Resincap Journal of Science & Engineering Volume 1, Issue 1, February 2017

A Review on Analysis and Design of Electromagnetic Pump

Miss. Pallawi C. Dekate Prof. S.M. Kulkarni Pursuing ME (EPS) in P.E.S College of Engineering Associate Professor, department of Electrical Engineering, Aurangabad P.E.S College of Engineering Aurangabad [email protected] [email protected]

ABSTRACT electromagnetic pump. One such pump had been Liquid metal loops are used for heat removal and for the study successfully designed and is operating at our lab at BARC. of certain magneto fluidic phenomenon like MHD (Magneto- 2. ELECTROMAGNETIC PUMPS Hydro Dynamic) effects. These loops operate at high In 1907 Northrup developed a hydrostatic pressure of several temperatures and carry fluids that are invariably toxic in inches of water via the interaction of a 600 ampere current nature. To ensure the purity of fluid in a closed loop and a in mercury. He postulated that this effect application, non-intrusive electromagnetic pumps are used. could be utilized in an ammeter for measuring large currents. We have designed and analyzed a prototype electromagnetic The movement of a liquid metal by using a sliding and pump to be used in mercury loop for carrying out various rotating magnetic field was proposed by Chubb in 1915. studies. This Electromagnetic pump is designed using Bainbridge tested an conduction pump in permanent magnets which are mounted on the periphery of 1926. Einstein and Szilard proposed an annular linear the rotor, driven by a DC motor. The liquid metal flows in a induction pump for use with alkali metals in 1928. Several semi-circular duct surrounding the rotor. The paper brings out working models of this pump rated at about 2 kw were the qualitative and quantitative analyses of the pump as operated with mercury and liquid alloys of sodium and function of of the permanent magnets, the potassium. The design equations for this type of pump using speed of rotation of the pump and magnet pitch. This liquid bismuth were presented in a report by Feld and Szilard electromagnetic pump has been developed and is running in 1942. The flat linear induction pump is only one of many successfully in our lab at BARC. types of electromagnetic pumps for liquid metals. The principal of operation is the same for all electromagnetic Keywords pumps. It is the source of the current and magnetic field that Electromagnetic pump, liquid metals, permanent changes. Electromagnetic pumps can be divided in two main magnets, MHD. categories; they are the conduction pumps and the induction pumps. Conduction pumps may be operated either on alternating or . Either type pump may be 1. INTRODUCTION identified by the electrodes, brazed to the pump duct wall, Electromagnetic pump is used for driving liquid metals in which supply the current from an external source to the liquid various industrial and research set ups. Liquid metals are metal. Conduction pumps have one primary advantage over invariable toxic and are mostly operated at high temperatures. the other electromagnetic pumps; they can be used to pump Loops used for the study of corrosion and MHD studies need even the typical heavy metals such as bismuth or mercury to maintain liquid metal purity within tight limits. with high resistivity, high density, and high viscosity. The Electromagnetic pumps provide nonintrusive method for current flowing through the liquid metal may be made as large driving liquid metals in loops. Mechanical seals are not as is necessary to overcome the effects of the heavy metals. required in these pumps; hence their chances of failures due to The biggest disadvantage of these pumps is the requirement of high temperatures and wear/tear get eliminated. extremely large currents, usually several thousand amperes at Electromagnetic pumps for liquid sodium loops are designed of one or two volts. A direct current conduction using electromagnets and flow is maintained in pipes. pump can be operated either with a permanent magnet or an Electromagnetic pumps can also be designed using MHD electromagnet to produce the magnetic field. The phenomenon. Both these EMP are similar to conventional disadvantage of the awkward excitation requirements, as linear pumps material. mentioned earlier, is partially overcome by the use of a The EMP presented in this paper is similar to conventional relatively efficient homopolar generator with liquid metal centrifugal pump. Its key components are rare earth brushes. The use of conventional rectifiers is not permanent magnets. Rotor, DC motor, semi-circular duct and recommended for the larger pumps since they are inefficient, CRNGO backing iron. Permanent magnets bars are fitted on bulky, and expensive. Another requirement (and not always a the periphery of rotor and magnetized alternately along the disadvantage) for satisfactory operation of a direct current radially in and radially out directions. High strength NdFeB pump is the wetting of the duct wall by the liquid metal. The magnets are used as they have large remnant flux density. A performance characteristics of the direct current conduction DC motor is used to rotate the rotor at various speeds. pump are excellent as the pump is applicable in systems Rectangular channels provide passage for liquid metal flow. requiTing wide variations in power, pressure, and flow. In CRNGO laminated magnetic steel has been used to provide efficiency too, the direct current pump is unsurpassed by the low reluctance path return path for the flux. This paper other types of electromagnetic pumps. In order to avoid the provides theoretical, analytical and practical aspects of use of a homopolar generator, an alternating current conduction pump with its associated step-down transformer is

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Resincap Journal of Science & Engineering Volume 1, Issue 1, February 2017 sometimes used. The immediate problems encountered with this pump are: lamination of magnetic circuit to reduce eddy- Where w is rotation speed of the motor-pump assembly in currents and iron losses and thereby improve the normally low revolutions per second and N is number of magnets mounted efficiency; physically larger pump; poor power factor; and on the rotor noisy operation. The alternating current conduction pump is ( ) limited in size because the power factor decreases rapidly with size at a constant frequency. However, larger pumps may V is velocity of fluid in the channel. be built if the frequency is sufficiently lowered. Normally, the reliable step-down transformer is employed near or is part of The pressure developed by the pump is directly proportional the pump, while alternate sources of supply may be located to rotational velocity of the pump and the square of magnetic remotely. The second category of electromagnetic pumps, the flux density. Another parameter which influences the induction pumps, always has alternating current induced in maximum pressure developed is the magnet pitch. In the the molten metal by a traveling or pulsating magnetic field. present context magnet pitch refers to the angular distance These pumps are normally, with one exception, used only between magnets. The dependence of maximum pressure with the typical light metals with higher conductivities so that developed, on magnetic pitch is not straight forward. The the induced currents will be sufficiently large. A classification pressure also depends on magnet size and dimensions of the of the most common types is: rotor. For optimum performance of the pump, magnet pitch  Single-phase annular should be judiciously decided. This paper also discusses the qualitative effect of magnet pitch on generation.  Polyphase helical  Polyphase flat linear 5. Use of COMSOL Multiphysics  Polyphase annular linear The FEM model of electromagnetic pump is solved as a  Rotating magnet quasi-static magnetic problem using perpendicular induction current vector potential included in AC/DC module of 3. THEORY COMSOL. The problem was modeled as a time varying 2- A rotating magnetic field is generated in the air-gap using dimensional problem. Analysis is carried out on a cross alternately magnetized permanent magnets oriented in the section through the axial center of the rotor of the pump. The radial direction. The magnetic field cuts the conducting metal motion between the rotor and the stator is accounted by proper filled inside the channels. This induces eddy currents boundary conditions. The PDE solved is given in (4). in the conducting metal, which thereby experience a Lorentz force, whose direction is defined by the Fleming’s left hand rule. When analyzed in cylindrical coordinate system, (4) has a radial component in the airgap. Lorentz The rotation is modeled using a deformed mesh application forces are generated due to the interaction between radial mode (ALE); the center part (rotor) rotates with an angular magnetic field and the perpendicular induced currents due to velocity with respect to the fixed coordinates of the stator. changing radial magnetic field. The vector multiplication of The rotor and the stator are drawn as two separate geometry perpendicular induced currents and radial magnetic field objects and concept of assembly [2] is used. Advantages of produces unidirectional Lorentz force in the azimuthal using assembly are discussed in [2]. (tangential) direction. The magnitude of Lorentz force is equal to magnitude of eddy currents multiplied by the magnitude of magnetic flux density. 4. Governing Equations Please use a 9-point Times Roman font, or other Roman font with serifs, as close as possible in appearance to Times Roman in which these guidelines have been set. The goal is to have a 9-point text, as you see here. Please use sans-serif or non-proportional fonts only for special purposes, such as distinguishing source code text. If Times Roman is not available, try the font named Computer Modern Roman. On a Macintosh, use the font named Times. Right margins should be justified, not ragged. Maximum pressure developed by the pump is given by equation 1. [1] Figure 1: Model of Electromagnetic pump in COMSOL (1) The model of the pump is shown in figure 1. Eight permanent Where electrical conductivity of liquid metal, VM is is magnets are fixed on periphery of the rotor. The magnets are velocity of alternating magnetic field in radians per second magnetized alternately in radially inward and radially outward given by equation (2), B[T] is average of magnetic fled directions. The direction of magnetization is shown in figure density along the width of liquid metal layer, s is slip defining 10 in section 7 of this paper. The stator consists of a relative velocity of magnetic field in respect to the velocity of semicircular duct, carrying the molten metal and a C-shaped liquid metal in duct of the pump given by equation (3), lmp is backing iron of CRNGO steel. The yellow line in the model the length of active part of pump’s channel and k is a signifies the pair formation. Pair formation is required for coefficient taking into account the influence of negative solving relative motion problems in COMSOL. The model is transversal end effects lowering maximal pressure developed solved at an angular velocity of 600 rpm. The conductivity of by pump. An optimum design of the pump should maximize the liquid metal is taken as 1.3e6 [S/m]. The remnant k. magnetic flux density of the permanent magnet is 1.3 [T]. ( )

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Resincap Journal of Science & Engineering Volume 1, Issue 1, February 2017 6. Post Processing Results And Analysis of Lorentz force in azimuthal direction (along the channel), magnetic flux density and induced currents shall be Figure 2 shows the normalized magnetic flux density profile perpendicular to each other. The time varying radial magnetic and magnetic potential profiles. Figure 3 shows the profile of flux density in the air-gap induces eddy currents in the z normalized Lorentz force generated in N/m3, arrows shows direction. The two fields interact to produce the necessary the direction of the force and arrows magnitude is Lorentz force. Figure 5 shows the variation of radial magnetic proportional to Lorentz force’s strength. Perpendicular flux density, perpendicular induced currents and tangential Induced currents density profile is shown in figure 4. The Lorentz force at t=50 msec along the arc passing through the induced currents are in axial z-direction (perpendicular to radial center of the channel carrying the liquid metal. The cross-section of rotor). Lorentz force generation is dependent variation of perpendicular induced currents and radial on magnetic flux density profile and perpendicular induced magnetic flux density is such that unidirectional azimuthal currents. For generation. Lorentz forces are generated.

Figure 5 : Variation of tangential Lorentz force [105N/m3], radial magnetic flux density (red)[T] and perpendicular Figure 2: Post processing results: Magnetic field density induction current (blue) [105A/m2] along the midway of (surface plot) and magnetic potential (Contour) liquid carrying duct.

7. Effect of angular velocity, Magnet strength magnet pitch The analysis of the electromagnetic pump was carried out for two angular speeds of 600 rpm and 300 rpm. The normalized surface integrated Lorentz force from 0 to 200 milliseconds was evaluated and is shown in figure 6.As evident from this figure; the Lorentz force is directly proportional to angular velocity. The strength of permanent magnets is an important parameter for maximizing the Lorentz force in EM pump. The Lorentz force is proportional to the square of air-gap magnetic field. Analysis was carried out for two sets of permanent magnets with remnant magnetic flux densities of 1.3[T] and 0.65[T]. The Lorentz force in the latter case is reduced by a Figure 3: Post processing results: Normalized Lorentz force factor of four when compared to former. The results are distribution[N/m3]. shown in figure 7.

Figure 6: Effect of angular velocity on Lorentz force at 600

rpm(blue) and 300 rpm(pink). Figure 4: Post processing results: Induced Perpendicular These results can be explained as follows. Two factors are [A/m2](z-direction). influenced by changing the magnet pitch, first is the velocity of travelling magnetic flux density which is proportional to 11

Resincap Journal of Science & Engineering Volume 1, Issue 1, February 2017 angular velocity of the rotor and number of permanent magnets. Second is the rate of change of magnetic flux density. When magnet pitch is reduced from 45 degrees to Table-1: Properties of permanent magnets used in EM pump 22.5 degrees, the magnets almost touched each other and the rate of change of magnetic flux density is reduced Parameter Value comparatively. The increase in travelling magnetic flux density is not able to compensate the decrease in magnetic Remnant magnetic field 1.3 T flux density change rate. On other hand increase in magnet Recoil permeability 1.04 pitch has reduced the travelling magnetic flux density velocity Curie temperature 320°C and rate change of magnetic flux density is not able to compensate it. The magnet pitch thus shall be optimized in Operating temperature 150°C order to use fruitfully the effect of travelling magnetic flux Coercive field 1285 kA/m density and change rate of magnetic flux density. BHMAX 45 MGOe 8. Design

A prototype EM pump is designed and fabricated to establish the principle. The pump is undergoing lab trials and its performance is being evaluated. Schematic drawing of EM pump fabricated is shown in figure 9. Pump can be divided into three sections, firstly stator, rotor and liquid metal. The rotor of the EM pump is rotated with a DC motor as shown in figure 9. This prototype EM pump is designed for mercury as it is the only liquid metal at room temperature. However it should be handled carefully as it is toxic in nature.

Figure 8: Rotor, liquid metal carrying duct and soft iron backing of EM pump

Figure 7: Schematics of EM pump

8.1 Stator The non-moving part of the EM pump consists of the semi- circular duct carrying the liquid metal, magnetic backing iron and other supporting arrangements for support. Soft iron confines the magnetic field and also provides support to the duct. The duct carrying the liquid metal is made of fiber plastic.

8 .2 Rotor arrangement The rotor arrangement along with semi-circular duct and back iron is shown in figure 10. The physical arrangement of magnets, their magnetization direction, direction of flow and soft iron backing is shown this figure. The circular arrangement next to semi-circular duct is the rotor portion of the EM pump. Neodymium iron boron magnets are used as permanent magnets. These magnets are strong magnets and are made up of rare earth elements. Strength of these magnets is superior to Alnico, ferrites and other rare earth magnets

Magnetic Properties of the Neodymium iron boron magnets are tabulated in table 1. Figure 9 shows Electromagnetic pump Figure 9: Electromagnetic pump fabricated and successfully fabricated on this principle. Bar magnets are arranged along running at BARC. the periphery. As seen in the figure the rotor is coupled to a

DC motor. Lower duct is the suction and upper duct is the discharge.

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Resincap Journal of Science & Engineering Volume 1, Issue 1, February 2017 9. Conclusions An electromagnetic pump based on the abovementioned [13] B. T. Ooi and D. C. White, “Traction and normal forces in the linear induction motor,” IEEE Trans. Power App. Syst., vol. PAS-89, theory has been developed. The pump design needs to be no. 4, pp. 638–645, 1970. optimized for optimum efficiency .The rotor’s angular velocity and magnetization strength of the magnets have direct bearing on the Lorentz force developed ,whereas About Authors magnet pitch optimization need further qualitative and quantitative analysis and optimization. Miss. Pallawi C. Dekate1, she received her BE from. 10. Acknowledgements Babasaheb Ambedkar Technical University, Lonere and It gives me an immense pleasure to submit this review paper currently perusing. ME (EPS) from Electrical Engineering entitled, “A Review on Analysis and Design of Department, P.E.s. College of Engineering Aurangabad, India.. Electromagnetic Pump”. I wish to express my sincere thanks 2 with profound gratitude to my guide Prof. S.M.Kulkarni and Mr. S.M. Kulkarni currently working as Associate H.O.D. Prof. B.N. Chaudhari for their valuable guidance and Professor Electrical Engineering Department, P.E.s. College constant encouragement without which it would have been of Engineering Aurangabad, India. impossible. I would like to extend my sincere thanks to our principal Dr. A.P. WADEKAR and the entire staff member for the guidance as and when required.

11. References [1] M. Garnier,“Technological and economical challenges facing EPM in the next century,” in Proc. Int. Symp. Electromagnetic Processing of Materials, Nagoya, Japan, Apr. 3–6, 2000, pp. 3–8.

[2] T. Fujii, “State of art an electromagnetic process in Japanese iron and steel industry,” in Proc. Int. Symp. Electromagnetic Processing of Materials, Nagoya, Japan, Apr. 3–6, 2000, pp. 14–19.

[3] E.Takeuchi and K. Miyazawa, “Electromagnetic casting technology of steel,” in Proc. Int Symp. Electromagnetic Processing of Materials, Nagoya, Japan, Apr. 3–6, 2000, pp. 20–27.

[4] D. Bialod, Ed., Electromagnetic Induction and Electric Conduction in Industry: Centre Français de l’Électricité, 1997, pp. 359–362.

[5] L. R. Blake, “Conduction and induction pumps for liquid metals,” in Proc. Inst. Elect. Eng., 1956, pp. 49–63.

[6] M. Rabiee and J. J. Cathey,“Verification of a field theory analysis applied to a helical motion induction motor,” IEEE Trans. Magn., vol. 24, pp. 2125–2132, July 1988.

[7] J. Partinen, N. Saluja, J.Szekely,and J.Kirtley Jr., “Experimental and computational investigation of rotary electromagnetic stirring in awoods metal system,” ISIJ Int., vol. 34, pp. 707–714, 1994.

[8] S.Yamamura, Theory of Linear Induction Motors. Tokyo, Japan: Univ. Tokyo Press, 1978, pp. 42–91.

[9] P. L. Alger, The Nature of Polyphase Induction Machines. New York: Wiley, 1951, pp. 96–99.

[10] E. R. Laithwaite, Propulsion Without Wheels. New York: Hart, 1968, pp. 81–117.

[11] T.Wildi, Electrical Machines, Drives, and Power Systems. Englewood Cliffs, NJ: Prentice-Hall, 1997, pp. 276– 278.

[12] P. L. Cochran, Polyphase Induction Motors. New York: Marcel Dekker, 1989, pp. 82–458. 13