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Authors
Advisor(s)
Abstract(s)
O signatĆ”rio da tese trabalhou aproximadamente oito anos em assistĆŖncia tĆ©cnica e
manutenĆ§Ć£o em sistemas de AVAC&R (Aquecimento VentilaĆ§Ć£o e Ar Condicionado &
RefrigeraĆ§Ć£o) sendo que pretendeu aprofundar os seus conhecimentos sobre os
fluidos frigorigƩneos naturais, nomeadamente do R-744, motivo pelo qual surgiu o
tema da presente dissertaĆ§Ć£o.
Com a finalidade de perceber os altos e baixos do R-744, analisou-se a histĆ³ria dos
fluidos frigorigƩneos e constatou-se que pode haver um enquadramento em cinco
geraƧƵes. A transiĆ§Ć£o da primeira geraĆ§Ć£o (qualquer fluido frigorigĆ©neo era utilizado)
para a segunda geraĆ§Ć£o (melhorar a fiabilidade e preservar a seguranƧa e a
durabilidade dos equipamentos e dos frigorigƩneos) resultou em diversas
oportunidades de melhorias tecnolĆ³gicas. As prĆ³ximas duas transiƧƵes, terceira
(proteĆ§Ć£o do ozono) e a quarta (mitigaĆ§Ć£o do aquecimento global) resultaram em
alteraƧƵes regulamentares para a proteĆ§Ć£o ambiental e, mais tarde, em oportunidades
de negĆ³cios. O R-744 deu os primeiros passos na primeira geraĆ§Ć£o por volta dos anos
60 do sƩculo XIX e teve o auge na dƩcada de 30 do seculo XX. Nos anos 60 do sƩculo
XX, durante a segunda geraĆ§Ć£o, perdeu importĆ¢ncia e quase foi extinto, fruto da
depressĆ£o, fraca modernidade da tecnologia e o aparecimento dos fluidos CFCs e
HCFCs. Na dĆ©cada de 90 do sĆ©culo XX, terceira geraĆ§Ć£o, o R-744 reaparece devido Ć
revisĆ£o da tecnologia de refrigeraĆ§Ć£o e por motivo ecolĆ³gico.
O R-744 destaca-se dos outros fluidos frigorigĆ©neos naturais por ser o Ćŗnico nĆ£o
inflamĆ”vel, nĆ£o tĆ³xico (nĆ£o excedendo os 4 a 5% de concentraĆ§Ć£o), com possibilidade
de operar num ciclo de compressĆ£o de vapor abaixo de 0 Ā°C e com a caracterĆstica de
ser o mais econĆ³mico no processo de produĆ§Ć£o. Verificou-se que o R-744, devido Ć s
suas propriedades, Ć© um frigorigĆ©neo que trabalha em ciclo subcrĆtico de compressĆ£o
de vapor ou transcrĆtico de compressĆ£o de vapor. Foram inĆŗmeras as dificuldades iniciais para recolher informaĆ§Ć£o sobre os sistemas
transcrĆticos com R-744 dado que ainda Ć© uma tecnologia que estĆ” em
desenvolvimento e a informaĆ§Ć£o disponibilizada pelos fabricantes Ć© reduzida.
Quando o R-744 trabalha em subcrĆtico, o lado da alta pressĆ£o do circuito situa-se
abaixo do ponto crĆtico (31 Ā°C, 73,6bar) e encontra-se num processo convencional
habitualmente chamado de ācondensaĆ§Ć£oā. Quando o R-744 trabalha em transcrĆtico,
acima do ponto crĆtico, nĆ£o existe condensaĆ§Ć£o e nĆ£o Ć© possĆvel transferir calor latente
do āgas coolerā para o meio ambiente, existindo sĆ³ transferĆŖncia de calor sensĆvel.
Constatou-se que, para o ciclo transcrĆtico com o R-744 ter melhor desempenho, tem
que se recorrer a tecnologia adicional como a compressĆ£o paralela, ejetores, entre
outras.
Na presente dissertaĆ§Ć£o mostraram-se vĆ”rias aplicaƧƵes reais, subcrĆticas e
transcrĆticas, com a finalidade de transmitir que o R-744 pode ser aplicado em
qualquer situaĆ§Ć£o, sendo apenas uma questĆ£o de tecnologia. Com o anteprojecto da
instalaĆ§Ć£o pretendeu-se demonstrar a complexidade e o custo de uma central de
refrigeraĆ§Ć£o transcrĆtica R-744 do retalho alimentar.
A presente dissertaĆ§Ć£o teve por finalidade verificar se o R-744 era um fluido
frigorigĆ©neo viĆ”vel na refrigeraĆ§Ć£o e ar condicionado ao nĆvel tĆ©cnico e econĆ³mico. A
conclusĆ£o que se chegou Ć© que o R-744 Ć© um fluido frigorigĆ©neo natural viĆ”vel e, nos
Ćŗltimos anos, existiu um aumento de sistemas supercrĆticos de refrigeraĆ§Ć£o no retalho
alimentar.
Importa, por fim, salientar que, ao nĆvel dos equipamentos de ar condicionado,
existem vĆ”rias aplicaƧƵes mas atĆ© ao momento nĆ£o se verificou uma aposta de grande
escala pelos maiores fabricantes mundiais.
The signer of the thesis worked approximately eight years in technical assistance and maintenance in HVAC&R (Heating Ventilation and Air Conditioning & Refrigeration) systems and wanted to deepen its knowledge about the natural refrigerating fluids, namely the R-744, reason for which the subject of this dissertation. In order to perceive the ups and downs of R-744, the history of the refrigerating fluids was analyzed and it was verified that there can be a frame in five generations. The transition from the first generation (any refrigerant was used) to the second generation (improving reliability and preserving the safety and durability of equipment and refrigerators) resulted in several opportunities for technological improvements. The next two transitions, third (ozone protection) and fourth (global warming mitigation) transitions have resulted in regulatory changes for environmental protection and, later, business opportunities. The R-744 took its first steps in the first generation around the 60s of the XIX century and peaked in the 30s of the XX century. In the 60s of the XX century, during the second generation, lost importance and was almost extinct, fruit of depression, weak modern technology and the emergence of fluids CFCs and HCFCs. In the 90's of the XX century, the third generation, the R-744 reappears due to the review of refrigeration technology and for ecological reasons. The R-744 stands out from the other natural refrigerant fluids because it is the only non-flammable, non-toxic (not exceeding 4 to 5% concentration), with the possibility of operating in a steam compression cycle below 0 Ā°C and with the characteristic of being the most economical in the production process. It has been found that R-744, because of its properties, is a refrigerant which works in a subcritical steam compression or transcritical compression cycle of steam. There were numerous initial difficulties in collecting information on transcritical systems with R-744 as it is still a technology that is in development and the information provided by the manufacturers is reduced. When the R-744 works in subcritical, the high pressure side of the circuit lies below the critical point (31 Ā°C, 73,6 bar) and is in a conventional process usually called "condensation". When the R-744 works in transcritical, above the critical point, there is no condensation and it is not possible to transfer latent heat from the āgas coolerā to the environment, with only sensible heat transfer. It was found that for the transcritical cycle with R-744 to have better performance, it has to resort to additional technology such as parallel compression, ejectors, among others. In the present dissertation several real applications, subcritical and transcritical, have been shown, in order to convey that the R-744 can be applied in any situation, being only a matter of technology. With the preliminary design of the installation it was intended to demonstrate the complexity and the cost of a transcritical refrigeration plant R-744 of the food retail. The purpose of this dissertation was to verify if the R-744 was a viable refrigerant in refrigeration and air conditioning at the technical and economic level. The conclusion reached is that R-744 is a viable natural refrigerant and, in recent years, there has been an increase in supercritical refrigeration systems with it in the food flap. Finally, it should be noted that there are several applications at the level of air conditioning equipment but so far there has not been a large scale bet by the world's largest manufacturers.
The signer of the thesis worked approximately eight years in technical assistance and maintenance in HVAC&R (Heating Ventilation and Air Conditioning & Refrigeration) systems and wanted to deepen its knowledge about the natural refrigerating fluids, namely the R-744, reason for which the subject of this dissertation. In order to perceive the ups and downs of R-744, the history of the refrigerating fluids was analyzed and it was verified that there can be a frame in five generations. The transition from the first generation (any refrigerant was used) to the second generation (improving reliability and preserving the safety and durability of equipment and refrigerators) resulted in several opportunities for technological improvements. The next two transitions, third (ozone protection) and fourth (global warming mitigation) transitions have resulted in regulatory changes for environmental protection and, later, business opportunities. The R-744 took its first steps in the first generation around the 60s of the XIX century and peaked in the 30s of the XX century. In the 60s of the XX century, during the second generation, lost importance and was almost extinct, fruit of depression, weak modern technology and the emergence of fluids CFCs and HCFCs. In the 90's of the XX century, the third generation, the R-744 reappears due to the review of refrigeration technology and for ecological reasons. The R-744 stands out from the other natural refrigerant fluids because it is the only non-flammable, non-toxic (not exceeding 4 to 5% concentration), with the possibility of operating in a steam compression cycle below 0 Ā°C and with the characteristic of being the most economical in the production process. It has been found that R-744, because of its properties, is a refrigerant which works in a subcritical steam compression or transcritical compression cycle of steam. There were numerous initial difficulties in collecting information on transcritical systems with R-744 as it is still a technology that is in development and the information provided by the manufacturers is reduced. When the R-744 works in subcritical, the high pressure side of the circuit lies below the critical point (31 Ā°C, 73,6 bar) and is in a conventional process usually called "condensation". When the R-744 works in transcritical, above the critical point, there is no condensation and it is not possible to transfer latent heat from the āgas coolerā to the environment, with only sensible heat transfer. It was found that for the transcritical cycle with R-744 to have better performance, it has to resort to additional technology such as parallel compression, ejectors, among others. In the present dissertation several real applications, subcritical and transcritical, have been shown, in order to convey that the R-744 can be applied in any situation, being only a matter of technology. With the preliminary design of the installation it was intended to demonstrate the complexity and the cost of a transcritical refrigeration plant R-744 of the food retail. The purpose of this dissertation was to verify if the R-744 was a viable refrigerant in refrigeration and air conditioning at the technical and economic level. The conclusion reached is that R-744 is a viable natural refrigerant and, in recent years, there has been an increase in supercritical refrigeration systems with it in the food flap. Finally, it should be noted that there are several applications at the level of air conditioning equipment but so far there has not been a large scale bet by the world's largest manufacturers.
Description
Keywords
Fluidos FrigorigĆ©neos DiĆ³xido de Carbono RefrigeraĆ§Ć£o Ar Condicionado Refrigerants Carbon dioxide Refrigeration Air Conditioning