DIY Water to water heat exchanger

I have created a hub that allows you to create a water-to-water heat exchanger for lab/home application.
4h 37m
2× print file
0.20 mm
0.40 mm
79.00 g
In the contest Plumbing Tools
165
76
1
5426
updated January 2, 2025

Description

PDF

Liquid heat exchanger

I need to cool down a bunch of instruments and our laboratory has a primary cooling water circuit. Yet it is dirty and the pressure difference between the supply and return line is too low. In order to decouple my devices from the primary cooling circuit I have created a small water circuit based on the AVTA valve (or you can use any motorized actuator with a suitable valve and PID controller+ probe), which according to the secondary circuit temperature controls the flow in the primary circuit (opens on rising temperature). The plastic PETG hub is designed for heat-fitting of 15/13 mm (internal) and 28/25.6 mm (external copper tubes). If anyone has a desire for some other combinations of the pipe diameter please let me know.

I use two versions - 
  1. The first method uses epoxy glue, which makes assembly both simple and reliable. There’s no need for a torch, making the process hassle-free.
  2. The second approach is more traditional and "plumber-like." It involves heating the copper pipe with a torch until a test filament begins to ooze, then pressing the part onto the heated pipe. This method has also proven to be very reliable—I tested it up to 6 bars of pressurized air with no leaks! However, it is more time-consuming, and there’s a risk of the parts bending out of shape if overheated.

Overall, I find the glue-based method far more appealing because of its simplicity and convenience.

To enhance heat transfer between water and the copper tube, I fill the 15 mm tube and the annular space between the 28 mm and 15 mm pipes with copper mesh.

This water-to-water heat exchanger is highly versatile, making it ideal for various applications. It can be used to decouple heating water for tasks like pool heating with an external furnace or solar water heater setups. Additionally, it’s adaptable for rapid wort cooling during beer brewing—though for brewing, I recommend using stainless steel components. Keep in mind the temperatures your application will involve. For resin printing, this setup can even work for certain vapor condensation tasks.

The completed heat exchanger, approximately 30 cm in length, delivers stable performance at 22°C with a nominal power of 1 kW. In my primary circuit, water flows at 2 liters per minute, entering at 13°C and exiting at around 24°C.

Updates:

  • 17 December 2024: New assembly tested (see step 9) which increases the heat transfer by 30%.
  • 3 December 2024: The 7-way high-flow heat exchanger hub is rather heavy. I have added a panel mounted version.
  • 2 December 2024: I’ve added a 7-way high-flow heat exchanger hub for those needing significant cooling capacity. The output port has been redesigned to accommodate 22/20 copper pipes.
  • 30 November 2024: Version 3 has been released, offering a sturdier build that is more resistant to bending during assembly and use.

Assembly Instructions for the Glue-In Version

Note: I use Loctite epoxy glue because I’ve tested its water resistance and found it reliable.

1. Prepare the Pipes:

  • Cut the 28 mm and 15 mm pipes to your desired lengths. Be sure to add an extra 2 cm to each end for the insets.
  • Debur both the inside and outside edges of the tubes to ensure a smooth fit.

2. Surface Preparation:

  • Use an abrasive sponge to thoroughly clean the inside and outside surfaces of the 15 mm tube. This improves heat transfer between the tubes.
  • Clean the inside surface of the 28 mm tube as well to ensure optimal adhesion.

3. Add the Copper Mesh:

  • Solder copper mesh to the outside of the 15 mm tube. I recommend using strips approximately 30 x 10 cm in size.
  • Ensure the mesh is securely soldered and free of loose bits to avoid debris inside the assembly.

4. Attach the 15 mm Tube to the Hub:

  • Securely glue the 15 mm tube to the hub using a water-resistant epoxy adhesive. Allow sufficient time for the glue to cure as per the manufacturer’s instructions.

5. Wrap the Mesh:

  • Roll the copper mesh around the 15 mm tube, ensuring the wrap is even and in one consistent direction.

6. Assemble the Outer Tube:

  • Carefully slide the 28 mm tube over the mesh. As you do this, roll the 28 mm tube in the same direction as the mesh wrap to ensure a snug fit and prevent the mesh from bunching or shifting during insertion.

7. Apply the Glue to the 28 mm tube:

  • Spread epoxy glue evenly on the inner surface of the 28 mm tube and along the groove.

8. Insert and Twist:

  • Slide the 28 mm tube into position. Once fully inserted, give it a counter-rotating twist. This action presses the mesh firmly against the outer tube, ensuring better contact, improved heat transfer and seals the low impedance water channel that might form.

9. Prepare the Inner Mesh:

  • Cut a strip of mesh that is slightly longer than the total length of the tube (about 4 cm extra).
  • Roll the mesh and insert it into the 15 mm tube, ensuring it fits snugly for optimal performance. Make sure there is enough material to ensure the efficient heat transfer to the outer layer.
  • OPTIONALLY: I coated the inner surface of the 15 mm tube with solder paste and heated the assembly to bond the inner mesh to the tube. This significantly enhanced heat transfer, with a quick measurement indicating a 30% improvement.

10. Unwind the Inner Mesh:

  • Use two flat screwdrivers to twist the mesh inside the 15 mm tube. This will slightly unwind the mesh, pressing it more firmly against the inner surface of the 15 mm tube for better contact.

11. Glue the Opposite Side:

  • Apply epoxy glue to the other end of the tubes and into the grooves.

12. Attach the Hub:

  • Slide the hub onto the tubes, ensuring it is aligned in your desired orientation. Double-check the fit before the glue sets.

13. Prepare the Copper Assembly:

  • Complete any soldering on the copper tube assembly before attaching it to the hub. Avoid soldering too close to the hub after it’s glued, as the heat could compromise the adhesive/hub.
  • For a 15 mm copper pipe, solder at least 10 cm away from the hub. To protect the glued joint, wrap the area near the hub with a wet cloth to dissipate heat effectively.
     

14. Assemble your circuit!

This is an example of a small circuit designed to cool down a strong magnet. Both the primary and secondary circuits are equipped with strainers to filter out unwanted particles. The primary circuit includes a motorized valve, which has a feedback in the secondary (device) circuit. A small tank with a one-way valve ensures there is sufficient water in the closed secondary circuit, and it also functions as an air eliminator. I have used a Wilo central heating pump in the secondary circuit to circulate the water effectively.


 

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