JP3094081B2 - Method and apparatus for damping convective transport - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for attenuating convective transport generated in a region where the density in a fluid becomes minimum under gravity.

[0002]

2. Description of the Related Art As a method for synthesizing a large amount of fullerenes and carbon nanotubes, which has recently attracted attention, a gas phase synthesis method from carbon vapor is widely used. In this method, a carbon vapor is generated by arc discharge or the like, and the carbon vapor is cooled in a surrounding atmosphere gas to synthesize clusters (ultrafine particles) such as fullerene.

In this synthesis method, the atmosphere gas itself is heated and reduced in density in the vicinity of the outlet of the high-temperature carbon vapor, so that strong convection of the atmosphere gas occurs under gravity on the ground,
The carbon vapor rides on this convection and is transported at high speed to the low temperature region of the atmospheric gas.

In general, heat and mass transport by convection are
Convective transport plays a major role in the carbon vapor cooling process because it is faster than by diffusion.

However, in order to improve the yield of fullerenes and carbon nanotubes, and to promote higher order (increase in size) or heterogeneity (intentionally incorporating elements other than carbon), the cooling rate of carbon vapor must be reduced. Is required to be changed to a region much smaller than before, and for that purpose, means for attenuating the convective transport of the atmospheric gas near the carbon vapor outlet is required.

[0006] Not limited to these fullerene and other synthesis devices,
In many liquid and gas phase reaction systems, there is a region where the density becomes extremely small due to heating or the like, and convection resulting therefrom is inevitably generated. Thus, if its convective transport could be attenuated, more precise control of the reaction conditions would be possible. Also, in various physical property measurements that are easily affected by convective transport, such as measurement of the thermal conductivity of a fluid or the diffusion velocity between fluids with different densities, applying a method of attenuating convection in the minimum density region will be more effective. It is expected that accurate measurement data can be collected.

As described above, generally, in a fluid system in which a region where the density becomes extremely small, a method of attenuating the convective transport in the region where the density is extremely small is extremely useful for both scientific and industrial fields.

[0008] The simplest way to attenuate convection in a fluid is to place some physical barrier near the area where the convection is to be attenuated, thereby mechanically disrupting the convection and causing the flow velocity to decrease. And direction can be changed or attenuated. However, in this method, for example, when cooling a high-temperature carbon vapor with an atmospheric gas, the installed physical barrier is also heated to a high temperature, so that the substance constituting the physical barrier contaminates the fluid or attenuates convection. The temperature field near the region to be attempted can change significantly due to the presence of physical barriers.

There has been reported a method of eliminating convection by utilizing a microgravity environment in an artificial satellite flying in an orbit around the earth.

However, this method currently requires enormous costs and considerable preparation time, and the size, weight,
Since power and experimental time are greatly restricted, they are not suitable for research that requires a trial-and-error process such as searching for reaction conditions, or for applications such as mass production.

[0011] For the purpose of creating a simulated microgravity environment on the ground and suppressing convective transport, the container containing the fluid is allowed to fall vertically vertically, or the airplane on which the container is mounted is dropped suddenly for about 20 seconds. Methods for creating a microgravity environment have been reported.

However, in this method, it is difficult to extend the generation time of microgravity, and the size, weight, and power of the experimental device are greatly restricted. Therefore, the above-mentioned method uses the microgravity environment in the artificial satellite. Similarly, it is not suitable for use in searching for reaction conditions or mass production.

By developing the above method, the entire experimental apparatus is suspended in the air using an elastic body on the ground, vibrated greatly in the vertical direction, and utilizing the microgravity state during a parabolic motion from ascending to descending, A method has been reported in which the total time of the microgravity state is increased by maintaining the vibration motion a plurality of times.

However, this method is also subject to great restrictions on the size, weight, and power of the experimental device, and also, when changing from descending to ascending, the acceleration acts in the direction of increasing gravity, so that at this point in the fluid, If there is a certain density distribution, a large convection is induced, and the possibility that the convection remains even in the microgravity state from rising to falling thereafter cannot be denied.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems in a system in which a region having a minimum density is generated in a fluid containing a gaseous phase or a liquid phase, for attenuating convective transport near the region. And a method for attenuating convective transport of a minimum density region in a fluid for an arbitrary time on the ground without significantly restricting the size, weight, and power of the experimental device, and an apparatus using the same. The purpose is to:

[0016]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a gas phase, a liquid phase including a region where the density is minimized, or a composite material thereof is rotated. As a result, the present inventors have found that convective transport in the minimum density region can be attenuated, and completed the present invention.

That is, according to the present invention, an arbitrary gas phase, liquid phase or a composite material thereof including a region where the density becomes minimum is sealed in a closed space or in a substantially closed state, and passes through the minimum density region. Center line (A line that is the axis of rotation.
It is called "center line". ), The centrifugal force and the Coriolis force are changed so that the flow velocity of the gaseous phase, the liquid phase or a composite substance thereof takes a distribution that can be regarded as symmetric with respect to the center line. The present invention provides a method for attenuating convective transport, wherein the method acts on these composite substances to attenuate convective transport in a region where the density is minimized.

Further, the present invention provides a container for enclosing an arbitrary gas phase, liquid phase or a composite material thereof in a hermetically or substantially hermetically sealed state, including a region where the density becomes extremely small, Means for rotating the composite material around a center line passing through the minimum density region so that the flow velocity has a distribution that can be regarded as symmetrical with respect to the center line. And a Coriolis force acting on the gas phase, the liquid phase, or a composite material thereof to attenuate the convective transport in the minimum density region.

Here, the "region where the density is minimal" means a region where the gas phase, the liquid phase or a composite substance thereof has a density difference due to heating or mixing, and in which the density is minimal. It is.

[0020]

The operation of the present invention will be described below together with its principle. Any gas phase, liquid phase or a composite material thereof including the region where the density becomes minimum is sealed or enclosed in a closed space, and the flow velocity is around the center line passing through the density minimum region. Are rotated so as to take a distribution symmetrical with respect to, that is, a distribution in which the flow velocity can be regarded as not changing along the rotation direction.

On the ground, gravity always acts on the minute volume ΔV in the fluid. However, when a rotational motion is given to the fluid, centrifugal force in a direction away from the center line is added in addition to gravity, and Coriolis in a direction of rotation. The forces are rω ² ΔVρ and-
It works with the magnitude of ωvΔVρ. Here, ρ is the density of the minute volume, r is the distance from the center line, v is the radial velocity, and ω is the angular velocity. However, v is positive in the direction in which the radius increases.

In the minimum density area and its vicinity, convection is generated by the action of gravity. However, the action of centrifugal force and Coriolis force is applied by rotation, so that convection having a different aspect from the case without rotation is generated.

Furthermore, since the centrifugal force and the Coriolis force are respectively proportional to the square and the first power of the angular velocity ω, it is possible to actively change the convection by adjusting ω.

Attenuation of convective transport in the minimum density region means that the sum of the inflow to the minimum density region and the outflow from the minimum density region is reduced.

From this viewpoint, the operation of the centrifugal force and the Coriolis force will be described as follows. First, the centrifugal force acts to move the fluid in the density minimum area and the fluid in the vicinity thereof toward the center line in the density minimum area, thereby increasing the radial component of the inflow amount into the density minimum area.

However, this action alone does not reduce the total inflow and outflow in the density minimum region, but may increase the total inflow and outflow as the centrifugal force becomes excessive.

On the other hand, the Coriolis force acts to attenuate the radial velocity component of the flow over the entire region of the fluid. Because, for example, in the case of a flow towards the central axis, the volume element of the flow has a negative radial velocity v, so that the Coriolis force becomes positive and the angular velocity ω of the volume element increases.
However, this causes an increase in centrifugal force, so that a force is applied to the volume element in a direction away from the central axis, and as a result, the velocity component toward the central axis is reduced.

Further, since the radial flow and the axial flow are interlocked with each other, if the radial flow is attenuated by the Coriolis force, the axial flow is inevitably also attenuated in conjunction with the Coriolis force. Will be.

As described above, in the radial velocity damping effect of the Coriolis force, the fluctuation of the angular velocity ω mediates, so that the action of the Coriolis force causes the speed component in the rotational direction to be remarkable. May increase. However, if the condition of the axially symmetric distribution is satisfied, the velocity component in the rotation direction does not contribute to the inflow and outflow in the minimum density region, so that the inflow and outflow does not increase.

As described above, according to the action of the Coriolis force,
Both the radial and axial inflows and outflows in the density minimum region can be reduced, and the degree of the reduction can be adjusted by the angular velocity ω.

Therefore, by setting an appropriate rotation speed in consideration of the effects of the centrifugal force and the Coriolis force, it becomes possible to attenuate the convective transport in the density minimum region.

In the present method, there is no need to install a physical barrier in the vicinity of the minimum density region, so that even when the fluid is heated to an extremely high temperature, the fluid may be contaminated or the region of interest may be contaminated. There is an advantage that the temperature field is not significantly changed.

Further, as compared with the conventional method of installing the device in an artificial satellite or making a large acceleration motion in the vertical direction, restrictions on the size, weight, and power of the entire device are much smaller. Since the simple operation of rotating the fluid is used, there is an advantage that the operation time is not limited in principle.

In the apparatus using this method, the shape, material, smoothness of the inner surface, the angle of the center line with respect to gravity, and the lower limit value of the rotation speed of the container for storing the fluid are such that the flow velocity is symmetric with respect to the center line. Any value may be set as long as a distribution that can be regarded as possible can be obtained. Also, the angular velocity of the fluid need not be uniform throughout the fluid.

As a method of rotating a fluid, a method is used in which an object having momentum is brought into contact with the fluid, and the entire fluid is rotated using the frictional force between the object and the fluid and the viscous stress between the fluids. In the case of a body or a magnetic body, a method of applying an electric field or a magnetic field to a fluid to apply an electromagnetic stress in the fluid to rotate the fluid, or a combination of these methods may be used.

[0036]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a fullerene synthesizing apparatus capable of attenuating convective transport near a carbon vapor outlet using the present invention and greatly reducing the cooling rate of carbon vapor. The fullerene synthesizing apparatus 1 includes a cylindrical container 2
And a helium gas as an atmosphere gas is hermetically sealed or substantially hermetically sealed therein, and the enclosed atmosphere gas can be convected in conjunction with the diametrical direction and the major axis direction in the cylindrical container.

A pair of arc discharge carbon electrodes 3, 3 symmetrically disposed at the center line XX of the cylindrical container 2 and having their respective ends opposed to each other are placed in the cylindrical container at the longitudinal center of the cylindrical container. It is arranged. These carbon electrodes 3
Power is supplied from the outside of the cylindrical container 2 by an appropriate power supply means (for example, a current collecting band slidably in contact with an external power supply piece is provided around the outer periphery of the cylindrical container 2 and power is supplied to the carbon electrodes 3 and 3). I have. Due to the arc discharge of the electrode, a carbon vapor gas heated to a high temperature of 5000 K is generated in the opposing central region, and the atmosphere gas is heated to a high temperature to generate a temperature difference and a density difference in the atmosphere gas by the region in the cylindrical container 2.

After all, according to the above configuration, a substantially central position in the longitudinal direction of the cylindrical container 2 on the center line XX of the cylindrical container 2, that is,
A hot carbon vapor outlet (generating portion) is provided in a substantially central region of the space in the cylindrical container 2,
A region 4 having a minimum density of the atmospheric gas is formed.

The cylindrical container 2 having such a configuration is rotated by an appropriate rotation drive mechanism around a center line XX passing through a region where the density of the atmospheric gas is extremely small. Note that the above configuration is one embodiment of the present invention, and specific means for rotating the gas phase, the liquid phase, or a composite material of the present invention around the density minimum region is not described here. It goes without saying that there are many other possibilities.

[0040]

EXAMPLE An example of the present invention will be specifically described by performing a fluid simulation assuming the apparatus described in the above embodiment of the present invention. The fullerene synthesizer 1 has an inner diameter of 10
It has a cylindrical container 2 having a height of 0 mm and a height of 100 mm, and a helium gas of 0.5 atm is sealed therein as an atmospheric gas. And the cylindrical container 2 has a center line X-
With X as a center, 0 to 1 per minute by an appropriate rotation drive mechanism
It can be rotated at 000 rotations. In calculation,
The carbon vapor heated to 5000K at the outlet is approximated as a 5000K point heat source that does not disturb the flow, and the helium gas near the heat source is heated to a maximum of 5000K due to the mixing of the carbon vapor, and the area with the minimum density is reduced. Will happen.

However, changes in the physical properties of helium gas other than changes in temperature due to the mixing of carbon vapor are ignored. The vessel inner wall temperature is fixed at 473 K (200 ° C.), and the center line is parallel to gravity. The flow rate and temperature of the helium gas in the container in the steady state were calculated for each rotation speed. The calculation was performed in a two-dimensional axisymmetric cylindrical coordinate system, and a variable density / laminar flow calculation code was used.

FIG. 2 shows the distribution of gas velocity and temperature along the center line. The horizontal axis represents the distance from the carbon vapor source on the center line, and the upper side in the vertical direction is positive.

When no rotation is given (0 RPM),
The gas flow velocity along the center line is an upward flow, and as it approaches the discharge position of the carbon vapor, the flow velocity increases rapidly, and the speed of the flow passing through the heat source, that is, the flow flowing into and out of the minimum density region, is , About 1.2 m / s.

Next, when the container is rotated at 100 RPM, it can be seen that the flow flowing into and out of the density minimum region is significantly attenuated and reaches a value of at most 0.2 m / s.

If the rotation is further increased to 1000 RPM,
It can be seen that the flow velocity at the center of the minimum density region is almost zero, and a weak flow that flows vertically from the minimum density region occurs.

The remarkable change in the convection near the density minimum region also changes the magnitude of the heat transport by the convection, and the temperature distribution of the gas near the heat source changes accordingly. I understand.

FIG. 3 is a graph obtained by focusing on a specific minute volume of a gas flowing along the center line and calculating a time change of the temperature. The origin of time is the time when the minute volume of interest passes through the heat source.

When no rotation is given, the time required for the gas passing through the heat source to cool from 5000K to 2500K is about 4 hours.
In the case of 100 RPM and 1000 RPM, they are 25 ms and 81 ms, respectively. That is, 10
By providing the rotation of 00 RPM, the cooling rate of the helium gas is reduced to about 1/20.

The calculation results show that the present invention can greatly reduce the convective transport of helium gas and reduce the cooling rate of carbon vapor mixed in helium gas to 1/20. .

[0050]

According to the present invention, the convective transport in the minimum density region is attenuated under gravity for any time in any gas phase, liquid phase, or a composite material including the region where the density becomes minimum. Can be done.

The apparatus according to the present method is also free from significant limitations on its size, weight and power, without contaminating the fluid or significantly changing the temperature field in the area of interest. Since the magnitude of heat and mass transport due to convection in a minimal region can be attenuated, various cluster (ultrafine) materials such as fullerenes can be created and enhanced, and reaction conditions in various liquid and gas phase reaction systems can be reduced. It is possible to provide precision control or various physical property measurements that are susceptible to disturbance of convective transport such as thermal conductivity of a fluid for use in improving the accuracy.

[Brief description of the drawings]

FIG. 1 is a calculation model of an example of a fullerene synthesizing apparatus capable of attenuating convection of an inert gas using the present invention.

FIG. 2 is a diagram illustrating a distribution of gas velocity and temperature along a center line in an embodiment of the present invention.

FIG. 3 is a diagram showing a temporal change in temperature of a gas flowing along a center line, focusing on a specific minute volume in the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fullerene synthesizer 2 Cylindrical container 3 Carbon electrode 4 Density minimum area

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yozo Kakudate 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Hiroyuki Yokoi 1-1-1, Higashi, Tsukuba, Ibaraki, Japan Within the Institute of Engineering Technology (72) Inventor Ryuji Kato 1-1-1, Higashi, Tsukuba, Ibaraki Pref. (56) References JP-A-10-45407 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 19/00, 19/28 C01B 31/02

Claims (2)

(57) [Claims] 1. A gas phase, a liquid phase, or a composite material thereof including a region where the density becomes minimum is sealed in a closed space in a closed or substantially closed state, and around a center line passing through the density minimum region. Then, the gas phase, the liquid phase or a composite material thereof is rotated so as to assume a distribution that can be regarded as symmetric with respect to the center line, and the centrifugal force and the Coriolis force are applied to the gas phase, the liquid phase or a composite thereof. A method for attenuating convective transport, wherein the method acts on a substance to attenuate convective transport in a region where the density is minimized. 2. A container for enclosing any gas phase, liquid phase or a composite material thereof in a hermetically or substantially hermetically sealed state, including a region where the density is minimal, and Having means for rotating the flow velocity around a center line passing through the minimum density region so that the flow velocity has a distribution that can be regarded as symmetrical with respect to the center line, and by performing the rotation, centrifugal force and Coriolis force are reduced. An attenuating device for convective transport, wherein the device acts on the gas phase, liquid phase, or a composite substance thereof to attenuate convective transport in the minimum density region.