Method and measuring apparatus for determining physical properties of gas

A method for determining physical properties and/or quantities relevant to combustion of gas or gas mixtures, the method comprising:

• flowing the gas or gas mixture under pressure through a critical nozzle and past a microthermal sensor into a gas reservoir, with the same mass flow being applied to the critical nozzle and the microthermal sensor;
• measuring a pressure increase in the gas reservoir as a function of time to obtain measured values of the pressure increase;
• determining a first gas property factor (Γ*) dependent on a first group of physical properties of the gas or gas mixture, on the basis of the measured values of the pressure increase;
• determining a second gas property factor (Γ), which is dependent on a second group of physical properties of the gas or gas mixture, from a flow signal of the microthermal sensor, with the second gas property factor containing or depending on a heat capacity (cp) of the gas or gas mixture;
• determining a thermal conductivity (λ) of the gas or gas mixture using the microthermal sensor;
• and
• determining a physical property or a quantity relevant to combustion using a correlation between the physical property or the quantity relevant to combustion, and the first and second gas property factors (Γ*, Γ) and the thermal conductivity (λ).

A method to use a gas reservoir and a critical nozzle for determining physical properties and/or quantities relevant to combustion of gas or gas mixtures, the method comprises:

• flowing the gas or gas mixture under pressure from the gas reservoir through the critical nozzle;
• measuring a pressure drop in the gas reservoir as a function of time;
• determining a gas property factor (Γ*), dependent on physical properties of the gas or the gas mixture, from the measured values of the pressure drop, wherein the gas property factor (Γ*) is derived using a time constant of the measured pressure drop;
• and
• determining a physical property or a quantity relevant to combustion through a correlation between the physical property or the quantity relevant to combustion and the gas property factor (Γ*).

A method to determine a physical property and/or a quantity relevant to combustion of a gas or a gas mixture using a gas reservoir and a microthermal sensor, calibrated for a specific calibration gas or gas mixture, the method comprises:

• flowing the gas or gas mixture under pressure from the gas reservoirpast the microthermal sensor;
• determining a flow rate (vx) of the gas or gas mixture using the microthermal sensor;
• determining a summed-up volume flow (vx·A) based on the flow rate (vx) over a period of time;
• comparing the summed up volume flow to a gas volume released from the gas reservoir;
• determining a gas property factor (S/v′x), dependent on physical properties of the gas or gas mixture, from the comparison, wherein the quantity (v′x) represents a flow rate determined from the released gas volume, and wherein the gas property factor comprises the heat capacity (cp) of the gas or gas mixture or is dependent on the same;
• and
• determining a physical property or a quantity relevant to combustion on the basis of the gas property factor through a correlation between the physical property or the quantity relevant to combustion and the gas property factor.

A method to determine a physical property of a gas comprising:

• flowing a gas from a reservoir through a critical nozzle and a microthermal sensor wherein the mass flow of the gas through the critical nozzle is the same mass flow through the microthermal sensor;
• measuring a pressure drop in the reservoir as the gas flows through the critical nozzle;
• determining a first gas property factor based on the measured pressure drop;
• determining a second gas property factor based on a flow signal generated by the microthermal sensor;
• determining a thermal conductivity of the gas using the microthermal sensor, and
• determining a physical property of the gas based on a correlation from the thermal conductivity and at least one of the first and second gas property factors.