does any one on her know about boat bilge fans/blowers??

[gaz_moose]

I have seen one or two boaty type threads on here so figured it was worth an ask,,

Basically I want to build a small heater for my track car to demist the screen, but im limited for space.
I have a small mocal oil cooler that I can use for the core and my plan was to use a bilge pump for the fan.

http://www.ebay.co.uk/itm/ATTWOOD-1...071556?hash=item33a8c8ea44:g:KOMAAOSwgQ9V6vua

Google suggests that these fans are quite noisy although I cant find a decibel reading, so how noisy is noisy??

my grand plan was something like this
http://www.ebay.co.uk/itm/Revotec-R...063104?hash=item566b572e80:g:-UwAAOSw7ThUfQ4N

with the fan mounted in the trunking a bit further away pushing air through the radiator.

these fans are rated at 120CFM but ive no idea of a car heater fans CFM ratings on any speeds??

so does that sound like its going to work?

 

[Fazerruss]

Have you seen the heaters from T7 design?

http://www.t7design.co.uk/index.php/heating/3-5kw-lightweight-heater.html

<<<< My car also short on space so will end up with one of their offerings fitted to pass IVA and make it useable in winter.

 

[normspanners]

I was planing a simililar design using a old mocal rad but was going to use two computer type fans to strap to it, to circulate the heat it was mainly to get heat up to the screen for damp nights on road rallies. I was going to drill two holes in bulk head and just push the threaded mocal fittings through, use o rings either side of the steel under the hydraulic fitting nuts so as it tightens home it locates and mounts itself .

 

[Pete.]

I have a pure aluminium intercooler core left over from my bike's charge cooler that could be used as a very compact heater rad. I think it's the same as used in the Mocal except mine is 350-400mm long. You could pipe the coolant through it and just blow air over the fins.

It's one of these, but longer as these were all cut down.

 

[gaz_moose]

I was planing a simililar design using a old mocal rad but was going to use two computer type fans to strap to it,

ebay adverts suggest that computer fans only kick out about 30CFM so I think the hot breeze they produced would only end up clearing a couple of inches from the bottom of the screen.
I did buy 1 of these years ago when I had an old transit to help get the ice off the inside of the screen and it was a total waste of time as it didn't get very hot and not much wind came out of it.it would demist an area the size of a football.
http://www.ebay.co.uk/itm/DC-12V-20...024359?hash=item259c0f1627:g:ZfQAAOSwyZ5Uqlph

your mounting method seems to be pretty much the same as mine. my turbo water lines run along the bulkhead so I planned to Tee into the return line. remote cooling the hottest thing in the engine bay would also be dead good and stuff.



ive scoured the internet for small heaters and I just wont have the space for some universal jobbie

 

[normspanners]

http://www.frozencpu.com/products/1...m_2000RPM_High_Speed_Fan.html?tl=g36c435s1104 1

http://www.frozencpu.com/products/1...m_2000RPM_High_Speed_Fan.html?tl=g36c435s1104
couple of eg that are very quiet and move well over 100cfm each that would be top side of 200cfm but virt silent

 

[gaz_moose]

good shout. thank you, I will get on and investigate some more.

 

[GW8IZR]

Those type of fan commonly known as axial fans are extremely poor at pushing air against a back pressure. Even simple filters will cut the flow rate down to a fraction of their free air rate. A centrifugal fan known often known as a snail blower is more suited to pushing air along a duct or round corners and through a vent.

Sometimes its helpful to measure the flow of an existing fan, maybe for comparison. You can mock up your air system in cardboard as the air won't know the difference. A simple technique is to use a black bin liner which can be taped across the fan or proposed duct outlet. Measure the volume of the bin liner and save that information, thats your 'cubic feet' - deflate the bag and get ready with a stop watch or just count if its not hyper critical. Turn on the fan and time how long it takes to fill the bag. If it takes 10 seconds to fill your 5 cubic feet bag you know its flowing 30 cubes a minute. If you make changes to the duct such as making it bigger or fitting a filter or other restriction you can measure what change you made for real - not a guess.

 

[drjim]

I tried cheapo solutions in my track car, electric jobbies off ebay and even considered chopping up the original heater box to make it smaller (until I remembered I had skipped it). T7 design one does exactly the job, ordered all the bits from them so it all fits together fine. Not 100% cheap but definitely the best solution.

 

[normspanners]

Those type of fan commonly known as axial fans are extremely poor at pushing air against a back pressure.

They do push air through a cpu cooler and a mocal is not that restrictive his problem is space a snail body is quite large to hide and if it is just to clear screen they may work the other plan could be to just used air ducted from the front of the car, then at least you will be getting fresh air change but thats not good when raining you will get more damp than dry.
Or? duct air from the front in a dry place and find a spot at the rear that forms a vacuum as the car goes through the air, it will then draw air out of the cabin and draw fresh air in through from the front as long as it is ducted through the mocal it will push the hot air up and over the screen?

 

[GW8IZR]

They do push air through a cpu cooler and a mocal is not that restrictive ....

No.. really they don't :-) and I have spent a lot of time cooling stuff with fans :-)

 

[normspanners]

This is the inside of one from a t7 type heater 3.5kw looks like an axial to me

 

[GW8IZR]

OK No axe(ial) to grind here, the cfm drops like a stone with the slightest restriction. If you use a bigger fan to compensate then you can get some flow back.

That fan you showed has a static pressure of nearly 3/4 inch whereas the ones you linked to have a whopping 3mm of head

Just trying to stop the OP wasting his money but we all have that privilege :-)

 

[normspanners]

from http://www.16vminiclub.com/showthread.php?t=34276 guys used t7 type heater in a mini now I was proposing using two similar sized fans side by side pushing through an old mocal oil cooler so in theory should get twice the heat output air flow ??

 

[GW8IZR]

No , not unless the fans can generate enough pressure to move the air. Similar size doesn't matter, the the flow specification is irrelevant if the blades are just chopping none moving air about inside the fan body, which is what such high speed fans do once you give them some work to do. After slowing the air down that fan then has to push the air along a tube to deliver it where you need it.. or depending on the layout even worse if it needs to suck air along a tube to the cooler. Once the air flow through the fan slows the marginal cooling of the motor and bearing leads to early mortality of the fan as well.

As per the original post you can easily measure the flow rate against whatever back pressure you need and its an illuminating experiment.

 

[normspanners]

I do realise the facts about axial fans but these people http://www.t7design.co.uk/index.php?main_page=index have been making that style for several years and people seem to be happy with them I was going to make a similar design with bits I already had, that would lend itself better to the inside of a competition car, by not having rubber hoses going through the firewall, but also get it positioned just under the windscreen with simple flat fans pushing the air upwards, and not through great lengths of ducting etc. Although the t7 do work through ducting, so must push some air.
Using a mocal and two fans the total depth of the heater would be about 60 80 mm leaving a slight gap between the rad and the fan blades for the air to 'get it'self organized' before it hit the heating fins.

 

[gaz_moose]

i don't really need it to heat the car as it gets boiling hot inside any way. I have Perspex windows etc.. that cause leaks in the rain which then cause it to steam up inside. so my aim was to dry the air that gets blew onto the screen.

some of my friends are 'into' computers so I will see if I can borrow some fans and knock up a few testers using cardboard.

it would be interesting to know what the CFM output of the T7 unit is. but I guess it would be stated as free flowing and not taking into account ducting etc..

 

[colnerov]

Hi, It's best to have the fans as close to the rad as possible, don't let the air get 'organised' it will decide to go round rather than through because that's easier.

Colin

 

[GW8IZR]

I do realise the facts about axial fans but ....

OK Look this is my last on this as there isn't much to add that's not been posted earlier.

The fan in that T7 thing that you posted has a static pressure of nearly 3/4 of an inch of water.

The ones in your link have a static pressure of 3mm of water

That's a big difference. The fast ones are intended to be quiet in a PC cabinet and are designed differently, will they shift some air .. well probably. Will they work as required.. well maybe. When vehicle manufacturers design electric cooling systems they often need to use axial fans for clearance reasons and they do shift some air but they dont use ones with 24w motors.

some of my friends are 'into' computers so I will see if I can borrow some fans and knock up a few testers using cardboard.

it would be interesting to know what the CFM output of the T7 unit is. but I guess it would be stated as free flowing and not taking into account ducting etc..

That's certainly a good approach with minimal outlay - you are the best one to judge if the air flow is enough. For demisting it wont need much airflow.

The specifications you asked for appear to be:

HTH

 

[normspanners]

Hi, It's best to have the fans as close to the rad as possible, don't let the air get 'organised' it will decide to go round rather than through because that's easier.

As far as I know, having the fans too close ie too small a stall area causes the air flow to chop its self and looses 'direction' whereas having a gap allows the air to keep in its an imaginary converging duct. https://en.wikipedia.org/wiki/Axial_fan_design