Performances Assessment of Natural Refrigerants as Substitutes to CFC and HCFC in Hot Climate

Transcription

1 Int. J. of Themal & Envionmental Engineeing Volume, No. 2 (2) 25- efomances Assessment of Natual Refigeants as Substitutes to CFC and HCFC in Hot Climate M. Boumaza * Depatment of Chemical Engineeing, College of Engineeing, King Saud Univesity, Saudi Aabia Abstact Due to the envionmental concens ozone depletion potential (OD) and global waming potential (GW) of the existing efigeants, industy and eseaches in this field ae investigating long-tem solutions. With extensive wok on altenatives to chloofluoocabons (CFCs) and hydo chloofluoocabons (HCFCs), initially hydo fluoocabons wee consideed to be long-tem solutions. The global waming of HFCs has become a hudle to accept them as long-tem solutions. Now, the focus is on the use of natual efigeants like hydocabons (HCs) such R29, R, ammonia, cabon dioxide and wate. These natual substances have vey low GW, and a zeo OD. This pape pesents simulation esults though a themodynamic analysis of R22 and thee of its altenatives natual efigeants (R29, Ra and R77) fo A/C and efigeation puposes opeating unde vaious outdoo tempeatues, epesented by the condense tempeatues. The examined new efigeants show vaying pefomance, depending on the evapoato tempeatues, but in evey case, the condense tempeatue seems to have an impotant impact on the pefomance of the cycle. Keywods: efigeants, substitutes, envionment, ozone, pefomances.. Intoduction Woldwide attempts ae being made to phase out the poduction and consumption of chloo fluoocabons, as these chemicals ae esponsible fo depletion of statospheic ozone laye. Refigeation, A/C and heat pumps sectos ae one of the pincipal uses of these chemicals. Duing the last decade, the numbe of efigeants likely to be used in efigeating machines has damatically inceased as a consequence of the elimination of the CFC s and HCFC s R22 (HCFC 22) is one of the impotant efigeant used in ai conditioning all ove the wold. R22 is contolled substance unde the Monteal otocol. It has to be totally phased out by 27.. In Euope, HCFCs have aleady been phased out in new equipment in 22, and the total phase out of HCFCs is scheduled in 25. HCF 22 eplacements options fo A/C, heat pumps and efigeation systems can be gouped in thee categoies, Fluoocabons that ae used in conventional vapo compession cycles such as Ra, Ra, R7C, altenatives fluids which include popane R29 and R77 and ae also used in vapo compession cycles, and finally altenatives cycles that include absoption systems, and use Tan citical fluids (CO2 and R7) and ai cycle. In geneal these altenative * Coesponding autho. Tel.: mouadb@ksu.edu.sa 2 Intenational Association fo Shaing Knowledge and Sustainability DOI:.5/ijtee..2. technologies do not cuently offe the same enegy efficiency as the vapo compession cycle. Seveal investigations have been caied out in ode to detemine the efficiency of potential substitutes to R22.Muee et al [] compaed the pefomances of R22 and R A woking at elevated condensing tempeatues up to.chin and Spatz [2] exploed some of the advantages and disadvantages of R A, and othe substitutes to R22. Bename et al [] have povided woking chaacteistics to optimize the components of the efigeating machines, while some epoted eseach [-7] concened specific outdoo tempeatues, as well modifications of the efigeation compession cycle. Devotta et al [9] as well othe eseaches [-2] has pesented a pefomance evaluation of R29 and othe natual efigeants as a dop substitute to R22 in a ai conditioning applications.. This pape pesents compaative themodynamic analyses of R22 and thee of its altenatives natual efigeants (R29, R, and R77) fo A/C and efigeation puposes opeating unde high and low outdoo tempeatues. These natual substances have the dual advantage of vey low global waming, nealy zeo and zeo depletion. Table pesents the envionmental data of selected efigeants. The study enables to detemine the effect of the condense and evapoato tempeatues on the coefficient of pefomance, the volumetic efigeating capacity, as well as the compesso dischage tempeatue. 25

2 Boumaza / Int. J. of Themal & Envionmental Engineeing, (2) 25- Table. Expeimental data of some efigeants Refigeants OD GW (time hoizons of yeas) 2. Refigeation cycle CFC CFC2 HCFC22 HCFC2 HFCa HFC52a R7C The efigeation cycle studied is a vapo compession cycle composed of fou main equipments: Evapoato, Compesso, Condense and a thottling valve as illustated in figue, while figue 2 shows the coesponding -h diagam. The following assumptions ae made: An evapoation at constant pessue, in the evapoato with an evapoato tempeatue, T ev, fom h to h. An adiabatic isentopic compession pocess in the compesso, coesponding fom () to (2) (h to h2). RA HC29 HCa R77 Wate CO < < A de supeheating followed by a condensation at (T=T c ) and pessue in the condense, fom (2) to (). (h 2 to h ). An expansion at constant enthalpy in the thottling valve, coesponding fom point to point (h = h ). The vapou leaving the evapoato as well as the liquid leaving the condense ae supposed to be at satuated states. Figue: Standad Vapo Compession Cycle 2

3 Boumaza / Int. J. of Themal & Envionmental Engineeing, (2) 25- Figue 2 Themodynamic -h Diagam. Modelling basis A Simulation model was developed in ode to investigate the effect of the evapoato and condense tempeatues (epesenting the ambient tempeatues) on the coefficient of the pefomance of the cycle (CO), the volumetic efigeating capacity (VRC), the compesso dischage tempeatue (T c ), and the compesso load capacity. The equied data fo the model ae: Specifying the natue of the efigeant by fixing the physical and themodynamics popeties. Fixing T ev and T c. Fixing eithe the mass flow ate of the efigeant o the efigeation capacity. The model enables to estimates the evapoato and condense pessues ( ev and c ), the compesso dischage tempeatue (T c ), as well as the diffeent enthalpies involved in the cycle. The themodynamic and tanspot popeties of the efigeant ae detemined though chemical themodynamics elations. Mass balances and enegy balances ae used to deive expession fo the Coefficient of efomance and the efigeation capacity. Fo the cycle studied, the main mechanical powe supplied to the system is supposed to be the powe supplied to the compesso, cp. Mass flow ate of the efigeant; is, M h 2 h () h = h (2) Enegy equied in the compesso (load) cp h h2 M ( h h2 ) ( ) () h h Enegy libeated in the condense cd h h2 M ( h h ) ( ) () h h Volumetic Flow ate (VRC) G M va (5) q q= Specific volumetic efigeation load, 27

4 C O C O C O Boumaza / Int. J. of Themal & Envionmental Engineeing, (2) 25- Coefficient of the pefomance, CO CO=Refigeation load / compesso load Detemination of the pessue at the end of compession Fo an adiabatic compession and an ideal gas CO h h h h R 2 () C. V cons tan t γ = Cp/Cv ; calculated at one atmosphee and C () The CO of the ideal cycle can be defined as follows CO Satuated pessue T ev ideal (7) Tev TC The empiical equations poposed by Lee and Kesle [] is used to estimate the satuated pessues, which is as follows sat f ( T ) w. f ( T ) sat = Reduced essue at the satuation liquid vapou f sat sat = elative fugacity at zeo ode (w=) c () (9) Using the ideal gas law and the tempeatue, equation () becomes,.. T cons tan t. Results () The calculations wee pefomed fo thee potential substitutes to R22, as well as R22, by consideing thee diffeent condensing tempeatues, and investigating the effect of the evapoato tempeatues on the coefficient of pefomance, the volumetic efigeating capacity the compesso load and the dischage tempeatue.. Coefficient of the pefomance (CO) Figues (f-g) show the vaiation of the CO with vaious evapoating tempeatues anging fom C to C, and fo thee condensing tempeatues (C, C, 5C), fo the altenatives efigeants consideed, as well fo the R22. It can be seen fom these figues that the CO vaies linealy with the evapoato tempeatue fo all the cases studied.. R 29 seems to be simila to R22, showing simila tends and simila vaiation fo all the cases studied. Ammonia and Ra exhibits smalle CO than R22, when opeating unde simila conditions. R 77 Tc 5 5 R 29 Tc 5 R a Tc Te [ ] T [ ] Te [ ] [ f ] [ g ] [ h ] Figue : Vaiation of the Coefficient of pefomance with espect to Tev and Tcond, fo the new efigeants and R22. (f) R22 / R 77, (g) R22 / 29, (h) R22 / a 2

5 uissance du compésseu (kw) uissance du compésseu [ kw ] uissance du compésseu [ kw ] uissance volumétique [kj/m ] uissance volumétique [kj/m ] uissance volumétique [kj/m ] Boumaza / Int. J. of Themal & Envionmental Engineeing, (2) Volumetic efigeating capacity Figues (f-g) show the effect of the evapoating tempeatues on the volumetic efigeating capacity (VRC) fo thee condensing tempeatues (C, C and 5C). It is seen that R29 which has a citical tempeatue below C, exhibits value of VRC close to the R22 values, fo the thee condensing tempeatues consideed. Ra gives lowe values of VRC, while ammonia on the hand show lage values of VRC, compaed to R22, but these values stat deceasing the evapoato tempeatues decease. Vaiation of the compesso load Figues 5 (f-g) show the vaiation of the compesso load with espect to the evapoato tempeatues fo thee diffeent condensing tempeatues (C, C, 5C). It is well known that the pessues have a diect impact on the pefomance of the cycle, moeove, the le lowe the pessue atio, the less enegy is equied to dive the compesso. It can be seen fom these figues that R29 show a slightly lowe values than R22, while ammonia and Ra exhibit espectively a highe value of 22% and % than R22. It can be seen fom this analysis, that ammonia possesses vey inteesting themodynamic popeties, such as its high latent heat but it exhibits dangeous popeties such as its flammability, toxicity, and theefoe the diect substitution of R22 to ammonia equies impotant changes to the existing equipment in ode to esist ammonia. R29 has physical popeties and themodynamic pefomances simila to R22, but with lowe flow ate, and theefoe equiing smalle equipment. This suggests its ecommendation as a potential substitute to R22. R, which is a flammable efigeant but less hamful to envionment, can also be a potential substitute to R22, despite its lowe themodynamic pefomance R R 29 Tc R a Tc Tc Te [ ] T [ ] Te [ ] [ f ] [ g ] [ h ] Figue : Vaiation of the volumetic efigeating capacity of the new efigeants studied and R22 with espect to Te and Tc (f) R22 / R 77, (g) R22 / 29, (h) R22 / a R 77 Tc R R a Tc Te [ ] [ f ] Te [ ] [ g ] Te [ ] [ h ] Figue 5: Vaiation of the compesso load with espect to Tev and Tcond fo the new efigeants and R22 (f) R22 / R 77, (g) R22 / 29, (h) R22 / a 29

6 Boumaza / Int. J. of Themal & Envionmental Engineeing, (2) Conclusions It is evident that today, seveal new efigeants whethe pues, mixtues o natuals, ae poposed to eplace R22. R29 (popane), R (iso butane) and R77 (ammonia), which ae consideed natual efigeants, seem to be the best potentials candidates to use efigeation, ai conditioning and heat pumps, as new lubicants have also been developed to opeate with these efigeants. The pesent analysis has enabled to show that,. R 29 may be diectly used a substitute to R22, fo smalle efigeation load, while ammonia which possess excellent themodynamic pefomance equies specific mateials due to its dangeous physical popeties. Fluids having low citical tempeatue exhibit an impotant decease in cooling capacity. Rate of compesso powe incease is simila fo all fluids. The new efigeants studied have lowe compesso dischage tempeatues than the R22, and theefoe will equie compessos opeating unde less seve conditions. h: Enthalpy (kj/kg) Nomenclatue M: Mass flow ate of the efigeant (kg/sec) c : Condensing essue (ba) ev : Evapoato essue (ba) sat = Satuated pessue (atm) c = Citical pessue (atm T c : Condensing tempeatue ( C) T ev : Evapoato tempeatue ( C) T comp : Compesso dischage tempeatue (ºC) V: Volume m γ: Ratio of the specific heat constant (C p /C v ) Acknowledgment The autho is vey gateful and thankful to d the eseach cente of the college of engineeing, King Saud Univesity, Riyadh, Kingdom of Saudi Aabia fo thei help and financial suppot which have enabled to conduct this pesent eseach. Refeences []. Meue.C, Buyle O, aulus, Compaison of R22 and Ra at elevated condensing tempeatues,, ROC 2th Intenational Congess of Refigeation, Sydney. [2]. Chin L, Spatz M.w, Issues elating to the adoption of R a In ai conditioning systes., ROC 2th Intenational Congess of Refigeation, Sydney. []. Bename A, Clodic D, 999, test bench fo compaative measuement of enegy efficiency of vaiable and fixed speed scoll compesso. []. Samuel F.Yana Motta, Domanski..A, efomance of R22 and its altenatives woking at high outdoo tempeatues, th Intenational Refigeation confeence, udue Univesitu, W.lafayetet, USA, 2. [5]. Robets.N.A; Detemination of the pefomance, leak scenaio flammability, and oil etun chaacteistics of a novel R22 eplacement, oceedings of the intenational efigeation confeence, udue, 99. []. Robets.N.A, Jawad.S.H; Investigation of the vapou-liquid equilibium behaviou of blends compising R25, Ra, and R o Ra, oceedings of the intenational efigeation confeence, udue, 2. [7]. Baumont.E, Fee.M, ilatte.a, simulation of efigeating machines, influences of the heat exchanges design fo low efigeant chages pn the woking point, Zeo leakage confeence, Intenational Institue of efgeation, Stockolm, 22. []. Samuel.F Yanna Motta, Domanski..A, efomance of R22 and its altenatives, oceedings of the intenational efigeation confeence, udue, 2. [9]. Devotta.S, adalka.a.s, Sane.N.K; efomance of HC 29 as a dop in substitute to HCFC 22 in a window ai conditione, Intenational jounal of efigeation, Vol 2, No, 25. http.dx.doi.og/./j.ijefig.2.9. []. Devotta.S, Waghmae.A.V, Sawant.B.M; Altenatives to HCFC -22 fo ai conditiones, Applied themal engineeing, Vol 2, No, 2. http.dx.doi.og/./s59-()79-x []. Hwang.Y, Gado.A, Rademache.R; efomance popane in a unitay heat pump, 2 st Intenational congess of efigeation, Washington, USA, 2. [2]. Loentzen.G; The use of of natual efigeants, a complete solution to CFC/HCFC pedicament, Intenational jounal of efigeation, Vol, No, 995. http.dx.doi.og/./-77(9)-e []. Smtith, Van Noss, Abott, Intoduction to Chemical Engineeing Themodynamics, 7 th edition, Ma c Gaw Hill.