Hi all As part of my work, I encounter a frost problem on a porthole system where I use a tangential fan associated with a resistor. The frost persists despite the use of components that should theoretically suffice. The porthole is mounted in a cold room where the outside is at room temperature, and the inside about -40 degrees. in fact the bottom of the window is defrosted but the top frosted, moreover the air that comes out of the heating box is at 30°! Components used: 550x400x12mm porthole
• Tangential fan REF EBM-PAPST QLZ06/2400-3030: air flow rate of 173 m³/h.
• 500 W Vulcanic resistor (5W/cm²).
• Distance between fan and resistor: tests with different positions, but the air comes out at about 30°C.
Do you think you can help me to resource this problem? Thank you in advance PS: on the attached photo, the fan plus resistance assembly is covered by a folded sheet metal cover to direct the airflow on the window.
If I understand correctly, the heated fan blows on the window?
It may be enough to rethink the output of the flow so that it licks the entire surface of the window, in a fairly homogeneous way, instead of concentrating it on the bottom of the window.
Well then I would rather use windows with integrated resistance (a bit like a car rear window) to defrost.
Thank you for your feedback, Indeed the fan blows on the window. That is to say rethink the exit so that it comes to lick the whole window? Unfortunately I don't have the possibility to use any other window than this one... (customer constraint)
Is the air intake on the -40°C side or on the ambient T° side? Otherwise maybe send it to the manufacturer of the heater to see if undersized, inappropriate or if it is indeed the outlet that needs to be reviewed.
Hello to you, @Sylk indeed the porthole was in the first configuration, I modified to go to the 2nd, there is less frost but still on the upper part of the porthole... (frost present on the heating side) @sbadenis Frost is present on the ambient temperature side (heating side), The heating system has been designed personally. The current output temperature is I think too low, do you think that switching to a 750W resistor instead of 500 can solve this problem?
It would be necessary to be able to measure the ambient temperature a few centimetres from the edge of the frost to check to what extent the warm air " bounced " off the window... this will make it possible to determine more precisely the Air exit angle to be used.
I will avoid the folds of sheet metal on this Air exit area in favor of rolled areas and will make it go up a little higher and closer to the window.
Thank you all for your feedback, here is a side image with the deflector attached to the cowling that guides the airflow to the window. No, not simulation because I don't have the knowledge to do it unfortunately. If the set is fixed on the top, the airflow will tend to go up I think the frost problem will be found on the bottom? What do you think of a more powerful resistance?
Absolutely not. The heat is rising. With a blower at the top, the heat will rise towards it instead of running along the glass. The window will be even less defrosted. At least starting from the bottom, the heat runs along the glass from bottom to top.
The exit doesn't seem to me to be optimal if you imagine a jet of water instead of air you can imagine picking up a lot of it if you're in front of the window. The jet would bounce off the glass (green line) Review the exit with the creation of an air gap that will run along the glass (red line) And maybe see with the heating manufacturer if there is enough power or not. Without calculation, only he can determine the functionality or not of the system
I understand what you mean. I will try to open the deflector even more so that it comes to " lick the glass " and keep you informed quickly of the result.
Yes and do one or more of the tests with why not put your fingers along the glass for example to feel if the hot air rises more or less or if it is expelled from the glass. Then see the power problem if it persists.
