Wax in my heating system instead of water

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Discussion Overview

The discussion centers around the feasibility of using paraffin wax as a thermal storage medium in a heating system instead of water. Participants explore the implications of this approach, including heat transfer dynamics and the physical properties of paraffin wax compared to water.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that paraffin wax has a specific heat capacity significantly higher than water, proposing its use in a heating system where water is circulated through coils embedded in the wax.
  • Another participant notes that common waxes melt at around 60°C, raising concerns about heat conductivity in the solid phase and suggesting the use of copper fins to enhance heat transfer.
  • A different viewpoint emphasizes that the length of the coil may depend on the thermal conductivity of the pipe material and the medium used for heat exchange, indicating that different materials could affect the design.
  • One participant questions the direction of the original proposal, mentioning that antifreeze, as a liquid, has excellent heat transfer properties and may be more suitable for thermal storage than solid wax.

Areas of Agreement / Disagreement

Participants express varying opinions on the practicality and efficiency of using paraffin wax versus traditional liquids like water or antifreeze for thermal storage. No consensus is reached on the best approach or the implications of using wax.

Contextual Notes

Participants highlight limitations regarding the thermal conductivity of solid wax and the melting point of paraffin, which may affect heat transfer efficiency. The discussion also touches on the need for further exploration of materials and designs for optimal thermal storage.

Who May Find This Useful

This discussion may be of interest to heating engineers, materials scientists, and individuals exploring alternative thermal storage solutions in engineering applications.

technicalm
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Hi, I'm a heating engineer.

part 1: I typically install 300 litre to 100litres stores of hot water (to be extracted at 40deg c for low temp heating).

I understand that the specific heat capacity of paraffin wax is something like ten times that of water.

So can I play around with a smaller volume of paraffin wax in place of the water. Then, if i ran a long coil of pipe inside the parafin and passed water through it, the water would pull heat from the paraffin.

We do this at the moment with standard water tanks.

part 2: Would there be a difference in the length of the coil (either longer or shorter) if the process is paraffin to water rather than water to water.

Thank you for helping out with this project, it's just something I am interested in and as a non physicist I am probably sounding very naive!

all the best, Matt
 
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Here are some thoughts. Common waxes melt at about 60C so your system would operate with coils embedded in a solid. Is the specific heat of the solid phase also high? Solidified wax has poor heat conductivity (high thermal resistance) so your coils would pull heat from wax immediately in contact with them but then you'd have trouble drawing heat from the rest of the solid. Maybe if you used a lot of copper fins--like embedding a car radiator in wax? Finally, if you found wax with a 40C melting point, you'd have the additional storage due to the phase change (it's called "heat of fusion"). This is quite large compared to the heat capacity and would permit you to store a lot of energy in a small volume.
 
marcusl's reply is quite good, I would like to add, that the length of the coil is dependent on the thermal conductivity between the system and the heat bath. If your pipes are made of copper then the outside medium will be the limiting factor in delivering the heat to your pipe, and the length will change if you exchange the medium. If the pipe is made of stainless steel (a bad heat conductor) then the length probably doesn't need to change.
 
Yeah, I guess I'm not sure where the OP is going with this.
Antifreeze, for example, has a great capacity for heat transfer, and, it's liquid.

If you are looking for thermal storage that's another matter.
 

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