scholarly journals Modeling Microwave Heating and Drying of Lignocellulosic Foams through Coupled Electromagnetic and Heat Transfer Analysis

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 2001
Author(s):  
Mohammad Tauhiduzzaman ◽  
Islam Hafez ◽  
Douglas Bousfield ◽  
Mehdi Tajvidi
Keyword(s):  
Heat Transfer ◽  
Microwave Heating ◽  
Microwave Power ◽  
Expanded Polystyrene ◽  
Experimental Results ◽  
Microwave Drying ◽  
Heat Transfer Analysis ◽  
Water Evaporation ◽  
Time Behavior ◽  
Novel Method

Microwave drying of suspensions of lignocellulosic fibers has the potential to produce porous foam materials that can replace materials such as expanded polystyrene, but the design and control of this drying method are not well understood. The main objective of this study was to develop a microwave drying model capable of predicting moisture loss regardless of the shape and microwave power input. A microwave heating model was developed by coupling electromagnetic and heat transfer physics using a commercial finite element code. The modeling results predicted heating time behavior consistent with experimental results as influenced by electromagnetic fields, waveguide size and microwave power absorption. The microwave heating modeling accurately predicted average temperature increase for 100 cm3 water domain at 360 and 840 W microwave power inputs. By dividing the energy absorption by the heat of vaporization, the amount of water evaporation in a specific time increment was predicted leading to a novel method to predict drying. Using this method, the best time increments, and other parameters were determined to predict drying. This novel method predicts the time to dry cellulose foams for a range of sample shapes, parameters, material parameters. The model was in agreement with the experimental results.

Application of an Object-Oriented CFD Code to Heat Transfer Analysis

2008 ◽  
Author(s):  
Luca Mangani ◽  
A. Andreini
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Lateral Spreading ◽  
Impinging Jets ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Specific Class ◽  
Turbine Cooling ◽  
Numerical Predictions ◽  
High Flexibility

This paper is aimed at showing the performances obtained with an open-source CFD code for heat transfer predictions after the addiction of specific modules. The development steps to make this code suitable for such simulations are described in order to point out its potentiality as a customizable CFD tool, appropriate for both academic and industrial research. The C++ library, named OpenFOAM, offers specific class and polyhedral finite volume operators thought for continuum mechanics simulations as well as built-in solvers and utilities. To make it robust, fast and reliable for RANS heat transfer predictions it was indeed necessary to implement additional submodules. The package coded by the authors within the OpenFOAM environment includes a suitable algorithm for compressible steady-state analysis. A SIMPLE like algorithm was specifically developed to extend the operability field to a wider range of Mach numbers. A set of Low-Reynolds eddy-viscosity turbulence models, chosen amongst the best performing in wall bounded flows, were developed. In addition an algebraic anisotropic correction, to increase jets lateral spreading, and an automatic wall treatment, to obtain mesh independence, were added. The results presented cover several types of flows amongst the most typical for turbomachinery and combustor gas turbine cooling devices. Impinging jets were investigated as well as film and effusion cooling flows, both in single and multi-hole configuration. Numerical predictions for wall effectiveness and wall heat transfer coefficient were tested against standard literature and in-house set-up experimental results. The numerical predictions obtained proves to be in-line with the equivalent models of commercial CFD packages obtaining a general good agreement with the experimental results. Moreover during the tests OpenFOAM code has shown a good accuracy and robustness, as well as an high flexibility in the implementation of user-defined submodules.

Heat Transfer Controlled Collapse of a Cylindrical Vapor Bubble in a Vertical Isothermal Tube

1977 ◽  
Vol 99 (3) ◽  
pp. 392-397 ◽  
Author(s):  
D. R. Pitts ◽  
H. C. Hewitt ◽  
B. R. McCullough
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Experimental Program ◽  
Bubble Collapse ◽  
Electric Heater ◽  
Vapor Bubbles ◽  
Experimental Apparatus

An experimental program was conducted to determine the collapse rate of slug-type vapor bubbles rising due to buoyancy through subcooled parent liquid in a vertical isothermal tube. The experimental apparatus included a vertical glass tube with an outer glass container providing a constant temperature water bath for the inner tube. The inner tube contained distilled, deaerated water, and water vapor bubbles were generated at the bottom of this tube with a pulsed electric heater. The parent liquid was uniformly subcooled with respect to the vapor bubble resulting in heat transfer controlled bubble collapse. Collapse rates and rise velocities were recorded by high-speed motion picture photography. Over a limited range of subcooling, the bubble collapse was well behaved, and a simple, quasi-steady boundary layer heat transfer analysis adapted from slug flow over a flat plate correlated the experimental results with a high degree of accuracy. Experimental results were obtained with tubes having inside diameters of 0.0127, 0.0218, and 0.0381 m and for a range of subcooling from 0.5 to 9.0 K.

Thermal Performance Model for Spacesuit Waste Heat Rejection Using Water Membrane Evaporators

2010 ◽  
Vol 2 (3) ◽  
Author(s):  
Y. Janeborvorn ◽  
T. P. Filburn ◽  
C. C. Yavuzturk ◽  
E. K. Ungar
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Waste Heat ◽  
Water Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Performance Model ◽  
Heat Transfer Analysis ◽  
Water Evaporation ◽  
Heat Rejection

Hydrophobic, micropore membrane evaporators are studied for use in waste heat rejection in new generation spacesuits developed by the U.S. National Aeronautics and Space Administration (NASA). The waste heat rejection is accomplished via evaporation of liquid water through membrane pores, whereby the hydrophobic membrane allows only water vapor to pass through and retains the liquid phase inside the membrane water channel, allowing the waste heat rejection through the proposed spacesuit water membrane evaporator (SWME) system to be significantly less sensitive to contamination while improving the overall contaminant and system control. Although SWME uses the same heat transport loop as used in current NASA sublimator systems, thus eliminating the need for a separate feedwater system, it permits the system configuration to be simpler and more compact while also eliminating corrosion problems and reducing system freeze-up potential. An improved thermal performance model based on membrane segment energy balances is presented, which is a spacesuit water membrane evaporator for a single circular annulus water channel bounded by two annular vapor channels. The model allows for the investigation of the local heat transfer characteristics along the annulus including temperature gradients in the membrane wall and the water channel using a steady-state approach. The model also accounts for the effects of thermal and hydraulic entry lengths, far field radiation, and energy carried away by the mass of water evaporation. The local heat transfer analysis enables the straightforward calculation of the overall magnitude of heat transfer from the SWME. A model validation is presented via the sum of the squares error analyses between the model predictions and the experimental results.

Numerical Simulation of Thermal Performance of a High Aspect Ratio Thermal Energy Storage Device

2012 ◽  
Author(s):  
Jingde Zhao ◽  
Jorge L. Alvarado ◽  
Ehsan M. Languri ◽  
Chao Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Aspect Ratio ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Aspect Ratio ◽  
Numerical Study ◽  
Experimental Results ◽  
Heat Transfer Analysis

Heat transfer analysis of a high aspect ratio thermal energy storage (TES) device was carried out numerically. The three dimensional numerical study was performed to understand the heat transfer enhancement which results from internal natural convection in a high aspect ratio vertical unit. Octadecane was used as phase change material (PCM) inside TES system, which consisted of six corrugated panels filled with PCM. Each panel had a total of 6 tall cavities filled with PCM, which were exposed to external flow in a concentric TES system. Unlike traditional concentric-type TES devices where heat transfer by conduction is the dominant heat transport mechanism, the high aspect ratio TES configuration used in the study helped promote density-gradient based internal convection mechanism. The numerical model was solved based on the finite volume method, which captured the whole transient heat transfer process effectively. The time-dependent temperature profiles of the PCM inside a single TES panel are compared with the experimental results for two cases. Numerical and experimental results of the two cases showed a reasonable agreement. Furthermore, convection cells were formed and sustained when the PCM melted within the space between the solid core and the walls. The promising results of this numerical study illustrate the importance of internal natural convection on the speed of the PCM melting (charging) process.

Experimental Measurement of Water Evaporation Rates Into Air and Superheated Steam

1988 ◽  
Vol 110 (1) ◽  
pp. 237-242 ◽  
Author(s):  
M. Haji ◽  
L. C. Chow
Keyword(s):  
Heat Transfer ◽  
Superheated Steam ◽  
Evaporation Rate ◽  
Free Stream ◽  
Experimental Results ◽  
Water Evaporation ◽  
Analytical Prediction ◽  
Conduction Heat Transfer ◽  
Inversion Temperature ◽  
Analytical Results

The rates of evaporation of water from a horizontal water surface into a turbulent stream of hot air or superheated steam at different free-stream mass fluxes and modulated temperatures were experimentally measured. The pressure of the free stream was atmospheric. For steam, the experimental results are mostly within 10 percent of the available analytical results. Two previous experimental results are about 50 percent and 300 percent higher than the analytical results. For air, the measured evaporation rates are consistently higher than the analytical results. An estimate of the conduction heat transfer from the walls of the test section to water was made for several air tests. If the conduction heat transfer were subtracted from the total heat transfer, the measured evaporation rates are actually quite close to the analytical results. The present experiment also confirms the existence of a temperature, called the inversion temperature, below which the water evaporation rate is higher in air than in steam, but above which the opposite is true. The inversion temperature is in good agreement with the analytical prediction. The results for both air and superheated steam show that a certain scaled expression for the evaporation rate is independent of the free-steam mass flux, also in agreement with the analytical prediction.

Study of Heat Transfer and Freezing Time-Temperature Behavior of Individual Pea Grains by Numerical and Experimental Methods

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Manoj Kumar Sharma ◽  
Anil Kumar Pratihar
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Transient Heat Conduction ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Temperature History ◽  
Transient Temperature ◽  
Freezing Time ◽  
Air Stream ◽  
Cooling Air

Abstract The present research demonstrates an accurate and simple numerical model for heat transfer analysis within spherical peas when exposed to the cold air stream in a rectangular duct. The transient heat conduction equation (THCE) is solved for spherical shaped pea grains. A detailed numerical and experimental study of freezing time-temperature history for peas has been carried out. Thermal conductivity and volumetric heat capacity are measured experimentally. Temperature-dependent thermophysical properties are used in the transient temperature prediction of peas throughout the phase change process. Crank–Nicolson method has been used for the formulation of the numerical model. The effect of important parameters, viz., the initial temperature of peas, cooling air temperature, and cooling air velocity over pea samples has been studied both numerically as well as experimentally and it has been found that there is good agreement between numerical and experimental results. The correlation coefficient of linear regression, R2, between numerically predicted and experimental results, is found to be 0.987.

Heat Transfer Analysis of a Wedge Shaped Duct With Pin Fin and Pedestal Arrays: A Comparison Between Numerical and Experimental Results

2004 ◽  
Author(s):  
Antonio Andreini ◽  
Carlo Carcasci ◽  
Andrea Magi
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Bottom Surface ◽  
Mean Flow ◽  
Trailing Edge ◽  
Pin Fin

The use of pin fin arrays in channels is one of the best choices to enhance overall heat transfer in gas turbine trailing edge blade cooling. Furthermore, in this particular application, the use of cross-pins in the trailing edge section of a turbine blade is a good way for supplying structural integrity to the blade itself. In this paper, results of several 3D RANS calculations performed in channels with cross-pins disposition such as in a typical trailing edge of a gas turbine blade are shown. Numerical calculations were compared with experimental results obtained on the same geometries using a transient Thermochromic Liquid Crystals (TLC) based technique. Goals of this comparison are both the evaluation of the accuracy of CFD packages with standard two equation turbulence models in heat transfer problems with complex geometries and the analysis of flow details to complete and support experimental activity. Two computational domains have been considered: they both consist in a wedge shaped channel with a stream-wise normal pin fin or pedestal arrays. The aim of the numerical analysis is the evaluation of convective Heat Transfer Coefficient (HTC) on the planar bottom surface of the wedge-shaped duct: this surface is commonly named “endwall” surface. Detailed analysis of the flow field points out the coexistence of an horse-shoe vortex, a stagnant wake behind the pin and a mean flow acceleration due to convergent shape of the channel. Calculations reveal the presence of a weak jet-like flow field toward endwall surfaces caused by the strong recirculation behind each pin.

CFD and Heat Transfer Analysis of Vortex Formation in a Solar Reactor

2014 ◽  
Author(s):  
Min-Hsiu Chien ◽  
Nesrin Ozalp ◽  
Gerald Morrison
Keyword(s):  
Heat Transfer ◽  
Room Temperature ◽  
Vortex Flow ◽  
Fluid Velocity ◽  
Vortex Formation ◽  
Flow Dynamics ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Axial Position ◽  
Solar Reactor

A hydrogen producing solar reactor was experimentally tested to study the cyclone flow dynamics of the gas-particle two-phase phenomenon. Two dimensional PIV (particle image velocimetry) was used to observe the flow and to quantify the vortex formation inside the solar reactor. The vortex flow structure in the reactor was reconstructed by capturing images from orientations perpendicular and parallel to the geometrical axis of the reactor respectively. The experimental results showed that the tangential components of the fluid velocity formed a Rankine-vortex profile. The free vortex portions of the Rankine profile were synchronized and independent of the axial position. The axial components showed a vortex funnel of higher speed fluid supplied by a reversing secondary flow. According to the inlet channel design, the geometry dominates the flow dynamics. A stable precessing vortex line was observed. As the vortex flow evolves towards the exit, the vortex funnel expands radially with decreasing tangential velocity magnitude peak as a result of the vortex stretching. An optimal residence time of the flow was found by changing the cyclone flow inlet conditions. The swirl number versus the main flow rate change was obtained. Upon the completion of the experimental studies, a thorough numerical analysis was conducted to model the flow dynamics inside the solar reactor and to verify the results by comparison to the experimental results. Three turbulence models including the standard k-ε, k-ε RNG and Reynolds Stress Transport models were used. CFD simulations were coupled with heat transfer analysis via Discrete Ordinate model. Particle tracing in Lagrange frame was applied to simulate the particle trajectory. A comparison between the turbulence modeling results for the room temperature and high temperature cases, as well as the experimental results for room temperature cases is presented.

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