Isı değiştiricilerinde kullanılan manifoldlarda akışın analitik ve hesaplamalı akışkanlar dinamiği ile modellenmesi
Analytical and computational fluid dynamics modelling of flow in heat exchanger manifold
Yazar: FATİH KANTAŞ
Danışman: PROF. DR. SEYHAN UYGUR ONBAŞIOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Analitik yöntem = Analytical method ; Manifoldlar = Manifolds ; Sayısal akışkanlar dinamiği = Computational fluids dynamic

Özet:
Akışkanı dağıtmak veya toplamak için bir ana boru ve bu boruya bağlı kanallardan oluşan sisteme manifold denir. Manifold sistemleri akışın olduğu bir çok endüstriyel proseste geniş yer bulur. Bunlar içinde kimya, biomedikal, makina, inşaat ve çevre mühendisliği prosesleri bulunur. Manifold sistemlerinde akış dağılım homojenitesi, verimliliği, sürekliliği ve proses içindeki ünite başına fiyatı belirleyen faktördür. Akışı dağıtmak için kullanılan manifoldlar kullanıldığı sektöre ve yere göre çok farklı şekillerde olabilir. Yoğun olarak kullanıldığı alanlardan biri ısıtma ve/veya soğutmanın gerçekleştirildiği makinalardır. Bu makinalarda kullanılan ısı değiştiricilerine akışkanı dağıtmak ve sonrasında toplamak için, ısı değiştiricinin pas sayısına göre kanal sayısı değişen manifold sistemleri kullanılır. Temel bir ısı değiştirici tasarımında akışkanın tüm paslara eşit dağıldığı kabulü yapılır. Fakat gerçek uygulamalarda dağılım homojen şekilde gerçekleşmez ve akışkan manifold kanallarına eşit olarak dağılmaz. Bu durum, ısı değiştirici performansında önemli ölçüde düşüşlere neden olur.Bu çalışmada, ısı değiştiriciler için tasarlanmış dağıtıcı manifoldlar ele alınmıştır. Çalışmada kullanılan manifoldlar ve benzerleri klima kondanserlerine akışkanı dağıtmak için kullanılır. Ayrıca kondanser içinde dolaşan akışkanı toplayıp sisteme vermek içinde toplayıcı manifoldlar kullanılır.Bu çalışmada, öncelikle manifoldlardaki akışın nasıl gerçekleştiğini anlamak için geniş çapta literatür araştırması yapılmıştır. Literatür araştırmasında, son elli yılda yapılan çalışmalar incelenmiş, bu çalışmalar içerisinde öne çıkan ve manifold tasarımına öncülük yapan araştırmalara yer verilmiştir. Son yıllarda yapılan çalışmalarda manifold içersindeki akışı anlamak ve genel şekilde tanımlamak için büyük adımlar atılmıştır. Bu tez çalışmasında ilk olarak; son elli yılda yapılan manifold çalışmaları araştırılmış ve son yıllarda yapılan akış dağılım teorileri detaylı olarak incelenmiş. İkinci olarak, Wang (2011) teorilerinin mevcut manifoldlara uygulanması ve akış dağılım teorisinin geçerliliğin ortaya konulması üzerine çalışılmıştır. Üçüncü olarak, Ing Youn Chen ve ar. (2011) deneysel çalışmalarıyla, bu tezde yapılan HAD analizlerinin güvenilirliği ortaya koymak için karşılaştırmalar yapılmıştır. Son olarak Wang (2011) teorik çalışması ele alınarak yeni manifold geometriler için analitik çalışmalar yapılmıştır, bu tezde yapılan HAD analiz sonuçlarıyla karşılaştırılmış ve sonuçları tartışılmıştır.

Abstract:
That the flow manifold systems in many industrial processes finds wide. Among them, chemical, biomedical, mechanical, civil and environmental engineering are processes. Manifold systems are often the homogeneity of the flow distribution, efficiency, continuity, and the factors that determine the price per unit is in the process. Manifolds used for distributing the flow in general is divided into two structures. These are the types of sequential and bifurcation.Bifurcate equally spaced within the organizational structure of a similar structure, similar to the fluid flow acts on a tree structure. So this is the correct length and diameter of the channel to bifurcate the final structure by shrinking the size of the smallest and the anchor reach the end. Forked structure is generally the longer the reaction channels. Best designs are usually a bifurcate channel without variation diameters. The one constant flow distribution of the different flow rates of high-Reynolds numbers structure. However, the homogenous distribution and manufacturing tolerance of the channel depends on the blockade. In addition, when a very large number of channels leads to large pressure losses encountered in pruning will cause great difficulties to the design and production. Is important because these systems are not suitable for the additional pressure losses.Manifolds with constant cross sectional area of the structure with sequential manifold pipes on the main channel birdan has more. Flow is fed into the manifold pipe manifolds sequential structure and so on continuously. According to bifurcate clearly seen manifolds of this type has its advantages. The flat structure having a less pressure loss, and trenches. This creates the potential benefits are great types of the manifold; developed to be more favorable,reduce production costs and faster. Reveals some of these advantages. Although it is difficult to ensure homogenous flow predisposed to develop a good design Unless non-homogenous distribution of the flow causes. Some of the fluid passing through very small channels, some channels may turn to excessive fluid. This also reduces the system performance and efficiency. The key point is the performance and efficiency of different manifold structures to estimate in advance. In this way a high efficiency and low cost by selecting an optimum geometry of the structure can be designed manifolds.In this thesis, with a large field of application are examined sequentially structured manifolds. Manifolds on the flow distribution and pressure drop are three approaches: Computational fluid dynamics (CFD), discrete modeling and analytical modeling methods.Computational fluid dynamics (CFD) in the real world to solve the three-dimensional engineering structures are very realistic and detailed modeling method has great potential. Coefficients of friction and pressure associated with the flow, such as rescue factors, without the information can be used to predict the flow distribution and pressure drop. However, the geometry of the manifold design and optimization is always done using the CFD may not be the first. Because for every new configuration to create new geometry and mesh to create a structure would be too costly.Discrete model also called the network model. Separately, in a model is represented as a network of linked to a manifold multiple t. Then, connection to the mass and momentum conservation equations written in every t. Finally, the program can be solved by iteration a series of difference equations. Used by many researchers due to the simplicity of this approach is relatively. However, the direct consequences of a designer cannot use a computer constantly to get results from this approach because it doesn?t requires any program. After that, even useless, because no clear relationship between the manifold geometry and flow performance. So first of all that is useful for the design and optimization of manifold information not be provided. HAD analytical models and discrete models of the manifold on the other main advantage is simple and flexible for designers. Solution using differential equations, difference equations of non-state case the account is installed above the liner, making simpler and more compact. In addition, the performance of the manifold generalized analytical model provides an opportunity to associate a unique. These flow distribution, pressure drop, manifold structure, dimensions, shape, length can be listed as. Especially for the initial design of the optimum geometry of the manifold shall have very little information. The main subject of discussion at this stage, the cost, durability, maintenance and performance from the front of the designer. In this case, the generalized model helps us to discover the streaming performance of different geometries of the manifold.Because of this clear advantage, drew attention to the analytical solutions is quite the last fifty years. Different areas have many different models to examine the distribution of manifold flow. Many of the models has been the traditional form of modification is used as a Bernoulli theory or small scale. However, McNown (1954) and Acrivos et al. (1959) was a problem arises as a result of his experiments. After the pressure is increased manifold channels by shown experimental results the authors. In this event, and Wang et al. (1998, 2001, 2008) is described by. This is because the channels in the boundary layer of fluid moving within the low-energy and high energy continues to flow in the middle of the pipe. Therefore, the flow cross-sectional area than that of the average specific energies. Energy up the balance of the flow cross-section are based on the average value. If highs specific energies cannot be correct , so this causes an error be corrected and the first law of thermodynamics according to the specific mechanical energy resulting mass flow rate multiplied by the term, after the dissolution of the manifold flow channels for the mechanical energy than the energy appear approachable. For these reasons, the Bernoulli pressure rise predicted theory, similar to the results of experiments would not be surprising observation. To avoid this problem in recent researchers on the subject dealing with the application of momentum conservation is preferred. The advantage of the implementation process, a detailed flow patterns and flow of momentum conservation known that there can be simplified without. Errors due to simplify the pressure correction factor, friction factor and corrected by a factor of discharge.Bernoulli and momentum theory is used to define the flow in manifolds. These must be the same for all areas. There are a wide range of models for different areas of practice, and among them there are uncertainties. Wang (2008, 2010) attempt to identify all of them under a single unified model is the first A special case of Bernoulli's equation, the momentum model is shown that an author. Chemical and mechanical engineers look for the combined theory model is important.Manifolds in this thesis were carried out on a wide range. Advances in the last fifty years, and especially the last fifteen years were examined. In experimental studies examining the effect of forming parameters: the geometry of the manifold, and also put forward by other investigators, including Wang toerik models mainly investigated. CFD studies in this thesis and the accuracy of the findings set forth in the previous studies were investigated and compared. As a result of these inferences were made. Optimization of the manifold is made in the light of these inferences.