A solar evacuated tube with a heat pipe is the most demanding product in the market. This type of solar hot water system has become more efficient. These heat pipes and vacuum tubes are not new names in the market; they have been used in other electronics products.
Both technologies make excellent and high-end amplifiers for the solar water system.
So, now we will discuss comprehensively how these two technologies work in the solar water heating system? So, let’s start with what is a heat pipe?
The Composition of the Heat Pipe Solar Collectors
Heat Pipe vacuum tubes consist of a
- Solar collector
- Water storage tank
- Central control unit
- Flow meter
- Pipes and fittings and valves.
Heat Pipe Evacuated Tube Collectors
These tubes are sealed and made with copper to increase the efficiency of heating water in extremely cold climates.
The main advantage of Heat Pipe Evacuated Tube Collectors is that this system has a unique dry connection between the manifold and the absorber plate, making the installation much easier than with direct flow collectors. Also, the other main advantage of a heat pipe evacuated tube is that if any tube breaks or is damaged for some reason, the vacuum becomes lost, and the individual tube and only certain tubes can be exchanged without emptying or dismantling the entire system.
This flexibility makes its best solar heating system worldwide and is also ideal for closed-loop solar designs as the modular assembly. That offers easy installation and the ability to easily expand by adding as many tubes as you want.
Construction of Solar Evacuated Vacuum Tube
A solar Vacuum Tube or also called an evacuated tube. An evacuated vacuum tube constructed with Borosilicate glass with low iron properties will help to throw a higher amount of solar radiation than ordinary glass. This borosilicate glass is very sturdy and strong. You may resample it the same way a thermos is made. The evacuated Vacuum tube is made of two glass layers: inner glass tube and outer glass. Inside the inner and outer layer, the air has been removed or “evacuated” to form the vacuum.
Due to the no air inside chances so, there is no way the heat may transfer to either side.
The inner glass layer coated with dark patented multiple selective coating layers such as (aluminum, copper, and nitrogen) compressed and enhanced the heating process. The dark coating helps to consume high amounts of radiation from the sun and is responsible for absorbing and transferring the sun’s rays efficiently. When heat absorbs, there is no chance of heat escaping and making these tubes 97% efficient.
Once the coating layers absorb sun rays, heat energy moves to a center heat pipe through an aluminum fin that wraps around the inside of the vacuum tube, making full contact with the coating you choose.
How is the Heat Pipe Process Done?
The Heat Pipe is fully sealed and designed based on a small fluid working process where the fluid’s temperature rises and evaporation begins. The heat pipe is fixed In the middle of an aluminium fin which is made of copper. The heat pipe was designed as a long slim tube installed in the middle of the vacuum tube and reached the end of the tube. This heat Pipe has a small amount of liquid inside the pipe and a small vacuum tube which is different from a real evacuated vacuum tube.
In a small vacuum tube, the liquid boil at the
86 F temperature approximately. The heating process becomes effective and efficient through this main principle behind heat pipe technology.
When the heat Pipe warms, the liquid inside the pipe also heats up quickly and turns to steam. The stream rises up and reaches the condenser bulb (where its heat is transferred to the solar heating fluid through a heat exchanger inside the manifold). When steam closes down its energy, its trunk back to the liquid, so how that is processed is repeated in a cycle.
This process of converting a liquid into a gas and back into a liquid again continues inside the sealed heat pipe as long as the sun shines.
The all-copper heat Pipe is attached to the copper sleeve within a sealed manifold, and heat is indirectly transferred to the heating liquid through conductivity. The manifold works independently and ensures no chance of heat pipe leakage, even if the heat pipe is removed.
These manifolds are insulted, and a small sleeve that a temperature sensor is inserted. With this method, the temperature is controlled by a digital control system, and you can enjoy your hot water whatever you want in just a second. In this way, the internal temperature of the heating fluid turns off the heating process at night when the sun goes down, and the manifold will cool off and signal the pump to stop the process.
What is the role of a condenser?
All heat processing is done under the vacuum by the fluid. When sun ray heat comes as input that works like the evaporator, that heat boils the fluid at a high temperature and pushes the fluid vapour to the cold water area ( cold water pipeline). The cold water pipes coupled to a heat sink are known as “the Condenser”. The fluid gives up its latent heat and condenses back to a liquid, and is again absorbed in the wick structure. The wick structure then passively pumps the fluid back to the evaporator. These processes worked like a cycle, and the entire process output at a low temperature depends on the length of the heat pipe.
HEAT PIPE Demonstration
The heat pipe efficiency rate increases with the copper road. The copper road and heat pipe both are coated with Thermochromic paint. When it’s heated, it changes its colour, and it transfers heat. So, here it’s important to learn.
What is a copper rod?
Copper is also called a thermal conductor, which is extremely strong and able to conduct 400 watts per meter K. When the copper rod is heated, it changes colour and transfers heat. The fluid vaporizes and transfers, and the heat pipe rapidly thermalizes and has a very consistent temperature for the entire heat pipe.
The solar vacuum tube is more effective in hot water supplies than the flat plate hot water solar system. These are less expensive than flat plates, and that is why they are in demand in the market today.
The selective coating of vacuum tubes and the heat pipe is what makes these solar heat collectors superior to any other collector on the market. The special selective coating helps to change the shortwave sun rays into long-wave heat radiation and is approximately 94% efficient, and only 6% of the sun’s energy is lost!
The demand for the heat pipe and the vacuum tube system are higher due to efficiency than open vacuum tubes but also come at a significantly higher price with the added copper materials.
What is a Direct Flow Evacuated Tube?
The direct flow evacuated tube system, also called “U” pipe collectors. This hot water heating system is different from the other. This consists of two heat pipes that are fixed in the middle of the tube. One pipe works as an input cold water flow pipe, and another acts as an output as the return pipe ( hot water). The bottom spaces are connected to Each other with a “U-bend”, that’s why the name implies U-bend.
The purpose of using U-Bend Heat pipe systems is that they are specially designed To produce more energy-efficient than heat pipe designs. Because in the heat pipe system, there is no heat exchange between fluids. This system is expensive and efficient for all-purpose use.
What is a Non-Pressurized Heat Tube?
This type of heat tube is designed based on an open vacuum tube. In this method, the groundwater is heated internally by the sun’s rays. This process is just like the thermos.
The hot water is lighter than the cold water when the heated water rises up and runs to the tube where it fills the collector. The cold water becomes heavier. That’s why they stay in the bottom of the vacuum tube and then replace the heated water and reheated by the sun. This method is known as thermo-siphoning. This is a very simple hot water supply and eco-friendly because it does not involve a copper piping heating system.
Advantages of Non-Pressurized Heat Tube
- It’s less expensive than copper pipe vacuum tube
- The best hot water system for swimming pool
- Best suitable for domestic purpose
- No regular maintenance required
- Easy to install
- Efficient performance in sunny climates
- The process is controlled by atmospheric pressure.
- Not suitable for extremely cold climates
What is a Pressurized Heat Tube?
These types of heat tubes are more effective in increasing the heated water for an extended period. This works like the open solar vacuum tube, except water does not run into the vacuum tube. Furthermore, This system was designed with a hollow copper heat pipe, making the pressurized system more expensive and efficient than other hot water systems. As we mentioned above, the copper heat pipes are excellent thermal conductors, and the copper coating helps conduct heat efficiently. The inside of the heat pipe contains pure water residing within a vacuum. In this vacuum, the water boils at less than 30 degrees temperature, and when the water is heated, it becomes lightweight and rises vapour rapidly to the top into a condenser tube.
Furthermore, These condenser bulbs will transfer the heat to the manifold that is coupled with it.
Using a condenser bulb is only to maintain a temperature of 200 Degrees Celsius or more. This system is very helpful in increasing temperature and translates to higher efficiencies using multiple tubes. The condenser is fixed into a copper heat transfer manifold and can withstand up to116 PSI of pressure.
Advantages of Pressurized Heat Tube System:
- Higher efficiency rate
- Long-time heated water
- Best suitable for both domestic and commercial use
- Works better in cold climates
- Maintain high temperature with multiple usages of faucet
Features and benefits of Heat Pipe:
- Higher quality with extremely effective for rapid payback
- No further maintaining requirements
- Warranty Up to 20 years lifetime
- It fits units by most manufacturers
- No external power require
Heat Pipe Selective Designed Options:
- Control for economizer
- Stainless steel casings
- Corrosion protection coatings
Where is the heat pipe solar system the Best Suitable application?
The heat pipe solar system is best suitable for Any reheat application. They perform excellently with higher efficiency rates and heat the maximum water in a shorter time. They are affordable and compact in size. That’s why they can be used in Schools, Laboratories, Hospitals, and industrial and Office Buildings.
SELECTING A HEAT PIPE WORKING FLUID
The efficiency of a heat pipe evacuated vacuum tube depends on evaporation and condensation of the working fluid. The performance of their high effective thermal conductivity can be as high as 100,000 W/m K.
During the heat pipe process, the working fluid is vaporized in the evaporator and condensed in the condenser, thus transferring heat.
The first step in selecting a heat pipe is only to choose those systems That must be in saturated conditions. Both liquid and vapour involved perform excellent operating temperature range for a copper/water heat pipe is 25°- 150°C.
Structure Of Heat-Pipe Vacuum Tube
Heat pipe evacuated vacuum tube designed strongly and quality control system. That system ensures its cleaning water production and the creation of a good quality heat pipe. If any impurities are found inside the heating element, it will affect the performance. This is designed with clean, high-quality copper material, and copper is the purest element that only contains small amounts of oxygen and other elements. If copper contains a high amount of oxygen or other elements, it will form a pocket of air at the top of the heat pipe. That will also affect the performance of the heat pipe from the high point to the condenser end.
Furthermore, Each evacuated vacuum tube heat pipe is tested for heat transfer performance and exposed to 300℃ temperatures before being approved for use.
The freeze protection was also tested, and each pipe performed excellently on that test. The testing based on the boiling point has been reduced to only 25-30℃, and the freezing point is the same as water at sea level, 0℃. The reason for selecting this lowest temperature is that the heat pipe is fixed in the middle of the vacuum tube; overnight temperatures below -40℃ will not cause the heat pipe to freeze.
While the Flat-plate collectors in that freezing point will be damaged, unfortunately, the water used in heat pipes sometimes freezes in cold areas where the temperature is extremely low overnight, but it freezes in a controlled way that does not cause swelling of the copper pipe.
Advantages of heat pipe solar collectors
- It can absorb and transfer solar energy more efficiently.
- It will be able to control operating temperature.
- Prevent from overheating
- Long life span
- Best domestic water heating systems.