Prof. Emeritus Wataru NAKAYAMA
Topic: Transport Phenomena in Information Processing Systems:
Impacts of System-level Scaling on Thermal Management
Information processing systems, from man-made computers to biological systems, need energy for their operations, thus, dissipate heat. Diffusion of heat from computing elements to the coolant is constrained by the system’s hardware organization. The demand for larger processing capacity has been driving the evolution of hardware morphology. In this lecture the morphological evolution of computers in the past decades is reviewed. Then, the evolutionary history to the present is extrapolated to develop a perspective into the future.
An attempt to scale up computing systems by extending the existing technologies will meet insurmountable barriers. In an extension scenario the system volume and power consumption will balloon to prohibitive levels for systems of more than exa-scale processing power. In an alternative sustainable scenario, the physical dimensions and the power consumption of elementary circuits will be reduced in a disruptive manner. The system’s physical volume will grow only at moderate rates, while it accommodates an explosively increasing number of computing elements. Concomitantly, thermal management will have to shift its focus from high-heat-flux cooling in a relatively wide space to low-heat-flux cooling in an extremely constrained space. In prospective future systems the coolant flows in a network of fine paths while creating uniform temperature environment for computing elements throughout the system. The system construction will emulate biological brains where computing, power supply, and cooling are synthesized in an ingenious way.
Prof. Sung Jin KIM
Topic: Recent Advances in Micro Pulsating Heat Pipes
During the past decades, cooling technology has become an important element in the successful development of engineering systems. Since Akachi introduced the pulsating heat pipe in 1990, it has become one of the promising solutions for the cooling of high heat-flux electronic devices and systems. Recently, micro pulsating heat pipes have been getting a lot of attention because of their potential for the thin and flexible electronic systems.
This talk is intended to provide a perspective and review of the recent advances in micro pulsating heat pipes. Compared to conventional pulsating heat pipes, micro pulsating heat pipes with hydraulic diameters of less than 1 mm were found to have interesting features like high frequency oscillation with a distinct phase difference between neighboring liquid slugs. In addition, several new ideas for thermal performance enhancement in the micro pulsating heat pipes were suggested. This talk will conclude with an overview of research activities associated with a prestigious 9 year grant by Korea’s Creative Research Initiative to develop Flexible and Thin Thermal Superconductors.
Prof. Yogendra JOSHI
Topic: Simulations of Flow Boiling in Surface Enhanced Microgaps
Microfluidic phase change cooling is a promising approach for the thermal management of high performance planar and three-dimensional microsystems. These applications are characterized by spatial and temporal heat flux non-uniformity, which makes existing transport correlations inapplicable. Also, requirements for routing of electrical interconnects and enhancement of heat transfer surface area typically result in additional geometrical complexity compared to the well-studied microchannel arrays and wide microgaps. Design of these systems requires knowledge of the thermal characteristics in these geometries. In this talk, I will discuss some of the recent Volume of Fluid (VOF) simulations of flow boiling in microgaps enhanced with arrays of micropins. The simulations allow for coupling of heat conduction in the solid regions, with the two-phase transport in the fluid. Heat transfer and pressure drop characteristics for the microgaps are computed for refrigerants for heat flux distributions representative of chip cooling applications. Transient computations are initiated from isothermal conditions with fully established single phase flow conditions. Convective boiling simulations are then performed following the initiation of surface heating. These simulations are advanced in time until quasi-steady conditions are achieved. Surfaces temperatures, heat transfer coefficients, and two-phase flow responses are examined for various representative heat flux distributions.
Prof. Chien-Yuh YANG
Topic: Boiling and Condensation Heat Transfer of Refrigerant HFO-1234yf in Small Tube
Owing to the global warming effect consideration, the refrigerants with GWP value higher than 150 will be banned for applying in automotive air-condition systems from 2017 by the European Commission. The study on the replacement of high GWP refrigerant such as HFC-134a becomes an important and urgent issue in the coming years. Recently, a new refrigerant, HFO-1234yf has been developed with similar thermodynamic properties to HFC-134a but much lower GWP value. It is expected as a good candidate for replacing the refrigerant HFC-134a. However, most of the heat transfer and flow performances of this refrigerant are still not very clear especially for condensation and boiling heat transfer.
This lecture will firstly provide a comprehensive review of the previous studies on the thermal physical properties and flow heat transfer performance of the refrigerant HFO-1234yf. Our recent experimental investigation results of the flow boiling and condensation heat transfer of refrigerant HFO-1234yf inside a small tube will be introduced. A comparison on the difference of two-phase heat transfer performance between HFC-134a and HFO-1234yf will be discussed based on the fluids transport properties and two-phase flow patterns. It is expected to provide a further understanding on the system and heat exchanger design for the replacement of new refrigerant.
Prof. Dereje AGONAFER
Topic: Experimental and Computational Thermal and Reliability Considerations in Data Centers
In this presentation, I will present research activities of my team that address thermal and mechanical challenges from the device to the system level in both containerized as well as large data centers.
At the board-level, we are concerned with thermal management of high-power modules through design and experimental testing of a “dynamic cold plate” concept (liquid cooling). Through implementation of sensing and control, this solution will distribute the cooling resource to different sections aimed at mitigating the hot spot effects on the chip and help towards uniform distribution of the heat across the package.
At the rack level, optimization studies for air cooling and liquid cooling are conducted. For air cooling, a potentially energy efficient practice is identified that reduces server cooling power by replacing conventional chassis enclosed smaller fans with larger rack mount fans. Combining experimental and computational approach, it is estimated that about 45% of cooling power is reduced per server, which scales significantly to a data center level (Best Poster Award, ITherm 2014). In another study, the tradeoff between fan cooling power and chip leakage current is studied when operating at higher air inlet temperatures. Related to immersion cooling, a thermal study will be presented on a single server fully submerged vertically in white mineral oil. Serviceability, maintenance and inefficiency of thermal/ dielectric properties of oil at high temperatures are the current challenges that are being investigated.
To expand the temperature and humidity range of outside air that can be used in airside economizer systems (chiller-less), we utilized direct and indirect evaporative cooling (D/IDEC) solutions along with air-side economizer systems. The design has been evaluated using various computational models. Performance parameters for various cooling media have been experimentally characterized and CFD models are being developed for further parametric studies. Dynamic cooling control methods proposed based on the neural network control framework for the D/IDEC unit are currently being investigated. The use of PCM to extend the temperature range is also discussed.
Use of air-side economizers has the associated risk of introducing gaseous and particulate contamination into data centers, thus, degrading the reliability of Information Technology equipment. It is necessary to first identify those contaminants which directly impact the IT equipment in the data center. In one study, effects of temperature and humidity on the corrosion rates of copper and silver in an IT equipment was experimentally studied and corrosion data was provided for the first time on the psychrometric chart for obtaining the x-factors from temperature and humidity for corrosion-related hardware failures. Subsequently, existing solutions will be evaluated for effectiveness in removing or preventing contamination in the data center and computational models and/or methodology will be developed to study the reliability impact of various sites when implementing economizers in the data center. Transient modeling of the high ambient data center room will also be discussed. Failure scenarios and typical time taken for the room to reach maximum thermal limits of the IT equipment will be investigated using CFD modeling.
Final program of ISTP27 at a glance
(The figure in each session shows your paper number.)
The detailed technical program is available HERE.
The conference rooms are located on the third floor (LEVEL 3) of
Hawaii Convention Center. Room information is available HERE.
The scientific program will include 5 keynote lectures, delivered by outstanding researchers on topics of broad interest to the transport phenomena community, along with contributed papers and poster sessions. Over 190 contributed abstracts are anticipated.
On September 20 (Tue), 2016 the registration desk will be open from 3pm to 8pm to give participants the opportunity to register prior to the conference. This will allow you to avoid long lines at the registration desks in the morning of the first conference day, and make registration easier for those who arrive later. The Registration Desk is available in front of Room 321B on the 3rd floor (LEVEL 3) of Hawaii Convention Center. All participants of ISTP27 are invited to the Welcome Reception, which will take place on September 20 (Tue) from 6pm until 8pm at Room 321 A&B of the convention center. The Welcome Reception will serve as an initial get-together for social networking in a relaxed atmosphere.
The official program will start September 21 (Wed), 2016 at 8:40am. The conference will end September 23 (Fri), 2016 at 4pm.
The official program also includes the Conference Banquet, which will be held on September 22 (Thu), 2016 at Hibiscus Ballroom of the Ala Moana Hotel.