JP2719201B2 - Liquid circulation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid circulating device used for circulating a liquid whose temperature is previously adjusted to a predetermined value through a heat exchanger coil.

[Conventional technology]

For example, instead of directly circulating a refrigerant such as chlorofluorocarbon in a cooling coil provided indoors in an air conditioner, a brine, which is previously adjusted to a predetermined temperature by a heat exchanger provided separately, is pumped into the cooling coil. The method of circulating using the pressure feeding means is conventionally known.

[Problems to be solved by the invention]

However, when the temperature to be realized in the ultra-low temperature storage, heat treatment equipment, environmental test equipment, etc. is considerably low or high (for example, −60 ° C., 200 ° C., etc.), the temperature for circulating brine or the like can be endured. Since there is no inexpensive pump, there is a problem that the liquid circulation system as described above cannot be adopted. Further, if the heat resistance and the cold resistance of the pump are intentionally improved by using a special heat-resistant material or a cold-resistant material, there is a problem that the pump is extremely expensive.

Accordingly, the present invention provides an inexpensive and reliable liquid that can circulate a considerably high or low temperature liquid without using a pump that is impossible or impossible to improve heat resistance and cold resistance. It is an object of the present invention to provide a liquid circulating device with high performance.

[Means for solving the problem]

According to the present invention, the present invention provides a main tank that stores a liquid to be circulated and maintains a predetermined temperature, a sub tank disposed at a higher position than the main tank, a heat exchanger, and a gas source for pressurization.
Gas circuit means for the main tank for guiding the gas for pressurization from the gas source for pressurization to the main tank, and primary circuit means for guiding the liquid to be circulated from the main tank to the heat exchanger,
A secondary circuit for guiding the liquid to be circulated from the heat exchanger to the sub tank; and tertiary circuit for returning the liquid to be circulated from the sub tank to the main tank, the gas circuit for the main tank. Means for guiding the liquid to be circulated in the main tank to the heat exchanger by the primary circuit means by the gas pressure guided to the main tank by means and means for guiding the liquid to be transferred from the heat exchanger to the sub tank by the secondary circuit means; When a predetermined amount of circulated liquid is accumulated in the tank, the liquid is circulated by repeating the operation of returning the liquid in the sub tank to the main tank by the tertiary circuit means. Is provided.

In the liquid circulation device, a sub-tank for guiding a pressurizing gas from the pressurizing gas source to the sub-tank so that the sub-tank liquid can be pressurized in returning the sub-tank liquid to the main tank. Gas circuit means may be provided.

A recovery circuit for guiding the liquid to be circulated in the heat exchanger to the main tank so that the liquid to be circulated in the heat exchanger can be recovered to the main tank; And a gas circuit means for a heat exchanger for guiding the gas for pressurization from the gas source for pressurization to the heat exchanger so that the gas can be pressurized.

The present invention also provides a liquid circulation device capable of handling two kinds of liquids, a high-temperature liquid and a low-temperature liquid, and according to the above object.

That is, first and second main tanks for storing the first and second circulated liquids and maintaining the same at a predetermined temperature, a first sub-tank arranged at a higher position than the first main tank,
A second sub-tank disposed higher than the second main tank, a heat exchanger, a pressurizing gas source, and pressurizing gas from the pressurizing gas source to the first and second main tanks. First and second main tank gas circuit means for directing, and first and second primary circuit means for directing the liquid to be circulated from the first and second main tanks to the heat exchanger; First and second secondary circuit means for guiding the liquid to be circulated from the heat exchanger to the first and second sub-tanks; and the first and second sub-tanks from the first and second sub-tanks. First and second tertiary circuit means for returning the circulating liquid to the main tank of the heat exchanger switch means for guiding the pressurizing gas from the pressurizing gas source to the heat exchanger;
A first and a second liquid circulation unit having first and second recovery circuit means for leading the liquid to be circulated in the heat exchanger to the first and second main tanks; In the above, the liquid to be circulated in the main tank is guided to the heat exchanger by the primary circuit means by the gas pressure guided to the main tank by the gas circuit means for the main tank, and from the heat exchanger by the secondary circuit means. The operation of guiding the sub-tank to the sub-tank and the operation of returning the liquid in the sub-tank to the main tank by the tertiary circuit means when a predetermined amount of the circulating liquid accumulates in the sub-tank The liquid pressure is guided to the heat exchanger by the gas circuit means for the heat exchanger to recover the circulated liquid in the heat exchanger to the main tank. To This is a liquid circulating device in which the liquid in the heat exchanger is directed to the main tank via the recovery circuit means.

In this liquid circulating device, in each of the liquid circulating units, the pressurizing gas is supplied from the pressurizing gas source to the sub tank so that the liquid in the sub tank can be pressurized when returning the liquid in the sub tank to the main tank. Sub-tank gas circuit means may be provided to guide the gas to the sub-tank.

In each of the liquid circulation devices, each circuit means includes:
If necessary, some or all of them may be common to other circuit means.

Further, each circuit means may be provided with opening / closing and switching means such as a solenoid valve for opening and closing the circuit and for switching the flow path as required.

[Action]

According to the liquid circulating apparatus of the present invention, whether it circulates one kind of liquid or circulates two kinds of liquids, the liquid circulating part is operated as follows.

That is, when the liquid is circulated, the pressurizing gas is led from the pressurizing gas source into the main tank through the main tank gas circuit means, and the circulated liquid in the main tank is transmitted through the primary circuit means by the gas pressure. A first operation of feeding the liquid to the heat exchanger and guiding it from the heat exchanger to the sub-tank via the secondary circuit means. When a predetermined amount of circulating liquid is accumulated in the sub-tank by the operation, it becomes necessary. The second operation of stopping the flow of the liquid from the heat exchanger to the sub-tank and dropping the liquid accumulated in the sub-tank into the main tank by the potential energy via the tertiary circuit means is repeated.

When a gas circuit means for the sub tank for introducing the gas for pressurization to the sub tank is provided, when returning the liquid accumulated in the sub tank to the main tank, the gas for pressurization is introduced into the sub tank. With the help of the gas pressure, the liquid in the sub tank can be dropped into the main tank.

When the gas circuit means for the heat exchanger and the liquid recovery circuit means for recovering the circulating liquid in the heat exchanger to the main tank are provided, the liquid is recovered as follows. That is, the introduction of pressurized gas to the main tank is stopped and the flow of liquid from the heat exchanger to the sub-tank is stopped, and the pressurized gas is led to the heat exchanger by the heat exchanger gas circuit means,
The gas pressure causes the liquid in the heat exchanger to flow to the main tank via the recovery circuit means. In this collection operation,
The liquid in the sub tank falls into the main tank via the tertiary circuit due to its potential energy.

The circulated liquid is adjusted to a predetermined temperature in the main tank, sent to a heat exchanger, and exchanges heat there.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The illustrated embodiment is a liquid circulation system that can circulate two types of liquid to a heat exchanger 2 for temperature control in a test tank provided on a peripheral wall of a test tank 1 of an environmental test apparatus for performing a thermal shock test or the like. The apparatus is composed of two liquid circulation sections A and B. The liquid circulation section A includes a main tank HMT containing a liquid L1 (for example, silicon oil, a fluorine-based inert liquid),
A sub-tank HST arranged above the tank, a heat exchanger 2, and a compressed air source 3 are provided.

The liquid L1 is maintained at a high temperature of about 200 to 220 ° C. by a heater HT provided in the main tank HNT.

The upper part of the main tank HMT can be opened to the atmosphere via a pipe 301.
Is provided.

Switch SW1 for detecting the liquid level in sub tank HST
Is arranged. The upper part of the sub tank SHT can be opened to the atmosphere via a pipe 201. The pipe 201 is provided with an open / close solenoid valve V16.

The compressed air source 3 converts the compressed air produced by the compressor C into a regulator tank RT, a filter F, a mist separator MS,
And a pressure regulating valve PR. The regulator tank RT is connected to a relief valve RV, a pressure switch PS for stopping the compressor C when the air pressure in the tank reaches a predetermined pressure, and a drain discharge valve VD. Auto drain AD for filter F
Is connected, and the drain is discharged through this.

The compressed air generated in the compressed air source 3 is supplied to the upper part of the main tank HMT via the main tank gas circuit 41.
The circuit 41 includes a three-way switching solenoid valve V1 and an opening / closing solenoid valve V13.
Is provided. Although not shown in the drawing, if necessary, a part of the circuit 41 may be passed through the tank HMT so that the temperature of the compressed air may be equal to or close to that of the liquid L1.

The compressed air generated in the compressed air source 3 is supplied to the upper part of the sub tank HST via the sub tank gas circuit 51. The circuit 51 includes a part of the circuit 41, and the sub tank HS
An opening / closing solenoid valve V14 is provided at a position close to T. Further, the compressed air of the compressed air source 3 is also supplied to the upper part of the heat exchanger 2 via the gas circuit 61 for the heat exchanger. The circuit 61 includes a part of the circuit 41 and a part of the circuit 51. The circuit 61 includes an opening / closing solenoid valve V15 for cutting off the supply of compressed air to the heat exchanger 2 and a three-way switching solenoid valve V12 near the heat exchanger 2.

The liquid L1 in the main tank HMT is supplied to the heat exchanger via a primary circuit 71 extending from the bottom of the main tank to the top of the heat exchanger 2. The circuit 71 includes a part of the heat exchanger gas circuit 61. Further, the circuit 71 includes an opening / closing solenoid valve V17 for cutting off the liquid supply from the main tank to the heat exchanger.

The lower part of the heat exchanger 2 is connected to the secondary tank HST via the secondary circuit 81.
Connected to the top. The circuit 81 includes an on-off solenoid valve V18 for stopping the flow of the liquid from the heat exchanger to the sub tank.

The bottom of the sub tank HST is tertiary circuit 91 on the top of the main tank HMT.
The circuit is provided with an on-off solenoid valve V12.

The lower part of the heat exchanger 2 is connected to the main tank HMT via the recovery circuit 101.
The circuit is provided with an on-off solenoid valve V3 and a three-way switching solenoid valve V4.

On the other hand, the liquid circulation section B is a main tank LMT containing a liquid L2 (for example, alcohol, Freon R11, or a fluorine-based inert liquid).
And a sub tank LST disposed above the main tank, the heat exchanger 2, and the compressed air source 3.

That is, the heat exchanger 2 and the compressed air source 3
And B are common.

The liquid L2 is maintained at about -70 ° C to -80 ° C by the refrigerant flowing through the cooling coil CL provided in the main tank LMT.

The upper part of the main tank LMT can be opened to the atmosphere by means of a pipe 302, which is provided with an on-off solenoid valve V21.

The sub tank LST has a switch S that detects the liquid level inside.
W2, the upper part of the tank can be opened to the atmosphere by a pipe 202, which has an on-off solenoid valve V2
6 are provided.

The compressed air from the compressed air source 3 can be supplied to the upper part of the main tank LMT via the main tank gas circuit 42. A part of the circuit 42 passes through the main tank LMT, thereby controlling the temperature of the compressed air supplied to the main tank LMT to the liquid LMT.
The temperature can be equal to or close to the temperature of 2. The steam trap ST or the auto drain is connected to a portion of the circuit 42 after passing through the main tank LMT, from which the drain can be discharged. The circuit 42 is provided with an opening / closing solenoid valve V23 for cutting off the supply of compressed air to the main tank. The main tank gas circuit 42 includes a three-way switching solenoid valve V1 in the gas circuit 41 in the liquid circulation section A.

The compressed air 3 can also be supplied to the upper part of the sub tank LST via the sub tank gas circuit 52, and a part of the circuit 52 includes a part of the circuit 42, An opening / closing solenoid valve V24 is provided at a position near the sub tank.

Further, the compressed air can be supplied to the upper part of the heat exchanger 2 via the gas circuit 62 for the heat exchanger. Circuit 62 is a circuit
Includes parts of 42 and 52. A three-way switching solenoid valve for switching a part of the gas circuit 61 in the liquid circulation section A
Included with V2. Further, the circuit 62 includes an on-off solenoid valve V25 for cutting off the supply of the compressed air to the heat exchanger 2.

The liquid L2 in the main tank LMT flows from the bottom of the tank to the primary circuit 7
2 can be supplied to the upper part of the heat exchanger 2.
Circuit 72 includes a portion of gas circuit 62. Also the circuit
72 is an open / close solenoid valve V2 for cutting off the liquid supply to the heat exchanger 2.
It has seven.

The lower part of the heat exchanger 2 is the liquid L2 contained in the heat exchanger.
Is provided to the auxiliary tank LST, and the circuit includes an on-off solenoid valve V28. This circuit 82 includes a part of the secondary circuit 81 in the liquid circulation section A.

The bottom of the sub tank LST is connected to the main tank LMT via the tertiary circuit 92.
The circuit 92 is provided with an opening / closing solenoid valve V22.

The lower part of the heat exchanger 2 is connected to the upper part of the main tank LMT via the recovery circuit 102. This circuit 102 includes a part of the recovery circuit 101 in the liquid circulation section A, together with a solenoid valve V3 and a three-way switching valve V4.

Next, the operation of the liquid circulation units A and B will be described with reference to FIGS. In FIGS. 2 to 7, the valves filled in black in each circuit are closed valves. Arrows indicated by dotted lines indicate the flow of compressed air, and arrows indicated by solid lines indicate the flow of the liquid L1 or L2.

 First, the operation of the liquid circulation unit A will be described.

Circulation of high-temperature liquid L1 As shown in FIG. 2, the three-way switching valve V1 in the gas circuit 41 is opened in the direction of the valve B13, and the three-way switching valve V2 connected to the heat exchanger 2 is opened in the direction of the valve V17. Let it open. The three-way switching valve V4 in the recovery circuit 101 is opened in the direction of the main tank HMT. In addition, valves V13, V1
6. Open V17, V18, and close valves V3, V11, V12, V14, V15, V28, respectively.

The compressed air obtained in the compressed air source 3 is led to the main tank HMT through the main tank gas circuit 41, and the high-pressure liquid L1 in the tank is transferred to the heat exchanger 2 through the primary circuit 71 by the gas pressure.
And the liquid L1 entering the heat exchanger 2 is further discharged to the sub-tank HST through the secondary circuit 81.
Flow into

When the liquid L1 in the sub tank reaches a predetermined amount and the switch SW1 in the tank detects this, as shown in FIG. 3, the valve V13 in the gas circuit 41 which has been opened is closed as shown in FIG. At the same time, the supply of compressed air to the main tank HMT is cut off, the valve V18 connected to the sub tank HST is closed to stop the flow of liquid from the heat exchanger to the sub tank, and the valve V16 connected to the sub tank is closed. To seal the inside of the sub tank.
Along with these operations, the valve of the gas circuit 51
V14, the valve V12 of the tertiary circuit 91, and the air release valve V11 connected to the upper part of the main tank are opened. Then, the compressed air is supplied to the upper part of the sub tank, and as a result, the liquid L1 in the sub tank HST falls to the main tank HMT via the tertiary circuit 91 by the potential energy and the compressed air pressure.

By repeatedly performing the respective operations shown in FIGS. 2 and 3 described above, the high-temperature liquid L1 can be circulated in the heat exchanger 2, whereby the inside of the test tank 1 of the environmental test apparatus is kept in a predetermined state. Maintained at high temperatures.

Recovery of high temperature liquid L1 in heat exchanger When switching test tank 1 to low temperature tank, heat exchanger 2
The high temperature liquid L1 is collected in the main tank HMT. This recovery is performed as shown in FIG.

That is, the valves V13 and V14 in the gas circuits 41 and 51 are closed, and the valve V15 in the gas circuit 61 is opened. Further, the valve V17 of the primary circuit 71 and the valve V18 of the secondary circuit 81 are closed, and the valve 12 of the tertiary circuit 91 is opened. The valve V3 of the recovery circuit 101 is also opened. Further, the valve V11 connected to the main tank HMT is opened to open the inside of the main tank to the atmosphere, and the valve V16 connected to the sub tank HST is opened to open the sub tank to the atmosphere.

Thus, the compressed air is supplied to the upper part of the heat exchanger 2, and the liquid L1 in the heat exchanger is recovered to the main tank HMT via the recovery circuit 101 by the air pressure, while the liquid L1 in the sub tank is recovered by its potential energy. Drop into main tank HMT.

In this way, the liquid L1 in the heat exchanger 2 and the sub tank HST is collected in the main tank HMT. After the high-temperature liquid L1 is collected in the main tank HMT, the liquid circulating unit B is operated as described below to maintain the inside of the test tank 1 at a low temperature.

 Next, the operation of the liquid circulation unit B will be described.

Circulation of low-temperature liquid L2 As shown in FIG. 5, the three-way switching valve V1 in the main tank gas circuit 42 is opened in the direction of the liquid circulation section B,
The three-way switching valve V2 connected to the heat exchanger 2 is opened in the direction of the valve V27. Further, the three-way switching valve V4 in the recovery circuit 102 is opened in the direction of the main tank LMT. Open valves V23, V26, V27 and V28 and open valves V3, V21 and V
22, V24, V25, and V18 are each closed.

The compressed air thus generated in the compressed air source 3 is guided to the upper part of the main tank LMT through the main tank gas circuit 42, and the low pressure liquid L2 in the main tank is exchanged with heat through the primary circuit 72 by the gas pressure. It is led into the vessel 2. Further, the liquid L2 that has flowed into the heat exchanger flows through the secondary circuit 82 into the sub tank LST that has been opened to the atmosphere.

When the liquid in the sub tank LST reaches a predetermined amount and the switch SW2 detects this, the valve V23 of the main tank gas circuit 42 is closed to supply compressed air to the main tank LMT, as shown in FIG. And the valve V28 of the secondary circuit 82 is closed to stop the flow of the liquid from the heat exchanger 2 into the sub tank LST. On the other hand, the valve V22 of the tertiary circuit 91 is opened, the air release valve V21 connected to the main tank is opened, and the air release valve V26 connected to the sub tank is closed.

In this way, the compressed air is guided into the sealed sub tank LST, and the liquid L2 in the sub tank is returned to the main tank LMT via the tertiary circuit 92 by the potential energy and the air pressure.

By repeating the operations shown in FIGS. 5 and 6 in this manner, the low-temperature liquid L2 is circulated to the heat exchanger 2 so that the test tank 1
The inside is maintained at a predetermined low temperature.

Recovery of Low Temperature Liquid L2 in Heat Exchanger In order to switch the temperature of the test tank 1 to a high temperature, the operation of recovering the low temperature liquid L2 from the heat exchanger 2 is performed as shown in FIG.

That is, the valves V23 and V23 in the gas circuits 42 and 52
24 to close the supply of compressed air to the main tank LMT and the sub tank LST, and close the valve V27 of the primary circuit 72 and the valve V28 of the secondary circuit 82 to supply liquid to the heat exchanger 2 and to the sub tank LST. Cut off the liquid supply. Further, V21 connected to the main tank and valve V26 connected to the sub-tank are opened to open the main tank and the sub-tank to the atmosphere, and the collection circuit 10
Open valve V3 at 2. Thus, gas circuit 6 to heat exchanger 2
Compressed air is supplied through the second tank 2, and the liquid L2 in the heat exchanger is recovered to the main tank LMT through the recovery circuit 102 by air pressure. The liquid L2 in the sub tank falls into the main tank via the tertiary circuit 92 by the potential energy.

Note that the present invention is not limited to the above embodiment,
It can be implemented in various other modes.

According to the above embodiment, two kinds of liquids can be circulated, but if only one kind of liquid needs to be circulated,
It is only necessary to provide a liquid circulation unit having substantially the same configuration as the liquid circulation unit A or B. Further, when the liquid in the heat exchanger 2 is not required to be recovered, gas circuits 71 and 72 for the heat exchanger provided for recovering the liquid and a recovery circuit connected from the heat exchanger 2 to the main tank are provided. 101 and 102 are unnecessary.

Further, in the liquid circulation operation, when returning a predetermined amount of liquid stored in the sub-tank to the main tank, the compressed air pressure is used in the above-described embodiment. By opening, the liquid in the sub tank can be dropped into the main tank only by its potential energy.

Further, in the above embodiment, when the liquid in the heat exchanger 2 is recovered to the main tank, the liquid in the sub tank is recovered to the main tank only by its potential energy. And may be recovered by the compressed air pressure. In this case, in order to prevent the backflow of the compressed air, the recovery from the heat exchanger and the recovery from the sub-tank are not performed at the same time but performed at a different time.

〔The invention's effect〕

As described above, according to the present invention, it is possible to circulate a considerably high or low temperature liquid without using a pump that is impossible or impossible to improve heat resistance and cold resistance. An inexpensive and highly reliable liquid circulation device can be provided.

[Brief description of the drawings]

Drawings show an embodiment of the present invention, FIG. 1 is a diagram showing the entire circuit configuration in a liquid circulating device, FIGS. 2 and 3 are explanatory diagrams of a liquid circulating operation in a liquid circulating section A,
FIG. 4 is an explanatory diagram of a liquid recovery operation in the liquid circulation unit A,
5 and 6 are explanatory diagrams of a liquid circulating operation in the liquid circulating unit B, and FIG. 7 is an explanatory diagram of a liquid collecting operation in the liquid circulating unit B. L1… High temperature liquid L2… Low temperature liquid HMT, LMT… Main tank HST, LST… Sub tank 2… Heat exchanger 3… Compressed air source 41, 42… Main tank gas circuit, 51, 52… Sub tank gas circuit 61 , 62 ... Gas circuit for heat exchanger 71,72 ... Primary circuit 81,82 ... Secondary circuit 91,92 ... Tertiary circuit 101,102 ... Recovery circuit

Claims (5)

(57) [Claims] 1. A main tank for storing a liquid to be circulated and maintaining a predetermined temperature, a sub-tank arranged at a higher position than the main tank, a heat exchanger, a pressurizing gas source, and the pressurizing gas. Gas circuit means for the main tank for guiding pressurized gas from a source to the main tank; primary circuit means for guiding the liquid to be circulated from the main tank to the heat exchanger; and the sub-tank from the heat exchanger. Secondary circuit means for guiding the liquid to be circulated to the main tank, and tertiary circuit means for returning the liquid to be circulated from the sub-tank to the main tank. An operation of guiding the liquid to be circulated in the main tank to the heat exchanger by the primary circuit means by the gas pressure and guiding the liquid to be circulated from the heat exchanger to the sub tank by the secondary circuit means; When the circulating liquid accumulates Liquid circulation system, characterized in that the sub-tank liquid was caused to perform a repeated liquid circulation operation and to return to the main tank by the tertiary circuit means. 2. A sub-tank gas circuit for guiding pressurizing gas from the pressurizing gas source to the sub-tank so that the sub-tank liquid can be pressurized when returning the sub-tank liquid to the main tank. 2. The liquid circulation device according to claim 1, further comprising means. 3. A recovery circuit for guiding the liquid to be circulated in the heat exchanger to the main tank, and the pressurizing gas from the pressurizing gas source so as to pressurize the liquid in the heat exchanger. 3. A liquid circulating apparatus according to claim 1, further comprising a heat exchanger gas circuit for leading to the exchanger. 4. A first and a second main tank for storing a first and a second circulating liquid and maintaining the same at a predetermined temperature, and a first sub-tank disposed at a higher position than the first main tank. When,
A second sub-tank disposed higher than the second main tank, a heat exchanger, a pressurizing gas source, and pressurizing gas from the pressurizing gas source to the first and second main tanks. First and second main tank gas circuit means for directing, and first and second primary circuit means for directing the liquid to be circulated from the first and second main tanks to the heat exchanger; First and second secondary circuit means for guiding the liquid to be circulated from the heat exchanger to the first and second sub-tanks; and the first and second sub-tanks from the first and second sub-tanks. First and second tertiary circuit means for returning the circulated liquid to the main tank, gas circuit means for a heat exchanger for guiding a pressurizing gas from the gas source for pressurization to the heat exchanger, A first for guiding the liquid to be circulated in the exchanger to the first and second main tanks; A first and a second liquid circulating section having a second recovery circuit and a second recovery circuit. In each of the liquid circulating sections, a gas pressure guided to the main tank by the main tank gas circuit means causes the main tank to be covered. An operation of guiding the circulating liquid to the heat exchanger by the primary circuit means and guiding the circulating liquid from the heat exchanger to the sub-tank by the secondary circuit means, and when a predetermined amount of the circulating liquid is accumulated in the sub-tank, The operation of returning the liquid in the sub tank to the main tank by the tertiary circuit means is repeated so that the liquid is circulated, and the recovery of the circulated liquid in the heat exchanger to the main tank is performed by the heat exchanger. A liquid circulation device wherein the liquid in the heat exchanger is directed to the main tank via the recovery circuit means by gas pressure guided to the heat exchanger by gas circuit means. 5. A pressurizing gas is introduced from the pressurizing gas source to the sub-tank in each of the liquid circulating sections so that the liquid in the sub-tank can be pressurized when returning the liquid in the sub-tank to the main tank. 5. The liquid circulation apparatus according to claim 4, further comprising a sub-tank gas circuit means.