Hava-su iki fazlı akış parametrelerinin deneysel incelenmesi
Investigation of air-water parameters on two phase flow
Yazar: AHMET BERK KURTULUŞ
Danışman: PROF. DR. NURDİL ESKİN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Kimya Mühendisliği = Chemical Engineering ; Makine Mühendisliği = Mechanical Engineering
Dizin: Akım ölçerler = Flowmeters ; Basınç ölçümleri = Pressure measurements ; Lazer optik sistem = Laser optic system ; İki fazlı akış = Two phase flow

Özet:
Bir iki fazlı akış olgusu olan gaz ve sıvı fazlarının birlikte gerçekleştirdikleri fiziksel duruma, kimyasal, mekanik, nükleer ve uzay uygulamalarında oldukça karşılaşılmaktadır. Bu şartlar altında özellikle nükleer güç santrallerinde kompleks yapıları sebebiyle oldukça fazla teste ve geniş analizlere tabi tutulmayı gerektirmektedir.
Gaz-sıvı akışı, manifoltlarda ve emniyet valfleri gibi endüstriyel uygulamalarda da geniş bir kullanım sahasına sahiptir. Boruların veya kanalların oluşturduğu bu tip sistemler içerisinde kesit değişimleri, sistem gereği tasarımcının karşısına önemli bir tasarım parametresi olarak çıkmakta ve mühendislik hesaplamaları açısından sabit kesitlerden farklı dikkat edilmesi gereken hususlar ortaya çıkmaktadır. Genişleme, daralma veya orifislerden oluşan kesit değişimleri, iki fazlı akışın kesit değişimi boyunca farklı konfigürasyon göstermesine sebep olmaktadır.
Çalışmanın kapsamı; yatay borularda düz ve daralma ile genişleme gösteren kısımlardaki iki fazlı akış parametrelerinin deneysel yöntemler ile araştırılmasıdır. Akışkan çifti olarak hava ve su kullanılan sistemde; ölçümler ikili optik prop ile gerçekleştirilmiş ve operasyonel parametrelerin saptanması sağlanmıştır. Kesit değişiminin etkisini görebilmek için düzgün daralan ve genişleyen kesit şeklinde iki durum kullanılmıştır. Düz bir test bölümünden geçen akış, kesit değişimi gerçekleşen bölüme gelerek her iki durum için de üç farklı açıda genişleme ve daralma gösteren alana giriş yapmaktadır. Deneyler kapsamında üç farklı hava debisi kullanılarak ilgili parametrelerin test bölümü öncesinde, sırasında ve sonrasındaki değişiklikler izlenmiştir. 
Bu tez kapsamında; ilk bölümde, iki fazlı akışa giriş yapılmakta ve gaz-sıvı akışı üzerinde durulup tezin amacı ve çok fazlı akışlar ile ilgili literatür araştırmaları sunulmuştur. 
İkinci bölümde, iki fazlı akış modelleri irdelenmiş ve kesit değişimini kapsayan modeller ile ilgili parametreler verilmiştir.
Üçüncü bölümde, tez çerçevesinde ortaya konulan deney metodolojisi anlatılmış, deney tesisatı ve ekipmanları ile ölçüm süreci ve akabinde oluşan belirsizlikler ve hatalar irdelenmiştir.
Dördüncü bölümde, deneysel çalışma sonuçları üç farklı kesit için verilmiş; sabit, düzgün daralan ve genişleyen borular boyunca iki fazlı akış değişim karakteristiği incelenmiştir.
Beşinci bölümde, deneysel çalışmanın bulguları yazılarak iki fazlı akışta önemli değişimlere sebebiyet veren fiziksel mekanizmalar açıklanmış ve çalışma kapsamında öneriler sunulmuştur.

Abstract:
A two-phase flow is the phenomenon that  both the gas and liquid phases physically implement together, encounters in chemical, mechanical, nuclear, and aerospace applications. Under these conditions, particularly in nuclear power plants due to the complex structure is being subjected rather than tests and require extensive analysis.
Two-phase flow consisting gas and liquid phases is a complex structure, because of having an interface structure which undergoes deformation and compressibility of phases. In this type of flow can be traced to a very broad interface configurations. Containing two-phase flow systems have a large area in the industry and nature; many engineering applications as petroleum, chemical and power generation industries, and fluid transfer lines are encountered in practice. In engineering  equipment design and process design, to be determined the relevant parameters and variability rates of these parameters under physical conditions is a significant engineering optimization. The effects of the transmission mechanism may generate results; heat, mass and momentum transfer would cause the results to see the design is an essential boundary condition. Economic and mechanical design, and optimization requirements in order to ensure safe operating conditions, hydrodynamic and thermal characteristics of two-phase flow within the framework of the experimental conditions can be estimated correctly in an appropriate range of values is important.
Flow maps basically pose to determine the distribution of interfacial phase in two-phase continuous media. The characteristics of flow play a major role in heat and mass transfer. Measurement of relevant parameters and operational characteristics of two-phase flow system provides the possibility to work on. Gas-liquid two-phase flow studies on the flow maps, in order to help achieve important practical results and research area is kept at the forefront of academic studies. Various types of flow and the resulting flow regimes, in particular a moving interface between phases in the design calculations is very important. Many parameters, can be effective in the formation of the flow map: temperature, pressure, void ratio, the phase velocity, etc..
Gas-liquid flow is used extensively in industrial applications such as safety valves and in manifolds. Cross-section changes in these systems consisting pipes or channels, are important design parameter for designers. In terms of engineering calculations, unlike the constant cross-section, is emerging issues that need attention. Expansion, contraction or changing in cross-section consisting of orifices, two-phase flow throughout the cross-section change causes to show different configurations. 
The disclosed parameters in determining the two-phase flow characteristics: mass flow and velocity, temperature, void fraction, critical heat flux, interfacial film thickness, flow regime, the wall shear stress and turbulence and velocity distribution in the form listed. 
The sudden change in cross section of two-phase flow, there are several approaches in the description. Process engineering is a condition frequently encountered in the security system. Pressure safety relief valve in such systems are preferred. Single-phase two-phase conversion is affected by pressure variations coming or already two-phase as the flowing fluid to determine the flow characteristics of the pair as a basis of design is an essential state. Would cause changes in the physical parameters of sharp corners and pressure changes, sudden changes in cross-section is an important result of the case. 
Aim of this study, to investigate the two-phase flow parameters performed by the expansion and contraction of the horizontally aligned pipe using experimental methods. As a pair of fluid, air and water are used in this system; measurements were performed with dual optical probe and determination of operational parameters are provided. To see the effect of changes in cross-sectional narrowing and expanding properly used in both cases. A straight flow through the test section, came to part of section exchange that took place at three different angles for both cases access to the area is showing expansion and contraction. Under air flow experiments are using three different test portion relevant parameters before, during and after changes were monitored.
Sudden changes in cross-section and high pressure resulting from exchange reasons from single phase flow from the inlet to the outlet flow passage may be two-phase. Scope of the study; enlarging the horizontal pipe part and narrowing in a flat two-phase flow parameters is to be examined with experimentally. 
Air and water, is used as fluid pairs in the two phase flow; are provided by performing measurements with dual optical probe to determine the operational parameters. To see the effect of changes in cross-sectional narrowing and expanding cross-sectional shape, two cases are used. A straight flow through the test section, come to the test section for both cases in three different expansion and contraction angle (4.5°, 9° and 15°) showing the test section is input. Three different experiments under air flow (30, 50 and 60 l/min) test section of the relevant parameter used before, during and after changes were monitored. 
As a result of the experiments, two-phase flow parameters vacancy rate number of bubbles and bubble size distributions were obtained for axial pipes. Also the system during a single-phase and two-phase flow pressure loss suffered was measured. 
During the measurements with dual optical probe carried out, to determine the operational parameters are provided. Scope of this thesis only the vacancy rate, the number of bubbles and bubble size were investigated for changes in the test assembly. Within the scope of the experiments, the water flow rate of the liquid phase 3 l/s capacity is kept constant; three different volumetric flow for the air in the gas phase (30, 50, 60 l/min) test section of the relevant parameter used before, during and after changes were monitored. 
This thesis consists of five chapters. The first part of this thesis gives information about the two-phase flow and focuses on gas-liquid flow, introduces the subject of the thesis and the research literature on multiphase.
In the second part, two-phase flow models are examined and parameters related with models including cross-sectional variation are given.
In the third part installment, equipment and methodology of the experiment, suggested within the frame of the thesis, is explained, and measurement process of the experiment, the uncertainity and errors of the process are discussed.
In the fourth part, the experimental study results for three different sections are given. Characteristics of two-phase flow through constant, uniformly shrinking and expanding pipes are examined.
In the fifth part, findings of the experimental study are presented. Mechanism, causing significant changes on two-phase flow, are explained and suggestions within the frame of the study are given.
Local void fraction distribution visually indicating graphics formation upstream to the vertical axis coordinates 100% value, while 30 l/min air flow rate 60% was sufficient, narrowing sections 30% and the expansion sections 100% values were included.
Graphical distribution of the number of bubbles being formed, the scale of the injector 50000, 20000 in the upstream region, the contraction in cross-section 40000, and 15000 bubbles in the expansion section number value is used.
Bubble size distribution graph being formed, the scale 20 in the injector, in the upstream 100, the contraction in cross section 25, and 100 mm were used in the expansion section.