# Control air density

I Need to build a circuit capable of controlling the density of air in a closed environment, heating and cooling the air as external adjustment. Could someone give me an idea of what components can I use to heat and cool the air within a closed environment?

Thanks Emilio

Depends on the volume - if it is a tiny convection accelerometer, or an environmental test chamber.

To create a defined density of gas in a confined insulated volume is straightforward: 1. Monitor vacuum (or pressure) with pressure and temperature transducers that are rated for the ranges you are interested in; 2. Control a vacuum (or pressure) source such as a gas sampling pump based on the output of the vacuum/pressure transducer; 3. Heat/cool the volume with thermoelectric (Peltier) array(s) that heat or cool depending on the direction of current flow - using the temperature transducer for feedback. A small DC powered pump (2 watts = 2 l/min.) can reduce the pressure in a 10 liter volume in a short time and can be shut off (or slowed down to maintain the desired pressure if there are leaks or the heated volume expands) - the built in check valve usually maintains the vacuum quite well. The thermoelectric array has to be sized to the task and has to have a heat sink on the outside of the insulated space to reject heat (or provide it if the volume is to be kept above ambient).

Could someone give me an idea of what components can I use to heat and cool the air within a closed environment?

You don't give much in the project details, so air conditioner and space heater comes to mind.

Sorry for bad details, it is my first post here. I gonna have a sealed tiny chamber with air inside, and I need expand and contract this chamber (like a ballon, for example). I guess one way is heating and cooling the air inside the chamber. The common pressure is around 30 psi, and I need to variate between 25 and 35 psi for example. The common temperature is around 28 ÂșC.

A balloon cannot take very much pressure inside but pneumatic tires have pressures in the range you mention. There are battery operated tire pumps that could be controlled to make the pressure go higher, with a solenoid valve to let out air to decrease the pressure. An Arduino can activate either of these depending on the pressure setpoint you want to maintain (measured with a pressure transducer).

If your system is always above ambient conditions, all you need is a small heater to raise the temperature to your desired temperature. Filament type lightbulbs can readily heat small areas to the temperature you mentioned.