Sürgülü yön denetim valflerinde yük kaybının yarattığı ısı miktarı

Abstract

Hidrolik, enerji iletiminin giderek yaygınlaşan ve benimsenen vazgeçilmez bir parçasıdır. Bir hidrolik devre elemanı olan ve sunulan çalışmanın konusu olan, sürgülü yön denetim valflerinin önemi her geçen gün daha da artmakta, uygulama alanları gelişmektedir. incelenen olayda kullanılan NG6 ve NG10 büyüklüğündeki sürgülü yön denetim valfleri, endüstride kullanılan valflerin sayıca %85'ni oluşturmaktadır. Sürgülü yön denetim valflerinin geometrisi ve akışkanın izlediği yol, şimdiye kadar üzerinde çalışılan basit geometrilere göre oldukça karmaşık ve analitik çözüm yapılamıyacak kadar da zor olduğu için tam bir teorik modeli yoktur. Bu nedenle simülasyonu bilgisayar yardımı ile gerçekleştirilen teorik bir model geliştirilmiştir. Sürgülü valflerin deneysel olarak incelenmesi pahalı, külfetli ve zaman alıcıdır. Bundan dolayı deneyler, tasarımı özel olarak yapılan dijital - analog çevirici bir elektronik kart ve özel olarak yazılan bilgisayar programı ile hassas olarak yapılmıştır. Yapılan teorik çalışma ile akışı simule eden bilgisayar programına sadece valfin geometrisi ve akışkanın giriş şartları girilerek, valfın içindeki akış incelenmiştir. Valf sürgüsünde yapılan geometri değişikliği ile sadece bazı valflerde basınç düşümünü ve sıcaklık artımını, düşük seviyede iyileştirici etkisi bulunmuştur. Mevcut ve geometri değişikliği yapılan sürgülü yön denetim valflerinde oluşan ısı ve basınç kaybının büyüklüğü için elde edilen sonuçlar detaylı olarak verilmiştir. Geliştirilen teorik modelin deneysel çalışma ile uyumlu olduğu görülmüştür. Yeni geliştirilecek olan valflerde, geometri değişiklikleri, bu model sayesinde ucuz, hızlı ve en önemlisi bilgisayar ile simule edilerek yapılabilecektir. Böylece çok değişik geometriye sahip valflerde, olabilecek ısı üretimi ve yük kayıpları imalattan önce, valfler imal edilmeden hesaplanabilecektir. Bu şekilde üretilecek olan verimi yüksek valflerin sağladığı ekonomik fayda çok fazla olacaktır.

Experience has shown that hydraulics is now indispensable as a modern method of transferring energy. Hydraulic drives and controls have become more and more important due to automation and mechanization. Today, a very large amount of modern and powerful machinery is controlled either partly or completely by hydraulics. The use of hydraulic systems for control and regulation has made possible important fields for automation. However, m spite of the wide range of application, the knowledge of this specialized field has not yet been circulated to a high enough degree. As a result of this, the application of hydraulic systems has been restricted. Whoever decides to use hydraulics for power transmission and movement, however, is not treading on a new ground. Examples of application from various sectors of industry can be divided into five sectors. These are Industrial hydraulics, Hydraulics in steelworks with Civil Engineering and Power Generation, Mobile hydraulics, Hydraulics in special technical applications, Hydraulics for marine applications. Naturally, this summary does not include all possibilities of application, since the variety of hydrauiically operated machines is too great. However, it can be seen that hydraulics have today made headway in almost all sectors of industry. Start, stop and direction of flow of a pressure fluid are controlled by means of a spool type directional control valve. In this study, a geometrical model of spool type valve has been made. The data acquisition of the experiments has been done with the help of a special electronic card, software and a PC. Geometry of the this study is too complicated. Directional spool valves consist of a moving spool which is situated in the valve housing. Depending on the number of flow paths to be controlled, two or more annular channels are formed or casted into a housing made of hydraulic cast iron, spherical graphite cast iron, steel or other suitable materials. These channels run either concentrically or eccentrically around a bore. Hence, control lands are formed in the housing, allowing moving spoils to act together with the control spooi lands. When the control spool is moved, it connects or separates the annular channels in the housing. Direct operated directional spooi valves imply that they are directional spooi valves and they may be operated directly by solenoid, pneumatic / hydraulic Xil forces or by a mechanically acting device without any intermediate amplification. In a housing with a central axial bore, radial channels are at fixed distances while in operation. These channels are fed from the outside as line ports. In the main axial bore, a spool with turned control grooves (annular grooves) is set at a predefined position with respect to the housing bore by means of the operating element. This is so that the channels may be isolated from or connected to each other via the annular grooves. The operating curves, pressure drop differences in the spool type directional valves are given with the accuracy of ± 30% in producers' catalogues. The new valves have a considerably lower pressure drop than the older design. The main reasons for this are the increase in spool diameter from 16mm to 18mm, longer spool travel of 4,2mm and improvements in the valve design. The process of energy conversion and transmission involves losses in which mechanical and hydraulic energy is converted into heat. The operating temperature is one of the factors governing the efficiency of a hydraulic system. Low pressure drop and low heat generation valves mean energy saving and low cost hydraulic system without adding a cooling system. Heat transfer from rough surfaces and corrugated ducts has received a great deal of attention due to the many practical applications for increasing the effectiveness of heat transfer and the difficulty in optaining analytical solutions for the temperature, pressure and velocity fields. Laminar flow heat transfer occurs in a variety of engineering problems and is of particular importance where viscous liquids are heated or cooled. Until now, only for simple geometries' pressure drop and heat generation have been tested, measured and calculated. Spirally fluted annuii, oscillatory wavy-walled-tube, externally enhanced inner tube, corrugated ducts with rounded corners have been studied, and the results have been given by the use of geometrical dimensions. Subject of this study's spool type valve geometry is too complicated to apply the same models studied earlier. This difficulty has forced us to use special software to simulate the flow. For the simulation, a geometrical model has been used and software the d_phoe20 has been used for this purpose and outputs are shown in the related chapter. For the simulation of the flow, below assumptions are made : xm a) the flow is laminar; b) the fluid with constant properties is Newtonian and incompressible; c) the flow is steady; d) inlet and outlet flow is uniform; Numerical simulation for steady, 3D laminar flow with BFC coordinate system utilizing finite volume procedure was performed. 8x22x64 grids are used in order to assess the sensitivity of the results for Navier-Stokes equations. The method has proved its accuracy for flows in complex geometries using non-orthogonal body-fitted coordinate systems. The method is based upon standart finite-volume techniques for discretising the governing equations for conservation of mass, momentum, energy etc. Gear type pump with 24 Ipm. and maximum 150 bar oil pressure supply, pressure relief valve, hand operated directional' control valve and a pressure gauge are used for the hydraulic unit which is to obtain flow and pressure to test the valves. Pressure, flow and temperature are always followed up with the help of specially designed electronic card, software and a PC. Turbine type flow sensor for measuring ranges of 0 + 60 Ipm. with direct analogue output 4-20 mA was used and for measuring ranges 0-50 bar piezo - resistive type pressure transducers were used. Temperature was measured with thermoelemans. Digital - analogue - digital electronic card was designed and used to collect all these output pressure, flow, temperature data to evaluate and display on a PC. A 80386 based PC's RS232 output was used for this purpose. This digital - analogue - digital electronic card is also has four voltage outputs for controlling proportional flow and pressure control valves. These voltage outputs are controlled with PC and voltages are monitored on the screen. "C" software program was written for all data acquisition from electronic card and monitoring / controlling on the PC monitor. This software and electronic card are enough for controlling a hydraulic machine with a PC. Directional spool valves size NG6 and NG10 were used for the experiments because these valves are among the 85% of the total number of the hydraulic valves used in general. Spool positions D, E, G, H, J, M, Q, W for size NG6 valve and D, E, G, H, J, M, Q for size NG1 0 valve were tested. The existing spool geometry differences In spool position J size NG6 valve was applied to the other spools for NG6 and NG10 vaives. Change in geometry was applied to the spool positions D, E, Q for size NG6 valve and D, E, J, for size NG10 valve. Discs' inner surfaces facing each other XIV were carved 0,8 mm and 1,2 mm for NG6 and NG10 size valves in respectively. It has a 21° inclination like half conic cave. The annular gap has little effect on the pressure drop and heat generation. Experimental results for each valve size is defined as below. New design has made a positive effect for NG6D(a), NG10D, NG10E(a), NG10J(a) valve positions to decrease temperature differences. For the pressure drop, NG6D(a), NG6E(b), NG6Q(a), NG10D, NG10E(a), NG10J(a) valves positions have also made positive effect. Results of this thesis can be given in four groups. a) Special digital - analogue - digital electronic card for dafa acquisition was designed and its software in "C" programming language was developed. Experiments were processed continuously with a PC in high precision. b) Outlet temperature and pressure were calculated with the d_phoe20 simulation program by describing the valve model to the software. Temperature, pressure and velocity distribution were also simulated in the valve. With the help of the simulation program and the model, the effect of the model geometry was simulated in the valve. This model will help to reduce high cost of experimental expense and time. c) The flow was simulated under adiabatic assumption. The effects of adiabatic assumption were calculated and given in the results, in the table below, the results of the existing NG10E(a) valve is given. The simulated results are compared with the experiments. d) The existing spool geometry differences in spool position J size NG6 valve are applied to the other spools for NG6 and NG10 valves. The changes in geometry made positive effects for some type of valves. Comparision of theoretical and experimental results are given below : a) Theoretical results : XV b) Experimental results : The present study is in complete agreement with experimental and theoretical study. Maximum experimental and theoretical result differences for the total pressure loss and heat generation are not more than 5%. Pressure drop and heat transfer in industrial valves are of importance in reducing cost and not having to add a cooling system. Experimental and analytical solutions until now have not been so sufficient. This experimental based, digital - analogue - digital electronic card data acquisition with software and simulation the d_phoe20 software support study will help valve design be more energy efficient in the future.