Heat Pipes and how they function

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Heat Pipe

Structure and Principle The heat pipe is hollow with the space inside evacuated, much the same as the solar tube. Inside the heat pipe is a small quantity of purified water. At sea level water boils at 100oC, but if you climb to the top of a mountain the boiling temperature will drop. This is due to the difference in air pressure. Based on this principle of water boiling at a lower temperature with decreased air pressure, by evacuating the heat pipe, we can achieve the same result. The heat pipes used in Solarlink collectors have a boiling point of only 30oC. Therefore, when the heat pipe is heated above 30oC the water vaporizes. This vapour rapidly rises to the top of the heat pipe transferring heat. As the heat is lost at the condenser (top), the vapour condenses to form a liquid (water) and returns to the bottom of the heat pipe to once again repeat the process. Quality Control Material quality and cleaning is extremely important to the creation of a good quality heat pipe. If there are any impurities inside the heat pipe it will affect the performance. The purity of the copper itself must also be very high, containing only trace amounts of oxygen and other elements. If the copper contains too much oxygen or other elements, they will leach out into the vacuum forming a pocket of air in the top of the heat pipe. This has the effect of moving the heat pipe's hottest point (of the heat condenser end) downward away from the condenser. This is obviously detrimental to performance, hence the need to use only very high purity copper.

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Copper Heat Pipe Freeze Protection Even though the heat pipe is a vacuum and the boiling point has been reduced to only 25-30oC, the freezing point is still the same as water at sea level, 0oC. Because the heat pipe is located within the evacuated glass tube, brief overnight temperatures as low as –10oC will not cause the heat pipe to freeze. If the heat pipe does freezes once or twice the heat pipe will not burst as the copper can expand, but repetitive freezing will result in the bottom of the heat pipe to swell and eventually rupture. In order to protect the heat pipe from this occurrence, in areas that regularly experience temperatures below –5oC, freeze protected heat pipes are recommended. The bottom end of the heat pipe has a stainless steel cover that strengthens the pipe, forcing the ice to expand upwards instead of outwards. This method effectively protects the heat pipe against damage from repetitive freezing in cold regions Bak to How Solarlink works To get further advice about this topic or talk to an expert please click here