This difference in temperature around the match is caused by effect of heat on the density of air. Hot air is less dense than cool air and will rise leaving the cooler air below. As the warm air rises, a pattern of air movement is formed called a convection current.

When the pipe is heated on fire the water neat the bottom surface of pipe becomes hotter i.e. at higher temperature and becomes less dense and hence move up and the colder water which is more dense comes down and convection current sets up. So; water inside the pipe can heated by conduction and free convection.

Convection is the process of heat transfer by the bulk movement of molecules within fluids such as gases and liquids. The initial heat transfer between the object and the fluid takes place through conduction, but the bulk heat transfer happens due to the motion of the fluid. It happens in liquids and gases.

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.

Convection-cooling is sometimes loosely assumed to be described by Newton’s law of cooling. Newton’s law states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze.

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.

Example of situation with conduction, convection, and radiation

• Conduction: Touching a stove and being burned. Ice cooling down your hand.
• Convection: Hot air rising, cooling, and falling (convection currents)
• Radiation: Heat from the sun warming your face.

In natural convection, the fluid motion occurs by natural means such as buoyancy. Since the fluid velocity associated with natural convection is relatively low, the heat transfer coefficient encountered in natural convection is also low. Mechanisms of Natural Convection. Consider a hot object exposed to cold air.

Natural convection is a method of heat transfer in which the motion of the fluid is influenced by natural means. Forced convection is a method of heat transfer in which the motion of the fluid is influenced by external means.

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.

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.).

Free convection, or natural convection, is a spontaneous flow arising from nonhomogeneous fields of volumetric (mass) forces (gravitational, centrifugal, Coriolis, electromagnetic, etc.):

Reynolds number

Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection. Liquids and gases expand when they are heated.

The most common example is boiling water in the pot or in the kettle , heating water at the bottom then hot water rises and cooler water moves down to replace it , causing a circular motion . another one is ( Heat Air Balloon) – A heater inside the balloon heats the air so the air moves upward .

Uses of convection – example

• 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.

Which of the following is an example of convection? A hair dryer is drying up your hair. When the AC or heater changes the temperature. When a car engine turns hot after being turned on.

Conduction is the transfer of thermal energy through direct contact. Convection is the transfer of thermal energy through the movement of a liquid or gas. Radiation is the transfer of thermal energy through thermal emission.

Q. What is the definition of CONVECTION? When heat transfers through waves. When heat transfers from objects that are touching.

1 : the action or process of conveying. 2a : movement in a gas or liquid in which the warmer parts move up and the cooler parts move down convection currents. b : the transfer of heat by convection foods cooked by convection — compare conduction, radiation.

A microwave oven cooking a meal.