Thermal conductivity measurement apparatus and related methods
Inventors
Roy, Ajit K • Wheeler, IV, Robert • Ganguli, Sabyashachi
Assignees
United States Department of the Air Force
Publication Number
US-9696270-B1
Publication Date
2017-07-04
Expiration Date
2034-06-09
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Abstract
An apparatus for thermal conductance measurement includes a first heater assembly having a beam, a platen disposed at an end of the beam, and a heating element and a Resistance Temperature Device (RDT) disposed on the platen. The embodiment further includes a second heater assembly having a second beam, a second platen disposed at an end of the second beam, and a second heating element and a second Resistance Temperature Device (RDT) disposed on the platen. A test rig is also included, and the first heater and second heater assembly are mated to the test rig and separated by a gap length.
Core Innovation
The invention provides an apparatus and related methods for performing thermal conductivity measurements on ultra-small test specimens such as micro- and nano-scale structures. It includes a first heater assembly with a beam, platen, heating element, and Resistance Temperature Device (RTD), and a second heater assembly with similar components. These two heater assemblies are mated to a test rig and separated by an adjustable gap, allowing a specimen to span the gap and maintain thermal contact during thermal conductivity measurement. The assemblies are independently controlled to maintain desired temperatures while measuring changes in power needed to maintain those temperatures to determine thermal conductivity.
The problem addressed arises from difficulties in accurately measuring thermal transport properties of very small specimens, particularly those exhibiting anisotropic thermal behavior such as carbon nanotube yarns, nonmetallic fibers, nanotube forests, and layered materials. Conventional bulk thermal measurement methods are inadequate for micro- and nanoscale specimens, especially those without macroscopic bodies. Existing techniques, including far-field and near-field optical methods, scanning thermal microscopy, and certain thermal conductance evaluations, provide qualitative or limited quantitative data and lack independent control of test temperature and heat flux, often necessitating active cooling to maintain fixed temperatures.
Claims Coverage
The patent includes several independent claims covering inventive features of the apparatus, heater assembly, and method for testing thermal conductance.
Thermal conductance measurement apparatus with two independently positionable heater assemblies
An apparatus comprising a first heater assembly and a second heater assembly, each having a beam, platen, heating element, and Resistance Temperature Device (RTD). The two assemblies are mated to a test rig as independently positionable subassemblies separated by an adjustable gap, configured to couple a specimen spanning the gap to maintain thermal contact for thermal conductivity measurement.
System with power supply, source measuring unit, and controller for temperature control
An apparatus including a power supply electrically coupled to the heating elements, a Source Measuring Unit (SMU) electrically coupled to the RTDs, and a controller configured to maintain each heating element at a desired temperature based on feedback from the SMU.
Test rig with adjustable stage, actuator, and load cell for applying force to specimen
An apparatus featuring a stage disposed between a heater assembly and test rig for three-dimensional orientation adjustment, and an actuator and load cell arranged to cooperatively apply and measure compressive or tensile force applied to the specimen.
Heater assembly structure with substrate, skeletonized beam, platen, heating element, RTD, and electrical connections
A heater assembly comprising a substrate, a skeletonized beam extending from the substrate to resist thermal conductance, a platen at the beam end, a heating element and RTD on the platen, pads forming electrically conductive regions, and conducting wires mating the pads to the RTD and heating element.
Method for testing thermal conductance using dual heater platens with RTDs under vacuum
A method including evacuating air proximate heating elements, using RTDs to obtain temperature data, applying power levels to maintain baseline temperatures in open-circuit conditions, placing a specimen bridging the gap between platens, applying power levels to maintain the baseline temperatures with the specimen in place, and recording differences in power levels required to maintain these temperatures to evaluate thermal conductance.
Method including application and measurement of force on specimen during testing
A method incorporating an actuator and load cell to apply and measure force on the specimen while testing thermal conductance.
Method calculating thermal conductivity using one-dimensional Fourier conduction
A method calculating thermal conductivity of the specimen using Fourier's conduction equation κ=−q(Δx/ΔT), where the heat flux q is derived from differences between power levels needed to maintain baseline temperatures with and without the specimen.
The independent claims cover an apparatus with dual independently controlled heater assemblies configured for thermal conductivity measurements, a heater assembly with a skeletonized beam and integrated heating and sensing elements, and a method for measuring specimen thermal conductance under controlled temperatures and vacuum conditions, including the ability to apply mechanical loading during testing.
Stated Advantages
Enables accurate thermal conductivity measurements on ultra-small micro- and nano-scale specimens where traditional bulk measurement methods fail.
Provides independent temperature control of dual heater assemblies, allowing stable temperature maintenance and measurement without active cooling above ambient temperature.
Minimizes radiation and convection heat losses by operating at low temperatures in a vacuum environment.
Allows thermal conductivity measurements under no load, static load, or dynamic loading conditions by applying mechanical forces via actuator and load cell.
Calibration method using metal micro-particles enables accurate temperature measurement and control of heater assemblies.
Compatible with various specimen sizes and shapes due to adjustable gap between heater assemblies and use of thermal paste for improved thermal contact.
Facilitates quantitative measurements of heat flow by detecting changes in power needed to maintain heater temperatures with and without specimen bridging the gap.
Enables thermal conductivity measurements over a wide temperature range, including cryogenic temperatures when placed on cooled substrates.
Documented Applications
Measurement of thermal conductivity of micro- and nano-scale specimens such as carbon nanotube yarns, nonmetallic fibers, nanotube forests, thin films, and layered materials exhibiting anisotropic thermal behavior.
Calibration and validation of thermal conductivity measurements using standard metal microwires.
Thermal testing of specimens under tensile or compressive load conditions by applying controlled mechanical forces during thermal conductivity measurement.
Measurements carried out within a Scanning Electron Microscope (SEM) or Focused Ion Beam (FIB) vacuum environment, or in a general purpose vacuum chamber equipped for electrical connections.
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