Computer Aided Modeling and Deign of a New Magnetic Sealing Mechanism in Engineering Applications

doi:10.4236/eng.2010.21003

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Engineering, 2010, 2, **-**

doi:10.4236/eng.2010.21003 Published Online January 2010 (http://www.scirp.org/journal/eng/).

Computer Aided Modeling and Deign of a New Magnetic

Sealing Mechanism in Engineering Applications

Jeremy (Zheng) LI

School of Engineering, University of Bridgeport, Bridgeport, USA

E-mail: [email protected]

Received June 6, 2009; revised August 3, 2009; accepted August 10, 2009

Abstract

This article introduces a new type of magnetic sealing mechanism that reduces the lubrication oil pollution

and media gaseous leakage in general reciprocating machinery including air compressors and refrigerators.

The feasible function and reliable performance of this new sealing mechanism are introduced and analyzed

in this paper. The computer aided design, modeling and analysis are being used to study this new sealing

mechanism, and the prototype of this sealing mechanism is being tested. The study indicated the proper

function of this sealing mechanism. The major advantages of this sealing mechanism include: improved

sealing capacity to prevent the gaseous leakage and oil leakage, simple and compact in structure, lower pre-

cision requirement on surfaces of reciprocating pistons and shafts in production and manufacturing, and

longer services in sealing life span. Also there is almost no frictional loss during the reciprocating motion of

piston or shaft.

Keywords: Magnetic Sealing, Magnetic Flux, Reciprocating Machinery, Self-Lubricated System

1. Introduction

The gaseous leakage and oil pollution in reciprocating

machines including compressors and refrigerators are

common problems that have not been well resolved and

it directly affects the machinery performance [1–4]. The

design and development of new sealing mechanism are

continued in these years [5–8].

In this research, a new magnetic sealing mechanism

using rare-earth magnet as permanent magnet is devel-

oped to solve these problems based on theoretic analysis,

computational modeling simulation, and prototype tests.

The permanent magnet is made from the materials that

stay magnetized. Materials that can be magnetized are

called ferromagnetic including rare earth magnets. The

current research and development of rare earth perma-

nent magnets have brought the renovation in the field of

magnetic separation and provided the magnetic products

that are an order of magnitude stronger than that of con-

ventional ferrite magnets. This leads to the development

of high-intensity magnetic circuits that operated energy

free and surpasses the electromagnets in strength and

effectiveness. Common applications of rare-earth mag-

nets include: computer hard drives, audio speakers, bicy-

cle dynamos, fishing reel brakes, mag-lev wind turbines,

and LED throwies.

The prototype testing of this new magnetic sealing

mechanism indicated that this sealing mechanism can

significantly reduce the leakage problem in reciprocating

machines including compressors and oil pollution in

cryogenic regenerator. It also shows that this sealing

mechanism can replace the oil separation system in re-

frigerating compressors. Through the prototype tests, the

sealing function of this new mechanism is better than

regular rubber seal, diaphragm seal, corrugated pipe seal

and magnetic fluid seal.

2. Magnetic Circuit in Sealing Mechanism

The rare-earth magnet steel can be performed as a per-

manent magnet steel which has the higher density of

magnetic flux Br, strong magnetic field Hg, and larger

product of magnetism and energy (BH)max as shown in

Figure 1. All these good features allow the magnetic par-

ticles to be firmly adhered onto the inside wall of magnet

steel. The major advantages of this magnetic circuit in-

clude higher Br in working gap of the circuit, longer and

durable in sealing lifetime, compact in system configura-

tion, light in unit weight, higher in performance efficien-

42 J. LI

Figure 1. Magnetic sealing mechanism.

Figure 2. Magnetic curve of circuit.

cy, and stable in sealing functioning.

The concept of this new magnetic sealing mechanism

can be briefly described as follows. When piston/shaft

reciprocates inside of the cylinder, lubricating oil is

sealed by magnetic particles, which are firmly adhered

on the inside surface of magnet steel, as oil particles

move to the seal. Then the oil droplets drop to the main

shaft chamber at the bottom of compressors by its gravity

which can prevent the oil in crank chamber from entering

the gas cylinder. Also the gaseous leakage can be pre-

vented because the gas could not pass through the strong

adhesive layers of magnetic particles. In this new mag-

netic sealing design, two critical factors that should be

considered to keep its well function are density of mag-

netic flux and magnetic stability of the magnet steel.

Thus the magnetic flux in magnetic circuit of this sealing

mechanism must be maintained over a long period of

time and magnetic field of this magnet steel should be

stable enough to withstand the external/disturbed mag-

netic fields, temperature change, mechanical vibra-

tion/shock, and severe environmental fluctuation. The

surplus density of magnetic flux Br, surplus intensity of

magnetic field Hg, and maximum product of magnetism

and energy (BH)max are required to keep their peak val-

ues in this magnetic sealing mechanism design.

The magnetic circuit in this sealing mechanism is in

static condition which can be analyzed using ampere

enclosed circuit and H-B curve of this rare-earth magnet

steel. This magnetic circuit can be considered as a series

magnetic circuit mainly made up from magnet steel and

working gap. Refer the Figure 1, the following equations

can be derived:

H * L + Hg * Lg = 0 (1)

H * L = - AgU

 (2)

Let Fm(



) = H * L, the intersection of Fm(



) and

straight line – [Lg / (U0 * Ag)] * at ordinate in Figure

2 is the magnetic flux in working gap that required to be

determined. This gap decreases from Lg to Lg’ after

magnetic particles being added into the space in mag-

netic circuit gap. When the thickness of magnetic parti-

cles in the gap between surfaces of magnet steel and cyl-

inder changes from 0 to b, the working point of magnet

steel changes along the straight line QK. The corre-

sponding solution of magnetic flux in working gap can

be found from line QK. The magnetic field is well dis-

tributed / maintained in this sealing mechanism that has

been verified from computational modeling simulation.

The coefficient of magnetic efficiency f is used to judge

if the magnetic field in this sealing mechanism is prop-

erly designed. Here,



f =

VHB

VgBg

*)*(

max

(3)

The higher f value indicates more feasible and rea-

sonable design on the magnetic circuit. The f value is

normally 40% in standard conditions. The computational

modeling solution shows that f value in this sealing

magnetic mechanism is 48.5% which verifies the proper

magnetic circuit design in this sealing mechanism.

Figure 3. Cross section view of magnetic steel.

J. LI 43

3. Analysis of Sealing Capacity netic lines of force applied in magnetic circuit should be

equal to the work that media pressure exerted to the body

of magnetic particles. So,

The formula of sealing capacity P can be derived

from energy balancing theory as follows.



P =

]}3)cos(*4)([cos*

)(sin**2{

])[sin(****)

(

2









TDB

Referring the cross section of this magnetic seal in

Figure 3,



R1 =

)sin(



b (4)

(12)

R2 =

)sin(



b (5)

This formula can be calculated by computational mod-

eling with numerical solution. The optimized computa-

tional simulation indicated that, when α and β are

changed to certain values, the P max can be determined

as follows:



S1 = R1 * α (6)

S2 = R2 * β (7)



P max = b

TDBC

*** = 28.5 Kg/cm2

S = S2 – S1 = [)sin()sin(





] * 2 * b (8) 

(13)

'OO = 2 * β * [ctg (α) – ctg (β)] (9) This result shows that the seal capacity of this mag-

netic sealing mechanism can prevent the oil leak-

age/pollution from crank chamber into the cylinders of

reciprocating machinery and refrigerating regenerators. It

can also keep the compressors from gaseous leakage.

The above mechanism analysis and computational simu-

lation have been verified through the prototype tests.

Furthermore, the sealing capacity in this mechanism can

be improved by increasing the number of this magnetic

seal, improving the magnetic material composite and

optimizing the magnetic circuit design.

Because the work that each magnetic line of force ap-

plied is T * S, total work that magnetic lines of force

applied in magnetic circuit is:



W1 = B*D*T*2b*[

)sin()sin(





] (10)

At the same time, the work that media pressure ap-

plied to the body of magnetic particles is:

W2 = 4 * b2 *P * [

)sin(

)sin(*8

]2)[cos(*)sin( 2







 ]

4. Prototype Testing Results

(11)

The prototype of this new magnetic sealing mecha-

Based on energy balancing theory, the work that mag-

Table 1. Estimated air leakage at different piston linear speed.

Piston Linear Speed

(Ft/Min)

Estimated Air Leak-

age (SCFM)

Piston Linear Speed

(Ft/Min)

Estimated Air Leak-

age (SCFM)

Piston Linear Speed

(Ft/Min)

Estimated Air Leak-

age (SCFM)

5 0.001 45 0.036 90 0.083

10 0.003 50 0.043 100 0.088

15 0.006 55 0.048 105 0.092

20 0.010 60 0.054 110 0.095

25 0.014 65 0.061 115 0.099

30 0.019 70 0.066 120 0.104

35 0.025 75 0.071 125 0.111

40 0.031 80 0.077 130 0.119

Table 2. Estimated air leakage at different air pressure.

Air Pressure (PSIG) Estimated Air Leak-

age (SCFM) Air Pressure (PSIG)Estimated Air Leak-

age (SCFM) Air Pressure (PSIG) Estimated Air Leak-

age (SCFM)

50 0.002 450 0.030 800 0.063

100 0.005 500 0.033 850 0.067

150 0.007 550 0.037 900 0.070

200 0.011 560 0.042 950 0.074

250 0.015 600 0.045 1000 0.079

300 0.018 650 0.049 1050 0.083

350 0.022 700 0.054 1100 0.088

400 0.026 750 0.058 1150 0.094

44 J. LI

Figure 4. Air leakage vs. piston linear speed.

Figure 5. Air leakage vs. air pressure.

nism has been tested and the preliminary results are

shown in Tables 1 and 2.

5. Computational Simulation Results

This new magnetic sealing system has also been simu-

lated by computational solution and results are indicated

in Figures 4 and 5.

Based on the above, the preliminary results from pro-

totype testing and computational simulation are closed to

each other, and this verifies the creditability and feasibil-

ity of this new magnetic sealing mechanism.

J. LI 45

6. Conclusions

Today the oil and gaseous media leakages are the tough

and difficult engineering problems that affect the recip-

rocating machinery function and performance. This new

magnetic sealing mechanism has been developed to re-

duce the oil and gaseous media leakages in reciprocating

machinery. All the theoretical mechanical and magnetic

analysis, computational simulation, and prototype tests

indicated that this sealing mechanism can significantly

decrease the oil and gaseous media leakages in recipro-

cating machinery. Its sealing performance is reliable due

to the firmly adhesive and strong forces between the

magnetic particles and reciprocating pistons/shafts. This

seal mechanism is also durable if compared with regular

seals including rubber seal, diaphragm seal, corrugated

pipe seal because of less frictional force between sur-

faces of seal and pistons/shafts in this new sealing

mechanism. Moreover, the development of this magnetic

sealing mechanism will further contribute to the exploi-

tation, popularization, and application of the rich rare-

earth elements/materials in today’s modern industrial

world.

. References

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[2] J. E. Hirsch, “The Lorentz force and superconductivity,”

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46 J. LI

Nomenclature

Ag = cross section area of working gap

Bg = density of magnetic flux in working gap

Br = density of magnetic flux

(BH)max = maximum product of magnetism and energy

C = coefficient

D = Width of magnetic steel

f = coefficient of circuit efficiency

H = intensity of magnetic field of magnet steel

Hg = intensity of magnetic field in working gap

L = length of magnet steel

Lg = length of working gap

T = intensity of magnetization

U0 = magnetic conductivity of vacuum

Vg = volume of working gap

V = volume of magnet steel

B = half length of working gap



= magnetic flux