An Investigation of the Effect of Nanoparticles on the Effectiveness of a Heat Exchanger

Convective heat transfer can be improved by enhancing the thermal conductivity of the fluid. It has been established that fluids containing suspended solid particles of metallic origin in nanoscale dimensions, display enhanced thermal conductivity. Nanoparticle suspensions have superior qualities than suspensions of larger sized particles, such as more particle surface area, less possibilities of agglomeration and clogging and better stability. An experimental investigation on the effect of the inclusion of nanoparticles into the cooling fluid on the effectiveness of a heat exchanger is presented in this paper. An experimental double pipe heat exchanger with the hot fluid flowing through the inner tube was used in the study. Aluminum oxide and copper oxide nanoparticles with a size range of 20 to 30 nm suspended in water using ultrasonic agitation was used as the hot fluid, and water was used as the cold fluid passing through the annulus. The concentration of the suspended nanoparticles was varied to investigate its effect on the performance of the exchanger. The operating temperature is also used as a parameter in the study. Typically, an enhancement of 4.5 to 7 percent was observed in the effectiveness of the heat exchanger for 0.26% weight fraction of the nanoparticles in suspension, in an operating temperature range of 50–70°C. The effectiveness of the heat exchanger was found to increase with the concentration of nanoparticles for both materials used.

Subcooled Pool Boiling Studies on Nano-Textured Surfaces

Heat transfer in subcooled pool boiling on nano-textured surfaces is reported in this study. Silicon wafers coated with Multiwalled Carbon Nanotubes (MWCNT) forests 9 microns (Type-A), and 25 microns (Type-B) in height and 8–15 nm in diameter with a randomized pitch of 16–30 nm, form the test surfaces. The test fluid is a fluoroinert (PF-5060, Manufacturer: 3M Co.) with a boiling point of 56°C. The test rig is of the constant heat flux type. Heat transfer enhancement of approximately 1.3 to 32% is observed in the nucleate boiling regime for Type-A at subcooling levels of 20°C. Type-B CNT shows an enhancement of about 13–30% in the nucleate boiling regime for 20°C subcooling. Digital images acquired during the tests show increased nucleation occurring on surfaces coated with MWCNT. Potential factors that could explain the observed heat transfer enhancement are: the enhanced surface area (nano-fin effect), disruption of the “microlayer” region in nucleate boiling, an increase in the size of cold-spots and the high thermal conductivity of MWCNT.

Genetic Algorithm for Nanoscale Electro-Thermal Optimization

In this paper, we are presenting a genetic algorithm adopted for electro-thermal optimization in nanoelectronics devices and systems. The model of nanoelectronic system is simplified. Each heat source will be approximated by a specific function. The presented optimization strategy is designated for any system containing a number N of nanoelectronic elements. Optimization for the overall structure of the system will be performed in conformity with the temperature minimization criteria in the chosen areas of the system. Regarding others non unexpected modifications of the optimization algorithm, we are using a modified complex objective function.

Challenges in Package Cooling of High Performance Servers

Cooling technologies for dealing with high-density and asymmetric power dissipation are discussed, arising from thermal management of high performance server CPU-packages. In this paper, investigation and development of associated technologies are introduced from a viewpoint of industrial application, and attention is focused on heat conduction and removal at the package and heatsink module level. Based on analyses of power dissipation and package cooling characteristics, properties of a new metallic thermal interface material are presented where the Indium-Silver composite was evaluated for integrating the chip and its heat-spreader, effects of heat spreading materials on package thermal performance are investigated including high thermal conductivity diamond composites, and evaluations of enhanced heatsink cooling capability are illustrated where high thermal conductivity devices of heat pipes or vapor chambers were applied for improving heat spreading in the heatsink base.

Thermo-Viscoelastic Analysis for Warpage in CSP With Different Viscoelastic Properties for Several Layers

In this study, a simple theory for estimating the warpage of chip size packaging (CSP) during a manufacturing process is presented. A single-sided CSP which is composed of IC, a resin and a substrate is modeled for an analysis as a three-layered material. Especially, the resin and the substrate have different thermo-viscoelastic properties. When the layered body is perfectly bonded, its warpage is caused by the difference of the thermal expansion coefficient in each layer when temperature varies. The warpage of CSP for a various thicknesses of the IC and the substrate is investigated. Finally, the warpage calculated using the theory is compared with the result in experiment, and both results are well agreed with each other. Then, it is shown that the simple theoretical analysis is valid. After that, this program is extended to be able to analyze the warpage in a CoC (Chip on Chip), and the result of the analysis is then presented.

Dimensional and Locational Integrity in the Replication of Polymeric Microdevices

In molding, geometric variation of molded parts is inevitable since the parts have a thermal history, including expansion and shrinkage, during the molding process. Shrinkage induces variation between the designed dimensions and locations of features on molded parts while the parts are cooled. Characterization of the variation is necessary to ensure dimensional and location integrity. Hot embossing and injection molding were performed in order to assess variation. Measurements were made using a Measurescope (MM-22, Nikon Corp., Kawasaki, Japan). The measured locations and dimensions were compared to estimates obtained using a simple model based on the linear thermal expansion coefficients (CTE) of the molded materials. The measured and the estimated shrinkage from hot embossing were incorporated in the fabrication of microtiter plate-based polymer microfluidic platforms.

Effects of Tooling Tip Wear and Fixture Rigidity on Solder Ball Shear and Ball Pull Tests

The present study is aimed at evaluating the effect of ball shear tool wear and fixture rigidity on ball shear and ball pull tests respectively. In particular, the emphasis is placed on understanding the progressive failure mechanism during the ball shear test. The location of crack initiating is investigated on two kinds of shear tool with different wear features. In this paper, the experimental investigation is presented. Specimens with PBGA solder balls are fabricated and a series of ball shear and pull tests are conducted. In the shear test, the shear tool is stopped at a certain stage during test, and then the specimens are inspected by SEM. The failure modes and location of cracks are characterized. From the ball attachment strength and crack location of the ball shear test, no significant difference is found between the shear tools with different wear features. For investigating the effect of fixture rigidity on the ball pull test, two kinds of PBGA package with different sizes was fixed on the fixtures with and without gluing on a rigid plate. The failure modes and ball pull strength with different fixture rigidity were compared. The test results indicate that more brittle failures are found on the specimens without gluing on the rigid plate during the ball pull test, both on two kinds of package with different sizes. In addition, the data scattering of ball pull strength is large on the case without gluing on rigid plate.

Finite Element Analysis of Laser Fabricated Microjoint Performance in Cerebrospinal Fluid

Assessment of neural biocompatibility requires that materials be tested with exposure in neural fluids. Laser bonded microjoint samples made from titanium foil and polyimide film (TiPI) were evaluated for mechanical performance before and after exposure in artificial cerebrospinal fluid (CSF) for two, four and twelve weeks at 37°C. These samples represent a critical feature i.e., the microjoint — a major weakness in the bioencapsulation system. The laser microbonds showed initial degradation up to four weeks which then stabilized afterwards and retained similar strength until twelve weeks. To understand this bond degradation mechanism better, a finite element modeling approach was adopted. From the finite element results, it was revealed that the bond degradation was not owing to the hygroscopic expansion of polyimide. Rather, relaxation of the process induced residual stresses may have resulted in weakening of the bond strength as observed from experimental measurements.

Transient Thermal Characterization of ErAs/In0.53Ga0.47As Thermoelectric Module

Embedded metallic nanoparticles in semiconductors have recently been proven to be of great interest for thermoelectric applications. These metallic nanoparticles play the role of scattering centers for phonons and a source of doping for electrons; they reduce simultaneously the thermal conductivity and increase the thermoelectric power factor of the semiconductor. It has also shown that metal/semiconductor heterostructures can be used to break the crystal momentum symmetry for hot electrons in thermionic devices, then increasing the number of electrons participating in transport. A thermoelectric module of 200 N-P pairs of InGaAlAs with embedded ErAs metallic nanoparticles has been fabricated. Network Identification by Deconvolution (NID) technique is then applied for transient thermal characterization of this thermoelectric module. The combination of this new representation of the dynamic behavior of the packaged device with high resolution thin film temperature measurement allows us to obtain information about heat transfer within the thermoelectric module. This is used to extract the thermal resistances and heat capacitances of the module.

Effect of Orientation and Draining on Linear Spray Array Thermal Management

Spray cooling is a candidate solution for high heat flux cooling applications, and previous work has investigated the impact of parameters of conical sprays such as volumetric flux and Sauter mean diameter on heat transfer performance. However, there has been little work on the impact of drainage and spray orientation on spray performances. In addition, conical sprays are not very practical for large area coverage in compact packages, so this study, presents a novel arrangment that uses linear sprays impinging at an angle such that fluid management and uniform droplet coverage of large areas are both improved. Results for the heat transfer coefficient and CHF of a constrained, practical implementation of a spray array (as opposed to a laboratory-only geometry) are presented for FC-72, FC-40 and HFE-7000.