Soğuk depo modelinin deneysel ve 3 boyutlu sayısal analizi

Abstract

Soğutma sanayinde sıcaklık ve nem kontrolü büyük önem taşımaktadır. Laboratuvar ortamında yapılan çalışmalar maliyet artışı ve zaman kaybına neden olduğu için sayısal analiz programları ile bu sorunun çözülmesi amaçlanmaktadır. Bu çalışmada, deney ortamında içi boş bir soğuk hava deposu kullanılarak sıcaklık ve hava dolanım hız verileri ile sayısal analiz programı ölçüm sonuçlarının karşılaştırılması amaçlanmıştır. Soğuk hava deposu ortam sıcaklığından set aralık değeri 275.15 K - 272.95 K olan değere inilip hız ve sıcaklık değerleri datalogger kullanılarak alınmıştır. Sayısal analiz için öncelikle hava akışının olacağı kabin üç boyutlu olarak modellenmiş ve ağ yapısı sonlu elemanlar yöntemi kullanılarak oluşturulmuştur. Tüm deney şartları hesaplamalı akışkanlar dinamiği hava akış simülasyon yazılım programı zamana bağlı olarak tanımlanıp deney sonuçlarıyla karşılaştırılmıştır. Sonunda deney ile yazılım programı arasında yakınsama görülmüştür. Sonuçların yakınsamasından dolayı 3 farklı fan hızı içinde programı çalıştırılmıştır. Kabin içindeki hız ve basınç dağılımları akış çizgileri, vektörler ve eş büyüklük eğrileri şeklinde grafik olarak gösterilmiştir. Alınan sıcaklık, basınç ve hız değerleri yorumlanmıştır.

Keywords

• soğuk depoculuk, sonlu elemanlar yöntemi (SEY), hesaplamalı akışkanlar dinamiği

Experimental and 3D numerical analysis of a cold store model

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 timedependently 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)