i have a dissertation in ünversity.I will model panel radiator in star-ccm+.How should i model this panel radiator? plz guide me to model this tell me which boundary condition will i use?

There are several approaches for this problem. The first and simplest would be to treat the radiator as a porous media. Flow across the radiator would simply be the transfer of heat from the radiator to the fluid at a variety of heat fluxes and temperatures, validated from experiment. However, for a dissertation, I would not recommend this approach because it does not do justice to the abilities of the code, nor to your time spent on the dissertation. This is a good, quick solution to arrive at engineering results.

Instead, the approach that would be more physical, more complimentary to your final product (dissertation), and more taking full advantage of capabilities of code would be to model all three portions of this problem. That is, internal fluid in the radiator, the solid of the radiator, and the fluid passing over/around the external region of the radiator. Make it even more physical by including other solids nearby. The complete radiator and the heat exchange from internal fluid through solid to external fluid would be very interesting. However, it may not be needed. It could be more productive to start simply and develop the problem using one loop of the radiator and find the results for this case. If it is accomplished quickly and accurately, then expand the model to include more geometry.

In STAR-CCM+, for conformal mesh between fluid-solid-fluid, the default condition may appear to be adiabatic. It isn't. Instead, the software has been coded to recognize that fluid-solid heat transfer will be going between these regions. To be sure, run simulation with adiabatic and another with an HTC or temperature condition set. If BCs are correct, you will see the resulting heating transfer to the fluid the same either way.

The hardest part of this problem is the cad and making sure you have conformal mesh.

Should i model the radiator that only one part of which? or all of which?

Perhaps describe your radiator. It has fluid region that is moving heat away from or to somewhere else, yes? It has a solid that contains that fluid region. And there is a fluid around the solid containing the internal fluid. If you are working with a different radiator please describe. Otherwise, create a connected, conformal mesh of these three regions with the latter being bounded by a farfield condition, i.e. not concerned about it. The others are walls. There could be multiple inlets/outlets, depending on how many fluids, probably two. The solid is the thickness of the radiator wall, probably only a few cells needed.

can i send you my panel radiator? can you model this panel radiator? because i wasnt succeded by talking

Can you post labeled screenshots on a website somewhere? Then we will see what kind of radiator you are working with and may be able to provide additional suggestions.