Repair of leakage caused by moisture in cast aluminum heater

Many electric heating appliances use cast aluminum heaters as heating elements. However, if the seals on the tube openings of cast aluminum heaters are poor, moisture can enter the magnesium oxide powder inside the tubes, causing leakage. During repair, first remove some of the original sealant, leaving room for the repaired seal. Then, power the heater for at least 10 minutes to allow the moisture to evaporate. After cooling naturally, check with a megohmmeter. If the insulation resistance between the tube shell and the heating wire lead is at least 1, the insulation is good. If it is less than 1, continue powering the heater for a while longer to allow the moisture to evaporate.

If the insulation of the cast aluminum heater is good, seal the tube with silicone rubber. Ensure that the heating wire lead remains centered within the tube. After the silicone rubber cures for 24 hours, it can be reused. Testing of cast aluminum heaters is divided into two stages. The following uses a sodium cast aluminum heater as an example.

1. Startup and Initial Operation of the Cast Aluminum Heater

The purpose of this test is to verify the proper operation of the cast aluminum heater. At the outset of the test, one end of the heat pipe was heated in a tubular resistance furnace. During the initial startup phase of the cast aluminum heater, the temperature rises slowly, allowing the sodium in the capillary structure to melt and reflux, thus preventing the evaporation zone from drying out. After approximately half an hour of startup, the cast aluminum heater enters normal operation and gradually heats up to approximately 700°C. At this point, the portion of the cast aluminum heater outside the furnace glows red due to the large amount of heat dissipated.

2. After the cast aluminum heater has been operating normally, the axial wall temperature distribution and the power delivered by the cast aluminum heater are measured.

During the test, the portion of the cast aluminum heater, excluding the high-frequency coil, is directly exposed to air. Heat is dissipated through high-temperature radiation and natural convection. The axial wall temperature distribution is measured at different power levels. The helium-to-air ratio in the air gap is adjusted, i.e., the amount of helium is increased or decreased. Each adjustment changes the input power, and the maximum power delivered by the cast aluminum heater is measured at different operating temperatures.