| Continuous cropping obstacles have gradually become a bottleneck restricting the sustainable and efficient utilization of soil resources in protected horticulture in China.Soil steam disinfection is an effective means to solve continuous cropping obstacles.At present,most of the soil steam disinfection equipment provide steam with coal-fired and oil-fired boilers by means of direct-burning heating.There are some problems,such as difficult to enter the shed,low efficiency and high pollutant discharge,which can not meet the needs of facility horticultural soil disinfection in China.In order to solve this problem,the soil steam disinfection machine based on pulsating combustion technology was designed.The specific research contents and conclusions are as follow:The soil steam disinfection machine was composed of steam generator,caterpillar chassis,hanging mechanism and steam cover.Pulsating combustion engines were used as heat source of steam generator which worded cooperatively.Caterpillar chassis was used to walk.Steam cover was used to transport steam to soil.The steam generator was horizontal in structure,which consisted of 2 parts:the pulsating combustion engine and the cylinder components.The pulsating combustion engine was Helmholtz type pulsating burner.According to Rayleigh Criterion and empirical formula,a dual carburetor pulsating combustion engine was designed.The throat was"Y"shape,and the angle between the2 branch pipes was 90 degrees.Each branch pipe was connected with a carburetor respectively.The combustion chamber was cylindrical,with an inner diameter of 0.08 m and a length of 0.16m.The spiral pipe was adopted in the tail pipe,and the inner diameter of the single tail pipe is 0.02m.The inner wall of the chamber was welded with fins,and the outer wall was welded with stainless steel angles.The performance of the pulsating combustion engine was tested.It turned out that the pulsating combustion engine had good start-up performance and working stability in both air and water.The frequency in the air was kept between 90.80 Hz and 90.89 Hz,with an average frequency of 90.86 Hz,a range of 0.09 Hz and a standard deviation of 0.03 Hz.Frequency in water was kept between 87.27 Hz and 87.81 Hz,with an average frequency of 87.51 Hz,a range of 0.54Hz and a standard deviation of 0.16 Hz.The pulse combustion engine power was 26.8 k W.The performance of the steam generator was tested.Under the rated condition,the steam output was 150 kg/h,the fuel consumption was 9.7 kg/h,the steam pressure was 0.6 MPa,the saturated steam humidity was 3%,the tail gas temperature was 108?,the tail gas excess air coefficient was 1.026,the power was 110.8 k W,and the thermal efficiency was 95.5%.Under the non-full rated condition,the output was 152 kg/h,the fuel consumption was 9.8 kg/h,the steam pressure was 0.59 MPa,the saturated steam humidity was 3%,the tail gas temperature was 102?,the tail gas excess air coefficient was 1.037,the power was 112.3 k W,the thermal efficiency was95.8%.Five temperature measuring planes were set up in the z direction of steam generator,and 16temperature measuring points were arranged on each plane.The temperature variation process of water inside the generator was recorded from the beginning to the stable working condition.According to NNI,the temperature field inside the steam generator was reconstructed.At the thirty-fifth minutes,most of the water inside the steam generator was close to saturation temperature.The temperature rise process of pulsating combustion engine under different throttle opening conditions was simulated and analyzed.It was found that Boltzmann method was the most suitable method for the process.R~2 of five throttle opening conditions were more than 0.9997.Comparing the fitting temperature with the measured temperature at each time,the absolute error of each time was less than 5.2?,and the relative error was less than 2.2%.Numerical simulation for the air temperature field on the cross-section of the combustion chamber was made.The temperature rise law obtained by fitting was taken as the boundary condition and added to the calculation model through UDF interface.The accuracy of the boundary condition ws verified.Under all the throttle opening conditions,the simulated temperature of each measuring point showed an"S"type growth trend.After a time,it became stable.The maximum relative errors of group a,group b and group c were 18.04%,18.17%and 16.59%,respectively.The minimum relative errors were 0.01%and no more than 0.27%.The average relative errors of each group ranged from 2.68%to 5.54%.The position relationship among four pulsating combustion engines was taken as the structural optimization parameter of steam generator and its range was determined.According to the results of numerical simulation,the average time required for the average temperature of the 12 groups of calculation models to rise from room temperature to the corresponding saturation temperature was422.62 s.The shortest time for group i was 407.1 s,which was 15.52 s faster than the average time,and the longest time for group k was 438.1 s,which was 8.22 s slower than the average time.When the No.?pulsating combustion engine was located at node i,the waiting time of steam production was the shortest.After optimizing the structure,the waiting time of steam production was reduced from 38 min to 34 min,which is reduced by 10.53%.The field test of the soil steam disinfection machine showed that the variation trend of temperature at each temperature measuring point was roughly the same.The temperature increased rapidly in a short time,and then decreased slowly.For the monolayer needle group,the temperature dropping rates of the five measuring points were 25 cm>5 cm>20 cm>10 cm>15 cm,respectively.For the double-layer needle group,the temperature dropping rates of the five measuring points were 25 cm>20 cm>5 cm>15 cm>10 cm,respectively.Under the same steam supply time,the time maintenance in the same temperature range of the double-layer needle group was longer than that of the monolayer needle group.Comparing six kinds of typical soil borne pests and pathogens and their lethal conditions,the soil steam disinfection device meet the design target and the disinfection effect meet the design requirements. |
PDF Full Text Request