The principle of the thermosyphon system is quite straightforward. As Warm water rises and cooler water falls. This natural convection current can be harnessed to circulate water through a closed system, without the need for a pump. The collector must be installed beneath the storage tank, so cold water from the tank will sink down into the collector. The warm water from the collector will rise up into the storage tank.

Thermosyphon systems are often used in solar water heating applications, as they are an efficient way to transfer heat from the collector to the storage tank.

Underlying Physics

Thermodynamics is the study of energy and work in systems that are in equilibrium or undergoing change.

The first law

With regards to the first law, thermodynamics is energy that cannot be created nor destroyed but can only be converted from one form to another.

The second law

The second law, on the other hand, is quite different. It claims that thermodynamics is concerned with the movement of energy in one direction. It says that energy will always flow from a hotter body to a colder body.

The third law

Lastly, we have the third law. This states that thermodynamics is the entropy of a perfect crystal at absolute zero is zero.

Planck’s law

I did say lastly, but Planck’s law comes at it from a different angle. It suggests that the energy of a photon is proportional to its frequency. The wavelength of radiation is inversely proportional to its frequency.

Passive Water Heating

Water thermosiphoning is the process of water circulation in a system without the need for a pump.

This can be accomplished by installing the collector beneath the storage tank, so that cold water from the tank will sink down into the collector. The warm water from the collector will rise up into the storage tank.

The thermosiphoning of water is a passive process that relies on convection currents to circulate the water.

Convection is the transfer of heat by the movement of fluids. When a fluid is heated, it expands and becomes less dense than the surrounding fluid. The hot fluid will then rise, while the cooler fluid will sink.

This convection current can be harnessed to circulate water through a closed system, without the need for a pump.

The collector must be installed beneath the storage tank, so that cold water from the tank will sink down into the collector.

The warm water from the collector will rise up into the storage tank.

Thermosyphon systems are often used in solar water heating applications, as they are an efficient way to transfer heat from the collector to the storage tank.

A thermosyphon system can also be used to circulate water in a radiant floor heating system.

In this type of system, the collector is installed below the floor and the storage tank is above the floor. The warm water from the collector will rise up through the floor, where it will radiate heat.

Close-coupled system

Close-coupled systems share the same principles as thermosyphon systems, but the collector and storage tank is usually installed next to each other, rather than with the collector below the storage tank.

In a close-coupled system, the water is circulated by a pump. The water is pumped from the bottom of the storage tank, through the collectors, and back into the storage tank.

The advantage of close-coupled systems is that they can be used in a wide range of applications, including residential and commercial solar water heating systems.

Materials:

Solar Energy

  • Insulation
  • Piping
  • Solar Collector
  • Storage Tank
  • Strong roof or other support systems
  • Water

Gravity-feed system

Gravity-feed systems utilize the same principles as thermosyphon systems, but the storage tank is installed above the collector.

In a gravity-feed system, water is heated in the collector and then flows by gravity into the storage tank.

The advantage of gravity-feed systems is that they can be used in locations where it is not possible to install the collector below the storage tank.

Gravity-feed systems are often used in commercial solar water heating applications.

Materials:

  • Insulation
  • Piping
  • Solar Collector
  • Solar Energy
  • Storage Tank
  • Strong roof or other support systems
  • Water

Active Water Heating

The active water system is water that is circulated in a solar heating system using a pump, also known as a pump system or split system.

The solar collector is usually installed below the storage tank, but can also be installed next to the storage tank in a close-coupled system.

The water is pumped from the bottom of the storage tank, through the collectors, and back into the storage tank.

Active solar heating systems are more efficient than thermosyphon systems but require more maintenance.

Active solar heating systems are often used in commercial and industrial solar water heating applications.

Materials:

  • Additional piping
  • Electrical energy
  • Electrical pump
  • InsulationSolar Collector
  • Solar Energy
  • Storage Tank
  • Water

Passive Air Exchange

A passive solar thermal heating system technique is Thermosiphon Heat Exchange (THE). Natural convection, or THE systems, relies on the movement of air or water. They employ heat pipes, also known as thermosyphons, to move thermal energy from one place to another.

A thermosiphon is a sealed container filled with a liquid that has a low boiling point, such as water or Freon. The thermosiphon is placed in contact with a heat source, such as the Sun.

The heat from the heat source causes the liquid to boil and turn to vapor. The vapor rises and expands in the sealed container, causing it to become less dense than the surrounding air or water.

As the vapor rises, it transfers heat to the air or water around it. The vapor then condenses back into a liquid and falls back down to the heat source, where the process begins again.

Thermosiphon systems are often used in solar water heating applications, as they are an efficient way to transfer heat from the collector to the storage tank.

Materials:

  • Frame
  • Glaze
  • Solar absorption plate
  • Solar collector
  • Vents

FAQs

What is thermosyphon circulation?

The Thermosiphon (or thermosyphon) is a form of passive heat exchange based on natural convection that circulates liquids and vapors without the need for a mechanical pump.

How does an ammonia thermosyphon work?

Heat exchangers are used with Thermosiphon oil cooling systems, which circulate oil without the need of a pump via pressure and gravity. A heat exchanger, expansion tank, and circulating lines make up the system.
The heat exchanger is placed in the engine compartment and connected to the engine’s oil supply and return lines. The expansion tank is located above the heat exchanger.
As the engine warms up, the oil expands and rises to the top of the heat exchanger. The expanding oil creates pressure, which pushes the oil through the circulating lines and into the expansion tank.
As the oil cools, it contracts and falls back down to the bottom of the heat exchanger, where the process begins again.

Does a vertical thermosyphon reboiler require a condenser?

A vertical thermosyphon reboiler does not require a condenser. The vapor generated in the reboiler will rise up through the floor, where it will radiate heat.

What is the difference between a thermosyphon system and a close-coupled system?

A thermosyphon system utilizes the natural convection of air to circulate the water. A close-coupled system utilizes a pump to circulate the water.

What does a reboiler do in distillation?

A reboiler is a heat exchanger that is used to heat the bottom of a distillation column. The reboiler transfers heat from a heat source, such as steam, to the distillation column. The heat causes the liquid in the bottom of the column to vaporize. The vapor rises up through the column and condenses on the packing material, where it is collected and removed from the system.

What is the difference between a reboiler and an evaporator?

Evaporators separate materials based on their boiling point, as opposed to reboilers, which separate materials based on weight.

About the Author

Passionate about helping households transition to sustainable energy with helpful information and resources.

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