Hi @heriyanto, thanks for posting on the forum and welcome to the SimScale Community 
Please share a project link so we can have a closer look at your simulation. Here’s a guide teaching you how: Guide to Clear and Understandable Forum Posting
From your explanation, a few comments:
- Yes, since you’re simulating a heat exchanger, the CHT v2 analysis type should be the way to go (here’s a tutorial that might help)
- Many times, simulation errors can be caused by a faulty/unprepared CAD models. Please take a look:
- Meshing is also a hot source of errors:
Cheers
Igor