Heat exchange – Intermediate fluent heat exchange material receiving and... – Liquid fluent heat exchange material
Reexamination Certificate
1997-05-15
2001-01-16
Lazarus, Ira S. (Department: 3743)
Heat exchange
Intermediate fluent heat exchange material receiving and...
Liquid fluent heat exchange material
C062S051100, C062S259200
Reexamination Certificate
active
06173761
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cryogenic heat pipe having a sealed tube and designed to cool an object (to be cooled) placed on the heat absorbing side by using a refrigerator installed on the heat dissipating side and, more particularly, to a cryogenic heat pipe which can efficiently perform heat transport by properly setting the inner diameter of the above tube and the length of a heat absorbing portion.
Superconductors are known to have zero electric resistance. It is expected that the energy consumed by power equipment will be saved by applying this property to power equipment.
In order to use a superconductor, it must be cooled to a critical temperature or less by some means. As a cooling means, a scheme of cooling a superconductor by immersing it in a cryogenic liquid such as liquid helium or liquid nitrogen is generally used. With such an immersion dip cooling scheme, however, since liquid helium or liquid nitrogen which is difficult to handle is used, it is inevitable that the operation cost will rise.
Under the circumstances, a direct refrigerator cooling scheme has recently been proposed, in which the cooling stage of a refrigerator is thermally connected to a superconductor through a heat conduction member to cool the superconductor.
In power superconducting equipments, however, since large currents are involved and AC is used, a larger amount of heat is generated than in DC superconducting equipment. In addition, in the power superconducting equipment, a sufficient distance must be ensured between the refrigerator and the object to be cooled owing to the large size of the equipment and the breakdown voltage. For these reasons, a large amount of heat needs to be transferred over a long distance. This makes the temperature difference between the refrigerator and the object large, resulting in a considerable deterioration in the efficiency of the system.
Demands have therefore arisen for the development of heat transfer elements for transferring heat with a small temperature difference over a long distance. Of these elements, elements for actively transferring heat by using the movement of a fluid flowing through a heat pipe, a dream pipe, or the like are especially expected to be developed. Of these elements, especially a cryogenic loop heat pipe having a loop capillary tube has advantages. For example, this pipe has good operability because it requires no special fluid driving source, and also exhibits a high degree of freedom in installation because it can have a flexible structure as a whole.
The structure of the cryogenic loop heat pipe will be briefly described below.
The cryogenic heat pipe is formed by sealing a working fluid into a capillary tube consisting of copper and shaped into a loop.
When the loop capillary tube is to be actually used as the heat pipe, a portion of the tube is thermally connected, as a heat absorbing portion, to an object to be cooled, and the other end of the capillary tube is thermally connected, as a heat dissipating portion, to a heat absorption object, e.g., a cooling source. In many cases, these portions are connected by using blocks or the like consisting of a good heat conduction material.
When the working fluid in the heat absorbing area is heated by heat entering the heat absorbing portion, a vapor bubble is generated in the working fluid. This vapor bubble displaces the liquid around the bubble. Although this displacement force acts toward the two sides of the loop with the heat absorbing portion serving as a boundary, the force in one direction can be made stronger by, for example, finely unbalancing the arrangement. As a result, the flow component of the liquid in one direction increases, and the working fluid circulates or oscillates in the loop. This movement of the working fluid contributes to heat exchange between the heat absorbing portion and the heat dissipating portion, thus performing heat transfer. Since the latent heat of evaporation is absorbed when the fluid is evaporated at the heat absorbing portion and releases it when gas condenses at the heat dissipating portion, at a small temperature difference, a large amount of heat can be transferred in particular. For this reason, heat can be transferred in an amount 10 to 100 times that transferred by using a copper member, as a heat transfer element, which has the same cross-sectional area as that of the capillary tube.
Although the cryogenic loop heat pipe has such advantageous characteristics, the pipe does not operate if the dimensions of the capillary tube fall outside the operating conditions. For this reason, a cryogenic loop heat pipe must be designed after a sufficient examination. For example, the inner diameter of the capillary tube is empirically determined by trial and error. In addition, when the operating temperature range is determined, the type of operating fluid that is suited for this temperature range must be used. However, since optimal capillary tube inner diameter varies from one working fluid to the other, the same trial-and-error testing must be repeated.
As described above, in order to design a cryogenic heat pipe, a test must be performed under each operating condition. Currently, this problem interferes with the applications of the cryogenic loop heat pipe.
BRIEF SUMMARY OF THE INVENTION
As described above, conventionally, in order to determine the inner diameter of a capillary heat pipe, each heat pipe must be independently tested for optimization in accordance with the operating conditions such as the temperature and working fluid, resulting in poor applicability.
It is, therefore, an object of the present invention to provide a cryogenic heat pipe capable of transporting optimal heat in accordance with the operating conditions under consideration.
In order to achieve the above object, according to the first means of the present invention, there is provided a cryogenic heat pipe comprising a sealed tube in which a working fluid circulates and which has a portion used as a heat absorbing portion and a portion, other than the heat absorbing portion, that is used as a heat dissipating portion, the tube being formed to satisfy
15
d
<l<
882
d
where l is a heat exchange length of the tube at the heat absorbing portion, and d is an inner diameter of the tube at the heat absorbing portion.
In this cryogenic heat pipe, the inner diameter d of the tube preferably satisfies L<d<3L where &sgr; is the surface tension of the working fluid, &rgr;
1
is the density of the working fluid in the liquid phase, &rgr;
v
is the density of the working fluid in the gas phase, g is the gravitational acceleration, and L is the Laplace constant given by L=[&sgr;/{(&rgr;
1
−&rgr;
v
)g}]
0.5
.
According to this arrangement, the working fluid is driven by a vapor bubble generated in the tube at the heat absorbing portion, and moves in the tube while performing heat exchange at the heat dissipating and absorbing portions. By setting the heat transfer area of the heat absorbing portion to be larger than the minimum area with which the heat pipe properly operates, the cryogenic heat pipe can be properly operated. In addition, by setting a proper inner diameter, a cryogenic heat pipe having a high heat transport capacity can be obtained. As the working fluid of heat pipe, a fluid selected from helium, hydrogen, neon, nitrogen, oxygen, argon, and mixtures thereof can be used.
According to second means of the present invention, there is provided a cryogenic heat pipe comprising a sealed tube in which a working fluid circulates and which has a portion used as a heat absorbing portion and a portion, other than the heat absorbing portion, that is used as a heat dissipating portion, the working fluid being one member selected from the group consisting of helium, hydrogen, neon, and mixtures thereof, and the tube being formed such that the inner diameter d at the heat absorbing portion satisfies L<d<3L where &sgr; is a surface tension of the working fluid, &rgr;
1
is a density of the workin
Chandratilleke Rohana
Nakagome Hideki
Ohtani Yasumi
Takahashi Masahiko
Yoshino Tatsuya
Kabushiki Kaisha Toshiba
Lazarus Ira S.
McKinnon Terrell
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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