Ayşe ATMACA, Aytunç EREK, Orhan EKREN, Mustafa ÇOBAN

EJEKTÖR GENLEŞTİRİCİLİ TRANSKRİTİK SOĞUTMA ÇEVRİMİNİN R744, R170 VE R41 İÇİN TERMODİNAMİK PERFORMANSI

On yıldan fazla bir süredir sıkı çevresel yönetmeliklerin küresel ısınma potansiyeli değeri kısıtlamalarına uyan çevre dostu soğutkanları bulmaya yönelik önemli bir arayış sözkonusudur. Aday akışkanlar arasından R744 (karbondioksit veya CO2), R170 (etan) ve R41 (florometan) bu çalışmada parametrik olarak incelenmek için seçilmiştir. Performans karşılaştırmaları üç soğutkan için ayrı ayrı hem transkritik (süperkritik) soğutma çevriminde hem de bu çevrimin ejektör genleştiricili olarak geliştirildiği soğutma çevriminde yapılmıştır. Birinci adım olarak, gaz soğutucu çıkış sıcaklığının, buharlaştırıcı sıcaklığının ve buharlaştırıcı çıkışındaki kızgın buhar sıcaklığının buharlaştırıcıya göre sıcaklık farkının toplam performans ve yüzdesel genleşme kayıplarına etkileri belirli bir gaz soğutucu basıncı aralığında incelenmiştir. Buharlaştırıcı çıkışındaki kızgın buhar için sıcaklık farkı performans üstündeki en az etkili parametre olarak bulunmuştur; böylece transkritik ejektör genleştiricili soğutma çevrimi sadece buharlaştırıcı sıcaklığı ve gaz soğutucu çıkış sıcaklığı için bir önceki analizlerle aynı gaz soğutucu basıncı aralıklarında incelenmiştir. Termodinamik modeller Matlab® ortamında oluşturulmuştur ve ejektör genleştiricili soğutma çevrimi için ejektör denklemleri sabit basınçta karışım varsayımına göre elde edilmiştir. Düşük kritik sıcaklığa sahip olan bu üç soğutkan arasındaki performans, yüzdesel kısılma kayıpları ve genleşme vanasının yerine ejektörün kullanılması ile oluşan performans iyileştirme potansiyeli kıyaslamaları, literatürdeki önceki araştırmalara katkı yapabilmek adına makalenin temel hedefini oluşturmaktadır.

Anahtar Kelimeler:

R744 (karbondioksit), R170 (etan), R41 (florometan), Genleşme kayıpları, Ejektör genleşmeli soğutma çevrimi, Sabit basınçta karışımlı ejektör

THERMODYNAMIC PERFORMANCE OF THE TRANSCRITICAL REFRIGERATION CYCLE WITH EJECTOR EXPANSION FOR R744, R170, AND R41

For more than a decade, there is a great demand for finding environmentally-friendly refrigerants obeying the global warming potential value restrictions of the tough environmental legislation. Among the candidate working fluids, R744 (carbon dioxide or CO2), R170 (ethane), and R41 (fluoromethane) are selected to be investigated parametrically in this paper. Performance comparison is made for these three working fluids individually in both transcritical (supercritical) refrigeration cycle and modification of this cycle with ejector expansion. As the first step, the effects of the gas cooler outlet temperature, evaporator temperature, and evaporator outlet superheat temperature difference on the overall performance and percentage expansion losses are investigated within a specific gas cooler pressure range. Evaporator outlet superheat temperature difference is found to be the least effective parameter on the performance; hence, secondly, the transcritical ejector expansion refrigeration cycle is analyzed considering only evaporator temperature and gas cooler outlet temperature based on the same gas cooler pressure ranges. Thermodynamic models are constructed in Matlab® and the ejector equations for the ejector expansion refrigeration cycle are established with reference to constant pressure mixing assumption. Comparisons of the performance, percentage expansion losses, and performance improvement potential through the implementation of the ejector instead of the expansion valve among these three refrigerants having low critical temperatures represent the main objective of the paper in order to make contributions to the previous researches in the literature.

Keywords:

R744 (carbon dioxide), R170 (ethane), R41 (fluoromethane), Expansion losses, Ejector expansion refrigeration cycle, Constant pressure mixing (CPM) ejector,

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