INTERNSHIP REPORT 1/3 (first of three) Period: from 10/02/2010 to 31/03/20100

Transcription

1 Universidade Federal de Santa Catarina Centro Tecnológico Departamento de Engenharia Mecânica Coordenadoria de Estágio do Curso de Engenharia Mecânica CEP Florianópolis - SC - BRASIL estagio@emc.ufsc.br INTERNSHIP REPORT 1/3 (first of three) Period: from 10/02/2010 to 31/03/20100 EMBRACO Slovakia s.r.o. Student s name: Janos Franzner da Silva Supervisor s name: Norbert Brath Orientator s name: César José Deschamps Spišská Nová Ves, April 2010

2 Table of Contents 1 THE COMPANY 2 2 RESEARCH AND DEVELOPMENT DEPARTMENT 3 3 THE INTERNSHIP INTRODUCTION REFRIGERATION THE COMPRESSOR PROPOSAL SCHEDULE NEU PROJECT COMPRESSOR INSTRUMENTATION EFFECTIVE AREA OTHER ACTIVITIES ALUMINUM CYLINDER HEAD THERMAL PROFILES LABORATORIES 14 4 DISCUSSIONS AND CONCLUSIONS 15 5 REFERENCES 16 6 ANNEXES CFX - EFFECTIVE AREAS OF FLOW AND FORCE ANSYS MECHANICAL NJ ALUMINUM CYLINDER HEAD 19 1

3 1 The Company Specialized in cooling solutions, EMBRACO is the world leader in hermetic compressors, and has the mission "Provide innovative solutions for a better quality of life". With factories in Brazil, Italy, China and Slovakia and productive capacity of 27 million compressors per year, it also produces cast iron, electronic components, condensers and evaporators that are used as part of condensing and sealed units, and electronic systems to make "intelligent" household appliances. Founded in 1971, in Joinville, Santa Catarina State, in the South of Brazil, Embraco started to produce compressors in 1974 with the initial purpose to supply the demand of the Brazilian refrigeration industry, which at that time relied entirely on imported compressors. In that same decade, it started exporting and in the next decade it had already negotiated compressors in all continents. In early 90 s, anticipating the globalization of the economy, Embraco started the process to open productive units outside Brazil and, consequently, to increase the global structure of sales. Soon it was already the world leader in the market. Today, EMBRACO employees about people worldwide. With the talent of its professionals and the constant investments in technology, it became a supplier of excellence, which products are preferred by great assembling companies of household appliances in the world and outstanding manufacturers of commercial cooling market. Since May 2006, Embraco has been operating in Brazil under the official name Whirlpool S.A. That change is due to the merge of Empresa Brasileira de Compressores S.A. Embraco and Multibrás S.A. Eletrodomésticos. However, Embraco's operation remains independent in its structure, once the business has its peculiarities. Extracted from Embraco s Homepage 2

4 2 Research and Development Department The Research and Development Department as the name says is responsible for the constant improvement of products and processes of the company. There are performed projects for raising efficiency, costs reductions, reliability and also innovations. The department is compound of an office and seven laboratories. In the office a group mainly formed by engineers and designers works aided by computational tools for designing new components, redesigning old ones and doing evaluations of their results. The laboratories are the following: Samples and Prototypes, Evaluation, Acoustic, Electrical, Application, Tribology and Mechanical and its main activity of is to perform the test or sample assembly following the customer request. Samples and Prototypes are responsible for the activities of assembling and dissambling compressors. There is this special laboratorie because of the special assemblies that may be required by the customers or by internal purpose. Evaluation performs the activities of acquiring data about the compressor. These are mainly the calorimeter tests. The calorimeter is a device used for testing the compressor and that is able to measure mass flow, refrigerant capacity, coefficient of performance, electrical consumption and others. Also this device can be set to various pressures and temperatures conditions of evaporation and condesantion and environment temperature too. Acoustic principally runs noise tests, impact tests and vibration measuraments. With this acquisitions it is possible to evaluate the noise and vibration level of the compressor. Additionally there are tasks for reducing the noise level of the compressor by changing or redesiging some componentes. Electrical is responsible by the motor and electrical components of the compressor. They evaluate electrical parameters but also design new components aiming the improving of performance of the compressor. Application performs the most varied tests. May be mentioned the slug test, defrost test, fan test and domestic and commercial cooling. The slug test measure the behaviour of the compressor in critical conditions of refrigerant charge. Defrost test verifies the amount of time that takes for desfroting ice when a hot air flow is passed through the evaporator. Fan test is for measuring the air flow of fans. Finally, the commercial and domestic cooling tests is about measuring refrigerators running in different conditions of temperature and humidity of the environment. Tribology analyzes the compressor components after the compressor stayed running for a specified time. This analysis focus on the wear of the moving parts but also check other things like the formation of parafin in the tubes. Lastly, Mechanical is where the compressor is instrumentated with thermocouples, pressures transducers and others electrical devices for specified purposes. With this paraphernalia it is possible to measure the thermal profile of compressor, pressure pulsations in the chambers, valve movement, pv diagram and others parameters that aids in the understanding of the compressor. 3

5 3 The Internship 3.1 Introduction Refrigeration A major application area of thermodynamics is refrigeration, which is the transfer of heat from a lower temperature region to a higher temperature one. Devices that produce refrigeration are called refrigerators, and the cycles on which they operate are called refrigeration cycles. The most frequently used refrigeration cycle is the vapor-compression refrigeration cycle in which the refrigerant is vaporized and condensed alternately and is compressed in the vapor phase. The ideal vapor-compression cycle is compound of four processes: 1. Isentropic compression in a compressor 2. Constant-pressure heat rejection a condenser 3. Throttling in an expansion device 4. Constant-pressure heat absorption in an evaporator The diagrams below in Figure 1 illustrate schematically the cycle: Figure 1 - System components and T-s diagram of a vapor-compression ideal cycle. Extracted from [1] However, the real vapor-compression cycle differs from the ideal due to irreversibilities inherent of the process. For example, two common sources of this phenomenon are: the fluid friction and the heat transfer to the environment or/and other components of the system. Thus, the real cycle presents some discrepancies compared to the ideal cycle. Again, some diagrams are presented for better understanding in Figure 2. Due to these irreversibilities the performance of the cycle is reduced, this means that more work will be spent for the same amount of heat removed from the cold environment. Therefore, is intended to minimize these irreversibilities to achieve the maximum efficiency of the cycle The Compressor It was already presented that the compressor is a part of the vaporcompression cycle. 4

6 Figure 2 - System components and T-s diagram of a vapor-compression ideal cycle. Extracted from [1] As well as any other component in the cycle the compressor has innumerous irreversibilities that prejudice the efficiency. When the fluid enters the compressor it starts to be heated by the environment and all others inside components, while the fluid is flowing in the tubes and orifices there are head losses, the compression process is far away from being ideal and many other things leads to a reduction of the performance. All these causes need to be identified, studied and when possible reduced for optimization. And this is the one of the main reasons for the Research and Development Department at Embraco. For example, a useful, and most common, graphic for identifying all these losses that are spread in the compression cycle is the pv diagram. Below is shown the pv and Ts diagram for an ideal and a real compression cycle. Figure 3 - pv and Ts diagram for an ideal and a real compression cycle. Extracted from [3] As we can see, the behavior of the cycles is quite different. Between the points 1 and 1 we can see the effects of backflow through the suction system, as the suction valve is not ideal it still stays opened in the start of the compression. 5

7 After this, heading to the point 2 it is possible to notice that the real cycle has a smaller pressure than the ideal one in the same displacement. This occurs mainly because there is a leakage between the piston and the cylinder. So, as the gas is being compressed and its pressure is rising it turns out inevitable to exist some gas escaping between this piston-cylinder leakage. The ideal region b-c corresponds to the real region 2-3. This is the region where happens the discharge of the high pressure gas. In the ideal cycle there is no restriction by orifices or valves, so any infinitesimal increase above the discharge pressure means that the gas will flow out of the compression chamber, making it as an isobaric process. However in the real cycle where exists head losses in the orifice and some kind of restriction created by the valve in addition to pressure pulsation in the discharge chambers the overpressure is necessary for surmounting these irreversibilities and making the gas flow out of the compression chamber. Expansion process also is disturbed by backflow, this time it is from the discharge chambers since the discharge valve does not has an ideal behavior. Other factor is that the real suction process is not isentropic. This results in this discrepancy between both cycles, real and ideal. Finally, ending this compression cycle, there is the suction process. As in the discharge process, it is mandatory to have a finite delta pressure for overcoming some inherent irreversibilities. In this case the pressure pulsation of the suction chambers or suction mufflers allied to the head losses of the orifice and the presence of the valve are the main factors of the differences between the ideal and real curves. Making this clear helps a lot for the better understanding of the compression cycle and it is possible to proceed to further deeper investigations. 3.2 Proposal The proposal of this internship is the application of computational tools, like computer fluid dynamics and the in-house code RECIP for supporting commercial compressor projects. This includes thermodynamics, fluid mechanics and heat transfer analysis. Also it will be provided assistance for the internalization of tools and procedures with the local specialists. 3.3 Schedule The first schedule proposed by the supervisor Norbert Brath is the following. Figure 4 Internship schedule. 6

8 3.4 NEU Project The NE family compressors are midi size and its main application is for commercial refrigeration, such as: can refrigerators, ice cream machines, refrigerated displays, juice dispensers, et cetera; cetera and air conditioning. This compressor started being produced by Aspera in 1956, named as AE. After the license expiration, the compressor family was named E. Then afterward afterw an Embraco project for improving the compressor, the family received the name NE. Finally another redesign was made and was born the NEK compressor with even better performance than the previous ones. Now there is a just--started project for designing an almost--new compressor but based on the NEK family compressors. The main goals are high efficiency, extended capacity models, cost optimization and platform standardization. Figure 5 - The NE compressor. These goals are expected to be achieved through the change or optimization of some components, mainly: mufflers, valves and valve plate. For predicting the result of the changes that can be applied to this compressor, Embraco has an in-house house code (named RECIP) capable of simulating simulati most of the processes that occurs inside the compressor like the compression, heat transfers and pressure pulsations. Although for making this possible the code should be loaded with some data that is acquired experimentally. The thermal profile, valve movement and effective areas of flow and force are some of these data that has to be collected by experimental means. means 7

9 Figure 6 - NE compressor application. So the first part of the project must be the setup of RECIP with all these experimental data. After this, proposals can be tested numerically and checked if there was improvement or not. This way it turns out to be possible achieving the goals Compressor Instrumentation For acquiring the experimental data a compressor should be instrumented, this means that some measuring devices will be inserted in the compressor, such as: thermocouples, pressure transducers and some others electrical devices used for acquiring valve movement and piston displacement. The compressor instrumentation was realized at the Mechanical Laboratory assisted by the employee Marek Pec. Below can be seen the list of the localization of all the thermocouples that were placed in the compressor. Table 1- Thermocouples list. ID Place ID Place 1 Oil 9 Discharge Muffler Right 2 Internal Environment Left 10 Winding Bottom 3 Internal Environment 11 Winding Top Right 4 Suction Muffler Input 12 Cylinder Head Discharge 5 Suction Muffler Output 13 Bomboloto 6 Cylinder Wall 14 Suction Tube 7 External Bearing 15 Discharge Tube 8 Discharge Muffler Left The thermocouples utilized were all of the type T (copper-constantan) and the union was made with a tin welding. Five pressure transducers were used for acquiring pulsations and static pressure throughout the compressor. The following table lists them: 8

10 Table 2 - List of pressure transducers. ID Place 1 Static Pressure Suction 2 Pressure Pulsation Suction 3 Cylinder 4 Static Pressure Discharge 5 Pressure Pulsation Discharge For the valve movement acquisition a coil was inserted in the valve plate, just below where the valve touches the valve plate when it is closed, Figure 7 helps the understanding. This way the voltage in the coil will vary according to the position of the valve. This device needed to be calibrated and the calibration procedure consisted in moving the valve to certain heights and registering the voltage referent to that value. This way a calibration curve could be constructed. Figure 7 - Detail of the coil for measuring the valve movement. Extract from [4] The piston displacement is acquired with the help of a magnet and a coil. The magnet is glued in the crankshaft and the coil is glued in the crankcase, in the exact position that the magnet crosses the coil the piston will be at the middle of its course in the suction process. It is done this way because this is the position where the piston (and also the crankshaft) is in its maximum velocity so the magnet and the coil will cross very quickly making smaller the probability of errors and noises. The figure below can make the explanation clear. The arrows that appears in it just has an auxiliary function for the construction of the device. Figure 8 - Detail of the piston displacement measuring device. Afterward the tests valorous information (e.g.: the thermal profile, valve movement, pv diagram, pressure pulsations) will be acquired and not just the RECIP will be loaded but it is also possible to make a complete profile of the compressor with its efficiency, refrigerant capacity and a detailed thermal losses inventory. 9

11 Figure 9 - Instrumented NEU compressor. So far the experimental tests were not run. These tests are scheduled for being realized during the month of April Effective Area The concept of effective area relies in the fact that when the flow is forced to pass through an orifice not all the orifice area will be used for the fluid drain. This occurs due to this sudden contraction and as the fluid is not able to change its direction abruptly the phenomenon called Vena Contracta occurs. Sum up this phenomenon with the presence of the piston, valve and other parts of the suction or discharge system; the result will be a more disturbed flow generating a further decreasing in the effective areas. Figure 10- The Vena Contracta phenomenon. Consequently it turns out to be indispensable to evaluate these effective areas for having a reliable simulation of the flow through the suction and discharge ports. In the past this data was acquired experimentally but nowadays with the progress and popularization of numerical simulations it is possible to use these new tools for this estimation. As Embraco have licenses for the CFX (ANSYS software of computer fluid dynamics) the numerical procedure was chosen for this task. The mounting of the case for calculating the values of effective areas of force and flow can be seen at Annex 6.1. Some of this data has already been evaluated for the discharge port and it is showed below in the form of graphics. 10

12 Effective Flow Area Effective Area [mm 2 ] Valve Height [mm] Figure 11 - Effective flow area for various cylinder and valve height Effective Force Area 30.0 Effective Area [mm 2 ] Valve Height [mm] Figure 12 - Effective force area for various cylinder and valve height. These simulations will be continued during the month of April and the final results are going to be shown at the next report. 11

13 3.5 Other Activities Aluminum Cylinder Head As the name says, this project has the objective of designing a new cylinder head made of aluminum instead of the actual that is iron casted. The main benefit of the project will be a cost reduction as long as it will be possible to produce this new cylinder head inside Embraco s plant and they plan to standardize this component for some families of compressors. The task for this project was to perform a mechanical analysis of the cylinder head submitted to the operation strains and check if the new designed shape will resist. There are three families involved in this project: T, NTU and NJ. So as Embraco has licenses for ANSYS Mechanical it was used for making this analysis. The case mounting can be seen at the Annex 6.2. Previous results about this analysis are shown below in Figure 13. The result shown in Figure 13 is based on the safety factor of the elements, calculated with respect to the yield tension of the material. Like the following formula: where is the safety factor, is the material tensile yield and is the maximum equivalent stress for the element. In other words, when the element is stressed by a tension bigger than the yield one, the safety factor will be under one and the color will be red. The orange areas means a safety factor between one and one and a half, the yellow areas between one and a half and two and all the other colors denote a safety factor over two, so they should have no problem at all. The areas in red and orange are the ones that should have attention on it. Also the most requested element is pointed with the little blue arrow and its safety factor is equal

14 Figure 13 - Mechanical analysis of the NJ compressor aluminum cylinder head. This result gives a first fi impression about the strains in the NJ cylinder head. However, it is now in phase of mesh analysis for or making sure that the values are reliable. Like the previous tasks, this one will also be continued in the following months: months will be performed the analysis for the other compressors families and the mesh validation must be done.. The final results are expected to be shown in the next report Thermal Profiles As mentioned above the thermal t profile of compressor is an input for the inin house code RECIP.. Besides, this kind of acquisition can gather important information about the behavior of the compressor under different operation conditions or just to check if it is possible to run the compressor in certain conditions. Figure 14 - NEK compressor instrumentated for thermal profile. 13

15 At the moment this data is still not available but it is a project to make a database with it. So, this activity was basically composed of instrumentation of compressors with thermocouples. As well as in the NEU compressor were used thermocouples type T (copperconstantan) united with a tin welding for temperature measuring. Until now two compressors were instrumented: NEK2168GK and NT2180U. The thermocouples list is shown in the following tables. Table 3- Thermocouples list for NT2180U. ID Place ID Place 1 Oil 9 Discharge Muffler Right 2 Internal Environment Left 10 Winding Bottom 3 Internal Environment 11 Winding Top Right 4 Suction Muffler Input 12 Cylinder Head Discharge 5 Suction Muffler Output 13 Discharge Chamber Left 6 Cylinder Wall 14 Discharge Chamber Right 7 External Bearing 15 Suction Tube 8 Discharge Muffler Left 16 Discharge Tube Table 4- Thermocouples list for NEK2168GK. ID Place ID Place 1 Oil 9 External Bearing 2 Internal Environment Left 10 Discharge Muffler Left 3 Internal Environment 11 Discharge Muffler Right Right 4 Suction Muffler Input 12 Winding Bottom 5 Suction Muffler Output 13 Winding Top 6 Cylinder Wall Center 14 Cylinder Head Discharge 7 Cylinder Wall Left 15 Suction Tube 8 Cylinder Wall Right 16 Discharge Tube Unfortunately, there are still no results for this activity. As the other tasks, these results will be shown in the next report Laboratories The schedule proposed by the supervisor contemplates mini-internships through all the laboratories of the plant. This was proposed in order to construct a better knowledge about the compressor, its design and the whole process behind it. Until now were visited the Mechanical Laboratory, where the instrumentation of the compressor and its components were made, the Quality Assurance, where they work to constantly improve the process and daily meetings are made for discussing the rejections of the line from the last day, and the Acoustic Laboratory, where tests are run in reverberant and acoustic chambers for registering the compressor noise level and impact tests are made for knowing the dynamic behavior of the components. 14

16 4 Discussions and Conclusions Prior to working with the optimization of the compressor it is mandatory to deeply know what happens to the refrigerant during not just the compression cycle but since it enters in the compressor. As it was presented, there is much irreversibility that reduces the efficiency of the compressor during its operation and it is a priority for Embraco to minimize these losses for improving the performance of its products. So this internship will be mainly focused in this: raising the global efficiency. Aided by Embraco s in-house code (RECIP) several analyses will be performed aiming for better efficiencies. The participation on the NEU project will continue until the end of the internship and it is expected some remarkable progress during this period. After gathering the experimental data many proposals for mufflers, valve plates, cylinder heads and other components can be tested numerically and this way it turns out to be possible achieving good results. The goal of the project is at least around 10% of improvement of the compressor efficiency. Further on the mechanical analysis of the cylinder heads will continue to be made and the results will be presented to the designers and specialists of the area. With this team play will be possible to blend their technical and experimental knowledge of the area with ability of the trainee to labor with computational tools. The outcome of this teamwork shall be good and by the end of the internship will be possible to evaluate it. Lastly, the micro-internships through the laboratories of the Research and Development Department are being of primordial importance for the better understanding of the compressor as a whole. This fusion between the theoretical knowledge acquired during the university with the practical one that is being exercised now results in an excellent solid formation that allows capacity and proactivity for dealing with engineering problems in general. Unfortunately until now there are no concrete results for making some kind of conclusion about the work done at Embraco Spisska. As it was said during the report, these activities will be continued and it is expected to have some results until the next report. 15

17 5 References [1] ÇENGEL, Yunus A.; BOLES, Michael A.. Thermodynamics: An Engineering Approach. 5. ed. Boston: Mc-graw-hill Book Company, p. [2] SCHREINER, João Ernesto. Metodologias de Simulação Numérica Aplicadas ao Gerenciamento Térmico de um Compressor de Refrigeração Doméstica f. Dissertation (Master) - Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina, Florianópolis, Available at: < D.pdf>. Access in: 02 apr [3] SERRANO, Joaquim Rigola. Numerical Simulation and Experimental Validation of Hermetic Reciprocating Compressors.: Integration in Vapour Compression Refrigerant Systems f. Thesis (Doctoral) Course of Industrial Engineering, Departament de Màquines I Motors Tèrmics, Universitat Politècnica de Catalunya, Terrassa, [4] EMBRACO s Internal Documents 16

18 6 Annexes 6.1 CFX - Effective Areas of Flow and Force 1. A simplified model of the compression chamber, discharge orifice, discharge valve and discharge chamber is created. Figure 15 - Simplified geometry of discharge system. 2. An unstructured mesh is generated for the model with refinement in the discharge orifice and in the valve face that is in contact with the flow. Figure 16 Mesh and the detail of refinement in the orifice. 3. Fluid is defined as air ideal gas at 25 C. 4. Boundary conditions are set according to Embraco s standards: a. Inlet: Perpendicular velocity of 1 m/s b. Outlet: Opening condition with relative pressure equal 0 Pa. 5. Equations for evaluating the effective areas of force and flow are loaded, also according to Embraco s standards: 17

19 where is the force that the flow is doing on the valve, is the total pressure in the inlet, is the total pressure in the outlet, is the mass flow in the outlet and is the average density in the outlet. Figure 17 Boundary conditions. 6. All other parameters like turbulence model and convergence criteria are the basic from CFX. 7. Simulation is run and the results are registered. Figure 18 - Pressure field, detail in the orifice. 18

20 6.2 ANSYS Mechanical NJ Aluminum Cylinder Head 1. Geometry is imported from a Pro/ENGINEER model. 2. Unstructured mesh is generated. 3. Thermal conditions, acquired in experimental tests, are set for obtaining the thermal profile: a. External surfaces and suction chamber: 70 C. b. Discharge chamber: 110 C. Figure 19 - Thermal profile. 4. Loads and supports are established: a. Loads: i. Screw s surfaces (in contact with): 18N ii. External pressure: 7 bar. iii. Suction chamber: 7 bar. iv. Discharge chamber: 32 bar. b. Supports: i. Screw s surfaces (in contact with): fixed support. ii. Crankcase s surface (in contact with): frictionless support. 19

21 Figure 20 - Loads and supports. 5. Simulation is run and results can be checked. A-A Section A-A Figure 21 Analysis results. 20