Heat and Mass Transfer With Phase Change and Chemical Reactions in Microscale

2010 ◽  
Author(s):  
Vladimir V. Kuznetsov
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mass Transfer ◽  
Phase Change ◽  
Heat And Mass Transfer ◽  
Chemical Reactions ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Microscale Flow ◽  
Explosive Evaporation

In recent years considerable attention has been paid to the study of microscale flow and heat transfer with phase change and chemical reactions. This article reviews the patterns of the microscale two-phase gas-liquid flow, the statistical parameters of slug flow and capillary phenomena in annular flow for a rectangular microchannel. The evaporative and condensing heat transfer model for the curved liquid microfilm in microchannel and near contact line is developed and discussed. The influence of forced convection, nucleate boiling and thin film evaporation on microscale flow boiling heat transfer is reviewed and analyzed. The model of forced boiling heat transfer in microchannel is developed and compared with the existing experimental data. The mechanism and patterns of microscale explosive evaporation in the MEMS system is determined at high external heat flux density and the acousto-thermal model of the explosive evaporation is considered. The results of calculations are compared with the experimental data. The peculiarities of heat and mass transfer in a micro channel with surface catalytic reactions producing the hydrogen are presented. The kinetics of sequence of chemical reactions at nanoscale catalyst under conditions of significant nonuniformity of temperature and species concentration fields is considered.

An Overview: Analysis of Heat and Mass Transfer in Fractal Media by Fractal Geometry and Technique

2010 ◽  
Author(s):  
Boming Yu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Porous Media ◽  
Heat And Mass Transfer ◽  
Oil Recovery ◽  
Fractal Geometry ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Fractal Media ◽  
Nucleate Boiling Heat Transfer

In the past three decades, fractal geometry and technique have received considerable attention due to its wide applications in sciences and technologies such as in physics, mathematics, geophysics, oil recovery, material science and engineering, flow and heat and mass transfer in porous media etc. The fractal geometry and technique may become particularly powerful when they are applied to deal with random and disordered media such as porous media, nanofluids, nucleate boiling heat transfer. In this paper, a summary of recent advances is presented in the areas of heat and mass transfer in fractal media by fractal geometry technique. The present overview includes a brief summary of the fractal geometry technique applied in the areas of heat and mass transfer; thermal conductivities of porous media and nanofluids; nucleate boiling heat transfer. A few comments are made with respect to the theoretical studies that should be made in the future.

Study of Condensation Flow Patterns and Heat Transfer Characteristic on a Horizontal Tube Bundle

2016 ◽  
Author(s):  
Hongfang Gu ◽  
Qi Chen ◽  
Zhe Zhang ◽  
Haiyang Guo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mass Transfer ◽  
Flow Regime ◽  
Heat And Mass Transfer ◽  
Tube Bundle ◽  
Flow Patterns ◽  
Heat Transfer Characteristics ◽  
Controlled Flow ◽  
Condensation Flow

The numerous studies on condensation flow patterns and heat transfer were focused on the horizontal inside single tube. A number of heat and mass transfer correlations are used for design of shellside condensers based on tubeside condensation flow regimes. Due to a complex geometry and measurement difficulty in a tube bundle, there are few publications reported on shellside condensation flow regime and heat transfer characteristics. To investigate the condensation flow patterns and heat and mass transfer mechanism at the different flow regimes, a horizontal shellside condenser was tested from a multipurpose condensation rig recently. The horizontal test bundle is made of 36 tubes with the staggered tube layout. The tube OD is 19 mm and the tube length is 1.0 m using stainless steel. Four visualization windows were placed on the front and back sides on the shell for photographing condensation flow patterns. Steam and steam/air mixture were used as the test fluids. The condensation flow patterns, condensate film thickness and droplets distribution were recorded using a high-speed digital camera at a wide range of condensation process conditions. The experimental data show that the condensation flow regime changes from the shear-controlled flow to gravity-controlled flow depending on the vapor and condensate loads, bundle location and the concentration of the non-condensable gas. These experimental data provide a fundamental approach for developing the heat and mass transfer correlateons at different shellside condensation patterns. This paper presents the experimental result on shellside condensation patterns associated with heat transfer characteristics.

scholarly journals Progress in understanding the four dominant intra-particle phenomena of lignocellulose pyrolysis: chemical reactions, heat transfer, mass transfer, and phase change

2019 ◽  
Vol 21 (11) ◽  
pp. 2868-2898 ◽  
Author(s):  
M. Brennan Pecha ◽  
Jorge Ivan Montoya Arbelaez ◽  
Manuel Garcia-Perez ◽  
Farid Chejne ◽  
Peter N. Ciesielski
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Phase Change ◽  
Chemical Reactions ◽  
Phase Changes ◽  
Lignocellulosic Materials

Four principal intra-particle phenomena occur in a highly concerted manner during the pyrolysis of lignocellulosic materials: heat transfer, mass transfer, chemical reactions, and phase changes.

Heat Transfer and Air Diffusion Phenomena in a Bed of Polymer Powder Using Apparent Heat Capacity Method: Application to the Rotational Molding Process

2007 ◽  
Author(s):  
M. Boutaous ◽  
E. Pe´rot ◽  
A. Maazouz ◽  
P. Bourgin ◽  
P. Chantrenne
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Heat And Mass Transfer ◽  
Granular Media ◽  
Transfer Model ◽  
Melting Front ◽  
Polymer Powder ◽  
Air Diffusion

The process of rotational moulding consists in manufacturing plastic parts by heating a polymer powder in a biaxial rotating mould. In order to optimise the production cycle of this process, a complete simulation model has to be used. This model should describe the phenomena of heat and mass transfer in a moving granular media with phase change, coalescence, sintering, air evacuation and crystallization during the cooling stage. This paper focus on the study of heat and mass transfer in a quiescent polymer powder during the heating stage. An experimental device has been built. It consists in an open plane static mold on which an initial thickness, e, of a polymer powder is deposited. This powder is then heated until it melts. An inverse heat conduction method is used to determine the heat flux and temperature at the interface between the mold and the powder. This interfacial heat flux is taken as a boundary condition in a numerical heat transfer model witch takes into account the heat transfer in granular media with phase change, coalescence, sintering, air bubbles evacuation and rheological behaviour of the polymer. For the numerical simulation of the heat transfer, the apparent specific heat method is used. This approach allows to solve the same energy equation for all the material phases, so one do not have to calculate the melting front evolution. This fine modelling, close to the real physical phenomena makes it possible to estimate the temperature profile and the evolution of the polymer powder characteristics (phase change, air diffusion, viscosity, evolution of the thermophysical properties of the equivalent homogeneous medium, thickness reduction, air volume fraction...). Several results are then presented, and the influence of different parameters, like the thermal contact resistance, the process initial conditions and the polymer’s rheological characteristics are studied and commented. Indeed the predictions of the temperature rises in the polymer bed, agree well with the experimental measurements.

Review: General Issues and Correlations for Predicting Flow Boiling Heat Transfer Coefficients in Micro-Scale Channels

2015 ◽  
Vol 23 (04) ◽  
pp. 1530003 ◽  
Author(s):  
Chang Yong Park
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Inertial Force ◽  
Viscous Force ◽  
Vapor Quality ◽  
Micro Scale ◽  
Continuous Decrease ◽  
Flow Boiling Heat Transfer

A review study was performed for basic heat transfer mechanism and quantitative analysis of correlations for flow boiling heat transfer in micro-scale channels. Several criteria for determining threshold diameter for micro-scale channels were discussed and the concept of confinement number was commented. The distinctive feature of flow boiling in micro-scale channels were considered and it was found out that the effect of the heat flux, latent heat, viscous force, surface tension, and inertial force was more significant. Important dimensionless parameters were summarized and it was pointed out that the boiling number, capillary number, and Weber number could be expected to play important roles at flow boiling in micro-scale channels. 17 correlations for flow boiling in micro-scale channels were reviewed in this study, and they were categorized by three types of correlations such as an equivalent Nusselt number correlation, a correlation with superposition of nucleate and convection boiling mechanism, and a flow pattern-based correlation. The predicted values by the correlations were compared with 536 experimental data from four different literatures and a correlation with smallest prediction errors was found. Some correlations showed distinct trends of convection heat transfer coefficient (h) change with respect to the variation of vapor quality. The trends are categorized by three trends such as noticeable increase of h with the increase of vapor quality and significant continuous decrease after dryout point, minor increase and decrease or decrease and increase of h, and gradual and continuous decrease of h with the increase of vapor quality. For each trend of h change, recommendable correlations and their basic equation forms were proposed to compare the prediction results with experimental data or to develop a new correlation by modifying existing correlations.

Study of Heat and Mass Transfer in MgCl2/NH3 Thermochemical Batteries

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Seyyed Ali Hedayat Mofidi ◽  
Kent S. Udell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Phase Change ◽  
Heat And Mass Transfer ◽  
Waste Heat ◽  
Experimental Studies ◽  
Reaction Rates ◽  
Solid Matrix ◽  
Dominant Factor ◽  
Gaseous Ammonia

Intermittency of sustainable energy or waste heat availability calls for energy storage systems such as thermal batteries. Thermochemical batteries based on a reversible solid–gas (MgCl2–NH3) reactions and NH3 liquid–gas phase change are of specific interest since the kinetics of absorption are fast and the heat transfer rates for liquid–vapor phase change are high. Thus, a thermochemical battery based on reversible reaction between magnesium chloride and ammonia was studied. Two-dimensional experimental studies were conducted on a reactor in which temperature profiles within the solid matrix and pressure and flow rates of gas were obtained during discharging processes. A numerical model based on heat and mass transfer within the salt and salt–gas reactions was developed to simulate the NH3 absorption processes within the solid matrix, and the results were compared with experimental data to determine dominant heat and mass transfer processes within the salt. It is shown that for high permeability salt beds, the reactor uniformly adsorbs gaseous ammonia until the bed reaches the equilibrium temperature, then adsorbs gas near the cooled boundaries as the reaction front moves inward. In that mode, the heat transfer is the dominant factor in determining reaction rates.

Progress in the Modeling and Simulation of Flow Boiling Heat Transfer of Binary Fluids Using Advanced Multi-Fluid Modeling Techniques

2012 ◽  
Author(s):  
Vedanth Srinivasan ◽  
Rok Kopun
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Wide Range

In this paper, we discuss the implementation and testing of a novel boiling mass transfer model to simulate the thermal and phase transformation behavior, generated due to boiling of binary mixtures, using the commercial CFD code AVL FIRE® v2011. The phase change model, based on detailed bubble dynamics effects, is solved in conjunction with incompressible phasic momentum, turbulence and energy equations in a segregated fashion, to study the flow boiling process inside a rectangular duct. Full three dimensional validation studies including the effect of flow velocity and exit pressure conditions, acting on a wide range of operating wall (superheat) temperatures, clearly shows the suppression of heat and mass transfer coefficients with enhancement in flow convection. Competing mechanisms such as phase change process and turbulent convection are identified to influence the heat transfer characteristics. In particular, the varying influence of the mass transfer effects on the heat flux characteristics with alteration in wall temperature is well demonstrated. Comparisons of the predicted total heat flux, computed as the sum of the convection and phase change components, indicate a very good agreement with experimental data, wherever available. Description of the flow field inclusive of phasic fraction, temperature and velocity field provides extensive details of the multiphase behavior of the boiling flow. Some preliminary results on the phase change work flow to model heat transfer in cooling jackets, for automotive applications, is also discussed.

Minichannel Heat Transfer: An Overview on Activities in Europe

2003 ◽  
Author(s):  
Manfred Groll ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Pressure Drop ◽  
Heat And Mass Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Pool Boiling ◽  
Current Status ◽  
Narrow Channels ◽  
Evaporation Heat

An overview will be given about investigations on heat and mass transfer in narrow channels and narrow cavities, from work carried out in the last years up to the current status of research of some relevant scientific groups in Europe. The major topics of this report are evaporation heat transfer and the flow boiling pressure drop in narrow channels; microscale heat and mass transfer phenomena in pool boiling from enhanced evaporator tubes with sub-surface channels are also addressed. In the last years a challenging topic has been the enhancement of the efficiency of heat exchangers by employing micro-structured heat transfer surfaces. The need for smaller heat exchangers with higher heat transfer rates and/or smaller thermal approaches is caused by the ongoing miniaturisation of mechanical and electronic components, leading to higher heat fluxes which can damage or even destroy the components. On the other hand, enhanced heat transfer in big equipment, e.g. heat exchangers for the petrochemical and chemical industries, can lead to significant materials and energy savings and thus reduce environmental pollution. Therefore the European Union, European industries and national organisations have supported various projects to develop and to investigate a new generation of heat transfer surfaces, to better understand the related heat transfer phenomena and to model the heat transfer from these micro heat exchanger elements. There is a very extensive research in this scientific field, comprising both flow boiling and pool boiling. The present paper deals with heat transfer in narrow channels and/or cavities and with the flow boiling pressure drop occurring during heat and mass transfer in narrow channels. Investigations of major European institutions, carried out in the past and at the moment will be presented as a contribution to the overview on the current state-of-the-art in Europe, without claim of completeness. Some recent results on microscale pool boiling and flow boiling obtained in our institute will also be presented (Shuai et al., 2002; Kulenovic et al., 2002; Chen et al., 2002a, b).

Assessment of Flow Boiling Heat Transfer Correlations for Application to Mini-Channels

2006 ◽  
Author(s):  
Nurudeen O. Olayiwola ◽  
S. Mostafa Ghiaasiaan
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Forced Flow ◽  
Transfer Mode ◽  
Micro Channels ◽  
Mini Channels ◽  
Feasible Range ◽  
Conventional Cooling

Cooling systems that consist of mini-channels (channels with hydraulic diameters in the 0.5 mm to 2.0 mm range) and micro-channels (channels with hydraulic diameters in the 100 μm-500 μm range) can dispose of large volumetric thermal loads that are well beyond the feasible range of conventional cooling methods. Mini/micro-channel systems that utilize boiling fluids are particularly useful due to the superiority of boiling heat transfer mode over single-phase flow convention. Flowing boiling in mini and micro channels has been investigated experimentally by several research groups recently, and a number of empirical correlations have been developed, usually based on only a single set of experimental data. In this study, the capability of a number of widely used forced flow boiling correlations for application to mini channels is examined by comparing their predictions with experimental data from three separate sources. The tested correlations include well-established methods for conventional boiling systems, as well as correlations recently proposed for mini-channels. The experimental data all represent mini-channels. Based on these comparisons, the most accurate existing predictive methods for the tested mini-channel boiling data are identified.

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