Randeep Singh

Data center energy conservation utilizing a heat pipe based ice storage system

Data centers constantly expand and upgrade their capacity due to the ever-increasing demand for remote file storage. It is estimated that around 50% of the total data center power consumption is for cooling. With this trend, a reduction in the cooling power consumption would result in a substantial reduction in overall power consumption, as well as C02 emission. With the focus going towards renewable and natural sources of energy, a heat pipe based ice storage system is being proposed. This system is being considered as one good solution to reduce the power consumption, as well as CO2 emission of data centers. This Ice storage system is aimed at utilizing the low temperature of cold areas to form ice and cold water. The freezing index, which is the combined duration and magnitude of below freezing temperatures at a given freezing season, would be the criteria for choosing the data center location. The data center will be constructed in cold regions wherein the freezing index is 400°C-days and above. The thermosiphon, which acts as a thermal diode, can effectively cool down the water until ice is formed. This ice storage system can be integrated with the existing cooling system and can be utilized as an alternate cooling system or a back-up cooling system. The existing cooling system may be utilized during the warmer periods of the year. The actual ice storage system container, which is made of concrete, is to be constructed under ground, and integrated in parallel with the existing cooling system.

Low profile cooling solutions for advanced packaging based on ultra-thin heat pipe and piezo fan

In this paper, heat pipes and piezo fan, in combination as well as individually, has been proposed to provide very thin thermal solutions for high density electronic packaging. Ultra-thin heat pipes with thickness in range of 0.6 to 2 mm have been developed to transfer maximum heat load of 0.8 to 68W respectively. These heat pipes have been fabricated from copper-water combination with center fiber copper wick. Different type of piezo fans (low frequency flapping type, high flow rate type and high velocity impingement type) with small thickness ~ 0.8 to 2 mm, low power consumption and high reliability has been proposed and characterized. These fans can provide direct cooling system or can be combined with thin heat pipe to provide remote heat exchanger. Using these thin advanced thermal technologies, cooling modules with thermal capability of 3 to 10 W and maximum thickness of 0.7 to 6 mm respectively has been designed and characterized. In summary, thermal technologies and cooling modules developed in this research work will provide energy efficient and thin thermal management solutions for space conservative high density electronics.

Design and Numerical Simulation of a Symbiotic Thermoelectric Power Generation System Fed by a Low-Grade Heat Source

All liquid heating systems, including solar thermal collectors and fossil-fueled heaters, are designed to convert low-temperature liquid to high-temperature liquid. In the presence of low- and high-temperature fluids, temperature differences can be created across thermoelectric devices to produce electricity so that the heat dissipated from the hot side of a thermoelectric device will be absorbed by the cold liquid and this preheated liquid enters the heating cycle and increases the efficiency of the heater. Consequently, because of the avoidance of waste heat on the thermoelectric hot side, the efficiency of heat-to-electricity conversion with this configuration is better than that of conventional thermoelectric power generation systems. This research aims to design and analyze a thermoelectric power generation system based on the concept described above and using a low-grade heat source. This system may be used to generate electricity either in direct conjunction with any renewable energy source which produces hot water (solar thermal collectors) or using waste hot water from industry. The concept of this system is designated “ELEGANT,” an acronym from “Efficient Liquid-based Electricity Generation Apparatus iNside Thermoelectrics.” The first design of ELEGANT comprised three rectangular aluminum channels, used to conduct warm and cold fluids over the surfaces of several commercially available thermoelectric generator (TEG) modules sandwiched between the channels. In this study, an ELEGANT with 24 TEG modules, referred to as ELEGANT-24, has been designed. Twenty-four modules was the best match to the specific geometry of the proposed ELEGANT. The thermoelectric modules in ELEGANT-24 were electrically connected in series, and the maximum output power was modeled. A numerical model has been developed, which provides steady-state forecasts of the electrical output of ELEGANT-24 for different inlet fluid temperatures.

Direct impingement cooling of LED by Piezo fan

In this paper, an innovative heat management solution for the Light Emitting Diodes (LEDs) based on direct impingement cooling by Piezo fan has been proposed and evaluated. Round Piezo fans with 26 to 30 mm blade diameter, 1 to 5 mm fan thickness and narrow flow orifice (~ 3 to 7.5 mm) were developed which could provide very high velocity air jet (> 10 m/s) for impinging heat source footprint directly. These fans were driven at high operating frequency (300 to 550 Hz) and voltage (40 to 50 Vrms) to get high impact air jet at fan outlet. Different test cases have been studied to demonstrate and characterize the cooling capability of the Piezo fan based thermal solutions. Direct impingement cooling of the 5 × 5 mm2 heat source with Piezo fan (30 mm diameter, 1.1 mm thickness and 7.5 mm orifice width) inclined at 35° to horizontal was tested which was able to reduce source temperature by 3 to 4 times as compared to natural convection cooling. Similarly, incorporation of Piezo fan for cooling multiple chips (x5) LED package with 9 W output heat load reduced the source temperature by more than 42 °C. Automotive headlamp with two LED packages and single heat sink was impinge cooled by two dedicated Piezo fans which reduce the source temperature by 7.6 °C and enhance the heat sink heat dissipation capacity by 48% due to improvement in the enclosure heat transfer coefficient. Piezo based impingement cooling can therefore increase the heat removal from heat source as well as can reduce the size of the heat sink designed for natural convection cooling. Based on these results, impingement type Piezo fan can be classified as standalone as well as heat sink integrated cooling solution for LED packages.

Air Impingement Cooling by Synthetic Jet

Modern consumer electronic trends point to a demand for thinner and more portable electronic devices. Conventional cooling systems of these portable electronic devices are challenging to miniaturize in thin profile applications that are typically on the order of several millimeters in thickness. In order to overcome some of these challenges, a synthetic jet, which is also considered as micro fluidic device, is developed. This device which operates based on Piezo electricity is called Dual Cooling Jet (DCJ). DCJ disturbs the boundary layer over a hot component and hence increases heat transfer compare to conventional blower. DCJ is typically defined as a device using a partially enclosed cavity with oscillating walls/diaphragms to create alternating suction and ejection of fluid across an interface or orifice. In this work, the results of cooling performance investigation of DCJ are shown and compared with natural convection cooling. Also, several experiments have been done to study the cooling effect of DCJ at different configuration with respect to heat source and the results are compared. At the end, the effects of heat source size is investigated which are helpful to understand how effective DCJ is when used for cooling several size chips. In addition, the results of this work show that DCJ can be combined with low profile heat sink as a promising next generation ultra thin thermal solution module.

High-performance nickel wick development for loop heat pipes

In the present investigation, high-performance capillary pump has been developed and evaluated for using inside loop heat pipes with 500 W heat transfer capability up to distance of 250 mm. Wick structure is one of the most critical components of the loop heat pipe that provides the necessary capillary pumping, liquid-vapour phase separation and heat leak barrier from evaporation section to the compensation chamber. In order to fabricate wick structure with appropriate physical characteristics, highly pure (>; 99.5%) nickel powders with average particle sizes of 2, 10, 12 and 75 μm were selected for sintering experiment. It was established that nickel powder can be effectively sintered when maintained at 750 - 850 °C temperature for one hour. Out of four nickel powders, NM-12 powder with average particle diameter of 12 μm was able to provide most qualified porous structure, sintered at 850 °C for one hour, with high porosity (>; 72 %), high permeability (>; 2 × 10-13 m2), finer pore radius (>; 7.2 μm), low shrinkage (<; 22%), good axial straightness and acceptable strength. The main issues faced in sintering trials and remedies to avoid them are explained in detail. Center rod extraction was the major problem faced in the sintering experiment which was rectified by replacing carbon rod with high strength, lubricious center rod made from stainless steel with boron nitride coating. The methodologies development in this study can be used for the fabrication of high performance capillary wicks for miniature to large-scale loop heat pipes.

Contribution of Heat Pipe to the Energy Conservation of Data Center and Cloud Computers

With the current increase of the electrical power consumption of the data center imposed a great concern in the world about sustainable energy and global warming and it is therefore required innovative ideas to conserve the energy consumption. Authors propose the use of heat pipe which is a best known passive heat transfer device that is well suitable apply for energy saving system in the current data center cooling system. In this paper, a design and economics of the novel type of thermal control system for data center cooling using heat pipe based cold energy storage system has been proposed and discussed. The cold water storage system is explained and sized for data center with heat output capacity of 8,800 kW. Basically, the cold energy storage will help to downsize the chiller and decrease its runtime that will save electricity related cost and decrease green house gases emissions resulting from the electricity generation. The proposed cold energy storage system can be retrofit or connected in the existing data center facilities without major design changes. Water based cold energy storage system provides more compact size with short term storage (hours to days) and is potential for both small to large size data center with yearly average temperature below the cold storage water temperature (∼ 25 °C). The cold water storage system is sized on the basis of metrological conditions in North America, USA. As an outcome of the thermal and cost analysis, an optimum size of cold energy storage system should be designed to handle 60% of the yearly data center load. The proposed system can be easily integrated into the existing conventional systems without any significant infrastructure changes. Preliminary results obtained from the experimental system design to test the ice formation potential of the heat pipe based cold energy storage system has been shown good result and validated the proposed concept.© 2011 ASME