An official website of the United States government
This work showcases an experimental sub-saturation spray cooling setup for a range of heat fluxes from 0.93 W/cm 2 to 4.66 W/cm 2 . The system consists of a 12” Aluminum square heat source unit with 28 embedded 1800 W cartridge heaters. An external high-pressure air tank provides the system with spraying pressures ranging from 500 to 3000 Psi. User-defined control algorithms command four piezoelectric actuated injectors allowing for the manipulation of the spray frequency, duration, duty cycle, and coordination between multiple piezo-injectors. Thus far, experiments in the horizontal configuration have shown that at 60°C, surface temperatures for all heat fluxes prove difficult to control. At 90°C, however, successful results show that heat fluxes of 1.86 W/cm 2 and 2.79 W/cm 2 are sustainable. Conducting experiments at aggressive power loads and surface temperatures significantly below saturation intro-duce spray-pooling, coolant pools which inhibit the evaporation rate, significantly diminishing the spray cooling efficiency. To counteract this effect, additional experiments were performed in a vertical configuration to avoid the pooling of non-evaporated coolant and enhance the heat transfer through the falling film. The results show surface temperature control for 60°C and 90°C within 6°C of the average surface temperature for heat fluxes up to 0.93 W/cm 2 and 3.72 W/cm 2 , respectively.
more »
« less
A Numerical Heat Transfer Investigation of Lattice Structures As an Alternative AM-Enabled Design for Cooled sCO2 Airfoils
Abstract Supercritical Carbon dioxide (sCO2) power cycles are rapidly developing and gaining popularity in waste heat recovery systems, as primary power cycles for a variety of heat sources such as nuclear, or as a stand-alone power cycle where fossil fuels are combusted. Akin to conventional gas turbines, sCO2-powered systems are pushing the boundaries for firing temperatures for higher efficiencies. Direct oxy-fired sCO2 systems will demand internal cooling of the airfoils for safe and reliable operations. Gas turbine cooling technology can be leveraged for that purpose. However, two key differences exist. First, the coolant medium is sCO2 instead of air, and second, sCO2 airfoils are much smaller compared to power-generation gas turbines. Novel AM manufacturing techniques promise advanced internal cooling geometries. This paper investigates a novel trailing edge cooling design to replace conventional pin fin arrays. Here, a lattice structure with microchannels is introduced. The study presents the changes in heat transfer due to the substitution of the heat transfer medium and the new geometry. The component is assumed to be printed Inconel 718. Based on an oxy-fired combustion sCO2 power cycle, coolant temperature and pressure and hot gas path temperature and pressure are chosen. The converging trailing edge duct is simulated in StarCCM+ using COOLPROP for sCO2 properties as a conjugate heat transfer model.
more »
« less
- PAR ID:
- 10475701
- Publisher / Repository:
- American Society of Mechanical Engineers
- Date Published:
- Journal Name:
- ASME Turbo Expo 2023
- ISBN:
- 978-0-7918-8707-3
- Format(s):
- Medium: X
- Location:
- Boston, Massachusetts, USA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Direct Liquid Cooling (DLC) has emerged as a promising technology for thermal management of high-performance computing servers, enabling efficient heat dissipation and reliable operation. Thermal performance is governed by several factors, including the coolant physical properties and flow parameters such as coolant inlet temperature and flow rate. The design and development of the coolant distribution manifold to the Information Technology Equipment (ITE) can significantly impact the overall performance of the computing system. This paper aims to investigate the hydraulic characterization and design validation of a rack-level coolant distribution manifold or rack manifold. To achieve this goal, a custom-built high power-density liquid-cooled ITE rack was assembled, and various cooling loops were plugged into the rack manifold to validate its thermal performance. The rack manifold is responsible for distributing the coolant to each of these cooling loops, which is pumped by a CDU (Coolant Distribution Unit). In this study, pressure drop characteristics of the rack manifold were obtained for flow rates that effectively dissipate the heat loads from the ITE. The pressure drop is a critical parameter in the design of the coolant distribution manifold since it influences the flow rate and ultimately the thermal performance of the system. By measuring the pressure drop at various flow rates, the researchers can accurately determine the optimum flow rate for efficient heat dissipation. Furthermore, 1D flow network and CFD models of the rack-level coolant loop, including the rack manifold, were developed, and validated against experimental test data. The validated models provide a useful tool for the design of facility-level modeling of a liquid-cooled data center. The CFD models enable the researchers to simulate the fluid flow and heat transfer within the cooling system accurately. These models can help to design the coolant distribution manifold at facility level. The results of this study demonstrate the importance of the design and development of the coolant distribution manifold in the thermal performance of a liquid-cooled data center. The study also highlights the usefulness of 1D flow network and CFD models for designing and validating liquid-cooled data center cooling systems. In conclusion, the hydraulic characterization and design validation of a rack-level coolant distribution manifold is critical in achieving efficient thermal management of high-performance computing servers. This study presents a comprehensive approach for hydraulic characterization of the coolant distribution manifold, which can significantly impact the overall thermal performance and reliability of the system. The validated models also provide a useful tool for the design of facility-level modeling of a liquid-cooled data center.more » « less
-
Miniaturization and high heat flux of power electronic devices have posed a colossal challenge for adequate thermal management. Conventional air-cooling solutions are inadequate for high-performance electronics. Liquid cooling is an alternative solution thanks to the higher specific heat and latent heat associated with the coolants. Liquid-cooled cold plates are typically manufactured by different approaches such as: skived, forged, extrusion, electrical discharge machining. When researchers are facing challenges at creating complex geometries in small spaces, 3D-printing can be a solution. In this paper, a 3D-printed cold plate was designed and characterized with water coolant. The printed metal fin structures were strong enough to undergo pressure from the fluid flow even at high flow rates and small fin structures. A copper block with top surface area of 1 inch by 1 inch was used to mimic a computer chip. Experimental data has good match with a simulation model which was built using commercial software 6SigmaET. Effects of geometry parameters and operating parameters were investigated. Fin diameter was varied from 0.3 mm to 0.5 mm and fin height was maintained at 2 mm. A special manifold was designed to maximize the surface contact area between coolant and metal surface and therefore minimize thermal resistance. The flow rate was varied from 0.75 L/min to 2 L/min and coolant inlet temperature was varied from 25 to 48 oC. It was observed that for the coolant inlet temperature 25 oC and aluminum cold plate, the junction temperature was kept below 63.2 oC at input power 350 W and pressure drop did not exceed 23 Kpa. Effects of metal materials used in 3D-printing on the thermal performance of the cold plate were also studied in detail.more » « less
-
Although supercritical CO2 (sCO2) heat transfer has been employed in industrial process since the 1960s, the underlying transport phenomenon in high-flux microscale geometries, as could be employed in concentrating solar receivers, is poorly understood. To date, nearly all experimental studies and simulations of supercritical convective heat transfer have focused on large diameter vertical channel and tube bundle flows, which may differ dramatically from microscale supercritical convection. Computational studies have primarily employed Reynolds averaged (RANS) turbulence modeling approaches, which may not capture effects from the sharply varying property trends of supercritical fluids. In this study, large eddy simulation (LES) turbulence modeling techniques are employed to study heat transfer characteristics of sCO2 in microscale heat exchangers. The simulation geometry consists of a microchannel of 750×737 μm cross-section and 5 mm length, heated from all four sides. Simulation cases are evaluated at reduced pressure P_r = 1.1, mass flux G = 1000 kg/m^2-s, heat flux q'' = 1.7 − 8.9 W/cm^2 , and varying inlet temperature: 20 − 100℃. Computational results reveal thermal transport mechanisms specific to microscale sCO2 flows. Results have been compared with available supercritical convection correlations to identify the most applicable heat transfer models for engineering of microchannel sCO2 heat exchangers.more » « less
-
Increasing power densities in data centers due to the rise of Artificial Intelligence (AI), high-performance computing (HPC) and machine learning compel engineers to develop new cooling strategies and designs for high-density data centers. Two-phase cooling is one of the promising technologies which exploits the latent heat of the fluid. This technology is much more effective in removing high heat fluxes than when using the sensible heat of fluid and requires lower coolant flow rates. The latent heat also implies more uniformity in the temperature of a heated surface. Despite the benefits of two-phase cooling, the phase change adds complexities to a system when multiple evaporators (exposed to different heat fluxes potentially) are connected to one coolant distribution unit (CDU). In this paper, a commercial pumped two-phase cooling system is investigated in a rack level. Seventeen 2-rack unit (RU) servers from two distinct models are retrofitted and deployed in the rack. The flow rate and pressure distribution across the rack are studied in various filling ratios. Also, investigated is the transient behavior of the cooling system due to a step change in the information technology (IT) load.more » « less
