What is the difference between free and forced convection?
For free convection tests, the heated air rises from the surface and up the duct. For forced convection tests, a variable-speed fan draws air up through the duct and across the surface. Thermocouples measure the air temperature upstream and downstream of the surface and the temperature at the heat transfer surface.
What are the types of free convection?
There are two types of convection, and they are: Natural convection. Forced convection.
What is free convection application?
This is quintessential natural convection. Applications of this are legion, for example, cooling of electronic equipment like transformers, heat transfer in double pane windows, solar collectors, thermal hydraulics in nuclear reactors, and so on. The list is endless.
Is forced convection better than free convection?
The rate of heat transfer in forced convection is higher which can be controlled by external equipment. Therefore the system with forced convection has a higher overall heat transfer coefficient than free convection.
What is meant by free or natural convection & forced convection?
In natural convection, any fluid motion is caused by natural means such as the buoyancy effect, i.e. the rise of warmer fluid and fall the cooler fluid. Whereas in forced convection, the fluid is forced to flow over a surface or in a tube by external means such as a pump or fan.
How is heat transferred through free or natural convection?
In free or natural convection, the flow is driven by buoyant forces: hot fluid rises and cold fluid sinks because density decreases as temperature increases. The house in (Figure) is kept warm by natural convection, as is the pot of water on the stove in (Figure).
What is meant by natural or free convection?
Natural convection is a type of flow, of motion of a liquid such as water or a gas such as air, in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.) but by some parts of the fluid been heavier than other parts.
How is convection heat transferred?
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises (see Ideal Gas Law).
How is heat transferred in convection?
Convection. Convective heat transfer is the transfer of heat between two bodies by currents of moving gas or fluid. In free convection, air or water moves away from the heated body as the warm air or water rises and is replaced by a cooler parcel of air or water.
Which of the following is the example of free convection?
3. Which of the following heat flow situations pertains to free or natural convection? Explanation: Cooling of billets in atmosphere is both free and natural convection.
What is the phenomenon of natural convective heat transfer?
The phenomenon of Natural Convective heat transfer over a vertical flat plate with constant surface heat flux and the thermal boundary layer formed due to convection is to be studied. This study will be conducted via an IR camera and results obtained will be compared with numerical solution of the phenomenon.
What is the history of laminar free convection heat transfer?
The problem of laminar free-convection heat transfer from a heated verical plate in still air was first considered by Lorenz (1) in 1881, by assuming that the temperature and velocity at any point of th eflow field depends only on the distance from the plate.
What is the Nusselt number for free convection?
At Ra x = Gr x Pr ≈ 10 9 on a vertical plate there takes place the transition from a laminar to turbulent flow ( Figure 1a ). Free convection heat transfer, similar to that under forced convection, is characterized by the Nusselt number Nu = αL/λ.
What is the emissivity of a heat transfer plate?
The plate transfers heat from only one of its sides. It is assumed to be insulated on the other. equation and calculator. Fluid Properties at Film Temperature , Except for Density. (Defaults are for Air at 20 °C). To account for convection only, make the emissivity equal to 0.