Humidifier doesn't last the whole night

archangle wrote: The graph is fairly linear, but not quite. I'm tempted to try to fit a curve to the data

Granny already found the curve that fits very well. I had my son check her calculation. From her post above:

ChicagoGranny wrote:I agree with your statement. Over the range in the example, the function is far from a straight line. A simple function that best fits is,

Y = 9.1906(X^0.5577)
correlation = 0.9998

where X = CPAP pressure in cm H2O, and Y = mask design vent flow in lpm.

Someone check my math.

I see no reason to fit the curve for pressures below four - the machines don't operate there as far as I know.

Good job, Granny!

archangle wrote: I would have thought the flow would be proportional to pressure, but apparently not. The flow increases more slowly than proportionally. Apparently air through an orifice is not proportional to pressure. This page is a bit interesting for airflow through an orifice. http://www.aircompressorworks.com/airfl ... fices.html

The relationship I described is for air that can be treated as incompressible (less than 1/3 the speed of sound).

A simple way to look at it is if you convert all the pressure energy to velocity energy, the (Velocity)^2 = Density X (Change in Pressure). There are other factors at play, and it is not quite as perfect a relationship, but for the flows we are talking about at relatively low pressure drops, it means that the square of the flow will be roughly proportional to the pressure.

While every one is doing the math.. On this very complicated math equation..

Let me suggest that you buy a room humidifier like Vicks room humidifier like I bought from the CVS drug store.
Here in Ohio it gets very dry with the furnace running all the time. In order for the humidifier water to make it through the night I run the room humidifier while I sleep. Its worked out very well for me. I like Vicks because I can wash the filters out in the sink.


I wish you well...

Edit: I bought and use the cool air humidifier..

Bill44133 wrote:In order for the humidifier water to make it through the night I run the room humidifier while I sleep. Its worked out very well for me.

How close do you place the room humidifier to your CPAP machine?

Setj wrote:

Bill44133 wrote:In order for the humidifier water to make it through the night I run the room humidifier while I sleep. Its worked out very well for me.

How close do you place the room humidifier to your CPAP machine?

It is a maybe 5 or 6 feet from the bi-pap machine.. Coming from a different direction.. Its close to the register where the heat comes out.

That was the only place I had room for it....

Setj wrote:

archangle wrote: The graph is fairly linear, but not quite. I'm tempted to try to fit a curve to the data

Granny already found the curve that fits very well. I had my son check her calculation. From her post above:

ChicagoGranny wrote:I agree with your statement. Over the range in the example, the function is far from a straight line. A simple function that best fits is,

Y = 9.1906(X^0.5577)
correlation = 0.9998

where X = CPAP pressure in cm H2O, and Y = mask design vent flow in lpm.

Someone check my math.

I see no reason to fit the curve for pressures below four - the machines don't operate there as far as I know.

Good job, Granny!

Yes, it does fit well. I don't know how well it fits between 0 and 4, but it's correct for pressure of zero.

MichaelWD64 wrote:

chunkyfrog wrote:A big humidifier in the bedroom might help.
There are auxiliary cpap humidifiers which might help.

Do you know the names or model numbers for them?

Thanks!
MWD

Here is the link to my post on making extra humidifier capacity work on my machine.
External Humidifiers

Sorry it took so long.
Here's one:
http://1800cpap.com/fisher-and-paykel-h ... ifier.aspx