Overview There are many problems in commercial gas cooker products that need to be solved and improved urgently. These problems include: high failure rate of products in use and low thermal efficiency. Commercial gas cooker products have great potential for energy saving and emission reduction. According to estimates, if the catering industry switches to energy-saving gas cookers, only Beijing can save 5000x104m3 of natural gas per year, which is equivalent to one month of natural gas consumption in the city's commercial gas cookers. Therefore, it is extremely urgent to adopt new technologies to improve the thermal efficiency of gas cookers and reduce the emission of carbon oxides and nitrogen oxides. Full premixed combustion technology is a high efficiency, high heat intensity combustion method. Taking advantage of the full premixed combustion technology, it is an irresistible trend to develop energy-efficient fully premixed gas cookers. Studies have shown that the full premixed burner has a good effect in suppressing the formation of pollutants. Reasonable design of the full premixed burner can achieve low NOPCO emissions. 0. However, how to ensure the air-fuel ratio of the fully premixed commercial gas stove is a big problem. . Ideally, the air and gas are pre-mixed according to the designed air-fuel ratio, so that the mixed gas can be burned completely and the heat loss of the exhaust gas is small, but this is often not the case. Differences in valve flow characteristics, fan operating point offset, user habits, etc., will cause the air-fuel ratio to be unreasonable, resulting in the burner not working properly. Therefore, controlling the air-fuel ratio is critical for a fully pre-mixed commercial gas cooker. The pre-mixed commercial gas cooker controls the air-fuel ratio through the direct linkage of the gas valve and the air valve, that is, the gas valve and the air valve are controlled by the proportional rotation of the chain. This adjustment process often fails to achieve satisfactory results. According to the flow characteristics of different valves, considering the influence of external interference, the paper establishes an accurate mathematical model to analyze the linkage relationship between gas valve and air valve, so as to ensure the accuracy of air-fuel ratio of full premixed commercial gas cooker. 2 Full premixed commercial gas cooker combustion system Full premixed commercial gas cooker combustion system mainly includes: full premix burner, gas valve, air valve, fan, pipeline, linkage mechanism, etc. See. The linkage mechanism is based on the opening degree of the gas valve, and controls the opening of the air valve. There are two modes of mechanical transmission and electronic transmission. g gas realizes the reasonable linkage between the gas valve and the air valve, that is, the air-fuel ratio of the burner is equal to the design value. It is necessary to find out the actual flow rate of the gas valve at different opening degrees, and determine the required air flow rate from the actual gas flow rate and the design air-fuel ratio. The required air valve opening is then determined based on the actual operating flow characteristics of the air valve. Finally, the linkage mechanism is designed by the corresponding relationship between the valve opening degrees. 3 The flow characteristic of the mathematical model regulating valve refers to a specific relationship between the relative flow rate of the fluid medium flowing through the regulating valve and the relative opening degree of the regulating valve, and is divided into an ideal flow characteristic and a working flow characteristic. When the pressure drop is fixed before and after the regulator valve, the resulting flow characteristics are called ideal flow characteristics. Namely: the flow rate of the qmax regulating valve when it is fully open, m3/s/function 1 adjusts the stroke of the valve core at a certain opening degree, the stroke of the spool when the mm 1max regulating valve is fully open, and the adjustable ratio of the mmR regulating valve The ideal flow characteristics of the regulating valve are linear flow characteristics, equal percentage flow characteristics, fast opening flow characteristics and parabolic flow characteristics. 1. Straight type 2. Equal percentage type 3. Quick opening type 4. Ideal flow characteristic of parabolic type regulating valve (R In actual use, the regulating valve is installed on a pipe with a certain resistance. The valve opening degree changes while changing the flow rate. It also changes the resistance of the pipeline, so at the same opening degree, the actual relative flow rate of the regulating valve is deviated from the ideal flow rate. The specific relationship between the actual flow rate and the relative opening degree of the regulating valve is called the working flow characteristic of the valve, and the relationship See la, g air, gas regulating valve stroke of the valve core at a certain opening degree, mm 1a, max, g, max air, the stroke of the valve core when the gas regulating valve is fully open, mm Ra, Rg air, gas regulating valve The adjustable valve ratios of Sa, v, Sg, air and gas regulating valves are visible, and different regulating valves have different correspondences. To obtain a reasonable air-fuel ratio, the working flow of gas valves and air valves must be obtained. The characteristic relationship is analyzed, and the linkage mechanism is designed according to the actual flow change, so that the gas valve and the air valve are associated with each other. 4 Valve opening calculation The ball valve is an equal percentage flow characteristic regulating valve, which has the advantages of large circulation capacity, short switching stroke and low noise. Therefore, all premixed commercial gas cookers use ball valves as regulating valves. The ball valve with the adjustable ratio of 25 and the valve weight of 0.5 is used as the air valve; the ball valve with the adjustable ratio of 30 and the valve weight of 0.9 is used as the gas valve; the air-fuel ratio is designed to be 9. 8. According to the characteristics of the ball valve Formula, the relationship between the working flow characteristics of the air valve is given in equation (5), and the relationship between the working flow characteristics of the gas valve is shown in equation (6). Table 2: Deviation between actual relative flow of air and required relative flow in direct linkage mode. Gas valve air valve air relative flow deviation /% relative opening /% actual relative flow /% actual relative flow /% relative opening 20%, deviation Up to 57%, the burner has not been able to burn stably and the flame may be extinguished. According to the above analysis and the mathematical expression of the equal percentage flow characteristics, the corresponding relationship between the maximum flow rate and the relative opening degree of the two valves must satisfy the following conditions: After calculation, the actual air-fuel ratio of the full premixed commercial gas cooker is equal to the design air-fuel ratio, which is different. The relative opening degree of the air valve corresponding to the opening degree of the gas valve is shown in Table 1. Table 1 Relative opening degree of the air valve corresponding to the opening degree of different gas valves and the relative flow rate of the gas valve Relative opening of the gas valve /% working relative flow /% work Relative direct linkage, the deviation of the actual relative flow of air and the required relative flow, see Table 2. It can be seen from Table 2 that in the direct linkage mode, the actual relative flow of the different opening degrees of the air valve and the required relative flow have a certain degree. 5 Interference control and optimization In actual work, the wind opportunity is affected by the resistance of the pipeline and accessories. The working point of the fan is offset, which affects the total pressure of the fan. 0 Especially when the heat load of the cooker is small, the air valve opening is small. The resistance at the end of the fan is large, the flow rate will be greatly reduced, and the flow rate reduction will indirectly affect the pressure drop of the air valve. Therefore, when designing a fully premixed commercial gas cooker, in order to more accurately control the air-fuel ratio, it is necessary to carry out certain experimental tests on the selected fan and pipeline, and the test results have a certain relationship between the air valve and the gas valve. Corrected. Commercial gas cookers generally operate at maximum heat load, with little or no partial load and little load. When the regulating valve is at a small opening degree, the flow rate is large, the resistance is large, the valve body is oscillated obviously, and the stability is poor. Some studies suggest that the maximum relative opening of the regulating valve should be kept at about 90%, and the minimum relative opening should be no less than 10%. 4. Therefore, in order to make the burner work more stably, the full premixed commercial gas cooker should be considered. Segment control. The analysis of the working flow characteristic curve of the ball valve shows that the relative opening degree of the ball valve is close to the linear relationship with the relative flow rate when the relative opening is greater than 40%, and the adjustment performance is good. Therefore, it is recommended to close the valve and stop working when the relative pre-mixed commercial gas cooker has a relative opening of less than 40%. In addition, considering the cooking habits of commercial gas cookers, it is recommended to set the relative opening of the gas valve to 3~4 gears to facilitate the actual operation and reduce the control difficulty. 1 Direct linkage often fails to achieve the air-fuel ratio required for the design. Taking this example as an example, the deviation is even as high as 57%, and the burner cannot burn normally. The corresponding linkage energy can better ensure the design air-fuel ratio of the burner, so that the burner works stably. The valve linkage mechanism of the fully premixed commercial gas cooker should be designed by analyzing the valve flow characteristics. When designing a fully premixed commercial gas cooker, the operating point offset of the fan should be considered, and the relationship between the air valve and the gas valve should be corrected. From the actual use habits, it is a worthwhile energy-saving design idea to directly close the gas valve under a small load and stop the full premixed burner. It is recommended to set the relative opening of the gas valve to 3~4 gears to facilitate the actual operation and reduce the control difficulty. As a derivative of Dog Harness or Pet Harness,Pet Life Jackets are widely used in the safety field. Pet Life Jacket,Pet Life Vest,Life Jacket for Pets,Life Vest For Pets Yangzhou Pet's Products CO.,LTD , https://www.paiqipets.com
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