What is external forced convection how does it differ from internal forced convection can a heat transfer system involve both internal and external convection at the same time give an example?
If the fluid is forced to flow over a surface, it is called external forced convection. If it is forced to flow in a tube, it is called internal forced convection. A heat transfer system can involve both internal and external convection simultaneously. Example: A pipe transporting a fluid in a windy area.
What is external convection?
Convective heat and mass transfer is the process of heat and mass transport through fluid flow. In external forced convection, the fluid has at least one side that is not bounded by a solid surface. Flow over a flat plate is a classic example of external flow.
What is internal forced convection?
. Liquid or gas flow through pipes or ducts is commonly used in heating and cooling applications. The fluid in such applications is forced to flow by a fan or pump through a tube that is sufficiently long to accomplish then desired heat transfer.
In which system the heat transfer is is to be analyzed as forced convection?
A floor heat register is part of the HVAC system that creates forced convection in a home. 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.
What is the physical significance of the Nusselt number?
A Nusselt number of value one represents heat transfer by pure conduction. A value between one and 10 is characteristic of slug flow or laminar flow. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 100–1000 range.
What is the physical significance of Biot number?
The Biot number is the ratio of the internal resistance of a body to heat conduction to its external resistance to heat convection. Therefore, a small Biot number represents small resistance to heat conduction, and thus small temperature gradients within the body.
How do you find heat transfer coefficient of convection?
Common units used to measure the convective heat transfer coefficient are:
- 1 W/(m2 K) = 0.85984 kcal/(h m2 ° C) = 0.1761 Btu/(ft2 h ° F)
- 1 kcal/(h m2 ° C) = 1.163 W/(m2 K) = 0
Which type of convection has the highest heat transfer coefficient?
The convective heat transfer coefficient h is usually a positive, experimentally determined value. There are two types of convection: natural convection and forced convection….Thermal Convection.
| Type of Convection | Convective Heat Transfer Coefficient h | |
|---|---|---|
| Btu/(h ⋅ ft2 ⋅ R) | W/(m2 ⋅ K) | |
| Air, forced | 2–100 | 10–500 |
How does convection heat transfer occur?
When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection. The fluid above a hot surface expands, becomes less dense, and rises.
Can you explain convection as a kind of heat transfer?
Convection is the transfer of heat by the movement of a fluid (liquid or gas) between areas of different temperature.
What is an example of convection current?
Convection currents are present in the air– A good example of convection current is the warm air that rises towards the ceiling in your house. The process happens as the warm air is said to be less dense than that of the colder air. Another good example of convection current is wind.
What is the process of convection currents?
Convection currents form because a heated fluid expands, becoming less dense. As it rises, it pulls cooler fluid down to replace it. This fluid in turn is heated, rises and pulls down more cool fluid. This cycle establishes a circular current that stops only when heat is evenly distributed throughout the fluid.
What are the effects of convection currents?
Magma is the molten rock below the crust, in the mantle. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. These currents cause the movement of the tectonic plates that make up the earth’s crust.
How do convection currents affect weather?
During convection, cooler water or air sinks, and warmer water or air rises. This movement causes currents. These currents move water all around the earth, bringing warm water to cooler areas and vice versa. This redistributes thermal energy and causes changes in the weather.
What would happen if convection currents stopped?
Answer 1: If all convection currents on Earth stopped that would be a natural disaster. The amount of heat which the sun radiates at us sets the temperature of the Earth’s surface. So if convection completely stopped the high and low temperatures would force people and animals to move away from the poles and equator.
What will happen if ocean currents stop?
The ocean currents carry warmth from the tropics up to these places, which would no longer happen. If the currents were to stop completely, the average temperature of Europe would cool 5 to 10 degrees Celsius. There would also be impacts on fisheries and hurricanes in the region.
What would cause the convection current of earth to stop?
If Earth’s interior cools down, the convection currents in the mantle will stop.
When would a convection current stop?
Without heat, the convection currents will eventually stop when all of the material has reached the same temperature. v Checkpoint What is convection? Figure 10 Heat from Earth’s mantle and core causes convection currents to form in the asthenosphere.