Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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COAR Access Rights: search.filters.coarAccessRights.open accessSubject: search.filters.subject.Heat transfer

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Now showing 1 - 6 of 6
  • Master Thesis
    Molecular Dynamics Studies on Heat Transfer Control Between Water and Silica Using Nanoscale Surface Patterns
    (01. Izmir Institute of Technology, 2020) Özen, Celal Can; Barışık, Murat; Barışık, Murat
    Due to recent advances in manufacturing, component sizes have tremendously decreased in computer electronics and communication devices. Miniaturization has led to a substantial increase in memory and computational power but also created heat dissipation problems. Understanding heat transfer and temperature distribution in these devices became crucial for thermal management. At nanoscale, heat transfer through dielectric materials is mostly determined by phonon transport. The phonon passage is interrupted through the interfaces which creates temperature jumps and dominates the heat transfer rates at nanoscale. Kapitza length characterizes the interfacial thermal resistance as a function of temperature jump at the solid-liquid interface. In this study, heat transfer from different nanoscale surface structures were investigated using Molecular Dynamics simulations. The systems were created by two parallel silica walls and water between them. Kapitza length values were calculated for seven different surface conditions for two different molecular surface interaction strength parameters yielding high and low wetting conditions. Measured Kapitza length values were characterized based on cavity width (w), cavity height (h), and unit crystal cavity volume (Vc). While the increase in pattern cavity width increased Kapitza length, increasing pattern cavity height decreased Kapitza value. However, a general characterization based on cavity volume could not be obtained. Instead, almost a uniform behavior was observed through the variation of Kapitza length of different size patterns as a function of Ac=Vch/w^2. Kapitza length decreased by approximately 19% and 29% for high and low wetting conditions, respectively, when Ac increased. Then, similar characterizations were done for variation of heat flux. Overall, heat flux increased by approximately 20% and 30% for high and low wetting conditions, respectively, when Ac increased. Results are important to better understand and control heat transfer between water and silica using nanoscale surface patterns.
  • Master Thesis
    Molecular Dynamics Studies on Wetting Behavior of Silicon Surfaces and Heat Transfer Characteristics of Electrolyte Solution Filled Silicon Nano-Channels
    (Izmir Institute of Technology, 2020) Özdemir, Abdullah Cihan; Barışık, Murat; Barışık, Murat
    Silicon has always been of interest to researchers from various fields, especially the semiconductor industry. Silicon and silicon-based materials are frequently used in integrated circuits and micro/nano-electro-mechanical systems. Interfacial phenomena between phases is important for these applications. In this study, surface wetting and heat transfer at the solid/liquid interfacial region were investigated using the Molecular Dynamics method. The control of wetting was examined by changing silicon structure at single crystal and amorphous forms and was correlated with the surface coating thickness. Contact angles on both single crystal and amorphous surfaces were calculated. To understand the molecular regions affecting the contact angle, the near interface height parameter was defined as the distance from the surface. Then, interface densities and contact angles of single crystal and amorphous structures were calculated at each height parameter. We defined an effective range of intermolecular forces for the control of wetting. Second, heat transfer characteristics at water/silicon interfaces were examined. Solid/liquid interface is important to determine heat transfer at nanoscale. We focused on the influence of ionic conditions on heat transfer for a water-NaCl solution between two silicon walls. The surface charge density showed variation by ionic condition. We calculated surface charges naturally forming at the corresponding electrolyte concentration. With the increase in salinity, the electrolyte solution density increased and thermal conductivity decreased. Results showed good agreement with the experimental measurements. Additionally, we observed a 35% increase in heat transfer due to a decrease in interfacial thermal resistance by increasing ionic concentration to the highest salinity value of standard conditions. Heat transfer at solid/liquid interface characterized by Kapitza length was correlated with the salinity.
  • Master Thesis
    Numerical Analysis of Thermal Performance of Glazing Systems
    (Izmir Institute of Technology, 2019) Şahin, Yağmur; Başaran, Tahsin
    Thermal performance of different glazing systems have been investigated with a comprehensive parametric study numerically. In order to analyze the heat transfer through the windows, CFD simulations have been performed considering many affecting parameters. The aim of the study is to determine the appropriate window configurations according to the different cities that have different climatic conditions of Turkey which are: Ağrı, Sivas, Amasya and İskenderun. For this purpose, the glazing part of the window has been analyzed because of having low thermal resistance due to the gap widths, temperature differences and the emissivity values. Four physical models of glazing systems were designed. The thickness of glazing units is 4 mm and the height is 1 m as a constant. For investigating the effect of the cavity dimension on the heat transfer, two gap widths usually used, are determined and combined in different ways which as 12–12 mm, 16–16 mm, 12–16 mm and 16–12 mm. Different boundary conditions are defined according to ambient temperature of inside and outside. Radiation heat transfer is included in the calculations and various low-e coatings are defined to analyze the radiation effect on the heat transfer coefficient. As a result of this study, temperature and velocity profiles are different in all scenarios. The effect of gap width on the U-value is more distinguished in the low temperature difference. Heat loss can be minimized significantly with using low-e material and the emissivity value is more effective on the wider gap widths. It is also shown that the optimum air layer thickness of the triple pane window differ from the temperature difference significantly. The highest U-values were obtained in 12-12 mm gap width glass. It was determined that the heat losses can be reduced by using 16-12 mm gap width glass about 2% and 8% in cold regions and in warm regions respectively.
  • Master Thesis
    The Effect of T-Shaped Fin Geometries on Heat Transfer Rate Enhancement
    (Izmir Institute of Technology, 2017) Çetin, Eylem; Çetkin, Erdal
    In this study, we show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effects of the cavities and the fins on heat transfer rate enhancement were compared while their volume fractions in a unit volume element were fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of flow characteristics and the design on the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case. Because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain and the heat transfer surface area. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries corresponds to thelower peak temperature. In addition, the results also show that there is an optimal cavityshape that minimizes the peak temperature. This optimal shape becomes thinner when thenumber of the cavities increase. In parallel flow case, fins with thicker and shorter stemand longer tributaries corresponds to the minimum excess temperature. In addition, longand thin cavity shapes increase the thermal performance in parallel flow case.
  • Master Thesis
    Production and Characterization of Heat Insulating Panels
    (Izmir Institute of Technology, 2016) Yörük, Osman Giray; Özdemir, Ekrem; Özdemir, Ekrem
    Hollow nano calcite particles were used as a core material in vacuum insulation panels (VIPs) and compared it with the fumed silica generally used in VIPs as the core material. Zinc-Tin-oxide (ZTO), ZnSnOx, was coated on the polyamide/polyethylene (PA/PE) polymeric films and used as the barrier material in VIPs to prohibit moisture and air transport. A fluidized bed filtration system was developed to separate the produced hollow nano particles from its slurry. ZnSnOx coating on the PA/PE polymeric films were optimized with respect to film rotation rate and oxygen content during film coating. Water permeation rate was measured as 8.32 gday-1m-2 for the commercial Aluminum-PET (Al-PET). The water permeation rate was measured as 1.15 gday-1m-2 for the 90 μm of PA/PE films coated with ZTO in 500 rpm of film rotation rate and 30 sccm Ar + 7.5 sccm O2 feed rate. It was shown that the produced ZTO coated PA/PE films had better barrier properties compared to the commercial Al-PET. The thermal conductivity was measured as 8.63 mWm-1K-1 for 3 wt% hollow nano calcite in 87 wt% of fumed silica compared to that of 9.9 mWm-1K-1 for fumed silica only. It was shown that when 3 wt% of hollow nano calcite were mixed with fumed silica as the core material, better thermal conductivity values were obtained.
  • Master Thesis
    A Study on Cop Improvement of a Household Refrigerator by Using an Adsorption Heat Pump
    (Izmir Institute of Technology, 2015) Arslan, Gizem; Barışık, Murat; Mobedi, Moghtada
    The thesis aims to increase the coefficient of performance of a domestic type household refrigerator. A household refrigerator is a kind of mechanical heat pump which works based on the vapor compression cycle. On the other hand, adsorption heat pump is a thermal heat pump and it can directly operate with any kind of third energy source such as solar, waste heat. The heat released from the condenser of a mechanical heat pump provides the desorption of the adsorbate in the adsorbent bed and helps the transfer of the adsorbate to the condenser of the adsorption heat pump. Then, the adsorbent bed which has low level adsorbate concentration provides the evaporation of the adsorbate in the evaporator and generates a cooling effect. By this way, an additional cooling effect can be generated without the increase of energy consumption of refrigerator. In this thesis, a detailed literature survey on the combination of hybrid cooling systems is done. The suggested hybrid cooling systems are classified, and their advantages and disadvantages are discussed. In order to analyze heat and mass transfer of an adsorption heat pump, different conditions for adsorbent bed design are studied, theoretically. To design an adsorption heat pump the effects on the heat and mass transfer should be well known. Theoretical studies on heat and mass transfer in a rectangular adsorbent bed is performed to understand what can be effected on the heat and mass transfer in an adsorbent bed. Heat and mass transfer equations for a rectangular adsorbent bed are derived for non-uniform pressure approaches and numerically solved to determine temperature and concentration profiles in the bed with using Comsol Software. Furthermore, our CFD program coded in FORTRAN language. The code is used to validate the obtained results from Comsol. An experimental setup was designed and constructed in the light of these numerical studies. The enhancement of performance of a household refrigerator is calculated by using an adsorption heat pump.