Natural or Forced Convection. Connect with us. Related Items. Steady State Flow. Fluid Structure Interaction. Transient State Flow. Aero Dynamics Study. Heat Transfer. Often this becomes places where certain parts of the house are warmer and certain parts are cooler. Forced convection creates a more uniform and therefore comfortable temperature throughout the entire home. This reduces cold spots in the house, reducing the need to crank the thermostat to a higher temperature, or putting on sweaters.
Creating forced convection is as easy as turning on a fan. Air is heated in the furnace and pushed through the house by the blower , which is a fan inside the ventilation system. This blower outputs a specific quantity of air, and this output air flow is divided among all of the output grills also called heater vents in a home. With help from natural convection this air then travels through the room, warming the room as it rises to the top by natural convection and slowly falls down to the floor as it cools.
The system of heating the air and pushing it throughout the house to warm it then begins again. How the treated air gets to the output vents makes a difference, as the structure of the ductwork can create resistance to airflow at elbows, divisions, or places where the ductwork size changes. This change in turn effects how well this forced air system can heat a home since they are all sharing the output flow of air from one source —the furnace.
Therefore, properly planning out the ducting is important. Wherever possible, this guideline should be followed to ensure that the air that is being forced out by the furnace heats the house properly.
In addition, ensuring output vents are not covered by furniture or installed behind curtains ensures that the warm air output by the furnace is able to circulate throughout the room. It is a common misconception that the more air that flows from a fan—or the more a fan "pushes" the air— the greater the effects of forced convection will occur, due to the large amount of heated or cooled air being pushed out by the fan.
However, this is not entirely true. Part of how air moves through a home or other building has to do with the pressure and temperature that exists in the room before more air is pushed through. For example, if a room has a cold spot and the goal is to heat the room evenly, the pressure change in the area between the cold and warm spots, known as transitional "warm" area, factors into how well a fan will be able to move warm air to the cold area. If the pressure drop in this warm area is higher, there will be a lower flow rate of air into the cold section of the room, making it more difficult for the fan to push warm air into this section.
This phenomenon is known as the pressure drop over the heat sink and it can be summed up easily by saying that it is more difficult for a fan to push warm or cool air through a region between two areas of different temperatures that also has a large pressure difference across its boundary. Therefore, the stream of gas or fluid needs to be adjusted accordingly. This is often accomplished by the addition of an artificial source to increase the flow of the liquids or gas.
The speed of the convection stream is also important. In general, faster streams are more efficient. Wind chill is a good example of this efficiency.
A person standing in heavy wind will cool faster than one in stagnant air, because the warm skin is being exposed to a greater volume of cold air within a given time. Difference in temperature also affects the rate at which forced convection occurs. Surfaces exposed to a convection current with a much higher temperature will heat faster.
Heat convection slows as the object approaches the temperature of the current. Thicker fluids and gases are usually more effective at heat transfer. This is problematic, because many thicker gases and fluids require more force to maintain effective speed in a convection current.
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