bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrowetting-Based Coalescence of Droplets During Dropwise Condensation of Humid Air
Authors: Wikramanayake Enakshi , Bahadur Vaibhav 
Published: December 2019

Abstract
Dropwise condensation yields higher heat transfer coefficients by avoiding the thermal resistance of the condensate film, seen during filmwise condensation. This work explores further enhancement of dropwise condensation heat transfer through the use of electrowetting to achieve faster droplet growth via coalescence of the condensed droplets. Electrowetting is a well understood microfluidic technique to actuate and control droplets. This work shows that AC electric fields can significantly enhance droplet growth dynamics. This enhancement is a result of coalescence triggered by various types of droplet motion (translation of droplets, oscillations of three phase line), which in turn depends on the frequency of the applied AC waveform. The applied electric field modifies droplet condensation patterns as well as the roll-off dynamics on the surface. Experiments are conducted to study early-stage droplet growth dynamics, as well as steady state condensation rates under the influence of electric fields. It is noted that this study deals with condensation of humid air, and not pure steam. Results show that increasing the voltage magnitude and frequency increases droplet growth rate and overall condensation rate. Overall, this study reports more than a 30 % enhancement in condensation rate resulting from the applied electric field, which highlights the potential of this concept for condensation heat transfer enhancement.
Effectiveness of Intermittent Personalized Ventilation Assisting Chilled Ceiling in Protecting Occupants Against Active Particles
Authors: Al-Assad Douaa , Ghaddar Nesreen , Ghali Kamel 
Published: December 2019

Abstract
In this work, an intermittent personalized ventilation (PV) system was coupled with a chilled ceiling system in an office space. The ability of this system in protecting occupants from active particulate matter due to an indoor contamination source was investigated. To perform this study, a 3D transient computational fluid dynamics model was used to determine the velocity, thermal, and particle concentration fields in the space. The fluid flow in the space was experimentally validated in previous works in a climatic chamber equipped with a thermal manikin representing an occupant in an office space. The validated model was used to perform a parametric study varying the intermittent PV operating frequency as well as the particle diameter. The results were used to recommend PV operating conditions, which would ensure the protection of occupant against the contaminants present in the macroclimate and deposited on nearby surfaces. It was found that the intermittent PV should operate at an average flow rate of 7.5 L/s and a frequency of 0.73 Hz. These conditions provided acceptable values of intake fraction in the breathing zone and surrounding microclimate and acceptable deposited fractions. Moreover, these conditions provided good thermal comfort levels (0.86: comfortable) and good protection against passive contaminants (εv,BZ = 64 %).
Performance of Intermittent Personalized Ventilation Assisting Mixing Ventilation in the Presence of Indoor Disturbance
Authors: Al-Assad Douaa , Ghali Kamel , Ghaddar Nesreen 
Published: December 2019

Abstract
In this work, an office space is considered, equipped with an intermittent personalized ventilation (PV) system assisting a conventional mixing ventilation system. In ideal offices with no disturbances, it was proven that an intermittent PV average flow rate of 7.5 L/s and frequency of 0.86 Hz could enhance comfort compared to a steady PV and provide protection against contaminants present in the macroclimate. However, office spaces are subject to many disturbances, which could deteriorate the performance of air ventilation systems. In this work, an office door is considered to open disturbing the flow field by establishing pressure gradients. To conduct this study, a 3D computational fluid dynamics model was developed to predict the airflow field variables as well as contaminants’ concentration in the occupant-breathing zone. The model was used to assess the ability of the ventilation systems in maintaining its optimal operating parameters (0.86 Hz) obtained in ideal conditions. Results showed that the optimal PV frequency did not assure the same level of air quality. In fact, ventilation effectiveness decreased by 18% due to the opening door which pulled the PV jet away from the occupant’s breathing zone (BZ). Therefore, in office spaces with high disturbance levels, it is better off to operate the PV under steady state conditions to avoid further disturbance of the jet, or to operate the intermittent PV at low frequencies of 0.3 Hz to 0.5 Hz to minimize turbulence intensities created by the jet fluctuations.
Magnetic Resonance Thermometry: An Emerging Three-Dimensional Temperature Diagnostic Technique
Authors: Benson Michael J. , Cooper Mattias , Van Poppel Bret P. , Elkins Christopher J. 
Published: December 2019

Abstract
Magnetic Resonance Thermometry (MRT) is a developing diagnostic technique that leverages advanced medical technologies to accurately measure the temperature of a fluid flow within and around complex geometries. The full three-dimensional temperature field obtained by MRT can be used to analyze heat transfer characteristics and potentially investigate thermal boundary layers near arbitrarily complex surfaces. This technique requires neither optical nor physical accessibility, thereby enabling a wide range of engineering applications. This paper describes the current state of the art for MRT measurement, detailing turbulent water channel tests, materials selection, scanning parameters, data analysis of time-averaged temperature measurements, and uncertainty estimates.
The purpose of this work was to evaluate and refine the MRT technique to increase the accuracy of temperature measurements and minimize the error in fully turbulent flow measurements. In the present study, a plate with a vertical cylinder extending from both of its sides was placed between two channels, and a diagonal hole was drilled through the cylinder from one side of the plate to the other. This enabled fluid from one channel to mix with the fluid in the other. This experiment studied the mixing of two fluids at different temperatures. The upstream temperatures of each fluid were measured with thermocouples. Both flows were fully turbulent, and the colder temperature channel had a Reynolds number of 11,800. Tests were run with four different fluid temperatures for calibration and to determine any temperature dependence of measurements. Three-dimensional temperature field measurements are reported and details about data processing and procedures to conduct the experiments are provided.
This work resulted in several notable improvements to MRT experimental methods. The test section and water channel were designed to limit the effects of thermal expansion in the stereolithography materials used for manufacturing the complex internal flow geometry. Multiple echo scans were used to minimize the effects of magnetic field drift commonly observed in extended scanning periods in MRI systems. Data analysis techniques were used to quantify expansion effects for both hot and cold flow cases. To quantify measurement uncertainty, the standard deviation of the mean was calculated at each data point across different scan numbers and confidence intervals established using a student t-test. An improved data processing code was used to filter data resulting in increased measurement accuracy and reduced uncertainty to less than 1 °C for most of the domain.
Future work will further refine the experimental techniques to improve scanning procedures, employ high conductivity ceramics and larger geometries with relevant applications, and simplify data processing methods to generate full-field flow temperature data.
A Novel Approach of Designing Aircraft Heat Exchanger for Continuous Working Conditions Using Modified Genetic Algorithm
Authors: Liu Qihang , Zhuang Laihe , Fu Yanchen , Dong Bensi , Wen Jie , Xu Guoqiang 
Published: December 2019

Abstract
A novel approach is proposed to design an aircraft heat exchanger considering multiple working conditions to develop the conventional approach that designs for only one working condition. Calculation results show that the performance of the heat exchangers designed by this novel approach meets the requirement of pressure drop and heat transfer for all working conditions (flight height varies from 0 m to 12,000 m, and Mach number varies from 0 to 1.2). After working conditions discrete and heat exchanger design, the extreme working conditions of pressure drop and heat transfer rate are found not coincided, which have been all considered in design without artificially screening. Therefore, it is not necessary to find a ‘seeming extreme working condition’ before design for this approach. In the optimization design, a deeply optimized structure of heat exchanger is proposed by changing the values of the selected structural parameters to reduce by roughly 30% of the total weight in comparison to common design results. Moreover, the pressure drop and the heat transfer rate of the optimal result can be reasonably distributed at different working conditions. Actually in this novel approach, more other specific criteria required could be also added into the integrate criterion of optimization to control the result. In addition, two detailed optimization methods, sacrifice of secondary objective parameters and ‘the macro-to-micro design method’, have been proposed in optimization design for further optimal structure.
Heat Transfer From a Row of Heated Pipes in Horizontally Layered Porous Media
Authors: Ngo C. C. , Al Edhari A. J. 
Published: December 2019

Abstract
A two-dimensional transient model has been developed using COMSOL Multiphysics modeling software to simulate the heat transfer processes from a row of heated pipes in horizontally layered media consists of two porous sublayers with different permeabilities. The application of the present study is related to thermal energy storage or radiant floor heating system using the embedded piping system as the heat source. The present numerical simulation was first compared and validated using a parallel experimental work. The transient temperature profiles of the layered system obtained from both the experimental and numerical work are in good agreement. Once the numerical code is validated, a parametric numerical study has been performed to investigate the effects of layered system configurations on the heat transfer characteristics. Porous media with different properties were modeled using the subsurface flow (Brinkman’s model formulation) and heat transfer module. Different layered system configurations were simulated by adjusting the sublayer thicknesses and using different permeability ratios for the layered system. For a layered porous system with different permeabilities, the dominant mode of heat transfer changes from heat conduction to heat convection depending on the ratio of the porous layer permeabilities. The interface location of the two media relative to the depth of the embedded heated pipes also plays an important role in the heat transfer results. The numerical results are presented in contour plots to examine the temperature distribution within the layered system (for energy storage application) as well as along the top surface of the system (for radiant floor heating application). The heat transfer results suggest that the layer configuration of the media plays an important role in the performance of radiant floor heating system.
The Effect of Chamber Pressure on the Thermal Performance of New Refrigerant R513a During Spray Cooling
Authors: Abdulrazzaq Nabeel M. , Salman Azzam S. , Anumbe Noble , Tikadar Amitav , K. Oudah Saad , Khan Jamil 
Published: December 2019

Abstract
In this paper, the performance of a new low-GWP refrigerant R513a was experimentally investigated, during spray cooling. A spray cooling system was designed to work as a sub-system within a closed-loop refrigeration system. The influence of chamber pressure on heat flux and heat transfer coefficient were experimentally investigated. A smooth plain copper surface heated by a cartridge heater was cooled by the refrigerant (R513a) while flowing through a nozzle in the spray chamber. The results showed that chamber pressure has a significant impact on the overall thermal performance of the spray cooling operation. It was also determined that higher chamber pressures resulted in higher thermal performance. The highest chamber pressure attained in this study was 0.6 MPa. Furthermore, the surface temperature of the heated surface increased due to the increase of the saturation temperature of the liquid over the surface.
Plasmonic Waveguiding in Subwavelength Particles Suspended in Various Dielectric Media
Authors: Yuksel Anil , Cullinan Michael , Yu Edward T. , Murthy Jayathi 
Published: December 2019

Abstract
Near-field electromagnetic coupling between nanoparticles in dielectric media has led to new advances in next generation technologies such as photonic integrated circuits and photonic sintering. Understanding the light confinement between nanoparticles at subwavelength dimensions is vital in such applications. For instance, the wavelength of the incident light, dielectric medium properties, nanoparticle size, interparticle spacing, and relative orientation between the nanoparticles affect the near-field plasmonic interactions that characterize the thermal energy transport. In this study, we perform a field intensity analysis by looking at the relative orientation of gold (Au) and copper (Cu) nanoparticles which have 25, 50 and 100 nm radius under 532 nm laser irradiation in different surrounding medium to understand the thermal energy transport between the nanoparticles at different relative orientations.
Numerical Simulation of Melting in Metal Foam/Paraffin Composite Phase Change Material Using a Physically More Reasonable Macroscale Model
Authors: Yao Yuanpeng , Wu Huiying 
Published: December 2019

Abstract
In this work, a macroscale model for melting phase change of metal foam/paraffin composite phase change material (MFPC) is developed by employing the enthalpy-porosity method and volume averaging technique. Both cases of varied and unvaried paraffin density during phase change are investigated in the model, and diffusion dominated interstitial heat exchange between paraffin and metal foam is considered along with the convection dominated interstitial heat transfer. The visualization experiments on melting phase change of copper foam/paraffin composite are carried out to validate the developed phase change model. It is found that with consideration of varied density of paraffin, the developed model can effectively solve the real melting problem of MFPC when metal foam is initially filled with solid paraffin. If the Boussinesq approximation is employed (i.e., unvaried paraffin density is considered during phase change), the model is more appropriate for the phase change problem on condition that metal foam can just be filled with liquid paraffin in the end of the melting process. Hence according to different treatments of paraffin density, the application of the phase change model needs to consider the influence of real paraffin filling condition of MFPC. The phase change model considering diffusion dominated interstitial heat transfer between stationary paraffin and metal foam can more accurately capture the solid-liquid phase interface positions as compared with the model only considering the convection dominated interstitial heat transfer. The present study can provide guidance for physically more reasonable simulation of the practical phase change problem of MFPC.
Optimization Strategy for Contradiction Between Intermitting Oxygen Consumption in Converter Steelmaking and Continuous Oxygen Production by Air Separation Unit
Authors: Tong Lige , Liu Yuxin , Hao Yang , Yin Shaowu , Liu Chuanping , Wang Li , Xie Raru 
Published: December 2019

Abstract
In order to solve the problem of overpressure release of oxygen supply network caused by the contradiction between continuous oxygen production by air separation unit (ASU) and intermitting oxygen consumption in converter steelmaking, a pressure balance strategy for pre-adjusting liquid-vapor ratio of ASU was proposed. Used Aspen Plus software, a full-compression model of an ASU in an iron and steel enterprise was established. Before stopping oxygen consumption in the converter steelmaking, method of pre-adjusting liquid-vapor ratio from the low-pressure distillation column to reduce the oxygen production of the air separation unit was calculated. This strategy consists of two steps. First step is pre-adjusting liquid-vapor ratio from the low-pressure distillation column to reduce the oxygen production of ASU, before stopping oxygen consumption in the converter steelmaking. The second step is the reduction of the supply oxygen production pipe network pressure, when stopping oxygen consumption in the converter steelmaking. The pre-adjusting oxygen production and the starting time are the key of the strategy. The energy consumption analysis of the strategy is carried out. The results show that the strategy reduces the pressure of the oxygen supply pipe network by 1.3% and reduces the large amount of oxygen release, while increase of the energy consumption of ASU is neglected.
Effect of Carbon Particle Seeding As Radiant Absorbent for Enhanced Heat Transfer
Authors: Najafabadi Hamed Abedini , Ozalp Nesrin 
Published: December 2019

Abstract
Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000°C would increase the surface and would recover the original activity as catalyst. In solar reactor, carbon particles are directly exposed to the high-flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in solar reactor is the presence and transport of carbon particles. This paper will present impact of carbon use in enhancing the heat transfer inside a solar reactor radiated by a solar simulator. Flux entering the receiver is determined using Monte Carlo ray tracing (MCRT) method which is coupled with energy balance equations to derive numerical model describing dynamic temperature variation in solar receiver. Simulation results indicated that feeding carbon particles results to lower temperatures for the cavity walls and working fluid compare to the case that no carbon is injected. This finding is in accordance with our experimental results obtained from a cylindrical cavity receiver radiated by a 7 kW solar simulator. The results indicated that heat transfer within the system is highly influenced by the particle size. At particle sizes larger than 450 μm, carbon feeding increases the thermal efficiency of the system.
Flowing Electrolyte As Coolant Inside the Microgrooves Embedded in the Electrodes: A Novel Thermal Management of Li-Ion Batteries
Authors: K. Mohammadian Shahabeddin , Zhang Yuwen 
Published: December 2019

Abstract
One way to enhance thermal performance of the Li-ion batteries is embedding microgrooves inside the porous electrodes and flowing the electrolyte through these microgrooves. A 2D thermal Lattice Boltzmann Method (LBM) was employed to predict electrolyte flow, heat transfer, and internal heat generation inside the positive porous electrode. Size and number of the microgrooves were investigated, and it was found that embedding microgrooves inside the porous electrode improved the thermal performance of the Li-ion battery by keeping the electrode in lower temperatures and improving its temperature uniformity. Furthermore, increasing the number of microgrooves (in a constant ratio between total size of the microgrooves to size of the porous electrode) kept the porous electrode in lower temperatures and enhanced temperature uniformity.
The Effect of Net-Type Spacer on the Performance of Direct Contact Membrane Distillation System for Seawater Desalination: Heat and Mass Transfer Analysis
Authors: Alwatban Anas M. , Alshwairekh Ahmed M. , Alqsair Umar F. , Alghafis Abdullah A. , Oztekin Alparslan 
Published: December 2019

Abstract
This work aims to study the effects of the net-type spacer on the performance of direct contact membrane distillation (DCMD) modules. Laminar and k-ω SST turbulence models are used to conduct simulations in three-dimensional modules with and without spacers. The spacers are placed in the middle of the feed and permeate channel. The net type spacers of diameter 0.25h and 0.5h were considered, where h is the height of each channel. The inlet temperature of the feed and the permeate channel set to 353 K and 293 K. The feed Reynolds number is varied (500, 1500) while the permeate Reynolds number is fixed at 330. We revealed that the presence of spacer in the flow channels mitigates both the temperature and the concentration polarization and yields higher vapor permeation. We also showed that the module containing larger size spacers yields better flux performance and lower level of temperature and concentration polarization. Moreover, the modules containing spacers become more efficient as the feed flow rate is increased.
Confined Impinging Slot Jets in Porous Media With Nanofluids
Authors: Buonomo Bernardo , di Pasqua Anna , Manca Oronzio , Sekrani Ghofrane , Poncet Sebastien 
Published: December 2019

Abstract
In this paper a numerical investigation on mixed convection in confined slot jets impinging on a porous media is accomplished. The working fluids are pure water or Al2O3/water based nanofluids and a single-phase model approach has been adopted in order to describe their behavior. A two-dimensional configuration is analized and different Peclet numbers and Rayleigh numbers are considered. The thermal non-equilibrium energy condition is assumed to execute two-dimensional simulations on the system. The examined foams are characterized by distinct values of pores per inch, PPI, equal to 5, 10, 20 and 40. The particle volume concentrations range from 0% to 4% and the particle diameter is equal to 30 nm. The target surface is heated by a constant temperature value, calculated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. The aim consists into study the thermal and fluid-dynamic behaviour of the system. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and nanoparticle concentration. Furthermore, the heat transfer coefficient presents a different behavior at varying PPI numbers for different Peclet numbers.