Comparation between welded finned tube and Integral finned tubes
The disadvantage of high frequency welded finned tubes
1, due to technology limitations , fin spacing, minimum spacing 4mm, fin height maximum 55mm, the general air cooler aluminum fins fin spacing is 2.3mm , 57mm fin height , therefore , lower than the wing of a maximum of only 13 about normal flaking or bulging piece is about 23 , meaning that the same area of the base pipe , finned aluminum fins of the small size of only about 55% z , limited heat transfer effects.
2, the fins of steel or stainless steel sheet , sheets thick , the thinnest 0.8mm, while aluminum is about 0.3 ~ 0.45mm, poor fin thermal efficiency, if it is stainless steel fins , stainless steel heat exchanger efficiency due to the worse ( pass the thermal efficiency of only 65% of aluminum ) , the heat transfer efficiency is low .
3 , high-frequency welded fin , while contact resistance is small, but finite area of the fin , heat transfer fin thickness difference , therefore, the overall thermal efficiency of the finned tube is not high . Except for some special process , in general, use less . Application:
Based on the above description, the high-frequency welded finned tubes in the air cooler is inappropriate , the case unless the temperature is higher than 500 ℃ . But based on their corrosion better, such as stainless steel fin - Stainless steel base tube , in methanol synthesis evaporative cooling applications can be used , however , the heat transfer efficiency is greatly reduced , and only 45% of the aluminum in the left and right ( area only 60% aluminum , the aluminum heat transfer efficiency of only 70% , the total effect of 0.6 × 0.7 = 0.45), so the difference between the water-saving effect .
Integral finned tubes with the following six advantages
1. Integral finned tubes can be extended heat effect ( area and heat transfer coefficient ) . With the same base pipe situations: ( to the base tube φ32X4 example, 12 high winged , wings from 12 ) 1 meter equals: 4 m or 2.6 m membrane -ray tube structure ( pitch 62X3, flat 30X3) or 1.5 m flat wound welded finned tubes ( flat 12X3).
2. Integral finned tubes wearable. As the overall finned tubes finned tube is integrally formed with the base , consistent with the crystal structure , stable performance , besides the shape of the fins were dunes , with a temperature gradient shape when heated match , consistent with the outer surface when heated fin temperature, thermal stress uniform , no focus , it will not produce the intensity weak point ( and the main reason is because the high temperature wear points should be σ low ) Also, the role of the fins on the flue gas has a diversion , diversion , while flue gas that the indicators ( temperature, flow rate , ash , etc. ) is more uniform , the drift does not produce smoke , smoke concentration , will not result in a region or a part of erosion . Therefore relatively resistant.
3. Integral finned tubes stiffness greatly enhanced. Size depends on the size of the stiffness of the moment of inertia , moment of inertia of the whole fin tube is 4.76 times the corresponding optical tube. (Φ32X4 moment of inertia 35168mm2, and moment of inertia of the finned tube 167613mm2,) light pipe bracket spacing is 2.71m (3.55m old REGULATORY ) , finned tube 5.28 m (6.91m old REGULATORY ) , if it reaches the wall temperature calculation when 460 ° near the bracket spacing will be reduced, so that the two rows of tubes in the middle of the stent fracture phenomena on some economizer . This phenomenon is neat fracture occurs . The material has found no problems.
4 Overall finned tubes not fouling . The reason is that fouling caused by Karman vortex : the flue gas stream through the tube , the tube will form the back of the negative pressure region , in this region, the gas velocity is zero or reflux , gas accumulates in this , the adhesion of ash the pipe surface. Ash thermal resistance is relatively large , gray piled thick , thermal resistance is growing less and less heat transfer , exhaust gas temperature , the efficiency of the boiler also declined. The finned tube diversion of flue gas to overcome the Karman vortex , while combing the ash distribution to distribution in the flue gas .
5 . Steady heat transfer performance. A body structure as the heating surface , in the years ( without soot blowing ) operation, the boiler exhaust gas temperature fluctuates little , no economizer tube bursting phenomenon.
6. long life . Under the same operating conditions ( coal , temperature, heating surface location ) , finned tube to ensure life of more than two times the light pipe . Under normal circumstances, the light tube life of 3 to 4 years , then the finned tube life of at least 7 to 8 years.