To achieve the complete combustion of gas, reduce the discharge temperature of flue gas, can only increase the effective area of ​​the heat transfer surface, one of the effective means is to achieve the high temperature zone of the gas flame to the central area of ​​the cooker.
From the principle analysis of gas stoves, most gas cookers use atmospheric combustion. An important feature of gas-fired atmospheric combustion is that the flame is divided into two parts: inner flame and outer flame: the inner flame is mainly gas and mixed air. The reaction produces an intermediate product process, the flame is visible to the naked eye, the flame temperature is low, and the heating ability is not strong; and the outer flame is the process in which these intermediate products are in contact with the surrounding secondary air to generate carbon dioxide and water, which is a gas reaction. The main exothermic process, the visible flame is not visible to the naked eye, the flame temperature is high, and the heating ability is very strong. In order to realize the movement of the high temperature zone of the gas flame to the central area of ​​the cooker, the key is to supplement the secondary air with higher oxygen content or higher secondary air temperature.
If you carefully analyze the characteristics of embedded stove gas combustion, you can find that it is possible to achieve the above goals. In the existing embedded gas stove, the flue gas emission after the combustion of the gas, and the secondary air required for the combustion of the gas are in the same space between the heating pot and the cooker panel, there is no clear boundary between the two, only the high temperature flue gas It is near the upper side of the bottom of the pot, and the secondary air is below the high-temperature flue gas, close to the side of the cooker panel, and the two directions of movement are opposite (see), so the high-temperature flue gas and the secondary air move in their respective movements. In the process, there must be a heat transfer and mass transfer process between the two, which has the exchange of heat and the exchange of gas components.
In this way, in the process of discharging high-temperature flue gas, part of the heat of the flue gas is transmitted to the secondary air, causing the temperature of the flue gas to decrease, thereby reducing the heating ability of the flue gas to the heated pan; at the same time, part of the smoke The gas is mixed into the secondary air, which causes the oxygen content of the secondary air to decrease, and the process is intensified along the secondary air replenishment route. The closer to the central area of ​​the cooker, the lower the oxygen content of the secondary air is. The low oxygen content of the secondary air causes the flame outer flame to lengthen, and the heating temperature region continuously moves to the opposite direction of the center of the cooker, which also reduces the heating ability of the flue gas to the heating pot. Of course, during the secondary air replenishment process, due to the heating effect of the flue gas and the mixing of some flue gas, the secondary air is continuously increased along the replenishing path, and then reacts with the gas. It is conducive to the full combustion of gas and improve the utilization of heat energy. However, the benefit of this effect on the thermal efficiency of the stove is far lower than the disadvantages caused by the two side effects mentioned above.
For the desktop stove, the secondary air is replenished from the bottom of the cooker. The above mentioned benefits and disadvantages will not occur. Therefore, the thermal efficiency of the desktop gas stove is higher than that of the embedded gas stove of the same configuration.
4 Analysis of the thermal efficiency improvement method of the gas cooker can design a secondary air replenishing passage and a high-temperature flue gas discharge passage to realize the high-temperature flue gas and the secondary air completely isolated during the working process of the gas stove so that there is no substance between the two Exchange, and at the same time minimize the heat exchange between the two, and the efficient use of high-temperature flue gas to the secondary air to achieve higher thermal efficiency of the gas stove, it becomes the key.
It can be seen from the previous analysis that under different conditions, the secondary air replenishment conditions are different, and the length of the gas stove flame is closely related to its thermal efficiency. The shorter the flame, the higher the thermal efficiency of the gas stove. We can imagine such a set of experiments, under the same experimental conditions, design three different secondary air replenishment methods (see): In the first way, the secondary air is directly replenished from below the fire hole; the second way, two The secondary air is replenished from above the fire hole and is in the same channel space as the exhaust gas. In the third way, the secondary air is replenished from above the fire hole, but is isolated from the exhaust passage, and the heat of combustion of the gas can be transferred through the metal wall. The secondary air is preheated, and the secondary air is replenished from the root of the flame to react with the gas flame to complete the complete combustion of the gas.
It is conceivable that in the second experimental mode, the flame is the longest because the gas flue gas interacts with the secondary air, and the secondary air supplemented by the third experimental method is not affected by the flue gas, and the secondary air passes through Preheating, increased diffusion capacity, and stronger ability to combine with gas flames, so the flame is the shortest.
In fact, the first experimental method, the secondary air replenishment method in the gas combustion process, is similar to the desktop gas stove; the second experimental method, the secondary air replenishment method in the gas combustion process, similar to the embedded gas stove; and the third The experimental method, the secondary air replenishment method in the gas combustion process, is the basic idea of ​​our high-efficiency cooker development, and it is possible to achieve higher thermal efficiency.
5 Energy-saving gas stove structure and test data In the actual product design, we adopted a heat collecting hood structure with a heat collecting cover as a secondary air passage. When the gas stove is working, the gas flame moves from the burner head to the outside in the direction of the heat collecting cover, and the secondary air is opened by the heat collecting cover, enters the heat collecting cover interlayer, and finally enters from the gap between the heat collecting cover and the burner head. Gas burning area.
Compared with the existing embedded gas stove, the embedded cooker with heat collecting cover has obvious advantages in heat utilization: the heat collecting cover completely separates the secondary air from the smoke generated by the combustion of the gas to ensure the secondary air. The composition is not interfered by the flue gas, and is directly transported to the root of the flame, effectively shortening the length of the flame, realizing the movement of the flame temperature to the center of the heating pot, and the effective heat exchange area is obviously improved; the heat collecting cover separates the flue gas from the secondary air. After the gas is burned, the high temperature flame is no longer affected by the secondary air cooling, and the flue gas temperature is higher, which is conducive to the convective heat exchange between the gas flame and the heating pot; during the working process of the gas stove, the high temperature flame radiates heat through the heat collecting cover The surface is reflected back to the bottom of the heating pot, which improves the utilization rate of heat energy, and also reduces the heat radiation of the flame to the surrounding environment, thereby improving the user's comfort; the secondary air is heated along the surface of the heat collecting cover during the movement of the secondary air. A part of the heat is absorbed by the secondary air, re-sent into the gas stove, converted into useful heat, and the heat energy utilization rate is improved; the double-layer heat collecting cover structure is also In order to reduce the radiant heat loss of the upper layer of the heat collecting cover to the surrounding environment, the heat radiation of the cooker to the surrounding environment is also reduced, and the user's comfort comparison test result is improved: Superman's model inner fire gas stove Under normal use conditions, the test thermal efficiency is 57%. After the heat collecting hood is increased, the measured thermal efficiency reaches 70% and the thermal efficiency increases by more than 20% under the condition of ensuring normal flue gas.
6 Conclusion Through the improvement of the secondary air passage, the thermal efficiency of the embedded gas stove can completely exceed the thermal efficiency of the same configuration of the bench furnace; compared with the existing embedded gas stove, the thermal efficiency can be increased by more than 20%.
This design has applied for a number of national patents.
(Finish)
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