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bobo5195 · 12-21-2005, 08:47 AM

bill there are reasons why automotive peeps use their wording. Also consider adding noise to price/reliability/ features

Pass = row in WC wording.

In automotive/ engineering notation; An extra pass is when the output from the rad (hot water) is fed back through the radiator again, creating an effective second rad in series with the first. An extra row would refer to thickening the rad by adding another virtual rad behind the first using a second row of fins. This create parallel flow paths and is akin (although not exactly equal performance wise) with doubling the thickness of the rad.

Keeping the two distinct is important because adding an extra row is a cheap and effective means of getting a little extra performance on the water side at the expense of a vast decrease in air side performance as the rad is a lot thicker. Two passes drastically improve overall efficiency as they make much better use of the air coming through the rad. They degrade water side flow rate but give the air a much better temperature gradient to work with.

You can have much more than 2 passes but it is generally not optimal, cost and air side performance wise. If memory serves me right power stations use many (7 or more) in some cases as efficiency is very important and capital costs and space are not important.

12-21-2005, 08:47 AM	#11
bobo5195 Cooling Savant Join Date: Aug 2005 Location: uk Posts: 400	Re: Thought you guys would like this.... bill there are reasons why automotive peeps use their wording. Also consider adding noise to price/reliability/ features Pass = row in WC wording. In automotive/ engineering notation; An extra pass is when the output from the rad (hot water) is fed back through the radiator again, creating an effective second rad in series with the first. An extra row would refer to thickening the rad by adding another virtual rad behind the first using a second row of fins. This create parallel flow paths and is akin (although not exactly equal performance wise) with doubling the thickness of the rad. Keeping the two distinct is important because adding an extra row is a cheap and effective means of getting a little extra performance on the water side at the expense of a vast decrease in air side performance as the rad is a lot thicker. Two passes drastically improve overall efficiency as they make much better use of the air coming through the rad. They degrade water side flow rate but give the air a much better temperature gradient to work with. You can have much more than 2 passes but it is generally not optimal, cost and air side performance wise. If memory serves me right power stations use many (7 or more) in some cases as efficiency is very important and capital costs and space are not important.