US20150114598A1

US20150114598A1 - Device of Downward Heat-Transfer Using Reverse Thermosiphon Loop

Info

Publication number: US20150114598A1
Application number: US14/332,629
Authority: US
Inventors: Heng-Yi Li; Tsair-Fuh Huang; Meng-Chang Tsai
Original assignee: Institute of Nuclear Energy Research
Current assignee: Institute of Nuclear Energy Research
Priority date: 2013-10-25
Filing date: 2014-07-16
Publication date: 2015-04-30
Also published as: TW201516369A; TWI548854B

Abstract

A device of heat transfer is provided. A heating pipe is connected with an external heat source. A communicating pipe set is contacted with a heat sink. A heat-transfer fluid spontaneously circulates inside reverse thermosiphon loop and transfers heat downwardly. A heat source is located at a higher level and the heat sink is located at a lower level. Heat transfer distance is long and no additional power is required. The heat transferred can be used for heating other fluid or solid. Besides, the heat can be used for transforming thermal energy into electric energy in conjunction with a Stirling engine, an organic Rankine engine or a thermoelectric module.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device of heat transfer; more particularly, relates to transferring heat downwardly by heat-transfer fluid spontaneous circulation inside reverse thermosiphon loop, where the present invention has a heat source at a higher level and a heat sink at a lower level; heat transfer distance is long and no additional power is required; and the transferred heat can be used for heating other fluid or solid or for transforming thermal energy into electric energy in conjunction with a Stirling engine, an organic Rankine engine or a thermoelectric module.

DESCRIPTION OF THE RELATED ARTS

With the great consumption of fossil fuels like oil, coal and natural gas, not only fuel prices get higher and economic development is impacted, but also the emission of greenhouse gases like carbon dioxide enhances green house effect and results in climate change. Therefore, clean energy development and environmental protection have received increasing attentions. Therein, developments of solar thermal energy and waste heat utilization technologies have become important issues in the world.
However, low temperature-difference heat transfer over long distance is a problem that these technological developments have to be encountered. Generally, long-distance heat transfer is adopted by circulating heat-transfer fluid between heat source and heat sink spontaneously or forcefully. Therein, the spontaneous circulating heat transfer has higher efficiency and lower cost. The principle of the spontaneous circulation is that, after the fluid inside the closed loop absorbs heat from heat source at low level, the heated fluid rises naturally by buoyancy and, after the heat is transferred to heat sink at high level, the cooled fluid falls by gravity. Such a heat transfer device, also known as thermosiphon or gravity return heat pipe, can only transfer heat upward. Furthermore, some heat pipes with wick structures can transfer heat horizontally, downwardly or in a non-gravity condition, whose fluid circulation is driven by capillary force. However, the heat-transfer distance of these heat pipes are limited by their capillary force, because the required driving force for fluid circulation is greater when the heat pipe length is longer. Moreover, the wicked devices capable of transferring heat more than 0.5 meters are manufactured with difficulty and high cost.
For solar thermal energy usage, the solar water-heating systems are the most common applications. Between solar collectors and hot water storage tank, there are two kinds of heat transfer loop: electric-pump-driven loop of forced circulation and thermosiphon loop of spontaneous circulation. The electric-pump-driven heat transfer loop requires additional power consumption, which thus reduces efficiency. On the other hand, conventional thermosiphon heat transfer loop can transfer heat without external power. However, it can only transfer heat upwardly, so that the position of the hot water storage tank must be higher than the solar collector. This results in the sheltering of the solar irradiation on the solar collector by the hot water storage tank, so that the heating time during the day is reduced.
In addition, energy-consuming equipments such as boilers and furnaces have a lot of exhaust gas waste heat, so that their efficiencies are less than 85%. Their exhaust gas exist ports are located above the furnaces. Therefore, induced draft fans and electric-pump-driven hot water circulation loops are required for waste heat recovery, which results in low recovery efficiency and high cost.
Some special thermosiphon solar collectors can transfer heat horizontally, but still cannot transfer heat downwardly.
Although the U.S. Pat. No. 3,951,204, “Method and apparatus for thermally circulating a liquid”, provides a device to transfer heat downwardly, owing that there exists the considerable amount of heat exchange between the downward and upward branch to lift the flow from cooler, so the heat transfer effectiveness is reducing and heat transfer distance is limited.
Hence, the prior arts do not fulfill all users' requests on actual use.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to transfer heat downwardly by heat-transfer fluid spontaneous circulation inside reverse thermosiphon loop comprising a heating pipe and a communicating pipe set respectively connected with an external heat source and a heat sink, where a heat source is located at a higher level and a heat sink is located at a lower level; heat transfer distance is long and no additional power is required; and the transferred heat can be used for heating other fluid or solid or for transforming thermal energy into electric energy in conjunction with a Stirling engine, an organic Rankine engine or a thermoelectric module.
To achieve the above purpose, the present invention is a device of downward heat-transfer using reverse thermosiphon loop, comprising a buffer tank, a heating pipe, a heat exchange pipe, a communicating pipe set and a heat-transfer fluid, where the heating pipe is communicated with the buffer tank and the heat exchange pipe; the heat exchange pipe is set inside the buffer tank and connected with the heating pipe and an inlet pipe; the communicating pipe set is communicated with the buffer tank and the heat exchange pipe; and the heat-transfer fluid is filled in the buffer tank, the heating pipe, the heat exchange pipe and the communicating pipe set. Accordingly, a novel device of downward heat-transfer using reverse thermosiphon loop is obtained.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present invention will be better understood from the following detailed descriptions of the preferred embodiments according to the present invention, taken in conjunction with the accompanying drawings, in which

FIG. 1 is the cross-sectional view showing the first preferred embodiment according to the present invention;

FIG. 2 is the cross-sectional view showing the second preferred embodiment; and

FIG. 3 is the view showing the assembled third preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following descriptions of the preferred embodiments are provided to understand the features and the structures of the present invention.
Please refer to FIG. 1, which is a cross-sectional view showing a first preferred embodiment according to the present invention. As shown in the figure, the present invention is a device of downward heat-transfer using reverse thermosiphon loop, comprising a buffer tank 1, a heating pipe 2, a heat exchange pipe 3, a communicating pipe set 4 and heat-transfer fluid 5.
The whole loop of the device is filled with the heat-transfer fluid 5 at first. The upper side in the interior of the buffer tank 1 has a space region 11 formed by accumulated vapor. The buffer tank 1 is located at the top position, which is used to absorb volume expansion change and uncondensed vapor. Under room temperature or operation temperature, the space region 11 is at saturated vapor pressure of the heat-transfer fluid 5.
The heating pipe 2 is communicated with the buffer tank 1 and the heat exchange pipe 3. The heat pipe 2 is heated with an external heat source 7 to provide thermal energy required for vaporizing the heat-transfer fluid 5. Therein, the external heat source 7 is solar heat, or waste heat, or a fuel combustion heat; the solar heat is from solar irradiation; the waste heat is from a boiler or a furnace; and the fuel combustion heat is obtained by burning fossil or biomass fuels.
The heat exchange pipe 3 is set inside the buffer tank 1 and is communicated with an inlet pipe 43 and a heating pipe 2.
The communicating pipe set 4 is communicated with the buffer tank 1 and the heat exchange pipe 3. The communicating pipe set 4 comprises an outlet pipe 41, a cooling pipe 42 and the inlet pipe 43, where the outlet pipe 41 is communicated with the buffer tank 1 and the cooling pipe 42; the cooling pipe 42 is contacted with a heat sink 8, and communicated with the outlet pipe 41 and the inlet pipe 43; and the inlet pipe 43 is communicated with the cooling pipe 42 and the heat exchange pipe 3. The cooling pipe 42 is used for absorbing the heat of the heat-transfer fluid 5. Therein, the heat sink 8 is a heat exchanger, a heat storage device, a thermoelectric power generator or a cooling fin set.
The heat-transfer fluid 5 is filled in the buffer tank 1, the heating pipe 2, the heat exchange pipe 3 and the communicating pipe set 4, where the heat-transfer fluid 5 is two-phase fluid, like water, carbon dioxide, ammonia, refrigerant, alkane, alcohol, benzene or liquid metal; or mixture thereof.
On using the present invention, the buffer tank 1, the heating pipe 2, the heat exchange pipe 3 and the communicating pipe set 4 are formed into a closed loop. When the heat-transfer fluid 5 in the heating pipe 2 is heated by the external heat source 7, density of the heat-transfer fluid 5 is reduced with bubbles generated simultaneously. Then, the bubbles are floated up and accumulated in the space region 11 at the upper side in the interior of the buffer tank 1. The pressure is thus gradually increasing. When the pressure is high enough to overcome the buoyancy and pipe friction resistance, the heat-transfer fluid 5 will be pushed out from the buffer tank 1 to reach the cooling pipe 42 through the outlet pipe 41 and release majority of heat by the heat sink 8. Then, the heat-transfer fluid 5 flows back through the inlet pipe 43 to the heat exchange pipe 3 inside the buffer tank 1 to absorb the heat of the heat-transfer fluid 5 in the buffer tank 1. At last, the heat-transfer fluid 5 flows back to the heating pipe 2.
Therein, the heat exchange pipe 3 has two functions: Firstly, partial heat of the heat-transfer fluid 5 in the buffer tank 1 is carried away by the heat-transfer fluid 5 flows back into the heat exchange pipe 3. Thus, the gas-phase heat-transfer fluid 5 is condensed to form a low pressure. At the moment, pressure difference formed between the space region 11 and the heat exchange pipe 3, and the increasing density of the cooling heat-transfer fluid 5 both help to push the heat-transfer fluid 5 to flow down out from the buffer tank 1. Secondly, the heat-transfer fluid 5 flowed back to the heating pipe 2 is preheated.
Besides, each outer surface of the outlet pipe 41 and the inlet pipe 43 and the buffer tank 1 have thermal-insulating 6 for preventing heat loss, respectively. Thus, the heat-transfer fluid 5 spontaneously circulates and transfers the heat of the external heat source 7 at higher level down to the heat sink 8 at lower level. The heat transfer distance is long and no additional power is required. The transferred heat can be used for heating other fluid or solid or for transforming thermal energy into electric energy in conjunction with a Stirling engine, an organic Rankine engine or a thermoelectric module.
Please refer to FIG. 2, which is a cross-sectional view showing a second preferred embodiment. As shown in the figure, a communicating pipe set 4 comprises an outlet pipe 44 communicated with the buffer tank 1 and cooling end 46; an inlet pipe 45 set inside the outlet pipe 44 and communicated with the heat exchange pipe 3 and cooling end 46; and a cooling end 46 communicated with the outlet pipe 44 and the inlet pipe 45. The outlet pipe 44 and the inlet pipe 45 are combined together into a concentric pipe for not only transferring heat as usual but also reducing volume size of the device. Thus, the heat-exchanging area between the outlet flow and inlet flow of the heat-transfer fluid 5 is increased; and, the surface area of heat-dissipation is reduced.
Please refer to FIG. 3, which is a cross-sectional view showing a third preferred embodiment. As shown in the figure, when an external heat source needs to transfer a lot of heat downward, a plurality of buffer tanks 1 are assembled together to transfer heat with a plurality of heating pipes 2, a plurality of heat exchange pipes (not shown), a plurality of communicating pipe sets 4 and a plurality of heat-transfer fluids (not shown).
In conclusion, the present invention is a downward heat-transfer device using reverse thermosiphon loop, where, in conjunction with a heating pipe and a cooling pipe contacted with an external heat source and a heat sink respectively, heat-transfer fluid spontaneously circulates inside reverse thermosiphon loop and transfers heat downwardly; the present invention has the heat source at a higher level and the heat sink at a lower level; the heat transfer distance is long and no additional power is required; and the transferred heat can be used for heating other fluid or solid or for transforming thermal energy into electric energy in conjunction with a Stirling engine, an organic Rankine engine or a thermoelectric module.
The preferred embodiments herein disclosed are not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.

Claims

What is claimed is:

1. A device of downward heat-transfer using reverse thermosiphon loop, comprising a buffer tank;

a heating pipe, said heating pipe being connected with said buffer tank and a heat exchange pipe;

a heat exchange pipe, said heat exchange pipe being located inside said buffer tank, said heat exchange pipe being communicated with said heating pipe and an inlet pipe;

a communicating pipe set, said communicating pipe set being communicated with said buffer tank and said heat exchange pipe; and

a heat-transfer fluid, said heat-transfer fluid being filled inside said buffer tank, said heating pipe, said heat exchange pipe and said communicating pipe set.

2. The device according to claim 1,

wherein, after filling the whole loop of the device with said heat-transfer fluid, a said space region is formed at the upper side in the interior of said buffer tank by accumulated vapor; said buffer tank is used to absorb volume expansion change and uncondensed vapor; and, under room temperature or operation temperature, said space region is at the saturated vapor pressure of said heat-transfer fluid.

3. The device according to claim 1,

wherein said heating pipe is contacted with an external heat source to provide heat needed to said heat-transfer fluid.

4. The device according to claim 3,

wherein said external heat source is selected from solar heat, or waste heat, or a fuel combustion heat; said solar heat is from solar irradiation; said waste heat is from a boiler or a furnace; and the fuel combustion heat is obtained by burning fossil or biomass fuels.

5. The device according to claim 1,

wherein said communicating pipe set is connected with a heat sink to absorb heat of said heat-transfer fluid.

6. The device according to claim 5,

wherein said heat sink is selected from a group consisting of a heat exchanger, a heat storage device, a thermoelectric power module, a Stirling engine, an organic Rankine engine and a cooling fin set.

7. The device according to claim 5,

wherein said communicating pipe set comprises

an outlet pipe, said outlet pipe being communicated with said buffer tank and said cooling pipe;

a cooling pipe, said cooling pipe being communicated with said outlet pipe and said inlet pipe, said cooling pipe being contacted with said heat sink; and

an inlet pipe, said inlet pipe being communicated with said cooling pipe and said heat exchange pipe.

8. The device according to claim 5,

wherein said communicating pipe set comprises

an inlet pipe, said inlet pipe being communicated with said cooling pipe and said heat exchange pipe; and

a cooling pipe, said cooling pipe being communicated with said outlet pipe and said inlet pipe.

9. The device according to claim 1,

wherein said heat-transfer fluid is selected from a group consisting of pure fluid and mixture thereof; and

wherein said pure fluid is two-phase flow and is selected from a group consisting of water, carbon dioxide, ammonia, refrigerant, alkane, alcohol, benzene and liquid metal.

10. The device according to claim 1,

wherein a thermal-insulating layer is obtained on outer surface of each of said buffer tank, said outlet pipe and said inlet pipe, separately.