Measurement of thermal conductivity and specific heat

• US 4,944,035 A
• Filed: 06/24/1988
• Issued: 07/24/1990
• Est. Priority Date: 06/24/1988
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Aagardl, Roger L., Bonne, Ulrich, Matthys, Robert J.
• Primary Examiner(s): Teska, Kevin J.
• Application Number:
  US07/210,892
• Time in Patent Office: 760 Days
• Field of Search: 364/556, 364/557, 364/558, 73/27 R, 73/204.14, 73/204.15, 73/204.16, 73/204.17, 73/204.33, 73/204.24, 73/204.25, 73/204.26, 374/43, 374/44, 374/1, 374/29, 374/144, 374/113, 374/166
• US Class Current: 702/136
• CPC Class Codes: G01N 25/005 by investigating specific heat
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18

Abstract

A method and apparatus for determining both the thermal conductivity, k, and specific heat, c_p, of a fluid of interest are disclosed. An embodiment uses proximately positioned resistive heater and thermal sensor coupled by the fluid of interest. A pulse of electrical energy is applied to the heater of a level and duration such that both a transient change and a substantially steady-state temperature occur in the sensor. The k of the fluid of interest is determined based upon a known relation between the sensor output and k at steady-state sensor temperature; and c_p of the fluid of interest is determined based on a known relation among k, the rate of change of the sensor output during a transient temperature change in the sensor and c_p.

Claims

1. Apparatus for determining thermal conductivity, k, and specific heat, c_p, of a fluid of interest comprising;

heater means;

thermal sensor means in proximate position to said heater means and in thermal communication therewith through the fluid of interest, said sensor means being one having a temperature dependent output;

adjustable energizing means connected to said heater means for energizing said heater means on a pulsed time-variable basis in a manner to induce both transient and substantially steady-state elevated temperature condition intervals in said thermal sensor means;

first output means for providing first output signal indicative of the temperature of said thermal sensor means;

means for determining the rate of change of temperature of said temperature sensor during a transient temperature interval based on time variation of said first output signal;

means for detemining k of the fluid of interest based upon the first output signal at steady-state elevated sensor temperature; and

means for determining C_p, of the fluid of interest based on k and the rate of change of the first output during a transient temperature condition.

3. The apparatus of claim 1 further comprising second output means for providing output signals indicative of k and c_p of the fluid of interest.

2. Apparatus for determining thermal conductivity, k, and specific heat, c_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_p of the fluid of interest based on k and the rate of change of the sensor output signal during a transient temperature interval.

4. The apparatus of claim 2 further comprising second output means for providing output signals indicative of k and c_p of the fluid of interest.

5. The apparatus of claim 2 wherein said resistive heater and resistive sensor portions are the same.

6. The apparatus of claim 2 wherein said microbridge resistive heater and resistive sensor portions comprise a sensor-heater-gap-heater-sensor configuration.

7. The apparatus of claim 2 wherein said microbridge resistive heater and resistive sensor portions comprise a heater-gap-sensor configuration.

8. The apparatus of claim 2 wherein said resistive heater and resistive sensor means are provided with an outer insulating layer to reduce heat flow through solid media.

9. The apparatus of claim 2 wherein said first output means includes a Wheatstone bridge which includes said thermal sensor.

10. The apparatus of claim 2 wherein said means for determining the rate of change of temperature of said sensor means further comprises counting means for measuring said time interval required for said sensor temperature to rise or fall between two of more known temperature values represented by known values of said first output.

11. The apparatus of claim 10 including means for varying said temperature values.

12. A method for determining thermal conductivity, k, and specific heat, c_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_p of the fluid of interest based upon the rate of change of sensor output during said interval of transient temperature change and k.

13. The method of claim 12 wherein the heater and sensor means are electrical resistance elements and the input to the heater is in the form of an electric pulse of elevated voltage level and known duration.

14. The method of claim 12 where the fluid is gas.

15. A method for determining thermal conductivity, k, and specific heat, c_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_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.

16. The method of claim 15 wherein c_p is determined with respect to an upward transient temperature change in the sensor.

17. The method of claim 15 wherein c_p is determined with respect to a downward transient temperature change in the sensor.

18. The method of claim 15 where the fluid is a gas.

19. The method of claim 15 wherein said output related to the rate of change of temperature of the sensor is obtained by the step of measuring the time interval for the sensor temperature to change between two known temperatures.

20. The method of claim comprising the step of adjusting the two known temperatures used for determining the rate of change of temperature said thermal sensor to produce the most accurate results for a given fluid of interest.

21. 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

space="preserve" listing-type="equation">k=a.sub.4 U+a.sub.5

where U is the sensor output and a₄ and a₅ are constants.

22. The method of claim 21 wherein the constants a₄ and a₅ are determined based on a known value of k for one or more fluids.

23. The method of claim 21 where the fluid is a gas.

24. A method of determining thermal conductivity, k, and specific heat, c_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

space="preserve" listing-type="equation">k=a.sub.4 U+a.sub.5

where U is the sensor output and a₄ and a₅ 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_p of the fluid of interest based on the relation

space="preserve" listing-type="equation">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

a₁, a₂ and a₃ are constants

P=pressure (psia)

P_o =reference pressure (psia)

(t₂ -t₁)=measured time span for the temperature of the thermal sensor to sensor to change between known temperatures.

25. The method of claim 24 wherein c_p is determined with respect to an upward transient temperature change in the sensor.

26. The method of claim 24 wherein c_p is determined with respect to a downward transient temperature change in the sensor.

27. The method of claim 24 comprising the step of adjusting the two known temperatures used for determining the rate of change of temperature said thermal sensor to produce the most accurate results for a given fluid of interest.

28. The method of claim 24 where the fluid is a gas.