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Axial and centrifugal fans ventilation comparative test

Time:2012-08-01 17:07 Author:admin Click:

Technology of mechanical ventilation in the country to promote the use of more than two decades, played an important role to reduce the grain temperature, inhibition or prevention of stored grain pests and microorganisms, is a low-temperature grain storage, the most effective way of green grain storage. In recent years, centrifugal fans and axial flow fans are widely used, centrifugal fan cooling, the precipitation speed, high energy consumption characteristics of a low-power axial fan ventilation has the advantage of low energy consumption and less water loss. The central grain reserves Dalian Depot quarter green jump the author of the library from October 2006 to December of the same period in warehousing, high moisture corn centrifugal fans and axial fans, ventilation comparison test.
1 test barn
Test barn to select tall cottage Dalian Depot warehouse PC11-1 position and PC11-2 position in the warehouse for the north-south length 54 m, width of 30 m high eaves 9.8 m, loaded grain height of 6 m. The barns things have five wind tunnel, the warehouse is equipped with a machine and two on the ground cage, something span gable from the ground 7 m with a 2 axial fan test warehouse grain storage grain corn.
2 Equipment and Instrument
Shijiazhuang production 4-72 type of power of 7.5 kW centrifugal fan 10; jackwood of production YFB100L1-4 power of 2.0 kW axial fan.
3 Test Method
3.1 PC11-1 position using intermittent axial fan ventilation, ventilation wind crossing open, close the windows, the use of axial flow fan out exhaust air by the wind crossing the ground-air distributor cage into the grain mass for hot and cold The air exchange, the discharge flowing through the grain surface from the axial fan position outside. PC11-2 position using a centrifugal fan with forced ventilation, the ventilation duct and position within the window open before, fan airflow was pressed into the grain bulk gas exchange positions of grain surface discharge.
3.2 during the period of ventilation were detected outside temperature, outside wet positions gentle layers of the grain temperature changes, every 8 h detection of the axial fan ventilation centrifugal fan every 4 h testing time.
3.3 per positions of eight moisture detection point, four-layer (of 0.5 m, respectively, from the grain surface, 2 m, 3.5 m and 5 m at) Sampling, ventilation and ventilation and moisture contrast.
3.4 ventilation during the observation of temperature and humidity changes at the same time, every day Jincang observe the changes of the grain surface grain quality, such as the local heat, moisture, combined with local suction single-pipe fan of cooling, turn the grain surface, playing ridge immediately to avoid food quality deterioration.
4 ventilation of
Ventilation in two phases, the first phase of ventilation is to rely on the wind so that the lower middle class "cold heart" Move to reduce the grain bulk surface, the second layer of grain temperature and temperature gradient, so that the grain mass to form a positive temperature, avoid temperature conversion season grain surface condensation; the second phase of ventilation is the natural low temperature in winter to reduce the overall temperature of the grain heap, grain mass temperature and moisture tends to be uniform, food low temperature, and safe storage.
PC11-1 position in the first phase of ventilation time from October 5 to 17, the cumulative ventilation 135 h of ventilation when the outside temperature 20 ℃, the grain heap, the lower the temperature of "cold heart" in 5.6 ~~ ​​10.3 ° C, local high temperature start ventilation grain bulk surface and the second layer, the grain temperature up to 30.2 ° C, accompanied by local wet phenomenon. Sucked out of the ventilation fan of single-tube axial fan ventilation at the same time, reduce the local heat point, combined with the grain surface to fight the ridge, to October 9, the high temperature and partial wet parts of the basic disposed of the grain situation stabilized, until October 17 diets heap lower "cold heart" impact to the surface, the entire grain mass temperature gradient narrowing and the formation of a positive temperature difference. PC11-2 position in the first phase of ventilation time from October 7 to 10 days at low temperatures, relatively low at night for ventilation, 10 wind turbines total ventilation time 28.9 h, the ventilation when the outside temperature 12 to 20 ℃ in individual parts of the lower temperature of "cold heart" in the 6.2 ~ 11.6 ℃, ventilation high temperature and humid phenomenon ventilation taken during the grain surface overturned and hit the ridge, the high temperature and humid parts with the decline of the surface and the second layer of the grain temperature returned to normal .
PC11-1 position in the second phase of ventilation time from November 22 to December 18, the cumulative ventilation 274 h ventilation when the outside temperature of -5 to 4 ℃; PC11-2 position from November 22 to 28, the use of 5 night ventilation, the ventilation when the outside temperature ~~ -4 ° C, 10 Typhoon aircraft accumulated ventilation 39.6 h.
5 Results and Analysis
5.1 The cooling effect
The first stage due to the ventilation when the outside temperature is higher than the grain bulk lower grain temperature, resulting in lower grain temperature slightly under-liter, but by the lower "cold heart", the highest grain temperature of the whole position of the second layer of the grain temperature decrease , which, PC11-1 positions in grain temperature decline of 10.9 ° C, the grain heap temperature gradient down to 2.8 ℃ 1.5 ℃; PC11-2 positions in grain temperature decline 11.1 ° C, the grain heap down to 1.3 ° C temperature gradient from 2.7 ℃ to eliminate the grain heap surface condensation risks.
The second phase of ventilation, temperature lower than the average grain heap lower grain temperature of 6 to 8 ℃ ventilation achieved good cooling effect, PC11-1 positions in the average grain temperature of 3 ° C, the grain temperature drop of 6 ° C; PC11- 2 No. warehouse full position of the average grain temperature is 2.7 ℃, the grain temperature drop of 6.7 ℃.
5.2 moisture change contrast
PC11-1 position ventilation an average moisture of 14.1%, humidity 60% ~ 80% in the ventilation period, 13.9% after ventilation, loss of 0.2%; average moisture content of 14.2% PC11-2 position ventilation, ventilation during the humidity 63 ~ 78%, 13.8% after ventilation, loss of 0.4%.
5.3 costs and energy consumption comparison
PC11-1 position using axial fan ventilation, twice the ventilation temperature decline of 11.2 ° C, the total power consumption of 1998 kW · h, the total cost was 1871.83 yuan, tons of food costs $ 0.27, the unit energy consumption of 0.026 kW · h / t, ℃; PC11-2 position using a centrifugal fan ventilation, twice the ventilation temperature drop of 12.5 ° C, the total power consumption of 5 137 kW · h, the total cost of 4250.72 yuan, tons of food costs $ 0.62, the unit energy consumption for the 0.06 kW · h / t, · ℃.
6 Discussion
6.1 Axial fan and centrifugal fan has a better cooling effect of higher grain temperature on the upper, more hot spots in stored grain and natural low temperature in winter the relatively short duration of the region, it is recommended to use the centrifugal fan ventilation and cooling, ensure the security of stored grain.
6.2 above phase of the ventilation tests showed that the axial flow fan can be completely replaced by a powerful centrifugal fan, especially the first phase of the anti-condensation ventilation grain heap lower the role of the cold source, ventilation, electricity is only 1 of the centrifugal fan / 4.
6.3 axial fan ventilation time is generally sustainable 20 ~~ 30 d within the grain mass, hot and humid surface exchange will have an impact in the ventilation period, to strengthen the inspection of 5 to 30 cm away from the grain surface of stored grain, to prevent surface condensation occurred.
Should do a good job in a timely manner after the end of the ventilation and cooling 6.4 insulation sealed grain storage, keep the grain bulk of the overall low temperature, is conducive to year-round to maintain stored grain quality, delay aging, reduce losses, control insects mold hazards.

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