Browsing by Subject "Electronics cooling"
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Item The Effects of Agitation on convective heat transfer with applications to electronics cooling(2014-01) Agrawal, SmitaWith continuously increasing number of chips and smaller and smaller CPU sizes, heat fluxes that need to be dissipated from computers are on a rapid increase. CPU cooling being critical to the performance of electronic devices, this field demands considerable research focus. Researchers have been pushing existing computer cooling technologies to their limits and also developing new cooling techniques. Forced convection, spray jet cooling, boiling heat transfer are a few to name. Different technologies have their respective merits and limits in terms of their cooling capability, reliability, ease of manufacturing and durability. Forced convection using air has always been preferred due to its cost effectiveness and reliability. The traditional way of employing this technique has been by using a blower fan that cools the heat sink that dissipates heat from the chips. However, the current heat removal demands better performance than that can be provided by a blower fan alone. Agitation is a strong mixing mechanism that can disturb the near-wall flow, thin the thermal boundary layer and enhance the convective heat transfer. This thesis study carries a detailed study of agitation alone through a Large Scale Mock Up (LSMU) unit which is dynamically similar to a single channel of a heat sink. The LSMU has a translationally oscillating plate (agitator) inside the channel cavity. Time averaged heat transfer coefficients and time resolved velocity measurements have been made along different regions of the channel to characterize the convective cooling performance of the agitator. The ensemble-averaged mean velocity variations show periods of acceleration, deceleration and flow reversal during a cycle as a result of agitator movement. Turbulence is found to increase toward the end of the acceleration phase and persist through the deceleration phase. A parametric study has been done to explore the effects of agitator frequency (f), amplitude (A) and agitation velocity (2πAf) on heat transfer and flow mechanism. The heat transfer coefficient increases with the increase in frequency and amplitude. At a fixed agitation velocity, heat transfer coefficient is mainly governed by the agitation velocity irrespective of the value of amplitude or frequency.Item A piezoelectric translational flow agitator for active air cooling of electronics.(2012-08) Yeom, TaihoAs heat dissipation from electronic components dramatically increases due to the rapid development of integrated circuits with micro-nano fabrication, the need increases for powerful cooling facilities. Different cooling schemes such as liquid cooling, direct sprays, boiling heat transfer, etc. have been developed to meet the needs of heat removal. Air cooling still has potential for improvement and continues to hold many advantages over liquid cooling in terms of simplicity, reliability, cost, etc. Conventional heat sink systems with blowers or fans are approaching maximum thermal management capability due to dramatically increased heat dissipation from the chips of high power electronics. In order to increase thermal performance of air-cooled heat sink systems, more active or passive cooling components are continually being considered. One technique is to agitate the flow in the heat sinks to replace or aid conventional blowers. In the present study, an active heat sink system that is coupled with a piezoelectric translational agitator and micro pin fin arrays on the heat sink surfaces is considered. The piezoelectric translational agitator generates high frequency and large displacement motion to a blade. It is driven by an oval loop shell that amplifies the small displacement of the piezo stack actuator to the several-millimeter range. Detailed vibration characteristics were studied through theoretical and experimental analyses. Dynamic operating frequency and displacement were estimated through the theoretical analysis. The blade, made of carbon fiber composite, is easily extended to a multiple-blade system without adding much mass. The micro pin fin arrays were created with the LIGA photolithography technique. The cooling performance of the heat sink system was demonstrated in single-channel and multiple-channel test facilities employing either plain or micro pin-fin surfaces. Intensive heat transfer experimental results are provided. A total Reynolds number was defined to characterize the combined effects of cross flow and agitation. The Stanton number developed from the relationship between the total Reynolds number and heat transfer coefficients enables predicting operating performance. Different configurations of the translational agitator with multiple blades were fabricated and tested in a 26-channel, full-size heat sink. The experimental results showed that the proposed active air cooling has a promising potential for the thermal management of high power electronics.Item Synthetic jet flow and heat transfer for electronics cooling(2014-05) Huang, LongzhongThe progressive increase of heat dissipation from modern electronics requires more and more powerful cooling systems. Various cooling technologies have been developed such as liquid cooling, micro-channel cooling, and active cooling. The present study focuses on applying a unique device called a synthetic jet to cool electronics. A synthetic jet is able to generate an unsteady flow with a simple structure that makes it effective in convective heat transfer. This study provides both practical and fundamental view of synthetic jets in the application of electronics cooling. A mock-up synthetic jet is fabricated to study heat transfer and fluid mechanics of synthetic jet cooling. The scaled synthetic jet is geometrically and dynamically similar to the actual jet. The heat transfer performance characteristics of a synthetic jet impinging on a fin are tested with different operating frequencies and with different orifice shapes. Flow visualizations and detail flow field measurements of the impinging synthetic jet flow are documented to support the heat transfer experiment. The optimized parameters obtained from the scaled experiment are applied to the actual synthetic jet design. The actual synthetic jet is realized using a piezoelectric stack and applied on a cooling system based on a full-sized heat sink module. The cooling performance of the whole system is documented. The noise characteristics of the actual synthetic jet is tested and analyzed. A muffler with optimized parameters is found and used for noise reduction. Numerical simulation is used to find the optimal design for the synthetic jets. The computation is realized by the commercial software ANSYS Fluent. The numerical model is verified by comparing the computational results with experimental results. A parametric study of heat transfer performance of synthetic jet cooling is documented.