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PTC heating tube is used for liquid heating (including water, diesel oil, hydraulic oil, etc.)

Article source:admin Popularity:Published time:2019-07-16 18:05

1, PTC liquid heater structure.

Yaxun produces immersion liquid PTC heater
 

Structure diagram of immersion liquid heater
figure 1 Is the structure diagram of the immersion liquid heater
 
figure 2 It is the position where the heater is placed in the container. Vertical heating tube installation is relatively simple, but the temperature of the upper and lower layers of the liquid is not uniform enough. The heating temperature of the flat heating tube is relatively uniform, but when installing, it is necessary to punch holes in the container, and the sealing hole needs to be sealed. The heating temperature of the curved heating tube is relatively uniform, and no punching is required, but the cost is high. When the bottom heater of the container is installed at the bottom, the heating temperature is relatively uniform.

The material of the metal casing that is in contact with the heated liquid can be selected: Aluminum-silicon alloy, aluminum-zinc alloy, aluminum-magnesium alloy, copper, brass, iron (galvanized, etc.), 304 stainless steel, 316 stainless steel, titanium, copper-nickel alloy, and the like. The metal casing material is selected according to the use, the nature of the liquid, the corrosiveness of the liquid to the metal, and the like. For the heating of oil, a lower cost aluminum alloy casing can be used; For the heating of washing water, aluminum alloy, copper, brass shell can also be used; The edible water can be heated by 304 stainless steel or 316 stainless steel. When the water quality is poor, or sea water, or heating for electroplating aqueous solution, titanium casing can be used; A highly corrosive liquid, available in copper-nickel alloy. In addition, a layer of fluoroplastic is attached to the surface of the metal casing to withstand the corrosion of most liquids at temperature tolerance, but the heating power is significantly reduced.

The bottom (or side) liquid heater of the container, the heater does not directly contact the liquid, and the liquid does not corrode the outer casing of the heater. However, such a heater has a large volume, a low power, and a high cost.

1.2 Heating power
The relationship between the heating power and the heating time of the PTC heating tube is quite different from that of the conventional heating wire heating tube. At the initial stage of heating, the power of the PTC heating tube is from small to large, and after reaching the maximum value (maximum impact power), it gradually decreases and finally stabilizes (boiled water stabilizes power). The stable power of dry burning is much smaller than the stable power of boiling water (dry burning power is about 8% of boiling water).

The steady power is related to the liquid temperature, and the higher the liquid temperature, the smaller the stabilizing power. A standard liquid temperature can be specified according to the conditions actually used. When the heating tube is heated, the liquid temperature is from low to high, and when the liquid temperature reaches the standard temperature, the recorded power is the stable power at the standard liquid temperature.

Stable power is related to the type of liquid. When the liquid is water, the power is relatively large, because the specific heat capacity of the water is large, the fluidity is good, and convection is easy to form; Stable power is generally less than water when heating other liquids.

The higher the surface temperature of the PTC heating tube is, the higher the stable power is. However, increasing the surface temperature causes an increase in power attenuation, an increase in the breakdown potential of the PTC heater, and a decrease in performance such as adhesives, wires, and insulation layers, and a decrease in reliability.

When the surface temperature of the PTC heating tube is the same as the liquid temperature, the heating power is substantially zero, that is, no heating is performed. Therefore, the surface temperature of the PTC heating tube dry burning will always be higher than the liquid temperature by 20 ° C or higher, otherwise it will not be heated. The smaller the difference between the surface temperature of the PTC heating tube and the temperature of the liquid, the smaller the power density of the heating tube, the larger the volume, and the higher the cost.

The heating tube with a large maximum impact power does not necessarily have a large stable power. If the maximum impact power is too large, it will affect the normal operation of the entire power supply circuit and switch; However, if the maximum impact power is too small, the stable power will not be met.


1.3 Power attenuation
Due to the difference in quality of each PTC manufacturer, the user feels that the PTC power attenuation is too large. Dongguan Yaxun's PTC liquid heating tube, the power attenuation for uninterrupted operation for one year in a row is generally around 10%, completely within the range acceptable to users. Some PTC manufacturers have a power of about 30% in one month, and the power attenuation in a year of continuous uninterrupted operation is 40~50%, which is actually unusable. Therefore, when purchasing a PTC heating tube, it is necessary to test the power attenuation test.

The power attenuation is positively correlated with the surface temperature of the PTC ceramic heater. The higher the surface temperature, the greater the power attenuation. That is to say, lowering the surface temperature of the PTC heating sheet can reduce the power attenuation, but the volume of the heating tube is increased and the cost is also increased.

There are two main reasons for power attenuation. First, the increase of the normal temperature resistance of the PTC ceramic heating sheet / the drop of the inrush current; Second, the heat transfer structure is loose, which makes the heat transfer worse.


2.4 Application occasion
Storage water heater, namely hot water heater, electric kettle, hot water dispenser, washing vegetables, washing dishes, washing face, bathing, bathing feet, hot water in foot bath, auxiliary heating of solar energy, heat pump water heater, electric heating of photovoltaic solar water heater, Range hood, cleaning agent hot water cleaning, hot water bed, electroplating tank, diesel car fuel tank, filter heating, hydraulic oil, lubricating oil, cooking oil heating, sauna, beauty, disinfection, humidification, steam generation, syrup fumigation, Insulation of aquarium and aquarium pool, antifreeze of water pipes, faucets, pipes and tubing, three-way catalysis, heating of urea solution, hydrothermal floor heating, oil-heating type, heating of water-heating fins, etc.

Stable heating power can range from 10W to 10KW. However, for a heating tube with a large power, the number of PTC ceramic heating sheets used is relatively large, which may increase the chance of breakdown of the PTC ceramic heating sheet; In addition, the insulation area is also relatively large, and the chance of failure of insulation increases. Therefore, it is best to divide into several heating tubes, each of which has a lower power, which can reduce failure and waste. The working voltage range is from 12V to 420V, and both AC and DC can be used. When the operating voltage is low and the heating power is large, the inrush current and the steady current are large, and the power supply is difficult to withstand, so when high power is required, it is preferable not to use a low voltage.

The advantage of a heating wire electric heating tube is that the cost is low.
Problems:
1) After using for a period of time, the insulation withstand voltage, leakage current, and insulation resistance exceed the standard;
2), can not dry, if the temperature protection device fails, the electric heating tube will burn out due to dry burning, or even burn out the surrounding materials, a fire occurs;
3) After the long-term work of the heating wire, it may be oxidized and burned, affecting the life and even causing leakage;
4) When the water quality is poor, the concentration of cations (calcium, magnesium, etc.) is relatively large, the surface of the electric heating tube is prone to scale, and the surface heat transfer is deteriorated, resulting in internal electric heating wire burning.


The PTC liquid heating tube can overcome the shortcomings of the electric heating wire electric heating tube, and the insulation withstand voltage, leakage current, and insulation resistance are excellent and stable, resistant to dry burning, long service life, and there is no scale burned.
However, if the PTC manufacturing quality is not good, there may be problems:
1), the PTC ceramic body breaks down and burns, causing a short circuit and burning the insulation layer;
2), the insulation layer breaks through the leakage, and the outer casing is charged;
3), the heating power is attenuated as the usage time increases;
4) The surge current is too large, causing the power supply line and the switch to malfunction.
PTC heating tube users should carefully select PTC heating sheets to ensure reliable quality.

Keywords:PTC heating tube

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