Numerical Simulation of Transient Boiling Convection in Microchannels

2003 ◽  
Author(s):  
D. W. Fogg ◽  
J. M. Koo ◽  
L. Jiang ◽  
K. E. Goodson
Keyword(s):  
Heat Exchangers ◽  
Energy Transport ◽  
Pressure Fluctuations ◽  
Bubble Nucleation ◽  
Transient Pressure ◽  
Two Phase ◽  
Convective Boiling ◽  
Periodic Distribution ◽  
Wall Superheat ◽  
Transient Boiling

Two-phase microchannel heat exchangers are receiving increasing attention from the microprocessor industry as power density levels in microchips increase. Previous numerical investigations of convective boiling in microchannels assumed steady flow within the channels. However, experimental data shows that two-phase flows in microchannels are highly transient even under steady heat loads. Little work has been done to model the dynamics associated with vapor generation in microchannels. The present work simulates the periodic distribution of vapor within microchannels filled with water by solving one-dimensional homogeneous equations for the mass, momentum and energy transport in conjunction with a transient wall conduction equation. A wall superheat constraint is incorporated to account for the excess superheat temperature required for bubble nucleation. Boiling events reduce the local wall temperature and change the pressure and enthalpy distributions within the flow. The transient pressure fluctuations predicted here are consistent with those observed in experiments. This study provides insight into the significance of bubble nucleation for forced convective boiling in microchannels and will be useful for the optimization of microchannel heat exchangers.

Numerical Solution for Transient Conjugate Two-Phase Heat Transfer With Heat Generation in the Pipe Wall

2002 ◽  
Vol 124 (6) ◽  
pp. 1213-1218 ◽  
Author(s):  
Yuri V. Fairuzov ◽  
Hector Arvizu
Keyword(s):  
Heat Transfer ◽  
Numerical Solution ◽  
Heat Generation ◽  
Two Phase ◽  
Convective Boiling ◽  
Wall Superheat ◽  
Boiling Flow ◽  
Rigorous Model ◽  
Two Phase Heat Transfer ◽  
Transient Boiling

A method developed earlier for modeling conjugate two-phase heat transfer in flashing flows was used to obtain a numerical solution for transient boiling flow in heated pipes or channels. Two criteria of applicability of the solution obtained were proposed and numerically tested using a more rigorous model, which accounts for the effects of heat conduction with heat generation in the wall and forced convective boiling. The solution obtained provides a simple and reliable alternative to more rigorous methods for modeling transient two-phase flow in heated channels when the material of the wall bounding the flow has a high thermal conductivity and the wall superheat is small.

Modeling of Two-Phase Flow Structure Evolution in Subcooled Nucleate Convective Boiling With Coupling of Bubble-Tracking and Two-Fluid Models

2008 ◽  
Author(s):  
Ivo Kljenak ◽  
Bosˇtjan Koncˇar ◽  
Luka Sˇtrubelj ◽  
Borut Mavko
Keyword(s):  
Fluid Model ◽  
Three Dimensional ◽  
Vertical Channel ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Structure Evolution ◽  
Two Phase ◽  
Convective Boiling ◽  
Tracking Model ◽  
Two Fluid

A model of subcooled nucleate boiling flow in a vertical channel at low-pressure conditions is proposed. The model consists of a three-dimensional bubble-tracking model and a two-dimensional two-fluid model which are coupled off-line. By taking into account dynamic phenomena (liquid flow, bubble motion and interaction) and thermal phenomena (liquid heating, bubble nucleation and condensation), the model is able to simulate the gradual evolution of void fraction profiles along the boiling channel. The model is assessed by simulating experiments that were performed at Purdue University (USA) at atmospheric pressure in a vertical annulus with a central heating rod.

CARPENTER STAINLESS No. 7-Mo

Alloy Digest ◽  
1974 ◽  
Vol 23 (7) ◽  
Keyword(s):  
Fracture Toughness ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Heat Exchangers ◽  
Heat Treating ◽  
General Corrosion ◽  
Annealed Condition ◽  
Two Phase ◽  
Temperature Performance ◽  
Resistance To Stress

Abstract CARPENTER STAINLESS No. 7-Mo is a two-phase alloy consisting of a ferritic matrix with pools of austenite. It has high resistance to stress-corrosion cracking and pitting, and good general corrosion resistance in many environments. Its principal use is for tubing and pipe in heat exchangers involving corrosive conditions. It is normally used in the annealed condition for maximum corrosion resistance and ductility. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on low and high temperature performance, and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-298. Producer or source: Carpenter.

Effects of Varying Geometrical Parameters on Boiling From Microfabricated Enhanced Structures

2003 ◽  
Vol 125 (1) ◽  
pp. 103-109 ◽  
Author(s):  
C. Ramaswamy ◽  
Y. Joshi ◽  
W. Nakayama ◽  
W. B. Johnson
Keyword(s):  
Heat Dissipation ◽  
Layer Structure ◽  
Single Layer ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Small Range ◽  
Two Phase ◽  
Wall Superheat

The current study involves two-phase cooling from enhanced structures whose dimensions have been changed systematically using microfabrication techniques. The aim is to optimize the dimensions to maximize the heat transfer. The enhanced structure used in this study consists of a stacked network of interconnecting channels making it highly porous. The effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid. While most of the previous studies on the mechanism of enhanced nucleate boiling have focused on a small range of wall superheats (0–4 K), the present study covers a wider range (as high as 30 K). A larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes. The effect of stacking multiple layers showed a proportional increase in heat dissipation (with additional layers) in a certain range of wall superheat values only. In the wall superheat range 8–13 K, no appreciable difference was observed between a single layer structure and a three layer structure. A fin effect combined with change in the boiling phenomenon within the sub-surface layers is proposed to explain this effect.

scholarly journals Prediction of Transient Pressure Fluctuations within a Low-Pressure Turbine Cascade Using a Lanczos-Filtered Harmonic Balance Method

2021 ◽  
Vol 6 (3) ◽  
pp. 25
Author(s):  
Jan Philipp Heners ◽  
Stephan Stotz ◽  
Annette Krosse ◽  
Detlef Korte ◽  
Maximilian Beck ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Harmonic Balance ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Harmonic Balance Method ◽  
Low Pressure ◽  
Filter Method ◽  
Turbine Cascade ◽  
Transient Pressure ◽  
Low Pressure Turbine

Unsteady pressure fluctuations measured by fast-response pressure transducers mounted in a low-pressure turbine cascade are compared to unsteady simulation results. Three differing simulation approaches are considered, one time-integration method and two harmonic balance methods either resolving or averaging the time-dependent components within the turbulence model. The observations are used to evaluate the capability of the harmonic balance solver to predict the transient pressure fluctuations acting on the investigated stator surface. Wakes of an upstream rotor are generated by moving cylindrical bars at a prescribed rotational speed that refers to a frequency of f∼500 Hz. The excitation at the rear part of the suction side is essentially driven by the presence of a separation bubble and is therefore highly dependent on the unsteady behavior of turbulence. In order to increase the stability of the investigated harmonic balance solver, a developed Lanczos-type filter method is applied if the turbulence model is considered in an unsteady fashion.

scholarly journals Picking up the hydrothermal whisper at Ischia Island in the Covid-19 lockdown quiet

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mariarosaria Falanga ◽  
Paola Cusano ◽  
Enza De Lauro ◽  
Simona Petrosino
Keyword(s):  
Pressure Fluctuations ◽  
Hydrothermal Fluids ◽  
Shallow Aquifer ◽  
Two Phase ◽  
Spectral Content ◽  
Ischia Island ◽  
Continuous Noise ◽  
Organ Pipes ◽  
Source Signals ◽  
Phase Fluid

AbstractIn this paper, we analyse the seismic noise at Ischia Island (Italy) with the objective of detecting the hydrothermal source signals taking advantage of the Covid-19 quiescence due to lockdown (strong reduction of anthropogenic noise). We compare the characteristics of the background noise in pre-, during and post-lockdown in terms of spectral content, energy release (RMS) and statistical moments. The continuous noise is decomposed into two independent signals in the 1−2 Hz and 2−4 Hz frequency bands, becoming sharpened around 1 Hz and 3 Hz respectively in lockdown. We propose a conceptual model according to which a dendritic system of fluid-permeated fractures plays as neighbour closed organ pipes, for which the fundamental mode provides the persistent whisper and the first higher mode is activated in concomitance with energy increases. By assuming reasonable values for the sound speed in low vapor–liquid mass fraction for a two-phase fluid and considering temperatures and pressures of the shallow aquifer fed by sea, meteoric and deep hydrothermal fluids, we estimate pipe lengths in the range 200–300 m. In this scheme, Ischia organ-like system can play both continuous whisper and transients, depending on the energy variations sourced by pressure fluctuations in the hydrothermal fluids.

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