EVAPORATOR FOR A THERMOGRAVIMETRIC ANALYZER

Described is a thermogravimetric analyzer system. The system includes an evaporator having first and second fluidic channels and a thermally controlled heater assembly. The first fluidic channel has a first channel inlet in fluidic communication with a gas supply module, a first channel outlet and an end portion extending from the first channel outlet. The second fluidic channel has a second channel inlet in fluidic communication with a source of liquid and a second channel outlet disposed on the first fluidic channel at a merge location between the first channel inlet and the first channel outlet. The end portion of the first fluidic channel includes a bend to redirect a flow within the first fluidic channel and improve a mixing of the gas and liquid received by the first and second fluidic channels, respectively.

FIELD OF THE INVENTION

The technology generally relates to thermogravimetric analysis. More particularly, the technology relates to an evaporator for a thermogravimetric analyzer. The evaporator may be used, for example, for enabling a steam environment for a furnace of a thermogravimetric analysis system.

BACKGROUND

Thermogravimetric analysis is a type of thermal analysis in which the mass of a sample is measured over time while the temperature of the sample changes. Thermogravimetric analysis measurements yield information about physical and chemical phenomena. For example, absorption, adsorption, desorption and phase transitions associated with a sample may be determined.

A thermogravimetric analyzer (TGA) is an instrument used to perform thermogravimetric analysis of a sample. The instrument typically includes a furnace that encloses a sample holder. The temperature of the environment inside the furnace is controlled. For example, the furnace temperature may be increased at a constant rate. The thermal reaction of a sample with respect to temperature may be monitored using different atmospheres, including different gases and different gas pressures.

For some measurements, a vapor-controlled atmosphere is desired. For example, a gas or a controlled mixture of gases under pressure may be combined with a flow of water to achieve a steam environment inside the furnace. An evaporator is a component that is used to heat a dry gas or gas mixture which is acting as a carrier gas to pick up liquid water and evaporate the water to create a homogeneous steam mixture. At the output of the evaporator the steam mixture enters the measuring cell of the TGA. Known evaporators generally are large in size and are provided as a separate component alongside the main TGA instrument. Furthermore, such evaporators typically require additional heated feed throughs or heated tubing to conduct the steam to the instrument and prevent the homogeneous steam mixture from condensing and separating prior to its use as a reactant in the heated measuring cell.

SUMMARY

In one aspect, a TGA system includes a gas supply module, a source of liquid, an evaporator, a furnace and a processor. The evaporator includes a first fluidic channel, a thermally controlled heater assembly and a second fluidic channel. The first fluidic channel has a first channel inlet in fluidic communication with the gas supply module, a first channel outlet and an end portion extending from the first channel outlet. The end portion includes a bend to redirect a flow within the first fluidic channel. The thermally controlled heater assembly is in thermal communication with the first fluidic channel. The second fluidic channel includes a second channel inlet in fluidic communication with the source of liquid and a second channel outlet disposed on the first fluidic channel at a merge location between the first channel inlet and the first channel outlet. The furnace has a furnace inlet in fluidic communication with the first channel outlet and a furnace outlet in fluidic communication with a back-pressure regulator. The processor is in communication with the gas supply module, the thermally controlled heater assembly and the back-pressure regulator and is configured to control a temperature, pressure and vapor concentration in the furnace.

The TGA system may include a gas-liquid separator in fluidic communication with the furnace outlet and may include a levitation balance module mechanically coupled to the furnace.

The source of liquid may include a water pump. The furnace may include a sample holder to support a sample during thermogravimetric analysis measurements.

In another aspect, an evaporator includes a first fluidic channel, a thermally controlled heater assembly and a second fluidic channel. The first fluidic channel has a first channel inlet configured to receive a flow of gas, a first channel outlet and an end portion extending from the first channel outlet. The end portion includes a bend to redirect a flow within the first fluidic channel. The thermally controlled heater assembly is in thermal communication with the first fluidic channel. The second fluidic channel includes a second channel inlet configured to receive a flow of liquid and a second channel outlet disposed on the first fluidic channel at a merge location between the first channel inlet and the first channel outlet of the first fluidic channel.

At least a portion of the first fluidic channel may be defined in a plane and a portion of the first fluidic channel between the bend and the first channel outlet may extend out from the plane. The end portion of the first fluidic channel may include a plurality of bends and a portion of the first fluidic channel downstream from one of the bends may extend out from the plane.

The liquid may be water.

At least a portion of the first fluidic channel may be defined in a plane of a diffusion-bonded body. The thermally controlled heater assembly may be in thermal contact with a side of the diffusion-bonded body.

DETAILED DESCRIPTION

TGAs are used to perform thermogravimetric analysis of a sample. A TGA typically includes a furnace that encloses a sample holder. The furnace provides a temperature-controlled environment for the sample. For example, the temperature can be increased over time while the mass of the sample is measured. Measurements may be made using a single gas or a mixture of gases and may be performed at different gas pressures.

FIG. 1is a schematic drawing showing a conventional configuration for an HP-TGA system10. The system10includes a furnace12, a levitation balance module13, a gas supply module14configured to provide one or more gases to the furnace12, a vacuum pump16and multiple pressure sensors and controllable valves configured to perform various functions before, during and after thermogravimetric measurements. For example, module18includes a back-pressure regulator, a pressure sensor20, multiple valves22A to22D, and the vacuum pump16. The module18is used to control the pressure inside the furnace12and to exhaust or purge the furnace12after a measurement. By way of a non-limiting example, the pressure may be controlled from approximately 0.02 MPa (200 mbar) to approximately 8 MPa (80 bar). Module24includes a pressure sensor26and valves28A and28B used to provide one or more inert gases such as nitrogen and/or argon to the furnace12.

A high-pressure gas mixture is provided by the gas supply module14. As illustrated, the gas supply module14may provide a single gas or a mixture of two or three gases to the inlet of the furnace12. The measurements are performed in a dry environment. During a measurement, the furnace12heats a sample according to a time-dependent temperature profile while the pressure of the furnace environment is controlled. Measurements of the mass of the sample are acquired throughout execution of the temperature profile.

For some analyses, it is desirable to use steam as oxidizing media for the sample.FIG. 2is a schematic drawing showing a configuration of a HP-TGA system30that can provide a steam environment for the sample. The system30includes similar components to the system10described above and further includes an evaporator32having a first inlet34that receives a flow of one or more gases, a second inlet36that receives a flow of water from a water pump40(or other source of liquid) and an outlet38to provide a mixture of the vapor and the gas or gas mixture to the furnace12. In some embodiments, the water is provided to the evaporator32with nanofluidic resolution. For example, the water flow may be as small as approximately 0.1 μL per minute and may exceed 80 μL per minute. Inside the evaporator32, the water is evaporated and mixed with the gas flowing to the furnace12.

The water arriving at the second inlet36of the evaporator32is cold relative to the furnace temperature. For example, the water temperature may be approximately equal to the ambient environment of the system30. Similarly, the gas flow received at the first inlet34is cold relative to the furnace temperature; however, the gas flow is preheated inside the evaporator32before the water is introduced into the gas flow. For example, the gas flow may be heated to a temperature in a range from approximately 200° C. to approximately 300° C. The preheated gas flow provides greater energy to the water for mixing. Steam may be exhausted from the furnace12into a module19which includes components similar to those in the module18ofFIG. 1and further includes a gas-liquid separator44. The dry gas is then used again to control the pressure in the measuring cell/furnace after separation at ambient temperature. Once the separator44is filled with water to a maximum level, water is automatically released via iteratively opening and closing the valves46A and46B. This iteration is necessary to avoid a high pressure drop in the system30and thus a disturbance of the measurement.

The water pump40can be controlled to control the moisture level. A processor or computer (not shown) is in communication with various sensors and components of the system30and calculates the volume flow rate of water used to achieve a desired concentration of water in the gas flow. By way of a non-limiting example, the percentage of steam can be controlled in a range from approximately 0.1% to 50%. An operator can set a desired water concentration via a software interface. The processor or computer controls the temperature, pressure and dry gas flow conditions to achieve the desired steam concentration without condensation. If the desired concentration would result in condensation inside the measurement cell, the processor or computer sets the water flow rate to the maximum flow rate that avoids condensation. The equation of state of water is used in the calculations along with data from multiple sensors in the measurement cell, such as temperature and pressure sensors. In this way, the TGA system adapts to avoid condensation from forming in the measurement cell.

In the various embodiments described below, the highly integrated evaporator components avoid the need for heated gas and water conduits (e.g., external tubing) typically used in conventional systems. Sealing components used in the evaporator32enable operation at pressures that can exceed 8 MPa (80 bar). The compact size and the ability to secure the evaporator32close to other system components results in an overall reduction in HP-TGA system size and easier system manufacturing and assembly.

FIG. 3AandFIG. 3Bare highly schematic drawings showing a top view and a side view, respectively, of an embodiment of an evaporator50that may be used in an HP-TGA system. The evaporator50includes a first fluidic channel52, a second fluidic channel54and a thermally controlled heater assembly56(shown as a dashed transparent element inFIG. 3Ato permit viewing of the first fluidic channel52). Arrows shown adjacent to the fluidic channels indicate the direction of fluid flow.

The first fluidic channel52has a first channel inlet58, a first channel outlet60and an end portion that extends from the first channel outlet60along a portion of the channel length. The heater assembly56is in thermal communication with the first fluidic channel52. For example, the heater assembly56may be in direct contact with a conduit that defines the first fluidic channel52or in direct contact with a structure that has an internal channel that defines the first fluidic channel52. The second fluidic channel54has a second channel inlet62to receive water and a second channel outlet disposed at a merge location66on the first fluidic channel52. The merge location66is where the water is introduced into the gas flow. In alternative embodiments, a liquid other than water may be used or a mixture including two or more liquids may be used.

The first fluidic channel52includes at least one bend. As used herein, a bend means a deviation, or jog, in a fluidic channel such that a fluid flowing in the fluidic channel experiences a substantial change in the direction of flow (e.g., a change in a range from approximately 45° to approximately 90° with respect to the original direction of flow). As illustrated, the first fluidic channel includes two bends68A and68B although in alternative embodiments only a single bend may be provided, or more than two bends may be provided. Each bend68results in a change in the flow direction of approximately 90° and assists in the mixing of the water with the gas flow, although in alternative embodiments, the change in the flow direction due to a bend may be different. The illustrated bends68are defined in a plane that also includes the remainder of the first fluidic channel52therefore the bends68are not observable in the side view ofFIG. 3B. In other embodiments, one or more bends may divert the flow direction out of plane and may be used to position the outlet60at a convenient location within an HP-TGA system.

Advantageously, each bend68acts as a simple mixer such that sufficient mixing occurs without the need for including a more complex structure of mixing paths and mixing wells.

FIG. 4AandFIG. 4Bshow a side view and an exploded perspective side view, respectively, of the components in an upper portion of an HP-TGA system. The evaporator80includes a plate having a circular aperture82near one end where the end of a fluidic channel provides steam to the furnace12. The circular region surrounding the opening82includes through holes84to pass bolts85used to secure the evaporator80to the furnace12. The approximately rectangular shaped section of the plate that is opposite the circular region is enclosed withing a top hood86and a bottom plate88. A heater assembly90and a layer of thermal insulation92are disposed between the upper surface of the evaporator80and a lower surface of a mounting plate94. By way of a specific and non-limiting example, the heater assembly90may include an etched foil resistive heating element laminated between flexible electrically-insulating layers (e.g., a Thermofoil™ heater model no. HM6953 available from Minco Products, Inc. of Minneapolis, Minn.). The lower side of the heater assembly90is held against the upper surface of the evaporator80to enable efficient heat transfer into the evaporator80. The thermal insulation layer92substantially limits thermal transfer to the mounting plate94so that most of the heat generated by the heater assembly90flows into the evaporator80.

The evaporator80, heater assembly90, thermal insulation layer92and mounting plate94are held in position under the top hood86by bolts100which extend through openings in each component. The bottom plate88is secured to the top hood86and against the bottom surface of the evaporator80by bolts100that extend through holes in the top hood86, evaporator80and bottom plate88. A temperature sensor104is secured to the underside of the evaporator80to allow for monitoring and controlling temperature during measurements.

The circular region of the evaporator80is secured to the upper portion of the furnace12with bolds85. A pair of O-rings83is used to seal the evaporator80to the furnace12and allows operation at high pressure. In this example, gold-plated copper O-rings are used for sealing.

FIG. 5is an exploded view of three layers110A,110B and110C that are bonded to each other to form an evaporator body112that includes an internal channel114that acts as the first fluidic channel52, as shown inFIGS. 3A and 3B. The evaporator body112is in the form of a plate formed by a solid-state diffusion bonding process to join together the layers110. More specifically, the layers110are forced against each other under pressure at an elevated temperature in vacuum. Examples of materials that may be used to create the diffusion-bonded body110include titanium, stainless steel, and various types of ceramics and polymers. As an example, U.S. patent publication no. 2020/0064313, incorporated herein by reference, describes a diffusion-bonded body having internal fluidic channels. The channels communicate with each other and/or ports on a surface of the body.

The channel114inside the evaporator body112is fabricated by forming a groove in the upper surface of the middle layer110B and then placing the upper layer110A, which has no grooves, against the upper surface of the middle layer110B and placing the lower layer110C against the lower surface of the middle layer110B. In one non-limiting numerical example, the groove has a 1.60 mm (0.0625 in.) of an inch in diameter. At the outlet end116of the channel114, a vertical opening through the thickness of the plate extends the fluidic channel to the lower plate surface where the steam can then pass through the upper portion of the instrument and into the furnace12.

The layers110are arranged with respect to each other so that features, such as bolt through holes84and circular aperture82, are properly aligned before performing the diffusion bonding process. Once bonding is completed, there is no discernible distinction between the layers110.

FIG. 6is a top view of the middle layer110B shown inFIG. 5. An external conduit (not shown) delivers the gas, or mixture of gases, to an inlet coupling fixed to the upper surface of the evaporator body112. The inlet coupling is at the top of an internal vertical channel leading to the inlet end118of the internal channel114which has a substantially serpentine path shape. By way of a non-limiting example, the internal channel114has a cross-sectional area of 1-2 mm2and a length of approximately 500-1,000 mm. The gas flows through the internal channel114and past a merge location116along its length. A second external conduit (i.e., the second fluidic channel ofFIGS. 3A and 3B) leads to a second inlet coupling at the top of the evaporator body112where a nanofluidic flow of water is coupled into another internal vertical channel that leads to the merge location116at its opposite end. The flows of gas and water are combined at the merge location116and the combined flow passes through the remainder of the internal channel114.

FIG. 7Ais an exploded view of the upper portion of another HP-TGA system120andFIG. 7Bis a similar view but also shows the components of the evaporator122separated from each other. The structure and components of the system120are similar to the system shown inFIGS. 4A and 4B; however, the evaporator122is constructed using conventional tubing and the fabrication process is simpler and less costly in comparison to fabrication of the diffusion-bonded evaporator body112(FIG. 6).

FIG. 8shows an exploded view of various components of the evaporator122as viewed from underneath. The evaporator body124is formed of a thermally-conductive material and includes recessed regions in a lower surface126(shown as top surface in the figure) to receive a first tubing128, second tubing130and a fluidic tee132. A thermally controlled heater assembly (not shown) is attached to the evaporator body124on a surface138opposite to the lower surface126. The inner diameter of the tubing128and130provide a similar cross-sectional area to that of the internal channel114.

The first tubing128conducts the gas (or gas mixture) flow. The fluidic tee132receives the gas flow at a first inlet134and a water flow at a second inlet136. The fluidic tee132provides the mixture of the gas and water flows (steam flow) at its outlet136. Thus, the fluidic tee132corresponds to the merge location66shown inFIGS. 3A and 3B. The path length through the tubing128and130is substantially less than the length of the internal channel114in the diffusion-bonded evaporator body112. The shorter length is sufficient to achieve the desired heating of the gas prior to mixing with the flow of water.

While various examples have been shown and described, the description is intended to be exemplary, rather than limiting and it should be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the scope of the invention as recited in the accompanying claims.