I worked in similar kind. please attache picture or 2D of your geometry, so that i can discuss briefly!

There is an analysis by Amir Karimi for helical condensers which may be of some use.

Karimi, A., "Laminar Film Condensation on Helical Reflux Condensers and Related Configurations," Int. J. Heat Mass Transfer, Vol. 20, 1977, pp. 1137-1144.

work as 3D model. make a helical geometry (the pipe will be wall, one side velocity inlet the other pressure outlet), the inner surface of the helical (not pipe) will subjected to a constant heat flux (steam generated) the challenge is to select the surface wich will be subjected to constant heat flux (you can divide the geometry from the start to be 2 zones )

We can develop the 3D Model  for helical tube by using Gambit Software and analyse the model heat transfer process by using ANSYS Fluient 

@ Osama A. Sharaf

  I am thankful for giving me valuable guidance. I have done with geometry in two zones. I am facing problem in calculating amount of heat generated by steam in heat pipe. It will helpful if you give some information regarding  heat pipe calculation or some link related to heat pipe

In this model problem overall heat transfer is considered and it is significant parameter. I suggest you to simulate all components. You can use constant heat flux approach but this problem little bit complicated. The conjugate heat transfer is also important such a this problem. Moreover pipe thickness is so important. You can develope this 3D geometry using gambit, solidworks, ansys-designer or such these softwares. If I understand your geometry correctly, your geomerty is not complicate. You should draw a big pipe including solid parts (thickness is known, thermo-physical properties is known). Then draw a helical pipe around it (also having thickness). You may draw the helical pipe with some tricks, for instance the contact arae can be increase to obtain good mesh quality. But the heat is to be transferred from this area, so becarefull while adjusting this part.  

May it be easy. 

   I have tried these things. There is no heat transfer from solid pipe to helical tube. I am unable to give boundary condition in such situation. Heat is not conducting from condenser to helical tube

So I think I did not understand the geometry. I understand tat, there is a big steam column (Pipe with flowing steam inside). And there is a helical pipe around that column and water flows through in this helical pipe. and steam condentate due to the heat rejection (from steam to the water part). 

And for this problem, (as I understand case) overall heat transfer depends on steam side heat transfer coefficient, water side heat transfer coefficient and conduction coefficient between steam wall and water wall (that are united). So these resistances are serial not parallel. so heat must be conducting from condenser to helical tube.

Or I did not understand the geometry.

do you want to simulate heat pipe?

if yes : model it ( I think its easy to modeled, if you have any problem send me) and subjected it to one of the following

1- constant heat flux have the same value of sun radiation and take into account the effect of the slope and the clearness and so one.

2-make a heat flux profile and subjected the model to it (you can make an EXCEL sheet for that profile or UDF)

note 1: the heat pipe will also divided into two zones upper and lower, the upper is that which will subjected to the radiation the lower can assumed as insulated wall

note 2: the target calculation or result is the heat flux from the heat pipe bulb.

all the above methods will give you a frame to start your work

if not :  that meant for me, that you want to calculate released heat analytically.  I will try to send you some useful papers 

I hope that answer help you

Simulation involves two situations

which we are all aware. If you want to understand behaviour of transport phenomenon in both solid and fluid systems use solid fluid interface. But As condensor is subjected to isothermal heat rejection at one end and varying temperature gradients at other end of the surface ( along radial directions), we can neglect the solid interface effect as we select a material of High Thermal conductivity. It is more appropriate to understand the rate of condensation.

never start solving situations on ANSYS. Solving HX / Condensors on ANSYS looks more confusing. Start with simple hand calculations or you can write a MATLAB program ( or any structered  Language interface) and estimate desired parameters such as consensation rate, pressure rise ( which is more important) , cooling fluid mass flow rate with pre-determined asssumptions and existing calculation in 1D or 2D flow situations.

Then in real time scenario, your assumptions do not hold good at a given geometry and given flow rate. This is area of criticality. Focus this area and apply CFD techniques to achieve these conditions.

Calculations for condensors and their design variables are available in may books but you can also look at a book by name " design of thermal systems by STOECKER"

Thanks 

The conduction is not taking place in your case.The only reason is the helical tube's surface is not coupled with the condenser surface of the heat pipe.This is a typical conjugate heat transfer problem.Since you are modeling in fluent,after creating the geometries,form them as a single part This ensures coupling.

It is amusing to hear that you aren't concerned about the challenging modeling involved in heat pipe simulation using fluent due to the sluggish nature of VOF model.

Osama A. Sharaf can you help me i am simulating a micro heat pipe in fluent

but using VOf + evaporation and condensation only one problem is there the pressure in Condenser reaches very low upto -6000 pa and even more less i have tried with varying heat flux but of no any help from your side is deeply appreciated

Thanks & Regards

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