<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:14.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-fareast-language:EN-US;} p.MsoBodyText3, li.MsoBodyText3, div.MsoBodyText3 {margin:0cm; margin-bottom:.0001pt; text-align:center; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} p.zetmetni, li.zetmetni, div.zetmetni {mso-style-name:"Özet metni"; margin-top:6.0pt; margin-right:0cm; margin-bottom:0cm; margin-left:0cm; margin-bottom:.0001pt; text-align:justify; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-fareast-language:EN-US; font-style:italic; mso-bidi-font-style:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Silindirik sıcak su depolama tankı içerisine dairesel plakanın f/H ve g/D oranlarında yerleştirilmesinin ısıl tabakalaşma üzerine etkisi sayısal ve deneysel olarak araştırılmıştır. Silindirik sıcak su depolama tankı modelleri, ortasına g/D oranlarında delik açılmış dairesel plakaların f/H oranlarında tank içerisine yerleştirilmesi ile oluşturulmuştur. Depolama tankının içerisine yerleştirilen dairesel plakalar ile tankın üst kısmındaki sıcak su ile alt kısmındaki soğuk suyun birbirleri ile karışması önlenmiş ve tank içerisinde bulunan sıcak suyun ısıl tabakası korunmuştur. Burada H ve D sırası ile tankın yüksekliği ve çapı, f tankın taban yüzeyinden dairesel plakaya olan mesafe ve g ise dairesel plakaya açılan deliğin çapıdır. Isı depolamak için kullanılan sıcak su depolama tankı güneş enerjisi uygulamaları için düşünülmüştür. Fakat bu çalışmada suyun ısıtılması işlemi güneş enerjisi ile değil de, ısıtma tankında bulunan elektrikli ısıtıcı ile yapılmıştır. Bu analiz süreklilik, momentum ve enerji eşitliklerinin üç boyutlu zamana bağlı durumu dikkate alınarak yapılmıştır. Sayısal çalışmanın geçerliliği deneysel olarak da ispatlanmıştır. Sayısal sonuçların elde edilmesinde FLUENT paket programı kullanılmıştır. Tank içerisindeki sıcaklık değerlerinin görünümü, sıcaklık ve sıcaklık farkı dağılımları, çeşitli f/H ve g/D oranlarında ve zamana bağlı olarak şekiller ve grafikler üzerinde gösterilmiştir. Sonuçlar; tank içerisine yerleştirilen dairesel plakanın ısıl tabakalaşmayı iyileştirdiğini ve bunun sonucunda da, engelsiz tank durumuna göre, tanktan sağlanan kullanım suyu sıcaklığını arttırdığını göstermektedir. En iyi ısıl tabakalaşma dairesel plakanın tank içerisine g/D=0.2 ve f/H=0.133 oranlarında yerleştirilmesi durumunda elde edilmiştir. Anahtar Kelimeler: Depolama tankı, ısıl tabakalaşma, dairesel plaka. In this study, effect of f/H and g/D ratios of circular plates placed in a cylindrical hot water storage tank on thermal stratification is investigated numerically and experimentally. The tank model is designed by placing a circular plate in the tank with a hole in the center at f/H and g/D ratios. Here H and D are the height and diameter of the tank respectively, while f is the distance from the bottom surface of the tank to the circular plates and g is also the diameter of the hole on the plates. This cylindrical hot water storage tank used to store heat for solar collector application is considered. The most commonly use of solar energy is the solar collector used for water heating. A hot water tank is used for storing part of the solar energy collected by the solar collector for later use. But in this study, the water remaining in the storage tank is heated by the heater tank with an electrical heater placed inside. As soon as hot water is drawn from the tank, cold tap water flows into the tank mixing with the remaining hot water, and therefore lowering the water temperature in the tank. This is an undesirable result. In this study, a solar hot water storage tank with a circular plate placed inside is considered and optimum plate dimensions are searched to minimize the mixing of hot and cold water so that water may be supplied at higher temperatures. This analysis is based on unsteady, three- dimensional continuity, momentum and energy equations. The governing equations are used to determine the temperature and velocity distributions in the flow field by using boundary and initial conditions. The thermodynamic properties of the water are considered in this study. The velocity is assumed to be zero at the beginning. The operation pressure in the tank is taken 1 atmosphere and the hot water temperature is assumed to be 335 K when the water usage started. The temperature and velocity of water supplied by the heater tank are taken 335 K and 0.8 m/s and these of cold tap water entering the tank are taken 290 K and 0.6 m/s, respectively. The time between the water is started to be used and the water usage was finished is assumed as calculation region. This time is taken as 30 minute and the problem was solved unsteady. The velocity and temperature distributions inside the tank were obtained by using FLUENT computer code. Three dimensional unsteady solutions are taken by using implicit method in segregated solver. The discretization is achieved by using Standard method for pressure and by using first upwind method for momentum, energy and continuity equations. The SIMPLE (semi-implicit method for pressure-linked equations) algorithm was used for flow calculations. A numerical investigation of optimizing dimensions of a plate placed in a hot water tank for thermal stratification is performed. A first observation of temperature distributions in the tank indicates that placing plate in the tank improves thermal stratification compared with no plate case. It appears that increasing f/H ratio increases temperature of stratified region whereas decreasing the volume of this region. In another words, increasing f/H decreases the amount hot water that can be taken from the tank. Increasing g/D ratio decreases the temperature of stratified region, and therefore, smaller values of g/D are desirable Temperature distributions in the tank, water temperature supplied by the tank, water temperature going to collector, various water temperature differences between tank outlet and inlet and appearance of the temperature values in the tank are shown on the graphs and figures for various f/H and g/D ratios and according to time. For higher thermal stratification, the temperatures T3 and T2 should be high and T1 should be low. In another words, the differences T3-T1 and T2-T1 should be as high as possible. An investigation of effects of g/D and f/H ratios of plate dimensions on these temperature differences shows that the best thermal stratification can be obtained for a g/D ratio of 0.2 and an f/H ratio of 0.133 among considered cases. Using circular plates in hot water storage tanks improves thermal stratification in the tank and consequently increases the temperature of hot water supplied by the tank. It also decreases the temperature of water supplied to the collector, and thus improving collector efficiency. Keywords: Storage tank, thermal stratification, circular plate
