EBME Forums Forums Maintenance Technical Assistance Incubator design

hi,

I am designing a humidifier for an incubator. I like to know the various techniques available for humidification.

If any one have experience in this design, please suggest some ideas. How to start this design.


regards,
Kuji

Kuji,

Nice to see a student on the forum.

There are 2 types of humidifier that I am aware of:
Ultrasonic - This uses an ultrasonic crystal to vaporise the liquid that is then tranferred to the patient through a hose to the patients mask / tube.

The second is a heated plate in a chamber which heats up the fluid causing evaporation that is then tranferred to the patient through a hose to the patients mask / tube.

Another way is the Vapotherm way. See page 6 of manual in this link.

http://vtherm.com/_pdfs/Operating%20Manual_2000i_Rev%20E.pdf

This is a variation on the heated chamber method John mentioned above.

Some incubators have Humidification built in using a small heated chamber and venting the vapour directly into the warm air circulation system

Hello,

Some designs have a feedback control system that utilises a hygrometer (humidity sensor) to measure the relative humidity (RH) in the incubator and this allows the operator to both display RH to the operator and then allow them to preset a desired RH within the incubator canopy.

Variation of the heater temperature, under feedback control, maintains the RH constant. Ultimately the volume of water vapour that can be maintained in a volume of humidified air is dependent upon the air temperature within the incubator and on gas flow rates.

Gas flow over a relatively large heater element, or an absorbent wick attached to the heater, suspended in water, is required to increase the surface area of the water exposed to air flow hence provide sufficient levels of humidification. The humidified air must be circulated effectively across the patient and RH sensor to maintain the feedback loop properly.

Richard.

Hi Kuji

Just a few things to add to the above posts. If you get lots of moisture on the inside of the incubator, usually in the corners, it means that the humidifier is not working correctly for the temperature/ gas flow inside the incubator.
If you do not get moisture, it may be that it is working perfectly instead of not good enough.
Your ultimate aim is too achieve and maintain 100% RH for your given temperature, therefore you will not see any moisture on the inside of your incubator canopy.
This will be very difficult to get right as not all the incubator manufacturers have got this completely right.
Also, the ambient temperature of the room the incubator is in can also affect this. If the room is too cold, the surface area of an incubator canopy could have an affect on the temperature inside the incubator. Be sure to check the temperature as well as the RH in all positions to find the best location for your sensors.
Good luck with your project

I like to proceed with the second technique.first i like to do mathematical modelling of the this system.can u give me some suggestion.

regrads,
Kuji

Sounds like a servo system model to me! What did we used to call those things ... was it Laplace transforms? When I was a whole lot younger, and still had more than a hundred brain cells, I used to amuse myself (yes, sad but true) writing integral equations to program imaginary Swingfire missiles to zoom around the parade ground and hit the Sergeants' Mess!

The second option (from John, that Kuiji appears to be referring to) sounds like a feedforward system to me, i.e. an open-loop one with plenty of disturbances plus the effects of varying airflow, heater power, and humidity output, to predict.

Analagous to a Standard fireworks rocket rather than a swingfire missle control system if you want to look at it like that.

Sounds like there'll be a need to do some modelling based on experimentation. This sort of design can be more difficult to predict or model than feedback systems that can be adapted to overcome disturbances that cannot be accurately modelled (trying to predict performance is useless).

I'd list all the variables that humdity output is going to be dependent upon and then consider which ones are going to be the most significant in the feedforward system and which ones are minor disturbances that are insignificant and can be ignored.

The input is heater power and the output of the system is humidity - the operator will adjust heater power to overcome losses and disturbances. Plotting humidity versus input power over a range of airflow, exposed water surface area/volume and ambient temperature is a start, perhaps?

Just to get a feel for how dependent changes in humidity are to changes (or disturbances) to these variables......

The problem with a feedforward system such as this is that the operator has to maintain the level of humidity. The only considerations are whether the heater can give up to 100% RH at a particular flow, ambient pressure and ambient temperature, really.

A closed loop control system is the only option worth considering when designing a neonatal incubator. All other options are non-starters. It's as simple as that!