2
$\begingroup$

I am releasing CO2 from a cylinder into a ventilated room and want to mimic a human breathing (let's ignore the in/out breath). Problem is that the gas that comes out is at room temperature (or lower due to decompression) not body temperature. How can I heat the gas that comes out of the cylinder to 37ºC?

$\endgroup$
2
  • $\begingroup$ The amount of CO2 exhaled per breath is very small. Which characteristics are the most important that have to be modeled? $\endgroup$ Feb 28 '19 at 13:25
  • $\begingroup$ This is true. There are a few variables but I think the buoyancy would be most valuable to start with. $\endgroup$
    – HCAI
    Feb 28 '19 at 13:47
2
$\begingroup$

Options

You could purchase something equivalent to this.

https://farnam-custom.com/standard-products/process-air-heaters

You could make something equivalent to this.

https://www.youtube.com/watch?v=mEExlOX458Y

Principles

The principles for the heat exchanger are comparable to this post, only using air inside and water outside.

Calculating heath exchange for custom boiler

When you are interested in the heat flow needed to change a the temperature of a flowing fluid, consider the equation below with $\dot{q}$ as heat flow (W), $\dot{m}$ as mass flow (kg/s), $\tilde{C}_p$ as specific heat (J/kg $^o$C), and $\Delta T$ as the desired temperature change.

$$\dot{q} = \dot{m}\tilde{C}_p \Delta T $$

For an ideal gas, mass flow and volume flow $\dot{V}$ are related as below with $M$ as molar mass (g/mol), $\dot{n}$ as molar flow (mols/s), $p$ as pressure (Pa), and $R$ as gas law constant (J/mol K).

$$ \dot{m} = M\dot{n} = M p \dot{V} / R T $$

When $T$ is not constant, the volume flow rate will change for the same mass flow rate. Basically, as an ideal gas is heated in a tube, it expands and moves faster to keep the same mass flow rate.

The total energy that you need to supply the heat is calculated from the efficiency of the power to heat conversion.

$\endgroup$
7
  • $\begingroup$ Hi Jeffrey, this looks exactly what I would need, thank you. I like the YouTube video too, very neat! $\endgroup$
    – HCAI
    Feb 28 '19 at 18:53
  • $\begingroup$ I think the other issue to deal with is that the pipe length that I can heat is very short (20cm) in comparison to the length of pipe in the room where the co2 is released (2m). I can't put the heat exchanger in the room as I can't have heat sources in there. Presumably I will have to overheat the co2 to compensate for this? $\endgroup$
    – HCAI
    Feb 28 '19 at 18:59
  • $\begingroup$ @HCAI I would be leery to heat a pressurized container of gas. $\endgroup$ Mar 1 '19 at 13:26
  • $\begingroup$ I didn't mean heat the cylinder (yikes). I mean overheat the co2 coming out of it to compensate for the fall in temperature by the time it arrives at its destination 2m further down the pipe. No? $\endgroup$
    – HCAI
    Mar 1 '19 at 13:29
  • $\begingroup$ There seems to be a formula to calculate heat required to increase temperature of the gas given a flow rate Q litres per minute and a temperature Change delT. W=DelT x Q/47.2. Ifd my Q is 10l/s and DelT is 20 then I only need 5W... Doesn't seem right? $\endgroup$
    – HCAI
    Mar 1 '19 at 13:31
1
$\begingroup$

take a cheap hair dryer apart so you can control the heater element separate from the fan blower. Connect the heater element to 120VAC through a variac (variable AC transformer) so you can control the voltage it sees. Put a temperature sensor in the outlet stream of the hair dryer and build a duct that carries CO2 from the tank to the inlet of the hair dryer. turn on the CO2 so it blows through the hair dryer with the dryer's fan off. adjust the variac to get the desired discharge temperature.

$\endgroup$
1
  • $\begingroup$ Use a heat gun - many already have the controller.... $\endgroup$
    – Solar Mike
    Mar 1 '19 at 5:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.