Fan positioning

[DragonGoby]

Hi all!

I just want to know how those peopl who use AC fans position them so as to create effective heat removal:

1) In-sump, in hood, or over display tank?

2) Placed horizontally downwards, or inclined at a downward angle?

Also, I found that the AC fans I got do generate heat as well. So here's the dilemma - if I place too close to the water surface, I get excellent water agitation and air flow, but fear that some heat will get transferred to the water; if I place too far away, air flow generated is way too low.

Any ideas? Thanks in advance!

Regards,

Hong Yee

[hotsoup]

I dun think positioning play a big role. The fan works on ###### in air from its environment. For example, if the air around your hse is warm, most likely the fan will be blowing warm air too. So, room temperature play a very impt role.

[hotsoup]

That's why most people used chiller to control the temperature which is too expensive to most of us to afford

[eprouve]

But the air movement also affects the rate of evaporation, which in itself brings temperature down.

I put it at 45 degree angle toward the surface, blowing at 45 degree to the side. You have to imagine a 3D space... to understand what I'm trying to say.

[dodo]

all depends on your tank surronding environment....if u find tat placing your fan 45 degree is not good enuf...place it horizontally and vice versa there is a previous thread on fan...some example of DIY fan too

Previous Fan Thread

[PLataX]

Hi guys....I'm currently doing my hons and this topic is my project....I'm studying the cooling effects of evaporation (its called forced convection) and theoratically its a sound concept.....would any of u be interested in helping me with a simple questionnaire?.....if so can i pm u guys when im ready with it....btw if all goes well by the end of aug the prototype will be ready...and im willing to share it with pple who cant afford chillers but luV this hobby....

[hotsoup]

I would love to help

[DragonGoby]

Me too, I'd love to help. Anyway, here's something to start with: I placed the fan 2cm closer to the water surface and tilted it to make a ~30 degree angle from the horizontal, and temps seemed to have decreased by at least 0.5cm, everything else remaining constant.

[jason]

MY TANK IS 6FT. WITHOUT AC FAN IS ARD 29 TO 30 DEG C. I PLACED ONE AC FAN ABOUT 4-5CM ABOVE WATER AT ONE CORNER IN MAIN TANK BLOWING DIRECT ON FOR 24 HRS A DAY.

MY TANK TEMPERATURE IS NOW ARD 26.5 TO 28. BUT NEED TO TOP UP AROUND 6 LITRES OF WATER EVERYDAY.

[nleong]

Platax,

Loved to help. Although I'm new to Marine, but I have used the fan for my previous FW tank. And the 2 fan i used is very effective during hot days.

It bring down the temperature from 30/29 to about 27 or even 26 occassionaly when the night is cool.

But need to top up water every 2 days or so.

I mounted the 2 fans horizontally facing downwards to the water surface powered by a disused computer power supply.

[hotsoup]

I just want to emphasis that the key factor is the room temperature!

[DragonGoby]

Hi Hotsoup,

I don't agree totally with that. Although room temp is a factor, esp. without fans, the cooling effect does not work by simply equilibrating tank water temperatures with room temp. As water evaporates it utilises energy (free energy of evaporation I think - my chemistry has gone haywire!) to escape from the water surface, which results in the cooling. By the collision theory, if absolutely no air movement is available directly above the surface of the water, the surrounding surface will rapidly reach full saturation in water vapour and no NET movement of water molecules out of the water surface is possible. However, by creating air movement we effectively clear out the evaporated water vapour from the immediate surface, hence allowing more water to evaporate and achieve better cooling. As such, this cooling effect is more dependent on ambient humidity and air movement, rather than on ambient temperatures.

Anyway, what kinds of fans do you guys use? AC fans meant for computers?

Regards,

Hong Yee

[nleong]

dragon,

i think most are DC fan. AC, you see your fan going in different direction every second

The fan is ripped off from the computer and reuse on the tank. same as the power supply. I use the old type where there is a power switch. so easier to on/off.

As for the debate on the temperature thing, well, do not forget our secondary school geography. hot rises and cold air comes in to replace its place. thats y got sea and land breeze.

so the notion of the room temperature does stand in some sense.

any other comments ?

[DragonGoby]

Oh yes, those with on/off switches sound great. Mine's a direct plu-in, so I work the on/off using the main switch.

That was geography? On second thoughts, I think it is. My brains have really deteriorated. Any tips for brain rejuvenation? LOL

Regards,

Hong Yee

[boxfish]

Hi Hotsoup,

I don't agree totally with that. Although room temp is a factor, esp. without fans, the cooling effect does not work by simply equilibrating tank water temperatures with room temp. As water evaporates it utilises energy (free energy of evaporation I think - my chemistry has gone haywire!) to escape from the water surface, which results in the cooling. By the collision theory, if absolutely no air movement is available directly above the surface of the water, the surrounding surface will rapidly reach full saturation in water vapour and no NET movement of water molecules out of the water surface is possible. However, by creating air movement we effectively clear out the evaporated water vapour from the immediate surface, hence allowing more water to evaporate and achieve better cooling. As such, this cooling effect is more dependent on ambient humidity and air movement, rather than on ambient temperatures.

Anyway, what kinds of fans do you guys use? AC fans meant for computers?

Regards,

Hong Yee

As water evaporates it utilises energy/heat to change state, which results in the cooling...that's a common explaining using fan cooling.

[Explorer]

[hotsoup]

Let's treat this as a learning experience instead of debating. There's no right or wrong answer.

[PLataX]

first of all...thanks for being so sponteneous abt the survey thingy....erm...i've done some research and relative Hunmidity is the main factor to the evaporation rate....if the RH% is low, the rate of evapoarion increases and thus cooling results....just like when we perspire and a cold wing blows across the sweaty skin...u feel the cooling effect...also when RH% is high, i.e the air contains too much water vapour, evaporation slows down....so when we reefers use a fan to blow across the surface, the high RH% air is moved away and evaporation can then increase .....also regarding the AC and DC issue, when we use PC power supply, DC fan is used here, coz the PC power supply converts the PUB's AC source to DC...if we wanna connect a fan directly to PUB mains..then we buy an AC fan from SIM Lim, hope I dint patronize anyone....btw guys....I'l b going Great barrier reef to scuba from 14-20 feb...hope i can bring back some nice photos for all....dun tink can stun any frags...haha...

As 4 the survey latest by 22feb PM or E-mail u all okie?

[hotsoup]

Good life! enjoy yrself