What does natural circulation mean?
- Definition from Corrosionpedia What Does Natural Circulation Mean? Natural circulation is the ability of a fluid in a system to circulate continuously, with the difference in density being the only driving force. In another way, natural circulation is caused by convection currents which result from the uneven heating of the water in a boiler.
How does water flow in a natural circulation system?
In a natural circulation unit the water tubes are connected to a loop, Fig. 4.3. Heat is applied to one leg, called the raiser tube, where the water–steam mixture flows upward. Denser saturated water flows downward in an unheated leg called the downcomer.
What is natural circulation in boilers?
What Does Natural Circulation Mean? Natural circulation is the ability of a fluid in a system to circulate continuously, with the difference in density being the only driving force. In another way, natural circulation is caused by convection currents which result from the uneven heating of the water in a boiler.
What is natural circulation solar water heating?
Natural circulation solar water heating system is the most widely used in developing countries, and it is also one of the most popular solar thermal utilization technology products in the world. This system uses fluid (water) as the heat-carrying medium.
What is natural circulation of water?
Natural circulation is caused by the density difference between saturated water and heated water partially filled with steam bubbles. In a natural circulation unit the water tubes are connected to a loop, Fig. 4.3. Heat is applied to one leg, called the raiser tube, where the water–steam mixture flows upward.
What is natural circulation system?
The circulation of the coolant in the reactor coolant system without the use of the reactor coolant pumps. The circulation is due to the natural convection resulting from the different densities of relative cold and heated portions of the system.
Which boiler has natural circulation of water?
In natural circulation steam boilers the circulation of water is by convection currents, which are set up during the heating of water. In most of the boilers there is a natural circulation of water the fundamental principle of which is based on the principle of Thermosiphon.
What is natural circulation loop?
Natural circulation loops (thermosyphons) are flow systems heated from below and cooled from above, such that the heat sink is higher than the heat source. This specific configuration creates a density gradient which generates the driving force.
How does a natural circulation boiler work?
In natural circulation boilers, the circulation of water depends on the difference between the density of an ascending mixture of hot water and steam, and a descending body of relatively cool and steam-free water. The difference in density occurs because the water expands as it is heated, and thus, becomes less dense.
What is natural circulation evaporator?
Natural circulation in an evaporator is caused by the thermal difference between the heating medium and the liquid. This thermal change is called "thermo-siphon action". Sufficient heat must be available to provide the necessary thermal difference to cause circulation.
What is natural and the forced circulation in boiler?
A forced circulation boiler is a boiler where a pump is used to circulate water inside the boiler. This differs from a natural circulation boiler which relies on current density to circulate water inside the boiler.
How does natural convection occur?
Natural convection arises from temperature differences among air parcels, or heat transfer at surfaces (i.e. surface-to-air temperature difference). In the absence of forced convection, natural convection becomes the only means of air mixing inside enclosed spaces.
What is natural circulation?
Natural circulation is the circulation of fluid within piping systems or open pools that is due to the density changes caused by temperature differences. Natural circulation does not require any mechanical devices to maintain flow.
What are the conditions for natural circulation?
Conditions Required for Natural Circulation 1 A temperature difference exists (heat source and heat sink exists). 2 The heat source is at a lower elevation than the heat sink. 3 The fluids must be in contact with each other.
What is the heat sink in a pool?
The heat sink is the bulk of the water in the pool. Water at the bottom of a fuel assembly absorbs energy generated by the assembly. The water increases in temperature and decreases in density. Gravity pulls cooler (more dense) water into the bottom of the assembly displacing the warmer water.
How to take advantage of the natural movement of warm and cool fluids?
To take advantage of the natural movement of warm and cool fluids, the heat source and heat sink must be at the proper elevations. The two areas must be in contact so that flow between the areas is possible. If the flow path is obstructed or blocked, then natural circulation cannot occur.
How does water absorb energy?
As water travels up the length of the assembly, it absorbs more energy. The water becomes lighter and lighter being continuously forced upward by more dense water moving in below it. In turn, the cooler water absorbs energy from the assembly and is also forced to rise as natural circulation flow continues.
Why does thermal driving head cause natural circulation?
The thermal driving head that causes natural circulation is due to the density change caused by a temperature difference. In general, the greater the temperature difference between the hot and cold areas of fluid, the greater the thermal driving head and the resulting flow rate. However, it is good practice to keep the hot fluid subcooled ...
Is it possible to have natural circulation in two phase flow?
However, it is good practice to keep the hot fluid subcooled to prevent a change of phase from occurring. It is possible to have natural circulation take place in two-phase flow, but it is usually more difficult to maintain flow. Various parameters can be used to indicate or verify natural circulation is occurring.
What is natural circulation?
Natural circulation is the ability of a fluid in a system to circulate continuously, with the difference in density being the only driving force. In another way, natural circulation is caused by convection currents which result from the uneven heating of the water in a boiler. It may be either free or accelerated, ...
What is a natural circulation evaporator?
Natural circulation evaporators are based on the natural circulation of the product caused by the density differences that arise from heating. Natural circulation evaporators are necessary in effluent treatment plants, and in both the chemical and pharmaceutical industry.
How do boilers work with natural circulation?
In a boiler with free natural circulation, the generating tubes are installed almost horizontally, with only a slight incline toward the vertical. When the generating tubes are installed at a much greater angle of inclination, the rate of water circulation is greatly increased .
Why is water less dense?
The difference in density occurs because the water expands as it is heated, and thus, becomes less dense. In most boilers there is a natural circulation of water, the fundamental principle of which is based on the principle of thermosiphon. In a boiler with free natural circulation, the generating tubes are installed almost horizontally, ...
