Table of Contents
- 1 How does boundary layer affect heat transfer?
- 2 What is the role of thermal boundary layer in convective heat transfer?
- 3 Why are heat transfer coefficients for natural convection much less than those for forced convection?
- 4 What is the relationship between velocity boundary layer and thermal boundary layer?
- 5 Is heat transfer coefficient function of temperature?
- 6 What is the relation between convection heat transfer coefficient and natural convection and forced convection?
- 7 What is a boundary layer in heat transfer?
- 8 Where is the thermal boundary?
- 9 What is the convective heat transfer coefficient of laminar flow?
- 10 What does the rate of heat transfer through a layer represent?
How does boundary layer affect heat transfer?
A significant effect of thickness of the separated boundary layer both on dynamic and thermal characteristics of the flow is shown. In particular, it was found that with an increase in the boundary layer thickness the recirculation zone increases, and the maximum heat transfer coefficient decreases.
What is the role of thermal boundary layer in convective heat transfer?
The thermal boundary layer, δt, is defined in a similar way to the velocity boundary layer, but using temperature instead. At the surface the velocity of the fluid is zero and so there is no fluid motion. At the surface, energy transfer only takes place by conduction (note 1).
Why does heat transfer coefficient increase with temperature?
So if velocity of flow is increased, heat transferred will increase. You can use Newtons law of cooling for a body which states- Heat tranferred= hA(Temp difference). Here heat tranfer has increased but temp diff and area remain same hence Heat tranfer coefficient must have increased.
Why are heat transfer coefficients for natural convection much less than those for forced convection?
Why heat transfer coefficient for natural convection is much lesser than that of forced convection? (NOV-DEC 13] The convection heat transfer coefficient will usually be higher in forced convection and lower in free convection since heat transfer coefficient depends on the fluid velocity, and free convection involves …
What is the relationship between velocity boundary layer and thermal boundary layer?
If the Prandtl number is less than 1, which is the case for air at standard conditions, the thermal boundary layer is thicker than the velocity boundary layer. If the Prandtl number is greater than 1, the thermal boundary layer is thinner than the velocity boundary layer.
Does heat transfer coefficient depend on temperature?
Factors influencing the heat transfer coefficient However, the temperature distribution in the fluid is different. This in turn influences the heat transfer coefficient, despite possible identical temperature differences. The heat transfer coefficient is therefore also dependent on the direction of heat flow.
Is heat transfer coefficient function of temperature?
An empirical relationship is then developed, giving the coefficient of heat transfer as a function of time, temperature and interfacial pressure.
What is the relation between convection heat transfer coefficient and natural convection and 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.
What is the relation between the natural convection and forced convection heat transfer coefficients?
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 |
What is a boundary layer in heat transfer?
In the theory of heat transfer, a thermal boundary layer occurs. The layer of air over the wing’s surface that is slowed down or stopped by viscosity, is the boundary layer. There are two different types of boundary layer flow: laminar and turbulent.
Where is the thermal boundary?
A thermal boundary is the dividing line between “inside” and “outside” You don’t want to be paying to heat and cool spaces you don’t live in, right? Your attic and your garage, for example, should therefore likely be considered “outside” your thermal boundary.
How does the thickness of the thermal boundary layer depend on distance?
The thickness of thermal boundary layer is thus proportional to with increase in distance from the leading edge, the effects of heat transfer penetrate further into the free stream and the thermal boundary layer grows.
What is the convective heat transfer coefficient of laminar flow?
Typically, the convective heat transfer coefficient for laminar flow is relatively low compared to the convective heat transfer coefficient for turbulent flow. This is due to turbulent flow having a thinner stagnant fluid film layer on the heat transfer surface.
What does the rate of heat transfer through a layer represent?
The rate of heat transfer through a layer corresponds to the electric current, the thermal resistance corresponds to electrical resistance, and the temperature difference corresponds to voltage difference across the layer.
What is the H value of the heat transfer coefficient?
Values of the heat transfer coefficient, h, have been measured and tabulated for the commonly encountered fluids and flow situations occurring during heat transfer by convection. Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow.