Laser Flash Measurement of Samples With a Transparent Reference Layer

2009 ◽  
Author(s):  
Heng Ban ◽  
Zilong Hua
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Temperature Response ◽  
Front Surface ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Thermal Diffusivity Measurement ◽  
Reference Layer

The laser flash method is a standard method for thermal diffusivity measurement. This paper reports the development of a method and theory that extends the standard laser flash method to measure thermal conductivity and thermal diffusivity simultaneously. By attaching a transparent reference layer with known thermal properties on the back of a sample, the thermal conductivity and thermal diffusivity of the sample can be extracted from the temperature response of the interface between the sample and the reference layer to a heating pulse on the front surface. The theory can be applied for sample and reference layer with different thermal properties and thickness, and the original analysis of the laser flash method becomes a limiting case of the current theory with an infinitely small thickness of the reference layer. The uncertainty analysis was performed and results indicated that the laser flash method can be used to extract the thermal conductivity and diffusivity of the sample. The results can be applied to, for instance, opaque liquid in a quartz dish with silicon infrared detector measuring the temperature of liquid-quartz interface through the quartz.

Laser Flash Method for Non-Opaque Materials

2005 ◽  
Author(s):  
Bochuan Lin ◽  
Heng Ban ◽  
Chao Li ◽  
Rosalia N. Scripa ◽  
Chinghua Su ◽  
...  
Keyword(s):  
Thermal Diffusivity ◽  
Absorption Coefficient ◽  
Laser Energy ◽  
Temperature Response ◽  
Sample Surface ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Thermal Diffusivity Measurement ◽  
Special Cases

The laser flash method for thermal diffusivity measurement is a standard method for opaque solid materials. It can also be used to measure liquid in a specially designed cell. The theoretical basis for the method is established based on pulse heating of one side of a thin opaque sample and measure the temperature response of the other side. In cases where the material is non-opaque or semi-transparent for the laser wavelength, existing theoretical models cannot be used directly. One way to overcome the problem is to coat a thin layer of graphite on the sample surface. The coating can absorb the laser energy and create a surface heating effect. However, coating may not be possible for special cases due to concerns of contamination of liquid samples. This paper reports the development of a theory that includes the transmission and absorption of the laser energy through out the sample thickness. The theory can be applied for samples with different absorption coefficient to obtain simultaneously thermal diffusivity and thermal conductivity of the sample. The original theory of the laser flash method becomes a limiting case of the current theory with an infinitely large absorption coefficient. The uncertainty analysis was performed and results indicated that that laser flash method can be used on non-opaque samples.

Method for Obtaining Thermal Conductivity From Modified Laser Flash Measurement

2005 ◽  
Author(s):  
Bochuan Lin ◽  
Heng Ban ◽  
Chao Li ◽  
Rosalia N. Scripa ◽  
Ching-Hua Su ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Rear Surface ◽  
Temperature Response ◽  
Laser Flash ◽  
Fused Silica ◽  
Laser Flash Method ◽  
Flash Method ◽  
Silica Cell

Laser flash method is commonly used to measure the thermal diffusivity of solids. In the original thermal analysis, adiabatic boundary conditions were used and the time for sample rear surface temperature to reach 50% of maximum value was used to calculate the thermal diffusivity. Later other boundary conditions were included in the analysis to compensate for the heat loss. The laser flash method can be modified to determine the thermal conductivity by comparing the temperature rise of the sample with a standard sample, both of which are coated to ensure identical surface emissivity. In our previous studies of applying the laser flash method to semiconductor melts, we have shown that it is possible to obtain thermal conductivity, specific heat capacity and thermal diffusivity from the experimental data. In these studies, the melt sample was sealed in a specially-designed fused silica cell. The heat transfer between melt sample and the fused silica cell allows the thermal conductivity to be included in the analysis. Therefore, the temperature response of the melt sample was controlled not only by the thermal diffusivity and conductivity of sample, but also by the thermal properties of fused silica cell. Using a computational fitting process, we obtained both thermal diffusivity and thermal conductivity of the sample. In this paper, an analytic solution for the transient heat transfer inside the sample and fused silica cell was developed. The influence of fused silica cell was included and the heat transfer to fused silica cell had a significant effect on the time-temperature response of the sample. Therefore, the rear surface temperature of the sample, described by an analytical solution, could be used to obtain both thermal diffusivity and thermal conductivity of the sample with known properties of the fused silica cell. The results indicated that this method was applicable for a wide range of sample and cell properties. The original solution for laser flash method became an extreme case in the current theory

Thermal Diffusivity Measurement for Thermal Spray Coating Attached to Substrate Using Laser Flash Method

2011 ◽  
Vol 50 (11S) ◽  
pp. 11RE01 ◽  
Author(s):  
Megumi Akoshima ◽  
Takashi Tanaka ◽  
Satoshi Endo ◽  
Tetsuya Baba ◽  
Yoshio Harada ◽  
...  
Keyword(s):  
Thermal Diffusivity ◽  
Thermal Spray ◽  
Spray Coating ◽  
Laser Flash ◽  
Thermal Spray Coating ◽  
Laser Flash Method ◽  
Flash Method ◽  
Thermal Diffusivity Measurement ◽  
Diffusivity Measurement

Modified Laser Flash Method for Thermal Property Measurements and the Influence of Heat Convection

2003 ◽  
Author(s):  
Bochuan Lin ◽  
Shen Zhu ◽  
Heng Ban ◽  
Chao Li ◽  
Rosalia N. Scripa ◽  
...  
Keyword(s):  
Heat Conduction ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Laser Pulse ◽  
Rear Surface ◽  
Front Surface ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Conduction Model

This study examined the effect of natural convection in the modified laser flash method for the measurement of thermo physical properties of semiconductor melts. Common laser flash method uses a laser pulse to heat the front surface of a thin circular sample and measures the temperature transient of the rear surface. Thermal diffusivity is calculated based on the analysis of the transient heat conduction process. For semiconductor melts, the sample is contained in a specially designed quartz cell with optical windows. When the laser pulse heats the melt front surface, the resulting natural convection can introduce errors in the calculation of thermal diffusivity based on the heat conduction model. The effect of natural convection was evaluated by Computational Fluid Dynamics (CFD) simulations in this study. The results indicated that natural convection can decrease the time needed for the rear surface to reach its peak temperature, and can also decrease the peak temperature slightly. Based on our experimental data for Tellurium, the calculation using only heat conduction model resulted in a thermal diffusivity about 3% greater than that using the heat transfer model with natural convection.

Sign in / Sign up

Export Citation Format

Share Document