Pülsatif akımlarda rotametre ile debi ölçülmesi
Flowrate measurements by means of a rotameter in pulsating flow
- Tez No: 21989
- Danışmanlar: PROF. DR. HASAN FEHMİ YAZICI
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 64
Özet
ÖZET Tesisatı ardaki çek valf, çeşitli tipteki vanalar çap ayarlamaya yarayan elemanlar akış içerisinde kararsızlıklar (hız süreksizlik yüzeyleri) meydana getirmektedirler. Bu ayrılıklar akışta sanki periyodik yapıda vorteks üretirler ve akışı pülsatif hale sokarlar. pülsasyonlar elastik dalga kar ak ter indedir ve tesisatta ses hızıyla yayılırlar. Bu pülsasyonlar çeşitli akış büyüklüklerinin zaman içindeki ortalama değerlerinin ölçümünde kullanılan cihazların yanlış sonuçlar vermelerine sebep olmaktadırlar. Bu durumda, genel olarak ölçü cihazları gerçek değere tekabül edenden daha büyük bir ortalama değeri göstermektedirler. Sıvı veya gaz debilerinin ölçümünde kullanılan rotametrenin de bu tür akımlardan ne ölçüde etkilendiğini araştırmak, bu çalışmanın konusudur. Bunun için bir deney tesisatı kurulmuş ve pülsatif hale getirilmiş hava debisi rotametre ile ölçülmüştür. Bu değerler aynı tesisatta pülsatif olmayan akış halinde aynı rotametre ile ölçülen ortalama debi değeri karşılaştırılmıştır. Pülsatif akım halinde rotametrenin daha büyük bir debi değeri gösterdiği ve özellikle belirli frekanslarda hatanın çok büyük mertbelere ulaştığı tesbit edilmiştir. Genel olarak ölçme hataları, cihaz için üretici firma tarafından verilen ve aletin klası olarak isimlendirilen hata sınırlarının çok çok üzerinde bulunmuştur. Küçük debilerde söz konusu hatanın nisbeten daha büyük olduğu görülmüştür. Büyük debi değerleri için rorametre daha karalı olmaktadır. Bu sonuçlara göre rotametrenin özellikle çeşitli aykırılık elemanlarına sahip tesisatlarda kullanılırken ölçtüğü debilere ihtiyatla bakılması »gerektiği, ölçme doğruluğunu artırmak için akıştaki pülsasyonların söndürülmesi gerektiği söylenebilir.
Özet (Çeviri)
SUMMARY FLOWRATE MEASUREMENTS BY MEANS OF A ROTAMETER IN PULSATING FLOW We are greatly interested in the mean flowrates of different types of fluids that we use in the homes or in the factories and measure those flowrates by means of an instrument that was developed for measuring flowrate how much true are these mean flowrates that we measure'?* What is the accuracy of the instrument that we use? The errors of flowrate measurements of an instrument may increase day by day. For example, think the natural gas or the water that we use them in our homes. We measure how much natural gas or water by means of a flowmeter. The errors in the mean flowrate measurement will be able to increase in years and reach great amount of errors. The mean flowrates of the fluids are measured by a flowmeter. In any case there have to be some elements in the plant. For example, these are such elements as different types of valves, orifices, fitting elements, swing check valves. These types of elements make some discontinuities surfaces for the flow. Many researchers have shown theoretically and experimentally that these surfaces generate almost-periodic vortices induced by flow separation and make the flow fuleative. Pulsations have the character of elastic wave and go ahead and back at sound speed in pipelines, A rotameter is basically vertical internally tapered tube mounted with the large end at the top. Afloat with an outer diameter sligtly less than the minimum diameter of the tube is placed inside the tube. The clearance space between the float and the tube forms an annular passage or orifice. As the tube is tapered, the area of this orifice is larger when the float Is near the top that it İ3 when the float near the bottom. By connecting the tube into a fluid flow line so flow direction is from bottom to top, the float will move upward and be supported at a point where the orifice is just enough to p»ass the fluid flowing through the system.. In float flowmeters, the rate of flow can be read directly from a scale on the glass tube, graduated experimentally the top edge of the float serving as a pointer. The precise position of the float wihhin the tube is determined by several forces acting on it; 1- The weigth of the float, 2- The pressure drop of the flowing fluid between the VItop of the float and the bottom of the float multiplied by the largest area of the float, 3- Buoyancy of the float (weight of fluid volume d i s p 1 ac ed by t he f 1 oa t ) 4- Viscous aerodynamic or hydrodynamic drag of the fluid on the float. The float weight acts dawnwards-while pressure drop, buoyancy and drag all act upward on it. When the motion becomes steady, the float remains in equilibrium under the action of the hydrodymamic thrust on its lower surface acting upwards and the apparent weight acting downwards. If viscous aerodynamic drag of the fluid is neglected. t P - p“i A + V..... = V v is written. The pressure drop within the annular orifice; v.Cr, - y'i AP - p - p r= Af is found. The mean velocity of the fluid in the annular passage ; / AP v = / 2g-v~ C3^ can be written. Actual rate of flow O = 5Cdn r f z TQe y' /,g - |- ^ j is found. Where Cj denotes the flow coefficient. >ş radius of the float rim, \J the volume of the float, A$ the largest horizontal cross-section area of the float, ty, specific weight of the float, 2© the cone angle of the glass tube, Z lift of the float its zero position. Since the lift of the float securing the right hand side of this equation is the only variable. The rate of flow in rotameter with a small cone angle is directly VIIproportional to the lift of the float. A flow coefficient Cd takes into account losses caused by the resistance to flow through the annular orifice. The value of the flow coefficient Cd depends both the shape of the float and the rotameter tube and on the fieynoulds number In pulsating flow because of the flow rate varying with respect to time periodically the float wlllvibrate. However both the area of annular passage and the mean velocity of the fluid in annular passage vary with time. In this case if Bernoulli equation is performed between below surface of the float and the above surface of the f 1 oa t » V = -.-. + '->.'”*=! "> n 1 * 2 f ^ 1 is written. In this equation 1 - 26 is the equivalent diameter of the annular area, k is a dimensionless term that depends on velocity distribution in the cross-sections in which PI and P'2 are measured, velocity fluctuations and pulsations of discontinuities surfaces. p is fluid density» qjr actual flowrate after necessary operations are performed and = constant; B = ? = constant gj-j-r^Tgö 2TgÖ 5 = Z Tgö._, 3~ d dq v B v *P = A - - + - - ? C6) Z~ ~ dt is written. The time averaging operation! s performed to the terms of q and Z qv= qv+ qv ; z = z + z where ^v is timeaverage value of. v, v is flowrate fluctuations and z is time average value of z and z' is the lift fluctuations of the float. Assuming that the flowrate fluctuations are very small with respect to the time average value of q and if some terms are neglected comparedto the others; VIIIAPS A n q i + ^M + C7') is found. This equation shows APn which corresponds to qy is corresponds to the same 3, in whether the sign of or positive f 1 uc t ua t i ons that in pulsating flow greater than APO that steady flow. Because of q' and z7 is the minus 1 + + > 1 CEO If average value of 2 thqjt is observed in pulsating flow is used for finding q in the flowrate expression which is obtained in the steady flow ; q is allways greater than the actual mean flowrate of qv The difference between the measured mean flowrate and the actual mean flowrate Ci.e the error) depens on how big the flowrate fluctuation compared to the value of mean flowrate. However the flowrate fluctuation may be amplified by the system. If the frequency of the mean flowrate fluctuation is equal to the acoustic frequency of the system, the value of flowrate fluctuation t q' 3 may reach great amount. In this study, the behaviour of a rotameter is experimentally investigated in the pulsating flow. The ambient air is used in the experiment. The flow is made pulsative by means of a pulsator and the mean flowrate is measured by the rotameter. Frequencies of the pulsations can be changed from ser o to 11 Hs. The mean flowrate is firstly measured in steady flow C i.e there is no pulsation in the flow ) and then it is measured in the pulsating flow. The mean flowrate is measured by the rotameter at each pulsation frequency and compared with the mean flowrate which is measured by the same rotameter in the steady flow. The experiments are repeated for five mean flowrates and the relationship between the mean flowrate and the error is also investigated. Experimental results have shown that the flowrate pulsations is amplified by the system especially at near acoustic frequency of pipe system. And it causes increases of relative error in the measured mean flowrate It has been shown that this relative error depends on the amplitude and frequency of the mean flowrate pulsations, the mean flowrate, and the geometry of the installation. The relative error increases sharply at a certain IXfrequency t at the acoustic frequency of the system ) and reaches a maximum value. The amplitude of this maximum is getting greater with decreasing mean flowrate in a pipe system. Although the rotameter has placed at the output end of the pipe great amount of relative error was found out, Whereas if an orifice had placed instead of the rotameter» the relative error would have been less and less amount, If the systematic relative error in the measured mean flowrate is wanted lesser, an orifice plate must prefer to a rotameter.
Benzer Tezler
- Simüle yetişkin CPB devresinde pulsatil flow esnasında hat basıncına bağlı şant akışlarının değerlendirilmesi
Evaluation of shelf flows through the line pressure on the pulsatil flow in the adult CPB circuit
LEVENT ÇİFTÇİ
Yüksek Lisans
Türkçe
2019
Sağlık EğitimiÇanakkale Onsekiz Mart ÜniversitesiKalp ve Damar Cerrahisi Ana Bilim Dalı
DOÇ. DR. TOLGA KURT
- Hepatosellüler karsinomanın ayırıcı tanısında Renkli Doppler Ultrasonografi'nin yeri
Başlık çevirisi yok
LEVENT NUMBUÇ
Tıpta Uzmanlık
Türkçe
1996
Endokrinoloji ve Metabolizma HastalıklarıDicle ÜniversitesiDOÇ.DR. VEDAT GÖRAL
- Kalp cerrahisinde pulsatil ve nonpulsatil akımların preoopreatif ve postoperatif etkilerinin karşılaştırılması
Comparison of the preoperative and postoperative effects of pulsatil and nonpulsatil flows in heart surgery
ÖZKAN SÖNMEZ
Yüksek Lisans
Türkçe
2019
Göğüs Kalp ve Damar Cerrahisiİstanbul Medipol ÜniversitesiPerfüzyon Ana Bilim Dalı
PROF. DR. KORHAN ERKANLI
- Açık kalp cerrahisi uygulanan hastalarda pulsatil ve nonpulsatil akımların karşılaştırılması
Comparision of pulsatile and nonpulsatile flows in patients undergoing open heart surgery
ELMAS KARTAL
Tıpta Uzmanlık
Türkçe
2009
Anestezi ve ReanimasyonSelçuk ÜniversitesiAnesteziyoloji ve Reanimasyon Ana Bilim Dalı
YRD. DOÇ. DR. GAMZE SARKILAR
- Kesikli yüksek frekanslı akımların mikroanastomozlar üzerine etkileri
Başlık çevirisi yok
HAYATİ DURMAZ
Tıpta Uzmanlık
Türkçe
1986
Ortopedi ve Travmatolojiİstanbul ÜniversitesiOrtopedi ve Travmatoloji Ana Bilim Dalı
DOÇ. DR. MİŞEL KOKİNO