Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity

Definitions

• the present invention relates to a method for continuously measuring the thermal conductivity of a multifunctional fluid in which a sample of said multifunctional fluid is passed through a space delimited by a first face, called the inlet, and a second face, said outlet, and in which an increase in the temperature of said multifunctional fluid sample is generated and this increase in temperature is measured.
• It also relates to a device for measuring the continuous thermal conductivity of a multifunctional fluid
• a device for measuring the continuous thermal conductivity of a multifunctional fluid comprising means for passing a sample of said multifunctional fluid into a space delimited by a first face, called the inlet, and a second face, called the outlet of said sample, heating means for varying the temperature of this sample and means arranged to measure the variation of this temperature.
• a multifunctional fluid is a fluid which can consist of several components which can be in different phases, liquid, solid or gaseous.
• a simple example of a multifunctional fluid is blood.
• Other multifunctional fluids are, for example, two-phase mixtures made up of phase change materials, commonly called PCM, suspended in a liquid and an ice slurry.
• Thermal conductivity in particular, defines the degree of heat propagation in a material as a function of the temperature gradient. Conduction is essentially a transfer of energy under the effect of movement, in particular the vibrations of particles.
• the conduction coefficient k (W / m.K) depends on the crystal structure in the solids, on the homogeneity, on the temperature, on the pressure, on the liquid, solid or gaseous phase and / or on the composition.
• liquids are better conductors than gases and solids better conductors than liquids.
• the conductivity of liquids depends primarily on their temperature.
• the German publication DE 199 49 327 A1 describes a method and a device for implementing this method for determining the concentration of a gas in a gas mixture comprising several components.
• the process is based on the measurement of the thermal conduction of the gas mixture which undergoes a rise in temperature between a minimum value and a maximum value determined by a temperature / time function. Analysis of the temperature variation curve as a function of time makes it possible to determine the concentration of a gas contained in the mixture.
• the device includes a temperature sensor which transmits a signal to a Fourrier analyzer. Such a device is not suitable for measuring the thermal conductivity of a multifunctional fluid.
• the object of the present invention is to overcome this drawback by providing a method and a device which make it possible to determine quickly, efficiently and economically the thermodynamic characteristics of a multifunctional fluid and to deduce the thermal conductivity therefrom.
• This object is achieved by a process as defined in the preamble and characterized in that: in addition, at least one very brief pulse of a thermal flux is transmitted to said sample, through said first input face, - the temperature is measured at at least three points spaced within this sample, this temperature determines the evolution of the temperature of the multifunctional fluid at these three points as a function of time, it is determined as a function of this evolution, the thermodynamic characteristics of the sample of said multifunctional fluid, and the thermal conductivity of this sample is calculated.
• said heat flux pulses are transmitted repeatedly and a thermogram is established, consisting of curves of temperature evolution as a function of the time elapsed between sending a heat flux through said first inlet face and the rise in temperature observed at said at least three points spaced inside the sample.
• the thermal conductivity is deduced from the following equation:
• T is the temperature k is the thermal conductivity depending on the temperature t is the time.
• ⁇ is the thermal diffusivity dependent on k and which is equal to: k (T)
• the device as defined in the preamble and characterized in that it further comprises means arranged to transmit to said sample, through said first input face, at least one very brief pulse of a flow thermal, means arranged to measure the heat wave at at least three spaced points inside this sample, means arranged to determine from the measured values the evolution of the temperature of the multifunctional fluid as a function of time at said times spaced points inside the sample, means arranged to deduce from this development the thermodynamic characteristics of the sample of said multifunctional fluid and means arranged to calculate the thermal conductivity of this sample.
• said means arranged to pass a sample of said multifunctional fluid into the space delimited by said first and second faces comprise an enclosure having a wall insulation and an internal coating of polished metal, which is continuously traversed by the multifunctional fluid.
• Said means arranged to transmit to said sample at least one very brief pulse of thermal flux comprises at least one laser.
• said means arranged to transmit to said sample at least one very brief pulse of thermal flux may comprise an emitting tube.
• Said means arranged to measure the heat wave having passed through the sample preferably comprise a receiving tube.
• said means arranged to determine the evolution of the temperature of the multifunctional fluid as a function of time comprise at least three temperature probes arranged to measure the temperature of the sample of multifunctional fluid at said at least three points.
• Said means arranged to deduce, from the evolution of the temperature at said three spaced points in the multifunctional fluid sample, the thermodynamic characteristics of this sample and calculate its thermal conductivity preferably comprise a calculating unit arranged to receive said temperature probes signals corresponding to the measured values.
• FIG. 1 is a block diagram illustrating the implementation of the method according to the invention
• FIG. 2 is a view schematically illustrating an embodiment of the device of the invention
• FIG. 3 is a sectional view of an advantageous embodiment of the device of the invention.
• FIG. 4 represents a sectional view of a measurement probe used in the device of the invention.
• the method firstly consists in selecting a sample 10 of a multifunctional fluid to be studied, for example by circulating it between two walls 11 and 12 thermally insulated from a conduit or enclosure of a suitable shape to define a first face, called the inlet face, 13 and a second face, called the outlet face, 14.
• the fluid is preferably subjected to a rise in temperature by usual means.
• at least one very short pulse of a thermal flux illustrated by arrow 15, is transmitted through the first input face 13, for example by means of a laser. Following this pulse, a heat wave propagates through the sample 10 and crosses said second outlet face 14. It is represented by the arrow 16 and measured by an equipment 17.
• At least three probes S1, S2 and S3 spaced inside the sample make it possible to plot the curve of the evolution of the temperature of the multifunctional fluid as a function of time by providing a thermogram.
• a calculation unit makes it possible to deduce from this evolution the thermodynamic characteristics of the sample of said multifunctional fluid and to calculate the thermal conductivity of this sample.
• the method preferably includes the repeated sending of heat flashes and the measurement is carried out repeatedly.
• the device 20 for implementing the method for measuring the thermal conductivity of a sample of a multifunctional fluid comprises a first tube transmitter 21 and a second receiver tube 22, disposed opposite so that the space separating their respective ends 21a and 22a define said first inlet face 23 and said second outlet face 24 of this sample.
• a pulse called thermal flux flash, is emitted by the emitter tube 21, passes through the sample in the form of a heat wave and is picked up by the receiver tube 22.
• the two tubes are advantageously a few centimeters long and a diameter less than 0.01m. They contain the electronic components necessary for pulse control and measurement management. They are respectively mounted on two supports 21b and 22b made up of rigid conductive wires.
• FIG. 3 is a sectional view of a measuring device 30 according to the invention. It mainly comprises an enclosure 31 having an insulating wall 32 and an interior coating of polished metal 33. This enclosure is continuously traversed by a multifunctional fluid, such as for example an ice slurry whose thermal conductivity is desired. This fluid enters the enclosure 31 through a conduit 34 and leaves this enclosure through a conduit 35. It is further equipped with a chamber 36 containing heating elements 37 which are arranged to vary the temperature of the sample. of multifunctional fluid.
• heat flux pulses represented by an arrow 38, are preferably generated repetitively, through the entry face, for example by a laser 40,.
• the heat waves generated pass through the sample of fluid contained in the enclosure 31, emerge from the enclosure (arrow 39) and are measured by at least three temperature probes S1, S2 and S3 spaced from each other and arranged inside the sample.
• the thickness e of the enclosure 31 is known with precision. This thickness can be variable to allow the measurement parameters to be varied.
• the device 30 is equipped with instrumentation (not shown) comprising a micrometer which makes it possible to precisely determine the thickness e of the enclosure 31.
• the two conduits 34 and 35 are respectively equipped with a valve 41 , 42 which makes it possible to control the continuous entry, exit and circulation of the multifunctional fluid in the enclosure.
• the probe 50 corresponds to an advantageous embodiment of the temperature probes S1, S2 and S3 mentioned above. It actually combines the measurement of temperature and the measurement of electrical conductivity. It is immersed in a multifunctional fluid 51. It comprises a temperature sensor 52 and a sensor for measuring the electrical conductivity 53 of the multifunctional fluid. These two sensors are for example mounted on the inner wall of a tubular element 54 carried by a support 55 immersed in the multifunctional fluid.
• the device according to the invention advantageously operates in the following manner.
• Means, for example the enclosure 31, make it possible to isolate a sample of said multifunctional fluid.
• Means, constituted for example by instrumentation comprising a micrometer, make it possible to determine the thickness of said enclosure.
• Means, for example constituted by the heating elements 37 make it possible to generate an increase in the temperature of the sample.
• Means such as the laser 40 make it possible to generate and transmit to the sample at least one very brief pulse of thermal flux and preferably a series of such pulses.
• Means such as the receiving tube 22, illustrated in FIG. 2 make it possible to measure the heat wave having passed through the sample.
• the temperature sensor 52 of FIG. 4 makes it possible to determine the evolution of the temperature of the multifunctional fluid as a function of time.
• a calculation unit (not shown) makes it possible to deduce from this evolution the thermodynamic characteristics of the sample of said fluid and to calculate the thermal conductivity of this sample.
• T is the temperature k is the thermal conductivity depending on the temperature t is the time ⁇ is the thermal diffusivity dependent on k and is worth: k (D p * Cp with p and Cp the density and the specific heat.
• thermogram which is based on the only available experimental data.
• heat equation should be rewritten by highlighting two temperature-dependent coefficients:
• Phase change materials commonly called PCM (Phase Change Material) are alkane polymers whose solid-liquid phase change temperature varies between 0 and 65 ° C. PCMs have an advantage for static uses, for example storage , and dynamic, for example the transport of thermal energy.
• PCMS liquid form
• PCMS is constituted by the ice slurry. Adding small flakes of ice to an aqueous solution results in a pumpable liquid mixture. This mixture gives the possibility to combine in an ecological and economical way the advantages of cold storage and indirect cooling with the high cooling capacity of the direct expansion.
• Temperature and conductivity sensors are commercially available. Their arrangement on a support immersed in the multifunctional fluid can be adapted according to needs and applications.

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• Physics & Mathematics (AREA)
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• Life Sciences & Earth Sciences (AREA)
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• Analytical Chemistry (AREA)
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• General Physics & Mathematics (AREA)
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• Investigating Or Analyzing Materials Using Thermal Means (AREA)

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• 2002
  • 2002-11-28 CH CH02007/02A patent/CH696042A5/fr not_active IP Right Cessation
• 2003
  • 2003-11-28 EP EP03773407A patent/EP1565731A1/de not_active Withdrawn
  • 2003-11-28 US US10/536,855 patent/US7350971B2/en not_active Expired - Fee Related
  • 2003-11-28 JP JP2004554149A patent/JP2006508341A/ja active Pending
  • 2003-11-28 CA CA002506759A patent/CA2506759A1/fr not_active Abandoned
  • 2003-11-28 WO PCT/CH2003/000788 patent/WO2004048953A1/fr not_active Ceased

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