Heat pipes have immense potential in the future of thermal management in electronic devices. As a... more Heat pipes have immense potential in the future of thermal management in electronic devices. As a passive device, they rely solely upon capillary forces to recirculate the coolant from the condenser to the evaporator via a wicking structure. In intermediate temperature heat pipes the limiting factor for heat removal is the capillary limit, which indicates the maximum recirculation rate that the capillary forces can induce. This capillary limit must be increased to allow heat pipes to remain a viable option for heat management within electronic devices. The aim of this work is to characterize and optimize the capillary limit of micropillared thermal wicks for heat pipe application in microelectronics cooling.
In the development of ablative materials, extensive small scale testing is necessary due to the h... more In the development of ablative materials, extensive small scale testing is necessary due to the high cost and scarcity of large scale testing facilities. To maximize the effectiveness of small scale testing, a large thermal impingement area is desired in order to better simulate the actual behavior of the material. An increased area testing platform was developed and validated, which substantially increased the area of applied uniform heat flux to the sample from a previously published 1.6 cm 2 to 9.0 cm 2 . The increased testing area is crucial to provide a more accurate study of the ablation characteristics. This paper details the selection process of a lampworking torch as the heat source through an analytical model and then verified using calibration and C/C material ablation experiments. The newly developed ablation testing setup was able to maintain a comparable heat flux of 3.4 M W/m 2 , while also significantly increasing the sample size that could be tested in the previous testing rig.
The properties of soft nanomaterials are hard to measure exactly due to their mechanical properti... more The properties of soft nanomaterials are hard to measure exactly due to their mechanical properties and unstable shape. In particular, hydrogels are a class of cross-linked polymers that can absorb large quantities of water changing their shape under the influence of various conditions such as humidity, temperature, and pH. This research addresses the fabrication of a material that has a significant contrast in properties under different conditions (e.g. temperature, wetting, and pH) and determine the physical mechanisms of heat transfer in this nanomaterial. The hydrogels are made using a several cycles of a freeze-thaw method. The method requires soluble material. We set the solution in chamber slide which give us a rectangular shape. We freeze the sample under -20 C for 21 hours and thaw at room temperature for 3 hours. The 3ω method measures the thermal conductivity of the soft nanomaterials including a polyvinyl alcohol (PVA) -polyvinyl pyrrolidone (PVP) hydrogel and a PVA-Dimethyl sulfoxide(DMSO) hydrogel. By analyzing the magnitude and the phase of the temperature response to a heating signal, we determine the thermal conductivity of each material. To enhance the thermal transport, these materials are embedded with gold nanoparticles. By comparing experimental value with theoretical value, we conclude fabrication methods have a significant impact upon the material properties. Further research will be focusing on different soft nanomaterials and include the impact of the nanoparticle concentration and hydrogel fabrication methods.
Soft materials like hydrogels have multiple tunable material properties because of their unique s... more Soft materials like hydrogels have multiple tunable material properties because of their unique structures. Due to the ability to respond to stimuli like temperature or chemical environment, they have numerous applications in different fields like delivering drugs inside the human body and other medical uses. Details of the thermal transport mechanisms, as well as the overall thermal properties, are critical for a variety of applications. Multiproperty measurements elucidate the underlying transport mechanisms in the soft materials. This research demonstrates a new methodology of measuring thermal properties of soft materials. This work uses the 3ω method [1,2] for measuring the thermal conductivity of soft hydrogels. In the 3ω method, heat is generated in thin heater line excited by a sinusoidal current at a frequency of ω. We measure the voltage response at the third harmonic of the input frequency (3ω). This response is related to the temperature rise and thus the thermal properties. Once the measurement technique is optimized, PVA-PVP hydrogels are tested. Using a 2D mathematical model of the heat transfer, the thermal conductivities of soft material are calculated from the experimental data. Based on the methodology built during this research, this technique is available now for other soft materials beyond hydrogels and the precision of this methodology can be improved by further studies.
Heat pipes have immense potential in the future of thermal management in electronic devices. As a... more Heat pipes have immense potential in the future of thermal management in electronic devices. As a passive device, they rely solely upon capillary forces to recirculate the coolant from the condenser to the evaporator via a wicking structure. In intermediate temperature heat pipes the limiting factor for heat removal is the capillary limit, which indicates the maximum recirculation rate that the capillary forces can induce. This capillary limit must be increased to allow heat pipes to remain a viable option for heat management within electronic devices. The aim of this work is to characterize and optimize the capillary limit of micropillared thermal wicks for heat pipe application in microelectronics cooling.
In the development of ablative materials, extensive small scale testing is necessary due to the h... more In the development of ablative materials, extensive small scale testing is necessary due to the high cost and scarcity of large scale testing facilities. To maximize the effectiveness of small scale testing, a large thermal impingement area is desired in order to better simulate the actual behavior of the material. An increased area testing platform was developed and validated, which substantially increased the area of applied uniform heat flux to the sample from a previously published 1.6 cm 2 to 9.0 cm 2 . The increased testing area is crucial to provide a more accurate study of the ablation characteristics. This paper details the selection process of a lampworking torch as the heat source through an analytical model and then verified using calibration and C/C material ablation experiments. The newly developed ablation testing setup was able to maintain a comparable heat flux of 3.4 M W/m 2 , while also significantly increasing the sample size that could be tested in the previous testing rig.
The properties of soft nanomaterials are hard to measure exactly due to their mechanical properti... more The properties of soft nanomaterials are hard to measure exactly due to their mechanical properties and unstable shape. In particular, hydrogels are a class of cross-linked polymers that can absorb large quantities of water changing their shape under the influence of various conditions such as humidity, temperature, and pH. This research addresses the fabrication of a material that has a significant contrast in properties under different conditions (e.g. temperature, wetting, and pH) and determine the physical mechanisms of heat transfer in this nanomaterial. The hydrogels are made using a several cycles of a freeze-thaw method. The method requires soluble material. We set the solution in chamber slide which give us a rectangular shape. We freeze the sample under -20 C for 21 hours and thaw at room temperature for 3 hours. The 3ω method measures the thermal conductivity of the soft nanomaterials including a polyvinyl alcohol (PVA) -polyvinyl pyrrolidone (PVP) hydrogel and a PVA-Dimethyl sulfoxide(DMSO) hydrogel. By analyzing the magnitude and the phase of the temperature response to a heating signal, we determine the thermal conductivity of each material. To enhance the thermal transport, these materials are embedded with gold nanoparticles. By comparing experimental value with theoretical value, we conclude fabrication methods have a significant impact upon the material properties. Further research will be focusing on different soft nanomaterials and include the impact of the nanoparticle concentration and hydrogel fabrication methods.
Soft materials like hydrogels have multiple tunable material properties because of their unique s... more Soft materials like hydrogels have multiple tunable material properties because of their unique structures. Due to the ability to respond to stimuli like temperature or chemical environment, they have numerous applications in different fields like delivering drugs inside the human body and other medical uses. Details of the thermal transport mechanisms, as well as the overall thermal properties, are critical for a variety of applications. Multiproperty measurements elucidate the underlying transport mechanisms in the soft materials. This research demonstrates a new methodology of measuring thermal properties of soft materials. This work uses the 3ω method [1,2] for measuring the thermal conductivity of soft hydrogels. In the 3ω method, heat is generated in thin heater line excited by a sinusoidal current at a frequency of ω. We measure the voltage response at the third harmonic of the input frequency (3ω). This response is related to the temperature rise and thus the thermal properties. Once the measurement technique is optimized, PVA-PVP hydrogels are tested. Using a 2D mathematical model of the heat transfer, the thermal conductivities of soft material are calculated from the experimental data. Based on the methodology built during this research, this technique is available now for other soft materials beyond hydrogels and the precision of this methodology can be improved by further studies.
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Papers by Collier Miers