![]() | ||
Heat transfer enhancement via a rotationally osciallting cylinder openfoam
Heat transfer enhancement is the process of increasing the effectiveness of heat exchangers. This can be achieved when the heat transfer power of a given device is increased or when the pressure losses generated by the device are reduced. A variety of techniques can be applied to this effect, including generating strong secondary flows or increasing boundary layer turbulence.
Contents
- Heat transfer enhancement via a rotationally osciallting cylinder openfoam
- Principle
- Internal flow
- Helically Coiled Tube
- References

Principle

During the earliest attempts to enhance heat transfer, plain (or smooth) surfaced were used. This surface requires a special surface geometry able to provide higher

The heat transfer rate for a two-fluid counterflow heat exchanger is given by


In order to better illustrate the benefits of enhancement, the total length 'L' of the tube is multiplied and divided in the equation

Where
The subscripts 1 and 2, describe the two different fluids. The surface efficiency is represented by
1. Size reduction. maintaining the heat exchange rate
2. Increased
3. Reduced pumping power for fixed heat duty. This will require smaller velocities of operation than the plain surface and a normally not desired, increased frontal area.
Depending on the objectives for the design, any of the three different performance improvements can be used on an enhanced surface, and using any of the three mentioned performance improvements it is fully possible to accomplish it.
Internal flow
There are several available options for enhancing heat transfer. The enhancement can be achieved by increasing the surface area for convection or/and increasing the convection coefficient. For example, the surface roughness can be used to increase
Helically Coiled Tube
The coil spring insert may enhance heat transfer without turbulence or additional heat transfer surface area. A secondary flow is induces the fluid creating two longitudinal vortices. This could result, (in contrast to a right tube) in highly non-uniform local
Maximum fluid temperatures near the tube wall are present when the fluid is heated, and because the heat transfer coefficient is strongly depended of angle (
The secondary flow:
The coil pitch S has negligible influence on the pressure drop and the heat transfer rates. For the helical tube, the critical Reynolds number to the onset of turbulence is,
where
The delays on the transition from laminar to turbulent state are strongly dependent on strong secondary flows associated with tightly wound helically coiled tubes. The friction factor for fully developed laminar flow with
and
and
For cases where
and can be evaluated from the correlation,
The correlations for the friction factor in turbulent state are based in limited data. Increased heat transfer due to the secondary flow is not significant in turbulent state constituting less than 10% for