Measurement of thermal conductivity and specific heat

Apparatus for determining thermal conductivity, k, and specific heat, c.sub.p, of a gaseous fluid of interest, comprising:

• a microbridge system including a thin film resistive heater portion and a thin film resistive sensor portion in juxtaposed spaced relation, said heater and said sensor portions each having terminals, said system further being positioned in direct communication with the fluid of interest, said resistive heater thereby being thermally coupled to said sensor via said fluid of interest;
• adjustable electrical pulse producing means connected in energizing relation to said heater terminals for providing an energy input to the heater of a level and duration such that both intervals of transient and substantially steady-state elevated temperature conditions are induced in the sensor means via the fluid of interest;
• first output means for providing an electrical potential output signal indicative of the temperature of said thermal sensor means;
• means for determining the rate of change of temperature of said thermal sensor during a transient temperature interval based on a time interval between selected temperaturs indicated by said first output signal;
• means for determining k of the fluid of interest based upon the sensor output at steady-state elevated sensor temperature;
• and
• means for determining c.sub.p of the fluid of interest based on k and the rate of change of the sensor output signal during a transient temperature interval.

A method for determining thermal conductivity, k, and specific heat, c.sub.p, of a fluid of interest comprising the steps of:

• providing proximately positioned heater and thermal sensor means coupled by said gaseous fluid of interest, said sensor means being one having a temperature sensitive output;
• providing an energy input pulse to the heater means of a level such that an interval of transient temperature change is correspondingly produced in the sensor means;
• providing an energy input to the heater means of a duration such than an interval of substantially steady-state elevated temperature is correspondingly produced in the sensor means;
• obtaining a sensor output related to the elevated temperature of the sensor at said steady-state temperature;
• determining k of the fluid of interest based upon the sensor output at said steady-state elevated sensor temperature;
• determining the rate of change of sensor output during a portion of said transient temperature change in the sensor;
• and
• determining c.sub.p of the fluid of interest based upon the rate of change of sensor output during said interval of transient temperature change and k.

A method for determining thermal conductivity, k, and specific heat, c.sub.p, of a fluid of interest comprising the steps of:

• providing proximately positioned microbridge thin film electrical resistance heater and thermal sensor means coupled by said fluid of interest, said sensor means being one having a temperature sensitive electrical output signal;
• providing an electrical energy input pulse to the heater means of a level such that the sensing means experiences an interval of transient temperature change and of a duration such that the sensing means experiences an interval of substantially steady-state elevated temperature;
• obtaining a sensor output related to the sensor temperature at said steady-state elevated temperature;
• determining k of the fluid of interest based upon the electrical sensor output signal at said steady-state elevated sensor temperature;
• obtaining an output related to the rate of change of temperature of the sensor during said transient temperature change;
• and
• determining c.sub.p of the gas of interest based on the rate of change of sensor output during said transient temperature change in said sensor and k.

A method for determining thermal conductivity, k, of a fluid of interest comprising the steps of:

• providing proximately positioned microbridge electrical resistance heater and thermal sensor means coupled by said fluid of interest, said thermal sensor having a temperature sensitive output signal;
• providing and electrical energy input pulse to the heater means of a known level and of a known duration such that the thermal sensor means achieves an interval of substantially steady-state elevated temperature;
• obtaining a sensor output signal related to the sensor temperature of at said elevated steady-state temperature;
• and
• determining k of the fluid of interest based upon the sensor output at said steady-state elevated sensor temperature substantially approximated by
• k=a.sub.4 U+a.sub.5
• where U is the sensor output and a.sub.4 and a.sub.5 are constants.

A method of determining thermal conductivity, k, and specific heat, c.sub.p, of a fluid of interest comprising the steps of:

• providing proximately positioned microbridge electrical resistance heater and thermal sensor means coupled by said fluid of interest, said thermal sensor having a temperature sensitive output signal;
• providing an electrical energy input pulse to the heater means of a known level and of a known duration such that the thermal sensor means achieves an interval of substantially steady-state elevated temperature;
• obtaining a sensor output signal related to the sensor temperature of at said elevated steady-state temperature;
• determining k of the fluid of interest based upon the thermal sensor output at said steady-state elevated sensor temperature substantially approximated by
• k=a.sub.4 U+a.sub.5
• where U is the sensor output and a.sub.4 and a.sub.5 are constants;
• obtaining an output indicative of the rate of change of temperature of the thermal sensor means by measuring the time interval for the thermal sensor temperature to change between two known temperatures;
• and
• determining c.sub.p of the fluid of interest based on the relation
• c.sub.p P/P.sub.o =a.sub.1 (t.sub.2 -t.sub.1)k+a.sub.2 (t.sub.2 -t.sub.1)-a.sub.3
• where
• a.sub.1, a.sub.2 and a.sub.3 are constants
• P=pressure (psia)
• P.sub.o =reference pressure (psia)
• (t.sub.2 -t.sub.1)=measured time span for the temperature of the thermal sensor to sensor to change between known temperatures.