bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Flow Boiling in Micro Channel to Study Bubble Dynamics
Authors: Alugoju Uday Kumar , Dubey Satish Kumar , Javed Arshad 
Published: December 2019

Abstract
With the recent developments in miniaturization techniques of electronic chips, the power density of these chips has risen drastically. Available thermal management technologies like air cooled heat sink and liquid cooled heat sink are unable to keep up with the demand. However, thermal management technologies using flow boiling in microchannel heat sink can dissipate higher heat fluxes. Flow boiling technologies in micro channel heat sinks are not commercially established due to issues such as reliability, flow reversal, dry out, critical heat flux, limited knowledge of bubble dynamics, correlations, etc. In this study, performance of flow boiling in a diverging microchannel with uniform heat flux condition has been investigated. Simulations have been performed on ANSYS Fluent using Volume of Fluid (VOF). VOF is used to track the interface between different phases. The impact of angle on the bubble dynamics of the coolant and flow patterns has been studied. The simulated numerical results are compiled and presented. The results provide a clear understanding of the impact of angle on the bubble dynamics in flow boiling microchannel heat sink.
The Testing and Model Validation of an Additively Manufactured Twisted Tube Heat Exchanger
Authors: Bernardin John D. , Ferguson Kyle , Sattler David 
Published: December 2019

Abstract
Performance enhancements in heat exchanger design and manufacturing have been achieved over the past several decades through a combination of improved thermal-hydraulic modeling and experimentation tools, enhancements in material formulations and associated property characterizations, and new manufacturing methods. Most recently, Additive Manufacturing (AM) methods have matured sufficiently that they are now being considered as realizable heat exchanger fabrication methods. More complex, compact, and efficient designs can be achieved with AM methods that could not be easily obtained through more traditional manufacturing techniques.
This study expands upon a previous work [1] in which an optimized twisted tube shell and tube stainless steel heat exchanger was designed, analyzed, and fabricated with a Direct Metal Laser Sintering (DLMS) AM method. In that study, the twisted tube heat exchanger performance was a considerable improvement over that of a traditional straight tube shell and tube heat exchanger. In the present study, the AM twisted tube heat exchanger was subjected to thermal-hydraulic tests to measure its performance and to identify any necessary refinements to the previous CFD model.
For the conditions used in this study, the experimental data will show how the previous CFD model over-predicted the twisted tube heat exchanger’s heat transfer rate of 2,297 W and under predicted its overall heat transfer coefficient of 1,008 W/m2/K. Interrogation of the CFD model found that this discrepancy was due to the utilization of a k-ε turbulence model. Once this turbulence characterization was replaced with a more suitable shear transport model, the numerical predictions and experimental measurements of total heat transfer rate and overall heat transfer coefficient were in very close (∼10%) agreement. When combined with the previous study, this current work reveals how a complex, twisted tube shell and tube heat exchanger can be designed with existing CFD modeling tools and efficiently manufactured with current AM technologies to significantly improve its performance over a more traditionally manufactured straight tube version of the heat exchanger.
Experimental Study of Refrigerant (R134a) Condensate Retention on Paraffin Coated Plates and Fin Structures
Authors: Jin Hong-Qing , Ni Wentao , Wang Xiaofei 
Published: December 2019

Abstract
The refrigerant retained on heat transfer surfaces has a deleterious impact on the performance of heating, ventilation, air conditioning and refrigeration systems, which not only increases the thermal resistance between the vapor and surface, but also requires a higher charge to the system. In this work, a new paraffin coating has been applied on condensation surfaces, and R134a condensate retention has been studied on both copper plate and fins with (without) coating. The heat transfer coefficient was measured based on the one-dimensional heat conduction method and the retention was quantified using image processing. The results show that the heat transfer has been enhanced on the coated surfaces under a wide range of subcool degree, with a maximum increase of 27.4% in heat transfer coefficient; a reduced liquid retention has also been observed on paraffin coated fins with the retention area ratio decreased by 35.1% to 47.1% (depending on different subcool) compared to the uncoated fins. This work shows great potentials for reducing retained liquid and enhance heat transfer during refrigerant condensation.
Multi-Source Thermal Model for Electrical Harness Design
Authors: Petitgirard Julien , Baucour Philippe , Chamagne Didier , Fouillien Eric 
Published: December 2019

Abstract
The challenges of improving wiring harness design are safety, ecology, weight and cost. To achieve this, a better prediction of the temperature in the wiring harnesses is necessary. In terms, this involves considering a lot of compact thermal sources with an uncontrolled layout. Up to now, the main methods dedicated to resolution are based on finite elements given that temperature’s evolution according to several thermal sources, Joule effect, without controlled wire layout is complicated to evaluate.
This paper deals with an alternative and faster method. An analytic equation : Infinite Line Source (ILS), is used to create a nodal network. This method coming from geothermal heat exchangers relies on a fully-connected node network which is called here full-graph method. It will be shown that, for compact heat sources, this method can be improved with a reduced model. A reduced model is a pruned node network: only the wires corresponding to the adjoining wires are selected.
The bundle is a complex system which has a variable environment and an uncontrolled wire layout. The adaptation required by the models requires many assumptions. This case study focuses on a 10 wire configuration with the following assumptions: stationary state, identical wires, axial heat fluxes and neglected heat convection.
Comparative studies between the two nodal methods and a Finite Volumes Method (FVM) are also presented and discussed. From a physical point of view, the results are more interesting. Further investigations, depending on the different parameters, should lead us to make more realistic nodal methods.
Transient Determination on the Bulk Thermal Conductivity of Sub-Millimeter Thin Films of Composite Phase Change Thermal Interfacial Materials
Authors: Zhang Yu-Hong , Feng Biao , Tu Jing , Fan Li-Wu 
Published: December 2019

Abstract
The bulk thermal conductivity of thin films having a sub-millimeter thickness, made of composite phase change materials (PCM) and utilized as an emerging thermal interfacial material (TIM) for thermal management of electronics, was determined using the transient plane source (TPS) technique. The actual bulk thermal conductivity of the thin film samples was obtained by deconvoluting the thermal contact resistance (TCR) during the measurement process, according to the linear relationship between the nominal bulk thermal resistance and the thickness. The slope of the correlation curve is the reciprocal of film sample thermal conductivity and the intercept is the overall TCR. For the PCM35 thin film samples (which melt at around 35 °C) having three nominal thicknesses of 271±1 μm, 460±2 μm and 511±2 μm, the corrected results in the solid and liquid state were found to be approximately 0.487 W/m·K and 0.186 W/m·K, respectively. It was shown that the corrected values are greater than the direct readings from the TPS instrument as the latter involves the effect of TCR across multiple interfaces. The results obtained in this work could serve as reference property data for design of thermal management systems involving such phase change TIM.
Experimental Investigation of Crossflow Diverters in Jet Impingement Cooling
Authors: Madhavan Srivatsan , Ramakrishnan Kishore Ranganath , Singh Prashant , Ekkad Srinath V. 
Published: December 2019

Abstract
Jet impingement is a cooling technique commonly employed in combustor liner cooling and high-pressure gas turbine blades. However, jets from upstream impingement holes reduce the effectiveness of downstream jets due to jet deflection in the direction of crossflow. In order to avoid this phenomenon and provide an enhanced cooling on the target surface, we have attempted to come up with a novel design called “crossflow diverters”. Crossflow diverters are U-shaped ribs that are placed between jets in the crossflow direction (under maximum crossflow condition). In this study, the baseline case is jet impingement onto a smooth surface with 10 rows of jet impingement holes, jet-to-jet spacing of X/D = Y/D = 6 and jet-to-target spacing of Z/D = 2. Crossflow diverters with thickness ‘t’ of 1.5875 mm, height ‘h’ of 2D placed in the streamwise direction at a distance of X = 2D from center of the jet have been investigated experimentally. Transient liquid crystal thermography technique has been used to obtain detailed measurement of heat transfer coefficient for four jet diameter based Reynolds numbers of 3500, 5000, 7500, 12000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. However, this comes at the expense of increase in pumping power. Pressure drop for the enhanced geometry is 1–1.5 times the pressure drop for baseline impingement case. At a constant pumping power, crossflow diverters produce 9–15% enhancement in heat transfer coefficient as compared to baseline smooth case.
Monte Carlo Ray Tracing Coupled CFD Modelling and Experimental Testing of a 1 kW Solar Cavity Receiver Radiated via 7 kW HFSS
Authors: Ophoff Cedric , Ozalp Nesrin , Moens David 
Published: December 2019

Abstract
Current state-of-the-art development of concentrated solar power (CSP) applications target cost-effective and highly efficient processes in order to establish commercialization of these technologies. The design of solar receivers/reactors and their respective flow configuration have a direct impact on the operational performance of the solar thermochemical processes. Thermal efficiencies, reaction kinetics and other key output metrics are the intrinsic result of the chosen configuration. Therefore, reactor design optimization plays a crucial role in the development of solar thermochemical applications. In this study a computational fluid dynamics (CFD) model of a directly-irradiated cavity receiver has been developed. The CFD-domain is coupled with incoming radiation that is obtained by using Monte Carlo Ray Tracing (MCRT). Experimental campaigns of the cavity receiver were carried out using a 7 kW High Flux Solar Simulator (HFSS) as radiative source. Temperature readings were obtained at different locations inside the cavity receiver for both wall and gas temperatures. In order to mimic naturally changing insolation conditions, the HFSS was run at different power levels. Heat flux at the aperture of the solar receiver was experimentally characterized. The acquired heat flux maps validated the intermediate results obtained with the MCRT method. The coupled computational model was validated against the measured temperatures at different locations inside the receiver. Computed temperature contours inside the receiver confirmed the experimentally observed non-uniformity of the axial temperature distribution. The validated analysis presented in this paper was then used as a baseline case for a parametric study. Design optimization efforts were undertaken towards obtaining temperature uniformity and achieving efficient heat transfer within the fluid domain. Enhanced flow circulation was achieved which yielded temperature uniformity of the receiver at steady state conditions. The outcome of this parametric analysis provided valuable insights in the development of thermal efficient solar cavity receivers. Hence, findings of this study will serve as a starting point for future solar reactor design. For example, it was found that reversing flow direction has an adverse effect on the temperature uniformity inside the receiver. Similarly, increasing the inlet angle does not positively affect the temperature distribution and hence should be chosen carefully when designing a solar reactor.
Separating Wickability and Wetting Effects During Water Droplet Evaporation on Superhydrophilic Nanoporous Surfaces
Authors: Cooney Alanna Y. , McClure Emma R. , Cabrera Samuel , Carey Van P. 
Published: December 2019

Abstract
The dynamic behavior of impinging water droplets is studied in the context of varying surface wettability and wickability on smooth and nanostructured superhydrophilic surfaces. This study distinguishes the separate effects of wetting (contact angle), wickability, and inertia on the spreading and vaporization of water droplets deposited on nanoporous surfaces by considering experimental results in tandem with axisymmetric, volume of fluid (VOF) simulations of droplet spreading. High speed videos were obtained for water droplets spreading on nanoporous surfaces which exhibit very low (&lt; 15°) contact angle and high wickability. In this study, the effect of wickability was assessed by comparing the experimental results, which include the low contact angle and high wickability effects, to predictions of the VOF model, which include only the ultralow contact angle. While a droplet touched to the nanostructured surface demonstrates spreading driven by wicking, droplets which hit the surface with a non-zero impact velocity demonstrate spreading characteristics similar to the smooth surface, which are driven by inertia and ultra-low contact angle. The presence of the nanoporous layer impacts the equilibrium position of the contact line and the final spread radius changes with impact velocity on the nanostructured surface. These results provide fundamental input for modeling of spray cooling systems with nanostructured surfaces.
Numerical Investigation on Thermal and Fluid Dynamic Analysis of a Solar Chimney in a Building Façade
Authors: Buonomo Bernardo , Cascetta Furio , Diana Alessandra , Manca Oronzio , Nardini Sergio 
Published: December 2019

Abstract
Solar chimney is a system to produce energy and it has several applications, such as production of electricity, buildings ventilation, heating and cooling. In this paper, a numerical investigation on a prototypal solar chimney system integrated in a south facade of a building is presented. The chimney is 4.0 m high, 1.5 m wide whereas the thickness at the inlet the channel has a gap equal to 0.34 m and at the outlet it is 0.20 m. The chimney consists of a converging channel with one vertical wall and one inclined of 2°. The analysis is carried out on a three-dimensional model in airflow and the governing equations are given in terms of k-ε turbulence model. The problem is solved by means of the commercial code Ansys-Fluent. Simulations are carried out considering the solar irradiance for assigned geographical location and for a daily distribution. Further, comparison between steady state and transient regimes is examined and discussed. Results are given in terms of wall temperature distributions, air velocity and temperature fields and transversal profiles. Performances are better when heat flux is higher and sun is in front of chimney and a low-emissivity glass improves solar chimney achievements. Analysis in transient regimes confirm results obtained in steady state regime.
Parametric Study of SLM Processing Parameters on In-Situ Residual Stress
Authors: Amoako Emmanuel Duodu , Mensah Patrick , Akwaboa Stephen , Ibekwe Samuel , Li Guoqiang 
Published: December 2019

Abstract
Additive Manufacturing (AM) particularly laser powder-bed fusion, is advancing rapidly in manufacturing industries. Selective laser melting (SLM) also known as 3D-printing has become one of the most recent developed and extensively used techniques for several manufacturing processes. However, processing parameters influence the defect formation mechanisms such as porosities, holes, cracks, incomplete fusion and molten pool configuration during the SLM process of metallic powders. Even though an extensive amount of work have been done in minimizing these defect formations by simply varying processing parameters such as laser power, deposition thickness and scanning speed, it is of great importance to study the heat transfer mechanisms in laser heating process and utilize the optimum process parameters in minimizing the residual stress and strain as well as improving the quality of a manufactured product. In this present work, the authors implement a numerical thermo-mechanical model approach to determine the residual stress and strain in 316L Stainless Steel built samples using a finite element method (FEM) software ANSYS® (Workbench version 19.0). We are able to predict the unsteady temperature distribution of temperature-dependent thermal properties, residual stress and strain as a result of the rapid melting and solidification of 316L Stainless Steel metallic powder with optimized processing parameters. From the simulation result, it is shown that the residual stress decreases with an increase in scanning speed, hatch distance and preheat temperature. However, an increase in melting temperature also increases the residual stress and strain in the simulated 3D built part.
CFD Analysis and Evaluation of Heat Transfer Enhancement of Internal Flow in Tubes With 3D-Printed Complex Fins
Authors: Wei Chao , Vasquez Diaz Gabriel Alexander , Wang Kun , Li Peiwen 
Published: December 2019

Abstract
Additive manufacturing (AM), also known as 3D printing technology, is applied to fabricate complex fin structures for heat transfer enhancement at inner surface of tubes, which conventional manufacturing technology cannot make. This work considered rectangular fins, scale fins, and delta fins with staggered alignment at the inner wall of heat transfer tubes for heat transfer enhancement of internal flows. Designed fin structures are trial-printed using plastic material to exam the printability. Laminar flow convective heat transfer has been numerically studied, and heat transfer performance of the tubes with 3D-printed interrupted fins has been compared to that with conventional straight continued fins. The benefit from heat transfer enhancement and the loss due to increased pumping pressure is evaluated using the total entropy generation rate in the control volume of heat transfer tube. As the conclusion of the study, better heat transfer tubes with 3D-printed internal fins are recommended.
Comparison of Volumetric to Surface Heating for Filament-Fed Laser Heated Additive Manufacturing of Glass
Authors: Capps Nicholas E. , Johnson Jason E. , Landers Robert G. , Bristow Douglas A. , Kinzel Edward C. , Marchi Alexandria N. , Bernardin John D. 
Published: December 2019

Abstract
This paper presents work using a laser-heated fiber-fed technique to deposit fully dense glass. A stationary laser beam is focused on the intersection of a quartz filament with the workpiece. The workpiece is articulated on a precision 4-axis stage. The laser beam continuously melts the glass filament so that its viscosity is low enough to wet and fuse the workpiece. The focus of this paper is to compare volumetric heating of the glass as opposed to surface heat flux. CO2 laser radiation (λ = 10.6 µm) strongly couples to the silica phonon mode (optical penetration depth &lt; 5 µm). This requires printing at very slow rates in order to allow the heat to diffuse from the surface of the glass to the interface of the filament and the workpiece. CO laser radiation (λ = 5.3 µm) provides volumetric absorption because of weaker coupling (optical penetration depth of ∼500 µm for fused quartz). This produces a more uniform temperature profile in the glass filament and supports deposition at greater speeds. The maximum deposition rates for 0.5 and 1.0 mm diameter fused quartz filaments are determined by extrapolating the power required to achieve wetting using both CO2 and CO lasers. The results show that volumetric heating (CO laser) produces surface wetting with significantly lower power. The results are compared to a 1D conduction model which suggests that still greater deposition speeds are possible as the optical penetration depth approaches the filament diameter.
A New Accelerated Approach for Spectral Radiation Calculation Using K Distribution and Discrete Ordinate Methods With Application in Industrial Combustion Systems
Authors: Feldick Andrew M. , Pal Gopalendu 
Published: December 2019

Abstract
The introduction of higher fidelity spectral models into a Discrete Ordinates Method (DOM) RTE solver introduces the challenge of solving the N(N+2) coupled equations in intensity over many spectral points. The inability to store intensity fields leads to a nonlinear increase in computational cost as compared to basic gray models, as the solution in an evolving field must be recalculated at each radiation time step. In this paper an approximate initialization approach is used to a reconstructed values of the intensities. This approach is particularly well suited to spectrally reordered methods, as the boundary conditions and scattering coefficients are gray. This approach leads to more tractable computational time, and is demonstrated using on two industrial scale flames.
A Planar Evaporator Design to Counter Parasitic Heat Flow During Device Startup of a Microscale Loop Heat Pipe
Authors: Dhillon Navdeep S. 
Published: December 2019

Abstract
Due to increasing power densities and decreasing device footprints, thermal management has become an important design requirement in modern electronic devices. Loop heat pipes are phase change-based devices that can absorb and transport large heat fluxes via the latent heat of evaporation of a working fluid. However, these devices are bulky and difficult to miniaturize due to the constraining effect of undesired parasitic heat flow and other thermodynamic considerations of the two-phase flow loop. Here, we present experimental results demonstrating the operation of an ultra-thin microscale loop heat pipe that employs a planar evaporator wick designed to counter the negative effects of parasitic heat flow. Despite the extremely low wick thickness (&lt; 0.5 mm), the device is able to successfully startup, with no apparent observation of a wick dry-out due to parasitic heat flow-induced disruptions of liquid supply to the evaporator. A latent heat flux of approximately 6.7 W/cm2 is absorbed per unit area of the evaporator during the device startup phase.
Molecular Dynamics Simulation on the Friction Properties of Couette Flow With Superhydrophobic Rough Surfaces Under Different Load
Authors: Hu Chengzhi , Tang Dawei , Lv Jizu , Bai Minli , Zhang Xiaoliang 
Published: December 2019

Abstract
To reveal the effect of superhydrophobic rough surface on the friction properties, molecular dynamics simulations are used to study the friction properties of Couette flow. In particular, the influence of load on the flow properties is considered in this work. Results show that there is a critical load (Pcrit), and the friction-reduction properties of superhydrophobic surfaces with stripes are only presented when the load is smaller than the Pcrit. With the decrease in the distance between stripes, the Pcrit is increased. Under a low load, the friction force is increased with increasing the distance between stripes. However, under high load condition we observe an opposite trend. The height of stripe has little impacts on the Pcrit.