Research of the Effect of Different Circular Moist Object Geometries for Air Jet Impingement Drying on Heat and Mass Transfer

Abstract

Drying is one of the most used methods for long-term storage by removing water from food. The physical and chemical changes occurring during storage are minimal due to the reduction of considerable amount of water and microbial activity of the food. In the present study, the effect of the two different new moist object geometries with whole and reverse semi-circular on the heat and mass transfer enhancement of drying with air jet was numerically examined. The drying jet was a laminar and 2D jet stationed at a constant jet distance (H) from the moist object. The diameter of the moist object, jet distance from the moist object and jet initial height were fixed for all cases. Streamlines and isotherms were acquired around the objects for different jet Reynolds numbers. A finite volume method was used to solve the governing equations by using ANSYS Fluent 17.0 software program. Calculations were carried out for different Reynolds numbers, namely, Re=100, 200 and 300. It was found good agreement with experimental and numerical data available in the literature. The results showed that the geometry of whole circular moist object had better performance of heat and mass transfer than that of the reverse semi-circular moist object geometry. In addition, increasing Reynolds number showed a positive effect on heat and mass transfer. Locally, jet drying was found to be most effective near the stagnation point on the leading side of the objects.

Keywords

• Drying,Air jet impingement,Mass transfer,Moist object,Numerical analysis

HAVA JETİ ÇARPMALI KURUTMA İÇİN FARKLI DAİRESEL NEMLİ NESNE GEOMETRİLERİNİN ISI VE KÜTLE TRANSFERİ ÜZERİNDEKİ ETKİSİNİN ARAŞTIRILMASI

Abstract

Kurutma, gıdadan suyun uzaklaştırılarak uzun süreli depolama için en çok kullanılan yöntemlerden biridir. Kurutma ile gıdadaki su miktarı ve mikrobiyal aktivitenin önemli ölçüde azalması nedeniyle depolama boyunca meydana gelen fiziksel ve kimyasal değişimler en az seviyede olmaktadır. Bu çalışmada, iki farklı yeni nemli nesne geometrisi olan tam ve ters yarı dairesel nesnenin hava jeti ile kurutulmasının ısı ve kütle transferi artışı üzerindeki etkisi sayısal olarak incelenmiştir. Jet kurutması, nemli nesneden sabit bir jet uzaklığında (H) konumlandırılmış olup laminer ve iki boyutludur. İncelenen tüm durumlar için nemli nesnenin çapı, nemli nesneden olan jet uzaklığı ve jet giriş yüksekliği sabit olarak alınmıştır. Nesnelerin etrafındaki akım çizgileri ve eş sıcaklık eğrileri farklı jet Reynolds sayıları için elde edilmiştir. Korunum denklemlerini çözmek için sonlu hacim yöntemi olan ANSYS Fluent 17,0 bilgisayar programı kullanılmıştır. Hesaplamalar, Re = 100, 200, 300 olarak farklı Reynolds sayıları için yapılmıştır. Çalışmanın, literatürde var olan deneysel ve sayısal çalışmayla iyi bir uyum içerisinde olduğu bulunmuştur. Sonuçlar, tam dairesel nemli nesne geometrisinin ters yarı dairesel nemli nesne geometrisinden daha iyi ısı ve kütle transfer performansına sahip olduğunu göstermiştir. Ayrıca, Reynolds sayısının artışının ısı ve kütle transferi üzerinde olumlu bir etkiye sahip olduğu görülmüştür. Yerel olarak, jet kurutmanın nesnelerin ön taraflarındaki durma noktasına yakın daha etkili oldukları bulunmuştur.

Keywords

• Kurutma,Hava jeti çarpması,Kütle transferi,Nemli nesne,Sayısal analiz

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