[AT] Airflow calculations of perforated metal for radiator screens
Dennis Johnson
moscowengnr at outlook.com
Fri Jun 18 22:07:14 PDT 2021
All,
There is one more factor than just “open area”. When a fluid (air) flows around something the fluid on the edge moves slower than the fluid in the center of the opening. This is more common in flow in pipes, but I am sure that it is a factor in flow across a screen. Imagine each open hole as a miniature pipe. I do not even want to think about how to calculate this, but that does not mean it does not exist. I am not sure how much of a factor this is.
In filters there is a term “filter cake” where the trash from the fluid being taken out reduces the flow through the filter. On my Zero Turn mower I had a condition that built up 1/4” to 3/8” layer of grass clippings that caused my mower to overheat. The first 2 hours of mowing was fine, and something changed and the grass started building up and plugged air flow the last few hours. The openings in the guard were about 3/16” wide and 1 1/2” long. The grass nearly stopped air flow.
The point is you want something that blocks air flow positioned where you can see it and clean it, and not in the core of the cooler. If you can have a large enough area where grass and junk come to the filter slow enough so the “suction” does not hold it in place and gravity allows it to fall you are doing good. Having the “screen” horizontal (like a vertical shaft engine air inlet) does not allow gravity to try and let the trash fall away.
Trying to remember to look at the air screen every 30 minutes is something I need to work on more. I also should try and make a vertical cylindrical screen about 3” high to raise the factory guard/screen so it gives more area for air flow, and lets gravity pull trash down.
Dennis
Sent from my iPad
> On Jun 19, 2021, at 6:17 AM, szabelski at wildblue.net wrote:
>
> Cecil,
>
> Made an assumption of 23 gauge for the screen a wire (.023 dia) and came up with 37% blockage. That’s about 56% of the blockage of the .188 holes. So you would almost double the air flow.
>
> Carl
>
>
> ----- Original Message -----
> From: szabelski at wildblue.net
> To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
> Sent: Fri, 18 Jun 2021 21:52:56 -0400 (EDT)
> Subject: Re: [AT] Airflow calculations of perforated metal for radiator screens
>
> Cecil,
>
> Sorry I’m late to the discussion, been on the road for two days and this is the first chance to go through my emails.
>
> If you’re looking for .188 holes that maximize air flow, why not just use 1/4 door screen? The “holes” are .25, but the spacing between “holes” is relatively small. You can stagger two pieces of screen so that the .25 opening is divided into four openings that are roughly .125 x .125. You would have more openings with less blocked space. The .188 hole equates to roughly .028 sq inches. The .125 square opening equates to roughly .016 sq inches, a smaller opening, but you would have so many more “holes” that you would gain a lot.
>
> If you make an assumption on the diameter of the wire used in the screen, you should be able to determine total blockage per square inch of screen easily by multiplying the diameter of the wire by .125, then multiply by 4 (4sides to a square), then multiplying by half the number of “holes” in a sq inch, roughly 32 (only half of the total holes since you will have shared sides between adjacent squares which you would have already accounted for).
>
> Good luck.
>
> Carl
>
>
> ----- Original Message -----
> From: Cecil Bearden <crbearden at copper.net>
> To: at at lists.antique-tractor.com
> Sent: Fri, 18 Jun 2021 08:46:22 -0400 (EDT)
> Subject: Re: [AT] Airflow calculations of perforated metal for radiator screens
>
> Steve:
>
> I remember all that and had to work with it in hydrology and flow
> calculations for the last 40 years. However for the last 10 I have had
> a computer program available that does all that stuff and all I have to
> do is plug in some numbers. Back when I was approving plans for new
> construction, I could look at an applications, the spillway size and the
> location and ddo it in my head....
> Cecil
>
>> On 6/18/2021 4:55 AM, Stephen Offiler wrote:
>> I haven't done flow calculations in a long, long time, and Fluids was
>> not among my favorite subjects back in school... so with that said, my
>> gut feeling is that Mark's 56% blockage is probably somewhere in the
>> right ballpark but dependent on factors like whether the airflow is
>> laminar or turbulent, maybe Reynold's numbers.... now I'm just spewing
>> stuff I learned 40 years ago. Mostly to say, there might not *be* a
>> good way to calculate this outside of a lab with a flow bench; really,
>> the thing to do is try it, and take measurements. No idea if you can
>> see high-side pressure while on the road but I doubt it. Any readouts
>> for coolant or trans temperatures?
>>
>> SO
>>
>>
>> On Fri, Jun 18, 2021 at 1:03 AM magreer67 <magreer67 at gmail.com
>> <mailto:magreer67 at gmail.com>> wrote:
>>
>> Wouldn't that be 56% blockage and 44% open to flow through?
>> Mark Greer
>>
>>
>>
>> Sent from my Verizon, Samsung Galaxy smartphone
>>
>>
>> -------- Original message --------
>> From: Cecil Bearden <crbearden at copper.net
>> <mailto:crbearden at copper.net>>
>> Date: 6/17/21 11:34 PM (GMT-05:00)
>> To: at at lists.antique-tractor.com
>> <mailto:at at lists.antique-tractor.com>
>> Subject: Re: [AT] Airflow calculations of perforated metal for
>> radiator screens
>>
>> The .188 diameter staggered pattern gives .444 sqin hole area over
>> a 1 sq in area. So I guess it would result in a 44% blockage.
>> However it would be tabout 5 inches from the grille and then the
>> A/C condensor sets about 6 inches back from that. I think there
>> would be sufficient room to pull air from above and below. It
>> just may cause some additional drag at high speeds. I think I
>> will try it and make it easy to remove in case it blocks too much
>> airflow. I have to do something. Time and ability to work on
>> this stuff gets more valuable daily...
>> Cecil
>>
>>> On 6/17/2021 7:48 PM, Brad Loomis wrote:
>>> The 455 diesel lawn tractor I use at work has a pull out screen
>>> ahead of the radiator. I'm not there so I can't measure it. But I
>>> will try tomorrow and report back. It does keep the foxtails,
>>> thistle, mustard, and whatever else I kick up out of the radiator.
>>> Brad
>>>
>>> On Thu, Jun 17, 2021 at 5:23 PM Cecil Bearden
>>> <crbearden at copper.net <mailto:crbearden at copper.net>> wrote:
>>>
>>> I had to wash the A/C condensor and radiator out on my 2011
>>> Chevy truck
>>> yesterday before I could make a trip to pick up some auction
>>> items. I
>>> put the gauges on my a/c system and it showed 35 low and 350
>>> high.
>>> before I did anything I went to the water hose and got it
>>> down to 150
>>> pretty quickly on the high side. The amount of bugs was
>>> crazy. I will
>>> have to remove the radiator and condensor to get them clean
>>> as there is
>>> no room to get anything in the front or behind the fan. I
>>> have one of
>>> those heavy cowcatcher style grill guards in the front. This
>>> truck has
>>> about 170K miles and has made 3 trips to Alaska, so it may
>>> have more
>>> bugs than usual, but the bugs and thi8stle seeds are terrible
>>> here and
>>> getting worse. I want to put a piece of perforated metal
>>> behind the
>>> grill guard to catch the bugs. If it cuts the air down, it
>>> can still
>>> come in between the screening and the grill. I don't think
>>> it will make
>>> a lot of difference in the amount of air entering the
>>> radiator, but
>>> maybe catch the bugs and fluffy crap in the air... When we
>>> figure
>>> airflow into a home, we cut the flow through a window in half
>>> when a
>>> screen is used. I am looking at a peforated metal with
>>> holes .188in
>>> in diameter and offset centers so it gets the most holes per
>>> square
>>> inch. Does anyone have any experience with this type of
>>> screening or
>>> have a formula to determine if it will cut the airflow too
>>> much. I think
>>> the area behind the grill guard and the grill is wide enough
>>> to keep
>>> from cutting down the air flow. Traveling down the road at
>>> 60mph it may
>>> deflect some air around the grill instead of through..
>>>
>>> I just don't want to have to remove this radiator again. I
>>> have to use
>>> a stepladder to work on the d&%$^d thing it is so tall. It
>>> is stock for
>>> that year, but the manufacturers want to see how far the
>>> drivers can
>>> jump to get into a pickup nowdays. I remember a 63 and 66
>>> chevy 1/2 ton
>>> pickup we worked out of on the farm every day. Hauled 20
>>> head of cows
>>> in a bumper trailer with no brakes into OKC Stockyards.
>>> Loaded 60
>>> bushels of wheat to haul to the elevator when the lines were
>>> long and
>>> the grain truck had not returned. Now, I have a 3/4 ton that
>>> I have to
>>> jump into or pull myself in with the steering wheel and 30
>>> bushels of
>>> rye in the bed causes it to squat, with twice as much tire
>>> under it than
>>> the old ones had.. It doesn't ride all that much better,
>>> just cooler
>>> when the A/C works. OK rant off.....
>>>
>>> Cecil
>>>
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