• Pondering heat transfer....

    Henrik Sorensen06/06/2020 at 18:16 0 comments

    So... was considering heat transfer...

    Flat surfaces and tubing really sucks! Limited area for the heat to be transferred to from the block to the tubing. What are the options?

    1. Wrapping the tubing around a block (or a cylinder) with a groove cut for it.
    2. Same as #2 with a matching outer casing.
    3. Submersing into a fluid.

    #1 : Only about half of the tubing gets the heat transferred from the heater.

    #2: Parts must match exactly in order not to damage the tubing. Also, makes the application of the heater much more difficult.

    #3: Add a liquid to the handling, and thus more risks.

  • Prototype heating block begun

    Henrik Sorensen06/05/2020 at 21:41 0 comments

    Got the block for testing the heat transfer of the tubing made. 

    I need to figure out how to transfer the heat from the heater while still having around 1 m of tubing inside it and avoid liquids. The easiest way would be to make a cool form, put the the tubing inside a container, add e.g. water and heat it up.

    This adds unwanted fluids and more issues regarding daily use. E.g. evaporation,  possibility of shorts etc.

    But, let's measure and see what happens

  • Electronics prototype done

    Henrik Sorensen06/05/2020 at 21:36 0 comments

    Today, the PCB got populated with the components.  Actually turned out OK for a first time attempt on milling a PCB on my cheap mill. 

    Getting ready for writing some code for controlling the temperature 

  • Brainstorming session...

    Henrik Sorensen06/03/2020 at 20:35 0 comments

    So... today, I got my gritty mittens on an IV kit (Braun Intrafix)  (and a blood kit) in order to get a better view of the task at hand.. 

    Initially, I wanted the system to handle both IV (such as saline) and blood, but the flow rates are of a concern to me. Even professional equipment rolls up about 1 m (!!!!) of tube in order to create enough heating surface to heat the liquid and they even struggle with the ambient cooling of the last length of tubing. 

    Further input was given from a nurse related to the daily use and problems. This lead me to redesign the heating block based on the specifications of the tubing: 


    Diameter: 4.1 mm 

    Max pressure : 2 bar (current solution is a gravity fed system, so this is not important)

    Max temperature: 40 C

    I had hoped on setting a higher temperature for compensating for the ambient temperature based on the thermal resistance of the tubing (adjusted by the software), but I'll have to limit the maximum temperature to below 40 C.