Transfer Drop Research Articles

Numerical Modeling of Heat Exchanger Filled with Octahedral Lattice Frame Porous Material

A numerical investigation into the fluid flow and heat transfer process in a 3D-printed shell-and-tube heat exchanger was carried out. The shell side of the heat exchanger was inserted with octahedral lattice frame porous material to enhance the heat transfer. In order to avoid establishing a complex grid system, the porous material of the shell side was modeled by a porous media model. The non-equilibrium model was adopted for the modeling of the heat exchange between the solid and fluid in porous media. An experimental investigation was carried out to validate the feasibility of this approach. The result indicates that the simplified approach is capable of providing an appropriate prediction of the pressure drop and heat transfer efficiency with moderate computational resources. The average error of pressure loss and heat transfer effectiveness is within 4% and 6.1%.

Effect of Weld Pool Flow and Keyhole Formation on Weld Penetration in Laser-MIG Hybrid Welding within a Sensitive Laser Power Range

The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration.

Thermophysical Properties and Heat Transfer Characteristics of Nanorefrigerants: Some Existing Results and Areas for Further Researches

Refrigerants are commonly used as heat transfer fluid in refrigeration, heat pumps, and air conditioning systems. Nanorefrigerants are a special kind of nanofluid synthesized by dispersing nanoparticles into refrigerants or lubricant oil to improve its thermophysical and heat transfer characteristics. The optimization of the thermophysical properties of nanorefrigerant strongly depends on the successful synthesis procedures used for producing a stable suspension of nanoparticles in the refrigerants. In this study, a review was carried out to understand the synthesis of nanorefrigerant and the effect of nanoparticle size, type and concentration, temperature, base fluid type on the thermophysical properties of the nanorefrigerant. The effect of nanorefrigerant on the pressure drop and boiling heat transfer within the vapour compression refrigeration system (VCRS) was reviewed. From the review, the thermophysical properties of the nanorefrigerants affect the pressure drop and heat transfer characteristics of the vapour compression refrigeration system.

Open-cell aluminum foams with bimodal pore size distributions for emerging thermal management applications

Recent advances in cellular materials for active thermal management applications involve the integral design of their porous structure. In this work, open-cell aluminum foams with porosities in the range of 0.60–0.76 are developed, containing pores with spherical geometry and a bimodal pore size distribution. The fabrication strategy involves the use of the replication method by infiltration with liquid aluminum of porous preforms formed by packing NaCl spheres of two largely different sizes (7 mm and 1 mm average diameter), which are then removed by water dissolution. The paper describes cellular materials with different proportions of coarse and fine pores. Their detailed characterization by pore volume fraction, pressure drop, permeability, thermal conductivity and heat transfer coefficient is supported by analytical schemes. In addition, these materials were characterized under realistic operating conditions using computational fluid dynamics simulations. The material with 67 percent coarse pores and 33 percent fine pores, which has the highest porosity (and thus permeability), has the most appealing heat dissipation properties with the lowest pressure drops, making it an excellent candidate for emerging thermal management applications in electronic systems.

Experimental and numerical investigation of dry pressure drop of 3D-printed structured packings for gas/liquid contactors

Separation units, such as distillation and absorption columns, are used widely in the chemical industry. Their efficiency depends on the performance of their packing, determined by their pressure drop, capacity, and mass transfer efficiency. Combining CFD and additive manufacturing allows the design/production of efficient and high capacity packing. In this paper, the dry pressure drops of newly developed wire-based structured packings are evaluated numerically via a single-phase CFD model. The k-ω-SST turbulence model in Ansys Fluent was used. The experimental and numerical dry pressure drops of three Tetraspline (TS) packings are compared. The numerical model is validated with average errors of 13% and 20% compared with experimental data for TS made in stainless steel and polyamide, respectively, over a capacity factor range of 0.9 to 3.1 Pa0.5. A Kelvin-cell-based packing is also studied to confirm the robustness of the model. This study allows the rapid optimisation of the different TS with different geometric parameters, such as wire diameter and length, based on the pressure drop. Indeed, the experimental values of the dry pressure drop of a column of packing that measures 16,500 cm3 have been reproduced numerically with only a small deviation using a periodic domain of 42 cm3.

Effects of alternating injection-interruption periods on the fine particle transport and retention in granular media

This study investigates the impact of interruption of injections on the transfer and retention of suspended particles (SP) in granular media. Columns packed with sand were operated in the laboratory, and a series of experiments of SP injections were conducted: the first by injecting SP without interrupting injection, the second and third experiments with 3 pauses of injection of 24 h and 48 h, respectively. Results showed that interrupted injections induced a significant release of particles showing peaks of concentration in the effluent immediately after the pause periods. These peaks increase with pause durations. Interruption of injections allowed the transport of coarser particles deeper into the columns. For all experiments carried out, the hydraulic conductivity, measured during injection, decreased with the number of pore volumes injected. This decrease is almost linear for continuous injection experiments. Whereas, the hydraulic conductivity decreased brutally when reinjecting SP, after pauses, highlighting the desaturation of the porous medium during pause periods. The results obtained show that all the phenomena (hydraulic conductivity drop, SP transport, and deeper transfer of coarser particles) occurred during the dynamic phase of the experiments for the first 75% of pore volumes injected. Beyond that, the porous medium is completely clogged.

New coal-charging method: analysis of force characteristics and velocity distribution of coal particles with dense phase continuous flow in cylinder

ABSTRACT Low-moisture coal used in coking has the advantages of increasing production capacity and reducing power consumption but produce a lot of dust during coal charging. A new method of coking coal charged into top-charge coke oven was built, in which the cylinder with telescopic and high-temperature resistant was used to realize the coal flow as dense phase continuous. Based on the 400 kg top-charged coke oven, theoretical analysis, calculation, and numerical simulation were used to study the forces and motion of coal particles under the conditions of temperature gradient. The temperature distribution and particle motion characteristics were simulated by FLUENT when the distance between the coal outlet and the bottom of the coking chamber is 0 mm, 0.5 m, 0.7 m, and 0.9 m. The results show that the dust formed by coal particles was mainly affected by thermophoretic force and air resistance. In the non-uniform temperature field, the radiative heat transfer drop reduces the deposition rate of coal particles. The initial thermal migration velocity of particles in the lower part of the coking chamber is 0.4 m/s, and that of particles in the upper is only 0.1 m/s. As the temperature gradient of coking chamber tends to be uniform, the thermal velocity of particles gradually stabilizes. After the time of particles in the furnace exceeds 0.5 ~1s, the thermophoretic velocity of each part tends to be the same. There was no dust escapes from the coal charging hole during the cylinder lifting process, the escape velocity of dust was controlled below 0.4 m/s by new method. Through simulation and experiment, the simulation results were similar to the experimental when the distance between coal outlet and the bottom of coking chamber is 0 m and 0.7 m, and the maximum error is less than 0.1.

Numerical investigation on the thermal-hydraulic performance of separated structure steam generator with different tube arrangements

The horizontal steam generator is generally used in nuclear power plant and industry to produce steam. To increase the heat load and reduce the size, a steam drum can be added above the shell. However, it makes the overall flow of water cycle complicated. In this article, the two-phase boiling flow and heat transfer inside tube bundle under the separated structure has been investigated numerically based on the previous experiment. The Drift-Flux model was utilized to solve the equations of heat and mass transfer in the mixture flow. The local pressure drop, void fraction and heat transfer characteristics have been presented and discussed for different arrangements in detail. The analysis results showed that the overall boiling HTC of the tube arrangements of 30°and 60° appear better for this steam generator under the same condition. The boiling heat transfer in both bottom and upper tube bundle was mainly controlled by the nucleate boiling mechanism. However, both heat flux and vapor void fraction were found to affect the heat transfer performance. Beyond this analysis, a new type of heat transfer correlation has been proposed herein to evaluate the local HTC with a good accuracy. These correlations allow better predictions of the boiling heat transfer inside the SS-SG, which provide designers with better reference and guidance.

Thermo-hydraulic behavior of alumina/silica hybrid nanofluids through a straight minichannel heat sink

In this study, the hydraulic and thermal performances of dissimilar particles of alumina–silica/water hybrid nanofluid are experimentally investigated in a minichannel heat sink. Stable alumina–silica/water hybrid nanofluid is used as a coolant having a volume concentration of 0.01%. A total of 12 rectangular minichannels with 1 mm depth, 1 mm width, and a hydraulic diameter of 22 mm are used. The effect of Reynolds number on the Nusselt number, heat transfer coefficient, thermal resistance, pressure drop, pumping power, and friction factor are analyzed for various heating powers. Results indicate that the alumina/silica hybrid nanofluid can enhance heat transfer and pressure drop in a straight minichannel heat sink as compared with the base fluid (water). For heating power at 55 W, the use of hybrid nanofluid enhances heat transfer rate, pressure drop, and thermal performance up to 13.79%, 4.35%, and 31.16%, respectively. Moreover, it can be concluded that heating power had a significant effect on pressure drop and heat transfer for hybrid nanofluids. Finally, the performance evaluation criteria (PEC) for all nanofluids in a straight minichannel heat sink is always greater than one.

Pressure drop and heat transfer characteristics of nitrate salt and supercritical CO2 in a diffusion-bonded heat exchanger

A lab-scale 316/L stainless steel diffusion-bonded heat exchanger was examined within a coupled high-temperature test facility consisting of an atmospheric-pressure nitrate salt loop and a supercritical carbon dioxide (sCO2) loop operating between 10 and 16 MPa. Pressure loss measurements collected for flow rates up to 0.55 kg/s of Solar Salt and up to 0.6 kg/s of carbon dioxide were used to generate friction factor correlations for the respective circular and semicircular zig-zag flow passages. Heat transfer measurements were also performed over a wide range of conditions to produce Nusselt correlations for the CO2 and nitrate salt geometries. The Nusselt number is deduced from a heat transfer resistance network and overall conductance measurements collected across the operating envelope of the coupled sCO2 – nitrate salt test facility. The CO2 side correlation showed excellent agreement with existing correlations in the literature. The salt side, having nearly circular channels with a different zig-zag angle and hydraulic diameter, yielded a new correlation applicable to the laminar flow regime. To examine the similitude of the friction correlations, pressure drop testing with water was performed on both sides of the component as well. Finally, results from non-destructive examination are discussed to provide insights regarding inspection methods and draining performance of high-temperature liquids in compact heat exchangers.

RETRACTED: Study of pressure drop and heat transfer in cooling of lithium-ion battery with rhombic arrangement with two different outlets and different inlet dimensions

This article models a two-dimensional battery pack (BAP) containing 45 battery cells. The cylindrical lithium-ion battery cells are arranged in a rhombic pattern in the pack. The pack has one inlet and two outlets so that laminar airflow exchanges heat with the battery cells. The temperature of the battery cells (TBC), the pressure drop (PD) in the BAP, the changes in the air velocity (Vair) in the BAP with the outlet air temperature (OAT) for each outlet separately are evaluated by changing the dimensions of the air inlet and two outlets, at four velocities of 0.005, 0.01, 0.015, and 0.02 m/s. The BAP is simulated using the COMSOL software. According to the findings of this research, an increase in Vair increases the pressure decrease in the BAP. Increasing Vair, on the other hand, lowers the maximum temperature (TMA) and the average TBC. An enhancement in the dimensions of inlet and outlets reduces the average and TMAs of the battery. As the Vair is intensified, the amount of OAT is reduced. Model D = 0.6 has the maximum OAT and model D = 1 has the minimum OAT at two outlets.

Optimal piston motion configuration for irreversible Otto cycle heat engine with maximum ecological function objective

Applying optimal control theory and finite time thermodynamics, a practical Otto cycle heat engine with friction, pressure drop and heat transfer losses is studied. The maximum ecological function is taken as optimization objective, and the optimal piston motion configuration of the Otto cycle is obtained with the Newton’s heat transfer law between the working fluid and the environment. The fuel consumption and the total cycle time are fixed in the optimization. The optimal piston motion laws corresponding to the maximum ecological function configuration when the piston motion accelerations are unconstrained and constrained are obtained, respectively. By numerical examples, the piston motion optimal configurations under different optimization objectives and heat transfer laws are compared.

Forced Convection Heat Transfer in V-Pattern Folded Core Sandwich Structures

Fully developed laminar flow and heat transfer performance of V-pattern folded core sandwich structures subjected to forced convection are numerically investigated. Based on the periodic feature of folded core, a methodology to simulate the fully developed flow and heat transfer state with a few unit cells is developed. The influences of geometric parameters on the coolant flow resistance and heat transfer behaviour are evaluated. Afterwards, approximate models are established based on design to optimize the heat dissipation efficiency. Design variables considered are geometric parameters of the V-pattern folded core, while the corresponding relative density is taken as a constraint. The simulation results show that the presented methodology makes it possible to analyse the fully developed regime with less computing resources. It is found that both pressure drop and heat transfer rate increase with the tortuosity of the flow channel and the inclination of the folded core. The optimization generates a design with a mildly tortuous feature in the streamwise direction to gain a maximum of heat dissipation efficiency under the current conditions.

Structured ZoneFlow™-Bayonet steam reforming reactor for reduced firing and steam export: Pressure drop and heat transfer modelling and evaluation of the reactor performance

The ZoneFlow™ reactor is an annular structured reactor that offers lower pressure drop and significantly better heat transfer than standard pellets used in Steam Methane Reforming. The annular ZoneFlow™ reactor is particularly suited for use in a bayonet configuration. The produced syngas then returns via the central tube, the so-called bayonet, allowing counter-current heat exchange between the return gas and the gas reacting in the ZoneFlow™ reactor. As such, the heat supplied by the furnace can be maximally used for the reactions and steam export can be reduced. To intensify the heat transfer between the gas in the bayonet and in the annulus, an insert is installed inside the bayonet, forming a second annulus that forces the gas to flow close to the bayonet wall at high velocity. In the present work, the pressure drop and heat transfer resulting from various bayonet configurations are experimentally measured at commercial scale reactor dimensions and air flow rates equivalent to commercial conditions. Correlations for the friction factors and the heat transfer coefficients are derived from the data. The correlations are then used to simulate a commercial scale ZoneFlow™-bayonet reactor and optimize the design.

RETRACTED: Utilization of a solar system to charge lithium-ion batteries and using the heat generated in an in-line lithium-ion battery to heat a guard room

In this research, three packs of cylindrical li-ion batteries inside the air duct used to heat a guard room are simulated numerically. Heat is generated inside lithium batteries due to the electrochemical process. To enhance the performance of the battery, the heat must be rejected; but the generated heat is used as a heating source in this study. The airflow passes through three battery packs and exits. The airflow exits from several outlets. The number of outlets varies from one to five, and their effect is examined. The room is studied in a cold environment and has dimensions of 2×3m. Carrier software is employed to estimate the room heat transfer and COMSOL software is used to simulate the battery. The results of this study show that an increment in the velocity increases the pressure drop and heat transfer coefficient (HTRC) in the system, but reduces the outlet temperature (Toutlet) and the maximum temperature (Tmaximum) of the battery. The model with 1 outlet has the lowest Tmaximum of battery cells and the lowest temperature of air outlet, while the model with 3 outlets has the highest Tmaximum of the battery cell and air outlet. Using this system is useful to provide heating energy for the guard room in the not-so-cold months and can provide up to 86.95% of the total energy required. But, in the very cold months, the system has a minor effect on the total heat required and provides less than 20% of the total energy needed.

Performance Enhancement of Finned Tube Heat Exchanger using New Vortex Generator

The present work aims to investigate a performance enhancement in an H-shaped finned tube heat exchanger using a new design of winglet vortex generator. The new design has an aerodynamic shape that reduces the pressure drop and enhances the heat transfer, resulting into an improvement in the overall thermo-hydraulic performance. A three-dimensional model is developed using ANSYS fluent to carry out simulations for Reynolds number varying between 5000 ≤ Re ≤ 11000 and to predict the net enhancement in the heat exchanger performance. The validation of the model is done using experimentally developed correlations of dimensionless pressure drop and heat transfer characteristics. Comparative results for the finned tube heat exchanger with and without vortex generator are presented. Results indicate a significant enhancement in the heat transfer characteristics of the finned tube heat exchanger with the new design of vortex generator. Volume goodness ratio and Colburn j-factor found to be 19.63% and 30.33% higher than the baseline finned tube heat exchanger without any vortex generator.

Experimental Investigation on Heat Transfer Enhancement with Passive Inserts in Flat Tubes in due Consideration of an Efficiency Assessment

This paper presents results of an experimental investigation on pressure drop and heat transfer for a wide range of Reynolds and Prandtl numbers ranging from 8 < Pr < 60 and 40 < Re < 3500, for flat tubes without and with passive inserts. For three different kinds of passive insert designs, the impact on heat and momentum transfer due to coaction of the total set of passive inserts with different shape and amount was investigated. Experimental results were analyzed regarding two main aspects: Heat transfer mechanisms and pressure drop induced by friction and form drag forces due to the presence of different shapes. After heat and momentum transfer mechanisms for each passive insert design were analyzed, heat transfer and pressure drop enhancement were compared to each other, leading to an efficiency discussion. Different concepts for efficiency evaluation, which are cited in literature, were applied to the presented experimental data. Pros and cons of the different concepts are discussed. Finally, we propose an equation for evaluation of total performance, which fully respects the energetic and exergetic aspects of heat transfer and pressure drop enhancement.

Analysis of a Stator-Rotor-Stator Spinning Disk Reactor in Single-Phase and Two-Phase Boiling Conditions Using a Thermo-Fluid Flow Network and CFD

Cryogenic liquid propellants are used in liquid rocket engines to obtain high specific impulse. The flow rates are controlled by turbopumps that deliver liquid propellant to the engine at high pressure levels. Due to the very low saturation temperature of the cryogenic propellant, in the first phases of the transient operation, in which the engine is at ambient temperature, its surfaces are subject to boiling conditions. The effect of boiling on the heat transfer between the solid and the fluid needs to be well characterized in order to correctly predict the cryopump metal temperature temporal evolution and the necessary amount of propellant. With the aim of benchmarking numerical tools against experimental data, a representative test case was chosen. This consists of a stator-rotor-stator spinning disc reactor studied under single-phase and two-phase heat transfer conditions. The numerical approaches used are represented by a 1D network solver, where the pressure drop and heat transfer are calculated by correlations, and Computational Fluid Dynamics (CFD) simulations, carried out with ANSYS Fluent. Both the numerical tools returned a reasonable agreement in single-phase conditions, also thanks to the use of adequate correlations in the flow network solver and typical conditions for the CFD simulations. Two-phase conditions on the contrary are more challenging, with underpredictions up to 20% and 80%, respectively. The issues are ascribable to the use of correlations that are inadequate to capture the two-phase phenomena occurring in the srs reactor and numerical limitations in the actual implementation of the boiling model in the CFD solver.

Influences of weaving parameters on dynamic characteristics and stability control of the droplet transfer in arc-weaving P-GMAW process

The dynamic characteristics of droplet transfer are extremely complicated with the combined effects of gravity force and weaving motion during the weaving vertical-up welding on thick plate. In this paper, we firstly observed the droplet transfer behavior under various weaving parameters with high-speed photography and electrical signals during pulsed gas metal arc welding (P-GMAW). Then, we investigated the influences of different weaving parameters on the arc shape and molten pool as well as droplet characteristics. By establishing a novel weaving-force model based on state force balance theory (SFBT), we further revealed the drop transfer mechanism in weaving P-GMAW process. Extensive experimental results demonstrated that the suitable weaving parameters could effectively improve the droplet transfer stability and suppress welding defects including incomplete root penetration and lack of sidewall fusion. The findings of this paper will provide a basis for enhancing the welding process stability and obtaining a high-quality weld joint.

Direct Pore-Scale Simulations of Fully Periodic Unit Cells of Different Regular Lattices

Abstract Open-cell metal foams are known for their superior heat dissipation capabilities. The morphological, pressure drop, and heat transfer characteristics of stochastic metal foams manufactured through traditional “foaming” processes are well established in the literature. However, employment of stochastic metal foams in next-generation heat exchangers is challenged by the irregularity in the pore- and fiber-geometries, limited control on the pore-volume, and an inherent necessity of a bonding agent between foam and the heat source. On the other hand, additive manufacturing (AM) is capable of printing complex user-defined unit cell topologies with customized fiber shapes directly on the substrates subjected to heat load. Moreover, the user-defined regular lattices are capable of exhibiting better thermal and mechanical properties than stochastic metal foams. In this paper, we present a numerical investigation on fully periodic unit-cells of three different topologies, that is, tetrakaidecahedron (TKD), rhombic-dodecahedron (DDC), and Octet with air as the working fluid. Pressure gradient, interfacial heat transfer coefficient, friction factor, and Nusselt number are reported for each topology. Rhombic-dodecahedron yielded the highest averaged interfacial heat transfer coefficient whereas Octet incurred the highest flow losses. Pore diameter, defined as the maximum diameter of a sphere passing through the polygonal openings of the structures, when used as the characteristic length scale for the presentation of Nusselt number and Reynolds number, resulted in a single trendline for all the three topologies.