Engineering, 2010, 2, **-**
doi:10.4236/eng.2010.21003 Published Online January 2010 (
Copyright © 2010 SciRes. ENGINEERING
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
Received June 6, 2009; revised August 3, 2009; accepted August 10, 2009
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
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 =
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.
Copyright © 2010 SciRes. ENGINEERING
J. LI 43
Copyright © 2010 SciRes. ENGINEERING
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 =
Referring the cross section of this magnetic seal in
Figure 3,
R1 =
b (4)
R2 =
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
*** = 28.5 Kg/cm2
S = S2 – S1 = [)sin()sin(
] * 2 * b (8)
'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*[
] (10)
At the same time, the work that media pressure ap-
plied to the body of magnetic particles is:
W2 = 4 * b2 *P * [
]2)[cos(*)sin( 2
 ]
4. Prototype Testing Results
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
Estimated Air Leak-
age (SCFM)
Piston Linear Speed
Estimated Air Leak-
age (SCFM)
Piston Linear Speed
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.
Copyright © 2010 SciRes. ENGINEERING
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
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Copyright © 2010 SciRes. ENGINEERING
46 J. LI
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
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