Transient Analysis of Non-Uniform Heat Input Propagation Through a Heat Sink Base

2016 ◽  
Author(s):  
Srivathsan Sudhakar ◽  
Justin A. Weibel
Keyword(s):  
Heat Sink ◽  
Temperature Response ◽  
Flow Distribution ◽  
Temporal Variations ◽  
Heat Sinks ◽  
Two Phase ◽  
Periodic Models ◽  
Temperature Solution ◽  
Periodic Heat ◽  
Complex Temperature

For thermal management architectures wherein the heat sink is embedded close to a dynamic heat source, non-uniformities may propagate through the heat sink base to the coolant. Available transient models predict the effective heat spreading resistance to calculate chip temperature rise, or simplify to a representative axisymmetric geometry. The coolant-side temperature response is seldom considered, despite the potential influence on flow distribution and stability in two-phase microchannel heat sinks. This study uses multi-dimensional transient and steady-periodic models to predict spatial and temporal variations of temperature within the heat sink base. The response to arbitrary transient heat inputs is obtained using Duhamel’s method. For time-periodic heat inputs, the steady-periodic solution is calculated using the method of complex temperature. Solution of the coolant-side temperature response in the presence of multiple different transient heat inputs is demonstrated. The degree of spatial and temporal non-uniformity in the coolant-side temperature profiles are mapped as a function of nondimensional geometric parameters and boundary conditions. Several case studies are presented to demonstrate the utility of such maps.

Transient Analysis of Nonuniform Heat Input Propagation Through a Heat Sink Base

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Srivathsan Sudhakar ◽  
Justin A. Weibel
Keyword(s):  
Heat Source ◽  
Heat Input ◽  
Heat Sink ◽  
Three Dimensional ◽  
Temperature Response ◽  
Flow Distribution ◽  
Temporal Variations ◽  
Step Response ◽  
Dimensional System ◽  
Two Phase

For thermal management architectures wherein the heat sink is embedded close to a dynamic heat source, nonuniformities may propagate through the heat sink base to the coolant. Available transient models predict the effective heat spreading resistance to calculate chip temperature rise, or simplify to a representative axisymmetric geometry. The coolant-side temperature response is seldom considered, despite the potential influence on flow distribution and stability in two-phase microchannel heat sinks. This study solves three-dimensional transient heat conduction in a Cartesian chip-on-substrate geometry to predict spatial and temporal variations of temperature on the coolant side. The solution for the unit step response of the three-dimensional system is extended to any arbitrary temporal heat input using Duhamel's method. For time-periodic heat inputs, the steady-periodic solution is calculated using the method of complex temperature. As an example case, the solution of the coolant-side temperature response in the presence of different transient heat inputs from multiple heat sources is demonstrated. To represent a case where the thermal spreading from a heat source is localized, the problem is simplified to a single heat source at the center of the domain. Metrics are developed to quantify the degree of spatial and temporal nonuniformity in the coolant-side temperature profiles. These nonuniformities are mapped as a function of nondimensional geometric parameters and boundary conditions. Several case studies are presented to demonstrate the utility of such maps.

Two-Phase Heat Sinks With Microporous Coating

2011 ◽  
Author(s):  
Tadej Semenic ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Porous Coating ◽  
Two Phase ◽  
Small Channel ◽  
Rectangular Channels ◽  
Microporous Coating ◽  
Channel Aspect Ratio

To minimize flow boiling instabilities in two-phase heat sinks, two different types of microporous coatings were developed and applied on mini- and small-channel heat sinks and tested using degassed R245fa refrigerant. The first coating was epoxy-based and was sprayed on heat sink channels while the second coating was formed by sintering copper particles on heat sink channels. Mini-channel heat sinks had overall dimensions 25.4 mm × 25.4 mm × 6.4 mm and twelve rectangular channels with a hydraulic diameter 1.7 mm and a channel aspect ratio of 2.7. Small-channel heat sinks had the same overall dimensions, but only three rectangular channels with hydraulic diameter 4.1 mm and channel aspect ratio 0.6. The microporous coatings were found to minimize parallel channel instabilities for mini-channel heat sinks and to reduce the amplitude of heat sink base temperature oscillations from 6 °C to slightly more than 1 °C. No increase in pressure drop or pumping power due to the microporous coating was measured. The mini-channel heat sinks with porous coating had in average 1.5-times higher heat transfer coefficient than uncoated heat sinks. Also, the small-channel heat sinks with the “best” porous coating had in average 2.5-times higher heat transfer coefficient and the critical heat flux was 1.5 to 2-times higher compared with the uncoated heat sinks.

Next Generation Devices for Electronic Cooling

2003 ◽  
Author(s):  
Ralph L. Webb
Keyword(s):  
Heat Sink ◽  
New Technology ◽  
Heat Removal ◽  
Cost Effective ◽  
Heat Sinks ◽  
Working Fluid ◽  
Two Phase ◽  
Conventional Technology ◽  
Removal Technology ◽  
R Value

Conventional technology to cool desktop computers and servers is that of the “direct heat removal” heat sink, which consists of a heat sink/fan mounted on the CPU. Although this is a very cost effective solution, it is nearing its end of life. This is because future higher power CPUs will require a lower R-value than can be provided by this technology, within current size and fan limits. This paper discusses new technology that uses “indirect heat removal” technology, which involves use of a single or two-phase working fluid to transfer heat from the hot source to an ambient heat sink. This technology will support greater heat rejection than is possible with the “direct heat removal” method. Further, it will allow use of higher performance air-cooled ambient heat sinks than are possible with the “direct heat removal” heat sink. A concern of the indirect heat removal technology is the possibility that it may be orientation sensitive. This paper identifies preferred options and discusses the degree to which they are (or or not) orientation sensitive. It should be possible to attain an R-value of 0.12K/W at the balance point on the fan curve.

Enabling Thermal Management of High-Powered Server Processors Using Passive Thermosiphon Heat Sink

2019 ◽  
Author(s):  
Devdatta P. Kulkarni ◽  
Priyanka Tunuguntla ◽  
Guixiang Tan ◽  
Casey Carte
Keyword(s):  
Heat Pipe ◽  
High Power ◽  
Heat Sink ◽  
Capital Investment ◽  
Thermal Design ◽  
Heat Sinks ◽  
Air Cooling ◽  
Liquid Cooling ◽  
Two Phase ◽  
Pipe Heat

Abstract In recent years, rapid growth is seen in computer and server processors in terms of thermal design power (TDP) envelope. This is mainly due to increase in processor core count, increase in package thermal resistance, challenges in multi-chip integration and maintaining generational performance CAGR. At the same time, several other platform level components such as PCIe cards, graphics cards, SSDs and high power DIMMs are being added in the same chassis which increases the server level power density. To mitigate cooling challenges of high TDP processors, mainly two cooling technologies are deployed: Liquid cooling and advanced air cooling. To deploy liquid cooling technology for servers in data centers, huge initial capital investment is needed. Hence advanced air-cooling thermal solutions are being sought that can be used to cool higher TDP processors as well as high power non-CPU components using same server level airflow boundary conditions. Current air-cooling solutions like heat pipe heat sinks, vapor chamber heat sinks are limited by the heat transfer area, heat carrying capacity and would need significantly more area to cool higher TDP than they could handle. Passive two-phase thermosiphon (gravity dependent) heat sinks may provide intermediate level cooling between traditional air-cooled heat pipe heat sinks and liquid cooling with higher reliability, lower weight and lower cost of maintenance. This paper illustrates the experimental results of a 2U thermosiphon heat sink used in Intel reference 2U, 2 node system and compare thermal performance using traditional heat sinks solutions. The objective of this study was to showcase the increased cooling capability of the CPU by at least 20% over traditional heat sinks while maintaining cooling capability of high-power non-CPU components such as Intel’s DIMMs. This paper will also describe the methodology that will be used for DIMMs serviceability without removing CPU thermal solution, which is critical requirement from data center use perspective.

Design and Performance of Novel Low-Profile Heat Sinks Created Through Additive Manufacturing

2016 ◽  
Author(s):  
Pratik KC ◽  
Sangeet Shrestha ◽  
Adarsh Radadia ◽  
Leland Weiss ◽  
Arden Moore
Keyword(s):  
Additive Manufacturing ◽  
Heat Sink ◽  
Heat Sinks ◽  
Two Phase ◽  
Printed Circuit ◽  
Immersion Cooling ◽  
Low Profile ◽  
Direct Immersion Cooling ◽  
Power Densities ◽  
Direct Immersion

Traditional thermal management techniques such as air-cooled plate- and pin-fin heat sinks are today being pushed to their limits by the increasing power densities of computing hardware (power supplies, controllers, processors, and integrated circuits). In comparison, direct immersion cooling within an alternative cooling medium such as commercial dielectric fluids offers the ability to handle high power densities while also accommodating tighter printed circuit board spacing. Together, these attributes are critical to facilitating higher computing densities. However, this type of high density setup also requires that any heat sink present be low profile so as to not obstruct adjacent printed circuit boards. Such a stringent limit on heat sink height can make achieving cooling targets challenging with existing designs. In this work, the performance of several low profile (height less than 6 mm) heat sinks of varying design are evaluated within a carefully controlled direct immersion cooling environment. Commercial copper heat sinks fabricated through conventional manufacturing (CM) approaches serve as baselines for these performance tests. These same heat sink designs are also replicated via additive manufacturing (AM) utilizing a conductive, carbon-filled printable polylactic acid (PLA) composite material. The performance of these AM heat sinks are then compared to the CM heat sinks, with special emphasis on differences in thermal conductivity between the constituent materials. Finally, novel bio-inspired heat sink designs are developed which would be difficult or impossible to achieve using CM approaches. The most promising of these designs were then created using AM and their performance evaluated for comparison. The overall goal of this is to ascertain whether the design and fabrication flexibility offered by AM can facilitate low profile heat sink designs that can meet or exceed the performance of conventional heat sinks even with perceived deficiencies in material properties for AM parts. Experiments were carried out within Novec 7100 dielectric fluid for single-phase natural convection scenarios as well as two-phase subcooled boiling conditions at atmospheric pressure. A custom test rig was constructed consisting of mirror-polished stainless steel plates and polycarbonate viewing ports to allow visual access. A rotating sample stage allows for data to be obtained at varying heat sink orientation angles from 0° to 90°. For two-phase experiments, multi-angle video capture allows for analysis of the two-phase dynamics occurring at the heat sink samples to be visualized and temporally linked to the associated temperature and heat flux data.

Vapor Chambers in Blade Server CPU Cooling Solutions

2007 ◽  
Author(s):  
Matt Connors
Keyword(s):  
Heat Sink ◽  
High Heat ◽  
Heat Sinks ◽  
High Heat Flux ◽  
Air Cooling ◽  
Vapor Chamber ◽  
Two Phase ◽  
Blade System ◽  
Overall Resistance ◽  
Aluminum Base

Current blade processors need air cooling solutions that dissipate 100–300 watts with heat sinks that are less than 30 mm high. In order to cool these processors, the heat sink base has to grow in length and width to compensate for the lack of available height. As these dimensions grow, decreasing the base spreading of the heat sink becomes an important factor is decreasing the overall resistance of the heat sink. A vapor chamber used as a substitute to common copper or aluminum as the base of the heat sink can increase performance by 20–25%. A vapor chamber is a two phase heat transport system that significantly reduces the spreading resistance in applications where there is a high heat flux processor coupled with a large heat sink. In this paper, a CFD model will be constructed to predict the performance gains realized by using a vapor chamber base in lieu of a copper or aluminum base. These predictions will then be experimentally tested to confirm the modeling parameters and the actual measured thermal performance of the heat sink. By utilizing vapor chambers in heat sink design, thermal engineers will gain valuable heat sink performance within the constraints imposed by the blade system architecture.

A Compact Integrated Thermosyphon Heat Sink for Power Electronics Cooling

2019 ◽  
Author(s):  
Ahmed Elkholy ◽  
Roger Kempers
Keyword(s):  
Natural Convection ◽  
Heat Sink ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
Heat Pipes ◽  
Heat Sinks ◽  
Working Fluid ◽  
Convection Heat ◽  
Two Phase ◽  
Spreading Resistance

Abstract The trend in miniaturization of power electronic components requires the development of new robust and passive cooling methods to meet increased heat flux demands. Conventional heat sinks encounter inherent shortcomings due to heat spreading resistance of the heat sink baseplate particularly in natural convection heat sinks used to cool small localized heat sources. Heat pipes embedded within the base of heat sinks can be used to improve spreading performance but are limited by the ability to conduct heat into and out of the heat pipes. In the current study, a small, naturally aspirated two-phase thermosyphon heat sink was developed and characterized experimentally. The proposed architecture integrates all thermosyphon components into one compact device, where the evaporator, riser and the downcomer are incorporated at the heat sink base. The downcomer also serves as the condenser within the base of a vertical finned natural convection heat sink. The side-heated evaporator consists of an array mini-channels configuration which can operate in either pool boiling or flow boiling configuration, which allows the thermosyphon heat sink to operate in either reflux mode or looped mode, respectively. Experiments were carried out using HFE 7000 as the working fluid. The effect of the of input power on the thermal performance is examined for both modes for powers ranging from 10 to 80 W. Results demonstrate that this approach significantly reduces the spreading resistance resulting in a net improvement which can be traded-off for a decrease the overall size or weight of the heat sink.

Numerical Evaluation of Clearance Requirements Around Obstructions in Finned Heat Sinks

2017 ◽  
Author(s):  
Steven Miner
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Temperature Rise ◽  
Heat Sink ◽  
Operating Temperature ◽  
Flow Distribution ◽  
Local Heat ◽  
Heat Sinks ◽  
Electronic Components

This study uses CFD to consider the effects of obstructions (bosses) on the fluid flow and heat transfer in finned heat sinks used for cooling electronic components. In particular, the effect of bosses, used for mounting components, on the fluid flow distribution and temperature distribution in the heat sink are evaluated. A typical heat sink has fins sandwiched between top and bottom plates, with electronic components mounted on the plates. The top and bottom plates spread the heat generated in the components to reduce the local heat flux. The fins substantially increase the heat transfer area, reducing the temperature rise from the coolant to the top and bottom plates. In this case a uniform distribution of flow across the heat sink can be achieved and there will be no localized hot spots. Ideally there are no protrusions into the finned portion of the heat sink which would cause disruptions in the uniform flow through the heat sink. However, a boss may be needed to bolt a component to the heat sink. The presence of the boss has three effects on the heat sink performance. The boss disrupts the flow in its immediate vicinity, increasing the thermal resistance. This will cause an increase in operating temperature at that location. In addition, the boss will change the flow distribution in the heat sink. Locations upstream and downstream of the boss may see reduced flow due to the obstruction, which in turn will cause an increase in operating temperature for these areas of the heat sink. Finally, the change in flow distribution may increase the pressure drop through the entire heat sink, increasing the power required to operate the system. The purpose of this study is to numerically evaluate the clearance requirements around circular bosses. Comparisons between an unobstructed heat sink and a heat sink with an obstruction are made for the maximum component temperature rise, the pressure drop and the flow distribution. Clearance ratios, diameter of the fin cut out to boss diameter, were varied from 1.1 to 3.3. The Reynolds number for the flow was varied from roughly 3000 to 70,000 based on the hydraulic diameter of flow passage.

scholarly journals Numerically Investigating the Effects of Cross-Links in Scaled Microchannel Heat Sinks

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Minh Dang ◽  
Ibrahim Hassan ◽  
Sung In Kim
Keyword(s):  
Pressure Drop ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Heat Sinks ◽  
Straight Channel ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
Cross Links ◽  
Channel Configuration

Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3. A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented.

Sign in / Sign up

Export Citation Format

Share Document