Flat Roll Bond Evaporator Source

[Caribsailors]

Well the old BD-2.5 finally died its final death. Time to rebuild.

I'm looking for a source for Roll Bond Evaps. I would like two - 8" wide by 36-42" in length that can be bent at 12 & 20" from line set.

I've found some on RPart.com but they're 11.38" wide. I've thought about sheering the edges to desired dimensions but have no experience with this small of equipment. (Commercial/Industrial Refrig.Tech by trade)

Any info you be most helpful.

Cheers with warm rum

[Richard Kollmann]

A BD 2.5 compressor failure would be extremely rare if it was on an air-cooled condensing unit. Finding an eight inch wide evaporator is going to be hard to find. Have you tried Dometic and Frigoboat.

Have you considered using 25 feet of ¼ inch OD refrigerant dehydrated copper tubing for an evaporator? I built these at one time clamped in back of a stainless steel 18 gauge sheet. I believe Frigoboat has this simple inexpensive type evaporator although it is wider than 8 inches. SeaFrost will make you an evaporator plate any size but it is not aluminum roll bond. On more than one boat where evaporator coil was behind box liner and failed I clamped 25 to 35 feet of ¼ aluminum tubing to box walls as a good solution.

[Caribsailors]

Thanks Richard...I went to Frigoboat and found an evaporator that would do the job. Then I checked the price crazy...Then I referred back to your comment about making my own evap.....why not.
Any suggestions on captube size & length? I'm just being lazy and didn't want to go dig out my school books.

Thanks again for the redirection

[foggysail]

Richard's suggestion for copper tubing makes sense. I thought about that technique for a future project. My earlier ideas included sandwiching the tubing in the box's fiberglass walls. That idea has risks because fiberglass and copper have different expansion rates that would ultimately break their bond.

Richard mentions clamping the tubing to a SS plate (also consider aluminum 6061 or 5052) but it might be easier to sandwich the tubing between two plates but either way, it will work. You might find more on this using Google.

[Caribsailors]

I took your advice Richard and built my own evap. and rebuilt the entire refrigeration system. I really am quite ashamed of myself that I didn't just do it in the first place. Refrigeration mechanic is my second trade.
Here are some pics

[Caribsailors]

80F ambient

I have a data logger in the box now. Will report back

[Richard Kollmann]

Looks good but two comments:
1. With an expansion valve expansion device it needs a small receiver to handle changes of refrigerant flow as evaporator plate freezes.
2. I hope you used the smallest valve orifice 00, 1300 btu or lower . If valve orifice is too large pressure differential will not occur on a warm 80 degree F temperature start up.

[Caribsailors]

Thank you.

I did make a small receiver out of inch & 1 and it seems to be doing its job as site glass is clear.
I currently have orifice 01 installed for testing, but can roll back to a 00 if need be. I also went for an MOP valve in hopes of getting some assistance during start up.
I did have one start up issue on initial start, but that was because I was over charged. I have also added a 2" scrubber fan in the box that runs when refrigeration is running as an experiment.

[Richard Kollmann]

The location of Data Logger is only relative to box temperature and thermostat setting but it appears thermostat is set at 40 degrees F. Most logger soft wear permit one area to be expanded to measure a complete compressor cycle time between one compressor start and the next start. From the number of cycles on graph it would seem that there is higher than necessary compressor speed.

This is the first time I have seen box Dew point and Humidity reaction to compressor cycles. I would have guessed they would both decrease as moisture collected and froze on evaporator.

Great System.

[foggysail]

Originally Posted by Richard Kollmann

Looks good but two comments:
1. With an expansion valve expansion device it needs a small receiver to handle changes of refrigerant flow as evaporator plate freezes.
2. I hope you used the smallest valve orifice 00, 1300 btu or lower . If valve orifice is too large pressure differential will not occur on a warm 80 degree F temperature start up.

Richard-- I am a novice here so most likely my question will make that obvious. You state the refrigerant flow will change as the evaporator plate freezes. I got lost on that. Does not the refrigerant flow independently of the evaporator plate condition? Even the cycling is determined by a temperature sensor someplace but does not control the flow.

Now if the system utilizes a variable pump rate governed by some type of external sensor, that is another matter especially if it monitors the plate.

Just trying to understand this stuff--

Thanks

Foggy

[foggysail]

Caribsailors--

Impressive evaporator! What material is your mounting plate and how did you secure the tubing to it?

Thanks--

Foggy

[Richard Kollmann]

Originally Posted by foggysail

Richard-- I am a novice here so most likely my question will make that obvious. You state the refrigerant flow will change as the evaporator plate freezes. I got lost on that. Does not the refrigerant flow independently of the evaporator plate condition? Even the cycling is determined by a temperature sensor someplace but does not control the flow.

Now if the system utilizes a variable pump rate governed by some type of external sensor, that is another matter especially if it monitors the plate.

Just trying to understand this stuff--

Thanks

Foggy

Refrigerant flow determines Btu of work accomplished while refrigerant’s boiling point controls heat absorption temperatures within evaporator. Both refrigerant Flow and refrigerant boiling point when condenser and evaporator are in balance are controlled by a refrigerant expansion device. When evaporator is warm refrigerant flow is highest. As evaporator temp decreases flow control device reduces refrigerant flow lowering boiling point of refrigerant and lowering evaporator temperature.

There are three different flow control devices used in small refrigeration systems, Long fixed orifice capillary tubes, Low fixed pressure control valves and Thermo Expansion Valves. Purpose of refrigerant flow control device is to insure that refrigerant’s liquid phase change to a gas occurs only inside evaporator where heat can be most efficiently absorbed. This temperature range change inside evaporator is defined as superheat range. Although capillary tubes on small Danfoss compressors are fixed orifice they have an evaporator temperature range that depends on evaporator/capillary size. Low pressure control valves maintain a fixed low pressure and limit refrigerant flow reducing Btu work done at warm evaporator temperatures. Thermo expansion valves provide an automatic evaporator temperature range from -40 to +50 degrees F. Because of thermo expansion valve’s wide temperature and refrigerant flow range a receiver is required to store excess refrigerant at low evaporator temperatures.

[foggysail]

WOW! I need to look this stuff up. Richard--- my printer is down now while I wait for my new desktop to arrive. But I am going to print out your post. It is technical but I believe there are some gold nuggets in it.

I was thinking back to my old thermodynamics class in college where the principles of refrigeration were covered. Great stuff although limited practical use. For example, a nozzle was just a nozzle. Most likely I will have other simple questions but I need to review what you just provided.

Thanks Rich--

Foggy

[Caribsailors]

Foggy

Thanks
The backing plate is 18 awg copper. I'm lucky enough on the little island I'm on presently, to have a friend who is an international award winning metal sculptor. So I was able to access sheet copper in the 2nd world.
I attached the perimeter tubing using 15% silfos, but got to much metal distortion moving inward because of the heat required for silfos, and moved to soft solder. I think if I had used a sand bed while welding it may have help, but I need to talk with my sculptor for his thoughts
I'm not really happy with it, but it seems to be doing the job. I did consider epoxy resin, but moisture and refrigeration can make some dramatic results, has been my experience. That said I still haven't given up on the thought of epoxy, maybe placed in a vacuum while curing? Just a thought.

Cheers.

[Caribsailors]

[QUOTE=foggysail;1116116]WOW! I need to look this stuff up. Richard-

I'd buy his book....Kollmann Marine

I'm seriously considering it. I'm a commercial/industrial refrigeration mechanic by trade. Refrigerant phase change is refrigerant phase change, but what I LOVE of the trade, is the different nuances in each genre, if I can use that. I've worked on ice machines that drop 250 Lbs of ice every 45 minutes, supermarkets, grow opp air filtration to morgue cooling and commercial fishing. What is currently stirring the brain of need to know, is the algorithm of the AEO controller. I love the LED diagnostics but need to see the parameters that determine its output. That's why refrigeration is COOL!