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Experimental investigation was performed to study the pressure drop characteristics of parallel-plate channels where model packages of various sizes are mounted. The ratio of channel height to package height and placement pitch to package height are 1.3∼2.7 and 1.8∼5.6 for packages without fins, and 1.2∼2.0 and 2.1∼3.4 for finned packages, respectively. A new flow model is proposed which incorporates the three-dimensional nature of wakes behind the packages. The predicted values of pressure drop based on this model correlate with the experimental results within ±20∼30%.

This study investigates the issues involved in the design of a compact two-phase thermosyphon in which the locations of evaporator and condenser need a high degree of freedom. Enhancement of boiling heat transfer in the compact evaporator space was achieved by a microfabricated structure. Anticipating situations where gravity does not provide sufficient potential to drive the condensate, a pump-assisted circulation loop was studied. The relative height between the evaporator and condenser and the pumping rate were systematically varied by utilizing two thermosyphon loops. Close examination of the data suggests that there could be an optimum point in the parametric domain where the thermal resistance is minimized with least assistance from the pump.

Carbon nanotubes (CNTs) have a large specific surface area and, thus, are expected to have applications as electrodes, e.g., in fuel cells. A CNT-containing composite metal film with high electrode performance could be realized by implementing a large number of CNTs on the film. However, a composite film with a high density of CNTs has not yet been obtained. In the thermal spray field, including cold spray, metal–CNT composite films with more than 20 wt% of carbon nanotubes has not yet been deposited. In this study, high-density CNT-containing metal-based composite films were deposited onto an aluminum substrate by low-pressure cold spray from electroless nickel-plated CNT particles. The electroless nickel plating process caused slight structural damage to the CNTs, whereas the cold spray process did not cause any significant structural damage to the CNTs. Two phases were observed in the films: a CNT-rich layer and a nickel-rich layer. However, the CNTs maintained sufficient adhesive strength to remain attached to the bottom nickel phase. Composite films with at least 65 wt% CNT were produced with our method.

Diamond-like carbon (DLC) films have a high hardness and a low friction coefficient. Therefore, DLC films are applied in industrial fields to reduce energy consumption. However, DLC films can only be obtained as coatings, and DLC films of only micrometer thickness can be deposited on substrates. In this study, we focused on the cold spray (CS) technique as a means of obtaining a DLC-containing metal composite. DLC-containing metal composite films with a millimeter thickness and a low friction coefficient were obtained by depositing DLC-coated metal [copper (Cu) and titanium (Ti)] particles by the CS technique. For Cu particles, DLC-coated particles were prepared with two different deposition times. Then, composite films were fabricated by the CS technique using these particles. The thickness of the DLC-containing Cu(Cu-DLC) composite film was 200 μm and that of the DLC-containing Ti (Ti-DLC30) composite film was 252 μm, and the introduction of DLC into the metal films was demonstrated by Raman spectroscopy. Then, we conducted a sliding test using a ball to evaluate the sliding characteristic of each film. The Cu-DLC composite films deposited from thin DLC-coated Cu particles behaved as a solid lubricant in the ball-on-disk test and Cu-DLC composite films deposited from thick DLC-coated Cu particles acted as an abrasive. For Ti particles, DLC was graphitized and acted as an abrasive.

This chapter discusses the cooling technologies for microelectronic equipment from the viewpoint of their efficiency in space-constrained heat transfer, focusing on the flow boiling cooling. Also, some practical issues involved in the design of microchannel cooling systems are discussed. The flow boiling cooling system has large heat transfer capacity and advanced characteristics that can be used to realize very low thermal resistances. The chapter discusses various cooling methods. They are low-velocity air cooling, heat sinking with low speed air flow, heat sinking with high-speed impinging air flow, direct single-phase liquid cooling, heat pipe and direct phase-change cooling. In order to contain the discussion within a manageable length, a simple situation is assumed and the emphasis is placed on forced boiling cooling. Riehl et al. made a comprehensive review of the recent literature on micro-channel cooling. They compared the correlations for single-phase and phase-change heat transfer proposed by various investigators and found considerable divergence among the predicted heat transfer coefficients.

This paper describes the thermal contact resistance and its effect on the performance of thermal interface material. An ASTM D 5470 based apparatus is used to measure the thermal interface resistance. Bulk thermal conductivity of different interface material is measured and compared with manufacturers’ data. Also, the effect of grease void in the contact surface is investigated using the same apparatus. The flat type thermal interface tester is proposed and compared with conventional one to consider the effect of lateral heat flow. The results show that bulk thermal conductivity alone is not the basis to select the interface material because high bulk thermal conductivity interface material can have high thermal contact resistance, and that the center voiding affects the thermal interface resistance seriously. On the aspect of heat flow direction, thermal impedance of the lateral heat flow shows higher than that of the longitudinal heat flow by sixteen percent.

A liquid bridge heat switch is investigated to ensure proper ON/OFF operation in the presence of a temperature gradient. A temperature gradient along a plate can lead to changes in liquid properties such as the surface tension and contact angle. Eventually, these changes deteriorate the stability of the switching operation. The stationary position of the liquid bridge moves toward the colder zone over repetitive operations, and residuals of the liquid bridge remain after retraction. In addition, the liquid bridge cannot be generated properly with a predetermined clearance that is sufficient to form the liquid bridge between two plates with a uniform temperature. In order to enable a repetitive switching operation, a conical surface is employed at the hot plate of a heat switch just above the liquid channel. The conical surface reduces the clearance between the top plate and the liquid channel. Also, it provides the highest wettability at the desired zone and maintains the stationary position of the liquid bridge. The effect of the conical surface is evaluated with an LED device in terms of cooling time and thermal resistance. The conical surface extends the thermal resistance range more than three times. As a result, a design methodology for the liquid heat switch system is suggested to guarantee a stable switching operation against changes in thermal conditions. Moreover, the cyclic switching operation reduces the cooling time by almost 20 s compared with the non-cyclic operation.

The Heat Transfer Society of Japan (HTSJ), herein “the Society,” was founded in 1961. A series of events have been held to commemorate its 50th anniversary during 2011–2012. I participated in the events, talking and writing on the history of the Society. This article is based on the materials I collected for my roles in the events, my recollections of the past, and my personal considerations about the Society and heat transfer research. Throughout the article I attempt to explain the Society's history in the light of organizational, technological, and industrial developments that have proceeded in the universities and the industry in the past 50 years. The Society made its start as a nationwide coalition of study groups organized by the founding academics. A symbolic feat of heat transfer research at the time, known as the Nukiyama curve, is briefly described. The evolution of the Society in subsequent years mirrors the industrial developments in Japan. The Society's commitments to the international heat ...

Thermal management of very large-scale computers will have to leave the traditional well-beaten path. Up to the present time, the primary concern has been with rising heat flux on the integrated circuit chip, while a space has been available for the implementation of high-performance cooling design. In future systems, the spatial constraint will become a primary determinant of thermal management methodology. To corroborate this perspective, the evolution of computer's hardware morphology is simulated. Simulation tool is the geometric model, where the model structure is composed of circuit cells and platforms for circuit blocks. The cell is the minimum circuit element whose size is pegged to the technology node, while the total number of cells represents the system size. The platforms are the models of microprocessor chips, multichip modules (MCMs), and printed wiring boards (PWBs). The major points of discussion are as follows: (1) The system morphology is dictated by the competition between the progress of technology node and the demand for increase in the system size. (2) Only where the miniaturization of cells is achieved so as to deploy a system on a few PWBs, ample space is created for thermal management. (3) In the future, the cell miniaturization will hit the physical limit, while the demand for larger systems will be unabated. Liquid cooling, where the coolant is driven through very long microchannels, may provide a viable thermal solution.

The present work reports the preparation of binderless carbon-coated porous films and the study of their performance as monolithic bioanodes. The films were prepared by coating anodic aluminum oxide films with a thin layer of nitrogen-doped carbon by chemical vapor deposition. The films have cylindrical straight pores with controllable diameter and length. These monolithic films were used directly as bioelectrodes by loading the films with d-fructose dehydrogenase (FDH), an oxidoreductase enzyme that catalyzes the oxidation of d-fructose to 5-keto-d-fructose. The immobilization of the enzymes was carried out by physical adsorption in liquid phase and with an electrostatic attraction method. The latter method takes advantage of the fact that FDH is negatively charged during the catalytic oxidation of fructose. Thus, the immobilization was performed under the application of a positive voltage to the carbon-coated AAO film in a FDH-fructose solution in McIlvaine buffer (pH 5) at 25°C. As a result, the FDH-modified electrodes with the latter method show much better electrochemical response than that with the conventional physical adsorption method. Due to the singular porous structure of the monolithic films, which consists of an array of straight and parallel nanochannels, it is possible to rule out the effect of the diffusion of the d-fructose into the pores. Thus, the improvement in the performance upon using the electrostatic attraction method can be ascribed not only to a higher uptake but also to a more appropriate molecule orientation of the enzyme units on the surface of the electrodes.

Thermal management is a key issue in various fields of engineering. The effective counterplan has to be come up with for achieving high thermal stability suitable for thermally-sensitive system. Here, the concept utilizing a liquid-based heat switching method was presented as one of the promising solutions in the thermal management, and the proposed system is composed of a hot plate, cold plate, fluid chamber and actuator. The heat switching works by means of controlling the formation of the liquid bridge between the two plates, and it enables to not only control the thermal resistance but also distribute the heat to the surroundings using the liquid bridge. Thus, the thermal performance of the proposed heat switch highly depends on the formation and motion of the liquid bridge. Empirically, the optimal geometry of the heat switch, the diameter of the liquid channel and clearance between two plates, was determined to be suitable for creating and rupturing the liquid bridge. To investigate the effects of its geometry, the pressure analysis and observation of the liquid bridge through CCD were conducted, respectively. The constructed heat switching system was applied to the LED-based testing module to control the LED junction temperature regulation and thermal resistance between the LED plate and the heat sink. As a result, the behavior of the liquid bridge and its effect on the heat switching were empirically understood.

Accurate prediction of operating temperatures in electronic parts at the component, package, board and system level computational fluid dynamics simulations, has engaged the engineering community for several years. The primary challenge was the difficulty of implementing accurate operating temperature predictions directly into system designs using near-exact physical models (known as detailed thermal models) due to the wide disparity in length scales that result in large computational inefficiencies. A compact thermal model (CTM) attempts to solve this problem by reducing the detailed model to a far less grid intensive representation, while preserving accuracy in predicting the temperatures at key points with a short calculation time. A CTM is condensed using thermal network modeling with thermal resistance and thermal capacitance. This paper focuses on the derivation of compact thermal network models to predict the transient temperature response of complex electronic equipment. The system model is based on a thermal interface material (TIM) measurement apparatus taking into consideration the lateral heat flow in the TIM. The thermal impedance and the temperature difference between the junction and ambient nodes are used to estimate the heat flow division on each heat transfer path. The validity of the dynamic thermal network method and the simple thermal analysis model is confirmed based on the result of the transient thermal analysis. In this paper we describe an application of the dynamic compact thermal network method to analyze the transient thermal response of a TIM measurement apparatus in multi-dimensional heat flow, and we propose a simple modelling procedure for the parametric estimation as a preliminary thermal design tool.

A mesoporous silica film (MSF, 20 × 20 mm in size) with 3D accessible mesopores (Fmmm symmetry) was synthesized on a current collector substrate, and then the entire pore surface was coated with an extremely thin carbon layer. The resulting carbon-coated mesoporous silica film (C/MSF), which well retains the continuous silica phase with its ordered mesopore network intact, has many advantages over conventional MSFs, porous carbons, or carbon electrodes. Thanks to the continuous carbon-coated layer, C/MSF is electrically conductive, and besides, it has remarkably better stability in an aqueous solution than MSFs. These features enable C/MSF to be used as a stable electrode in aqueous electrolyte solutions. In addition, C/MSF exhibits a much higher rate of performance as an electrode of an electric double layer capacitor than conventional powdery electrodes, indicating that the C/MSF electrode has excellent electrical conductivity, which can be ascribed to the continuous film shape of C/MSF. Another noticea...

A methodology for modeling and simulating the electro-thermal behavior of an enclosed electronic package is presented and validated. The electro-thermal model is constructed using system dynamics. The system model, in which the electrical and the thermal domain are combined, is presented. The developed model describes the dynamic thermal behavior system that was an electronic device in the test enclosure. An effective way to identify the thermal parameters of the system, especially the thermal contact resistance, is suggested. In detail, the new method for thermal resistance identification is based on the temperature difference behavior between the component and the air temperature inside the enclosure. Based on the proposed model, either the variation of the heat source or the ambient temperature can be estimated. Simulated results were in good agreement with the measured temperature in the transient state accompanying with the variation of the environment.

This work is concerned with the thermal design of portable projection display equipment (i.e., a portable projector). The portable projector is being made smaller and lighter to better serve the carrier, while its luminance is enhanced to benefit the viewer. The confluence of these demands increases the thermal loading on the projector. The design of cooling airflow path is becoming evermore important; however, the complex internal organization of the projector hampers an attempt to conduct flow and heat transfer analysis. A particularly important issue for the projector designer is to predict the effect of shrinking box size of the next generation product on cooling airflow. This paper describes a way to foresee the effects of reducing the key geometric dimensions of the projector on the distribution of airflow. The analysis is conducted using a computational fluid dynamics (CFD) code. CFD results are obtained on sampled points in the parameter domain and used to find the effects of various geometric par...

Two new merosesquiterpenes, verruculides A ( 1 ) and B ( 2 ), were isolated from a culture broth of the Indonesian ascidian-derived Penicillium verruculosum TPU1311, together with three known congeners, chrodrimanins A ( 3 ), B ( 4 ), and H ( 5 ). The structures of 1 and 2 were assigned on the basis of their spectroscopic data (1D and 2D NMR, HRMS, UV, CD, and IR). Compound 2 had a linear sesquiterpene moiety and was considered to be the derivative of the biosynthetic precursor for 1 and 3 – 5 . Compounds 1 , 3 , and 5 inhibited the activity of protein tyrosine phosphatase 1B (PTP1B) with IC 50 values of 8.4, 8.5, and 14.9 μM, respectively. Compound 2 showed 40% inhibition at 23.1 μM, while 4 was not active at 20.7 μM.

Two new octaketides, trichoketides A (1) and B (2), were isolated from a culture broth of the seawater-derived fungus Trichoderma sp. TPU1237 together with two known analogs, trichodermaketones C (3) and D (4), by ODS column chromatography followed by preparative ODS and chiral HPLC. The structures of 1 and 2 were elucidated on the basis of their spectroscopic data, and absolute configurations were assigned by comparing their experimental electronic circular dichroism (ECD) spectra with the calculated ECD spectra. Compounds 1 and 2 were epimers at the C-8 position (α-position of dihydrofuran ring). The IC50 values of compounds 1–4 against protein tyrosine phosphatase 1B were 53.1, 65.1, 68.0 and 55.9 μM, respectively.

A semi-analytical model of the bubble dynamics is proposed based on the experimental results reported in the literature on boiling from porous enhanced surfaces. The model considers the ‘flooded mode’ regime of enhancement boiling and is validated for data covering a range of tunnel and pore dimensions. The dynamic model accounts for the temporal evaporation rate variation inside tunnels to arrive at the latent heat flux due to internal evaporation and frequency of bubble formation. The population density is predicted using an empirical formulation, and in turn used to estimate the total heat flux from the porous enhanced surface. The model predicts the heat flux for pool boiling from structured surfaces within ±30% of the experimental data. The model is subsequently used in the prediction of the thermal performance of a novel two-phase heat spreader that employs porous structured surfaces for enhancing boiling heat transfer.

Geometric data is among the first items to be fed to the computer when one embarks on heat transfer analysis using a computational fluid dynamics (CFD) code. The creation of geometric data involves...

The seismic safety of city gas supply has been the major research topic of the writers in past decades. To avoid earthquake hazards due to leakage of gas from breakage of buried pipes, a real-time safety control system, SUPREME, has been deployed and put into practical use. SUPREME employs 3,800 new spectrum intensity sensors and remote control devices to achieve quick gas supply shut off. It monitors the earthquake motion at a large number of sites on a real-time basis, interprets the data, and assesses gas pipe damage in order to decide whether or not the gas supply should be interrupted. The present paper first describes the philosophy behind this system. Second, it describes the performance of the system during the recent Taiwan earthquakes as well as more significant design earthquakes. This system represents the state-of-the-art of computer-operated safety measures, achieved by advanced geotechnical engineering.

Computational Fluid Dynamics (CFD) codes have proved their high potential as a tool of thermal design of electronic equipment. However, as the product development cycle is shortened, the CFD-based thermal design needs a new format that allows the packaging designer fast and versatile searches for better design options. The most serious factor that slows the CFD-based design is geometric complexity created by packing various components in a tight space of the system box. In a proposed methodology coined “Build-up Approach (BUA),” CFD simulations are conducted on a set of hardware models to gain insight into the effects of component placement on the junction temperature. Two algorithms are introduced before and after CFD simulations: one defines the geometric parameters through singular value decomposition (SVD) of components placement patterns and the other identifies important geometric parameters by means of the Taguchi method. A case study was conducted on a simple hardware model (benchmark model) that embodies essential features of portable electronic equipment. The results proved the effectiveness of these algorithms in measuring the relative importance of geometric parameters and weeding out unimportant geometric details.

Results from various enhancement techniques to improve the performance of a recently developed two-phase heat spreader are reported. The spreader has a central evaporator section, with an integrated condenser along the edges. A micro-fabricated three-dimensional enhancement structure is employed to improve the heat transfer performance of the spreader. This study considers the performance of several liquid coolants to be used with the device and evaluates the effect of initial pressures on the thermal performance of the spreader plate. Liquids with lower boiling points were found to result in lower wall temperatures of the spreader plate due to earlier onset of boiling. Studies also showed an improvement in heat transfer performance with increase in stack height of the enhancement structures used in the evaporator section.

The present paper attempts to shed light on issues that so far have been unaddressed in research on micro-channel heat transfer. The first part of the paper summarizes the uncertainty sources likely to be present in micro-channel cooling devices incorporated in the electronic package. The effects of uncertainties on the heat transfer performance of the cooling device are difficult to assess due to the coupling of diverse factors in a narrow physical space. The CFD simulation offers a means to sort out the effects from multiple factors by assuming uncertainties from one of the sources or a set of selected sources into an analytical model. A model channel is defined to illustrate the application of the CFD-based methodology to situations involving geometric uncertainties. The model has a 20 mm × 20 mm heater plate set in a channel having an adiabatic cover and side-walls and cooled by a dielectric coolant. The tilt of the cover plate is chosen as an uncertainty factor from among all possible factors. CFD si...

To cope with earthquake related secondary disasters, the new real-time disaster mitigation system for a city gas network has been developed by Tokyo Gas Company since 1998 for the purpose of realization of dense real-time seismic motion monitoring, quick gas supply shut-off, prompt emergency response and efficient restoration work. In 2001, Tokyo Gas successfully started the operation of SUPREME, which employs 3,800 new SI sensors and remote control devices at all the district regulator stations in its service area (3100km 2 ). SUPREME can observe the status of 3,800 district regulators and shut them off remotely, if necessary. The remote shut-off using SUPREME can realize quick gas supply shut-off and effectively reduce gas leakage risk during earthquakes.

This paper presents a novel orientation independent two-phase heat spreader for constrained space applications. 1 The two-phase spreader plate has a central evaporator section with an integrated condenser along the edges. A micro-fabricated three-dimensional enhancement structure is employed to improve the heat transfer performance of the spreader plate. The thermal performance of the system is characterized at different power levels and also for various inclination angles. At the maximum heat flux of 6.3 W/cm 2 under natural convection conditions, the junction temperature of the two-phase spreader was found to be 47.6 8C less than the junction temperature predicted for an equivalent solid metal plate subjected to similar boundary conditions. The performance of the spreader plate is found to be orientation independent as long as the enhancement structure in the evaporator remains flooded with the coolant liquid. q 2003 Elsevier Ltd. All rights reserved.

Understanding of the fundamental mechanism of boiling from enhanced structures is currently incomplete. The main focus of the present study was to develop a semi-analytical model to predict the bubble departure diameter, frequency, and nucleation site density for a boiling enhancement structure. Existing models in literature were used as a framework to develop this. Salient feature of the model is the improvements on sub-models for bubble departure diameter, evaporation within the channels and convective heat transfer from the external surfaces of the enhanced structure. The model was used to calculate the total heat dissipated from the structures. Comparisons to experiments revealed that the bubble departure is predicted within ±10%, frequency within ±30% for all data points except a couple, nucleation site density within ±40% and the heat flux within ±50%. Sample calculations have been included to show its use in optimizing the geometrical parameters for maximizing heat transfer.

Geometrical complexity considered in the present study is characterized by a large degree of freedom in placement of constituents in a composite system. The constituent sizes are not negligibly small compared to the system’s expanse, so approximations of their configurations and placement patterns by some simple equivalents are not feasible. Numerical analysis is a means to estimate heat transfer performance of the system, but a strategy is required to navigate through a vast number of possible constituent patterns to find ones that produce higher heat transfer performance. In the proposed methodology the constituent pattern is captured as a two-dimensional mosaic image of solid cells embedded in a substrate. On an image assumed as a starter, the singular-value decomposition (SVD) analysis is performed to find its (SVD) building block elements. By shuffling the building block elements variants of the starter image are created. Heat transfer analysis is performed on sample systems that are picked up from the ensemble of variants. Using the Taguchi method and through a genetic algorithm-type reasoning, those element arrangements that do not significantly affect the heat transfer performance are weeded out. The methodology is demonstrated on the cases of heat conduction through composite slabs.

東京ガスの新防災システム「SUPREME」は, 供給エリア内約3,700箇所の新SIセンサーにより地震動モニタリングを行うとともに迅速な緊急対応を行うためのシステムである. SUPREMEは1998年より開発が行われ, 2001年7月より実稼働を開始した. 本システムでは地震発生時に地区ガバナを遠隔遮断することにより迅速に供給停止を実施することで, これまでに比して大幅なリスクの軽減を可能とした. また, 防災GISを開発し, 供給エリア内の約6万本のボーリングデータ, 微地形分類データ等を利用して表層地盤の地震動増幅度分布や液状化危険度分布等の広域かつ細密な分析・整備を行うとともに, 低圧ガス導管の面的被害推定について諸検討を行った.

This paper reviews the existing knowledge base about thermal contact resistance in cooling electronic equipment, and also highlights some novel issues that are emerging with the advent of compact electronic equipment. Where a high contact pressure is tolerable, such as in cooling power electronic devices, the experimental data and the theoretical models that have been developed to this day provide useful guides for the management of contact resistance. In such applications the compression load and a technique to enhance interface heat transfer need be examined, weighing their relative importance in the entire heat transfer system. Using the Yovanovich correlation for contact resistance and assuming water-cooled or air-cooled heat sinks, the contact pressure ranges of practical importance are identified. The case studies revealed that contact pressures around and less than 1–4 MPa are often sufficient to make the contact conductance comparable to the convective conductance in the water-cooled channel. The threshold pressure is much lower for the air-cooled case, around 0.2–0.6 MPa. However, heat transfer data in such intermediate pressure ranges are relatively few. For compact electronic equipment, such as laptop computers, the contact conductance to a thin heat spreader plate is becoming an issue of prime importance. In a constrained space the heat flow across the interface is affected by the heat conduction paths beyond the interface. This is illustrated using an example where warped heat sources are in contact with a heat spreader. It is shown that, with decreasing heat spreader thickness, the warping of the heat source has an increasing influence on the contact resistance.

A theoretical model of liquid plug dynamics powered by vapor explosion in a capillary duct has been proposed in order to provide guidance for designing a fluid propulsion device. The model can evaluate performance parameters such as the amount of useful work, efficiency of energy conversion, generated vapor volume and displacement volume rate of liquid. For example, the efficiency of energy conversion for water under atmospheric pressure and room temperature is calculated at 2.8%. The prediction of the vapor volume agrees well with existing experimental result. The prediction of the displacement volume rate also agrees well with the experimental result and suggests the existence of optimum heat flux at which the displacement volume rate is maximum.

The current study involves two-phase cooling from enhanced structures whose dimensions have been changed systematically using microfabrication techniques. The aim is to optimize the dimensions to maximize the heat transfer. The enhanced structure used in this study consists of a stacked network of interconnecting channels making it highly porous. The effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid. While most of the previous studies on the mechanism of enhanced nucleate boiling have focused on a small range of wall superheats (0–4 K), the present study covers a wider range (as high as 30 K). A larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes. The effect of stacking multiple layers showed a proportional increase in heat dissipation (with additional layers) in a certain range of wall superheat values only. In the wall superheat range 8–13 K, no appreciable difference was observed between a single layer structure and a three layer structure. A fin effect combined with change in the boiling phenomenon within the sub-surface layers is proposed to explain this effect.

Using high-speed photography (1500 frames/s) bubble growth data on microporous structures immersed in a pool of dielectric coolant (FC-72) were obtained. Wafer dicing and wet etching was used to fabricate a net of interconnected microchannels on a 10 mm ×10 mm piece of silicon wafer. The resultant structure has pores that communicate the interior of microchannels to the liquid pool. The pore diameter was varied in a range 0.12–0.20 mm and the pore pitch in 0.7–1.4 mm. The data were collected maintaining the system pressure at one atmosphere and increasing the wall superheat up to 12 K. Among the geometrical parameters, the pore diameter was found to be most influential on the bubble departure diameter. The findings about the bubble growth rate, the bubbling frequency, and the bubble site density were largely in accord with the previously reported data. However, the coverage of wider ranges of wall superheat and the structural parameters in the present study revealed new bubble characteristics that was used in implementing an analytical model for boiling heat transfer on the porous structure.

The present paper reports the results of an experimental study of forced convection boiling heat transfer from a 2 cm x 2 cm simulated chip to a fluorocarbon coolant (FX-3250) in a parallel-plate channel. The experimental parameters were the channel height (1 and 5 mm), the surface geometry of the simulated chip (flat and microfinned), and the coolant velocity (0.125-4 m/s). Longitudinal microfins (0.5 mm high x 0.5 mm wide) on the finned chip increased the actual surface area to about twice that of the flat surface. Attention was focused on the data of the 1-mm high channel. When compared with the flat chip data on the footprint area basis, the microfins produced 40% of heat transfer enhancement at coolant velocities less than 1 m/s; however, the enhancement diminishes at higher velocities. The boiling curves of the finned chip, based on the actual area, seem to reflect that there is an effect due to the bypassing of flow through the cross-section over the fins. For both the flat chip and the finned chip...

Finned heat sinks are used in computers to promote heat transfer from the Integrated Circuit (IC) chips to cooling air. This chapter provides the background information and the tutorial materials about heat sinks. First, the mechanism of heat generation by electronic circuits is explained. This is followed by a short history of heat dissipation from the large-scale computers of the 1980s and the present. The formulas to calculate the performance of heat spreaders and finned heat sinks are presented with explanations about the physics of heat transfer and coolant flow. The manufacturing methods of finned heat sinks are summarised. Finally, it is pointed out that the space for finned heat sinks is shrinking due to the growing demand for compact packaging of computers. In the future, computers would emulate biological brains in their performance as well as cooling mechanisms. It is thought-evoking to consider the role of heat sinks in such ultimate computers.

An experimental study of forced convection in impinging flow, using fluorocarbon FX3250 and a simulated electronic chip, was performed. A test section consisting of a 35 mm long, 1 mm wide slot nozzle in a 2 mm thick plate offset 2 mm from the heat source was used. The simulated chip array consisted of five foil strip (4 mm wide) heaters, positioned with the center strip directly beneath the slot nozzle. The velocity of the coolant was varied from 0.53 to 5 m/s, and the subcooling in the range from 2 to 21 K. The experiments were conducted focusing on two cases. First, only the center strip was heated. Second, all the heaters were energized, and the strip-by-strip variations of heat transfer were measured. The critical heat flux (CHF) on the center strip, determined by sensing the onset of oscillations and subsequent rapid rise of foil temperatures, was found considerably lower than those predicted by the existing correlations. It is pointed out that the thermal mass of the test heater could be an important factor for the CHF. The heat transfer behavior of other strips showed channel-flow or jet-impingement mode depending on the strip location and the coolant flow rate. [S1043-7398(00)00202-4]

This report presents a study of microfabricated enhanced structures for enhancing the thermal performance of a two-phase thermosyphon loop. The structures used in this study have an array of channels and pores that make it highly porous. The structures were fabricated in silicon using wafer dicing, wet-chemical etching, and laser milling, and details are included in this report. The structures were employed inside the evaporator section of a thermosyphon loop for enhancing the boiling performance. Preliminary results show that the heat dissipation with these structures is at least three times better than that of a plain polished silicon surface, at a wall superheat of 30 degrees C. The results also indicate that increasing the channel width resulted in better thermal performance.