The temperature of the air adjacent to the hot object is higher, thus its density is lower. As a result, the heated air rises . This movement is called the natural convection current.
What do you mean by natural convection?
Natural convection is a mechanism of heat transportation in which the fluid motion is not generated by an external source . Instead the fluid motion is caused by buoyancy, the difference in fluid density occurring due to temperature gradients.
What is meant by natural or free convection?
Natural convection, known also as free convection is a mechanism, or type of mass and heat transport , in which the fluid motion is generated only by density differences in the fluid occurring due to temperature gradients, not by any external source (like a pump, fan, suction device, etc.).
What is natural convection with example?
Natural convection: When convection takes place due to buoyant force as there is a difference in densities caused by the difference in temperatures it is known as natural convection. ... Examples of forced convection are using water heaters or geysers for instant heating of water and using a fan on a hot summer day.
Why the heat transfer coefficient in natural convection is less than forced convection?
and subjected to free (natural) convection or forced convection. In general heat transfer coefficient in natural convection is far less compared to forced convection. In natural convection, the heat is taken away slowly by buoyancy force and in forced convection, the heat is taken away fastly by velocity.
What are 4 examples of convection?
- Breeze. The formation of sea and land breeze form the classic examples of convection. ...
- Boiling Water. Convection comes into play while boiling water. ...
- Blood Circulation in Warm-Blooded Mammals. ...
- Air-Conditioner. ...
- Radiator. ...
- Refrigerator. ...
- Hot Air Popper. ...
- Hot Air Balloon.
How do we use convection in everyday life?
Everyday Examples of Convection
radiator – A radiator puts warm air out at the top and draws in cooler air at the bottom. steaming cup of hot tea – The steam you see when drinking a cup of hot tea indicates that heat is being transferred into the air. ice melting – Ice melts because heat moves to the ice from the air.
What is the reason for free convection?
The driving force for natural convection is gravity . For example if there is a layer of cold dense air on top of hotter less dense air, gravity pulls more strongly on the denser layer on top, so it falls while the hotter less dense air rises to take its place. This creates circulating flow: convection.
Why is natural convection important?
The phase change process is mostly driven by natural convection. ... The influence of natural convection becomes more important for designing water used LHTES systems , because the density inversion point of water is very close to its melting temperature.
What are the types of convection?
There are two types of convection: natural convection and forced convection . Natural convection is produced by density differences in a fluid due to temperature differences (e.g., as in “hot air rises”). Global atmospheric circulation and local weather phenomena (including wind) are due to convective heat transfer.
What are the three main sources of convection?
The primary sources of thermal energy for mantle convection are three: (1) internal heating due to the decay of the radioactive isotopes of uranium, thorium, and potassium ; (2) the long-term secular cooling of the earth; and (3) heat from the core.
What is convection definition and example?
Convection is the transfer of heat by circulating it through air or liquids . ... A heat source at the bottom of the balloon heats the air molecules around the flame, and those molecules rise. Warmer air is less dense than cold air, so as the warm air rises the molecules spread out.
What are the applications of convection?
- Car engines are cooled by convection currents in the water pipes. ...
- Land and sea breezes are caused due to convection currents.
- Rising air over the land are convection currents and are used by glider pilots to keep their gliders in the sky.
What is difference between natural and forced convection?
The key difference between natural and forced convection is that in natural convection, the motion of the fluid is influenced by natural means whereas, in forced convection, the motion of fluids is influenced by external means.
What is meant by forced convection?
Forced convection is a mechanism or a type of transport in which fluid motion is generated by an external source (such as a pump, fan, suction device, etc.
What is the relation between convection heat transfer coefficient?
Mechanism of Forced Convection
The fluid motion enhances heat transfer (the higher the velocity the higher the heat transfer rate). The convective heat transfer coefficient h strongly depends on the fluid properties and roughness of the solid surface, and the type of the fluid flow (laminar or turbulent) .
