If you have a higher pair vs a lower pair the higher pair is 80% probable pre flop.
So in this spot if your ran it twice or ran it 3 times
What would the math be on twice and three times if the
Lower pair misses the 1st turn and river.

It depends which cards come out on the first run.
e.g. If it's AA v 66 and the aces make an unnecessary set on the first run, and the board is all high cards, then 66 will have more chance of winning the second run, since it still has 2 outs, has less chance of being oversetted, and more chance of making a random straight.

But it's academic. You don't ask to run it twice or three times after you've lost the first one. You run it two or three times when you've got your 18% equity at the start. With 18% equity, I think the most common outcome is to lose all three runs, but there's a fairly high probability of winning one out of three.
Variations of your question have been asked in the theory forum and also the probability forum.