Simulation of Buoyancy-Driven Flow for Various Power Levels at the NSTF

2016 ◽  
Author(s):  
Adam R. Kraus ◽  
Rui Hu ◽  
Darius D. Lisowski ◽  
Matthew Bucknor
Keyword(s):  
Natural Convection ◽  
Cooling System ◽  
Heated Surface ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Heated Wall ◽  
Test Facility ◽  
Cfd Simulations ◽  
Wide Range ◽  
Convection Model

The Reactor Cavity Cooling System (RCCS) is an important passive safety system that is being incorporated in a number of high temperature reactor design concepts. The Natural convection Shutdown heat removal Test Facility (NSTF), located at Argonne National Laboratory, is an experiment with the objective of investigating the flow and thermal behavior of a particular air-cooled RCCS design. It consists of 12 ducts surrounded by a cavity with a heated wall, through which air flows via natural convection before exiting through two chimneys. The NSTF is a ½-scale facility, and is well instrumented in order to provide data for code validation, including Computational Fluid Dynamics (CFD)-grade data in a number of locations. Instrumentation includes fiber-optic Distributed Temperature Sensors (DTS) throughout one of the riser ducts and in the upper plenum. In conjunction with the experimental tests, CFD simulations were performed to support the design and optimization of these natural convection systems. The CFD simulations were performed using the “as-tested” geometry of the NSTF. All CFD simulations were steady-state. Both a full natural convection model and a smaller forced primary flow model were tested. The influence of boundary conditions, notably at the cavity walls, was tested. Initial simulations assumed adiabatic walls but these were later adapted to simulate heat losses, aided by thermal images taken of the exterior NSTF surfaces during testing. Simulations were run for tests at two different power levels. A number of turbulence models were compared to test their influence. Simulation results were compared with experimental data. Convergence was generally good for both models. It was found that the natural convection model was indeed beneficial for correctly estimating local temperatures in a number of areas, particularly near the top of the riser ducts and from DTS measurements along the flow path. Flow in the heated cavity was complex. In general, the experimental trends were predicted well by CFD, although magnitudes could be improved in some areas. The turbulence models tested had a relatively small effect on the shape of the temperature profile in the ducts and on heated surface temperatures. Results from the simulations have been of direct use in improving test procedures and choosing locations for more accurate instrumentation. In future work, full natural convection simulations of more tests will be performed. After this has been completed, best practices can be established for accurately simulating these general types of natural convection systems across a wide range of operating conditions.

Experimental and Numerical Study for Improved Understanding of Mixed-Convection Type of Flows in Turbine Casing Cavities During Shut-Down Regimes

2021 ◽  
Author(s):  
Oguzhan Murat ◽  
Budimir Rosic ◽  
Koichi Tanimoto ◽  
Ryo Egami
Keyword(s):  
Natural Convection ◽  
Flow Field ◽  
Mixed Convection ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Scale Model ◽  
Unsteady Temperature ◽  
Numerical Predictions ◽  
Wide Range ◽  
Turbine Casing

Abstract Due to increase in the power generation from renewable sources, steam and gas turbines will be required to adapt for more flexible operations with frequent start-ups and shut-downs to provide load levelling capacity. During shut-down regimes, mixed convection takes place with natural convection dominance depending on the operating conditions in turbine cavities. Buoyant flows inside the turbine that are responsible for non-uniform cooling leading to thermal stresses and compromise clearances directly limits the operational flexibility. Computational fluid dynamics (CFD) tools are required to predict the flow field during these regimes since direct measurements are extremely difficult to conduct due to the harsh operating conditions. Natural convection with the presence of cross-flow -mixed convection has not been extensively studied to provide detailed measurements. Since the literature lacks of research on such flows with real engine representative operating conditions for CFD validation, the confidence in numerical predictions is rather inadequate. This paper presents a novel experimental facility that has been designed and commissioned to perform very accurate unsteady temperature and flow field measurements in a simplified turbine casing geometry. The facility is capable of reproducing a wide range of Richardson, Grashof and Reynolds numbers which are representative of engine realistic operating conditions. In addition, high fidelity, wall resolved LES with dynamic Smagorinsky subgrid scale model has been performed. The flow field as well as heat transfer characteristics have been accurately captured with LES. Lastly, inadequacy of RANS for mixed type of flows has been highlighted.

A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

3-E Analysis of a Heat Pump Driven by a Micro-Cogenerator

2005 ◽  
Author(s):  
Maurizio Sasso ◽  
Raffaello Possidente ◽  
Carlo Roselli ◽  
Sibilio Sergio
Keyword(s):  
Heat Pump ◽  
Thermal Energy ◽  
Primary Energy ◽  
Operating Conditions ◽  
Environmental Benefits ◽  
Test Facility ◽  
Cooling Mode ◽  
Simplified Approach ◽  
Wide Range ◽  
Network Losses

The cogeneration, or the combined production of electric (and/or mechanical) and thermal energy, is a well established technology, which has important environmental benefits and it has been noted by the European Community as one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, the study will be focused on the micro-cogeneration process with micro-combined heat and power system, or MCHP (electric power output ≤ 15 kW), which represents a valid and interesting application of this technology applicable, above all, to residential and light commercial users. This paper presents the Energy, Economic and Environmental (3-E) analysis of a natural gas-fired MCHP in combination with an electric heat pump (EHP). The 3-E analysis of the MCHP/EHP begins with the results of a detailed experimental activity developed in a test facility [1] for a wide range of conditions. Two operating conditions were simulated: a heating mode with co-production of electric and thermal energy, and a cooling mode with co-production of electric, thermal and cooling energy (tri-generation). The annual operating performance, also based on the typical features of the Italian market, is also discussed with a simplified approach.

Experimental Validation and Design Simulations of a Passive Two-Phase Cooling System for Datacenters

2020 ◽  
Author(s):  
Jackson B. Marcinichen ◽  
John R. Thome ◽  
Raffaele L. Amalfi ◽  
Filippo Cataldo
Keyword(s):  
Thermal Performance ◽  
Experimental Validation ◽  
Cooling System ◽  
Electronics Cooling ◽  
Operating Conditions ◽  
Two Phase ◽  
Data Set ◽  
Pressure Drops ◽  
Wide Range ◽  
Important Challenge

Abstract Thermosyphon cooling systems represent the future of datacenter cooling, and electronics cooling in general, as they provide high thermal performance, reliability and energy efficiency, as well as capture the heat at high temperatures suitable for many heat reuse applications. On the other hand, the design of passive two-phase thermosyphons is extremely challenging because of the complex physics involved in the boiling and condensation processes; in particular, the most important challenge is to accurately predict the flow rate in the thermosyphon and thus the thermal performance. This paper presents an experimental validation to assess the predictive capabilities of JJ Cooling Innovation’s thermosyphon simulator against one independent data set that includes a wide range of operating conditions and system sizes, i.e. thermosyphon data for server-level cooling gathered at Nokia Bell Labs. Comparison between test data and simulated results show good agreement, confirming that the simulator accurately predicts heat transfer performance and pressure drops in each individual component of a thermosyphon cooling system (cold plate, riser, evaporator, downcomer (with no fitting parameters), and eventually a liquid accumulator) coupled with operational characteristics and flow regimes. In addition, the simulator is able to design a single loop thermosyphon (e.g. for cooling a single server’s processor), as shown in this study, but also able to model more complex cooling architectures, where many thermosyphons at server-level and rack-level have to operate in parallel (e.g. for cooling an entire server rack). This task will be performed as future work.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

scholarly journals Modeling of Natural Convection in Electronic Enclosures

2005 ◽  
Vol 128 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Peter M. Teertstra ◽  
M. Michael Yovanovich ◽  
J. Richard Culham
Keyword(s):  
Natural Convection ◽  
Numerical Data ◽  
Composite Model ◽  
Circuit Board ◽  
Flow Conditions ◽  
Transition Flow ◽  
Cfd Simulations ◽  
Wide Range ◽  
Using Data ◽  
Good Agreement

An analytical model is developed for natural convection from a single circuit board in a sealed electronic equipment enclosure. The circuit card is modeled as a vertical isothermal plate located at the center of an isothermal, cuboid shaped enclosure. A composite model is developed based on asymptotic solutions for three limiting cases: pure conduction, laminar boundary layer convection, and transition flow convection. The conduction shape factor and natural convection models are validated using data from CFD simulations for a wide range of enclosure geometries and flow conditions. The model is shown to be in good agreement, to within 10% RMS, with the numerical data for all test configurations.

Unsteady Simulations of a Low NOx LDI Combustor for Environmentally Responsible Aviation Engines

2015 ◽  
Author(s):  
Scott A. Drennan ◽  
Gaurav Kumar ◽  
Erlendur Steinthorsson ◽  
Adel Mansour
Keyword(s):  
Experimental Data ◽  
Complex Geometry ◽  
Mesh Refinement ◽  
Operating Conditions ◽  
Design Parameters ◽  
Nox Emissions ◽  
Fuel Injector ◽  
Cfd Simulations ◽  
Wide Range ◽  
Environmentally Responsible

A key objective of NASA’s Environmentally Responsible Aviation (ERA) research program is to develop advanced technologies that enable 75% reduction of LTO NOx emissions of N+2 aviation gas turbine engines relative to the CAEP 6 standard. To meet this objective, a new advanced multi-point fuel injector was proposed and tested under the NASA ERA program. The new injector, called the three-zone injector, or 3ZI, uses fifteen spray cups arranged in three zones. Swirling air flows into each cup and fuel is introduced via pressure swirl atomizers within the cup. Multiple design parameters impact the performance of the injector, such as the location of the atomizer within the spray cup, the spray angle and cup-to-cup spacing. To fully understand the benefits and trade-offs of various injector design parameters and to optimize the performance of the injector, detailed CFD simulations are an essential tool. Furthermore, the CFD methodology must allow easy changes in design parameters and guarantee consistent and comparable accuracy from one design iteration to the next. This paper investigates the use of LES in reacting and non-reacting flows and compares against the NOx experimental data for the multi-point atomization strategy of the injector. The CFD simulations employ an automatically generated Cartesian cut-cell meshing approach with mesh refinement applied near complex geometry and spray regions. Adaptive Mesh Refinement (AMR) is used to refine mesh in regions of high gradients in velocity and temperature. The CFD simulations use boundary and operating conditions based on experimental data for air flow and spray atomization obtained from LDV and PDPA characterizations of the spray respectively. The results are extended to reacting flow using a detailed reaction mechanism and predictions of NOx emissions are compared to experimental data. Overall NOx predictions were consistently less than experimental values. However, the NOx prediction trends showed excellent agreement with experimental data across the wide range of equivalence ratios investigated.

scholarly journals Climate- and Technology-Specific PUE and WUE Predictions for U.S. Data Centers using a Physics-Based Approach

2021 ◽  
Author(s):  
Nuoa Lei ◽  
Eric Masanet
Keyword(s):  
Water Use ◽  
Data Centers ◽  
Cooling System ◽  
Operating Conditions ◽  
Sensitivity Analyses ◽  
Real World Data ◽  
Climate Zone ◽  
System Type ◽  
Tower Equipment ◽  
Wide Range

Abstract The onsite water use of data centers (DCs) is becoming an increasingly important consideration within the policy and energy analysis communities, but has heretofore been difficult to quantify in macro-level DC energy models due to lack of reported water usage effectiveness (WUE) values by DC operators. This work addresses this important knowledge gap by presenting thermodynamically-compatible power usage effectiveness (PUE) and WUE values for a wide range of U.S. DC archetypes and climate zones, using a physics-based model that is validated with real-world data. Results enable energy analysts to more accurately analyze the onsite energy and water use of DCs by size class, cooling system type, and climate zone under many different operating conditions including operational setpoints. Sensitivity analyses further identify the variables leading to best-achievable PUE and WUE values by climate zone and cooling system type—including operational set points, use of free cooling, and cooling tower equipment and operational factors—which can support DC water- and energy-efficiency policy initiatives. The consistent PUE and WUE values may also be used in future work to quantify the indirect water use of DCs occurring in electrical power generating systems.

Machine Learning-Based Model for Optimal Operating Conditions of Thermosyphons for Electronic Cooling Applications

2021 ◽  
Author(s):  
John Kim ◽  
Raffaele L. Amalfi
Keyword(s):  
Machine Learning ◽  
Thermal Performance ◽  
Cooling System ◽  
Electronic Cooling ◽  
Operating Conditions ◽  
Complex Nature ◽  
System Control ◽  
Optimal Operating ◽  
Two Phase ◽  
Wide Range

Abstract Two-phase cooling systems based on the thermosyphon operating principle exhibit excellent heat transfer performance, reliability, and flexibility, therefore can be applied to overcome thermal challenges in a wide range of electronic cooling applications and deployment scenarios. However, extremely complex nature of two-phase flow physics involving flow patterns and phase transitions has been the major challenge for technology adoption in industry. This paper demonstrates a machine learning (ML) based model for evaluating the thermal performance and refrigerant mass flow rate, of a thermosyphon cooling system for telecom equipment. Unlike conventional laboratory approach that requires numerous sensors attached to a cooling system to capture their thermal performance, the new model requires a minimum number of sensors to monitor the health of a thermal management solution. Using the proposed model, a system control module can be further developed which could identify optimal operating parameters in real-time under dynamically changing heat load conditions and actively maintain safety and thermal requirements.

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