Both of these are text files that you could just directly open in Excel if you really wanted to (for the .CEL file, the formatting wouldn't be great, but it's not meant to be).
The question is why you would ever want to do such a thing. Excel is a program for spreadsheets. It's generally not great with math and is an all around clunker with non-spreadsheet tasks. There is inevitably a better tool for doing whatever it is that you want to do with these files. I'll add that if you want to do any sort of analysis on these files in Excel, do yourself a favor and simply don't do that. Excel is simply not cut out for such tasks.