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制约电热管效率的因素和提高方法

发布时间: 2015-11-19 23:05 作者: 浏览次数: 字号:
制约电热管效率的因素和提高方法

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  • 制约电热管效率的因素和提高方法

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防干烧电热管效率和普通电热管那个高?
首先电热管效率和防干烧没有太大的关系
电热管效率和材质等因素有关系,使用316L材质不锈钢电热管,相对较好
下面介绍一下制约电热管效率的因素和提高方法
使用316L材质不锈钢电热管,相对较好
一、材料的三大因素
1、镁粉的纯度问题:氧化镁纯度大小直接决定了镁砂的导热系数,导热系数愈大,热阻愈小。热传效率愈高。
2、镁粉的密度问题:密度大小由填充密度、缩管或整形密度来决定电热管最终的密度。密度值愈大,电热效率愈高,反之愈低。
3、电热管的管材的选用
(1)管材选用时口径的选择方法一定要计算正确,即通过面积压缩比的变化率来预估电热管最终密度是否满足3.05g/cm³之最低要求,例如一支φ9.4×0.6的不锈钢管,最终成管为φ8,试论证此方案的可行性,基本的评估计算方式如下:
①空管内截面积S1= ≈52.81mm²
②成形后管内截面积S2= ≈36.32mm2
③管面积压缩比值为A≈0.688
在填充过程中,目前镁粉颗粒搭配及设备匹配较理想的时候,原则上保证2.35g/cm³的指标可以达到,而在最终3.05g/cm³的最低管内密度要求指标下,此时密度的增加值为:1.297倍。
而经过上述面积压缩比计算出A=0.688,即面积减少了31.2%。故相对于镁粉密度增加了31.2%,此时管内的真实密度值理论上为2.35×131.2%=3.08g/cm³,故可以判断此选择为正确的,当然上述结论正确的是缩管过程管壁没有拉薄为前题。
(2)镁粉目数搭配与填充密度之关系
目前在应用的镁粉表中,基本颗粒在所有说明书中都标明为40~325目范围,各种目数搭配比例不同时,其流速是完全不同的结果;在此过程中,一是制造商(镁粉)是否按此比例进行搭配,实际使用检验数据基本存在粗砂和细砂严重超标的问题;二是此产品长途运输过程中必定会出现不同目数砂粒的分筛现象,在使用前如无重新混合而直接倒入粉仓使用,则流速就无法确保;三是我们曾介绍过的填充机在震荡的过程中一定会造成粉仓砂粒的分筛,故当操作时为什么同样的管其填充重量有较大区别就是因为上述三大因素,当然影响流速的因素除目数搭配比率之外,防潮剂的粘湿性对流速也有相当大的影响,这也是镁粉厂所必须实时关注的一个细节。
二、结构设计
众所周知,螺旋状发热丝的外径至金属壳体内壁之距离愈大,其电气绝缘耐压值就愈高,但热传路径就增加,这种路径的增加相当在热传路径上串接了一个衰减器,必然导致电热效率的下降,而缩短这种爬电距离所存在的不利点是常态耐压值将出现较大的下降,现在的关键是要如何评估电热效率偏低而对电热管性能影响而最终作出权衡。
发热丝单位时间所产生热量是一常量值,由于各种因素导致热传效率的下降,而在管内逐步产生热积聚,这种现象一旦发生,除加速防潮材料快速碳化之外,热态击穿比例将大幅增加,而且随着管内温度的增加,管的热疲劳程序也会加剧出现刚性强度的下降,爆管现象几率的增加是一种危险的结果,这种管内温度的增加,除CT效应导致在线功率下降之外还将导致发热丝因工作环境温度增加而加速高温氧化,从而缩短寿命等一系列问题,从笔者在综述上面内容的结果看,提高精度确保同心度的同时,以减少爬电距离提高电热效率之功率具有极为重大的现实意义,而且是大势所趋。
上述以镁砂特征和爬电距离为对象描述了对电热效率之间的关系,但是除上述内容对电热效率有较大影响之外,还有热传路径上的最后环节,即管壳材料,除管壁厚度对热阻有关联之外,还要关注在目前四大应用材料中热阻由小至大的基本排列次序:
铜→铝→铁→不锈钢,按实际允许条件时尽可能采用导热性较好的材料,这对提高电热效率和提高电热管的性能寿命有一定的促进作用。
Prevent dry heating tube efficiency and general electric heat pipe that high?
First of all, the efficiency of heat pipe and the dry not too big relations
Efficiency and material factors such as electric heating tube, the use of 316 l stainless steel material, electric heating tube is relatively good
To introduce the following factors restricting the efficiency of the electric heating tube and improve method
Using 316 l stainless steel material, electric heating tube is relatively good
One of three factors, the material
The purity of 1, magnesium powder problem: magnesium oxide size directly determines the coefficient of thermal conductivity of sinter and purity, the greater the coefficient of thermal conductivity, the smaller the thermal resistance. The higher the heat transfer efficiency.
2, the density of magnesium powder problem: density by filling density, size shrinkage tube or plastic density to determine the density of electric heat pipe end. The greater the density value, the higher the heating efficiency, lower instead.
3, the selection of electric heat pipe pipe
(1) the selection method of pipe when choosing diameter must calculate correctly, namely through the area of the rate of change of compression ratio to estimate the final density electric heating tube whether meet the minimum requirement of 3.05 g/cm after, for example a phi 9.4 x 0.6 stainless steel tube, eventually into a tube for phi 8, try to demonstrate the feasibility of this scheme, the basic evaluation calculation is as follows:
(1) within the atc cross-sectional area S1 = 52.81 mm material squared
(2) pipe after forming sectional area S2 = material was 36.32
(3) tube area of compression ratio for A material of 0.688
In the process of filling, the collocation of magnesium powder particles and ideal equipment matching, in principle, guarantee of 2.35 g/cm after index can be achieved, and in the final 3.05 g/cm after minimum tube density index, the density of the added value of for: 1.297 times.
And through the area of compression ratio calculated A = 0.688, that area is reduced by 31.2%. Therefore, relative to the magnesium powder density increased by 31.2%, and the tube of the real density value theory of 2.35 x 131.2% = 2.35 g/cm after, so can judge this choice is right, of course, the above conclusion is correct shrinkage process of tube wall does not pull thin as before.
(2) magnesium powder mesh collocation and packing density
At present in the application of magnesium powder in the table, the basic particles in all the instructions are marked as the range of 40 ~ 325 mesh, all kinds of mesh proportion is not at the same time, its velocity is completely different results; In the process, is a manufacturer (magnesium powder) is tie-in, according to the proportion of actual use test data of basic problems of coarse sand and fine sand exceeds bid badly; Second, the product will appear in the process of long-distance transportation points of different mesh sand screen phenomenon, before use, such as not to mix and use directly into the powder storehouse, cannot ensure the velocity; Three is filling machine which we introduced in the process of shock will cause sand powder storehouse sieve, so why when operating the same tube has a big difference is that the filling weight for the above three factors, of course, factors influencing the velocity of except mesh match ratio, moistureproof agent wet sex is have a considerable effect on flow velocity, this also must be real time to the magnesium powder factory attention to a detail.
Second, the structure design
It is well known that spiral heat wire diameter to the metal shell inner wall of the greater the distance, its electrical insulating pressure value is high, but the heat transfer path increases, the increase of the path is concatenated in the heat transfer path a attenuator, inevitably led to a decline in heating efficiency, the existing drawbacks and shorten the creepage distance is a decline in the normal pressure value will be larger, the key now is how to evaluate electric heating efficiency is low and influence on electric heat pipe performance and eventually make trade-offs.
Heat wire per unit time heat is generated by a constant value, due to various factors led to the decrease of the heat transfer efficiency, and generate heat accumulation in the tube, once the phenomenon happens, in addition to accelerate moistureproof materials rapid carbonization, thermal state breakdown ratio will increase dramatically, and with the increase of temperature of the tube, pipe thermal fatigue procedures also exacerbate the decrease in the strength of a rigid, increase the rate of tube phenomenon is the result of a dangerous, the tube temperature increases, except CT effect led to the decrease of the on-line power will also lead to accelerated by increase working environment temperature of heat wire high temperature oxidation, so as to shorten the life of a series of problems, from the results of the author in this paper the above content, improve accuracy to ensure concentricity at the same time, in order to reduce creepage distance of improving the efficiency of electric power has very great realistic meaning, and it is the trend of The Times.
Above with magnesia as object describes the characteristics and creepage distance on the relationship between the electric heating efficiency, but in addition to the above content has a greater effect on heating efficiency, and the last part of the heat transfer path, namely the shell material, in addition to the wall thickness of thermal resistance are linked, but also pay attention to in the present thermal resistance of the big four applied materials from small to large the basic order of:
Copper to aluminum, iron, stainless steel, according to the actual permit conditions as far as possible with good thermal conductivity materials, this to improve the performance of electric heating efficiency and heating tube life have a certain role in promoting

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