DE19910924A1 - Calorimeter; has coolant-evaporation device to produce complete phase transition of coolant from liquid to gas in front of cooling area in contact with edge of heatable measuring cell - Google Patents

Abstract

The calorimeter (1) has a heatable measuring cell (2) fixed to a cryostat. A cooling device formed as a cover (16) has a cooling area in thermal contact with the inner edge. A temperature sensor and a heat flow sensor are arranged in the measuring cell. A cover (5a) for the measuring cell and a coolant-evaporation device produces a complete phase transition of the coolant from liquid to gas in the flow direction in front of the cooling area.

Description

The invention relates to calorimeters for operation at temperatures below Ambient temperature, especially for the lowest temperatures. The common measurement systems are used, for example, as DSC (differential scanning calorimeter) or as TMDSC (temperature-modulated differential scanning calorimeter) and around contain a measuring cell designed as an oven, which can be cooled by a cooling device. A highly sensitive sensor for heat flow detection is arranged in the furnace Differences between the heat flow to the sample crucible and the heat flow to Makes reference crucible detectable.

Because the known calorimeter has a weak cooling coupling between the furnace and the cooling device can usually not take measurements down to the deepest Temperatures up to almost zero are carried out. Deeper Temperatures cannot be set stably. In addition, these cooling devices are on due to their high coolant consumption and poor controllability (rain temperature distribution, or their homogeneity, not efficient. It also occur Condensation or icing problems, especially in combination with one Sample change by a robot. To ensure exact measurements even at low temperatures To be able to carry out solutions, the measuring line or the Oven when measuring in a cup-shaped or cylindrical cryostat, e.g. B. a Dewar vessel to be arranged (Meas. Sci. Techol. 9 (1998) 1866-1872; Jan K. Krüger et al.). The measuring cell is connected to at least one chrome steel tube Cryostat-closing lid attached. To ensure sufficient cooling the cryostat has a depth for the measuring cell of more than 15 cm. The This high free space above the measuring cell enables disruptive convection currents. That is why there are two metal disks on the tubes above the measuring cell Convection and radiation shields arranged. Because the metal washers make a ring if left blank, convection currents can occur despite these disks. The Changing a sample is very cumbersome because the lid of the cryostat together with the Measuring cell and its connection lines removed and changing in the en must be carried out in the space below the lower metal disc. A car Matic sample change is excluded.  

High measuring accuracy at low temperatures and with long-term measuring processes gen also places high demands on the cryostat. In addition to good insulation with a vacuum jacket, should preferably be an uninterrupted, efficient cooling cable performance with low coolant consumption. The cryostat is said to be in Be the measuring cell ensures that the temperature and temp Make division achievable. To provide low measuring temperatures has already been done beaten (Meas. Sci. Techol. 9 (1998) 1866-1872; Jan K. Krüger et al.) nitrogen or helium as cooling liquid from a Dewar vessel without overpressure by a Pump the cooling line of the cryostat. The cooling line runs in the cooling area Del-shaped around the cylindrical inner edge of the cryostat. To be a good and Heat exchange between the cooling line and the interior is as homogeneous as possible To ensure that the cooling line is in good condition Thermal conductivity. Because the coolant supply is not under pressure, can during the cooling operation, coolant can be refilled, which can be measured for any length of time operations enabled. A small coolant consumption and a constant tem temperature distribution could be guaranteed as far as possible with the described vacuum jacket to be achieved. Nevertheless, temperature time series show an apparently constant temperature fluctuations in the range of over 0.02 ° K. Such temperature fluctuations can affect the accuracy of the measured specific heat.

The object of the present invention is to find a calorimeter at which the measurement can be carried out in a cryostat without the measurement Disruptive factors such as convection currents, condensation / icing and / or temporal Temperature fluctuations in the cryostat are affected. In addition, the rehearsal change can be done easily and especially automatically. Under no circumstances condensation or freezing during operation and especially when changing samples solution occur.

This object is solved by the features of claim 1. The dependent types sayings describe alternative or advantageous embodiments.

When completing the task, it was recognized that the measuring cell was not on the end cover of the Cryostat, but on a fixed part of the cryostat, preferably on the ground or if necessary, to be attached to the side wall. This allows the connection connections on an immovable part from the cryostat, which the  Sample change simplified. In addition, the cooling rate is transferred by the heat increased heat conduction.

In order to avoid convection flows in the area of the sample, an operable one Measuring cell cover arranged at the opening of the measuring cell or the furnace. The Ab the end cover only ensures that the cryostat is closed and can be closed with a any known actuator can be provided. The calorimeter should be possible As simple as possible, especially with known robots for automatic changing of samples, can be used. For this purpose, a common actuation of the End cover and the measuring cell cover or the furnace cover provided. To le Only the need for a small space above the end cover enables be preferred operating device when opening and closing the end cover Lift-swivel movement, in which the cover is only slightly more than the insertion depth is raised. The measuring cell cover should preferably be opened so that it claimed a small cross-sectional area in the cryostat when open. If Both covers are open, the entire opening of the measuring cell is freely accessible from above.

When eliminating the interference, it was recognized that the measurements were not only from Convection currents can be influenced. It also goes from cooling with a ver vaporizable cooling liquid, such as liquid nitrogen or helium. If that liquid coolant in the cooling lines provided for cooling the cryostat vapors, there are areas in the lines in which there is only liquid, only Gas, or gas and liquid. This can differ from area to area temperatures. Because these areas are not stationary, but different temperature fluctuations occur locally in the cryostat or on the inside thereof border on. In addition, the gas bubbles generated during evaporation lead to vibrations NEN or acoustic signals that interfere with the measurements of the highly sensitive Chen sensor impact. Tests have shown that with an evaporation chamber rich or an evaporation device in front of the cooling effective Kühlleitungsbe of the cryostat, the amplitudes of the temporal temperature fluctuations are essential can be reduced in size. The evaporator is designed to ensure that the coolant evaporates completely and the resulting gas is not heated unnecessarily but a temperature close to that corresponding to the present pressure Evaporation temperature has.  

It is particularly expedient to use evaporation with a control loop check. The control loop preferably comprises at least one temperature sensor sor, an evaporation heater and a controller. The control regulates the heating performance of the evaporation heater according to the temperature of the cooling gas the further cooling line arrives. That from the evaporator in the Cooling gas entering the active cooling area of the cryostat is said to be an essentially solid Have temperature.

In order to dampen the vibrations arising in the evaporation device, the Evaporation device have sufficient mass and / or mechanical as much as possible of the inner edge of the cryostat and / or the attachment of the measuring cell or the Sensors are decoupled. In particular, the design of the evaporator device and the connection of the cooling line prevents vibrations can spread in the cooling gas or the cooling pipe wall. It goes without saying that the evaporation device may also only be a heatable one Cooling line section can be formed.

With the embodiments according to the invention, measurements of the specific Heat a sample in a cryostat without the measurements due to disruptive factors such as convection currents and / or temporal temperature fluctuations against the cryostat. The sample change can be simple and in particular which can also be carried out automatically because after opening the cover and the measuring cell cover the sample crucible is freely accessible from above.

The drawings explain the calorimeter according to the invention using an embodiment example. It shows

Fig. 1 shows a vertical section through a calorimeter with a Bowden cable

Fig. 2 shows a schematic side view of a ramp guide for actuating the end cover

Fig. 3 shows a vertical section through a calorimeter with a Hebelbetantriebvor direction

Fig. 1 shows a first embodiment of the inventive calorimeter 1. A measuring cell 2 is arranged on the inner bottom 3 of a cryostat 4 . The measuring cell 2 comprises a cup-shaped receiving part 5 , on the inner bottom of which a sensor 6 is arranged. The receiving part 5 can be closed by a measuring cell cover 5 a, so that when the measuring cell cover 5 a is closed, no measurement disturbances due to convection currents can occur. In order to lead the connecting lines of the sensor 6 , which may be made of ceramic, to the outside and possibly also to provide a purge gas supply to the receiving part 5 , there is an insertion area 7 of the sensor 6 through the inner bottom 3 , a lead-through tube 8 and an outer bottom 9 of the cryostat 4 led out of the cryostat 4 and attached to a fastening device (not shown). The fastening device optionally includes a pressing unit, which presses the sensor 6 with its underside onto the receiving part 5 . The connecting lines and the purge gas supply are connected to further lines, not shown, via a vacuum-tight connecting device 10 . Through the inner floor 3 lead connection holes 3 a, to which dry gas feeds (not shown) are connected, so that in an open cryostat 4 by the supply of dry gas, entry and condensation or freezing of ambient air can be prevented. The inner floor 3 ent holds an annular recess, not shown in the drawing, to the underside of which the dry gas line is connected. At the top of the inner nenboden 3 there are nozzles that connect the annular recess with the inner chamber. The drying gas is preheated in the annular recess.

On a connecting ring 11 of the outer base 9 , an outer cylinder jacket 12 of the cryostat 4 is tightly connected to the outer base 9 . At the upper end of the outer cylinder jacket 12 , a connection flange 13 with cable bushings is arranged over a further connection ring 11 . On the connecting flange 13 , a closing ring part 14 is arranged with a central cryostat opening 15 . The Kryostatöff opening 15 is from a cover 16 , preferably with a sealing ring 17 , essentially tightly closed. In order to bring the measuring cell 2 to a desired temperature, a heating part 18 is preferably arranged with two insulation washers under the receiving part 5 . Between the heating part 18 and the inner bottom 3 , an intermediate layer 24 is arranged, which preferably has a deep thermal conductivity. In the receiving part 5 , a temperature sensor, not shown, is net angeord. The connecting lines of the heating part 18 and the temperature sensor (not shown) are led through at least one protective tube 19 from the measuring cell 2 to a passage in the connection flange 13 and then to a control / regulation of the calorimeter 1 , not shown.

The inner edge of the cryostat 4 is formed by a thin-walled inner cylinder jacket 20 which is tightly connected at the top to the connecting flange 13 and at the bottom tightly to the upper edge of the contact jacket 21 with the inner bottom 3 . The cavity between the inner and the outer cylinder jacket 20 or 12 is sealed off from the outside and a vacuum is built up therein to ensure good insulation. In order to be able to cool the inner edge 20 and thus the interior of the cryostat 4 efficiently and homogeneously, a contact jacket 21 is arranged in a cooling area with a helically extending groove 22 on the outside thereof for receiving a cooling line 23 shown only at the beginning and end of the groove. The liquid coolant passes through a coolant connection 13 a in the connection flange 13 into a first region of the cooling line 23 leading downwards. In the cavity between the outer floor 9 and the inner floor 3, the cooling line 23 connects to a heat conduction plate 25 , preferably a copper plate, of a coolant evaporation device 26 . The heat conduction plate 25 is preferably arranged on the coolant supply line 23 and on the connecting line to the inner bottom 3 carrying the measuring cell 2 and in particular attached to the lead-through tube 8 . The heat conduction plate 25 has a sufficiently large central bore to avoid any thermal contact with the feed-through tube 8 .

The heat conduction plate 25 is in contact with a, preferably arranged on the top, evaporative heating 27 in heat conduction. The coolant passes through cavities 28 in the plate 25 and / or through an area of the cooling line, not shown, which is in thermal contact with the plate. In order to ensure efficient heat conduction contact, depressions or grooves for the cooling line are optionally formed on the underside of the plate 25 . The coolant evaporation device 26 is to ensure, by means of the heat supplied by the evaporation heater 27 , an essentially complete phase transition of the coolant from the liquid to the gaseous state, so that in the coolant line 23 cooling gas with a temperature close to the evaporation temperature corresponding to the present pressure flows on. It is particularly expedient to control the evaporation with a control circuit (not shown). The control circuit preferably comprises at least one temperature sensor, a supply for the evaporation heater 27 and a controller. By controlling the supply depending on the current temperature value, it can be ensured that the cooling gas flowing on has the desired temperature.

In order to dampen the vibrations that may occur in the evaporation device 26 during evaporation, the evaporation device should have sufficient mass and / or be mechanically decoupled as well as possible from the inner edge of the cryostat and / or the attachment of the measuring cell or the sensor. Instead of the Darge presented attachment to the lines 23 , the attachment could also be provided on the outer cylinder jacket 12 or in particular on the outer bottom 9 and would then have to be thermally shielded from the cylinder jacket via sufficiently thin and long holders.

From the evaporation device 26, the refrigerant gas passes through the cooling pipe 23 for cooling the contact area with jacket 21st After flowing through the cooling coil on the contact jacket 21 , the cooling gas is guided through a coolant connection 13 a in the connection flange 13 from the cryostat 4 . The contact jacket 21 has a surface artificially enlarged by a milled spiral (not shown in the figure) to improve the thermal transition to the contact gas.

In order to simplify the use of the calorimeter 1 , a cover actuating device for opening and closing the measuring cell cover 5 a and the end cover 16 is provided. For actuation, a common Antriebsein unit 29 is preferably formed. In the exemplary embodiment shown, a rotary drive drives an eccentric disk 30 . The eccentric disc 30 makes a vertically guided actuation pin 31 up and down movable. It goes without saying that the actuation pin 31 could also be actuated by a linear drive or a fluidically actuable actuating cylinder.

With automatic calorimeters, sample changes are carried out by a robot or manipulator. If only movements in the vertical and especially only over short distances have to be carried out for the sample change, simply constructed manipulators can be used. The cover actuating device comprises between the drive unit 29 and the end cover 16, a first transmission device 32 , which preferably makes it possible to lift it off and swing it to the side, but possibly only to open the end cover 16 . In order to enable lifting and swiveling, a ramp guide 33 is formed in a sleeve 34 around the pin 31, which ramps the vertically movable actuating pin 31 with a guide part 35 engaging in the ramp guide 33 according to FIG. 2 only vertically and in a second height range vertically and rotatable about its own axis. The movement of the actuating pin 31 is carried over a radially extending from the actuating pin 31 carrier 36 on the end cover 16 on.

Between the drive unit 29 and the measuring cell cover 5 a, a second transmission device 37 is formed , in particular with a Bowden cable 38 . The upward or downward movement of the actuating bolt 31 is transmitted in an up and down pen of the measuring cell cover 5 a. In order to take over only the vertical movement of the actuating bolt 31 , a first arm 40 is fastened to the upper end of the actuating bolt 31 via a pivot bearing 39 . On the arm 40 , a sleeve 41 is mounted with an internal thread. In the sleeve 41 , an adjusting bolt 42 is screwed adjustably with the pull cable 43 of the Bowden cable. A flexible guide sleeve 44 of the Bowden cable 38 is fastened to a housing part 46 by means of a clamp holder 45 . At its other end, the guide sleeve 44 is in contact with a closing part 47 . The end part 47 is on a guide cylinder 48 which is fastened to the connecting ring 11 be. In the guide cylinder 48 , a piston 49 is fastened to the pull cable 43 and pressed upwards by a spring 52 . In order to limit the range of motion of the piston 49 , a longitudinal slot 50 is provided on the guide cylinder 48 and a projecting part 51 is provided on the piston 49 .

The movement of the piston 49 is transmitted via, a second arm 53 and a connec tion pin 54 to one end of a rocker arm 55 , the rocker arm 55 being pivotally mounted about a rocking axis 56 on a bearing part 57 connected to the receiving part 5 . The other end of the rocker arm 55 is connected to the measuring cell cover 5 a. Raising the actuating bolt 31 is transmitted via the Bowden train 38 to lowering the connecting pin 54 , which leads to an opening of the measuring cell cover 5 a. The connecting pin 54 has in the area of the spring sleeve 59 a plate-like enlargement (not shown in the figure). In this integrated plate an O-ring for the vacuum seal of the measuring space for the closed lid 16 and 5 a is embedded in the top. A return spring 58 in a spring sleeve 59 presses the plate integrated in the connecting pin 54 with a restoring force upward and thus additionally prevents gas exchange with the outside space. If measurement errors occur due to a possible heat input via the spring sleeve 59 , this reset arrangement can also be arranged above the end ring part 14 . When the lid is closed, there is no flow. The measuring cell is filled with contact gas, e.g. helium. When the lid is open, a dry gas flow takes place, for example helium or nitrogen.

Fig. 3 shows a calorimeter 1 in which the cover actuating device comprises a pneumatic drive unit 129 with a compressed air connection 129 a. A piston part 149 actuates the connecting pin 54 and thus the measuring cell cover 5 a via a lever arrangement 153 . The end cover 16 is opened and closed analogously to the measuring cell cover 5 a via a rocker arm 155 . The rocker arm 155 is pivotally mounted on a La gerteil 157 and is actuated by the piston part 149 via a second lever assembly 153 '.

It goes without saying that any cover actuation devices known to the person skilled in the art can be used. A control unit (not shown), preferably the control of the calorimeter, controls the drive unit 29 , 129 in each case. In the embodiments with only one common drive unit 29 , 129 , the two covers 5 a, 16 can only be moved together, which is usually advantageous. If the covers 5 a, 16 are to be operated independently of one another, a separate drive must be provided.

The advantage associated with the present invention is, inter alia, that the inner lid at any temperature, especially at very low temperatures up to close to absolute zero, can be opened and closed without condensation or icing takes place. This is partly due to the Ab stood by the laboratory air and the dry purge gas allows.

Claims (10)

1. calorimeter with a heatable measuring cell ( 2 ), a cooling device which is designed as a cryostat ( 4 ) which can be locked with an end cover ( 16 ) with a cooling region ( 21 ) arranged in thermal conduction contact with the inner edge and the measuring cell ( 2 ) in the cooled interior makes recordable, a temperature sensor for detecting a temperature of the measuring cell ( 2 ) and a sensor ( 6 ) arranged in the measuring cell ( 2 ) for determining a heat flow, or a difference between the heat flows to a sample and / or a reference crucible , characterized in that the measuring cell is attached to the cryostat and that a measuring cell cover ( 5 a) for closing the measuring cell ( 2 ) and / or a coolant evaporation device ( 26 ) for achieving an essentially complete phase transition of the coolant from the liquid to the gaseous Condition in the coolant flow direction is provided in front of the cooling area ( 21 ). 2. Calorimeter according to claim 1, characterized in that a cover actuation device for opening and closing the measuring cell cover ( 5 a) and the end cover ( 16 ) is provided, wherein preferably a common drive unit ( 29 , 129 ), in particular a for actuation Rotary, if necessary, eccentric drive, a linear drive or a fluidically drivable actuating cylinder is provided. 3. Calorimeter according to claim 2, characterized in that the cover actuation device between the drive unit ( 29 , 129 ) and the end cover ( 16 ) comprises a first transmission device ( 32 ), which preferably has a lifting and lateral pivoting, but possibly only opening the end cover ( 16 ) makes it achievable. 4. calorimeter according to claim 3, characterized in that the first transmission device ( 32 ) comprises a ramp guide ( 33 ) having a vertically movable actuating bolt ( 31 ) with a in the ramp guide ( 33 ) engaging guide part ( 35 ) in a first Height range only vertically and in a second height range vertically and rotatable about its own axis. 5. Calorimeter according to one of claims 2 to 4, characterized in that the cover actuating device between the drive unit ( 29 , 129 ) and the measuring cell cover ( 5 a) comprises a second transmission device ( 37 ), in particular with a Bowden cable ( 38 ) , which preferably opens the measuring cell cover ( 5 a) in the cryostat ( 4 ). 6. calorimeter according to claim 5, characterized in that the second transmission device ( 37 ) comprises a rocker arm ( 55 ) which is connected at one end to the measuring cell cover ( 5 a) and at the other end by a downwardly moving connecting pin ( 54 ) can be pressed into the open position, a return spring ( 52 ) preferably pressing the connecting pin ( 54 ) upward with a return force. 7. Calorimeter according to one of claims 1 to 6, characterized in that the coolant-evaporation device ( 26 ) comprises a control system with at least one evaporation temperature sensor, an evaporation heater ( 27 ) and a controller, the controller being the heating power of the evaporative heating ( 27 ) depending on the signal from the temperature sensor, preferably corresponding to the temperature of the cooling gas which enters the further cooling line ( 23 ). 8. Calorimeter according to one of claims 1 to 7, characterized in that the coolant evaporation device ( 26 ) in the insulating vacuum area of the cryostat ( 4 ), preferably from the measuring cell ( 2 ) carrying cryostat inner bottom ( 3 ) spaced, arranged and in particular on a lead-through tube ( 8 ) for receiving an insertion area ( 7 ) of the sensor ( 6 ) is BEFE Stigt. 9. Calorimeter according to one of claims 1 to 8, characterized in that the coolant evaporation device ( 26 ) comprises a heat conduction plate ( 25 ), preferably a copper plate, with which the evaporation heater ( 27 ) is in heat conduction contact, wherein the coolant can be guided through cavities ( 28 ) in the plate and / or through cooling lines which are in thermal contact with the plate ( 25 ). 10. Calorimeter according to claim 9, characterized in that the evaporation temperature sensor is in contact with the heat conduction plate ( 25 ).