I'm looking for an equation to estimate the area required for a tube/fin heat exchanger array (5 staggered tubes). The tubes are electrically heated, the only moving fluid is the air flowing perpendicular to the tube/fins. I have the temperatures, air flow, etc. Thank you.

You mean this, or was there something more you are looking for? This assumes you have the data specifications for your heat exchanger, calculating these values is somewhat more complicated but is also pretty well documented online(having just gone through a good deal of it myself :/.)

Calculate the heat transfer coefficient, which means you must probably calculate the Nusselt number, and/or some other numbers. It's very different for turbulent or laminar flows, but since you have all the numbers you can decide yourself what applies.

 

Then calculate the area.

 

I normally do not approach it as a single equation, but if you really feel like it, you can integrate the whole lot into 1 equation.

Also, if you already have the heat transfer coefficient, then you might just need this equation.