HEAT FLUX CONTROL METHOD AND APPARATUS FOR CALORIMETRY, ADIABATIC SHIELDING, PRECISE TEMPERATURE SETTING AND THE LIKE

Abstract: A method and an apparatus of heat flux control for calorimetry, adiabatic shielding, precise temperature setting and the like, on an object (2). The steps are provided of arranging a shield (1) about the object (2); heating uniformly (5) the shield (1) and monitoring (3) the heating step to maintain the shield (1) at a chosen temperature; arranging about the shield a thermal bath (7) at a known temperature in any case lower than the temperature of the shield (1); measuring the temperature of the object (2); and controlling (8) the heat flux (5) between the object (2) and the shield (1) by checking the temperature (4) of the object (2) and the temperature (3) of the shield (1). The application in the field of the calorimetry allows advantages and the use of a same calorimeter both in the classic adiabatic way, and in the temperature scanning adiabatic way as well as in the modulated way.

Description: TITLE HEAT FLUX CONTROL METHOD AND APPARATUS FOR CALORIMETRY, ADIABATIC SHIELDING, PRECISE TEMPERATURE SETTING AND THE LIKE. DESCRIPTION Field of the invention The present invention relates to a heat flux control method for calorimetry, adiabatic shielding, precise temperature setting and the like. In particular, but not exclusively, the invention relates to a method for analysing the thermodynamic characteristics on samples and the kinetics of the active processes in said samples. The present invention relates also to an active shield for controlling the heat flux for calorimetry, adiabatic shielding, and the like. Furthermore, in particular, the invention relates to a calorimeter that uses this shield, operating both in adiabatic and in modulated way as well as in temperature scanning way. Description of the prior art In the field of calorimetry, it is felt the need to encompass in an effective and substantially not complex way .all the problems of heat flux precise control from and towards an object and then of its temperature, also in the presence of energy delivered by the object controlled. These control could also be exploited in measuring instruments, optical devices, electronic circuits, solid state components delivering heat, sensors, etc. A particularly felt need is to minimise the temperature gradient on the object, also when its temperature has to be thoroughly changed, such as in calorimeters known as temperature scanning calorimeters . For carrying out precise heat measures of quantities such as for example heat capacity of bodies or substances, or the heat delivered by chemical reactions, it is necessary to provide calorimeters having good sensitivity, precision, adaptability, to the characteristics of the sample, as well as the possibility of inspecting wide temperature ranges. In particular, calorimeters of this kind can be used for controlling industrial processes and for product testing, provided they are not too complicated and they can be put in automatic measuring procedures. Modern calorimetry provides new methods that allow also measuring the kinetic characteristics and the analysis of systems far from the thermodynamic equilibrium [M. Cassettari, et al . , Rev. Sci. Instrum. , 64, 1076-1080 (1993)] . In some advanced industrial calorimeters measuring techniques with temperature modulation are provided applied to traditional DSC calorimeters, operated by computer and data analysis software. It is possible, this way, to measure at the same time complex heat capacity and enthalpy of processes by modulating the temperature through sinusoidal signals [M. Reading, et al . , J. Therm. Anal., 40, 941 (1993)] or triangular signals [J.E.K. Shawe, Thermochim. Acta, 261, 183 (1995)], at a frequency normally less than 0.1 Hz, in addition to the normal linear temperature scanning . Literature documents relating to these methods [C Schick, et al . , Temperature Modulated Calorimetry, Special Issue, Thermochim. Acta, 304 (1998)] analyse the drawbacks of the structure of DSC calorimeters, which does not allow an accurate control of the sample temperature . So called adiabatic calorimeters presently known have the problem of providing thick insulation, or insulation under vacuum, reflective surfaces, etc., which increase the costs, make their use complicate and, in any case, are not suitable for slow measures requiring long time, since the adiabatic condition can be maintained only within limited time ranges. Other prior art calorimeters are described in previous patent specifideations [CNR -D.Bertolini, et al . , IT9528A/86; CNR-G . Salvetti , et al . , IT9471A/90; M.Cassettari, et al . , IT/FI91A000226 ; D.Bertolini, et .al . , IT/FI93A/000013] . Summary of the invention It is an object of the present invention to provide an improved method for calorimetry which has not the drawbacks of the prior art . It is another object of the present invention to provide a method for calorimetry that allows the measures, for both liquid and solid samples: i) (in an adiabatic way) of heat capacity at equilibrium, of enthalpy variation during slow processes and of transition temperatures; ii) (in a modulated temperature scanning way) contemporaneously of heat capacity real and imaginary parts w.r.t. the modulation frequency, of enthalpy variation speed due to the chemical/physical processes occurring in the sample, of the characteristic temperatures and of the kinetic constants. It is another object of the present invention to provide a calorimeter safe to use and having a not too complicated structure of the head and of the calorimetric cell. Particular object of the invention is to provide a method of heat shielding and a correspondent calorimeter that allow one or more of the following advantages: - filtering the environment temperature fluctuations about an object, minimising the temperature gradient; - achieving equivalent adiabatic conditions for an object to analyse, without the use of vacuum and reflective surfaces; - working in isothermal conditions even when in the object chemical -physical slow energy production processes are present; - working in a programmable way in case of temperature and/or heat controlled conditions also for long periods; - monitoring in a precise way the temperature of an object in which energy production processes occur, without the use of auxiliary heat sources located on the object same ; - modulating the temperature of the object according to a predetermined time law without the use of hot or cold sources located on it, also with the possibility of up or down variation of the temperature of the sample, by adjusting the heat flux; - minimising the heat spurious couplings on the sample; - allowing a preliminary automatic calibration test on temperature, heat capacity, and heat flux; - arranging more than one measuring cell in parallel to one another and minimising the heat capacity of such cells; - allowing the use, for particular temperature ranges, of punctual sensors (i.e. NTC) , which are much more sensitive than thermoresistors provided the temperature on the sample is constant. These and other objects are achieved by the method according to the present invention of heat flux control for calorimetry, adiabatic shielding, precise temperature setting and the like, on an object, comprising the steps of: - arranging a shield about the object; - heating uniformly the shield and adjusting the heating to keep the shield at a chosen temperature, - arranging about the shield a thermal bath at a known temperature in any case lower than the temperature of the shield; - measuring the temperature of the object; - controlling the heat flux between the object and the shield by checking the temperature of the object and the temperature of the shield. In an adiabatic functioning, the shield is kept at a temperature equal to the object, whereby said heat flux between the object and the shield is substantially zeroed. In a temperature scanning functioning, successive steps are provided of heating the object for transmitting to the object a predetermined heat flux and/or for bringing in turn the object to different chosen temperatures, the heating step of the shield keeping the temperature of the shield at predetermined distance from the temperature of the object. According to another aspect of the invention, an apparatus for controlling the heat flux for calorimetry, adiabatic shielding, precise temperature setting and the like, on an object, comprises - a hollow shield suitable for containing the object; - heating means distributed uniformly on at least a portion of the shield; - means for measuring the temperature of the shield distributed uniformly on at least a portion of the shield at least in partial superimposition with the heating means, - a thermal bath arranged about the shield kept at a known temperature in any case lower than the temperature of the shield; - means for measuring the temperature of the object; - means for controlling the heat between the object and the shield flux delivered by said heating means as a function of temperature signals of the means for measuring the temperature of the shield and of the means for measuring the temperature of the object. A embodiment of the apparatus for carrying out also temperature scanning calorimetry, comprises heating means distributed uniformly on at least a portion of the object, suitable for transmitting to the object a predetermined heat flux, the means for controlling the heat flux operating the heating means of the shield setting in turn a fixed difference between the signals of the means for measuring the temperature of the shield and the signals of the means for measuring the temperature of the object. Brief description of the drawings Further characteristics and the advantages of the method and of the apparatus, according to the invention, will be made clearer with the following description of some its embodiments, exemplifying but not limitative, with reference to attached drawings, wherein: - figure 1 shows a sectional view according to a vertical plane of a calorimeter associated to an active heat shield that carries out the method according to the invention; - figure 2 shows a sectional view according to a vertical plane of the assembly of a calorimetric head and of a cell of a calorimeter according to the invention; - figure 2A shows the calorimetric head of the calorimeter of figure 1; - figure 2B shows the calorimetric cell associated to the head of the calorimeter of figure 1; - figure 3 shows a sectional view according to a vertical plane of a calorimeter according to the invention having a double cell; - figures 4A and 4B show two different embodiments of the cell of figure 2, 2B or 3 ; - figure 4C shows a cross sectional view of a shield according to the invention capable of housing four cells like those shown in figures 2, 2B, 3, 4A, 4B . - figure 5 shows a block diagram of the calorimeter that carries out the method according to the invention; - figures 6A-6D show flow-sheets of the operations controlled by the software of the calorimeter of figure 5 in the adiabatic way; - figures 7A-7D show flow-sheets of the operations controlled by the software of the calorimeter of figure 5 in a modulated way and in a temperature scanning way. Description of the preferred embodiments According to the present invention, with reference to figure 1, for a precise control of the temperature of an object 2, a calorimeter is provided having a shielding side surface or shield 1 having cylindrical symmetry closed by plugs of insulating material 6. Obviously, for its simplicity cylindrical symmetry is preferred, even if the geometry, in the respect of the conditions described hereinafter, may have various shapes, not described but obvious for a man of the art . Shield 1 of the calorimeter is associated to a first uniformly distributed winding thermoresistor 5, for heating shield 1, and to a second thermoresistor 3 for measuring the average temperature of shield 1 and for the calculus the radial heat flux. Outside a thermal bath 7 is provided having a predetermined reference temperature, in any case lower than the temperature of shield 1. The control of shield 1 is carried out by adjusting the power fed by a programmable supplier 8 (PPS) to heater 5, for keeping it at the working temperature that must, as above said, be higher than the temperature of the thermal bath 7 in which it is located. A software residing in a PC 9, according to a suitable Proportional-Integrative-Derivative procedure (PID) , carries out a control of supplier 8 (PPS) calculated as a function of temperature T of object 2, read by a multimeter scanner 10 (MS) through a thermometer 4. Thus a difference of temperature δT is set between shield 1 and object 2, fulfilling an equation of equilibrium described hereinafter, to obtain a control of shield 1 enough quick and with reduced power, it is necessary to minimise its heat capacity and use material having high heat conductivity. Considering now the equilibrium thermodynamic of object 2 at the temperature T, whereas: - object 2 houses energy production processes that cause a variation of enthalpy ΔH; - exchanges with the environment outer an amount of heat δq; - exchanges an amount of heat δQ with shield 1. The state of equilibrium at a temperature steady is data from the equation: δQ + ΔH + δq =0 (1) that, referring to the power exchanged, that better expresses the actual exchanges in shield 1, becomes P s + dH/dt + Pa = 0 (2) , wherein - Ps = λδT is the power exchanged with shield 1, equal to the product of the coefficient of heat exchange λ, function of the temperature T, multiplied by difference of temperature δT between object 2 and shield 1; - dH/dt is the difference of variation of the enthalpy; - Pa is the power exchanged with the environment through the plugs of material insulating 6, function of the temperature T. In many calorimetric applications it is necessary to adjust progressively temperature T of object 2, or more precisely of a sample inserted in object 2 that may be a calorimetric cell. Eq. (2) becomes: Ps + dH/dt + Pa + Pe = Cp dT/dt (2') wherein C is the heat capacity of the sample and Pe a power external supplied in way suitable to the sample for changing its the temperature or to provide an amount predetermined of heat. The difference of temperature δT between shield 1 and object 2 It is, then, according to the two functioning different of the calorimeter: a) kept fixed for working to flow fixed of heat between object 2 and shield, and in particular with the δT = 0 for working in way adiabatic; b) calculated for fulfil the Eq. (2'), in order to modulating in turn the temperature T. Per to obtain the better operation of shield 1 is necessary making Pa through the plugs 6 minimum and slight with respect to Ps exchanged between object 2 and shield 1. In the case of a cylindrical symmetry to the that shown in Figure 1 this is traduce in a big ratio length/diameter and in the use of plugs 6 insulating heat located suitably also considering the characteristics of the thermal bath 7. Furthermore is necessary use sensors 3 and heaters 5 uniformly distributed on all the surface controlled of shield 1. Finally, vanno scelti the material to the precise of to minimize the time characteristic of heat exchange and to provide the better conditions of invarianza of equal. In fact, the time of intervento of the procedure of control PID of the temperature of shield 1 have to be reduced to the minimum, in order to avoid fluctuation on the temperature of the object controlled, a good shield 1 according to the invention can, with the interventi of control to the range about of the second, keep the temperature fixed to less of 0.001°C, also for time very long. The equation (2') contains all the information necessary for investigating calorimetric of the sample. for ricavarla with the maximum of sensitivity and precision is necessary ricorrere to modi calorimetric different which, in type, require also the use instruments different . According to the invention, instead, a same calorimeter hereinafter described with reference to figures 2, 2A, 2B, can be used for working both in way adiabatic that in way to modulation of temperature. The calorimeter 20 comprises a head 30 and a cell 40, in which is inserted a sample 25, suspended to a wire 21. The head 30 (figure 2A) of the calorimeter comprises a block 7 cylindrical of aluminium or other material metal to high heat conductivity, with a hole central 32 of diameter sufficient to containing the calorimetric cell 40. the block 7 houses a 0-ring of kept 33, for support of a plug cylindrical 34, connected to the block 7 and fact of equal material, suitable for supporting the calorimetric cell 40 and provided of passing electrical 34a. on the plug 34 is fixed coaxially a tube 35 to thin walled, for example of steel stainless of length and diameter such by to allow the introduction of the sample 25 from the outer. The calorimetric head 30 is sized in order to work from thermal bath 7 of figure 1, designed in order to assuring the necessary steadiness heat (±0.002°C) and the temperature working minimum demand, the function unwound from the calorimetric head 30 it is therefore that of creating an environment at a temperature uniform and exchanges heat radial about the calorimetric cell 40. the gap 41 between the head 30 and the calorimetric cell 40 are minimum in order to prevent from the convection and reducing to the maximum the exchanges along the axis of the cell 40. Nel block 7 of the head 30 is made a hole 36 for housing the probe of a thermometer of reference, for example a thermometer to the platinum, necessary for adjustment absolute of the calorimeter both in direct phase of testing that for possible check following. The cross section vertical of the calorimetric cell shown in Figure 2B comprises - a cylinder of metal 49, with a recess inner 48 suitable to receive the sample 25, for example a test tube containing a substance from analyse . - lo shield cylindrical 1, of aluminium or other good conducting of heat, located coaxially to the cylinder 49, in order to to provide a gap circular 45 of some mm. Shield 1 is closed in low with a plug hollow metal 6 that houses in a cylinder of material insulating 50 and is shaped with a flange 16 to the precise of reducing the exchanges heat towards the low and assuring the centering of cell 40 inside of the recess 32 of the calorimetric head 30. A plug metal upper 51 is screwed to stop shield 1. It supporta both of the support insulating 43, in tube capillare of steel stainless to which is fixed the cylinder metal 49, which passing for conducting electrical (not shown) . Sul cylinder 49 are arranged, in way uniform and uninductive, two windings: a first winding inner 46 formed by a resistor of manganine, longer and a second winding inner 4, shorter, formed by two thermoresistors in material thermoresistive, for example platinum or alloy 99 delivered by Driver-Harris. the three resistors are suitably insulated between of thereof with the material insulating to the web of Teflon, varnish polymeric, material ceramic etc. the characteristics fisico-chemical of the material used to the insulating electrical cause the temperature range wherein the calorimeter can be used. Sullo shield 1 are made, in way similar to figure 1, a first winding outer 5 (i.e. of manganine ), longer and a second winding outer 3 (i.e. of alloy 99), shorter, the first windings longer, -5 and 46, are, respectively, the heaters of shield 1 and of the sample cell 40, whereas the seconds windings shorter 3 and 4 are the thermoresistors for measuring the temperature average and for definition the heat flux radial used hereinafter, the windings 5 and 3 extends for height equal, respectively to windings 46 and 4. Cell 40 (figure 2) is fixed to the plug 34 of the head 30 from the support 43. The gap circular 41 that separates cell 40 from the block 7 of the head 30 is for example of 1-2 mm, to the precise of substantially prevent from exchanges for convection. are furthermore shown electrical connections 37 and 38, the heat insulator 39, located in order to reducing the convection towards the above of the recess, and the sample 25, suspended to the wire thin 21. A characteristic relevant of the head 30 and of the calorimetric cell 40, according to the invention, is the cylindrical symmetry of the whole structure, which achieves the maximum reduction of the exchanges heat along the axis vertical. With reference to figure 3, is shown a different embodiment of the calorimeter of figure 2, having two cells contiguous, a sample cell 40a and a cell of reference 40b. The head 30 has a single block cylindrical 7, of aluminium or other material metal to high heat conductivity with a hole central 32 of diameter sufficient to containing the cells 40a and 40b, formed by the single shield 1 on which are provided the windings 5 and 3. The head 30 has a structure that avoids the continuity heat between the cells and the outer. More precisely, a plug cylindrical 62 upper, which comprises the insulating axial 66, is connected to the block 7 to keep hanging the cells 40a and 40b and the passing electrical (not shown) , by means of a thin walled stainless tube 65. A lower plug 64 contains another axial insulation 66. two tubes 35a and 35b, to thin walled of steel stainless, are connected protruding from the plug upper 62, of length and diameter such by to allow the introduction from the outer of the sample 25a from analyse and of the sample 25b of reference. The characteristics and the functions unwound from the calorimetric head of figure 3 are the same to the described for calorimeter of figure 2. In both cases, the calorimetry can be made always to the in a calorimeter differential: - in. the case of figure 2 the cell of reference is virtual and is simulated through a thermogram obtained, once for tutte, in a measure preliminary fatta on cell 40 without sample 25. During the measure preliminary the data are recorded in order to being utilizzabili in all the measuring following, made in equal conditions. The use of the reference virtual it is possible since the temperature of the sample cell 40, of shield 1 and of the thermal bath 7 follow equal time ranges, connected by the program, and are fixedmente under control in every measure. Eventi improvided that dovessero invalidare the assunzioni on which is basa the use of the reference virtual not can then sfuggire to the operator, which can tenerne conto or repeat the measure . - in the case of figure 3 the cell of reference 40b is actualmente present and the presence of the two cells twin 40a and 40b allows a calorimetry differential of high sensitivity, for example particularly suitable to the studio of samples biologici . the gain in sensitivity is due to the possibility measuring with the techniques lock-in the difference of temperature between the two cells 40a and 40b, by subtracting thus also the contributo of the cell of reference 40b, enpty or containing quanto of inpredetermined is sommi to the fenomeno and/or to the substance present in 25a that is to be studiare. Furthermore it is possible usare on the cells 40a and 40b, for temperature between 0°C and 100°C, sensors NTC puntuali 4, whose sensitivity is very higher of the thermoresistors uniformly distributed described for calorimeter of figure 2. This it is possible for uniformity of the temperature on the sample 25a, assured by shield 1 according to the invention, whereas a temperature not uniform would frustrate the high precision of these sensors. The calorimeters of figures 2 and 3 can adapt to different dimensions of sample, as shown in figure 4A, with the cell for volumi smaller (i.e. from 0.1 to 0.2 cc) , and in figure 4B, with the cell for volumi any more grandi (i.e. from 10 to 15 cc) . Obviously, in way similar to the single shield 1 for two cells, as shown in figure 3, is also possible to provide a double calorimeter or a calorimeter with the three cells sample and a cell of reference for measuring multiple simultaneous. In figure 4C shield 1 has four recess 32 for corresponding cells, not shown, and has five holes 69 with the function of reducing the heat capacity of the shield same. Hereinafter, the examples made for case of figure 2 can be clearly being extended to the case of figure 3 without troubli.e. In figure 5 is shown the block diagram of the calorimeter of figure 2, with the indicazione also of the control electronic unit. a PC 70, wherein resides a software hereinafter described, is connected con: - suppliers 71 and 72, of the first winding inner 46 and of the first winding outer 5 of shield 1; - a amplifier lock-in, 73, which measure with the „ big sensitivity the resistance of the sensor of temperature 3 located on the cell sample; - a multimeter scanner 74, which measure the resistance of the other two sensors of temperature coupled ; - a thermometer 75 of the thermal bath 7. The particular configuration of the calorimeter of figure 2 (o of figure 3) according to the invention, allows to obtain, cambiando single the software, different functionings, from choose according to the characteristics of the sample and the object of the measure, is thus possible working. a) nel way adiabatic classic [A. V. Voronel ' , et al., Sov. Phys . JETP 18, 568 (1964)], b) nel way adiabatic to scanning [F.A. Lipa et al., Phys. Rev. Lett., 25, 1086 (1970) ] and c) nel way modulated to scanning. In all these operative ways shield 1 is essential since beyond to the task of thermal bath, has the task additional of follow the evolution heat of the cell sample, keeping to a distances fixed ΔT with the operation to heat flux fixed. The way of operation adiabatic a) is obtained giving that the flow total of heat on cell 40 both zero; this condition is obtained adjusting on the value of ΔT and is verificata from the constancy time of the temperature of the sample, the way adiabatic is executed without to make the vacuum in the recess 32 of the calorimetric head 30, with the considerable esemplificazione and reduction of the costs. The way of operation adiabatic to scanning b) is obtained setting the flow total to a value negative suitable, setting i.e. the temperature of shield 1 some degrees any more in low of that of the sample cell 40. in the way adiabatic to scanning it is possible to make measuring very accurate of heat capacity in heating, supplying a succession of pulses of energy equal, ΔQ, to the sample cell 40, to the range of time predetermined. The chosen temperature range is swept following ΔT xi steps. The heat capacity C p of the sample at temperature T + T xi /2 is calculated by the equation: C P (T+ΔT xi /2) = ΔQ(l/ΔT xi - 1/ΔToi) (3) wherein ΔToi is the correspondingly measured temperature step, in equal conditions, with the container 25 of the empty sample holder. To work in the adiabatic temperature scanning way b) it is necessary set ΔT equal to several centigrade degrees, so that the adiabatic condition of zero heat flux is obtained supplying to the sample cell a power Po. if the power is reduced from Po to Pr, then the temperature T of the cell decreases under the equation: For working in the modulation way according to c) and sweeping the temperature, both heating and cooling, it is always necessary that a temperature difference ΔT between sample cell 40 and shield 1 is available so that shield 1 is a cold source. The manganine winding 5 acts as hot source and allows to set cell 40 according to profile of temperature T s (t), normally of the type Ts(t) = Ti + βt + Tmcosωt (5) wherein Ti is the starting temperature, β is the sweeping difference, Tm is the amplitude of modulation at the frequency ω/2π. The cell sample, which has under vacuum heat capacity Cs, when contains a sample of heat capacity Cx, has a heat balancing given by the equation dHx(t,Tβ)/dt + CsdTs/dt + KsΔT = Ps(t,Ts) (6) wherein dHx/dt = dH/dt + Cxβ; Ks is the coefficient of heat exchange, which depends from the geometry and from the nature of the facing surfaces; Ps(t,Ts) is the power supplied to cell 40 for follow the profile of temperature predetermined Ts(t) . the term δH/dt contains the difference of variation of the enthalpy given to the occurring of processes chimico-fisici in the sample and the response of the internal energy of the sample to the modulation of the temperature . Without sample can be written an equation similar to the Eq. (6) where not compare the first term to left, whereas the term to right is the value of the power P v (t,Ts), from to provide to the cell empty. Pv(t,T s ) is acquisita during the measure to obtain the reference virtual. By subtracting from the Eq. (6) the similar written for cell without sample, is obtained Ps(t,T s ) -Pv(t,Te) = dHx(t,T s )/dt (7) Dalla Eq. (7) segue that all the information thermodynamic and dynamic relative to the sample is contained signal difference of the power fed to the cell, with the and without sample. The equation (7) is verac measure wherein the assunzioni made are tradotte in the progetto costruttivo and executed in the instrument, the difference of variation of the enthalpy of the sample in the Eq. (7) can be written, when the temperature both fatta adjusting according to the Eq. (7) and both possible have conditions of response linear, to the dH (t,T s )/dt = dΑ/dτ + C β - ωC 'Tmsin(ωt) + ωC "Tmcos (ωτ) (8) X X X wherein C x ' and C x " are the part oscillating in direct phase and in opposed phase respectively of the heat - In capacity of the sample. The Eq.7, introducing the expression of 9H/3T contained Eq.8, diviene P s (t,T s ) - Pv(t,T ε ) = - δH/έ>T-C x β + ωC x 'Tmsin(ωt) - ωC x "TmCθs (ωτ) (9) The software provides the analysis of the signal of power acquisito in the ^ range time nτ < τ < (n+l)τ versus trasformata discreta of Fourier to the frequency ω, assumendo that the enthalpy deliver δH/δT both approssimabile with a production in serie of Taylor limitato at the end of first ordine, and that the components of the heat capacity possano considerarsi constants during the range of time τ. Is obtained thus: P s (t, T s ) - P v (t, T s ) = Pn + P'cos(ωτ) + P"sin(ωt) (10) wherein Pn is the average value of the power range of time considerato; P' and P" are the components in direct phase and in opposed phase, respectively. Dall'Eq. (9) and (10) is obtained: (d /dτ + c x β) τ=nτ = -P * n C x '(ω,t=nτ) = l/ωT m . (Pn" - (P * n+1 - P * n ) /π) (11) The software provides then, to the time ranges r, the heat capacity complex C=C x '+iC x " and the difference of variation of the enthalpy of process, according to the first of the Eq. 11. The possibility of working both in way adiabatic that in scanning modulated of temperature allows the calibration of the calorimeter in way not complex and automatic and gives to the calorimeter a further characteristic advantageous of adjustment, hereinafter given, of all the physical quantities that characterise the instrument: steadiness and trend of the temperature; value of the power supplied, time characteristic etc.. Per calibrating the scale of temperature has been used a thermometer digital with the probe PtlOO, adjusted to the standard secondary of temperature, located hole 36 of the head 30 (figure 2A) . the temperature of the bath has been swept to steps of 1-5°C with delays of 15000s. the values of the resistance of the sensors have been read and recorded from the software of the program of calibration, calculating ^ the average of the measuring recorded in the last 600s, together with the value of the temperature of equilibrium determined by the thermometer, to the equilibrium heat the temperature of the head 30 has been located equal to that of the sensor 3 of the cell 40, being slight the heat flux due to couplings residues with the environment or to power electrical delivered onto the heaters or onto the sensors for measuring their the resistance, from the calibration of the thermoresistors obtained to the functions Ri (T) , for inversion, is calculates the calculus of the function thermometrical Ti (R) , i.e. the law of variation of the temperature of the sensors with electrical resistance of equal . the value absolute of the temperature of the sample, can be chosen at the temperature average of the surface external of the cell, since is located in conditions steady and without temperature gradient, the steadiness of the thermal bath allows to obtain the calibrations of the three sensors with a big precision (better of ± 0.001°C) . It is also possible the calculus of the time characteristic for process of relaxation of the temperature gradient heat inside of the cell sample, a relevant parameter from consider for a correct use of the calorimeter. The calibration absolute of the scale of temperature needs of a reference inner, which can be formed by a sample of water, which can be easily product from the operator or provided to the kit of the instrument from the manufacturer, the sample of water is preferably water ultrapure put into sample holder, partially filled and sealed forn being subcooled of many degrees, when the water freezes the heat latent of transition is thus big that not allows to all the mass of the liquid of solidficare: to the beginning is obtained a mixture water, ice and vapour at the ternperature of the triple point of the water (+0.01°C) . This condition can be kept time if the heat capacity of the cell empty is not too big with respect to that of the sample water and if is active automatically the way of step adiabatic, i.e. the shield salt quickly at the temperature of the cell sample, the thermometrical scale of the instrument, this way, has a precision better of 0.01°C The other calibration necessary is power P, delivered by heater 5 of the cell. This depends from the measuring precision of the voltage applied to the ends of the heater, a given this of kit of the multimeter used, considering of the even little according at the temperature of the electrical resistance of the manganine, of which is preferably made the heater, to obtain the calibration of the amount of heat, Q, is suitable also a calibration of the time scale. At the end of the calibrations, the precision obtainable is, using a multimeter with six digits: absolute temperature ± 0.01°C; power ± 0.001 mW; amount of heat ± O.OOlmJ. Hereinafter a possible embodiment of the software is described. A program which can be used is LabVIEW 3.0 of National Instruments, Austin, Texas, U.S.A. The flow diagrams of the software can drive the calorimeter in two main functioning: the adiabatic way (Figure 6A-6D) and the temperature scanning modulated way (Figure 7A-7D) . Adiabatic Way. With reference to figure 6A the Adiabatic way program starts with a step of thermalisation at the lowest temperature of the experiment (T threshold ) ; then it continues with a while-loop, which continuoes up to when temperature T c of the sample achieves predetermined value Tax,- every iteration of the loop is a temperature step during which is measures the step of temperature of the sample caused by the deliver of a known heat amount. At the end of every iteration there is a variable delay so that the duration of the iteration is exactly 3000 milliseconds . In Figure 6B is shown the routine of the ther alisation program of the sample at T threshold of figure 6A. During this step a first while-loop is active so that the temperature T c of the sample reaches a value T threshold . A second loop of 300 iterations brings the temperature of the shield T s to that of the sample T c by means of a procedure PID (proportional-integrative-derivative) that calculates the power P s to deliver to the heater of the shield. At the end of this step the program carries out the linear interpolation of the last 100 data recorded (see Figure 6D) . In Figure 6C are given in detail the operations carried out during the measure. A single loop of 300 iterations has two different steps: in the first 30 iterations a predetermined power P c is delivered to the sample; in the following iterations the power P c is set equal to zero. During all the loop the temperature T s is linked to T c by means of the PID procedure. Actually T s is kept to a value different from Tc of a little amount δT=αm, where α is a constant depending on the heat capacity of the cell and m is the slope of the temperature function T c (t), calculated in the linear interpolation of the previous step. Finally, in Figure 6D is given the diagrammatical operative view of the linear interpolation. Among the 300 data stored in the last loop, the last 100 are selected to execute a linear fit of the temperature T c as a function of the index of iteration of the FOR loop: To (i) =Tf+m*i , where and m is the slope of the line of fit. From the real value of Tf and from the values of T_ and m of the previous loop the step of temperature ΔT of the sample is obtained caused by power P c supplied for a predetermined time. The program graphs and stores on Hard Disk in real time the values of T c and T s every three seconds and the values C p and m every 300 iterations of three seconds. The duration of a step is measured by the value of the characteristic heat relaxation time of the cell sample, determined through the exponential start of the step, when the temperature of the cell relaxates towards the value of equilibrium. The described program contains the most favourable parameters for a cell of the type of Figure 4B, containing a sample of water of lOcc. Temperature scanning modulated way. The general diagrammatical view of the flow- sheet of the program that operates the calorimeter in this operative way is shown in Figure 7A and has structure similar to that of the adiabatic way of Figure 6A; the differences is the type of measuring procedure and shown hereinafter. In Figure 7B the step is shown of thermalisation of the sample at temperature T threshold . There is a single for- loop of 500 iterations of 3000ms each, during which two different procedure PID bring temperatures Tc and T s of the sample cell and of the shield, respectively to the values T thresh „i d and T tnreshold -ΔT s by means of the control of the power P c and P s supplied to the heaters. In Figure 7C the operations are shown carried out during the measure. The structure is equal to that of Figure 7B . Temperature T c is in this case linked, by means of the PID, according to a temperature Tro e chosen previously (i.e. a slope) and modulated with a sinusoidal function of amplitude dT and frequency ω. Temperature T s is linked at temperature T C -ΔT S . Finally, in Figure 7D the diagrammatical view is given of an Analysis of Fourie made on the 500 data of power P c stored in the last loop. Firstly the average value, P c , and the components in direct phase, P c , and in opposed phase,' P c ", of the power P c (i) are obtained, and then starting from them, according to the Eq. 8 of the text, are obtained the real part, Cp', and imaginary part, Cp", of the heat capacity and the enthalpy deliver, δH/5T, of the sample. The program graphs and stores on Hard Disk in real time the values of P c , P c ' P c " , and Cp' , Cp" , δH/δT every 500 iterations of 3s. The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that other s can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalent of the disclosed embodiments. The means and material for carrying out various disclosed functions may take to variety of alternative forms without departing from the invention. It is to be understood that the phraseology or terminology employed herein is for purpose of description and not of limitation.

Claims: CLAIMS 1. Heat flux control method for calorimetry, adiabatic shielding, precise temperature setting and the like, on an object. (2), comprising the steps of: - arranging a shield ( 1 about said object (2) ; - heating uniform (5) of said shield (1) and monitoring (3) of said heating to keep said shield (1) at a chosen temperature, - arranging about said shield a thermal bath (7) at a known temperature in any case lower than the temperature of said shield (1) ; - measuring the temperature of said object (2) ; - control (8) the heat flux (5) between said object (2) and said shield (1) checking the temperature (4) of said object (2) and the temperature (3) of said shield (1). 2. Heat flux control method according to claim 1, wherein said shield (1) is kept at a temperature equal to said object (2) , whereby said heat flux between said object (2) and said shield (1) is substantially zeroed. 3. Heat flux control method according to claim 1, wherein successive steps are provided of heating (46) said object (2) for transmitting to said object (2) a predetermined heat flux and/or for bringing in turn said object (2) to different chosen temperatures (4) , said heating step (5) of said shield (1) keeping the temperature (3) of said shield at predetermined distance from the temperature (4) of said object (2) . 4. Heat flux control method according to claims 2 or 3 , wherein by adjusting said heat flux it is possible to operate a measuring instrument, such as a calorimeter, following different functioning ways, chosen among: - classic adiabatic way; temperature scanning adiabatic way; - classic temperature scanning way; - modulated temperature scanning way. 5. Heat flux control method according to claim 1, wherein within said shield a calorimetric cell (2,40) is provided which is suitable for containing at least a sample (25) and operates as a differential calorimeter, a step of simulation of the presence of a virtual reference calorimetric cell being provided by means of a thermogram obtained preliminarly on said calorimetric cell (2,40) without said sample . 6. Heat flux control method according to claim 5, wherein on said sample (25) temperature scanning calorimetric tests are carried out at predetermined time ranges, said thermogram carried out preliminarily on said calorimetric cell (2,40) without said sample having been obtained following the same time ranges, controlled by software means . 7. Apparatus for heat flux control for calorimetry, adiabatic shielding, precise temperature setting and the like, on an object (2), comprising: - a hollow shield (1) suitable for containing said object (2) ; - heating means (5) distributed uniformly on at least a portion of said shield (1) - means for measuring (3) the temperature of said shield (1) distributed uniformly on at least a portion of said shield (1) at least in partial superimposition with said heating means,, - a thermal bath (7) arranged about said shield (1) kept at a known temperature in any case lower than the temperature of said shield (1) ; - means for measuring (4) the temperature of said object (2) ; - means for controlling (8) the heat flux delivered by said heating means (5) between said object (2) and said shield (1) as a function of temperature signals of both said means for measuring (3) the temperature of said shield (1) and said means for measuring (4) the temperature of said object (2) ; 8. Apparatus for heat fl\ix control according to claim 7, wherein heating means are provided (46) distributed uniformly on at least a portion of said object (2) , suitable for transmitting to said object (2) a chosen heat flux, said means for controlling (8) the heat flux operating said heating means (5) of said shield (1) setting a temperature difference in turn fixed between the signals of said means for measuring (3) the temperature of said shield (1) and the signals of said means for measuring (4) the temperature of said object (2) . 9. Apparatus for heat flux control according to claim 7 or 8, wherein said thermal bath is the head (30) of a calorimeter and said shield (1) contains at least a calorimetric cell (40) . 10. pparatus of heat flux control according to claims from 7 to 9, wherein said shield (1) and said thermal bath have tubular co-axial shape, the length of said shield (1) being very higher than the diameter of said shield (1) . 11. Apparatus for heat flux control according to claims from 7 to 10, wherein said heating means (5) of said shield (1) comprise a winding of thin wire made of conducting material with electrical resistance having very low coefficient of temperature, whereas said means for measuring (3) the temperature of said shield (1) are distributed on said heating means (5) and comprise a winding made of conducting material with electrical resistance having high coefficient of temperature. 12. Apparatus of heat flux control method according to claims from 7 to 11, wherein said heating means (46) of said object (2) comprise a winding of thin wire made of conducting material with electrical resistance having very low coefficient of temperature, whereas said means for measuring (4) the temperature of said shield (2) are distributed on said heating means (46) and comprise two windings parallel to each other made of conducting material with electrical resistance having high coefficient of temperature. 13. Apparatus for heat flux control according to claims from 7 to 12, wherein said object (2) is a sample holder (49) having a recess (48) suitable for containing at least a sample (25) to measure, 14. Apparatus for heat flux control according to claim 13, wherein said recess is cylindrical and said sample (25) is a cylindrical test tube, guiding tubes (35) being provided for inserting from the above said sample (25) and not coupled with said object (2) . 15. Apparatus for heat flux control method according to claims from 7 to 14, wherein means are provided (43, 65) to keep hanging said object and said shield with respect to said thermal bath (7) for eliminating spurious heat couplings . 16. Apparatus for heat flux control according to claims from 7 to 15, wherein end axial plugs are provided (50, 51, 62, 64), containing heat insulators (6, 66).

Inventors: FERRARI CARLO, PAPUCCI FABIO, SALVETTI GIUSEPPE, TOMBARI ELPIDIO, FERRARI, CARLO, PAPUCCI, FABIO, SALVETTI, GIUSEPPE, TOMBARI, ELPIDIO
Applicants: CONSIGLIO NAZIONALE RICERCHE, FERRARI CARLO, PAPUCCI FABIO, SALVETTI GIUSEPPE, TOMBARI ELPIDIO, CONSIGLIO NAZIONALE DELLE RICERCHE, FERRARI, CARLO, PAPUCCI, FABIO, SALVETTI, GIUSEPPE, TOMBARI, ELPIDIO
Application year: 1999
Main classification: G01K17
IPC codes: G01K17, G01N25