Contents
- 1 Can you mix forced and free convection?
- 2 What are the three special cases in combined free and forced convection?
- 3 Which dimensional number is used in force convection heat transfer?
- 4 What is the difference between forced convection and free convection?
- 5 What are the applications of forced convection?
- 6 What is the mechanism of forced convection?
- 7 How are dimensionless groups related to forced convection?
- 8 Which is the characteristic length of free convection?
Can you mix forced and free convection?
Mixed convection flows, or combined forced and free convection flows, arise in many transport processes in engineering devices and in nature.
What are the three special cases in combined free and forced convection?
Three special cases that have been studied extensively correspond to buoyancy-induced and forced motions:
- Assisting flow. The buoyant motion is in the same direction as the forced motion.
- Opposing flow. The buoyant motion is in the opposite direction to the forced motion.
- Transverse flow.
What are the dimensions parameters used in forced convection?
Dimensional Analysis for Forced Convection
| S. No. | Variable / Parameter | Dimensions |
|---|---|---|
| 2 | Dynamic viscosity of fluid | ML-1T-1 |
| 3 | Fluid Velocity | LT-1 |
| 4 | Thermal conductivity of fluid | MLT-3 θ-1 |
| 5 | Specific heat of fluid | L2T-2 θ-1 |
Which dimensional number is used in force convection heat transfer?
So, the Nusselt number may be viewed as the ratio of convection to conduction for a layer of fluid. If Nu=1, we have pure conduction. Higher values of Nusselt mean that the heat transfer is enhanced by convection.
What is the difference between forced convection and free convection?
Convection is classified as natural (or free) and forced convection depending on how the fluid motion is initiated. 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.
What is the 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 are the applications of forced convection?
Forced convection is typically used to increase the rate of heat exchange. Forced convection is often encountered for designing or analyzing pipe flow, flow over a plate, heat exchanger, Computer case cooling and so on.
What is the mechanism of forced convection?
Forced convection is a special type of heat transfer in which fluids are forced to move, in order to increase the heat transfer. This forcing can be done with a ceiling fan, a pump, suction device, or other. Many people are familiar with the statement that “heat rises”.
Can a mixture of forced and natural convection be used?
Simply adding or subtracting the heat transfer coefficients for forced and natural convection will yield inaccurate results for mixed convection. Also, as the influence of buoyancy on the heat transfer sometimes even exceeds the influence of the free stream, mixed convection should not be treated as pure forced convection.
The fluid properties needed for calculating the values of dimensionless groups pertaining to forced convection are generally evaluated at the bulk temperature, unless stated otherwise. Flow passages for fluids in forced convection take many forms.
Which is the characteristic length of free convection?
1. Free Convection: L is Characteristic length and it is the height of the plate or cylinder ha is average heat transfer coefficient. L is Characteristic length and in this case it is the diameter of the cylinder ha is average heat transfer coefficient. For horizontal hot surface facing upward or cold surface facing downward.
What is the mechanism of forced convection heat transfer?
Mechanism of Forced Convection Convection heat transfer is complicated since it involves fluid motion as well as heat conduction. The fluid motion enhances heat transfer (the higher the velocity the higher the heat transfer rate).