Helical Coil HEX Design

[dkmag]

I wanted to get some feedback on an idea I have for a dual purpose helical coil heat exchanger that can be used for both maintaining mash temps and chilling. The design consists of a 24" long, 3" diameter Tri-clamp spool and 17' long coil made with 1/2" flexible corrugated stainless steel tubing. The HEX would stand vertically and water (hot or cold) would enter and exit at the top of the HEX while wort would enter at the bottom and out the top (in a crossflow arrangement).



For maintaining mash temps, hot water from the HLT would be pumped through the coil and for chilling cold water from the tap.

Advantages:
1. Dual purpose HERMS/Chiller
2. Easy cleaning. Having coil connections going in and out at the top of the HEX (built into a Tri-clamp end cap or orifice plate) the coil can be easily removed for cleaning. Only water is ever pumped through the coil.
3. Wort flow restriction would be minimized when mashing.
4. Corrugated tubing provides larger surface area for heat transfer then regular stainless tubing (it's also thinner - 0.01").
5. Compact all stainless steel design.

Disadvantages:
1. To step or mash out the entire volume of water in HLT must be heated (although this is no different then having a coil in the HLT).
2. Flow rate through coil may be restricted due to coil diameter and corrugated tubing.
3. ???

I guess one of the bigger issues I can see is if the length of the coil is too short for cooling. I don't think there would be a problem with the length for maintaining mash temps. I used this online calculator to determine the length of coil that could fit in a 24" long spool (http://www.deepfriedneon.com/tesla_f_calchelix.html). If the length of the spool is 36" long the coil could be 24' in length.

Any feedback would be greatly appreciated.

Cheers,
Dan

 

[jCOSbrew]

Interesting design.
I am not a thermal expert but you could probably compare the surface area of the inner coil to standard CFC designs to check if you are in the correct ball park.

I know the plate chillers are very efficient due to the large surface area which allows the exit wort temp to drop close to the inlet water temp. For plate chiller, more plates = higher flow rate and longer plates = more contact time/area.

 

[dkmag]

Interesting design.
I am not a thermal expert but you could probably compare the surface area of the inner coil to standard CFC designs to check if you are in the correct ball park.

Good thought!

So here are some quick, back of the envelope, calculations of the total surface area of the inner tube (length * surface area of inner tube/meter)

I found some numbers (length and inner tube diameter) for a stainless steel CFC and get a inner tube surface area of:

(4.1m)(0.053m^2/m) = 0.22m^2

For a 25'-3/8" diameter inner tube DIY garden hose/copper tubing style CFC:

(7.6m)(0.03m^2/m) = 0.23m^2

For this design:

(5.2m)(0.047m^2/m) = 0.24m^2

So, it looks like it's in the ball park. At least in terms of the inner tube surface area.

Thanks for the feedback.

 

[AlCophile]

Wouldn't efficiency be greater if wort were in inner tube?; any liquid that passes along the inside of the outer tube may not mix as well as liquid in inner tube. Remember something called laminar flow?

 

[jackyl]

I agree that it's an interesting design, but I don't see how wort in the top of that cylinder (top being perspective for the diagram, basically the side without the exit) is getting through. All the moving wort is going to follow the path of least resistance, which is along the bottom, where the coils go with the flow. Nor will the flow start snaking through the coils unless you introduce strategic block points.

Not trying to bash your design, I just don't see how this improves on a traditional CFC.


Sent from my iPad using Home Brew

 

[dkmag]

Wouldn't efficiency be greater if wort were in inner tube?; any liquid that passes along the inside of the outer tube may not mix as well as liquid in inner tube. Remember something called laminar flow?

True. My concern with wort flowing through the inner tube would be getting it thoroughly clean after chilling. With the wort flowing in the outer tube it can be easily clean and visually inspected.

Good point on the laminar flow. Although, it should be possible include some baffles or maybe even design the the wort inlet such that it creates a whirlpool motion to induce turbulence.

 

[dkmag]

I agree that it's an interesting design, but I don't see how wort in the top of that cylinder (top being perspective for the diagram, basically the side without the exit) is getting through. All the moving wort is going to follow the path of least resistance, which is along the bottom, where the coils go with the flow. Nor will the flow start snaking through the coils unless you introduce strategic block points.

Not trying to bash your design, I just don't see how this improves on a traditional CFC.

I think you may have missed the point where I stated the HEX would stand vertically. Sorry, I made the diagram showing the HEX horizontal (rotate the diagram 90 degrees counter clockwise). The wort will flow in through the bottom and exit out the top of the outer tube. Water will enter at the top of the coil and flow downward and then up through the center of the coil and out the top. The wort will be flowing nearly perpendicular to the water flow in the coil.

No worries about bashing the design, that why I posted it. In my opinion I would say that the main improvement over a convoluted copper or stainless CFC would be the ease of cleaning.

 

[jackyl]

I think you may have missed the point where I stated the HEX would stand vertically. Sorry, I made the diagram showing the HEX horizontal (rotate the diagram 90 degrees counter clockwise). The wort will flow in through the bottom and exit out the top of the outer tube. Water will enter at the top of the coil and flow downward and then up through the center of the coil and out the top. The wort will be flowing nearly perpendicular to the water flow in the coil.

No worries about bashing the design, that why I posted it. In my opinion I would say that the main improvement over a convoluted copper or stainless CFC would be the ease of cleaning.

I was just saying "top" as a point of reference to the diagram since I was phone posting, so I couldn't generate a terrible MSPaint diagram like the attached one.

I know it is vertical and that the water loops, I was just saying that the wort is probably going to go in a straight path from entrance to the exit, meaning that a lot of the surface area is going to end up unused.

 

[ANGELofDEBT]

As far as efficiency goes nothing beats a CFC either in tube or plate form.

The leg that returns at the end of the coil will reduce your efficiency. If you ran your coil in one end and out the other that would work better.