Time filter

Source Type

Jeong S.-H.,Gwangju Institute of Science and Technology | Nam S.-K.,Gwangju Institute of Science and Technology | Nakayama W.,ThermTech International | Lee S.-K.,Gwangju Institute of Science and Technology
Applied Thermal Engineering | Year: 2013

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. © 2013 Elsevier Ltd. All rights reserved.

Nakayama W.,ThermTech International
Heat Transfer Engineering | Year: 2013

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 50years. 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 transfer community are summarized. Also, the issue of industry/academia collaboration is discussed. Finally, a short discussion on the present and future generations of HTSJ members concludes the article. © 2013 Copyright Taylor and Francis Group, LLC.

Jeong S.-H.,Korea Institute of Science and Technology | Nakayama W.,ThermTech International | Lee S.-K.,Korea Institute of Science and Technology
Applied Thermal Engineering | Year: 2012

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. © 2011 Elsevier Ltd. All rights reserved.

Fukue T.,Toyama Prefectural University | Ishizuka M.,Toyama Prefectural University | Nakagawa S.,Toyama Prefectural University | Hatakeyama T.,Toyama Prefectural University | Nakayama W.,ThermTech International
2010 14th International Heat Transfer Conference, IHTC 14 | Year: 2010

In recent years, thermal design of electrical equipment becomes importance and fast thermal design is required due to the fast development of electrical devices. We have proposed the flow and thermal resistance network analysis (coupled network analysis) as a fast thermal design method for electrical equipment. In this paper, we described analytical accuracy of the coupled network analysis of thin electronic equipment including the finned heat sink. We especially focused on the prediction of thermal performance on heatsink by using the coupled network analysis. For considering the accuracy of the coupled network analysis, we compared the results of the coupled network analysis with those of CFD analysis and the experiment. The results showed that the coupled network analysis can predict accurate thermal performance of heat sink and moreover accurate temperature distribution of electrical equipment. © 2010 by ASME.

Nakayama W.,ThermTech International | Koizumi K.,COSEL Co. | Fukue T.,Toyama Prefectural University | Ishizuka M.,Toyama Prefectural University | And 3 more authors.
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, ITherm 2010 | Year: 2010

The high-density interconnection substrate invariably poses enormous difficulty to thermal design analysts due to complex metal layout patterns embedded in the dielectric matrix. A modeling method is proposed, which produces effective thermal conductivity values for elements of the substrate under a specified boundary condition. A novel parameter, the indexed metal volume fraction, is employed to highlight the importance of contiguous metal elements in providing highly effective heat conduction paths. Also taken into account is the thermal coupling between metal elements through dielectric interstices. A model PCB that has a reasonable level of structural complexity is employed to validate the present modeling method. The benchmark is provided by the numerical analysis that is performed on the model without sacrificing any structural details. The prediction by the present method and the benchmark agree within a reasonable range, while the traditional method of estimating effective conductivities grossly under-predicts the temperature. ©2010 IEEE.

Nakayama W.,ThermTech International | Koizumi K.,COSEL Co. | Fukue T.,Toyama Prefectural University | Ishizuka M.,Toyama Prefectural University | And 3 more authors.
Proceedings of the ASME InterPack Conference 2009, IPACK2009 | Year: 2010

The issue addressed in the present study is how to model wiring substrates to perform heat conduction analysis on moderate computational resource. Equivalent thermal conductivity is a convenient measure in thermal modeling. However, its notion needs re-examination where higher accuracy of heat conduction analysis is pursued. Proposed is a scheme where the indexed volumetric metal contents are used to estimate the equivalent conductivity of representative volume element (RVE). The index is designed to reflect the effect of metal pattern on heat flow through RVE. In order to illustrate the core concept we report the analysis performed on template models of high-density interconnect (HDI) substrates. The element of HDI contains copper in several forms; through-via, continuous plane, and cross wires. Five heat flow directions are assumed; two are linear and three are right-angled turn. From combinations of the metal pattern and the heat flow direction twenty five templates are created, then, they are subjected to detailed numerical analysis. The values of equivalent thermal conductivity derived from the numerical solutions reveal that the gross volumetric metal content is totally inadequate as a parameter of thermal characterization. The paper also outlines the overall organization of our analysis system which is being developed in an industry-academia cooperative effort under the auspices of JSME. Copyright © 2009 by ASME.

Jeong S.-H.,Korea Institute of Science and Technology | Nakayama W.,Thermtech International | Lee S.-K.,Korea Institute of Science and Technology
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2010

Various types of heat switch have been suggested as the promising solution of thermal management in the extremely low temperature condition. Recently, the heat switch based on the liquid for the room temperature condition has been investigated to control the thermal resistance of the electronic devices. The presented heat switch was composed of several micro channels. The key technology of the heat switch operation for room temperature is the fluid control. The existing studied indicates that the flow regulation was achieved by simple channel geometry design based on the burst pressure theory. In this research, the design of the liquid bridge heat switch was presented and the pressure characterization of the designed switch was carried out. The supplying liquid generates the liquid bridge between two plates. The thermal resistance between two plates depends on the liquid bridge diameter and height. The liquid bridge size control is achieved based on the pressure characterization. Copyright © 2010 by ASME.

This paper intends to elucidate challenges in some aspects of the hardware design of future generation computers. We use a system model, a stack of integrated circuit cards cooled by a dielectric coolant (FC77). A set of equations is developed to describe the relationships between the system throughput, the volume, the power consumption, and those concerning the details of internal organization such as signal and power line dimensions and coolant path width. The calculated values of throughput, volume, and power are projected on a state point in a graph of the figures-of-merit pair, the computational density, and the computational efficiency. By manipulating the empirical parameters imbedded in the model, the state point is steered to follow the evolutionary line that runs through the points corresponding to the existing supercomputers of several generations. Then, calculation is extended on state points for future prospective computers with target system throughputs. The results point to the needs for research and development effort on thermal management and materials development. As for thermal management of exa- and zeta-scale computers, we need to refocus heat transfer research. Coolant channels will have very large length-to-width ratios (several thousand), while the heat flux on the channel surface is quite low. Micro-fluidics to guarantee stable coolant flow in such long micro-channels will be of primary importance in place of the means to deal with high heat flux. We also need to develop novel materials for signal transmission lines and cooling, particularly in the development of zeta-scale computers. © 2013 IEEE.

Nakayama W.,ThermTech International
Journal of Electronic Packaging, Transactions of the ASME | Year: 2013

Heat conduction analysis is performed on a model system to survey the effects of geometric and thermal parameters on the temperature of an embedded heat source. A box model has the geometric characteristics of hand-held devices and has a laminar organization composed of a printed circuit board (PCB), air gap, and a system casing. Exploiting the laminar organization and thinness of the laminate an approximate solution is derived. The solution is used to produce a guide for thermal design analysts, which is concerned with the sensitivity of the heat source temperature to the effective thermal conductivity of the PCB. Numerical examples are shown for the models that have typical dimensions and material properties of actual equipment and PCB. Copyright © 2013 by ASME.

Loading ThermTech International collaborators
Loading ThermTech International collaborators