Equipment and methods for measuring the thermal diffusivity of materials

Abstract

An apparatus (1000) for determining the thermal diffusivity of disc-shaped, opaque, solid or quasi-solid materials using high intensity short duration flashes from a single LED, planar LED array or laser diode light source (504 / 400). The apparatus (1000) comprises an axially and radially indexed cylindrical sample holder (501) capable of holding a plurality of test samples (1) and sequentially placing them in a designated test position with one face (A) of each sample (1) exposed to the flash lamp while the opposite face (B) of the sample (1) is detected by a temperature measuring device (505) to record the resulting thermal excursion. From the experimental data detected during each test, a modified calculation method is employed to calculate the thermal diffusivity.

Description

Technical Field

[0001] This disclosure pertains to the field of apparatus and methods for measuring thermal diffusivity. Background Technology

[0002] Thermal diffusivity is an inherent property of all materials. It describes the rate at which heat diffuses through a material from a hotter region to a colder region. Thermal diffusivity plays a crucial role in thermal design and modeling. Summary of the Invention

[0003] This invention discloses an apparatus that utilizes a high-intensity, short-duration flash from a single LED, a planar LED array, or a laser LED source to determine the thermal diffusivity of a disk-shaped opaque solid or quasi-solid material. The apparatus includes a cylindrical sample holder with axial and radial rotation, capable of accommodating multiple test samples and sequentially placing them in designated test positions, exposing one side of each sample to the flash lamp. Simultaneously, a temperature measuring device monitors the reverse side of the disk to record the resulting thermal shift. Based on experimental data observed during each test, an improved calculation method is employed to calculate the thermal diffusivity.

[0004] This disclosure relates to the field of thermal diffusivity, and more specifically to an apparatus and method for measuring the thermal diffusivity of a material. In a first example, this disclosure includes an apparatus for measuring the thermal diffusivity of a material, the apparatus comprising a system for measuring thermal diffusivity, the system including a light-emitting diode (LED) light source, wherein at least one light pulse from the LED light source impinges on one surface of an opaque solid material sample having a uniform thickness L, generating a temperature change or thermogram over time on the other surface of the sample, and wherein a computing device included in the system analyzes the thermogram and calculates the time t required for the temperature to rise to half of its maximum value. 1 / 2 The thermal diffusivity of the sample is calculated using the formula: α = c·L 2 / t 1 / 2 Where c = 0.13879, corresponding to the temperature increase t 1 / 2 The device may include at least one light-emitting diode (LED), a concentrator, a light condenser, and a light transmission device. The LED light source or at least one laser diode is controlled by a controller with a program that commands the generation of at least one light pulse. When at least two light pulses of predetermined duration and intensity are generated, the program calculates the thermal diffusivity using the at least two light pulses, denoted as P1 and P2, respectively. Each light pulse has a t value associated with the at least two light pulses. 1 / 2 , respectively using (t 1 / 2 )1 and (t 1 / 2 )2 indicates that at least two t 1 / 2The values ​​were subjected to regression analysis with the corresponding pulse durations, and the resulting function was then derived for pulse durations shorter than 100 ms to obtain the corresponding t. 1 / 2 Then use it in the formula: α=c·L 2 / t 1 / 2 Where c = 0.13879. In another case, the LED light source or laser diode can be commanded to provide multiple pulses according to the proportional-integral-derivative (PID) control principle, thereby heating the sample to the desired temperature before the time pulses used for thermal diffusivity measurement.

[0005] In a second example, this disclosure provides an apparatus for measuring the thermal diffusivity of a material, the apparatus comprising: a) a thermally controlled environment; b) a sample holder including at least two sample cavities; c) a sleeve within the thermally controlled environment for receiving the sample holder, the sleeve including openings at the top and bottom; and d) a transducer. The sample holder may be cylindrical or have a polygonal cross-section. The transducer may sequentially or simultaneously move the sample holder axially and radially relative to the sleeve. In one embodiment, at least two sample cavities are radially offset from each other, or each sample cavity may be part of a row of sample cavities, each row of sample cavities being parallel to the longitudinal axis of the sample holder, wherein each row of sample cavities contains at least one sample cavity. Furthermore, at least two sample cavities extend through the sample holder, each sample cavity including an opening on a first side and an opening on a second side, the opening on the first side being larger than the opening on the second side. The two openings are concentrically arranged and 180° apart, and are interconnected by a channel. The larger opening accommodates the sample, wherein a sleeve prevents the sample from falling out of the holder when the holder rotates relative to the sleeve, the sleeve remaining stationary. The axis of the concentric openings is perpendicular to the longitudinal axis of the sample holder.

[0006] The sample holder and sleeve can be withdrawn from a thermal environment for loading and unloading samples. The indexer may include: a linear actuator; a rotary actuator; a linear position sensor; a rotary position sensor; a splined component; and a first magnet and a second magnet. In the second example device with an indexer just described, the device is configured such that: the movable end of the linear actuator is connected to a first end of the splined component via a backlash-free axial / rotary connector; the rotary actuator is connected to the splined component via a radially movable but axially restricted collar, on which a pin is fixed, which protrudes into a longitudinal groove of the splined component when the collar rotates, causing the splined component to rotate; the backlash-free rotary / axial connector includes a first magnet connected to the first end of the splined component and a second magnet connected to the movable end of the linear actuator; the first magnet contacts the second magnet; wherein the movable end of the linear position sensor is connected to the movable end of the linear actuator, the connection being axially restricted and radially free to slide.

[0007] The third example device may include: a thermally controlled environment; a sample holder, a sleeve, and a transducer, wherein the sample holder includes at least two radially offset cavities capable of accommodating at least two samples, one opening of which is larger than the other; the sleeve includes at least two openings, each at least as wide as the larger opening of the at least two cavities, and each opening is 180° spaced apart from each other on its surface; a temperature rise detector including a temperature sensor and a recording device; a light source including at least one light-emitting device, a condenser, a columnarizing device, and a light-transmitting device; and a program that calculates the thermal diffusivity using at least two predetermined pulses from the light source, the two pulses being of increasing duration and denoted as P1 and P2, respectively, each pulse having a associated t. 1 / 2 , respectively represented as (t 1 / 2 )1、(t 1 / 2 )2, and there are at least two t 1 / 2 Regression analysis was performed on the value and the corresponding pulse duration. The resulting function was then derived for pulse durations shorter than 100 milliseconds to obtain the corresponding t. 1 / 2 Then use it to calculate: α = c·L 2 / t 1 / 2 Where c = 0.13879. The light source of the third example device may include at least one LED. In another embodiment, the light source may include at least one laser diode. Multiple devices in any of the above examples may be controlled by a single controller and program.

[0008] This disclosure also includes a fourth example of an apparatus for measuring thermal diffusivity, the apparatus comprising: means for creating a thermally stable environment; means for providing an LED light source capable of increasing the temperature of at least one sample; means for accommodating at least two radially offset samples; means for aligning a first side of at least one sample with the LED light source; means for reading the temperature change of a second side of at least one sample and recording a thermogram; means for calculating the thermal diffusivity based on the thermogram; and means for making each of the at least two radially offset samples part of a row of axially offset samples. In the fourth example apparatus, the means for calculating the thermal diffusivity of at least one sample includes software program encoded to calculate the thermal diffusivity using a sequence of at least two predetermined light pulses of increasing duration, denoted as P1 and P2, each light pulse having an associated t. 1 / 2 , represented as (t 1 / 2 )1、(t 1 / 2 )2, there are at least two t 1 / 2 Regression analysis was performed on the value and the corresponding pulse duration. The resulting function was then derived for pulse durations shorter than 100 milliseconds to obtain the corresponding t. 1 / 2Then use it to calculate: α = c·L 2 / t 1 / 2 , where c = 0.13879.

[0009] This disclosure provides a method for measuring thermal diffusivity, the method comprising the steps of: creating a thermally stable environment; irradiating a first side of at least one sample with at least one light pulse generated by an LED or laser diode light source; measuring the temperature rise of a second side of at least one sample; recording the temperature rise to create a thermal map; and calculating the thermal diffusivity for t using a formula. 1 / 2 Thermal diffusivity α: α = c·L 2 / t 1 / 2 , where for t 1 / 2 c = 0.13879, t 1 / 2 By t 1 / 2 The value of (t) 1 / 2 )1、(t 1 / 2 )2, through regression analysis, t 1 / 2 The value of t is obtained from a heatmap associated with a predetermined order and duration of at least two light pulses (denoted as P1, P2), and the resulting t 1 / 2 That is, (t) 1 / 2 )1、(t 1 / 2 )2, corresponding to pulse durations shorter than 100 milliseconds. Attached Figure Description

[0010] Figure 1 is a schematic diagram of the components of a flash diffusion device in the prior art.

[0011] Figure 2 is a thermal image obtained using a flash diffusion device based on existing technology.

[0012] Figures 3 and 4 illustrate a multi-sample flash diffusion device in the prior art.

[0013] Figure 5 This is a cross-sectional side view of an embodiment of the flash diffusion device 1000 disclosed herein.

[0014] Figure 6 This is a partial orthogonal view of the sample holder structure and the indexing mechanism.

[0015] Figure 7 This is a partial orthogonal view of the sample holder structure, with the sample holder in the loading position.

[0016] Figure 8 The sample holder structure in the loading position is perpendicular to Figure 7 A view of the cross section of the X-axis.

[0017] Figure 9 This is a partial orthogonal view of the sample holder in the unloading position.

[0018] Figure 10 The sample holder structure in the unloading position is perpendicular to Figure 9 A view of the cross section of the X-axis.

[0019] Figure 11 This is a plan view of an embodiment of the LED light pulse source disclosed herein.

[0020] Figure 12 It is a graph illustrating multiple thermal images obtained using light pulses of different durations and the relationships between feature points.

[0021] Figure 13 This is a block diagram of the operating elements of an embodiment of the present disclosure.

[0022] Before explaining the embodiments of this disclosure in detail, it should be understood that the application of this disclosure is not limited to the details of the specific arrangement shown, as other embodiments of this disclosure are also possible. Furthermore, the terminology used herein is for description only and not for limitation.

[0023] Existing technology

[0024] Parker et al. first proposed a simple and commonly used method for assessing thermal diffusion (J. Appl. Phys., 32(9): 1679-1684, 1961). This method is schematically illustrated in Figure 1. It uses a high-intensity light pulse 100 from a xenon light source or pulsed laser 2, which falls on one face (face A) of a small disk-shaped sample 1, and measures the temperature change 101 on the opposite face (face B), i.e., the temperature rise as a function of time. The temperature change data is used to plot a thermogram T, as shown in Figure 2.

[0025] The points obtained from this characteristic heatmap can be used to derive the thermal diffusivity. For example, once the maximum temperature offset point (P) is determined based on (ΔT), it is projected onto the ΔT axis at point 110, marked with MAX at the intercepted position. Then, 50% of this ΔT value is calculated, marked with MAX / 2, and displayed as point (R). This is then projected back onto heatmap 111, intercepted at point (S). The time at which point (S) occurs is called the "half-maximum time," projected onto point (W) on the TIME axis at point 112, yielding t. 1 / 2 L is the thickness of the sample. The relationship between this characteristic and thermal diffusivity (α) is as follows:

[0026] α=c·L 2 / t 1 / 2 Equation 1

[0027] Where for t 1 / 2 c = 0.13879.

[0028] Other points on the heatmap show similar relationships, and the value of the constant c changes accordingly. Equation 1 is based on a theoretical model that assumes the pulse is infinitely short and the sample has no heat loss.

[0029] This method, commonly used to determine thermal diffusivity, is known as the "flash method." It is suitable for opaque, homogeneous solid or quasi-solid samples with uniform thickness. Quasi-solids are materials that will not deform in size as long as the mechanical force applied to them remains constant, or for encapsulating non-solid and transparent materials used to mimic solid samples. It is favored for its speed and accuracy, and most importantly, it does not require knowledge of the heat transferred by the pulse 100. Thermal diffusivity (α) is related to thermal conductivity (k), specific heat capacity (Cp), and density (ρ), as shown in equation (2).

[0030] α=k / (ρ·Cp) Equation 2

[0031] The flash method quickly became the preferred method for measuring the derivative of thermal conductivity.

[0032] Typically, when testing at non-ambient temperatures, the sample is enclosed in a thermally controlled environment, such as the heater or cryostat 200 shown in Figure 1. As the temperature rises, the heat loss of the sample will promote non-uniaxial heat flow after the pulse energy is absorbed, such as radiation loss from the surface of surface A in Figure 1, the surface of surface B, and edge loss C. Each type of loss will cause a deviation in the basic relationship in Equation 1.

[0033] The thermal control environment is used to transfer heat to the sample, and also typically to the sample holder via radiation, conduction, and convection. In one case of testing molten metal droplets, high-frequency induction heating is used to raise the temperature of the suspended sample from within.

[0034] Pulse energy between 0.1 and 3 joules generates an analyzable thermal map depicting the temperature rise over time of surface B of sample 1, opposite surface A, where the light pulse energy is deposited on surface A. This temperature change data, referred to as a thermal map, is based on a sample with a diameter of 0.5 mm and a thickness of 0.08 mm. The currently disclosed implementation uses an LED light source of at least 10,000 lumens to generate sufficient energy with pulses lasting 1000 milliseconds.

[0035] Common practices with light sources show that pulse widths of hundreds or thousands of milliseconds can distort the thermal map obtained from surface B in Figure 1, adversely affecting the resulting data. Therefore, numerous analytical correction methods, generally referred to as pulse width correction, have emerged in the literature. These methods obtain an approximate theoretical thermal map by analyzing and processing the test results derived from the thermal map, which assumes extremely short pulses and no heat loss. Severe losses in surfaces A, B, and C can also lead to further data degradation. Published analytical correction methods can also correct this distortion. However, complicating matters further is that the surface treatment of each material and each sample significantly affects its emissivity, ultimately influencing its radiative heat loss. Therefore, even with the same material, the corrected value obtained for one sample may differ from that of another, and the difference can be even greater at different temperatures. For decades, these corrections have been based on theoretical predictions and applied to the thermal map data at the end of the test. They cannot change the test parameters in real time, but can only process the obtained data after the test. It is well known that the thermal diffusivity of all materials varies with temperature, thus necessitating testing in temperature ranges beyond ambient temperature. In any practical device used for testing at non-ambient temperatures, the sample must first be enclosed in a precisely controlled hot container, such as a uniform portion of the hot zone of a heater, and the sample must be provided with firm support.

[0036] In existing technology, the xenon light source 2 in Figure 1 directly illuminates the sample placed on a support. This approach proves very limited because such a light source emits light almost hemispherically, with only a small fraction of the energy reaching the sample. This problem can be solved by using an elliptical or parabolic condenser lens in a suitable position, along with other collimating components. Furthermore, pulsed lasers, ruby, YAG, and neodymium glass are options due to their inherently collimated beams, extremely high power densities, and relatively short pulses. Collimation is necessary to deliver the beam into a heater or cryostat without significant divergence. Both direct xenon flash lamps and xenon-pumped pulsed lasers introduce very high electrical noise from the high-voltage (>800V) discharge of the large capacitor and the ultra-high-voltage (>10,000VDC) trigger pulse of the xenon flash lamp, radiated and conducted through the circuitry. Flash diffusion devices based on these two pulsed sources have been available for some time, but they all suffer from significant electrical noise release, requiring costly and complex hardware and software mitigation measures.

[0037] In practical devices, one of the fundamental requirements of any sample holder is to physically support a solid sample while exposing one side A (Figure 1) of the sample to the pulse of the pulse source 2 and presenting the other side B to the temperature rise detector 3. Early measurement devices were equipped with holders for single samples. For the purposes of this disclosure, the solid can be solid or quasi-solid. Obtaining data to plot a thermogram of a single pulse takes only a few seconds, but it takes several times longer for the sample to reach its equilibrium temperature before the pulse is triggered. For example, reaching the highest temperature of 2500°C and 8 to 10 intermediate temperatures in a single test cycle can take 10 to 20 hours. To make testing more time-efficient, devices using sample holders with multiple samples were designed. As shown in Figure 3, the first version uses a circular platform 4 with up to six radially spaced samples 1 on its plane. These samples are rotated around a Z-axis for indexing 113, the Z-axis being perpendicular to the plane of the sample 1 and the plane of the sample holder 4. These samples 100 are then pulsed sequentially, and the temperature changes 101 on the back side are recorded. In another version of the prior art shown in Figure 4, one or more linear sequences of sample 1 are designed on the plane of platform 5.

[0038] In all cases, the plane of all sample faces (A) is parallel to the plane of the support and the planes of rotation 113, lateral displacement 114, and longitudinal displacement 115. In contrast, this disclosure introduces a rotational indexer. Detailed Implementation

[0039] The flash diffusion apparatus disclosed herein includes a thermally controlled environment, a multi-sample holder that moves via synchronous radial and axial indexers, a temperature rise detector, an LED light pulse source (which raises the temperature of the sample by light pulses emitted from the LED), electronic circuitry connected to a computer with operating software to control the apparatus, and a novel analysis algorithm (based on real-time empirical model evaluation) that allows for changes to test parameters during the test after the pulse, rather than performing hypothesis analysis and corrections after obtaining test data, as is the case in the prior art.

[0040] 1. Thermal control environment

[0041] Figure 5The schematic diagram is shown for illustrative purposes to incorporate elements of this disclosure within its contents, providing a method for manufacturing a thermal environment 27 that, after sufficient equilibration time, generates a highly uniform (at least + / - 2 °C / in) and stable (at least + / - 1 °C / min) thermal volume 500 within its thermal zone 513 at any set temperature. The thermal environment includes a temperature sensor, a heater, and a controller. Alternatively, a proportional-integral-derivative (PID) control algorithm can be used to directly heat the sample 1 with a long-duration light pulse to reach the desired temperature without a separate heater 512, followed by the application of the light pulse for measurement. The thermal environment 27 may also be referred to as a heater or cryostat, and includes a housing 510 accommodating an insulation element 511 and a heater or heating element 512. The thermal environment described in this disclosure is covered at its longitudinal end with a movable end plate 22, which may also serve as a base or sample support structure, including a sample holder and sleeve, and a positioner 502. The thermal environment, including the end plate / base 22, is enclosed by the housing 510 and the insulation 511 to maintain the internal temperature, but for ease of explanation, the housing wall opposite the end plate 22 is not shown in the figure.

[0042] The thermal control environment 27 is equipped with two sets of channels 514 and 515 that allow light to pass through. Each set of channels passes through the housing 510, the thermal insulation 511, and the heating element 512. The two sets of channels are coaxial with each other and with the optical axis Y of the light pulse source 504 and the temperature rise sensor 505.

[0043] When the longitudinal axis of the disc-shaped sample 1 coincides with the axis Y, the light pulse 12 can illuminate surface A of the sample, i.e., the illuminated surface. This position will be referred to as test position 60.

[0044] In the technique disclosed herein, multiple light pulses of varying intensities can be used sequentially to heat the sample to the desired temperature according to the proportional-integral-derivative (PID) control principle before the test pulse is emitted. This direct heating does not involve heat transfer from an external heater, and is therefore a method for generating a thermally controlled environment.

[0045] 2. Multi-sample scaffold structure

[0046] The main features of this disclosure are Figure 6 The sample holder structure 501 shown is capable of axial translation and rotational displacement. (Example) Figure 6 As shown, the sample holder structure 501 includes multiple sample holders 20 and a surrounding sleeve 21. As illustrated, the sample holder 20 may include a cylindrical body or have a polygonal cross-section, with at least three, four, five, or six sides or more. The sleeve 21 serves to fix the sample in place. Figure 7 At the position shown, and Figure 9Except for the test location shown. Sleeve 21 is fixedly mounted on the movable end plate / sample holder base 22, which separates the internal environmental space of the thermal control environment 27 from the environmental space of the surrounding environment 23. It can be envisioned that the base 22 constitutes part of the wall of the thermal control environment 27. Figure 7-10 The sample holder 20 and its function are further described. The sample holder 20 includes at least one sample placement cavity 601 located on a cylindrical surface of the sample holder. Each sample placement cavity is connected to a coaxial optical channel 600, which has an opening on one side (first face) of the cylinder with a diameter smaller than the opening on the opposite surface (second face) of the cylinder. The larger cavity opening is slightly larger in size, but its cross-sectional shape is the same as that of the sample 1, allowing for uninterrupted sample placement and removal. The depth of each recess is sufficient to accommodate the sample 1 without any sample protruding and interfering with the sleeve 21 or hindering the rotation of the sample holder 20 within its cylindrical opening. These interconnected and concentric cavities, with one opening larger than the other, are spaced 180° apart.

[0047] For ease of explanation, the samples in this disclosure are all cylindrical discs; however, it is also conceivable that other shapes of samples, such as rectangular plates, may be used in the implementation without affecting other disclosed details.

[0048] Figure 7 An example configuration of sample holder 20 for six solid samples 1 is shown. The first row of samples 1 are located at axial positions k, l, and m, respectively, where the planes defined by k, l, and m also include the longitudinal axis of the cylindrical samples. While the preferred configuration of cavity 601 includes a tubular recess, polygonal recesses may also be used for samples other than circular disks, likely connected to light channels or cavities of similar shape. For practical reasons, the use of samples with a diameter less than 0.125 inches or greater than 2 inches is generally discouraged. Typical thicknesses range from 0.020 inches to 0.200 inches, depending on the material. Typical sample 1 has a diameter of 0.500 or 1.00 inches and a thickness of 0.08 to 0.125 inches.

[0049] like Figure 8As shown, the rows of cavities 601 in the sample holder 20 are radially offset from each other (R1, R2), so that at least two samples are radially offset from each other. The size and shape of adjacent cavities can vary as needed. The number of cavities in a row or number of rows is limited only by the actual situation and can be 1 or 2, 3 or 4, or 6 or more. In all configurations, adjacent cavities must not encroach on the space of any adjacent cavity. Therefore, the number of such radially rotated rows is limited only by the circumference of the holder. These rows can be arranged radially or staggered to achieve the optimal arrangement per unit length of holder. Throughout the disclosure, example embodiments of two rows arranged axially with three positions per row are presented, while 1 to 30 cavities per row and 1 to 10 rows of cavities are considered feasible, with no limitation on the number of cavities. The sleeve 21 surrounding the holder 20 ( Figure 7 There are two opposing slots, 26 and 29. The length of each slot is such that all cavities in a row can be fully exposed when the vertical axis of the cavity coincides with the optical axis Y.

[0050] Sample 1 ( Figure 6 The sample cavity 601 is inserted by pulling out the sample holder structure 501. Figure 5 This is accomplished by removing the sample holder structure 501 by moving the movable base 22 to which the sample holder structure 501 is connected a sufficient distance away from the thermal environment 27, thereby fully exposing and allowing it into the slots 26 and 29. In this position ( Figure 7 Sample 1 is placed into a separate cavity 601 through slot 26, and cavity 601 coincides with positions k, l, and m at rotational position R1. The support 20 is rotated 141 degrees to a sufficiently large angle to reach R2, so that the next row coincides with slot 26. Multiple samples 1 are then loaded into this row of cavities, similar to the case at R1. Meanwhile, as... Figure 8 As shown, sample 1 located at radial position R1 is fixed and confined within the corresponding cavity 601 by the inner wall of sleeve 21. The above process is repeated for other radial sample positions 601. Figure 7 The two radial positions R1 and R2, and the axial positions k, l, and m are shown for illustrative purposes only. During unloading, the sample holder 20 is rotated 180°, and each placement row ( Figure 9 The sample is moved from the corresponding loading position to the unloading position, and then dropped through slot 29. During the test, the loaded sample 1 will never coincide with the radial position of the unloading. It is conceivable that in another design, the sample holder can be pulled out far enough from the base 22 to load the sample without moving the base 22.

[0051] Although the degree of coincidence between axis X and the horizontal line is not important, it is preferable to operate close to the horizontal line, with the loading slot 26 on the bracket 20 located at the top.

[0052] Use the previously defined name, such as Figure 7 The positions k, l, m…z along the longitudinal axis X and R1, R2, R3…Rn along the circumferential direction are... Figure 8 The test sequence can include a lateral translation of 140 degrees. Figure 6 The multi-sample scaffold structure 20 enables R 1k Enter the test location (e.g.) Figure 5 (As shown in section 60), then R 2k R 3k Wait, then R 1l R 2l The above sequence can be achieved through sequential transposition or synchronous transposition.

[0053] Another significant advantage of this axial / radial rotation configuration is that it requires a much smaller thermal volume within the uniform thermal zone of the thermally controlled environment 27 compared to any previous multi-sample holder (such as the circular platform mentioned above (Figures 1, 4)), thereby reducing the thermal volume required per sample. Figure 5 (513), saving energy and thus providing a more environmentally friendly operation. The six sample disc holders (Figs. 1, 4) require a uniform thermal volume of at least 2.5 inches in diameter × 2 inches (equivalent to 1.6 in) in the hot zone of a 2500°C thermally controlled environment. 3 / sample), while the transposition sample holder structure 501 disclosed herein only requires a thermal volume of 1.5 inches in diameter × 2 inches in length to accommodate 9 samples, equivalent to 0.4 inches. 3 The sample requires nearly 75% less energy and also reduces thermal pollution to the environment by nearly 75%.

[0054] See Figure 5 The multi-sample holder structure described above supports one or more samples. By controlling the axial and radial movement of the sample holder 20 relative to the fixed sleeve 21, the axis of the selected sample (perpendicular to its surface A) can be aligned with the axis of the light beam 12 emitted from the light source, thereby causing the first surface of the selected sample 1A to face the pulsed light source. Simultaneously, the device can also orient the second surface of the aforementioned sample 1B toward a suitable temperature rise detector 505, thereby inducing a radiation signal 509 upon impact by the light pulse 12. By installing several rows of radially offset cavities on the sample holder 20 as sample placement areas 601, it can also be used as a device for samples with one or more radially offset surfaces.

[0055] An example of an axial / radial indexer 502 (see details) Figure 6Located in an ambient space 23 outside of a thermally controlled environment 27. The axial / radial indexer includes a rod or arm 49 connected to a sample holder 20, which passes through a movable base 22 via a rotating sleeve 42. The sleeve 42 is fitted with a pin 43, which engages with a longitudinal groove 44 in the extension 49 parallel to the axis X of the extension 44. Since the pin 43 is securely connected to the sleeve 42, rotation of the sleeve 42 will correspondingly rotate the extension. To achieve axial displacement of the extension, a linear actuator 45 is required. The axial displacement is indicated by a linear position sensor 650 connected 651 to the linear actuator 45. The end of the extension 49 terminates in a powerful disc magnet 48, which contacts a steel disc 46 of a corresponding size or another disc magnet of opposite polarity, the steel disc 46 and the other disc magnet of opposite polarity being rigidly connected to the moving end 47 of the linear actuator 45. The magnet 48 and the steel disc 46 can be reversed. Because magnet 48 exerts a strong attraction on the steel in the direction aligned with the X-axis, but a weak attraction in any other direction, rotational sliding is permitted between the surfaces of 46 and 48 without creating a gap. This connection ensures precise axial X-displacement 140 while also ensuring unobstructed and precise rotation 141 about the X-axis for radial indexing. Rotational drive can be achieved via actuator 51 (e.g., a geared motor or stepper motor) connected to an internal or external rotation sensor 201 (e.g., a potentiometer or encoder) and connected to sleeve 42 via connecting device 52 (e.g., a timing belt, gear, or O-ring). Various components complement the functions of the actuator, sensor, and magnet, and their interactions, as is known in the art, to achieve simultaneous rotation and lateral actuation.

[0056] Therefore, a device for accommodating at least two samples includes a sample holder ( Figure 5 ,20), having at least two sample placement cavities radially offset from each other on its cylindrical surface ( Figure 5 , 601), the sample is placed in the cavity inside the sleeve 21 and connected to the axial / radial indexer ( Figure 5 ,502) connected.

[0057] 3. Temperature rise detector

[0058] Still refer to Figure 5 The pulse source 504 can be located below the thermal control environment 500 housing 510, with the temperature rise detector 505 located on top, or vice versa. Lateral positioning is also possible, but is generally more difficult to achieve. Figure 5 A temperature rise detector 505 is shown, which can be an intrinsic thermocouple, a beaded thermocouple, or a light radiation detector (not shown), for sensing the temperature rise of surface B of sample 1 at the test position after receiving an energy pulse, with surface B opposite to the irradiated surface A.

[0059] 4. LED pulse source

[0060] In this disclosure, such as Figure 11 As shown, the light source is at least one light-emitting diode (LED) 10, which can be single or an array. This LED light source, composed of one or more LEDs, provides a pulsed light source with minimal electrical noise simply by switching a low-voltage current (typically less than 100V DC) to a quasi-resistive load. Existing devices utilize lasers or xenon flash tubes, which generate significant electrical noise during the production of short pulses of light by discharging large high-voltage capacitors and triggering pulses with very high voltages (>10,000V). Furthermore, the use of high-voltage lasers is dangerous. Controlling the pulse width of light pulses is difficult with lasers or xenon flash tubes. In contrast, LED pulse width control is simple and precise because it can be turned on and off on command, with extremely short rise and decay times (<0.01 milliseconds), and can produce variable intensity based on the controlled voltage level. Using LEDs also reduces costs, improves safety, and reduces device complexity.

[0061] The energy density of most LEDs themselves is generally insufficient compared to the energy required for testing, so an array of multiple LEDs may be considered. Using at least one LED 10, the emitted light 11 (which may or may not be focused 15) forms a columnar beam, which comprises multiple parallel rays 12. Figure 5 As shown, this highly columnar beam passes through the channel ( Figure 5 , 514), enter the interior of the ambient space 27 and the thermal volume 513 without significant loss of energy transferred to the surface A of the sample arranged along its optical axis Y. In another embodiment, at least one laser diode can be used instead of the LED.

[0062] like Figure 11 As shown, light 11 emitted from one or more LEDs or any combination of LED arrays 11 placed on base 520 can be focused or shaped by conventional optical means (such as combinations of lenses 504), and then formed into a parallel light beam 12 through columnar or transmission components (such as optical fibers or light guides 521). There may be a variety of methods for focusing, columnarizing, and transmission, as is well known in the art.

[0063] These different configurations share a common characteristic: they are used to concentrate the light output 11 of a single LED or multiple LEDs in an array operating in pulse mode into a high-power-density columnar beam 12, thereby generating sufficient power density to produce the desired thermal offset of 0.1–3°C (C) on the surface B of the sample.

[0064] 5. Improved data analysis solutions

[0065] Because the energy density of the light pulse is limited to some extent by the energy density provided by the LED, or due to other experimental reasons, it may be necessary to use a longer light pulse to obtain the total energy input required for the sample. Figure 5 A measurable temperature rise was generated on surface B of sample 1, with most materials showing a temperature rise ranging from 0.1 to 3 °C.

[0066] The analysis in the operating and analysis software of this disclosure largely overcomes the aforementioned problems caused by heat loss and thermal distortion due to finite-length pulses. In the prior art, these problems are corrected by processing post-test data based on theoretical considerations. Since all factors are interdependent, corrections for heat loss and individual corrections for finite pulse widths rarely yield satisfactory results without extensive testing. In these cases, the goal is to process the test data through theoretical corrections so that the test data closely matches a theoretically perfect thermal map.

[0067] In contrast, the device disclosed herein can change the intensity and duration of pulses according to instructions, thereby generating a series of pulses of different widths that can (virtually in real time) iterate to the desired result within the same test cycle. Therefore, this method comprehensively processes all interacting factors by using continuous pulses with different parameters occurring in real time. Figure 12 As shown, within a test cycle, for a specific material sample, at least a sequence of two pulses, namely P1 and P2, is used, but it may also be three or more pulses, with P3 representing the third pulse. x This indicates the subsequent pulses, each with a specific duration. Then, t is calculated for each case. 1 / 2 and this t 1 / 2 Data is stored in a database, thus providing a method for calculating thermal diffusivity from heatmaps. The database can be placed, stored, or saved on a computer's storage device. For example, the shortest pulse P1 produces the maximum temperature rise Max1. From this, (t...) 1 / 2 )1, and is obtained through the method described above. Similarly, (t 1 / 2 )2 and (t 1 / 2 )3. Results were obtained for pulses P2 and P3, where P3 is the longest pulse and P2 is longer than P1. Different pulse durations were used, increasing or decreasing sequentially according to their duration. Then, with the pulse intensity constant, the time offset of the obtained heatmap and its corresponding t were analyzed based on the corresponding pulse width. 1 / 2 By considering t as a function of pulse duration 1 / 2Perform linear regression or higher-order regression analysis on the value sequence, and derive the resulting function to an extremely short pulse duration, where t 1 / 2 Much less than 100 times the corresponding pulse duration, then the result t 1 / 2 Used in Equation 1. The aim of this process is to control the error to 1% or less. The number of multiple pulses in this analysis is at least two. By varying the pulse intensity, the temperature rise range of the rear face B can be further optimized and determined.

[0068] In real-time analysis, the evaluation of each pulse-related thermogram is performed individually after the thermogram is determined. Then, regression analysis is performed after the last pulse in the desired sequence, at which point the thermal environment of the sample has not changed significantly. Based on the statistical parameters of the regression analysis and determining whether the results are acceptable, a decision is made to either iterate using the pulse sequence with altered intensity and pulse width parameters or move the test to the next temperature point. Alternatively, analysis can be performed after the test, but without the need for real-time iteration with different parameters as described above.

[0069] Figure 11 A block diagram of the operation of a flash diffusion system is described, which uses a light source described in this disclosure, including at least one LED light source 400. As is generally the case, arrows indicate signal flow. Computer 401 includes software program 402 and real-time analysis software 404, software program 402 being used to control the thermal environment 27 (e.g., ...) via general control circuitry 403. Figure 5 The heating or cooling of the thermal control environment 27 (513) is performed by real-time improved analysis according to the real-time analysis software 404 programmed as described above. According to the software programming instructions, the time-varying pulse generator circuit 406 is triggered, and then the light-emitting diode light source 400 is "turned on" and "turned off" at the desired intensity within a predetermined time period. The resulting light pulses impact the sample ( Figure 5 ,1) on, so that its front A ( Figure 5 The temperature of surface B on the back side of the sample rises rapidly, and the heat passes through the sample, eventually causing the temperature of the sample to gradually increase. This temperature is continuously measured by a temperature rise detector, which is shown as a ΔT measurement sensor. The output of the detector is amplified and modulated by a digitization circuit 405, and the digital equivalent of the electrical signal is transmitted back to a computer 401 and its software program 404 to analyze and determine the thermal diffusivity.

[0070] Although the invention has been described with reference to the disclosed embodiments, many modifications and variations can be made, and the results remain within the scope of the invention. No limitation is intended for the specific embodiments disclosed herein, nor should any limitation be inferred. Many equivalents exist for each device embodiment described herein.

Claims

1. An apparatus for measuring thermal diffusivity of a solid material, the apparatus comprising: a. a heater for creating a thermally stable environment; b. an LED array light source capable of raising the temperature of at least one sample with light pulses emitted therefrom; c. a sample holder for placing at least two radially offset samples; d. the LED array light source for illuminating a first side of at least one sample; e. a temperature rise detector for reading the temperature change of a second side of at least one sample and recording a thermal map after a light pulse is applied to the first side; f. a computer for calculating thermal diffusivity from the thermal map; and g. a sample placement section having at least two radially offset samples, each sample being part of an axially offset row of samples, wherein the heater for creating a thermally stable environment further comprises being programmed to provide a plurality of pulses according to a proportional-integral-derivative (PID) control principle, first heating the samples to a desired temperature and reaching a thermally stable state before issuing a measurement pulse.

2. The apparatus according to claim 1, wherein the computer for calculating the thermal diffusivity of at least one sample comprises a software program which calculates the thermal diffusivity using a sequence of at least two predetermined different duration light pulses, the light pulses being denoted P1, P2, each having associated therewith t 1 / 2 , denoted (t 1 / 2 )1, (t 1 / 2 )2, and at least two t 1 / 2 values are regression analysed with the corresponding pulse duration and the resulting function is extrapolated to pulse durations shorter than 100 milliseconds to obtain the corresponding t 1 / 2 , which is then used to calculate: a = c • L 2 / t 1 / 2 , where c = 0.13879 and L is the thickness of the sample.

3. The apparatus of claim 1, wherein the LED array light source further comprises: a. at least one LED; b. a condenser; and c. a light transmitting columnizer.

4. The apparatus of claim 1, wherein the LED array light source further comprises at least one laser diode.

5. The apparatus of claim 1, wherein the sample holder for housing at least two radially offset samples from each other further comprises an axially and radially movable sample holder, a fixed sleeve, and an index for moving the sample holder relative to the fixed sleeve, wherein the sample holder comprises at least two radially offset cavities from each other, the openings of the at least two cavities connected to each other and concentric, one of the openings being larger than the other, the openings being 180° apart from each other, the sleeve comprising at least two openings, each opening having a width at least the same as the larger opening of the at least two cavities and being 180° apart from each other on a surface.

6. The apparatus of claim 5, wherein the sample holder and the sleeve are extracted from the thermal environment for loading and unloading the samples.

7. The apparatus of claim 5, wherein the at least two cavities are parallel to a longitudinal axis of the sample holder and radially offset from each other, and wherein each row of axially offset samples comprises at least one sample cavity.

8. The apparatus of claim 5, wherein the at least two cavities extend through the sample holder, each cavity comprising an opening on a first side and an opening on a second side, the opening on the first side being larger than the opening on the second side, the openings being concentric and along an axis perpendicular to the longitudinal axis of the sample holder.

9. The apparatus of claim 5, wherein the sample holder is cylindrical in shape.

10. The apparatus of claim 5, wherein the sample holder is polygonal in cross-section.

11. The apparatus of claim 5, wherein the index moves the sample holder axially and radially relative to the sleeve while the position of the sleeve remains unchanged. ​

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