing pressure.

      3. GENERAL CONCLUSION

         In order to improve COP and reduced cost for solar absorption refrigeration, this work is devoted to geometric changes to an absorption chiller (dual engine effects constitute two boilers, condenser, evaporator and two absorbers) as the latter can operate with solar panels plans. This study allowed us to analyze the absorption refrigeration systems coupled with solar energy. Thermodynamic analysis of the refrigeration cycle with double effect absorption running torque (NH3/H2O) showed that the boiler temperature is inversely proportional to the coefficient of performance of the installation the latter more(COP) with the proportional pressure level of boilers. On the other hand, the temperature of evaporator and absorber are in proportion with the COPof the installation. The COP is very important for low pressure at the evaporator.

         The geometric modifications we made on this system (number of boilers)does not require distillation column.

         Their operationis possible fromtemperatureswhich varygoshawks70°C.The possibility of using solar collectors, less expensive and available in the market,allows us to reduces the overall cost of this type of facilities.

         NOMOCLATURE REFERENCE

         Nomenclatures	Désignations	Unité
         T	Température	K
         P	Pression	Pa
         X	Titre du frigorigène ou de l'absorbant dans la solution	%
         Q	Puissance	Kw
         Qe	Puissance frigorifique de lévaporateur	Kw
         Qb	Puissance frigorifique de bouilleur	Kw
         Qc	Puissance frigorifique de condenseur	Kw
         Wp	Puissance de la pompe	Kw
         H	Enthalpie	KJ/kg
         	Débit massique	Kg/s
         COP	Coefficient de performance	–

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