DOĞAL VE SENTETİK SOĞUTUCU AKIŞKAN ÇİFTLERİ KULLANILAN BİR KASKAD SOĞUTMA SİSTEMİNİN ULTRA DÜŞÜK SICAKLIK UYGULAMALARI İÇİN TEORİK ANALİZİ

Öz

Bu çalışmada, ultra düşük sıcaklık (UDS) (-50 oC ile -100 oC) uygulamalarında farklı dizayn ve çalışma parametrelerinin kaskad sistem performansına etkilerini incelemek için EES yazılımı kullanılarak teorik bir model oluşturuldu. Kaskad sistemlerde kullanılan sentetik soğutucu akışkan çiftine çevre dostu bir alternatif bulmak için doğal ve sentetik soğutucu akışkan çiftleri için analiz yapıldı. Önerilen modelde; yüksek sıcaklık çevrimi (YSÇ) yoğuşma ve düşük sıcaklık çevrimi (DSÇ) buharlaşma sıcaklıkları ve kaskad ısı değiştiricisi sıcaklık farkı gibi parametrelerinin etkileri incelendi. Ayrıca, UDS uygulamalarında aşırı soğutma şartlarına ulaşabilmek için kritik çalışma parametreleri olan genleşme valfi sonrası soğutucu akışkanın buhar kalitesi ve ön soğutma amaçlı ısı değiştiricisi kapasitesinin sistem performansına etkileri incelendi. Bu çalışmada UDS uygulamalarında kullanılabilecek doğal akışkan alternatiflerinin performans ve çevresel etkileri açılarından teorik olarak karşılaştırılmalarına katkıda bulunulmaktadır. Yapılan analiz çalışmaları sonucunda soğutma sisteminde R1270/R170 doğal soğutucu çiftinin kullanılması ile, R404A/R508B sentetik soğutucu çiftine kıyasla %5 civarında daha iyi sistem performans katsayısı ve yaklaşık olarak yarısı kadar CO2 emisyon salımı gerçekleştiği belirlendi.

Anahtar Kelimeler

• Ultra Düşük Sıcaklık
• Kaskad Soğutma Sistemi
• Doğal Akışkanlar
• STK
• TEWI

THEORETICAL ANALYSIS OF A CASCADE REFRIGERATION SYSTEM WITH NATURAL AND SYNTHETIC WORKING FLUID PAIRS FOR ULTRA LOW TEMPERATURE APPLICATIONS

Öz

In this study, a theoretical model is established using Engineering Equation Solver (EES) software in order to investigate the effects of different design and operation parameters on the performance of the cascade systems for Ultra Low Temperature (ULT) between -50 oC and -100 oC. The analysis is performed for natural and synthetic refrigerant pairs to find an environmentally friendly alternative to commercial synthetic refrigerants. Effects of common parameters such as the evaporation temperature of low temperature cycle (LTC), the condensation temperature of high temperature cycle (HTC) and the temperature difference in the cascade heat exchanger (HX) have been investigated with the proposed model. Furthermore, influence of operation parameters including vapor quality of the refrigerant after the expansion valve and the precooler heat exchanger (PCHX) capacity, crucial to reach ULT conditions, on the system performance are examined. This study also contributes to the theoretical evaluation of the feasible natural refrigerant alternatives for ULT applications and the comparison of these refrigerants with synthetic ones in terms of performance and the environmental aspects. It is found that the natural refrigerant R1270/R170 pair results in about 5% better COP and almost half less CO2 emissions compared to synthetic refrigerant R404A/R508B pair.

Anahtar Kelimeler

• Ultra-Low Temperature
• Cascade Refrigeration System
• Natural Refrigerants
• COP
• TEWI

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