Method and apparatus for measuring the relative density of gases

A method for measuring the relative density of a gas comprising:

• flowing said gas under an applied pressure through an orifice or pore in a line;
• periodically restricting flow of said gas at a point in said line upstream from said orifice or pore;
• measuring the fall of pressure in said line with respect to time to obtain the flow rate through said orifice or pore;
• and
• calculating said relative density, which is inversely proportional to the square of said flow rate;
• said orifice or pore being very small relative to said line and sized with respect to the applied pressure so that deviations from ideal behavior of said flowing gas are substantially balanced by other flow effects, thus rendering an orifice discharge coefficient unnecessary in calculating relative density.

Apparatus for measuring the relative density of a gas comprising:

• a flow line having an orifice or pore therein;
• means for flowing said gas under an applied pressure through said orifice or pore;
• means for measuring the pressure drop across said orifice;
• means for calculating the flow rate of said gas based on said pressure drop;
• said orifice or pore being very small relative to said flow line and sized with respect to the applied pressure so that deviations from ideal behavior of said flowing gas are substantially balanced by other flow effects, thus rendering an orifice discharge coefficient unnecessary in calculating flow rate from said measured pressure drop, the square of said flow rate being inversely proportional to said relative density.

A method for determining the relative density of a gas comprising:

• flowing said gas under applied pressure through an orifice in a line to change its pressure to the extent that the gas deviates from ideal behavior due to supercompressibility of the gas;
• measuring the pressure drop in said gas;
• sizing said orifice with respect to said line and to said applied pressure to achieve cooling effects that offset said deviations from ideal behavior;
• and
• calculating the density of said gas from said measured pressure drop without the necessity of considering an orifice discharge coefficient.

A method for determining the relative density of a gas comprising:

• flowing said gas under an applied pressure through an orifice in a line to change its pressure to the extent that the gas deviates from ideal behavior due to the supercompressibility of the gas;
• periodically restricting flow of said gas at a point in said line upstream from said orifice;
• measuring the pressure deviations in said line with respect to time;
• sizing said orifice with respect to said line and to said applied pressure to achieve cooling effects that offset said deviation from ideal behavior;
• and
• calculating the density of said gas from said measured pressure deviations without the necessity of considering an orifice discharge coefficient.