rough surface of heat exchanger tube improve heat transfer enhancement. during work consider about surface roughness too.

I think the paper of Bergles et al. is a very good reference on the heat transfer enhancement methods. 

See the attached file. 

you can contact to me to do some theoretical work on heat transfer enhancement of nanofluid flow. For that you may follow my research profile. 

 1. Fluid modification - nanofluids

2. Improve heat exchanger material thermal conductivity 

3. Geometrical modification such as rough surface, or protrusions

For your case i recommend you start with geometrical modification as you must be familar with this cocept.  After getting some results, then introduce nanofluids. Both methods are proven to improve heat exchange. A combination of both is rare, hence wil make a good research for you. Also keep in mind how much pressure losses you can allow in your design.

Good luck

Faizal

For heat transfer surfaces in heat exchangers  I recommend an old bok.

"Compact Heat Exchangers", by William Kays and A.London, Stanford University.

It's a good beginning.

Then it's good to know if you work with recuperative or regenerative heat exchangers.

I guess that you are closer to the recuperative type og heat exchangers.

Please follow the link of slide share given below for more details.

http://www.slideshare.net/smilingshekhar/heat-transfer-enhancement 

I also recommend the book

"Compact Heat Exchangers", by William Kays and A.London, Stanford University.

You also have to study the flow conditions as well as the friction phenomena.

Dear Lakshman

I advise you to read the paper of  G. Huminic and A. Huminic '' Application of nanofluids in heat exchangers: A review'' , (2012). this paper summarizes the important published articles on the enhancement of the convection heat transfer in heat exchangers using Nano fluids.

Regards

Nabil

Enhancement of Heat transfer in conduction- convective environment  depends on the fluid, fluid flow behaviour and Thermal environment, apart from geometry of the Heat exchanger. So, Nano fluid flow characteristics . properties to be evaluated. 

enhancement also involves creating turbulence in both cold and hot fluid environments which enhances the U value. You can use twisted alumnium strips in the internal geometry which creates artificial swirl.

Please follow  " Heat transfer " by dewitt and incorperera 

the new edition has given more examples and good practical orientation of heat exchange process.

Heat transfer in the heat exchanger can be improved by increasing the heat transfer area.

The heat transfer expressed by Colburn number can be expressed as a function of the Reynolds number. My experience is that 1500

A good book to find Colburn and Fanning factors is "Compact Heat Exchangers" by William Kays and A.L.London, Stanford University. There you can find data to compare your simulation results with.

Concerning CFD I recommend to start with the attached paper by City University.

I Think CFD in the laminar region as well as the turbulent region can be OK. However, around Re= 2000. I.e. the zone where you go from laminar to turbulent flow is tricky to simulate, 

Dear Sir,

There are two types of Heat transfer enhancement; Passive Technique; that no power applied to increase the heat transfer. Active Techniques; with power applied to increase the heat transfer. Moreover, there is a compound techniques which mix the two methods above.

Best regards

Enhancement of Heat transfer in Heat exchangers is obtained by increasing turbulence. I recommend to use some twisted plates to be inserted at entry which will create swirl and enhance heat transfer. Easy and best way.

To increase turbulence at the inlet usually has a small effect.

The turbulence must be generated inside the heat transfer plates.

My experience at least approx. at every distance = 5 *dh, where dh=hydraulic diameter. A tighter distance only causes extra pressure drop, so called 'overkilled' heat transfer plates. Crossed undulated elements is a typical overkilled element.

Furthermore it collects dirt when used in Heat Exchangers for Oil- Coal-fired power stations.

This my experience from development of heat transfer plates for large rotary heat exchangers, type Ljungström.

Yes nanofluid and baffles are the best method to enhance the heat transfer

Try to study the effect of turbulent nanofluid in tube with a combination between corrugated tube and twisted tape insert.

Article Thermo-hydraulic performance of nanofluids flow in various i...

When I worked with mixing of gases at AGA company (today belonging to Linde group) we find out the bending of tubes was a very efficient mixer. Consequently that also means increasing the turbulence and heat transfer. But also increasing the pressure drop.

There are several papers investigate the heat transfer improvement inside heat exchangers , you can use different shapes of fins mounting on the walls or artificial roughtness .

http://www.abbesazzi.com/wp-content/uploads/2011/05/2004_HMTJ_Dellil_Azzi_Jubran.pdf

heat exchanger

This article presents a good overview of available technologies

Article The Heat transfer Enhancement Techniques and Their Thermal P...

And this article should also be read when designing advanced heat exchanger technologies Article What Exactly is the Nusselt Number in Convective Heat Transf...

This is general question as heat exchangers may be shell and coil type or free convection heat transfer in various type of enclosers. Therefore it is better to specify the type of heat exchanger then we can help with what kind of enhancement type can be used ether passive or active, nanofluid or porous media etc..