Doctor of Philosophy

dissertationThe primary focus of this work is an assessment of heat transfer to and from a reversible thermosiphon imbedded in porous media. The interest in this study is the improvement of underground thermal energy storage (UTES) system performance with an innovative ground coupling using an array of reversible (pump-assisted) thermosiphons for air conditioning or space cooling applications. The dominant mechanisms, including the potential for heat transfer enhancement due to natural convection, of seasonal storage of "cold" in water-saturated porous media is evaluated experimentally and numerically. Winter and summer modes of operation are studied. A set of 6 experiments are reported that describe the heat transfer in both fine and coarse sand in a 0.32 cubic meter circular tank, saturated with water, under freezing (due to heat extraction) and thawing (due to heat injection) conditions, driven by the heat transfer to or from the vertical thermosiphon in the center of the tank. It was found that moderate to strong natural convection was induced at Rayleigh numbers of 30 or higher. Also, near water freezing temperatures (0°C-10°C), due to higher viscosity of water at lower temperatures, almost no natural convection was observed. A commercial heat transfer code, ANSYS FLUENT, was used to simulate both the heating and cooling conditions, including liquid/solid phase change. The numerical simulations of heat extraction from different permeability and temperature water-saturated porous media showed that enhancement to heat transfer by convection becomes significant only under conditions where the Rayleigh number is in the range of 100 or above. Those conditions would be found only for heat storage applications with higher temperatures of water (thus, its lower viscosity) and large temperature gradients at the beginning of heat injection (or removal) into (from) soil. For "cold" storage applications, the contribution of natural convection to heat transfer in water-saturated soils would be negligible. Thus, the dominant heat transfer mechanism for air conditioning applications of UTES can be assumed to be conduction. An evaluation of the potential for heat transfer enhancement in air-saturated media is also reported. It was found that natural convection in soils with high permeability and air saturations near 1 becomes more important as temperatures drop significantly below freezing

Volcanogenic Deposits of Non-ferrous Metals in the Lesser Caucasus and Eastern Pontides

The paper presents brief characteristics of geological environments of ore deposit occurrences in Turkey, Georgia and Armenia. They can be attributed to Kuroko-type deposits, being distinguished by the character of ore accumulation. To the west, in Turkey, there are epigenetic and hydrothermal-sedimentary copper-zinc deposits that were formed in deep restricted basinal settings. An example of the latter is the Chayeli deposit.To the east, in the Caucasus, we have predominantly only epigenetic deposits. Besides, in the Bolnisi mining district (Georgia) there is the Madneuli deposit which represents an example of polyformational deposit. Here, within the restricted territory, have been concentrated:barite, barite-polymetallic, gold-bearing secondary quartzite, large-scale stockworks of copper ores. Judged by the 87Sr/86Sr ratios, some volcanites which are spatially associated with ores, might have been products of the “differentiation” of undepleted mantle, or other magmas that were generated in the lower part of the earth crust.In the Alaverdi ore district in Armenia, there are Jurassic volcanodepressions that host copper, copper-zinc and barite-sulfide ores. All the deposits of the Alaverdi district, porphyry copper including, contain economic reserves of ores.On the basis of available literature material and our own data, there has been created a mental-logical geological-genetic model of volcanogenic deposits

KÜÇÜK KAFKASLAR VE DOĞU KARADENİZ METALOJENİK KUŞAĞINDA BULUNAN DEMİR İÇERMEYEN METAL YATAKLARI VE BUNLARIN VOLKANOJENİK SEDİMENTER ARDALANMALARINDA CEVHER OLUŞUM SİSTEMLERİ

-Alp-Himalaya kıvrım kuşağı orta kısmının (Doğu Karadeniz metalojenik kuşağı ve Küçük Kafkaslar) volkanojenik demir içermeyen metal yatakları örneğinde olduğu gibi bu yerlerin hidrotermal sistemlerinin Avrasya ve Gondwana’nın karasal parçaları ve mikro levhaların aktif etkileşimlerinin değişik seviyelerinde doğal olarak ortaya çıktığı gösterilmiştir. Ayrılma fazı süresince, marjinal deniz içerisindeki mikro levha sınır bölgesinde, hidrotermalsedimenter, Cu ve polimetalik maden yatakları oluşmuş; erken çarpışma fazında, paleo-ada-yay sistemlerinde, epijenetik Cu ve daha az miktarlarda barit-polimetalik (Küçük Kafkaslar), daha sonra da ikisi birleşip (hidrotermalsedimenter ve ağsal) ve epijenetik (çoğunlukla Cu ve Zn içeren) yataklar ortaya çıkmıştır (Doğu Karadeniz metalojenik kuşağı). Çarpışma evresinin başlangıcında, zıt yöne dalımlı yay gerisi volkanik yapıların içerisindeki volkanizma ile bağlantılı olarak, poliformasyonal yataklar (barit, barit-polimetalik. Cu, Au) oluşmuştur. Bu eğilim bütün çarpışma evresi boyunca levha içerisinde devam etmiş ve Eosen volkanik çöküntülerinde Ag içeriğinin Au içeriğine göre fazla olduğu polimetalik yataklar ortaya çıkmıştır. Yazarlar öncelikle Cu, Zn yatakları için yüksek metal anomalisi veren ortamların özellikle temel ve orta-asidik volkanikler olabileceğini; buna karşın barit ve baritli-polimetalik yataklar için, yüksek miktarda mineralize olmuş tuzlu sulardaki gri renkli ve evaporitik serilerin volkanik yapısal tabanlar için en uygun olabileceği fikrini paylaşmaktadırlar

Subductions, obduction and collision in the Lesser Caucasus (Armenia, Azerbaijan, Georgia), new insights

In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the autochthonous South Armenian Block (SAB), a Gondwana-derived terrane; (2) the ophiolitic Sevan–Akera suture zone; and (3) the Eurasian plate. Based on our field work, new stratigraphical, petrological, geochemical and geochronological data combined with previous data we present new insights on the subduction, obduction and collision processes recorded in the Lesser Caucasus. Two subductions are clearly identified, one related to the Neotethys subduction beneath the Eurasian margin and one intra-oceanic (SSZ) responsible for the opening of a back-arc basin which corresponds to the ophiolites of the Lesser Caucasus. The obduction occurred during the Late Coniacian to Santonian and is responsible for the widespread ophiolitic nappe outcrop in front of the suture zone. Following the subduction of oceanic lithosphere remnants under Eurasia, the collision of the SAB with Eurasia started during the Paleocene, producing 1) folding of ophiolites, arc and Upper Cretaceous formations (Transcaucasus massif to Karabakh); 2) thrusting toward SW; and 3) a foreland basin in front of the belt. Upper–Middle Eocene series unconformably cover the three domains. From Eocene to Miocene as a result of the Arabian plate collision with the SAB to the South, southward propagation of shortening featured by folding and thrusting occurred all along the belt. These deformations are sealed by a thick sequence of unconformable Miocene to Quaternary clastic and volcanic rocks of debated origin

Electromechanical Evaluation of a Double-Core Motor With Ceramic Elements

This study investigated the prospect of embedding ceramic elements in the body of a double-core transverse-flux machine to mitigate heat in the machine’s coil. In addition, the ceramic elements were used to hold the coil above the permanent magnets in order to reduce the negative flux leakage of the magnets into the coil. Three types of ceramics were investigated for this purpose: glass ceramic, aluminum oxide, and silicon nitride. Steady-state thermal analysis demonstrated a significant temperature drop in the motor coil when the ceramic element was embedded in the design. The back electromotive force of the winding improved by 30% as a result of reduced leakage flux. Structural analysis of the motor demonstrated high endurance of the ceramic elements to thermal stress and motor vibration. The results of computer thermal analysis were verified in the laboratory by performing a test on a section of a motor