Heat transfer investigation of compressed-water absorbed snow spheres

Yaz aylarında dağlarda bulunabilecek karın soğutma amacıyla kullanılabilmesi için borular vasıtası ile taşınması mümkündür. Ancak karın, bulunduğu formda veya su ile salamura şeklinde taşınması sıkıntılıdır. Dirsek gibi akışın yön değiştirdiği yerlerde karın boruları tıkaması ve dağda sahip olduğu soğu enerjisini daha kolay kaybetmesi gibi problemler vardır. Bu nedenle karın sıkıştırılıp su emdirildikten sonra soğutularak buzlaştırılması düşünülmüştür. Bu sayede kar küre, boru içerisinde hareket ederken dışarıdan içeriye doğru eriyeceği için kolaylıkla parçalanmayacak ve salamura oluşmayacaktır. Bu çalışma kapsamında sıkıştırılarak küresel hale getirilen karın, önce sıfır dereceye getirilmesi, sıfır derecede su emdirilmesi ve son olarak da soğutularak buzlaştırılması prosesi ele alınmıştır. Soğutma hem doğal taşınım ile hem de zorlanmış taşınım ile yapılmıştır. Oluşturulan deney sistemi ile sıkıştırılarak yarım küre haline getirilmiş karın su emdirildikten sonra soğutularak buzlaştırılması süresince gerçekleşen ısı transferi deneysel olarak incelenmiştir. Kar, geliştirilen sıkıştırma aparatı ile 80 mm çapında yarım kürelere dönüştürülmüştür. Farklı yoğunluklarda yarım küreler elde edilerek farklı gözeneklilikler elde edilmiştir. Bu yarım küreler daha sonra sıfır dereceye getirilmiş ve sonrasında da sıfır derecedeki suya daldırılarak su emmeleri sağlanmıştır. Deneyler yorumlanırken kar kürelerin homojen gözeneklilikte olduğu ve homojen su emdikleri kabulü yapılmıştır. Yapılan deneysel çalışma sonucunda farklı gözenekliliklerdeki kar kürelerin soğuma süresince iç bölgelerindeki sıcaklık dağılımları, buzlaşmanın zamana göre değişimi oluşturulan eğrilerle verilmiştir. Deneysel çalışmalarda gözeneklilik azaldıkça su emmenin azaldığı, yoğunluğu 0.82 g/cm3’ten büyük olan numunelerin ise su emmediği gözlemlenmiştir. Anahtar Kelimeler: Kar, buz, faz değişimi, ısı transferi.It is possible to use the natural snow accumulated on mountains for the aim of refrigeration when needed, especially in summer times. Making ice spheres from snow is suggested for transferring this accumulated snow from mountains to the places where refrigeration is needed. In this study, ice-sphere making process and heat and mass transfer mechanisms during this icing process are investigated experimentally. Today, transferring of ice for long distances is realized in the mixture form of snow and water. The most important disadvantage of transferring of snow mixture in pipe lines is the blockage of the flow because of accumulation of the snow in the elbows which is the place of flow direction changes. Another important disadvantage is large pressure losses. To overcome all these problems ice-spheres are being suggested. In this study, firstly making snow balls by compression, and then, saturating them with water and lastly, getting ice ball by cooling is aimed. To prevent the blockage of the balls in the pipeline's elbows, the diameter of the balls should be chosen bigger than the radius of the pipe. Otherwise, we will meet a flow characteristic called slush flow in the literature. In this study, the aimed flow is known as plug flow. In the literature, the plug flow of the plastic balls examined by Ulusarslan (2003) experimentally. In the mentioned study, the plug flow of the plastic balls was investigated and pressure losses of the flow determined experimentally. In addition, plug and slug flow are compared with each other. According to the study in the plug flow;  Pressure losses are less. There is no blockage risk. It is possible to carry more mass. Less power is required to carry. During the transfer of the balls in the pipelines, icing of the snow balls has to be done to prevent breaking into pieces. The icing process is done by compression of the snow into the form of sphere and saturating it with water. Water can be used as a binder. The most important think here is how much water should be used in the penetration process. The excess water causes the balls breaking into pieces. On the other hand, the less water amount causes insufficient binding of the snow granules. By compression of the balls, the air gaps inside the snow balls are decreased. Thus the density of the snow increases depending on the compaction level. At the end, the bonds between snow granules will be stronger. Compaction level, compaction velocity and temperature are very important parameters affecting the process. It is very important to determine correctly which values of the parameters should be used to have enough strength of the snow ball during the transfer process. The experimental studies have been carried out to get correct values and to investigate the heat and mass transfer characteristics of the snow. The following experimental results have been obtained; It is possible to produce strengthened ice balls by cooling the snow ball after compression of snow into the form of sphere and saturating it with water. After compression step, since close cellular structure is gained, the snow ball can't absorb any amount of water if the density of the snow ball is greater than 0.82 g/cm3. Experimental results in various conditions have been compared. The same trend-lines have been obtained for the same conditions. The differences between forced convection and natural convection cooling processes have been determined for the samples absorbing same amount of water. In natural convection cooling process, the total icing time is about 4 hour. However, in forced convection, it is about 1 hour. Absorbed water amount increases with the cooling time. During the cooling process, the temperature vs time profile of all the samples have been determined experimentally and all these results are given in the form of graphs in this study for various spheres having different porosities. Keywords: Snow, ice, phase change, heat transfer

Investigation Of Heat Transfer In The Phase Changing Capsules Used In Thermal Energy Storage Systems

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada, sıkıştırılarak küresel hale getirilen karın, önce sıfır dereceye getirilmesi, bu sıcaklıkta, sıfır derecede su emdirilmesi ve son olarak da zorlanmış taşınım ile soğutularak buzlaştırılması prosesi ele alınmıştır. Su emdirilmiş buz kürelerin zorlanmış taşınımla soğuması esnasındaki ısı geçişinin deneysel verileri elde edilmiştir. Ayrıca, literatürdeki çalışmalarla ve sözkonusu deneysel sonuçlarla doğrulanan, entalpi formülasyonu ve sonlu hacimler yönteminin kullanıldığı nümerik çalışmalar ile, çap ve diğer parametreler (taşınım katsayısı, gözeneklilik ve ortam sıcaklığı) değiştirilerek, genelleme yapılabilecek nümerik veriler üretilmiştir. Üretilen tüm verileri kapsayacak şekilde her bir çap (R20, R40 ve R60) için genel bir ampirik formül geliştirilmiştir. Geliştirilen ampirik formüllerin sonuçlarla uyumlu olduğu (maks. R^2 = 0,9996) görülmüştür. Nümerik veriler deneysel veriler ile doğrulanırken artan gözeneklilik ile nümerik sonuçlar ile deneysel sonuçlar arasındaki farkın arttığı gözlemlenmiştir. Bu farkın nedenleri çalışma kapsamında detaylı olarak izah edilmiştir.In this study, the process of first cooling to 0 ºC, then saturating with water, and finally icing by forced convection of snow compressed and made in spheres has been discussed. Experimental data of heat transfer during cooling of ice spheres -saturated with water- by forced convection have been obtained. Additionally, generalized numerical data have been produced by changing diameter and other parameters (convection coefficient, porosity and ambient temperature) in the numerical studies in which finite volume method and enthalpy formulation validated by literature survey and experimental studies given had been used. A general empirical formula holding for all data produced for each diameter (R20, R40 and R60) has been developed. It was seen that the empirical formula and results were in accordance with each other (R^2 = 0,9996 max). During the verification of numerical results with experimental results, it was observed that the difference between numerical and experimental results increased with increasing porosity. The reasons for this difference have been explained in the study in detail.DoktoraPh

Right coronary artery fistula with significant left-to-right shunt

We present an image of giant fistula between severely enlarged right coronary artery and coronary sinus, which was evaluated by echocardiography, conventional coronary angiography and multislice computed tomography coronary angiography. J Cardiovasc Med 9:1182-1183 (C) 2008 Italian Federation of Cardiology

Investigation of a novel soil analysis method in agricultural areas of Çarşamba plain for fertilizer recommendation

In this study, a novel soil analysis method for fertilization recommendation was developed and validated with 161 soil samples taken from Turkey - Çarşamba plain for determination of potassium as a plant nutrient. In conventional soil analysis methods, available potassium (K) nutrient was determined by ammonium acetate extraction with flame photometer. In this study an alternative to existing method was proposed by developing extraction solutions suitable for interference dynamics of ion selective electrodes in a flow injection setup. Flow injection analysis system was optimized and K ion concentration of 161 soil samples taken from Turkey – Çarşamba plain was determined with potentiometrically. For the same soil samples, K+ ion concentration was determined with ammonium acetate extraction using flame photometer in parallel. Fertilization recommendations for potassium was calibrated on ammonium acetate extraction based measurements. In order to evaluate available potassium nutrient analysis results from new generation soil analysis method in fertilization recommendation process, a correlation model is required for relating new generation method results to conventional method results. An artificial neural network based soft sensor system was developed for this task. Potentiometric K+ ion measurement of soil sample in flow injection analysis system was presented as input to soft sensor system. Soft sensor predicted available K in soil sample based on artificial neural network model which can be used in fertilizer recommendation. Prediction performance of soft sensor was validated with experimental data and fitted with high correlation coefficient (R2= 0.902). Experimental studies have shown that K determined by potentiometric measurements can be used in fertilization recommendations in Çarşamba plain by using soft sensor approach

Experimental and numerical investigation of ground heat exchangers in the building foundation

The current study proposes a novel method with the experimental and numerical studies for the ground source heat pumps, which are known as environment-friendly and efficient heating & cooling systems to overcome their economic drawbacks in the applied engineering operations. The experimental studies are carried out in the newly built Central Laboratory of Yildiz Technical University, Davutpasa Campus, Istanbul, Turkey. The long parallel heat exchanger pipes are placed in two different layers of the ground that are (1) under the building foundation (ground layer), and (2) in the building foundation (concrete layer), respectively. Besides, a unique numerical model is developed in MATLAB environment to obtain temperature distributions in ground and concrete layers. Then, the numerical outputs are validated with the observed experimental results. The daily average of the energy amount extracted from the Ground and Concrete Loops was found as 5.51 and 4.63 kWh/day, respectively. The results are found satisfying for real applications in the building foundations.Ministry of Science, Industry, and Technology of Turkey under SAN-TEZ program [0472.STZ.2013-2]; Mir Unique Solutions (company)This research work was jointly supported by Ministry of Science, Industry, and Technology of Turkey under SAN-TEZ program (No. 0472.STZ.2013-2) and by Mir Unique Solutions (company)

Zinc(II) and cadmium(II) coordination polymers containing phenylenediacetate and 4,4 `-azobis(pyridine) ligands: Syntheses, structures, dye adsorption properties and molecular dynamics simulations

Two new coordination polymers (CPs) - {[}Zn(mu(4)-PPda)(mu-abPY)(0.5)](n) (1) and {[}Cd(mu(3)-opda)(mu-abPY)(0.5)(H2O)](n) (2) (o/ppda = 1,2/1,4-phenylenediacetate, abpy = 4,4 `-azobis(pyridine)) - have been synthesized by using Zn(II)/Cd(II) salts in the presence of o- and p-phenylenediacetic acid and abpy under hydrothermal conditions. Their structures have been characterized by FT-IR spectroscopy, elemental analysis, X-ray powder diffraction and single crystal X-ray diffraction techniques. The structural diversities were observed depending on anionic ligands and metal centers in the synthesized complexes. Complex 1 consists of a 2-fold interpenetrated 3D +3D -> 3D framework with pcu topology while complex 2 has a 2D structure with sql topology. The adsorption of methylene blue (MB) was studied to examine the potential of the title CPs for removal of dyes from aqueous solution. Molecular dynamics (MD) simulations were also performed to examine diffusion of MB in 1 and 2. Thermal and optical properties of two complexes were also discussed