Pumpless Loop for Narrow Channel and Micro-Channel Boiling

2003 ◽  
Vol 125 (3) ◽  
pp. 431-441 ◽  
Author(s):  
Swaraj Mukherjee ◽  
Issam Mudawar
Keyword(s):  
Cooling System ◽  
Narrow Channel ◽  
Separation Distance ◽  
System Response ◽  
Two Phase ◽  
Small Surface ◽  
Two Fluids ◽  
Pass Through ◽  
Cooling Loop ◽  
Narrow Gaps

A compact cooling system is examined which capitalizes upon fluid density differences between two vertical, parallel, interconnected tubes to achieve a pumpless cooling loop. A heat-dissipating device is incorporated into a boiler at the bottom of the hot tube. The large density differences between the two tubes produces a substantial nonequilibrium in hydrostatic pressure, drawing liquid downwards through the cold tube as a two-phase mixture is released upwards in the hot tube. Cooling with this pumpless loop is fundamentally different from, and far superior to, pool boiling thermosyphons because of the former’s ability to separate the path of replenishment liquid from that of the released vapor. Experiments were performed to explore the effects of boiler gap (separation distance between the boiling surface and opposite insulating wall) on cooling performance and critical heat flux (CHF) for water and FC-72. The gap, which is the primary measure of boiler miniaturization, was varied from 0.051 to 21.46 mm. For large gaps, CHF showed insignificant dependence on the gap for both fluids. However, small gaps produced CHF variations that were both drastic and which followed opposite trends for the two fluids. Decreasing the gap below 3.56 mm produced a substantial rise in CHF for FC-72. For water, CHF was fairly insensitive down to 0.51 mm, below which it began to decrease sharply. These trends are shown to be closely related to the small surface tension and contact angle of FC-72 producing very small bubbles which can easily pass through narrow gaps in FC-72, while much larger bubbles in water obstruct liquid replenishment in narrow gaps. A numerical model is constructed to determine how the gap influences the various components of pressure drop, velocities, coolant flow rate, and hence system response to heat input.

Modeling Size Effects of a Portable Two-Phase Electronics Cooling Loop With Different Refrigerants

2010 ◽  
Author(s):  
Tom Saenen ◽  
Martine Baelmans
Keyword(s):  
Size Effects ◽  
Cooling System ◽  
Electronics Cooling ◽  
Simple Algorithm ◽  
System Model ◽  
Two Phase ◽  
Component Mixture ◽  
Pressure Losses ◽  
Microchannel Cooling ◽  
Cooling Loop

A one dimensional dynamic system model is developed to accurately simulate a two-phase microchannel electronics cooling loop. This model is based on the single component mixture equations for mass, momentum and energy. These equations are solved numerically using a finite volume method in conjunction with the SIMPLE algorithm. To calculate the pressure losses and heat transfer state of the art empirical correlations are used. Furthermore size effects of a typical microchannel cooling system are investigated with the new model. Special attention is given to the accumulator size and its limitations for portable applications. A simple model to investigate the accumulator size effect on the loop is developed and compared to numerical results obtained from the system model. The influence of various loop parameters and possible improvements are also investigated. Finally the effect of using different coolants is studied.

Experimental Measurements and Numerical Simulations of Two-Phase Stratified, Wavy and Slug Flow in a Narrow Rectangular Channel

2005 ◽  
Author(s):  
Steven P. O’Halloran ◽  
B. Terry Beck ◽  
Mohammad H. Hosni ◽  
Steven J. Eckels
Keyword(s):  
Numerical Simulations ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Rectangular Channel ◽  
Measurement Techniques ◽  
Narrow Channel ◽  
Experimental Measurements ◽  
Phase Flow ◽  
Two Phase ◽  
Two Fluids

Flow pattern transitions in two-phase flow are important phenomena for many different types of engineering applications, including heat exchangers. While two-phase flow is not understood as well as single-phase flow, advancements in both measurement techniques and numerical simulations are helping to increase the understanding of two-phase flow. In this paper, stratified/wavy flow is investigated, along with the transition from wavy to slug flow. For the experimental setup, a narrow channel with a length of 600 mm, height of 40 mm, and a width of 15 mm was fabricated using clear acrylic plastic, and water and air were the two fluids used for testing. The water in the channel was initially at rest, and the transition in flow patterns was created by increasing the velocity of air flowing over the water surface. Particle image velocimetry (PIV) was used to measure the velocity of the flow for stratified and wavy flow conditions, and also the velocity at the onset of slug flow. Along with the experimental measurements, computational fluid dynamics (CFD) simulations were conducted on a similar geometry using the volume of fluid (VOF) two-phase model. A commercial CFD software package was used for the simulations, and comparisons were made between the experimental measurements and numerical results. Favorable agreement was found between the experimental measurements and the numerical simulations. In particular, the transition from wavy to slug flow compared well to previously developed two-phase flow transition models, including the slug transition developed by Taitel and Dukler.

Sensitivity Analysis of a PWR Response During a Loss of Coolant Accident Under a Hypothetical Core Blockage Scenario Using RELAP5-3D

2014 ◽  
Author(s):  
Timothy Crook ◽  
Rodolfo Vaghetto ◽  
Alessandro Vanni ◽  
Yassin A. Hassan
Keyword(s):  
Cooling System ◽  
Safety Concern ◽  
System Response ◽  
Flow Paths ◽  
Pressurized Water ◽  
The Core ◽  
Loss Of Coolant Accident ◽  
Loss Of Coolant ◽  
Pass Through ◽  
Core Cooling

During a Loss of Coolant Accident (LOCA) a substantial amount of debris may be generated in containment during the blowdown phase. This debris can become a major safety concern since it can potentially impact the Emergency Core Cooling System (ECCS). Debris, produced by the LOCA break flow and transported to the sump, could pass through the filtering systems (debris bed and sump strainer) in the long term cooling phase. If the debris were to sufficiently accumulate at the core inlet region, the core flow could theoretically decrease, affecting the core coolability. Under such conditions, the removal of decay heat would only be possible by coolant flow reaching the core through alternative flow paths, such as the core bypass (baffle). There are certain plant specific features that can play a major role in core cooling from this bypass flow. One of these of key interest is the pressure relief holes. A typical 4-loop Pressurized Water Reactor (PWR) was modeled using RELAP5-3D to simulate the reactor system response during the phases of a large break LOCA and the effectiveness of core cooling under full core blockage was analyzed. The simulation results showed that the presence of alternative flow paths may significantly increase core coolability and prevent cladding temperatures from reaching safety limits, while the lack of LOCA holes may lead to a conservative over-prediction of the cladding temperature.

Passive Thermosyphon Cooling System for High Heat Flux Servers

2015 ◽  
Author(s):  
Sylwia Szczukiewicz ◽  
Nicolas Lamaison ◽  
Jackson B. Marcinichen ◽  
John R. Thome ◽  
Peter J. Beucher
Keyword(s):  
Heat Flux ◽  
Cooling System ◽  
Cost Savings ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Net Benefit ◽  
Operation Performance ◽  
Two Phase ◽  
Cooling Loop

The main aim of the current paper is to demonstrate the capability of a two-phase closed thermosyphon loop system to cool down a contemporary datacenter rack, passively cooling the entire rack including its numerous servers. The effects on the performance of the entire cooling loop with respect to the server orientation, micro-evaporator design, riser and downcomer diameters, working fluid, and approach temperature difference at the condenser have been modeled and simulated. The influence of the thermosyphon height (here from 5 to 20 cm with a horizontally or vertically oriented server) on the driving force that guarantees the system operation whilst simultaneously fulfilling the critical heat flux (CHF) criterion also has been examined. In summary, the thermosyphon height was found to be the most significant design parameter. For the conditions simulated, in terms of CHF, the 10 cm-high thermosyphon was the most advantageous system design with a minimum safety factor of 1.6 relative to the imposed heat flux of 80 W cm−2. Additionally, a case study including an overhead water-cooled heat exchanger to extract heat from the thermosyphon loop has been developed and then the entire rack cooling system evaluated in terms of cost savings, payback period, and net benefit per year. This approximate study provides a general understanding of how the datacenter cooling infrastructure directly impacts the operating budget as well as influencing the thermal/hydraulic operation, performance, and reliability of the datacenter. Finally, the study shows that the passive two-phase closed loop thermosyphon cooling system is a potentially economically sound technology to cool high heat flux servers of datacenters.

scholarly journals Numerical Study of a Cooling System Using Phase Change of a Refrigerant in a Thermosyphon

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3634
Author(s):  
Grzegorz Czerwiński ◽  
Jerzy Wołoszyn
Keyword(s):  
Mass Transfer ◽  
Phase Change ◽  
Heat Dissipation ◽  
Cooling System ◽  
Numerical Study ◽  
Relaxation Parameter ◽  
Phase Changes ◽  
Transfer Time ◽  
Two Phase ◽  
Time Relaxation

With the increasing trend toward the miniaturization of electronic devices, the issue of heat dissipation becomes essential. The use of phase changes in a two-phase closed thermosyphon (TPCT) enables a significant reduction in the heat generated even at high temperatures. In this paper, we propose a modification of the evaporation–condensation model implemented in ANSYS Fluent. The modification was to manipulate the value of the mass transfer time relaxation parameter for evaporation and condensation. The developed model in the form of a UDF script allowed the introduction of additional source equations, and the obtained solution is compared with the results available in the literature. The variable value of the mass transfer time relaxation parameter during condensation rc depending on the density of the liquid and vapour phase was taken into account in the calculations. However, compared to previous numerical studies, more accurate modelling of the phase change phenomenon of the medium in the thermosyphon was possible by adopting a mass transfer time relaxation parameter during evaporation re = 1. The assumption of ten-fold higher values resulted in overestimated temperature values in all sections of the thermosyphon. Hence, the coefficient re should be selected individually depending on the case under study. A too large value may cause difficulties in obtaining the convergence of solutions, which, in the case of numerical grids with many elements (especially three-dimensional), significantly increases the computation time.

A Pumped Two-Phase Cooling System for Spacecraft

1983 ◽  
Author(s):  
S. Ollendorf ◽  
F. A. Costello
Keyword(s):  
Cooling System ◽  
Two Phase ◽  
Two Phase Cooling

Model Predictive Control of a Pumped Two-Phase Cooling System With Microchannel Heat Exchangers

2018 ◽  
Author(s):  
Oyuna Angatkina ◽  
Andrew Alleyne
Keyword(s):  
Heat Flux ◽  
Model Predictive Control ◽  
Predictive Control ◽  
Heat Exchangers ◽  
Cooling System ◽  
High Heat ◽  
High Heat Flux ◽  
Two Phase ◽  
Cooling Systems ◽  
Two Phase Cooling

Two-phase cooling systems provide a viable technology for high–heat flux rejection in electronic systems. They provide high cooling capacity and uniform surface temperature. However, a major restriction of their application is the critical heat flux condition (CHF). This work presents model predictive control (MPC) design for CHF avoidance in two-phase pump driven cooling systems. The system under study includes multiple microchannel heat exchangers in series. The MPC controller performance is compared to the performance of a baseline PI controller. Simulation results show that while both controllers are able to maintain the two-phase cooling system below CHF, MPC has significant reduction in power consumption compared to the baseline controller.

Harmonic Synthesis Design Methodology for Dynamic Spring Balancing

1996 ◽  
Vol 118 (4) ◽  
pp. 733-740 ◽  
Author(s):  
Eungsoo Shin ◽  
D. A. Streit
Keyword(s):  
Dynamic System ◽  
Initial Conditions ◽  
Phase 1 ◽  
System Optimization ◽  
Optimization Method ◽  
Optimization Techniques ◽  
System Response ◽  
Two Phase ◽  
Walking Machine ◽  
Synthesis Design

A new spring balancing technique, called a two-phase optimization method, is presented. Phase 1 uses harmonic synthesis to provide a system configuration which achieves an approximation to a desired dynamic system response. Phase 2 uses results of harmonic synthesis as initial conditions for dynamic system optimization. Optimization techniques compensate for nonlinearities in machine dynamics. Example applications to robot manipulators and to walking machine legs are presented and discussed.

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