Domestic pulse combustor tail pipe drying research
    From 1996 to 1999 , Li Baoguo , etc. in China Agricultural University on pulse combustor tail pipe drying detailed experimental study , the main purpose is to understand the tail pipe dry material law , analyze the burner structure parameters and process parameters on the drying performance effects , compared pulse combustion drying tail pipe adaptability to different materials and the drying effect under various conditions . Pulse combustor tail pipe drying test device consists of pulsating burner , with water cooling jacket of the tail pipe , feeding device , adjust the length of the sand drying tube , cyclone and rack and other components. Experimental pulse combustor used for the diaphragm valve Helmho1tz type combustion chamber diameter of 100mm, 250mm long , cylindrical , vehicles using liquefied petroleum gas as fuel , power of 25kW, frequency adjustment range 50-100Hz. Feeding port in the tail pipe with a water cooling jacket after 1.1m away from the combustion chamber office, avoid feeding port at the combustion chamber too close , when the pulse combustor operates in the suction stroke, the negative pressure in the combustion chamber into the combustion chamber of the material interference pulse combustor to work properly, from the mouth to the cyclone feed tail pipe segment is drying tube , drying tube by a number of single- section tubes, from 1-3.5m to 0.5m units of adjustable length . The amount of feed by changing the opening size of the feeding port to regulate, in a dry tube feeding drying tube outlet port and a test port , respectively , for measuring the air temperature and velocity . Experimental factors have ripple frequency , drying tube length , feed rate , heat load, the material out of water and type of material . To investigate the pulse combustion drying tail pipe adaptability of materials , selection of rice , rapeseed and soybean side three kinds of different drying characteristics , different size and different initial moisture content of the material , respectively, and dried under different experimental factors Study select the precipitation rate , drying rate , evaporation intensity and energy consumption per unit in order to examine pulse combustor tail pipe dry material performance. Due to seasonal restrictions , rice, rapeseed parked by the water used to make the material moisture soaking 12h saturated , then Airing necessary moisture to the test after the drying test . Soy beans after soaking treatment is separate from the refiner refiner , after three washed fresh bean dregs , its moisture content of 82% -83 % .
    Pulse combustor operating frequency is changed by adjusting the length of the tail pipe to be achieved, as the pulse frequency increases , the precipitation rate of the material to be dried , the drying rate and evaporation intensity. Energy consumption is reduced , increase the frequency is advantageous for the drying process . This is because the higher the frequency , the combustion intensity of pulse combustion , thermal efficiency is higher , the exhaust gas flow rate and temperature were increased, and thus speed up the drying process ; addition , pulse frequency increases , the strengthening effect of the reverse flow enhancement , acoustic energy increases, exhaust increasing levels of flow turbulence , the particulate material of the layer to increase the oscillation stream .
Acoustic energy in strong and pulsating flow under the effect of particulate material moisture evaporation surface boundary layer is destroyed or thinned , reducing heat and mass transfer resistance. Pulse combustor tailpipe is more suitable dried in a high content of free water surface of small particles of material humidity , internal bond -containing particulate material in water, drying of larger particles is poor. The reason may be due to pulsating combustion tube drying , the material residence time is short, the internal rate of diffusion of bound water intrusion , so its strengthening effect less surface moisture diffusion process .
    With the drying tube length increases , rice, rapeseed and soybean residue of precipitation rate , drying rate began to increase slowly , when the drying tube length of about 1.6m , the rapeseed precipitation rate and the drying rate reaches a maximum , and then dried with tube length is increased precipitation rate and the drying rate but decreased ; rice precipitation rate and drying rate when drying tube reaches a maximum length of about 2m , and then , with the dry bake tube length decreases with an increase ; Okara precipitation rate relative drying rate with drying length growth , began to increase rapidly, when the drying tube reaches 2m , the dregs of the precipitation rate and the drying rate increased slowly . This can be drawn : pulse combustor tail pipe type drying and air drying , drying tube length was increased although the increase of drying time, but also because the end of the drying tube portion of the tube , and the pulse frequency and the wave energy with reduced tailpipe growth . Meanwhile, with the increase in tail pipe
Long , the pressure amplitude of the pulsating combustion , the combustion efficiency and discharging exhaust gas temperature and speed are lower . So when drying tube is long, the material to be dried and the drying rate of precipitation magnitude smaller . With the drying tube length increases , rice, rapeseed and soybean residue of evaporation intensity decreased, unit energy consumption began to decline up quickly, when the drying tube length of about 2m , with the drying tube length increases , the unit energy consumption decreased by slowing and there are an increasing trend , whereby : Although beneficial in extended drying times to remove the moisture in the material , but does not significantly enhance the drying process , but because of the increased length of the drying tube , lower pulse frequencies, so the drying index declined. Pulse combustor tail pipe for dry materials , the desire to get a good drying effect , there is an optimum drying tube length length range .
       As the feed increases, the precipitation rate drying process , the unit energy consumption decreased , the drying rate is increased , this is because with the feed increases, the pulse combustion drying tube in the particle concentration increases , the particle stream effective heat transfer between the area increases, resulting in increased drying rate . At the same time , because the feed increases, the evaporation of water with the material increases, the drying medium temperature is decreased, resulting in the material flow and the mean temperature difference between the particles decreased , so that the precipitation rate of decline . As the feed rate increases, the drying rate increases , so the unit energy consumption decreased . In the feed rate is small, rapeseed and soybean residue unit energy consumption decreased with the increase of feed rate faster drying rate increased rapidly, a large amount of time in the feed . With the feed rate increases, the unit energy consumption decreased slowly , the corresponding rate curve is slowly drying up , precipitation rate increases with the feed rate of decline . This shows that at low feed rate zone , the feed rate changes on energy consumption and the drying rate greater impact ; while at high feed rate zone , the feed rate change on these performance indicators in the dry little effect . From the above analysis, the increase in the amount of feeding people can reduce energy consumption and improve the drying rate , and can improve productivity. However , persons with the feed increases, the precipitation rate will be reduced ; addition, with the increase in feeding persons , drying the concentration of material within the tube increases, the pulse combustor tail pipe resistance increases, the pulse frequency is reduced , affect the drying results. If the feed is too large, but also affect the normal pulse combustor stability . Therefore, considering a variety of factors, pulse combustor tail pipe for dry materials , you should select the appropriate material feed rate .
    Further tests also found that as the pulse combustor increases the thermal load , the precipitation rate of the material to be dried , the drying rate were increased , decreased energy consumption , mainly due to thermal load increases with frequency , exhaust gas temperature and the speed increases, so the material precipitation rate , drying rate increases, energy consumption is reduced. Pulsating gas burner at its rated capacity when operating combustion efficiency, the highest thermal efficiency , it is best to make pulsating burner gas flow is at its rated load at rated thermal work . With the reduction of initial moisture of materials , rice and rapeseed precipitation rate and the drying rate decreased rapidly , unit energy consumption is increasing rapidly. For materials with higher water content Okara , along with its initial moisture reduction , precipitation rate , drying rate decreased more gentle , unit energy consumption is increasing rapidly, once again shows pulse combustor tail pipe surface dry and suitable for containing water wet particulate material and liquid materials.