阅读说明：本技术 一种燃料电池系统 (Fuel cell system ) 是由 刘志祥 于 2020-06-16 设计创作，主要内容包括：本发明提供了一种燃料电池系统,包括电堆、氢气氧化加热器、储氢罐、气水分离器、氢气循环泵、空气过滤器、空气压缩机、中冷器、空气加湿器、冷却液循环泵、节温器、散热器。本发明的燃料电池系统通过设置氢气氧化加热器,利用氢气和空气的氧化反应产生的热量来对冷却液进行加热,从而能够在较短的时间内实现燃料电池系统的冷启动；同时,利用空气中经过燃烧反应后剩余的氮气来填充阳极流道,从而在启动和停机过程中避免电堆中出现氢空界面,从而提高燃料电池电堆的寿命。(The invention provides a fuel cell system which comprises a galvanic pile, a hydrogen oxidation heater, a hydrogen storage tank, a gas-water separator, a hydrogen circulating pump, an air filter, an air compressor, an intercooler, an air humidifier, a coolant circulating pump, a thermostat and a radiator. The fuel cell system of the invention is provided with the hydrogen oxidation heater, and heats the cooling liquid by utilizing the heat generated by the oxidation reaction of the hydrogen and the air, thereby realizing the cold start of the fuel cell system in a short time; meanwhile, the anode flow channel is filled with residual nitrogen in the air after combustion reaction, so that a hydrogen-air interface in the galvanic pile is avoided in the starting and stopping processes, and the service life of the fuel cell galvanic pile is prolonged.)

1. A fuel cell system is characterized by comprising a galvanic pile, a hydrogen oxidation heater, a hydrogen storage tank, a gas-water separator, a hydrogen circulating pump, an air filter, an air compressor, an intercooler, an air humidifier, a coolant circulating pump, a thermostat and a radiator; the hydrogen oxidation heater is provided with a cooling liquid inlet, a cooling liquid outlet, a hydrogen inlet, a hydrogen outlet and an air inlet;

a cooling liquid outlet of the galvanic pile is connected with an inlet of the cooling liquid circulating pump, an outlet of the cooling liquid circulating pump is connected with an inlet of the radiator, a branch in a connecting pipeline between the outlet of the cooling liquid circulating pump and the inlet of the radiator is connected with a first inlet of the thermostat, an outlet of the radiator is connected with a second inlet of the thermostat, an outlet of the thermostat is connected with a cooling liquid inlet of the hydrogen oxidation heater, and a cooling liquid outlet of the hydrogen oxidation heater is connected with a cooling liquid inlet of the galvanic pile;

the hydrogen storage tank is connected to a hydrogen inlet of the hydrogen oxidation heater through a hydrogen switch valve, a hydrogen outlet of the hydrogen oxidation heater is connected with a hydrogen inlet of the galvanic pile, a hydrogen exhaust port of the galvanic pile is connected with an inlet of the gas-water separator, a water outlet of the gas-water separator is connected with a hydrogen tail exhaust valve, an exhaust port of the gas-water separator is connected with an inlet of the hydrogen circulating pump, and an outlet of the hydrogen circulating pump is connected to a connecting pipeline between a hydrogen outlet of the hydrogen oxidation heater and the hydrogen inlet of the galvanic pile;

the export of air cleaner with air compressor's entry links to each other, air compressor's export with the entry of intercooler links to each other, the export of intercooler with the dry air entry of air humidifier links to each other, the intercooler with there is a branch road to open through the air in the connecting line of air humidifier and stops the control valve and be connected to the air inlet of hydrogen oxidation heater, the dry air export of air humidifier with the air inlet of pile links to each other, the air gas vent of pile with the humid air entry of air humidifier links to each other, the humid air export of air humidifier links to each other with the tail calandria, the air gas vent of pile with the pipeline that the humid air entry of air humidifier links to each other has a branch road to pass through the air tail calandria valve with the tail calandria links to each other.

2. The fuel cell system according to claim 1, wherein a hydrogen flow control valve is further connected between the hydrogen on-off valve and the hydrogen oxidizing heater.

3. The fuel cell system of claim 1, wherein the hydrogen oxidizing heater is of a jacketed tube construction, the hydrogen oxidizing heater comprising a coolant outer jacket tube and a hydrogen oxidizing burner tube, the hydrogen oxidizing burner tube being jacketed inside the coolant outer jacket tube.

4. The fuel cell system of claim 1, wherein the air inlet of the hydrogen oxidizing heater is provided with an air inlet valve at one end.

5. The fuel cell system of claim 1, wherein an igniter is disposed within the hydrogen oxidizing heater, the igniter configured to: and starting ignition when the hydrogen oxidation heater is filled with hydrogen and air.

6. The fuel cell system according to claim 3, wherein the hydrogen oxidizing combustor tube is filled with a hydrogen catalytic oxidizing material.

Technical Field

The invention relates to the technical field of fuel cells, in particular to a fuel cell system.

Background

In recent years, fuel cells have been widely regarded as an efficient and clean power generation technology for use in power systems of vehicles and ships. When the proton exchange membrane fuel cell system serving as vehicle power is applied in northern winter environment, the problem of low-temperature starting must be solved, otherwise, water generated by power generation of the fuel cell can be condensed into water in a galvanic pile to block a gas flow passage, so that starting failure is caused.

At present, the low-temperature start of a fuel cell system mainly has two technical paths, one is to add a cold start heater in a cooling liquid circulating system, during cold start, the cold start heater is powered by an external storage battery, a cooling liquid circulating pump is started at the same time, cooling liquid is raised by the heater, the temperature of a cell stack is raised to a certain degree by the cooling liquid, water generated by the cell stack is ensured not to be frozen into ice again, and then hydrogen and air are introduced to smoothly start the fuel cell system. This method is widely used in practical systems, but has the disadvantage of limited electrical heating power, usually only a few kilowatts, resulting in long start-up heating times, usually requiring more than ten minutes, and longer start-up times in cold regions. The heating time of the cooling liquid can be shortened by increasing the power of the starting heater, but if the heating time of the starting heater is shortened to less than one minute, the power of the starting electric heater needs to be increased to tens of kilowatts, which is a great challenge to the design of the heater, and the weight and the volume of the system are increased, so that the energy density of the fuel cell system is reduced.

Another low-temperature starting technique for fuel cells is to make the fuel cell stack work at a lower voltage during the starting process, and most of the energy of hydrogen is converted into heat energy, so that the temperature of the stack can be raised to the working temperature in a shorter time. The low-temperature starting technology is simple in system architecture, other components are not needed to be added, the control process is very complex, the voltage of the cell stack is directly loaded to a very low value at low temperature, partial single cells in the cell stack are easily subjected to reverse polarization, local reverse polarization in the single cells is also easily caused, and therefore the method for directly loading the low-temperature starting can possibly have certain influence on the service life of the cell stack.

For the commercial vehicle, cold starting can be carried out in an electric heating mode, and the starting time is a little longer without causing much trouble to users. However, for a passenger vehicle, a user often has insufficient patience to wait for ten minutes to start the vehicle, and the market reaction of the fuel cell vehicle is directly influenced by too long starting time. The fuel cell passenger vehicle needs to finish cold start within 20-30 seconds, which is a great test for the fuel cell cold start technology.

In addition, after the fuel cell system is shut down for a long time, air is filled in the cathode flow field and the anode flow field in the fuel cell stack, when the fuel cell system is started, hydrogen is introduced into the anode, and in the process that the hydrogen blows out the air out of the fuel cell stack, the anode forms a hydrogen-oxygen interface, which can cause high potential on the cathode side to cause corrosion of a catalyst carbon carrier, thereby shortening the service life of the fuel cell stack. When the fuel cell system is subjected to bench test in a laboratory, a hydrogen-air interface is usually avoided by introducing nitrogen into the anode for purging, but in the fuel cell system in practical application, the nitrogen system cannot be added. In the fuel cell system, the corrosion caused by a hydrogen-air interface can be avoided by sealing the cathode inlet and outlet of the stack, consuming oxygen in cathode air and only remaining nitrogen in a cathode flow channel, but the difficulty of cathode control is increased.

In summary, the defect problems of the existing cold start technology of the fuel cell are not effectively solved.

Disclosure of Invention

Embodiments of the present invention are directed to a fuel cell system, so as to solve the above technical problems, thereby achieving a cold start of the system in a short time and improving the life of a fuel cell stack.

In order to solve the technical problem, an embodiment of the present invention provides a fuel cell system, including a stack, a hydrogen oxidation heater, a hydrogen storage tank, a gas-water separator, a hydrogen circulation pump, an air filter, an air compressor, an intercooler, an air humidifier, a coolant circulation pump, a thermostat, and a radiator; the hydrogen oxidation heater is provided with a cooling liquid inlet, a cooling liquid outlet, a hydrogen inlet, a hydrogen outlet and an air inlet;

a cooling liquid outlet of the galvanic pile is connected with an inlet of the cooling liquid circulating pump, an outlet of the cooling liquid circulating pump is connected with an inlet of the radiator, a branch in a connecting pipeline between the outlet of the cooling liquid circulating pump and the inlet of the radiator is connected with a first inlet of the thermostat, an outlet of the radiator is connected with a second inlet of the thermostat, an outlet of the thermostat is connected with a cooling liquid inlet of the hydrogen oxidation heater, and a cooling liquid outlet of the hydrogen oxidation heater is connected with a cooling liquid inlet of the galvanic pile;

the hydrogen storage tank is connected to a hydrogen inlet of the hydrogen oxidation heater through a hydrogen switch valve, a hydrogen outlet of the hydrogen oxidation heater is connected with a hydrogen inlet of the galvanic pile, a hydrogen exhaust port of the galvanic pile is connected with an inlet of the gas-water separator, a water outlet of the gas-water separator is connected with a hydrogen tail exhaust valve, an exhaust port of the gas-water separator is connected with an inlet of the hydrogen circulating pump, and an outlet of the hydrogen circulating pump is connected to a connecting pipeline between a hydrogen outlet of the hydrogen oxidation heater and the hydrogen inlet of the galvanic pile;

the export of air cleaner with air compressor's entry links to each other, air compressor's export with the entry of intercooler links to each other, the export of intercooler with the dry air entry of air humidifier links to each other, the intercooler with there is a branch road to open through the air in the connecting line of air humidifier and stops the control valve and be connected to the air inlet of hydrogen oxidation heater, the dry air export of air humidifier with the air inlet of pile links to each other, the air gas vent of pile with the humid air entry of air humidifier links to each other, the humid air export of air humidifier links to each other with the tail calandria, the air gas vent of pile with the pipeline that the humid air entry of air humidifier links to each other has a branch road to pass through the air tail calandria valve with the tail calandria links to each other.

Preferably, a hydrogen flow control valve is further connected between the hydrogen switch valve and the hydrogen oxidation heater.

Preferably, the hydrogen oxidation heater is of a jacket structure, the hydrogen oxidation heater comprises a cooling liquid outer jacket pipe and a hydrogen oxidation combustion pipe, and the hydrogen oxidation combustion pipe is sleeved inside the cooling liquid outer jacket pipe in a sleeved mode.

Preferably, an air inlet valve is arranged at one end of an air inlet of the hydrogen oxidation heater.

Preferably, an igniter is provided in the hydrogen oxidizing heater, and the igniter is configured to: and starting ignition when the hydrogen oxidation heater is filled with hydrogen and air.

Preferably, the hydrogen oxidation combustion tube is filled with a hydrogen catalytic oxidation material.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a fuel cell system which comprises a galvanic pile, a hydrogen oxidation heater, a hydrogen storage tank, a gas-water separator, a hydrogen circulating pump, an air filter, an air compressor, an intercooler, an air humidifier, a coolant circulating pump, a thermostat and a radiator. The fuel cell system of the invention is provided with the hydrogen oxidation heater, and heats the cooling liquid by utilizing the heat generated by the oxidation reaction of the hydrogen and the air, thereby realizing the cold start of the fuel cell system in a short time; meanwhile, the anode flow channel is filled with residual nitrogen in the air after combustion reaction, so that a hydrogen-air interface in the galvanic pile is avoided in the starting and stopping processes, and the service life of the fuel cell galvanic pile is prolonged.

Drawings

Fig. 1 is a schematic structural diagram of a fuel cell system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a hydrogen oxidation heater according to an embodiment of the present invention;

wherein the drawings are described as follows:

11-a hydrogen storage tank, 12-a hydrogen switch valve, 13-a hydrogen flow control valve, 14-a hydrogen circulating pump, 15-a gas-water separator and 16-a hydrogen tail discharge valve;

21-an air filter, 22-an air compressor, 23-an intercooler, 24-an air start-stop control valve and 25-an air humidifier; 26-air exhaust valve;

31-a cooling liquid circulating pump, 32-a radiator and 33-a thermostat;

50-a hydrogen oxidation heater;

100-electric pile.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1 to 2, an embodiment of the present invention provides a fuel cell system, which includes a stack 100, a hydrogen oxidation heater 50, a hydrogen storage tank 11, a gas-water separator 15, a hydrogen circulation pump 14, an air filter 21, an air compressor 22, an intercooler 23, an air humidifier 25, a coolant circulation pump 31, a thermostat 33, and a radiator 32; the hydrogen oxidation heater is provided with a cooling liquid inlet, a cooling liquid outlet, a hydrogen inlet, a hydrogen outlet and an air inlet;

a coolant outlet of the galvanic pile 100 is connected with an inlet of the coolant circulating pump 31, an outlet of the coolant circulating pump 31 is connected with an inlet of the radiator 32, a branch in a connecting pipeline between an outlet of the coolant circulating pump 31 and an inlet of the radiator 32 is connected with a first inlet of the thermostat 33, an outlet of the radiator 32 is connected with a second inlet of the thermostat 33, an outlet of the thermostat 33 is connected with a coolant inlet of the hydrogen oxidation heater 50, and a coolant outlet of the hydrogen oxidation heater 50 is connected with a coolant inlet of the galvanic pile 100;

the hydrogen storage tank 11 is connected to a hydrogen inlet of the hydrogen oxidation heater 50 through a hydrogen switch valve 12, a hydrogen outlet of the hydrogen oxidation heater 50 is connected with a hydrogen inlet of the galvanic pile 100, a hydrogen exhaust port of the galvanic pile 100 is connected with an inlet of the gas-water separator 15, a water outlet of the gas-water separator 15 is connected with a hydrogen tail discharge valve 16, an exhaust port of the gas-water separator 15 is connected with an inlet of the hydrogen circulating pump 14, and an outlet of the hydrogen circulating pump 14 is connected to a connecting pipeline between the hydrogen outlet of the hydrogen oxidation heater 50 and the hydrogen inlet of the galvanic pile 100;

an outlet of the air filter 21 is connected to an inlet of the air compressor 22, an outlet of the air compressor 22 is connected to an inlet of the intercooler 23, the outlet of the intercooler 23 is connected with the dry air inlet of the air humidifier 25, a branch of the connecting pipeline between the intercooler 23 and the air humidifier 25 is connected to the air inlet of the hydrogen oxidation heater 50 through an air start-stop control valve 24, the dry air outlet of the air humidifier 25 is connected to the air inlet of the stack 100, the air outlet of the stack 100 is connected to the wet air inlet of the air humidifier 25, the wet air outlet of the air humidifier 25 is connected with a tail pipe, and a branch of a pipeline connecting the air outlet of the galvanic pile 100 and the wet air inlet of the air humidifier 25 is connected with the tail pipe through an air tail valve 26.

Preferably, a hydrogen flow control valve 13 is further connected between the hydrogen on-off valve 12 and the hydrogen oxidation heater 50.

In the embodiment of the invention, a hydrogen oxidation heater 50 is arranged in a cooling liquid loop of the fuel cell system, and heat is provided for cooling liquid flowing through the hydrogen oxidation heater 50 through hydrogen oxidation reaction, so that the low-temperature starting function of the fuel cell system is realized; wherein, a path of hydrogen in the hydrogen supply system is connected with the hydrogen oxidation heater 50 to provide hydrogen fuel for the hydrogen oxidation heater; one path of air in the air supply system is connected with the hydrogen oxidation heater 50 to provide an oxidant for the hydrogen oxidation heater; the exhaust port of the hydrogen oxidation heater 50 is connected to the hydrogen inlet of the fuel cell stack 100, and the exhaust gas after the hydrogen and air oxidation reaction is supplied to the fuel cell stack 100 through the hydrogen inlet.

It should be noted that the basic difference between the present system and the conventional fuel cell system is that the hydrogen oxidation heater 50 is used to heat the coolant loop to achieve the low temperature start-up function. The hydrogen oxidation heater 50 is connected in series in a main heat dissipation loop of the fuel cell system, when the fuel cell system is started at a low temperature, the cooling liquid circulating pump 31 is started, the cooling liquid flows in the small circulating loop, flows out of the galvanic pile 100, passes through the cooling liquid circulating pump 31, flows through the thermostat 33, enters the hydrogen oxidation heater 50, is heated by the hydrogen oxidation heater 50, then rises in temperature, and flows back to the galvanic pile 100, so that the temperature of the galvanic pile 100 rises gradually.

When the fuel cell system is started at a low temperature, the coolant circulation pump 31 is started to circulate the coolant through the fuel cell stack 100; starting the air compressor 22, opening the air start-stop control valve 24 and providing air for the hydrogen oxidation heater 50; at the same time, the hydrogen switching valve 12 and the hydrogen flow rate control valve 13 are opened to supply hydrogen to the hydrogen oxidizing heater 50; hydrogen and air undergo a hydrogen oxidation reaction in the hydrogen oxidation heater 50, the generated heat is the cooling liquid flowing through the hydrogen oxidation heater 50 to heat, and the temperature of the fuel cell stack 100 is heated to above zero by the cooling liquid with increased temperature flowing through the fuel cell stack 100; the hydrogen and the oxygen in the air react in the hydrogen oxidation heater 50 to generate water, nitrogen is left in tail gas, and the nitrogen enters the anode flow channel of the galvanic pile 100 through a pipeline connected with the anode of the galvanic pile 100 by the hydrogen oxidation heater 50, so that the purging of the anode flow channel is realized, and the formation of a hydrogen-air interface at the anode of the galvanic pile 100 in the starting process is avoided; when the cooling liquid is heated to a certain degree, the air start-stop control valve 24 for supplying air to the hydrogen oxidation heater 50 is closed, hydrogen flows through the hydrogen oxidation heater 50 and enters the electric pile 100, nitrogen is gradually blown out of the electric pile 100, and air enters the electric pile 100 through a cathode pipeline, so that the electric pile 100 establishes voltage, and low-temperature start and anode protective purging of the fuel cell system are realized.

The hydrogen oxidation heater 50 is directly connected in series to the hydrogen supply loop, when the hydrogen oxidation heater is started, the hydrogen switch valve 12 is controlled to be opened, hydrogen flows out from the hydrogen storage tank 11, enters the hydrogen oxidation heater 50 through the hydrogen switch valve 12 and the hydrogen flow control valve 13 in sequence, the hydrogen flow entering the hydrogen oxidation heater 50 is controlled through the hydrogen flow control valve 13, the hydrogen and air in the hydrogen oxidation heater 50 are subjected to oxidation reaction, and heat is released to heat the cooling liquid.

In the air loop, after the air compressor 22 is started, air passes through the air filter 21 and flows through the air compressor 22, the temperature is raised, the air passes through the intercooler 23 and is divided into two paths, one path enters the air humidifier 25 and then enters the fuel cell stack 100, the other path enters the hydrogen oxidation heater 50 after passing through the air start-stop control valve 24 and then undergoes a combustion reaction with hydrogen, oxygen in the air after the combustion reaction is consumed, the remaining nitrogen enters the fuel cell stack 100, the hydrogen circulating pump 14 and the hydrogen tail discharge valve 16 are started, all air in an anode flow channel inside the fuel cell stack 100 is blown out of the fuel cell stack 100, and the inside of an anode is filled with nitrogen.

When the temperature of the fuel cell stack 100 rises to a certain degree, the air start-stop control valve 24 is closed, hydrogen flows through the hydrogen oxidation heater 50 and enters the fuel cell stack 100, nitrogen in an anode flow field is blown out of the stack 100, the voltage of the stack 100 rises, and the starting process is completed. In the whole starting process, the hydrogen and the air flow entering the hydrogen oxidation heater 50 are controlled, so that the rapid heating of the temperature of the cooling liquid can be realized, meanwhile, a hydrogen-air interface in the anode is avoided, the corrosion of a catalyst carbon carrier is avoided, and the shortening of the service life of the fuel cell stack 100 is avoided.

When the fuel cell system is shut down, the air valve leading to the hydrogen oxidation heater 50 is gradually opened, so that oxygen in the air reacts with hydrogen in the hydrogen oxidation heater 50 to generate water, the residual nitrogen enters the anode flow channel of the fuel cell stack 100, the hydrogen in the stack 100 and the pipeline is swept out of the fuel cell system and is completely filled with the nitrogen, and the valve is closed, so that the anode protection in the shutdown process is realized.

In the shutdown process, the air start-stop control valve 24 is opened, air is introduced into the hydrogen oxidation heater 50, hydrogen in the anode flow field is consumed, and meanwhile, the anode flow field is purged by residual nitrogen in the air, so that the voltage of the electric pile 100 can be rapidly reduced. When the purging is completed, the hydrogen switch valve 12 and the hydrogen tail valve 16 are closed, so that the anode flow field of the electric pile 100 is only filled with nitrogen, the safe shutdown of the electric pile 100 can be realized, and a hydrogen-air interface is avoided.

Preferably, the hydrogen oxidation heater 50 is a jacket tube structure, the hydrogen oxidation heater 50 includes a cooling liquid outer jacket tube and a hydrogen oxidation combustion tube, and the hydrogen oxidation combustion tube is sleeved inside the cooling liquid outer jacket tube.

Preferably, an air inlet valve is disposed at one end of the air inlet of the hydrogen oxidation heater 50.

Preferably, an igniter is provided in the hydrogen oxidizing heater 50, and the igniter is configured to: ignition is initiated when the hydrogen oxidizing heater 50 is purged with hydrogen and air.

Preferably, the hydrogen oxidation combustion tube is filled with a hydrogen catalytic oxidation material.

In the embodiment of the present invention, the hydrogen oxidation heater 50 is installed in the coolant circulation main loop, the gas loop is connected in series to the hydrogen supply main loop, and a path of air is divided from the air loop after passing through the intercooler 23 and enters the hydrogen oxidation heater 50. The hydrogen oxidation heater 50 is of a jacket pipe structure, the hydrogen oxidation combustion pipe is located inside, and the cooling liquid flows through the outer sleeve, so that when the hydrogen is oxidized and combusted in the pipe, heat can be fully transferred to the cooling liquid flowing through the outer sleeve. The hydrogen oxidizing heater 50 is integrated with an air start-stop control valve 24, and the air start-stop control valve 24 is opened only when the burner is operated. An igniter is integrated in the hydrogen oxidation heater 50, and when hydrogen and air are introduced at low-temperature start, the igniter is started, so that the hydrogen oxidation heater 50 can be started to work smoothly. The hydrogen oxidizing heater 50 is filled with a hydrogen catalytic oxidizing material inside the tube to sufficiently oxidize and burn hydrogen in the oxidizing burner and to rapidly conduct heat generated by the combustion to the coolant.

Referring to fig. 2, it should be noted that the hydrogen oxidizing heater 50 in the embodiment of the present invention is a key component for realizing the function of the fuel cell system of the present invention. The hydrogen oxidizing heater 50 is a jacket structure, and has a hydrogen oxidizing combustion tube inside, which is a place where the combustion reaction of hydrogen and air occurs, and a coolant flows through the jacket. The heat generated in the hydrogen oxidation combustion pipe is transferred to the cooling liquid through the pipeline, and the effect of heating the cooling liquid is achieved. An air inlet valve is integrated into the hydrogen oxidation heater 50 to control whether air enters the reactor to participate in the oxidation reaction. The hydrogen enters the hydrogen oxidation combustion pipe through a pipeline, and an igniter is further arranged in the hydrogen oxidation combustion pipe so as to realize the ignition of the hydrogen at low temperature and generate oxidation reaction. The inside hydrogen oxidation catalyst that has filled of hydrogen oxidation combustion tube can make the hydrogen that gets into the hydrogen oxidation combustion tube fully oxidized, and simultaneously, the heat that the oxidation produced can effectively be given the reaction tube wall, realizes the heating function of coolant liquid.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.