bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation on Pool Boiling Over a Vertical Tube Coupled With In-Tube Condensation
Authors: Ren Shuai , Zhou Wenzhong 
Published: December 2019

Abstract
Pool boiling and in-tube condensation phenomena have been investigated intensively during the past decades, due to the superior heat transfer capacity of the phase change process. In passive heat removal heat exchangers of nuclear power plants, the two phase-change phenomena usually occur simultaneously on both sides of the tube wall to achieve the maximum heat transfer efficiency. However, the studies on the effects of in-tube condensation on external pool boiling heat transfer are very limited, especially in numerical computation aspect. In the present study, the saturated pooling boiling over a vertical tube under the influences of in-tube steam condensation is investigated numerically. The Volume of Fluid (VOF) interface tracking method is employed based on the 2D axisymmetric Euler-Euler multiphase frame. The phase change model combining with a mathematical smoothing algorithm and a temporal relaxation procedure has been implemented into CFD platform by user defined functions (UDFs). The two-phase flow pattern and bubble behavior have been analyzed. The effects of inlet steam mass flow rate on boiling heat transfer are discussed.
Numerical Heat Transfer Simulations and Parametric Investigations Using Crossed Array Design of Experiments Approach During RFA of Breast Tumor
Authors: Sulake Sandeep , Dubey Satish Kumar , Javed Arshad 
Published: December 2019

Abstract
In the present work, a heterogeneous breast model comprising of fat, glandular and muscle tissues along with a spherical tumor of 2 cm diameter is modelled. The efficacy of Radio Frequency Ablation (RFA) is mainly judged by the extent to which the tumor cells are damaged and hence the volume fraction of necrotic tissue (VFNT) is a response parameter. Several critical factors affect the volume of necrotic tissue, among which the blood perfusion rate, target tip temperature of electrode and location of tumor from the body core are considered as prime input parameters. This work focuses on the selection and the significance of tolerance of these critical factors using ‘cross-array design of experiment’ (CA-DOE) approach. The loose and tight ranges of tolerances of these factors are selected to form Taguchi’s inner and outer orthogonal array and experimental combination sets are prepared. In this study, the effect of each possible set of tolerance on the output parameter i.e. tumor ablation volume generated is analyzed. The different values of the ablation volume generated for each experiment are obtained from finite element analysis. The entire analysis is carried out using a bioheat transfer module coupled with electric currents module in COMSOL multiphysics software. Additionally, target tip temperature is controlled by the implementation of proportional-integral-derivative control strategy. The simulations results are validated with the available published experimental results. The simulation results are further analyzed using statistical methods, such as signal to noise ratio, analysis of mean, and analysis of variance. The presented analysis will be helpful to achieve robust and targeted values of ablation volume with least effort of maintaining process accuracy. The proposed methodology and results are useful for clinicians in the RFA.
In-Situ Thermal ROM-Based Optimization Using Borg MOEA: A Preliminary Study
Authors: Irick Kevin , Brown Erich 
Published: December 2019

Abstract
High-fidelity computational thermal models (HFMs) of mechanical systems typically incorporate multi-disciplinary data sources to define boundary conditions, constraints, and dynamic system inputs. Oftentimes, HFMs are used during the planning, design, fabrication, testing, and operational phases of the mechanical systems, however, most of that data is processed during the modeling and test phases to discover and verify system responses. This approach can lead to much unused data and engineering effort that could otherwise provide useful information during the operational phases of the systems. One major bottleneck in using HFMs during the operational phase is data volume and computation time. Reduced-order models (ROMs), such as Gaussian processes, can consolidate data volume, data complexity, and time complexity needed for processing HFMs. The Borg multi-objective evolutionary algorithm (MOEA) presents a possible effective approach for processing ROM information in conjunction with real-time true process data to better understand the real-time state of a system. An investigation is being performed into the use of ROMs with the Borg MOEA to capitalize on engineering effort and simulation data that would otherwise be abandoned. This paper discusses the results of such a study in a steady-state conductive-radiative heat transfer system.
Evaporation-Based Microfluidic Pump Using Super-Hydrophilic Diatom Biosilica Thin Films
Authors: Jarrett Hunter , Wade Micah , Kraai Joseph , Rorrer Gregory L. , Wang Alan X. , Tan Hua 
Published: December 2019

Abstract
Diatoms are a group of single-celled photosynthetic algae that use biochemical pathways to bio-mineralize and self-assemble three-dimensional photonic crystals with unique photonic and micro- & nano-fluidic properties. In recent years, diatom biosilica has been used in surface-enhanced Raman scattering (SERS) based optofluidic sensors for detection of a variety of chemical and biological molecules. In this paper, we present a study to develop a microfluidic pumping system using super-hydrophilic diatom thin films. The desire to develop such a system stems from the requirement to create a low-cost, self-powered microfluidic pumping system that can sustain a continuous flow over an extended period of time. The diatom biosilica acts not only as the driving force behind the flow, but also serves as ultra-sensitive SERS substrates that allows for trace detection of various molecules.
Liquid is drawn from a reservoir to the tip of a 150μm inner diameter capillary tube positioned directly over the diatom film. A thin and long horizontal reservoir is used to prevent flooding on the diatom film when the liquid is initially drawn to the diatom film through a capillary tube from the reservoir. The connection of the meniscus from the capillary to the film was maintained from a horizontal reservoir for a recorded time of 20 hours and 32 minutes before the partially filled reservoir emptied. Flow rates of 0.38, 0.22 and 0.16μL/min were achieved for square biosilica thin films of 49mm2, 25mm2, and 9mm2 at a temperature of 63°F and 45% relative humidity respectively. A temperature-controlled system was introduced for the 49mm2 substrate and flow rates of 0.60, 0.82, 0.93, and 1.15μL/min were observed at 72, 77, 86, and 95°F at 21% relative humidity respectively. More testing and analysis will be performed to test the operation limits of the proposed self-powered microfluidic system.
Study of Pool Boiling Heat Transfer on Concave Nanostructured Surface With Molecular Dynamics Simulation
Authors: Liu Runkeng , Liu Zhenyu , Wu Huiying 
Published: December 2019

Abstract
The nanoscale boiling phenomena on solid surface is significantly distinct from that at macroscale. In this work, the pool boiling process of liquid argon thin film on smooth/concave aluminum surfaces were simulated using non-equilibrium molecular dynamics (NEMD) simulation, in which the nonuniform hydrophilic/hydrophobic surfaces were considered. For each surface, the superheat degree was progressively increased and the MD simulations were carried out to record the variation of atomic motion trajectory, mass density, the number of vapor and liquid atoms, kinetic energy and internal energy as time elapses. The predictions show that heat flux can reach critical heat flux (CHF) with increasing of wall superheat degree. Under the same superheat degree, the hydrophilic surface has the higher heat flux value than the hydrophobic surface, but it is earlier to reach CHF compared to the hydrophobic one. In addition, it also demonstrates that, with the same surface morphology, liquid-solid interaction strength has a significant influence on the heat transfer transition from nucleate boiling to film boiling. The surface morphology has more favorable effect on the pool boiling compared to the surface wettability at nanoscale. The obtained results in this work can guide the design and fabrication of enhanced heat transfer surface with nanostructured modification.
Wettability Effects on Falling Film Heat Transfer Over Horizontal Tubes in Jet Flow Mode
Authors: Karmakar Avijit , Acharya Sumanta 
Published: December 2019

Abstract
The performance of a falling-film heat exchanger is strongly linked to the surface characteristics and the heat transfer processes that take place over the tubes. The primary aim of this numerical study is to characterize the influence of surface wettability of tubes on the falling film flow mode and its associated surface heat transfer. Surface wettability is generally characterized by the contact angle and, in this study, the wettability characteristics ranged from superhydrophilic to a superhydrophobic tube surface. The dynamic motion of the triple contact line connecting the solid, liquid and gas phases over the tube surface is replicated with the help of the Kistler’s dynamic contact angle model. The volume of Fluid (VOF) simulations was carried out for the flow and heat transfer of liquid flow over horizontal tubes with different surface wettabilities. The mass flow rate is such that the flow is in the jet mode where the liquid flows in the form of jets in between the horizontal tubes. This corresponds to a liquid mass flow rate per unit tube length of 0.06 and 0.18 Kg/m-s, under which the inline and staggered jets modes of flow are observed. Under the two flow rates and different surface wettabilities, the liquid flow hydrodynamics over the tube surfaces was explored in terms of the liquid film thickness, the contact areas (solid-liquid and liquid-air) between the different phases, and the heat transfer coefficient. The axial resistance imposed by the increasing contact angle tends to inhibit the extent of the liquid spreading over the tube surface and this, in turn, influences the liquid film thickness and the wetted area of the tube surface. A significant decrement in the heat transfer rate from the tube surfaces was observed as the equilibrium contact angle ranged from 2° to 175°. Heat transfer characteristics were quantified over a wide range of contact angles for the two mass flow rates. Fluid recirculations were observed in the liquid bulk which had a major impact on the heat transfer distribution over the tube surface.
Modified Manifold-Microchannel Heat Exchangers Fabricated Based on Additive Manufacturing: Experimental Characterization
Authors: Yameen William C. , Piascik Nathan A. , Miller Andrew K. , Clemente Riccardo C. , Benner Jingru Z. , Santamaria Anthony D. , Niknam Seyed A. , Mortazavi Mehdi 
Published: December 2019

Abstract
In this study, the additive manufacturing technique has been utilized to fabricate air-water heat exchangers for the application of thermoelectric power plants. Additive manufacturing is a powerful fabrication method that has enabled fabrication of complex geometries that are either challenging or impossible to fabricate based on conventional techniques. Three manifold-microchannel heat exchangers with different interior designs were fabricated by additive manufacturing and from stainless steel. The heat exchangers were tested at different air flow rates and different inlet water temperatures. One heat exchanger was designed and fabricated based on an original design of the manifold-microchannel heat exchanger. Two other heat exchangers were designed with some modifications compared to the original design. In one modified heat exchanger, cylindrical pin arrays were considered on air manifold walls in order to enhance air disturbance, and thus, increase heat transfer between water and air. The second modified heat exchanger contained same pins and also had microchannels in the perpendicular orientation compared to the original design in the outlet manifolds. This design modification was done in order to reduce air-side pressure drop in the heat exchanger. The heat transfer characteristics along with air-side pressure drop were measured and compared with the original design of the manifold-microchannel heat exchanger. Results indicated that the heat flow rate, convection heat transfer coefficient, and pressure drop did not significantly change in modified heat exchangers. For air Reynolds number between around 800 and 4,000, the heat flow rates obtained in the original heat exchanger (type A) and for 50° C water inlet temperature were between 63.9 and 228 W for the lowest and the highest air flow rates, respectively. For the same inlet water temperature, these heat flow rates were between 64.2 and 211 W for the lowest and the highest air flow rates and in one of the modified heat exchangers (type B), respectively. Similarly, while the highest air-side pressure drop in the original heat exchanger was 3458 Pa, this property was measured at 3525 (type B) and 3884 (type C) for the two modified heat exchangers.
Comparison of Droplet Evaporation and Nucleate Boiling Mechanisms on Nanoporous Superhydrophilic Surfaces
Authors: Cabrera Samuel , Carey Van P. 
Published: December 2019

Abstract
Recent studies have indicated that at slightly superheated surface temperatures, droplet evaporation on a nanoporous superhydrophilic surface exhibits onset of nucleation and nucleate boiling effects similar to pool boiling processes. This paper discusses water droplet evaporation experiments and pool boiling experiments conducted on nanostructured surfaces of a 45° downward facing pyramid copper and aluminum substrate. The nanostructured surfaces were used to conduct both droplet evaporation experiments and pool boiling experiments and thus allow direct comparison of the underlying heat transfer performance and mechanisms for these two different processes. The four surfaces tested were the following: bare copper surface, nanostructured surface on copper, bare aluminum surface, and nanostructured surface on aluminum. Mean heat flux values at varying superheats were obtained through temperature and time measurements. To better understand the heat performance of each surface, the wetting and wicking characteristics of each surface were also tested. Experimental results indicate that many of the mechanisms associated with pool boiling may also play a role in droplet vaporization, and their presence can produce levels of heat transfer performance comparable to, or even higher than, that observed in pool boiling at a comparable wall superheat. The results demonstrate that the nanostructured surface affects onset of nucleate boiling and maximum heat flux in both droplet vaporization and nucleate boiling on these surfaces. The implications of these results for strategies to enhance spray cooling and pool boiling are also discussed.
Influence of Overweight Acceleration on Heat Transfer of Hydrocarbon Fuel in a Vertical Tube at Supercritical Pressures
Authors: Lv Lulu , Fu Yanchen , Dong Bensi , Wen Jie , Xu Guoqiang 
Published: December 2019

Abstract
The presented study numerically investigated the heat transfer characteristics of supercritical hydrocarbon fuel RP-3 in a vertical tube under overweight conditions with gravitational accelerations from 1g to 5g. The model was simplified as a vertical tube with the diameter of 1.8mm and the length of 250mm. Constant heat flux was applied to the wall, varying from 200kW/m2 to 700kW/m2. Variations of wall temperature and heat transfer coefficient under overweight conditions were obtained by simulation. The dimensionless buoyancy and thermal acceleration under different conditions were analyzed. The results show that the heat transfer is normal at low heat flux, while two types of heat transfer deterioration were observed in both upward and downward supercritical flow at high heat flux. The heat transfer coefficient of downward flow is generally higher than upward flow, and the difference between them becomes larger with the increase of gravitational acceleration. At high heat flux, when bulk temperature reaches the pseudo-critical temperature, the thermal acceleration will increase by 50% leading to the deterioration of heat transfer. However, after the pseudo-critical point, both buoyancy force and thermal acceleration decrease to negligible. The rise in gravitational acceleration enhances buoyancy force, but has no impact on the thermal acceleration. Based on the numerical analysis, two different criterion, Bo* and Kv, for supercritical RP-3 are obtained to present the influence of buoyancy and thermal acceleration.
Numerical Study of Gas-Liquid Two-Phase Flow in Ultra-High-Aspect-Ratio Microchannel With Capillary-Structured Wall
Authors: Mei Xiang , Liu Zhenyu , Wu Huiying 
Published: December 2019

Abstract
The understanding of the liquid-gas flow and heat transfer in the high-aspect-ratio microchannel is very important to realize the high-efficiency phase change chip cooling. In this work, a novel ultra-high-aspect-ratio microchannel with capillary-structured wall was developed to enhance the evaporation heat transfer in microchannel, in which the capillary grooves on the side walls (capillary-structured wall) were designed to avoid the dryout phenomenon. A three-dimensional VOF model was established to predict the immiscible gas-liquid flow in microchannel. The influences of wettability of capillary grooves on the gas-liquid two-phase flow behavior in microchannel were investigated based on the numerical predictions. The slug bubble can be observed for different inlet flow conditions. Variation of pressure loss between inlet and outlet of microchannel with time were studied for different flow rates and gas-liquid ratios. The results show that the existence of capillary structured wall has a significant influence on the liquid-gas two-phase flow behavior in the microchannel. The liquid flow in microgrooves is driven by the capillary force, which can supply more liquid to the side wall to promote the evaporation heat transfer process. The design of capillary-structured wall for ultra-high-aspect-ratio microchannel in this work provides a new approach to improve the performance of the chip cooling technique with microchannels.
The Effect of Forced Convection on Mass and Heat Transfer During Single Coal Particle Combustion
Authors: Feng Lele , Zhang Yang , Wu Yuxin , Xu Kailong , Zhang Hai , Zhang Man , Yang Hairui 
Published: December 2019

Abstract
MILD coal combustion is one of promising technologies for clean coal utilization due to uniform heat flux and low NOx emission, while the effect of turbulent mixing on single coal particle combustion under high temperature and low oxygen concentration remains to be studied for micron level particles. In this paper, a 1-D transient coal combustion model was applied to describe mass and heat transfer around a single particle, and the effect of forced convection was modeled to represent turbulent mixing according to similarity analysis. Based on that, effect of particle Reynolds number (Rep) on single coal particle combustion was investigated at various temperature (Ta), oxygen concentration (xO2) and particle diameter (d0). As Rep increases, ignition time (ti) decreases quickly at first and then decreases slowly. ti of larger particle is more sensitive to Rep. As Rep increases, flame temperature (Tf) for 40 μm coal particle decreases, while Tf for 80 μm coal particle barely changes, and that for 160 μm coal particle increases a little. The recommended d0 for MILD coal combustion is smaller than 80 μm. As xO2 decreases from 21% to 5%, ti apparently increases and Tf decreases. ti at lower Ta is more sensitive to Rep. Tf decreases with increasing Rep when Ta &lt; 1200 K. But it appears the opposite trend at Ta = 1600 K. The recommended Ta for MILD coal combustion is lower than 1400 K, while it cannot be too low considering the burnout of char particle.
The Effects of 3D Printing Parameters and Surface Roughness on Convective Heat Transfer Performance
Authors: Pereira Lucas , Letcher Todd , Michna Gregory J. 
Published: December 2019

Abstract
Additive manufacturing technology and applications have quickly expanded into many industries over the last several years. Improvements in resolution, strength, and material options have helped propel further growth of the industry. This study focuses on an additive manufacturing technology called fused filament fabrication (FFF). FFF involves the extrusion and layer-by-layer deposition of a molten thermoplastic material to create the desired part. One potential new application of FFF is the manufacture of heat exchangers and heat sinks. This study focuses on developing baseline experimental data related to convective heat transfer coefficients over surfaces of commonly used polymers in FFF 3d printing while varying printing parameters. Samples with layer heights (LH) of 0.1 mm, 0.2 mm and 0.3 mm were printed. As the layer height increases, the surface roughness also increased. Sample 1 of LH = 0.1 mm had a roughness of 9.72 μm and at a Reynolds number of 13,200 had a heat transfer coefficient of 72.2 W/m2-K and sample 1 of LH = 0.3 mm had a roughness of 28.83 μm and at a Reynolds number of 13,600 had a heat transfer coefficient of 84.6 W/m2-K.
Model and Sensitivity Analysis of the Reciprocating Biomass Conversion Reactor (RBCR)
Authors: Adhikari Roshan , Parziale Nick J. 
Published: December 2019

Abstract
The capabilities of a pilot-scale reciprocating biomass conversion reactor (RBCR) and its sensitivity to changes in various input parameters are examined. The RBCR is a 4-stroke diesel engine repurposed as a novel reactor to produce bio-oil by fast-pyrolysis of biomass. An external source powers the RBCR through the intake, compression/heating, expansion and exhaust strokes. Biomass is carried to the RBCR by an inert gas and is converted during compression as part of the compression work provides the heat of pyrolysis. A control-volume energy balance is coupled with a biomass decomposition mechanism from literature to predict the evolution of bio-products during compression and expansion strokes. The RBCR calculations are compared to experimental results from the state of the art considered to be a lab-scale fluidized-bed reactor (FBR). Calculations predict that the RBCR will increase the biomass throughput, and decrease the energy requirement for biomass conversion with a 6.8 times return on energy investment. The sensitivity analysis indicates the need for finely pulverized biomass for significant conversion, and highlights the versatility of the RBCR since operation parameters can be adjusted to achieve near complete conversion to bio-gas or to yield bio-oil up to 70% of biomass weight.
Heat Transfer Characteristics of a Phase Change Material Fluid in Microchannels Under Pulsating Flow Condition
Authors: Shuvo Abdul Aziz , Morshed AKM M. , Emon Md. Shariful Alam , Tikadar Amitav , Paul Titan C. 
Published: December 2019

Abstract
In this study numerical investigation has been conducted employing pulsating flow in a MicroChannel Heat Sink (MCHS) with phase change material (N-eicosane) as the coolant. The numerical investigation was conducted with H1 boundary condition and laminar pulsating flow condition using commercial software FLUENT. Heat transfer and pressure drop characteristics of the MCHS was calculated for the PCM with different amplitude and frequency of the pulsation and compared with that of the water and PCM under constant velocity flow. Heat transfer performance of the MCHS for both the PCM fluid and water increases for the pulsating flow and it increases with the amplitude of the pulsation; however, pressure drop in case of pulsating flow of PCM fluid remains same compared to the steady flow of PCM. Simulation also has been repeated in this study for two different aspect ratio of the channel.