EFFECT OF NOZZLE DIAMETER ON JET IMPINGEMENT COOLING SYSTEM DULFHARAH NIZAM BIN MEMTH ALI

Transcription

1 EFFECT OF NOZZLE DIAMETER ON JET IMPINGEMENT COOLING SYSTEM DULFHARAH NIZAM BIN MEMTH ALI A report submitted in partial fulfilment of the requirements For the award of the degree of Bachelor of Mechanical Engineering Pure Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG NOVEMBER 2009

2 ii SUPERVISOR S DECLARATION I hereby declare that I have checked this project and in my opinion this project is adequate in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering. Signature Name of Supervisor: WAN AZMI BIN WAN HAMZAH Position: LECTURER Date:

3 iii STUDENT S DECLARATION I hereby declare that the work in this thesis is my own except for quotations and summaries which have been duly acknowledged. The project has not been accepted for any degree and is not concurrently submitted for award of other degree. Signature Name: DULFHARAH NIZAM BIN MEMTH ALI ID Number: MA06046 Date:

4 iv I humbly dedicate this thesis to my lovely mom and dad, Rogayah Mahmud and Memth Ali my dearest sister, Shakina Shanaz, Nurul Anizah and Balqis Faradilla my dearest brother, Hariz Irfan my heart and soul, Nurul Farahdilah who always trust me, love me and had been a great source of support and motivation.

5 v ACKNOWLEDGEMENTS First I would like to express my grateful to ALLAH s.w.t. as for the blessing given that I can finish my project. In preparing this paper, I have engaged with many people in helping me completing this project. First, I wish to express my sincere appreciation to my main thesis supervisor Mr. Wan Azmi Wan Hamzah, for encouragement, guidance, advices and motivation. Without his continued support and interest, this thesis would not have been the same as presented here. The next category people who help me to grow further and influence my project are my colleagues especially my projectmate Mr. Mohammad Khyru Bin Aris and Mr. Khaider Bin Abu Bakar who always help me in order to finish this project. I would like to express my gratitude especially to all FKM laboratory instructors for their help and advices. I appreciate very much to them because of the idea and information given. I acknowledge my sincere indebtedness and gratitude to my family for their love, dream and sacrifice throughout my life. My father, mother, brother and sisters that always support, motivation and encourage me to success.i cannot find the appropriate words that could properly describe my appreciation for their devotion, support and faith in my ability to attain my goals. Special thanks should be given to my presentation s panel members. I would like to acknowledge their comments and suggestions, which was crucial for the successful completion of this study. Thank you all.

6 vi ABSTRACT This research focused on the study about the effect of nozzle diameter on jet impingement cooling system. The impinging jet can be described as a phenomenon in which the fluid exiting from a nozzle or orifice hits a wall or solid surface usually at normal angle. Impinging air jets have been widely used in many industrial applications in order to achieve enhanced coefficients for convective heating, cooling or drying. A single air jet or arrays of air jets, impinging normally on a surface are an effective method to enhance heat and mass transfer. Engineering applications that widely use air jets include cooling of hot steel plates, tempering of glass plates, drying of textiles and paper, cooling of turbine blades, electronic components and de-icing of aircraft. Experiments were conducted to determine the effect of nozzle diameter on the heat transfer coefficients from a small heat source to a jet impingement cooling system, submerged and confined air. The experiment were carried out with a single jet with three different nozzle diameter, d; 0.5, 1.0, 2.0 cm and four dimensionless jet to heat source spacing, S/d (6, 8, 10, 12) were tested within the laminar jet Reynolds number ranging from The results indicate that the heat transfer coefficient, h increase with the increasing nozzle diameter at the stagnation point region corresponding to 0< r/d <4. This may be attributed to an increase in the jet momentum and turbulence intensity level with the larger nozzle diameter, which results in the heat transfer augmentation. However, the effect of the nozzle diameter on the Nusselt numbers does not exist at the wall jet region corresponding to r/d>4. This may be attributed to the fact that the impinging jet flow characteristics are almost lost in the process of the redevelopment of the boundary layer after the jet impinges on the plate. By the increasing of the heat transfer coefficient, h the local Nusselt number, Nu also will be increase. This research are significant to improve the overheat component and devices problem nowadays. The results can also significantly increase the performance of the needed component in order to improve product reliability and customer satisfactions.

7 vii ABSTRAK Penyelidikan ini difokuskan pada kajian tentang kesan daripada diameter nozel pada sistem pendingin hentaman jet. Hentaman jet dapat digambarkan sebagai sebuah fenomena di mana bendalir keluar daripada nozel atau lubang hits dinding atau permukaan pepejal biasanya di sudut normal. Sistem penyejukkan hentaman jet telah banyak digunakan di banyak aplikasi industri untuk mencapai peningkatan pekali untuk konvektif pemanasan, pendinginan atau pengeringan. Sebuah jet udara tunggal atau array daripada jet udara, biasanya menghentam pada suatu permukaan adalah kaedah yang berkesan untuk meningkatkan perpindahan haba dan perpindahan jisim. Teknik aplikasi yang digunakan secara meluas meliputi pendinginan jet udara panas plat baja, penemperan daripada kaca piring, pengeringan tekstil dan kertas, pendinginan kipas turbin, komponen elektronik dan penyejukan pesawat. Eksperiment dilakukan untuk menentukan kesan diameter nozel pada pekali perpindahan haba dari sumber panas kecil untuk sistem penyejukkan hentaman jet, tenggelam dan terkurung udara. Eksperiment dilakukan dengan satu jet dengan tiga diameter nozel yang berbeza iaitu 0.5, 1.0, 2,0 cm dan dengan tiga jarak berdimensi dari hujung jet ke sumber panas, S / d (6, 8, 10, 12) yang diuji dalam nombor Reynolds jet laminar berkisar Hasilnya menunjukkan bahawa pekali perpindahan panas, h meningkat dengan peningkatan diameter nozel pada titik stagnasi pada daerah sesuai dalam lingkungan 0< r/d <4. Hal ini mungkin disebabkan oleh peningkatan momentum jet dan peningkatan intensitas ombak dengan diameter nozel yang lebih besar, yang menghasilkan perpindahan panas augmentasi. Namun, kesan daripada diameter nozel pada nombor Nusselt pada jet dinding tidak wujud dalam lingkungan untuk r/d > 4. Hal ini mungkin disebabkan fakta bahawa ciri aliran hentaman jet hampir hilang dalam proses pembangunan semula lapisan batas selepas jet menghentam pada permukaan rata. Dengan meningkatnya pekali perpindahan panas, h nombor Nusselt, Nu juga akan meningkat. Penyelidikan ini adalah penting untuk peningkatan kajian komponen terlalu panas dan masalah peranti saat ini. Hasilnya juga dapat secara signifikan meningkatkan prestasi komponen yang diperlukan dalam rangka untuk meningkatkan kehandalan produk dan kepuasan pelanggan.

8 viii TABLE OF CONTENTS SUPERVISOR S DECLARATION STUDENT S DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF ABBREVIATIONS Page ii iii iv v vi vii viii xi xiii xv xvii CHAPTER 1 INTRODUCTION 1.1 Project Background Problem Statement Project Objectives Project Scopes 3 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction Jet Impingement Configurations of Impinging Jets Characteristic Zones in the Impinging Jet Prior Study Theory of Study Convection Heat Transfer Laminar Flow Reynolds Number Newton s Law of Cooling Steady State Equation Nusselt Number 20

9 ix CHAPTER 3 METHODOLOGY 3.1 Introduction Project Flow Chart Apparatus Experiment Setup Heat Source Configuration Procedures of Experiment Flow of the Experiment Experiment Data Distribution 30 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Introduction Data of Experiment Results Calculation of Important Parameter Result and Discussions Analysis 1: Graph by Reynolds Number varies Nozzle 37 Diameter Analysis 2: Graph by Distance Ratio varies Nozzle 45 Diameter Analysis 3: Graph by Nozzle Diameter varies Reynolds 53 Number Analysis 4: Graph by Nozzle diameter varies Distance ratio, S/d Project Constraint 55 CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 5.1 Conclusions Recommendations Suggestions Problem of The Research 58

10 x REFERENCES 59 APPENDICES 61 A Table A B1-B6 Data of Experiment 62 C Sample of Calculation 68 D1-D2 Graph of Plate Temperature After Impingement Versus 69 Dimensionless Radial Distance from The Stagnation Point E1-E2 Graph of Heat Transfer Coefficient Versus Dimensionless Radial 71 Distance from The Stagnation Point F1-F2 Gantt Chart 73 G Experiment Progress 75

11 xi LIST OF TABLES Table No. Title Page 3.1 List of the equipments typically required for the experiment effect of nozzle diameter on jet impingement cooling system Experiment data distributions for d = 0.5cm Experiment data distributions for d =1.0cm Experiment data distributions for d = 2.0cm Experiment data distributions for d = 2.0cm Distribution data of mass flow rate, for all case Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 2300 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 2300 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 2300 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 2300 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 500 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 950 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 1960 and S/d = Value of heat transfer coefficient, h and Nusselt number, Nu for Re = 2300 and S/d = Table A Temperature distributions for nozzle diameter, d = 0.5 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 0.5 cm and Reynolds number, Re =

12 xii 6.4 Temperature distributions for nozzle diameter, d = 0.5 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 0.5 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 1.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 1.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 1.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 1.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 2.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 2.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 2.0 cm and Reynolds number, Re = Temperature distributions for nozzle diameter, d = 2.0 cm and Reynolds number, Re = Experiment progress 75

13 xiii LIST OF FIGURES Figure No. Title Page 1.1 Jet impingement heat transfer mechanism An impingement jet a) Submerged jet; b) Free impinging jet a) Unconfined impinging jet; b) Confined impinging jet Characteristic zones in impinging jets Local heat transfer coefficient distribution for d = 0.5mm, 1mm and 1.5mm, H/d = 2 and Re = 5000 (Air) Local heat transfer coefficient distribution for d = 1mm, H/d = 1, 2 and 4 and Re = (Air) Heat convection current triggered by a radiator and in boiling water Laminar boundary layer Project process flow chart Arrangement of the experiment Heat source configuration Process of the experiment Effect of nozzle diameter on the local Nusselt number distribution for Re = 2300 and S/d = Effect of nozzle diameter on the local Nusselt number distribution for Re = 2300 and S/d = Effect of nozzle diameter on the local Nusselt number distribution for Re = 2300 and S/d = Effect of nozzle diameter on the Nusselt number distribution for Re = 2300 and S/d = Effect of nozzle diameter on the Nusselt number distribution for S/d = 6 and Re =

14 xiv 4.6 Effect of nozzle diameter on the Nusselt number distribution for S/d = 6 and Re = Effect of nozzle diameter on the Nusselt number distribution for S/d = 6 and Re = Effect of nozzle diameter on the Nusselt number distribution for S/d = 6 and Re = Nusselt number distribution for d = 2.0cm, S/d = 6 and Re = 500, 950, 1960 and Nusselt number distribution for d = 2.0cm, Re = 2300 and S/d = 6,8,10, Nusselt number distribution for d = 1.0cm, Re = 2300 and S/d = 6,8,10, Plate temperature versus r/d for Reynolds number, Re = 500, and S/d (a) 6, (b) 8,(c) 10, (d) Plate temperature versus r/d for Reynolds number, Re = 2300, and S/d (a) 6, (b) 8,(c) 10, (d) Heat transfer coefficient versus r/d for Reynolds number, Re = 500, and S/d (a) 6, (b) 8, (c) 10, (d) Heat transfer coefficient versus r/d for Reynolds number, Re = 2300, and S/d (a) 6, (b) 8, (c) 10, (d) Gantt chart for FYP Gantt chart for FYP 2 74

15 xv LIST OF SYMBOLS or t μ Thickness, (m) Dynamic viscosity of the fluid, (Pa s or N s/m²) Mass flow rate, (kg/s) Heat convection rate, (Watt) Rate of net heat transfer, (kj/s) ρ ν d D Density of the fluid, (kg/m³) Kinematic viscosity, (ν = μ / ρ), (m²/s) Nozzle diameter, (m) Wall diameter, (m) h Convection heat transfer coefficient, (W/m 2. ⁰ C) k Thermal conductivity, (W/m.K) A c Plate cross-section area, (m 2 ) A s Heat transfer surface area, (m 2 ) C p L or r L h Nu Q Re S T T T s Constant pressure specific heat, (kj/kg.k) Radius of the impingement region, (m) Hydrodynamic entry length, (m) Nusselt number Volumetric flow rate, (m³/s) Reynolds number Exit nozzle to heat source plate distance, (m) Temperature different, (K) Ambient temperature, ( C) Surface temperature, ( C)

16 xvi T p Tp avg Plate surface temperature, ( C) Average temperature of the plate surface, ( C) V Mean fluid velocity, (m/s)

17 xvii LIST OF ABBREVIATIONS FKM FYP Fakulti Kejuruteraan Mekanikal Final year project

18 CHAPTER 1 INTRODUCTION 1.1 PROJECT BACKGROUND Impingement heat transfer is considered as a promising heat transfer enhancement technique. Among all convection heat transfer enhancement methods, it provides significantly high local heat transfer coefficient. At the surface where a large amount of heat is to be removed /addition, this technique can be employed directly through very simple design involving a plenum chamber and orifices. For instance, in gas turbine cooling, jet impingement heat transfer is suitable for the leading edge of a rotor airfoil, where the thermal load is highest and a thicker cross-section enables accommodation of a coolant plenum and impingement holes. This technique is also employed in turbine guide vanes (stators). Other applications for jet impingement could be combustor chamber wall, steam generators, ion thrusters, tempering of glass, electronic devices cooling and paper drying, etc. Jet impingement cooling (or heating as well) is a very effective heat transfer mechanism. The main reason is that jet impingement flow forms a very thin boundary layer, as shown in the top plot in Figure 1.1. Impingement means collision that the coolant flow collides into the target surface and guarantees a thin stagnant boundary layer at the stagnant core for cold coolant contacting the hot surface without damping. The bottom plot in Figure 1.1 shows that the heat transfer coefficient decays as radius increases except that a second peak occurs when jet is close enough to target surface (small z).

19 2 Figure 1.1: Jet impingement heat transfer mechanism Source: Osama M. A. Al-aqal, (1999). 1.2 PROBLEM STATEMENT A wealth of information exists on the basic cases on individual and array jet impingement heat transfer. This information is widely used within the gas turbine design community for applicable impingement configuration and flow parameters. However, lately, newer and more specific cases of cooling design require additional information to account for affect on the impingement heat transfer of film coolant extraction, prefilm impingement chamber, compartmentalized or zonal impingement, roughened target surfaces, and confined impingement within various wall structures. The present study is undertaken to investigate the effects of nozzle diameter on impinging jet heat transfer and fluid flow. Nusselt numbers are determined for a submerged air jet issuing from a long straight nozzle. Of interest in such geometry is the heat transfer on the target surface or impingement wall. In integral structures of airfoils, end walls, or liners, the total heat transfer distribution is important to the proper assessment of thermal mechanical loading in the component.

20 3 1.3 PROJECT OBJECTIVES Experimental studies of an impingement jet cooling system. The primary objectives are: To study about the effect of nozzle diameter on the jet impingement cooling. To define the relationship between the heat transfer coefficient, h with the Reynolds number, Re and the distance from end nozzle to the heat source, S. 1.4 PROJECT SCOPES This experimental study was carried out using air as the coolant medium that impinge with laminar flow region from the nozzles to the heat source which has Reynolds number in the range of (500, 950, 1960, and 2300). The diameter of nozzle was varies for the purpose of this study by use three different diameter of nozzle, started with 0.5cm,1.0cm and 2.0cm. The heat source will be at constant temperature with 100 C which used steel as the material and had dimensions (12 x 12 x 0.8) cm with 6.5cm diameter impingement region. But the nozzle length is constant for this case with 50cm and the material of nozzle is PVC (diameter-2.0cm) and the other of the diameter use vinyl as a material. The dimensionless parameter that was defined in this study is diameter ratio, D/d (3.25, 6.5, and 13) and the dimensionless jet to heat spacing, S/d (6, 8, 10, and 12). Then, the temperature effect is measured on the heat source plate by using Non-contact Thermometer by pointing on the heat source plate point prepared. The nozzle jet impingement was designed and fabricated with the appropriate dimension (diameter and length) of nozzle.

21 CHAPTER 2 LITERATURE REVIEW 2.1 INTRODUCTION The use of impingement jets for the cooling of various regions of modern gas turbines is widespread, most especially within the high pressure turbine. Since the cooling effectiveness of impingement jets is very high, this method of cooling provides an efficient means of component heat load management and gives sufficient available pressure head and geometrical space for implementation. Regular arrays of impingement jets are used within turbine airfoils and endwalls to provide relatively uniform and controlled cooling of fairly open internal surface regions. Such regular impingement arrays are generally directed against the target surfaces by the use of sheet metal baffle plates, insert, or covers that are fixed in position relatives to the target surface. These arrangements allow for the design of a wide range of impingement geometries, including in-line, staggered, or arbitrary pattern of jets. In more confined regions of airfoils such as the leading edge or trailing edge, spanwise lines of impingement jets are sometimes used to focus cooling on one primary location of high external heat load like the airfoil s stagnation region. In these cases, impingement jets may be delivered by orifices that have been cast or machined into the internal structural members of the airfoil. There also exist many other applications for the individual impingement jets on selected stationary and rotating surfaces. Vane endwalls, blade platforms, and unattached shroud may all have specific local cooling requirement well suited to the use of individual jet cooling. Impingement jets are also used on rotor disk cavity faces, and in some applications may provides additional functions of sealing. The use of impingement cooling is not confined to the turbines component, however, as

22 5 combustor component such as liners, transition pieces, and splash plates also make good use both individual and array impingement cooling. 2.2 JET IMPINGEMENT The impinging jet can be defined as a high-velocity coolant mass ejected from a hole or slot that impinges on the heat transfer surface (Figure 2.1). A characteristic feature of this flow arrangement is an intensive heat transfer rate between the wall and the fluid. It predetermines the fluid jets to be widely used in industrial applications where intensive heat transfer rates are needed, for example for cooling of turbine blades, laser mirrors and electronic components, for paper drying, and so forth. Figure 2.1: An impingement jet Source: Osama M. A. Al-aqal, (1999) Configurations of Impinging Jets Two qualitatively different flow configurations can distinguish: submerged impinging jets and free impinging jets (Figure 2.2). In the former case, the fluid issuing from the nozzle is of the same nature as the surrounding. In the latter case, the fluids are of a different nature (e.g., a water jet issuing in air). The dynamics of both cases are different. In submerged jets, a shear layer forms at the interface between the jet and the surrounding

23 6 fluid. This shear layer is unstable and it generates turbulence. In free jets, this kind of instability is usually not important, and the turbulent motion in the shear layer does not have a substantial effect on the flow. Figure 2.2: a) Submerged jet; b) Free impinging jet Source: Osama M. A. Al-aqal, (1999) In terms of geometry, there are two cases: a planar case with the jet issuing from a slot, and an axisymmetric case with a round nozzle. The dynamics of both cases are different: round jets exhibit formation of axisymmetric vortex rings, which are stretched during their convection along the wall. In plane jets, the vortices are formed as filaments parallel to the slot. They are created on both sides of the jet, either in symmetric or antisymmetric mode. These vortex filaments are not stretched. Many others geometries are also possible--jets issuing from square, rectangular, or elliptical nozzles; oblique jets; and others.

24 7 Figure 2.3: a) Unconfined impinging jet; b) Confined impinging jet Source: Osama M. A. Al-aqal, (1999) There is a further distinction between unconfined and confined jets (Figure 2.3). Confinement, which is common in industrial applications, causes flow recalculation around the jet. In industrial applications, the cooled surfaces are usually large, and a single jet is usually not sufficient for cooling it. In this case, an array of jets is used. The flow in arrays is rather complex Characteristic Zones in the Impinging Jet The flow field in an impinging jet can be divided into three characteristic regions (Figure 2.4): the jet zone, the stagnation zone, and the wall jet zone. The jet zone is situated directly beneath the nozzle. The fluid issuing from the nozzle mixes with the quiescent surrounding fluid and creates a flow field, which is up to a certain distance from the wall identical with the flow field of a submerged nonimpinging jet. The jet flow is undeveloped up to six or seven nozzle diameters from the nozzle lip. Consequently, in most applications, the nozzle-to-plate distance is too small to enable the developed jet flow condition. A shear layer forms around the jet. Its properties depend strongly on the nozzle type. In most situations, except a laminar flow from a tube nozzle, the shear layer is initially relatively thin compared to the nozzle diameter, and therefore its dynamical behavior is similar to that of a plane shear layer. The shear layer thickness