Magnetic heating and cooling systems

A magnetic heating and cooling system is disclosed. A magnetic fluid is pumped through at least a portion of the heating and cooling system. The fluid moves through the field of a superconducting or other type of magnet. When the fluid enters the magnetic field, it is heated as a result of the magnetization. Heat from the magnetic fluid is then transferred to a regenerator chamber. When the fluid leaves the magnetic field it is chilled. Heat from a regenerator chamber is then transferred to the fluid. External loads or sinks are heated or cooled.

BACKGROUND OF THE INVENTION 
This invention pertains to the art of heating and cooling systems, and more 
particularly to magnetic heating and cooling systems. 
The invention is particularly applicable to magnetic heating or cooling 
systems which comprise ferromagnetic or ferrimagnetic materials, and will 
be described with particular reference thereto. It will be appreciated, 
however, that the invention may be advantageously employed in other 
environments and applications. 
U.S. Pat. No. 4,069,028 which issued on Jan. 17, 1978 to Gerald V. Brown, 
fully incorporated herein by reference, discloses a system for effecting 
heating or cooling. The system calls for the use of a solid ferromagnetic 
material which functions as a refrigerant with its Curie point near room 
temperature (e.g., the rare earth element gadolinium). The use of an 
appropriate magnetic field to achieve magnetic heating and cooling of the 
ferromagnetic material or refrigerant, combined with a liquid accumulator 
or regenerator, together extend the temperature differential there to a 
wider level than was achieved in the past. 
The system disclosed in Brown employs a solid ferromagnetic material 
immersed in the liquid of the accumulator. A variety of geometries of the 
solid ferromagnetic material are described The various geometries are used 
and described in an effort to disclose an appropriate system for 
maximizing the heat transfer, and further to simplify the achievement of 
relative motion between the solid refrigerant and the accumulator liquid 
while minimizing liquid turbulence. Liquid turbulence is an undesirable 
factor in attempting to achieve temperature stratification within the 
system. 
Brown provides a system for achieving cost effective heating and cooling in 
a number of applications surrounding the approximate room temperature 
regime. It appears, however, that the complexity of the mechanical design 
required to implement the Brown system may make the system economically 
uncompetitive. Furthermore, the complexity of the Brown design may achieve 
a less-than-desired level of reliability. 
It would be desirable to modify the system disclosed in Brown in such a way 
as to alleviate some of the mechanical design complexity in order to 
produce an economically competitive magnetic heating and cooling system. 
It would be further desirable to design a magnetic heating or cooling 
system which would operate within reliable parameters. 
The present invention contemplates a new and improved apparatus and process 
to overcome all of the above-referenced problems and others. The present 
invention provides a reliable magnetic heating and cooling system which is 
less complex than that disclosed in Brown, and offers an economical 
alternative to Brown.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS 
Referring now to the drawing wherein the showings are for purposes of 
illustrating the preferred embodiment of the invention only and not for 
purposes of limiting same, the FIGURES show preferred and alternative 
embodiments of a magnetic heating or cooling system in accordance with the 
present invention 
As stated above, the system taught by Brown calls for a solid ferromagnetic 
material immersed in the liquid accumulator. The present invention is 
directed to a modification of the Brown system for the purpose of reducing 
the complexity of mechanical design as well as making the system 
economically competitive. In addition, the present invention offers 
consistent, reliable results. 
The present invention addresses replacing the solid rare earth 
ferromagnetic refrigerant (gadolinium) of Brown with a ferromagnetic fluid 
comprised of an appropriate liquid and a colloidal dispersion of an 
appropriate ferromagnetic material. In the Brown system, the ferromagnetic 
material would be gadolinium or a similar element or compound. Other 
materials, however, having different Curie points could be chosen for use 
in different temperature regimes. The material chosen preferably has a 
Curie temperature reasonably near to the temperature which is desired to 
be achieved in surrounding areas. 
Preparation of a ferromagnetic fluid has been described in the Papell 
patent, U.S. Pat. No. 3,215,572, incorporated herein by reference. In that 
patent, Papell discloses a low viscosity magnetic fluid that is obtained 
by the colloidal suspension of magnetic particles. According to the Papell 
patent, a low concentration of ferromagnetic material in the liquid yields 
a low viscosity, pumpable magnetic fluid. 
In addition to Papell, others have produced magnetic fluids with 
substantially higher magnetic material concentration. For example, U.S. 
Pat. No. 3,278,441 to Manuel, also incorporated herein by reference, 
teaches a method of preparing a magnetic metal-containing polymer 
composition. Magnetic polymers, such as, for example, those disclosed in 
Manuel, can be used in their liquid form as the magnetic fluid used in the 
present invention. 
For purposes of the present invention, it is desirable to obtain a magnetic 
fluid having an optimum solid material concentration in order to achieve 
an efficient magnetic heating or cooling effect by the system. Heating and 
or refrigeration capacity, with a given magnetic field strength, is a 
function of the mass flow rate. Efficiency requires a balancing of the 
solid material concentration against the power required for pumping. Along 
these lines, it is important to achieve an appropriate concentration of 
solid ferromagnetic material (i.e., packing fraction). Accordingly, it may 
be preferable to form a solution which is a ferromagnetic fluid by 
creating a liquid/solid slurry of desired solid concentration in place of 
a colloidal suspension. Alternately, the two methods may be combined. 
Attention is now directed to FIG. 1 which shows a magnetic heating or 
cooling system. Ferromagnetic fluid 12 circulates or flows about the 
system in a closed loop. The material flows through a conduit 16 which 
provides a sealed, continuous path for the circulating fluid. Arrows show 
the general direction of the flow of the ferromagnetic material as it 
completes its circuit. A mechanical pump 20 provides the necessary 
assistance which causes the fluid to flow. While FIG. I shows only a 
single pump, it is foreseeable that additional pumps could be used. 
Further, a variety of pumping techniques and configurations can be used to 
cause the ferromagnetic fluid to flow. 
A cryogenic or electromagnetic superconducting magnet 26 surrounds a 
portion of the conduit 16 through which the ferromagnetic fluid 12 flows. 
The conduit 16 passes through a magnetic bore 32 defined by 
superconducting magnet 26. When the fluid enters the magnetic field 
approximately at the point designated 36, the magnetic bore, the 
temperature of the ferromagnetic fluid undergoes a change. The 
ferromagnetic fluid temperature rises as a result of its exposure to the 
magnetic field provided by the superconducting magnet 26. 
In general, the system is comprised of a regenerator chamber 40 and a 
series of heat exchangers denoted generally as 46. Regenerator fluid or 
liquid 50 is present inside the regenerator chamber 40. 
As will be noted in FIG. 1, the pump 20 causes the ferromagnetic fluid or 
slurry to circulate through the magnetic bore 32 and the regenerator 
chamber 40. FIG. 1 also shows that a portion 56 of the ferromagnetic 
fluid's circuit is outside the regenerator chamber. As the ferromagnetic 
fluid 12 flows along portion 56 outside the regenerator chamber, its 
temperature approximates the ambient temperature. Once the fluid reaches 
the regenerator chamber at 58, it warms up a bit as a result of a transfer 
of heat from the regenerator fluid 50. 
The ferromagnetic fluid flows through a first heat exchanger 62 wherein the 
ferromagnetic fluid 12 receives heat from regenerator liquid 50. The 
somewhat warmed fluid 12 continues on through the regenerator chamber 40 
and at 36 it enters the magnetic bore region 32. At this point, the 
magnetic fluid 12 is exposed to a magnetic field emanating from the 
superconducting magnet 26. Because the ferromagnetic fluid 12 has entered 
the magnetic field, the ferromagnetic fluid undergoes heat of 
magnetization. Heat is generated within the magnetic fluid as a result of 
its entry into the magnetic field. Its temperature does not further 
increase as a result of being exposed to the magnetic field for a period 
of time. 
Additional heat exchangers 66, 68 and 70 are shown inside the portion of 
the regenerator chamber that is within the magnetic bore 32. Although FIG. 
1 shows three (3) heat exchangers 66, 68, and 70 inside the bore 32, the 
total number is arbitrary. It is possible that there could be one, two, or 
even four, five or six or more heat exchangers within the bore. The number 
and configuration of the heat exchangers is such as to transfer heat most 
effectively from the magnetic fluid to the regenerator fluid. 
When the ferromagnetic fluid 12 is exposed to heat exchanger 66, the heat 
from the ferromagnetic fluid 12 is transferred to the regenerator liquid 
50 in the regenerator chamber 40. At point 72 in the regenerator chamber, 
when the temperature of the regenerator liquid has been substantially 
elevated, the heated regenerator liquid circulates out of the regenerator 
chamber through outlet 74 where heat is rejected or transferred to an 
external load or heat sink 75. When the regenerator liquid from which heat 
has been transferred circulates back into the regenerator chamber at inlet 
76, its temperature has been decreased from its level at point 72. 
Once the ferromagnetic fluid 12 leaves heat exchanger 66, it flows through 
heat exchanger 68, and additional heat is transferred from the magnetic 
fluid to the regenerator liquid 50. The ferromagnetic fluid 12 then enters 
heat exchanger 70 and additional heat is removed from the ferromagnetic 
fluid and transferred to the regenerator chamber fluid 50. As the 
ferromagnetic fluid 12 exits the magnetic bore at 80, it is abruptly 
chilled as a result of being demagnetized, and the temperature decreases. 
An insulating liquid separation diaphragm 84 divides the regenerator into 
two sections, namely the hot section 86 and the cold section 88. 
Regenerator liquid 50 does not flow through the separation diaphragm 84, 
and the fluid in the hot section 86 thus does not mix with the fluid in 
the cold section 88. 
As stated above, when the ferromagnetic fluid leaves the magnetic bore at 
80, it is suddenly "chilled" as a result of leaving the magnetic field. 
Upon leaving the bore 32, the fluid 12 enters heat exchangers 92 and 94, 
respectively, wherein heat present in the surrounding regenerator liquid 
50 is transferred to the ferromagnetic fluid. In effect, the cold from the 
ferromagnetic fluid is transferred to the regenerator fluid. The cold 
which is achieved in the regenerator fluid in portion 88 of the 
regenerator chamber can be used for external refrigeration or air 
conditioning purposes. Specifically, cold regenerator liquid 50 is 
circulated out of the regenerator chamber at 96 to a heat source 97 for 
refrigeration or air conditioning purposes at which point heat is 
transferred to the liquid 50. Regenerator liquid 50 is returned to the 
regenerator chamber at 98 at an elevated temperature. It is to be 
understood that the location of exit ports, at 74 and 96, and reentry 
ports, at 76 and 98, will be selected for most efficient system 
performance. 
Magnetic fluid 12 continues to flow through conduit 16 and exits the 
regenerator chamber at 100 where it is once again exposed to ambient 
temperatures. The cycle is repeated. 
As will be noted, the system includes a cooling system 102 which is used to 
cool the superconducting magnet 26. 
As discussed above, regenerator fluid separation diaphragm 84 divides the 
regenerator fluid into two regions, the hot region 86 and the cold region 
88. The temperatures generated in the two regions are substantially 
stratified. 
By contrast, the Brown system sets forth a mechanical system in which the 
physical motion of the solid elements can cause a resulting turbulence in 
the fluid, mixing cold and hot regions. The design of the Brown system and 
its operating speeds must be chosen to minimize this turbulent mixing at 
cold and hot regions. 
The present system provides more efficient heating and cooling than Brown 
in part because the regenerator liquid is not turbulently mixed by virtue 
of passage of the ferromagnetic material through the magnet bore. 
A generally continuous ring of magnetic fluid is present throughout the 
system. In other words, there are no gaping areas within conduit 16 which 
are substantially void of ferromagnetic fluid. Since the fluid is 
continuous throughout the system, the heating and cooling provided by the 
ferromagnetic system prove reliable within a predictable range. 
With respect to the ferromagnetic fluid 12, the fluid portion can be 
comprised of either gas or liquid. An important feature of the fluid, 
however, is that it can carry ferromagnetic particles with it through the 
magnetic bore when the fluid is pumped. When the fluid is a liquid, the 
ferromagnetic particles can be in a colloidal dispersion or suspension 
within the fluid. Or, the particles could be otherwise disposed in the 
liquid and form a simple slurry; or, the two methods can be combined. 
The ferromagnetic fluid is comprised of an appropriate fluid as well as an 
appropriate ferromagnetic material. It is suggested that the "appropriate" 
specific components be selected so as to most effectively operate properly 
within a desired temperature range. Furthermore, it is important that the 
materials be selected to provide the desired flow rates, both volumetric 
and mass. 
The ferromagnetic material in the fluid may be supplied in a powdered form, 
requiring protection from oxidation. It is suggested that oxidation 
protection be obtained by using a non-oxidizing fluid carrier. On the 
other hand, it is possible that somewhat larger ferromagnetic particles 
could be supplied with a very thin anti-oxidation polymer coating applied 
thereon for use in certain applications. 
The ferromagnetic material of choice is that material which has its Curie 
point in the temperature region of interest for the operating system. 
Also, it is possible to use mixes of different ferromagnetic powders or 
particles with different Curie points to provide an extended range of 
operating temperatures. Table I below includes a number of representative 
substances, and their respective Curie temperatures, which can be used as 
the ferromagnetic material in a magnetic heating-cooling system operating 
generally in the "room temperature" regime of interest in commercial 
refrigeration and air conditioning units. For other refrigeration 
requirements at substantially different temperatures, other ferromagnetic 
materials would be used. 
TABLE 1* 
______________________________________ 
Substance Curie Temperature (Kelvin) 
______________________________________ 
Gd 293 
Gd.sub.3 Al.sub.2 
287 
Gd.sub.5 Si.sub.4 
336 
Y.sub.2 Fe.sub.17 
317 
MnAs 318 
MnP 298 
CrTe 333 
______________________________________ 
*Hashimoto, T., et al. "Magnetic Refrigeration in the Temperature Range 
from 10 K to Room Temperature: The Ferromagnetic Refrigerants." 
Cryogenics, Nov. 1981, pp. 647, 652. 
The mass flow rate of the ferromagnetic material through the magnet bore 
determines the maximum amount of heating and cooling. Maximum performance 
depends on a variety of design factors which include the efficiency of the 
regeneration performance; the efficiency of the heat transfer design; the 
efficiency of the pumping system; and other areas of the system. 
FIG. 2 sets forth an alternate embodiment of the present invention. Like 
elements are denoted by primed (') numerals, and new elements are denoted 
by new numerals. 
In FIG. 2, ferromagnetic fluid 12' flows through conduit 16'. The flow is 
assisted by one or a series of mechanical pumping means 20', and arrows 
show the direction of flow. Magnetic fluid 12' enters regenerator chamber 
40' at 58'. Regenerator fluid 50' is present in the regenerator chamber. 
Once the fluid enters a magnetic field at 36' provided by cryogenic magnet 
26', the fluid undergoes heat of magnetization. Heat exchanger 66' 
transfers heat from the ferromagnetic fluid to the regenerator fluid 50'. 
As with the system set forth in FIG. 1, the regenerator fluid in this warm 
portion 86 of the regenerator chamber is circulated out through outlet or 
channel 74' to a heat sink 75' where heat is transferred from the 
regenerator fluid. The regenerator fluid is then circulated back in to the 
chamber 40' through inlet 76'. 
The fluid continues to flow until it exits the magnetic field at 80' at 
which transition point the temperature of the magnetic fluid decreases. 
Heat present in the regenerator fluid 50' in portion 80' of regenerator 
chamber 40' is transferred to the ferromagnetic fluid by way of heat 
exchanger 92'. 
FIG. 2 shows that the ferromagnetic fluid is circulated outside of the 
regenerator chamber at a portion of conduit labelled 104; however, it is 
not necessary that the fluid actually leaves the chamber. Instead, the 
conduit 16 could simply be contained within the chamber. 
The main difference between the system shown in FIG. 2 and that of FIG. I 
is that instead of returning the fluid to the entry 58' of the chamber 40' 
via a route that is outside the field of magnet 26', the ferromagnetic . 
fluid is returned to entry 58' by a route which flows back through 
magnetic bore 32'. Upon reentry into the magnetic field, the ferromagnetic 
fluid once again undergoes heat of magnetization. Heat exchanger 106 
transfers heat from the ferromagnetic fluid to the regenerator chamber. 
The ferromagnetic fluid flows out of the magnetic field at 107 and is 
chilled. It then enters into a chamber 108 divided from regenerator 
chamber portion 86' by insulating diaphragm 109. Heat present in 
regenerator chamber 108 is transferred to ferromagnetic fluid by way of 
heat exchanger 110. Regenerator fluid present in chamber 108 is cooled and 
is circulated to a heat source 112. As an alternative, the cool 
regenerator liquid of chamber 108 can be used to supplement the magnet 
cooling system 102'. 
FIG. 3 shows a second alternate embodiment of the present invention. 
Specifically, FIG. 3 shows an electromagnet (switchable) system. This 
system undergoes a heating and cooling cycle. 
Specifically, high pressure pump 120 provides a reservoir or accumulator 
for ferromagnetic fluid. When the reservoir is filled with ferromagnetic 
fluid or slurry, the high pressure pump is turned on. It pressurizes the 
volume of fluid or slurry to a level sufficient for the volume to flow as 
a "slug" fully through the system. When a set pressure level is reached, 
sensor 124 switches on electromagnet 128 and opens valve 130. The 
resulting fluid "slug" flows into the magnetic field wherein heat is 
generated. It flows through heat transfer coils 134 which transfer heat to 
the liquid in container 138. 
When the fluid slug trailing edge passes sensor 140, the electromagnet is 
turned off. This causes the fluid to absorb heat from the liquid in 
chamber 138 as it flows through heat transfer coils 134. The fluid slug 
flows through open valve 142 into the pump accumulator 144. Sensor 146 
senses the trailing edge of the fluid slug and closes valve 142 and turns 
on pump accumulator 144. When a preselected pressure is reached, sensor 
148 opens the valve 142 and turns off the pump 144. The fluid slug flows 
from the right to left through the system (with the electromagnet 128 off) 
and through open valve 130. Sensor 150 senses the trailing edge of the 
fluid slug and closes valve 130 and turns on pump 120. 
The efficiency of operation of the system may make desirable a partition 
151 separating the container C into two chambers, the hot chamber 152 and 
the cold chamber 154. As shown, heat is rejected from the hot chamber 152 
to a heat sink 156, and heat is absorbed by the cool chamber 154 from heat 
source 158. 
The cycle set forth in FIG. 3 repeats and continues until the system is 
turned off. The ferromagnetic fluid is finally contained or stored in pump 
accumulator 120. 
The invention has been described with reference to the preferred 
embodiment. Obviously modifications and alterations will occur to others 
upon a reading and understanding of the specification. It is intended to 
include all such modifications and alterations insofar as they come within 
the scope of the appended claims or the equivalents thereof.