The selection of the diameter thickness of the extraction rod and the power size of the electric heat pipe

The power of the electric heat pipe is usually determined by the temperature value and heating time of the heating system, so once the power voltage is determined, what material and diameter size of the extraction rod can meet the design and use requirements. The following is a list of the material used to extract the rod:

   Since the electric tube processing is completed, the general sealing material is RTV silicone, the temperature resistance is about 250 ° C, so the maximum working temperature of the selected extraction rod must be ≤250 ° C (RTV silicone maximum temperature resistance), then how to ensure this requirement?



Through application examples to illustrate: the design of an electric heat pipe, the specification is 2040000, using the leadout rod material is stainless steel, the leadout rod outer diameter size is 2. 6*75mm, this size selection is correct and reasonable? We can only figure it out by calculation.



Solution :2.6 Extraction rod, whose length of 75 m is equal to 0. 075 m

① The current flowing on the extraction rod is:

I=P/04000/220≈ 18.18 amperes



② Calculate the resistance value with a length of 75 mm and an outside diameter of 2.6 mm

Because K= P.L /S= 0.7X0.075/3.142X 1.32≈0.01 ohm



③ The power P generated by the 75 mm outlet rod when it flows 18.18 amps is

P=I2F= 18.182X 0.01 ≈3.31 watts (that is, the length of the extraction rod is 75 mm and the power generated is 3.31 watts)



④ At 75 mm, the tube surface load corresponding to 2.6 in the extraction rod is q rod

q rod =P/S= 3.31/3.142 x 0.26X7.5≈ 0.54 W/cm 2≤



⑤ The stainless steel extraction rod with a diameter of medium 2.6 generates a total power of 3.13 watts when flowing 18.18 amps, and the surface load of the corresponding rod is 0.54 watts/cm 2, according to the temperature corresponding to the surface load of the tube and the tube surface, the surface temperature of the stainless steel extraction rod can be obtained in about 200~220℃.



Conclusion: When the diameter of the outlet rod of the heating electric tube is medium 2.6 and the current flowing is 18.18 amp, the temperature of the outlet rod is about 200~ 220℃, which is lower than the normal temperature resistance of silica gel 250℃, so it meets the design requirements. If the normal temperature resistance of silica gel is higher than 250 ° C, the silica gel is easy to gradually age and crack at the temperature of the extraction rod, resulting in a decline in insulation and electrical performance. It may also cause the carbonization of silica gel under normal temperature resistance, resulting in a decrease in insulation of the electric heat pipe and even breakdown of the extraction rod and tube shell due to the carbonization of silica gel.



In view of the above situation, such as more than 250 ° C can be improved as follows:



① According to the outer diameter of the electric tube, such as ≥10 mm, the outer diameter of the leading rod can be appropriately increased or lengthened, so that the change can reduce the resistance value per unit length and reduce the load on the leading rod surface, so that although the leading rod still flows 18.18 ampere current, the temperature of the leading rod surface will drop to the temperature that the silicone can withstand or even lower temperature.



② If the pipe diameter is less than 10 mm, it is still at 18.18 amps current, and the material of the extraction rod can be appropriately lengthened or replaced, such as pure nickel extraction rod and so on. It should be noted that although the resistivity of the iron extraction rod is lower than that of stainless steel, it is recommended not to use it, because the surface of the iron extraction rod is easy to oxidize, the strength is small, and the contact resistance is not good.