Interior Frig Fans

Fan dynamics include the provision that the negative air pressure area is a anulus around the tip of the blades. Shroud the intake side of the fan and prove this for yourself.

CJW8 wrote:

mike-s wrote:
Blowing into the fins, because then the airflow across the fins is maximized. For a shelf, depends on which one. Blow down if on an upper shelf, blow up if on a lower shelf. The idea is to push the cold air down, or the warmer air up. Fans blow in a specific direction much more than they suck from a direction.

But, simply moving the air around is 90 percent of it.

Well, not exactly correct. Fact- air volume into fan = air volume out of fan. Don't confuse velocity with volume.

Agreed "But, simply moving the air around is 90 percent of it."

Yes, it is correct. Put a feather a foot in front of a fan, and watch it move. Now put one a foot behind the fan and, nothing. Even though it's the same amount of air in/out, the airflow out of the fan is much more focused/directed.

Or, instead of pointing a room fan at you, point it away from you. Do you feel a breeze on your back?:R

mike-s wrote:
Blowing into the fins, because then the airflow across the fins is maximized. For a shelf, depends on which one. Blow down if on an upper shelf, blow up if on a lower shelf. The idea is to push the cold air down, or the warmer air up. Fans blow in a specific direction much more than they suck from a direction.

But, simply moving the air around is 90 percent of it.

Well, not exactly correct. Fact- air volume into fan = air volume out of fan. Don't confuse velocity with volume.

Agreed "But, simply moving the air around is 90 percent of it."

I have my small Sunon 40MM 0.03 amp fan blowing into the small freezer portion of my 1.8 cubic foot Vitrifrigo c51is compressor fridge.

I removed the freezer door on day one of ownership. Have not bothered with other fan orientations/locations. I put a half gallon of warm tomato juice(~80f) in my fridge yesterday at 2:30 pm.
At 8:30 pm it was cold enough to hurt my teeth.

My condenser is also well ventilated with no chance of recycling preheated air. The NOctua NF-f12 fan sucks coolest possible filtered ambient air from below, pushes it once through condenser, across compressor and compressor controller and out of the cabinet, where a louvered vent allow its exit from vehicle, or the adjacent (electrical) cabinet which has an 80MM fan sucking air out too. I've found I keep the louvered vent mostly closed and let the 80Mm fan suck some air through condenser and across compressor, even when compressor is not running.

I could speed up the compressor rpm from the minimum 2000 rpm as well to further improve ability to remove heat faster. My fridge came with a 270ohm resistor to speed rpms to 2500, but I have no need of it, 99% of the time. My duty cycle rarely exceeds 20 minutes per hour. Usually much less.

But I am a bit of a potentiometer nutjob and might add one anyway for when warm beer has to be made cold even faster.

This is the 0.03 amp, 6.3 cfm, 40Mm fan I employ in my small fridge. If I had a larger absorption fridge I would use the Noctua NF-f12 at 0.05 amps mounted to fins blowing against/ across them.

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I would not be using just any computer fan on a fridge interior, but one with a low amp draw and relatively low CFM rating. No need to add a lot of heat load to the cooling unit.

Larger slow fans are more efficient than smaller faster. I went with 40MM as my fridge is tiny and the sunon linked above, at 0.03 amps, was the lowest amp draw I could find, and 6.3 CFM is more than enough inside a 1.8 cubic foot fridge.

WA4HTZ wrote:
I have read this thread and several others on interior fridge fans and the one thing I don't recall being discussed is the direction of air flow. If you mount the fan (or fans) on the front of the evaporator fins do you have the air blowing toward the fins or toward the door? Also, if you mount a fan to the underside of a shelf, which way do you have the air blowing, up or down?

I hope this isn't considered a thread jack but this has been a very good discussion of fridge fans and I have been puzzled about the direction of the air flow.

Thanks is advance for all of you knowledge and experience.

Ken

I have mine attached to the middle rack close to the front blowing up. The idea for me was to blow the air up to the top and back where it hits the fins and sinks to the bottom to be pulled back up.

I have an analog fridge temp gauge which I used before the fan. The fan moves enough air to keep the temperature even (I move the thermometer around and readings stay the same) and it returns to safe temperature much faster after opening a few times like when cooking. With natural convection it seemed to take forever for the temp to go back down.

In the case of our fridges, nearly all heat transfer from the fridge to the fins is by convection, and the amount of heat transferred is directly dependent on the amount of air moving across the fins. Think of it like this. You are hot and walk into a cool room with virtually no air movement. You will cool down but are depending on the natural convection of the air rising as it is warmed by your skin. It will take a while. Now point a fan at you, even a small one. It makes a big difference in how fast you cool off.

Blowing into the fins, because then the airflow across the fins is maximized. For a shelf, depends on which one. Blow down if on an upper shelf, blow up if on a lower shelf. The idea is to push the cold air down, or the warmer air up. Fans blow in a specific direction much more than they suck from a direction.

But, simply moving the air around is 90% of it.

I have mine resting above the fins blowing down. This was mainly logistics, this takes no room away from the food, no chance of it getting knocked out, and since cold air prefers to go down this helps it along (guessing, I don't really know, but it works well) This does require very small fans (I used 3 out of a Laptop cooling plate, in series they want 15 volts which is close enough to the 12-14.8 it gets).

I have read this thread and several others on interior fridge fans and the one thing I don't recall being discussed is the direction of air flow. If you mount the fan (or fans) on the front of the evaporator fins do you have the air blowing toward the fins or toward the door? Also, if you mount a fan to the underside of a shelf, which way do you have the air blowing, up or down?

I hope this isn't considered a thread jack but this has been a very good discussion of fridge fans and I have been puzzled about the direction of the air flow.

Thanks is advance for all of you knowledge and experience.

Ken

Hank MI wrote:

The sensor is on the cooling fins in the fridge. Without air movement they may be cold enough to turn of the cooling unit. A fan will move the air around making the cooling unit run longer as it's now trying to cool the entire fridge instead of just the cooling fins.

That makes perfect sense to me now. Thanks! I've got a temperature probe I'm going to tape to the fins and monitor fin temperature as close to this sensor as I can and monitor that for a while.

Off hand, I'd say my fridge tracks the outside air temps by about a 40 degree negative off set; 90 outside is 50 inside the fridge, 65 outside is 25 inside the fridge, and so on. When the outside air gets cooler, I suspect there will be a point where the fridge stays the same and no longer tracks, finally at it's set point regardless of the outside air temp.

landyacht318 wrote:


Part of those amps gets turned to heat which the fridge must then remove.

Well even the high wattage fan mentioned is only 3 watts, seems to me the issue is battery use and propane use. My experience is even a tiny fan helped a lot (more than the large one in the chimney) and that seems consistent with other people so ya go with the smallest one that works.