Heat pipes and uses Revised

The heat pipe and some important uses for it

The heat pipe is a simple device. Although it is not new, I believe that there are some important applications for it that have not been exploited. These applications could provide a low-cost way of improving life for people in many places in the world.
You are probably familiar with the fact that when you have wet hands and they dry in the wind, they feel cold. That is an example of heat being absorbed due to liquid becoming a gas, or evaporating. When gas condenses back to liquid, that heat is released. This principle is used to transfer heat in a heat pipe. One end of the pipe absorbs heat because liquid is becoming a gas, and the other end releases heat (or becomes warm) because the gas is changing back to a liquid. In a heat pipe, the same liquid is constantly being vaporized (and absorbing heat) and then condensing at the other end of the pipe and releasing the heat. The liquid then returns to the other end where it evaporates again. You can think of it as similar to a bar of copper that is a good conductor of heat, but a heat pipe is a much better conductor of heat than any metal and can conduct a lot of heat over long distances while keeping the hot and cold ends of the pipe at nearly the same temperature. You might think of it as a kind of superconductor for heat.

The following type of heat pipe will transfer heat in only one direction. It is a sealed pipe that has one end higher than the other. It contains a liquid in its bottom and the gaseous vapor of that liquid in the top. Air has been eliminated, leaving only the liquid and its vapor. There are several liquids that can be used for this purpose including Freon and ammonia, but one practical and low cost choice is propane. Whenever the temperature of the liquid in the bottom of the pipe is higher than the temperature at the top of the pipe, the liquid boils, turning it to gas. As the liquid turns to gas, heat is absorbed. The gas will condense back into liquid at the top because it is cooler there, and the liquid will then run back to the bottom of the pipe. This process can efficiently transfer a lot of heat from the bottom of the pipe to the top, and it can do it with very little temperature difference between the bottom and top. Since the applications discussed here all use the pipe to transfer heat from the bottom of the pipe to the top, the fact that it will not transfer heat from the top to the bottom is important and welcome.
(See construction hints and further explanations of the heat pipe at the end of the article below)

Here are some suggested uses:

residential temperature control for hot dry areas.

In areas such as southern California, the Middle East, and in deserts, the days are hot but the nights are much cooler, particularly when the sky is clear and heat can easily radiate into space. In places such as these, any pool of water can be cooled at night and used as a source of cold water for air conditioning during the day. The process of cooling the water during the night uses no power at all because it uses a heat pipe.
This is how it works: The heat pipe will cool the pool of water whenever the water is warmer than the top of the pipe. This will happen during the night, when the outside temperature drops well below the daytime temperature.
To increase the efficiency of cooling the pool, the bottom of the pipe, where heat is absorbed, can be divided into branches that are spread near the surface of the water pool. Heat should be removed from the top of the water since cool water is denser than warm, therefore the warmest water will always be at the top. If the heat were removed from the bottom, the water at the top would remain warm and only the bottom water would be cooled. The result would be a pool with temperature stratification and reduced ability to store heat.
The top of the pipe can also be divided into branches that are thermally connected to a large radiating surface on the roof of the house or, if not on the roof, at least somewhat higher than the pool. (This is because this type of heat pipe only works if the end that is cooled is higher than the end that provides the heat.) For example, if the pool is underground, the radiating surface can be at ground level. Placing the radiator over the pool insulation can save space. The radiator should consist of metal panels coated with a material that efficiently radiates heat during the night. Copper panels that have been soldered to the heat pipe and then painted black will work effectively. If possible, the radiator panels should face the open sky to maximize the amount of heat that is radiated. The cold night air will also help cool the radiator.
The heat that is dissipated during the night will lower the temperature of the water pool so that the cold water can be used to cool the inside of the house during the day. Since the inside of the house is insulated to reduce the amount of heat that can enter from the outside environment, a modest amount of cold water can keep the house comfortably cool all day. This system only needs to use a small amount of power to circulate the cold water through radiators inside the house during the day. This power will be far, far lower than the power necessary to run an air conditioner. Note that if the water pool is above the living area in the house, then no power at all need be used as a thermosiphon can be used to circulate the cold water below the pool above the living space. An alternate system would simply use the bottom of the pool as the ceiling of the living space. Either of these systems would use no power, but would need manual control to avoid having the living area too cold. The thermosiphon would simply need a valve to shut off the water flow. The cold ceiling would need movable insulation to stop the cooling process when necessary .

Use of water for fire protection ETC

Recently, uncontrolled forest fires in California and in Australia caused the destruction of many houses and also loss of lives, because the size and speed of the fires made it impossible for the local fire protection services to protect the houses and residents.
Houses that used the cooling system described above would have a large amount of water available if needed for firefighting or dealing with temporary water shortages due to drought. When wildfires approach, residents are required to leave the area for their own safety. In addition, electrical power is usually not available. However, a house can protect itself from forest fires by use of a battery powered automatic system that senses the heat of an approaching fire and responds by spraying a large amount of water on the house and from the roof of the house to soak the house and the area around the house for about 100 feet. This system could save the house even if an uncontrolled fire destroyed the surrounding region. I do not know of any houses that had this kind of system installed, but people may wish to do so now to avoid future losses.. Fire insurance companies may encourage use of this system by offering reduced rates for houses that are protected in this way. They can also make sure that the system is properly sized and installed by requiring that the installation meet standards for functionality before qualifying for the reduced rate.
Investing in this system combined with the free or low cost air conditioning described above would definitely be a long term investment that would pay for itself by saving energy costs, and quite possibly, by saving the house itself

Creating large amounts of ice in temperate areas

In temperate areas, lakes and other bodies of water will freeze on the surface during the winter. However, the surface ice is a poor conductor of heat, so the deep water below does not freeze. If it is desired to freeze the deep water, the heat pipes can be used to conduct the heat from the deep water and transfer it to the air whenever the air temperature is below the temperature of the water.
In this way, a small lake or a disused quarry can be completely frozen and can serve as a summer source of ice or icy water for a nearby community. This can be also used for low cost air conditioning during the summer. Covering the surface of the water with an insulating blanket so that the ice will not melt too quickly during the hot days of summer will help preserve the ice.

For recreational skating, the thickness of the ice on a lake or pond can be rapidly increased to make a safe ice skating area that will be available much sooner in the winter than usual, and the thicker ice will last longer in the spring.



preserving permafrost in arctic areas.

Permafrost is found in areas where the average year round temperature is below freezing. The ground water is permanently frozen and so the ground, which is actually a very deep bog was hard enough to support heavy structures.
As a likely consequence of global warming, the permafrost in large areas of Alaska and similar places is slowly melting. This is causing major problems because the frozen ground was relied on for the support of many structures As the permafrost melts, the ground often turns into a soft bog that cannot support anything heavy. Although the permafrost does not melt quickly, as the average yearly temperature increases, it does eventually melt and structures begin to sink into the soft bog

The Trans Alaska Pipeline uses heat pipes in the support posts for the pipeline to prevent melting of the permafrost under the supports. This is successful but the heat pipes used are very expensive. The pipes that are described in this article are much less costly and can be made and installed by anyone with basic mechanical skills.

The heat pipes described here can refreeze the ground during the winter when very cold temperatures are common. If there is a heat pipe that penetrates deeply into the ground and extends above the ground, the above ground portion that is cooled by the extremely cold winter air will transfer the heat from deep underground and reduce the underground temperature around the pipe rapidly to the temperature of the air. To increase the efficiency of this process, the top of the heat pipe can be fitted with fins that help remove the heat. During the summer, the underground temperature will remain low because the pipe will not transfer heat down and the soil will insulate the subsurface frozen ground from the warm air above. The volume of the subsurface frozen region will increase over several seasons as the heat pipe continues to remove heat from deep below the surface.
The heat pipes described here are low in cost because they consist of nothing but a sealed pipe that has a small amount of propane or similar liquid in it. If the pipes are made of a metal that will not corrode, the pipes will last for many years. A large number of them can be used to protect, roads, buildings, or anything else that relies on permafrost for support.
Here is a simple technique to get the heat pipes into the frozen ground. Since the heat pipes are made from copper tubing, which is too soft to be driven into the ground directly, we can use a strong steel pipe to penetrate the ground. The steel pipe must be long enough to reach the necessary depth of the heat pipe. The pipe should have a pointed insert at the bottom end, which can be driven into the ground by the pipe. When the steel pipe reaches the depth desired, the copper tube can be inserted into the top of the pipe, and then the pipe can be extracted from the ground, leaving the pointed insert and the bottom of the copper tube both at the bottom of the hole that the pipe made in the ground. As the steel pipe is pulled out, the copper tube can remain stationery. It may be useful to pour sand down the pipe as it is being extracted so that the copper tubing will have good thermal contact with the walls of the hole made by the steel pipe. When the steel pipe is completely extracted, the copper tube will remain with one end buried as far as the steel pipe was driven, and the remainder of the length of the copper tube will be above ground and ready to be fitted with fins to help cool the ground deep below the surface. It will probably be necessary to provide some mechanical support and protection for the copper heat pipe and the heat-radiating fins near the ground surface.



Construction Hints

In order to keep costs down, the pipes should be constructed on site. A practical and economical method of construction is to use copper pipe filled with liquid propane up to the highest level where you want to absorb heat. The top of the pipe can have a common tire valve fitting to permit filling and sealing. Use a vacuum pump to remove air from the pipe then admit a pre-computed weight of propane. This weight can be found by multiplying the length of pipe that you want filled with propane by the cross sectional area of the pipe. This will give you the volume of liquid propane needed. Then multiply that volume (in liters) by 540 grams to get the weight of propane needed to fill the pipe. Start by weighing the propane tank on a scale then, using a flexible hose, start filling the pipe and stop when the scale shows that the desired weight of propane has entered the pipe. Any residual air can be removed by releasing a small amount of gas from the top of the pipe. Screwing a cap onto the valve can then securely seal the pipe. Since the propane is flammable, it would be best to keep the entire pipe outdoors so that in the event of a leak the propane would be safely dispersed to the atmosphere.
Most types of plastic pipe are unsuitable because the propane will slowly diffuse through the plastic and escape.
Propane would be suitable for use because the pressure that would be generated would be well within the capability of ordinary half to one inch copper pipe that can be assembled with sweat solder fittings using the common tin/antimony solder that is used in domestic water systems. The rated working pressure of ordinary one half to one inch copper tubing is around 500 PSI and the pressure of propane at 250 degrees F is about half that, so the heat pipe system has a good pressure safety factor. Keep in mind that the pressure in the system is determined by the temperature of the water in the pool and not by the temperature of the radiating surface at the top, so the propane pressure will never get very high. For more information about copper pipes see: http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
As for transferring a large amount of heat, this should not be a problem. Think of a common residential steam heating system. This operates with water as a working fluid but is otherwise similar. Many of these systems use a single pipe to carry the steam to radiators several floors above the boiler. The same pipe carries the liquid condensed water back to the boiler. This familiar system is capable of transferring the heat necessary to heat a house in very cold weather. It also contains nothing but liquid water and water vapor. In operation, the air has been eliminated by the automatic valves found at the radiators that vent air out of the system but close to prevent steam from escaping. If the descending liquid interferes with the rising gas, there are two symptoms that would indicate the problem. The first is that the temperature difference between the top radiator, and the heat source would increase, and the second one is that there may be audible gurgling sounds from the turbulent flow of condensate. There are two simple solutions to this problem. They are both often used in steam heating systems, the first is to use a large pipe for a single pipe system and the second is to provide a separate pipe for returning the liquid condensate to the boiler. Either of these solutions could be used in the heat pipe system described above, but will probably not be necessary because this system works slowly over a long time period and never needs to quickly transfer a lot of heat.
If the system is for use inside a residence, it would be preferable to use Freon as the working fluid to avoid any danger in case of leaking propane. This would work equally well but the cost of the Freon would be higher.

Labels: Free water chilling, fire protection, how heat pipes work, low cost air conditioning, preserving permafrost

memories of my brother

This is not a technological solution, but a more personal entry about my brother Conrad, who died May third 2010.
My Brother, Conrad OHO, made his living by modifying and repairing advanced bikes. His living space in an unheated garage exposed his values. The combination of his meticulously ordered tools and his political statements on practically every flat surface, along with the Spartan living space and lack of the "comforts of home," confirm the central driving force that guided my brother’s life.
I know that from childhood Conrad was always trying to live in a way that made the world better. We came from parents who had planned to spend their lives as missionaries in China, but WWII intervened. However, my parents did not give up on trying to fix the world, and Conrad got that passion, even though he rejected the religious part of the motivation for it.
There were times that Conrad tried to live in a commune of like minded people, but he was disappointed. He could never find one to live in with enough people who shared his values, his need for strict organization, his mechanical vision, and his way of doing things. And my brother was not good at compromise. Despite all of his efforts to join existing groups, or to start new ones, his attempts at living in a commune were unsuccessful.
But Conrad still longed for community, and he finally found a wonderful one in the people that he grew to love and trust among the bike lovers of the SF and the Marin County area. I only heard small bits of information about his community during my long phone talks with Conrad. Unfortunately, I did not know the depth of Conrad's engagement until after his death. I now see that he chose his friends well, and the mutual respect that was developed over the years is crystal clear. It makes me very happy to know that Conrad had such a wonderful group of people who shared his love of human powered transport, and who respected his mechanical elegance and his values. This community became his real family.
Conrad and I did not speak of family very much during our long phone conversations. We mostly spoke of alternative energy, politics, and nutrition. I fear that his intense interest in alternative nutrition and his avoidance of mainstream medicine did not serve him well, but there is now no way to be sure what really led to his death. I now have his autopsy report, and the doctor mentioned that, in addition to the ruptured aorta, he had hypertrophic cardiovascular disease. But, because he never got a conventional checkup, he did not know that his health was precarious. He had no insurance, and as a result, most all conventional medicine was priced at levels that he considered out of reach. As a result, he relied on his belief that if he got optimum nutrition, he would have optimum health.
Conrad did recognize that his hip was in terrible condition, but he did not want to get a hip replacement operation in this country because it would have bankrupted him. He investigated overseas operations, and he told me that he would eventually go that route if absolutely necessary. However, he first wanted to try restoring the structure and function of his hip with nutrition. He had told me that an x-ray showed very extensive damage, with no remaining cartilage and a seriously misshapen femur, so it seemed to me that the nutritional cure was hopeless. But the choice was Conrad’s and I will never know if his hip was improving because he died suddenly of a problem that he never knew he had.
After his death I met many of his close and valued community of friends and I have seen the qualities that Conrad grew to love. I understand the reasons that my brother trusted, and was trusted by this community. Even though I live far away from this community we share a love for Conrad and we share his passion for making the world a better place. I hope that we can grow close to each other over time and help to realize some of Conrad’s dreams.
Bill Isecke
There is a story of My and Conrad's growing up on a boat in the Harlem River in the Inwood section of NYC at http://gothamcenter.org/blotter/?p=96.