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Dicle niversitesi Mhendislik Fakltesi mhendislik dergisi
*Yazmalarn yaplaca yazar: Mehmet Sira ZERDEM. [email protected]; Tel: (412) 248 80 30 (3540)
zet Soutma sanayinde scaklk ve nem kontrol byk nem tamaktadr. Laboratuvar ortamnda yaplan almalar maliyet art ve zaman kaybna neden olduu iin saysal analiz programlar ile bu sorunun zlmesi amalanmaktadr. Bu almada, deney ortamnda ii bo bir souk hava deposu kullanlarak scaklk ve hava dolanm hz verileri ile saysal analiz program lm sonularnn karlatrlmas amalanmtr. Souk hava deposu ortam scaklndan set aralk deeri 275.15 K - 272.95 K olan deere inilip hz ve scaklk deerleri datalogger kullanlarak alnmtr. Saysal analiz iin ncelikle hava aknn olaca kabin boyutlu olarak modellenmi ve a yaps sonlu elemanlar yntemi kullanlarak oluturulmutur. Tm deney artlar hesaplamal akkanlar dinamii hava ak simlasyon yazlm program zamana bal olarak tanmlanp deney sonularyla karlatrlmtr. Sonunda deney ile yazlm program arasnda yaknsama grlmtr. Sonularn yaknsamasndan dolay 3 farkl fan hz iinde program altrlmtr. Kabin iindeki hz ve basn dalmlar ak izgileri, vektrler ve e byklk erileri eklinde grafik olarak gsterilmitir. Alnan scaklk, basn ve hz deerleri yorumlanmtr. Anahtar kelimeler: souk depoculuk, sonlu elemanlar yntemi (SEY), hesaplamal akkanlar dinamii
Souk depo modelinin deneysel ve 3 boyutlu saysal analizi
Semin KAYA, Enver YALIN *, G. Alevay KOYT Balkesir niversitesi, Mhendislik Fakltesi Makine Mhendislii Blm,10145, Balkesir
mhendislikdergisi
Cilt: 3-9Dicle niversitesi Mhendislik Fakltesi
Nisan 20134, 1, 23-35
Enver YALIN, [email protected] ; Tel:(266)6121194(4120)
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S. Kaya, E.Yaln, G. A. Koyiit
Experimental and 3D numerical analysis of a cold store model Extended abstract Temperature and humidity control are vital in the cooling industry. As laboratory works cause increased costs and loss of time, the study aims at solving this problem by numerical analysis software. This study has aimed to compare the temperature and air-circulation rate data with numerical analysis software measurement results using an empty cold room in an experimental environment.
The cold room temperature has been dropped to the set range value of 275.15 K to 272.95 K and temperature and air velocity values have been obtained using a datalogger. For numerical analysis, first, the cabin where the airflow will occur has been modeled as 3D and the network structure has been formed using a finite elements method. All experimental conditions have been defined time-dependently by the Computational Fluid Dynamics (CFD) airflow simulation software and compared with the experiment results.
A convergence has been seen between the experiment and the software. CFD software has been started under 3 different fan rates due to the convergence of the results. Rate and pressure distributions inside the cabin have been shown in a graph with flow lines, vectors, and isosize curves. Values of temperature, pressure and velocity have been interpreted.
There are two basic approaches in the design and analysis of engineering systems. These are calculation and experimentation. The results of calculation must tested experimentally. Today, designers use both experimental and CFD analyses, because these two different methods complete each other. While general characteristics such as pressure, temperature, velocity can measured experimentally, detailed properties such as shear stresses, velocity distributions, temperature and pressure distributions and flow lines can calculate using experimental data.
One of the most effective numerical methods, which allow the use of differential equations in order to construct mathematical models and to solve these equations by means of computer software is the
finite elements method. The method is based on the formation while expressing the system characteristics of an element, and then a linear equations set by combining the equations formed for each element to express the whole system. The finite element method, which is capable of solving all complicated problems such as various boundary conditions, time dependent linear and non-linear problems rapidly spread in application and theoretical scientific fields in the last half-century
An important point to note is that even though a fine mesh provides a better solution, since the physical refinement of the solution always depends on the physical refinement of the model, details were ignored in the model.
In cold store, velocity control of temperature and air circulations carried as much importance as humidity control. Many parameters should be evaluated together for this aim and the most appropriate conditions should be met. In this study, ventilator velocity, ventilator position, product storage type, evaporator surface areas, working times of systems and pressure distribution inside cabin were evaluated separately.
High air movement is desiccated fresh products. On the other hand, very slow air movement causes freeze of humidity inside the cooling unit. Therefore, air velocity must kept within the limits by sufficient for product quality. Relative humidity in cold store depends on storage temperature, air flow rate, evaporator surface areas, number of ventilators, and cross sectional areas of ventilators.
With the method used in this study, air circulation velocity and storage temperature can select for all products. In this way, by definition of time dependent boundary conditions, CFD simulations achieved. Many parameters such as ventilator position, air velocity, temperature distribution inside the cabin. can monitored easily according to storage conditions.
Keywords: cold storage ,finite element method (FEM), computational fluid dynamics(CFD)
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Souk depo modelinin deneysel ve 3 boyutlu saysal analizi
Giri Mhendislik sistemlerinin tasarm ve analizinde iki temel yaklam vardr; hesaplama ve deneysel alma. Deneysel alma, test edilecek modelin inasn gerektirirken, hesaplama ise diferansiyel denklemlerin saysal olarak zlmesini gerektirir. Deneysel alma verileri ile hesap deerlerinin rtmesi yntemin doruluunu ortaya koyar. Deneysel maliyetleri minimize etmek asndan bilgisayar ortamnda sistemlerin modellenmesi olduka elverili bir yoldur. Deneysel ve saysal analizler birbirini tamamladklar iin gnmzde her ikisi birlikte kullanlmaktadr. Kaldrma, diren, basn d veya g gibi genel zellikleri deneysel yollarla elde edebilirken kayma gerilmeleri, hz, scaklk, basn dalmlar, aka ait akm izgileri gibi ayrntlar elde etmek iin ise zellikle deneysel elde edilen veriler kullanlr (engel vd,, 1996). Hesaplamal akkanlar dinamii kullanlarak literatrde bir ok alma mevcuttur. Deney sonular ve saysal analiz sonular kyaslanarak, jetli soutma sistemleri kullanldnda soutma kabininde homojen bir scaklk ve hz dalm oluturulduu grlmtr (Gngne, 2007). Buhar sktrmal bir soutma sistem bileenlerinin ktle ve enerji denge denklemlerini belirleyerek bir model oluturularak maliyet parametreleri birletirilmitir (Al-Otaibi vd., 2004). Tersinir Carnot s makinesi sisteminin optimum alma artlarn belirlemek iin termodinamik analizler yaplm ve sisteme termoekonomik optimizasyon metodunu uygulanmtr (Chen, 2001). Soutma sistemlerinin termodinamik analizini ve ekonomik optimizasyonunu yapan bir bilgisayar program ile bir soutma sisteminin optimum alma artlarn belirlenmitir (Usta, 1993). Deneysel verilerin, iki ve boyutlu saysal simlasyonu neticesinde byk lekli trblansl aklarn tekrarlanamamas nedeniyle iki boyutlu yaklamn olduka zayf olduu tespit edilmitir (DAgaro vd., 2006). Yatay ve dikey
soutucu dolaplar zerine yaplan saysal modellemelerinde, hava ak modeli nceden tahmin edilerek kabin ii scaklk deerlerini incelenmesi ve bu tarz simlasyonlarn olduka yararl ve gvenli bir ara olduunu tespit edilmitir (Cortella, 2002). Dikey konumlu ak bir soutma kabini zerine teorik ve deneysel almalar yaplmtr. Yaplan almada SEY ile kabin iindeki hz ve scaklk dalmlar incelenmitir. Kabin performansn etkileyen nemli faktrlerden biri olan giri hava hznn artmas halinde hava srklenmesinden dolay oluan s aknn artt dolaysyla hava perdesinin veriminin dt grlmtr. (Cortella vd., 2001). Kabin iine d ortamdan srklenen havann hz profili ve Reynolds saysna bal olarak nasl deiim gsterdii deneysel ve saysal simulasyon modellemesi ile yaplmtr (Navaz vd., 2005). Hava perdeli yatay geometrili bir soutma kabinin bulunduu bir soutma dolabnn enerji performans ve optimizasyonu zerine saysal simulasyon modellemesi ve deneysel test yapmlardr. Deneysel llen deerler ile saysal sonularnn olduka yakn olduu, hz dalmlarnda genel bir eilimin olmad tespit edilmitir (Cui vd, 2004). Bilinen standart soutma dolaplar ile s borulu soutma dolaplar iin raflardaki rnlerin scaklk dalmlar deneysel ve saysal modellemesi yaplmtr. Yaplan tartmada optimum hz, scaklk ve trblans younluuna sahip hava perdelerinin sistemin toplam performansn ykselttii grlmtr (Wang vd., 2005). Hesaplamal akkanlar dinamiinde akn karmaklnn yannda boyutlu olmas ve trblans faktrnden dolay denklemlerin, ilgili snr koullar saysal tabanl zlmesi mmkn olmamaktadr. Bu nedenle denklemlerin zlmesi iin eitli analitik metotlar kullanlmaktadr. Sonlu farklar, sonlu hacimler ve sonlu elemanlar gibi yntemler bulunmaktadr. Bu yntemlerin hepsi akkanlar mekanii iin kullanlmaktadr ancak yaplan aratrmalarda sonlu elemanlar yntemi (SEY) ile hassas zmler elde edilebilecei grlmtr. Dolaysyla bu almada SEY
