Time lag approach for measuring thermal conductivity and specific heat
First Claim
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1. Apparatus for determining a selected property of a fluid of interest, comprising:
- heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature;
heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a transient elevated temperature condition in said heater means;
sensor means in thermal communication with the fluid of interest and spaced from said heater means, said sensor means having a resistance that changes with temperature;
first time lag means for determining a first time lag between the transient elevated temperature condition of said heater means and a transient elevated temperature response of said sensor means; and
determining means for determining the selected property of the fluid of interest using the first time lag.
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Abstract
A method and apparatus for providing a more direct approach to determine the thermal conductivity, thermal diffusivity and specific heat of a fluid of interest, independently of the amplitude of the sensor output. This is preferably accomplished by measuring one or more variable phase or time lags between selected input and output AC signals, and directly deriving the thermal conductivity, thermal diffusivity and specific heat therefrom. Such derivation is therefore less dependent than amplitude-based sensors on occasional or unpredictable drift in sensor resistive elements.
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Citations
17 Claims
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1. Apparatus for determining a selected property of a fluid of interest, comprising:
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heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature; heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a transient elevated temperature condition in said heater means; sensor means in thermal communication with the fluid of interest and spaced from said heater means, said sensor means having a resistance that changes with temperature; first time lag means for determining a first time lag between the transient elevated temperature condition of said heater means and a transient elevated temperature response of said sensor means; and determining means for determining the selected property of the fluid of interest using the first time lag. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. Apparatus for determining selected characteristics of a fluid of interest, comprising:
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heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature; heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a periodic time-varying input signal to said heater means to induce a transient elevated temperature condition in said heater means; sensor means in communication with the fluid of interest and spaced from said heater means, said sensor means having a resistance that changes with temperature; and sensor energizing means connected to said sensor means for energizing said sensor means, said sensor energizing means providing a periodic time-varying input signal that has a phase relative to said time-varying input signal of said heater energizing means so that substantially no heat is transferred from the fluid of interest to said sensor means during the transient elevated temperature condition. - View Dependent Claims (12)
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13. A method for determining selected characteristics of a fluid of interest under non-vacuum conditions using a heater means and a sensor means, wherein each of said heater means and said sensor means are in thermal communication with the fluid of interest and have a resistance that changes with temperature, the method comprising the steps of:
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energizing the heater means with a periodic time-varying input signal to induce a transient elevated temperature condition in said heater means; energizing the sensor means with a periodic time-varying input signal that has a phase relative to said period time-varying input signal that is provided to the heater means such that substantially no heat is transferred from the fluid of interest to said sensor means during the transient elevated temperature condition. - View Dependent Claims (14, 15, 16, 17)
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Specification