# Evacuated Tube with Steam

• aluminumholds
In summary, the individual is building an evacuated tube solar oven and is using half inch type K copper pipes with water as a heat transfer fluid. They are putting a vacuum on the tubes and want to have the water in vapor form to superheat the steam and achieve temperatures higher than 212F. Their highest pressure can be 120 psi according to Copper.org, so they want to know the amount of water needed to not exceed this pressure. The maximum temperature they are looking to operate at is 400F, but they are considering limiting it to 340F to stay below 120psi and keep a liquid phase. They also mention needing saturated steam to capture the latent heat of water condensing.

#### aluminumholds

Hey everyone,

I'm building my first evacuated tube solar oven and I seem to run into a problem I can't get around. First of all, I am going to use half inch type K copper pipes with water as a heat transfer fluid. I am putting a vacuum (100 mbar or so) on the tubes to lower the boiling point of the water. The tubes are about 10 feet long, giving me a volume of 23.56 in^2. I'm doing this in order to have the water in vapor form most of the time in order to superheat the steam and achieve temperatures higher than 212F. If my highest pressure can be 120 psi, according to Copper.org which describes pressure rating for brazed joints using saturated steam, what is the amount of water I need to add to the pipes in order not to exceed that pressure?

What is the maximum temperature you are looking to operate at?

BoB

rbelli1 said:
What is the maximum temperature you are looking to operate at?

400F would be my max temperature in the heat pipes.

might be helpful. I don't know how to calculate for your situation. I just know that the temperature is important.

If you keep the vapor pressure below your 120psi then any amount of water is OK. Could you limit the temperature to 340F? If I am reading the linked tables correctly you then stay below 120psi at any volume. You would also keep a liquid phase at all times.

BoB

rbelli1 said:
might be helpful. I don't know how to calculate for your situation. I just know that the temperature is important.

If you keep the vapor pressure below your 120psi then any amount of water is OK. Could you limit the temperature to 340F? If I am reading the linked tables correctly you then stay below 120psi at any volume. You would also keep a liquid phase at all times.

Thanks for the table BoB, they'll definitely be useful. As of know I don't have a way to limit temperatures...however I've done some more reading and know that I need to have saturated steam, not superheated steam; to capture the latent heat of water condensing.

## 1. What is an evacuated tube with steam?

An evacuated tube with steam is a type of solar thermal collector that uses a series of vacuum-sealed tubes to collect and store solar energy in the form of steam. The tubes are made of borosilicate glass and are coated with a special material to enhance their ability to absorb sunlight and convert it into heat.

## 2. How does an evacuated tube with steam work?

The evacuated tubes are filled with a small amount of water, which is heated by the sun's rays. As the water heats up, it turns into steam and rises to the top of the tube, where it is collected and stored in a central chamber. This stored steam can then be used to power a variety of applications, such as heating water or generating electricity.

## 3. What are the benefits of using an evacuated tube with steam?

There are several benefits to using an evacuated tube with steam. Firstly, it is a highly efficient way to collect and store solar energy, as the vacuum-sealed tubes prevent heat loss. Additionally, the system is modular, meaning that more tubes can be added as needed to meet increasing energy demands. Finally, evacuated tube with steam systems are low maintenance and have a long lifespan.

## 4. Is an evacuated tube with steam suitable for all climates?

An evacuated tube with steam is most effective in areas with high levels of sunlight, but can still be used in colder climates. The vacuum-sealed tubes are able to retain heat even in colder temperatures, and the system can be designed with additional insulation to further improve its performance in colder climates.

## 5. How does an evacuated tube with steam compare to other solar energy systems?

An evacuated tube with steam is considered one of the most efficient and reliable solar energy systems currently available. It outperforms traditional flat-plate solar collectors, and can even be used in areas where traditional solar panels are not feasible due to limited space or shading. However, it may have a higher upfront cost compared to other systems, but the long-term energy savings make it a worthwhile investment.