Stainless Steel Microchannels Research Articles

A Microchannel Heat Exchanger Produced From a Metal Matrix Composite by Hybrid Laser Powder Bed Fusion and Inkjet Printing

Abstract This paper explores the production of an oxide dispersion strengthened (ODS) 304L stainless steel microchannel heat exchanger (HX) using a hybrid additive manufacturing process of laser powder bed fusion and inkjet printing. The study investigates the capabilities and economics of the hybrid inkjet-laser powder bed fusion (LPBF) process and evaluates the dimensional accuracy, functionality, and mechanical properties of the resulting ODS alloy. The effectiveness and pressure drop of the ODS heat exchangers produced by the hybrid LPBF tool are also determined. Results show that the inkjet-doped samples have a lower mean channel height with higher standard deviation than samples produced by LPBF alone. This is attributed to greater absorption of laser energy for the powder coated with the oxide precursor. The economic analysis shows that the hybrid process has a potential for reducing the unit cost of the heat exchanger based on cost modeling assumptions.

Understanding Inconsistencies in Thermohydraulic Characteristics Between Experimental and Numerical Data for DI Water Flow Through a Rectangular Microchannel

Abstract Facing discrepancies between numerical simulation, experimental measurement, and theory is common in studies of fluid flow and heat transfer in microchannels. The cause of these discrepancies is often linked to the transition from the macroscale to the microscale, where the flow dynamics might be expected to deviate due to possible changes in dominant forces. In this work, an attempt is made to achieve agreement between experiment, numerical simulation, and theoretical description within the usual framework of laminar flow theory. For this purpose, the pressure drop, friction factor, and Poiseuille number under isothermal conditions and the temperature profile, heat transfer coefficient, Nusselt number, and thermal performance index under diabatic conditions (heating power of 10 W) in a heat sink with a stainless steel microchannel with a hydraulic diameter of 850 μm were investigated numerically and experimentally for mass flow rates between 1 and 68 gmin−1. The source of inconsistencies in pressure drop characteristics is found to be linked to the geometrical details of the utilized microchannel, for example, the design of inlet/outlet manifolds, the artifacts of manufacturing technique, and other features of the experimental test rig. For the heat transfer characteristics, it is identified that an appropriate estimation of the outer boundary condition for the numerical simulation remains the crucial challenge to obtain a reasonable agreement. The paper provides a detailed overview of how to account for these details to mitigate the discrepancies and to establish a handshake between experiments, numerical simulations, and theory.

A New Process for Efficient Recovery of Rhodium from Spent Carbonyl Rhodium Catalyst by Microreactor.

Triphenylphosphine acetylacetone carbonyl rhodium (ROPAC) is an important catalyst in the petrochemical industry, and its deactivated waste catalyst holds significant value for recovery. This study focuses on the existing forms of rhodium (Rh) in waste catalysts and the current status of traditional processes. A green, efficient, and continuous recovery technique was developed using a sealed stainless steel microchannel reactor. The influence of reaction temperature, reaction time, and phase ratio on the Rh recovery rate was investigated, and the process parameters were optimized using response surface methodology (RSM). The results indicate that the magnitude of the impact on the Rh recovery rate follows the order: reaction temperature > reaction time > phase ratio. The optimized process parameters were determined as follows: a reaction time of 29 min, a reaction temperature of 110 °C, and a phase ratio of 1:1, with a corresponding maximum recovery rate of Rh of 66.06%. Furthermore, secondary treatment was performed on the organic phase after primary recovery using the same process conditions, resulting in an overall Rh recovery rate of 95.6%, indicating satisfactory recovery efficiency. Moreover, the application of FTIR and ICP-OES analysis provided definitive evidence that the oxidative dissociation of the rhodium-phosphine chemical bond by H2O2 within ROPAC leads to the conversion of Rh+ into Rh3+. Subsequently, Rh forms chloroaquorhodium (III) complexes that enter the aqueous phase, enabling effective recovery of Rh.

Intensification of catalytic reaction of nitrous oxide decomposition into a replaceable wall-coated microreactor using electrophoretic deposition method

The novel replaceable wall-coated micro-reactor has been introduced to eliminate the hazardous nitrous oxide by utilizing the direct catalytic decomposition method. The commercial Pd/ γ-Al2O3 catalyst (containing 0.5 wt.% Pd) is coated on SUS304 stainless steel microchannels walls by using electrophoretic deposition (EPD) and then investigated at the temperature range of 300-400 °C. The main scope of this study is to define the optimum parameters affecting EPD such as deposition time, electrophoretic voltage, and solvent as the suspension media to reach the complete decomposition of nitrous oxide. The catalytic activity of the coated microchannels is verified at various gas hourly space velocities (GHSV). The nitrous oxide decomposition is enhanced 300% by raising the deposition time from 1 minute to 3 minutes and then remarkably is declined 80% at times higher than 3 minutes. The optimum electrophoretic deposition parameters including deposition time of 3 minutes at the voltage of 120 V in the range of 30-160 V and isopropanol as the solvent, resulting in 100% decomposition of nitrous oxide at 400 °C and GHSV of 1000 mL h−1 g−1cat . Moreover, the performance of the wall-coated micro-reactor at optimum EPD conditions compared to the equivalent packed-bed reactor caused 40% improvement in nitrous oxide decomposition and its energy consumption is 33.3% lower than packed-bed reactor for equal N2O decomposition.

Development and performace evaluation of a combustor with silicon carbide microchannel cooling

ABSTRACT This study developed a combustor with silicon carbide (SiC) microchannels cooling (SiC MC) at the walls by the motivation of the excellent physical properties of SiC and its promising application in aerospace areas. Its thermal and combustion performance was experimentally explored by the comparison of a combustor with stainless steel microchannel cooling (STS MC). Results showed that the combustor with SiC MC induced much more complete combustion, an 18–20% increase in combustion efficiency, and a 5.3–5.6% decrease in CO emissions than the STS MC counterpart. Besides, the effects of coolants on the performance of combustor with SiC MC were also evaluated.

Scale-up of high-pressure F-T synthesis in 3D printed stainless steel microchannel microreactors: Experiments and modeling

Scale-up of Fischer-Tropsch (F-T) synthesis using microreactors is very important for a paradigm shift in the production of fuels and chemicals. The scalability of microreactors for F-T Synthesis was experimentally evaluated using 3D printed stainless steel microreactors, containing seven microchannels of dimensions 1000 µm × 1000 µm × 5cms. Mesoporous silica (KIT-6), with high surface area, containing ordered mesoporous structure was used to incorporate 10% cobalt and 5% ruthenium using a one-pot hydrothermal method. Bimetallic Co-Ru-KIT-6 catalyst was used for scale-up of F-T Synthesis. The performance of the catalysts was evaluated and examined for three different scale-up configurations (stand-alone, two, and four microreactors assembled in parallel) at both atmospheric pressure and 20 bar at F-T operating temperature of 240 °C using a syngas molar ratio (H2:CO) of 2. All three configurations of microreactors yielded not only comparable CO conversion (85.6–88.4%) and methane selectivity (~14%) but also similar selectivity towards lower gaseous hydrocarbons like ethane, propane, and butane (6.23–9.4%) observed in atmospheric F-T Synthesis. The overall selectivity to higher hydrocarbons, C5 + is in the range of 75–82% at 20 bars.A CFD model was used to investigate the effect of different design features and numbering up approaches on the performance of the microchannel reactor. The effect of the reactor inlet, the mixing internals and the channel designs on the dead zone %, the quality index factor, the cooling requirement and the maximum dimensionless temperature within the microreactor were quantified. There is no significant effect of increasing the channel width on the microreactor performance and operation of the microchannel reactor at lower Nusselt number that results in higher CO conversion. Increasing the channel width reduced the maximum temperature exhibited in the channel. Finally, the effect of increasing the y/x stacking ratio, i.e. having more reactor units in parallel compared to series, was investigated. Increasing the y/x ratio increased the cooling requirement and the maximum dimensionless temperature increase within the unit decreased the productivity. To minimize the productivity losses, numbering up in series is the better approach; however further analysis must be done to delineate heat removal requirements.

Forced Convection Nanofluid Heat Transfer as a Function of Distance in Microchannels.

As electronic devices become smaller and more powerful, the demand for micro-scale thermal management becomes necessary in achieving a more compact design. One way to do that is enhancing the forced convection heat transfer by adding nanoparticles into the base liquid. In this study, the nanofluid forced convection heat transfer coefficient was measured inside stainless-steel microchannels (ID = 210 μm) and heat transfer coefficient as a function of distance was measured to explore the effects of base liquid, crystal phase, nanoparticle material, and size on heat transfer coefficient. It was found that crystal phase, characteristics of nanoparticles, the thermal conductivity and viscosity of nanofluid can play a significant role on heat transfer coefficient. In addition, the effects of man-made and commercial TiO2 on heat transfer coefficient were investigated and it was found that man-made anatase TiO2 nanoparticles were more effective to enhance the heat transfer coefficient, for given conditions. This study also conducted a brief literature review on nanofluid forced convection heat transfer to investigate how nanofluid heat transfer coefficient as a function of distance would be affected by effective parameters such as base liquid, flow regime, concentration, and the characteristics of nanoparticles (material and size).

Preparation of astaxanthin by lipase-catalyzed hydrolysis from its esters in a slug-flow microchannel reactor

Natural astaxanthin is widely used as a food and cosmetics additive because of its multiple biological activities. However, astaxanthin produced by Haematococcus pluvialis is generally esterified, and its activity is far less than that of free astaxanthin. Hydrolysis of astaxanthin esters to free astaxanthin by enzymes can overcome the drawbacks of chemical saponification methods. In this paper, a slug-flow microchannel reactor was constructed and tested in enzymatic hydrolysis of astaxanthin esters. The reactor consists of a “T” slug-flow generator, a stainless-steel microchannel, two constant-flow pumps, and a temperature controller. The reactor has the advantages of simple configuration and easy scale-up, and is suitable for two-phase biochemical reactions. Using the microchannel reactor, astaxanthin esters in H. pluvialis oil were efficiently hydrolyzed to free astaxanthin by lipase from Aspergillus niger. After hydrolysis, the content of free astaxanthin in H. pluvialis oil was 18.8 mg/L, 7.83-times higher than that before hydrolysis (2.13 mg/L). The hydrolysis rate reached 75.4 %. These results indicate that the microchannel reactor can be useful for the production of free astaxanthin from its esters.

Composite mesoporous SiO2-Al2O3 supported Fe, FeCo and FeRu catalysts for Fischer-Tropsch studies in a 3-D printed stainless-steel microreactor

Composite oxide support, SiO2-Al2O3, with high surface area, was prepared by one-pot procedure, and 10 wt%Fe, 10%Fe5%Co, and 10%Fe5%Ru were impregnated for Fischer-Tropsch (FT) studies. BET studies show the hysteresis loop for mesoporous (m) structure of the composite. H2-TPR studies showed the effect of Ru and Co on iron oxide reduction at lower temperature and XPS studies confirmed two oxidation states for cobalt and iron with different binding energies. The FT studies in a 3D printed stainless steel (SS) microchannel microreactor were performed at 1 atm at 300 °C. 10Fe5Ru catalyst showed better CO conversion and higher selectivity to C1–C3 hydrocarbons.

Fischer-Tropsch studies in a 3D-printed stainless steel microchannel microreactor coated with cobalt-based bimetallic-MCM-41 catalysts

Fischer-Tropsch (FT) synthesis was carried out using 3D-printed stainless steel (SS) microreactors, containing channels of dimensions 500 μm × 500 μm ×2.7 cm, to study the effect of Fe, Ru, and Ni on Co-MCM-41 catalyst. The mono and bimetallic cobalt-based catalysts: 15 % Co-MCM-41, 10 %Co5% Ru MCM-41, 10 %Co 5%Ni MCM-41, and 10 %Co 5%Fe MCM-41 were synthesized using one-pot hydrothermal method and characterized by SEM-EDX, TEM, TPR, FTIR, XPS, and low and wide angle XRD techniques. All the catalysts exhibited high surface area without the loss of ordered mesoporous structure as confirmed by large BET surface areas (400- 1000 m2/g) and low angle XRD data. The metal nanoparticles were in the range of 35−50 nm and well dispersed in a hexagonal matrix of MCM-41. TPR data indicate that all other metal oxides except that of cobalt can be reduced with H2 below 600 °C. Cobalt is present most likely as cobalt silicates that can only be reduced with H2 at a temperature over 650 °C. The microchannels of SS reactor were uniformly coated by dip coating a slurry of the catalyst with polyvinyl alcohol (PVA). The catalytic performance for FT synthesis was carried out in the SS microreactor at atmospheric pressure in the temperature range of 180–300 °C with H2/CO molar ratio of 3. Incorporation of the second metal in the Co-MCM-41 framework and the operating temperature had a significant effect on CO conversion and selectivity towards C1-C4 alkanes in FT synthesis. While the highest CO conversion of 74 % was obtained for CoFe-MCM-41 at 240 °C, the highest selectivity towards butane (11 %) and propane (39 %) was observed for CoRu-MCM-41 at 240 °C and CoFe-MCM-41 at 210 °C, respectively. The rate of deactivation of the catalysts -followed the order: CoRu-MCM-41> CoNi-MCM-41> Co-MCM-41> CoFe-MCM-41, indicating that CoFe-MCM-41 is the most suitable catalyst for F–T synthesis in terms of long term stability.

Modeling of Subcooled Boiling Heat Transfer to Cool Electronic Components in a Micro-Channel

This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working fluid. The heat flux varies from 600 - 750 kW·m-2, input velocity from 1 - 2 m·s-1, and the subcooled temperature varies from 59.6 - 79.6 K. The working pressure and saturation temperature are 1 atm and 372.75 K, respectively. The results show that, the flow boiling keeps the temperature of the channel wall lower and more uniform than a single-phase flow, as long as the flow boiling does not reach the dry-out point. The onset point of dry-out depends on three factors, heat flux, inlet velocity, and subcooled temperature. In addition, the dry-out occurs at a point near the channel inlet with increased heat flux and subcooled temperature. Decreasing the inlet velocity would also cause the dry-out point to shift closer to the inlet of the channel.

Application of a micro-channel reactor for process intensification in high purity syngas production via H2O/CO2 co-splitting

A stainless steel micro-channel reactor was tailor-made to an in house-design for process intensification propose. The reactor was used for a two-step thermochemical cycles of H2O and CO2 co-splitting reaction, in the presence of La0.3Sr0.7Co0.7Fe0.3O3 (LSCF). LSCF was coated inside the reactor using wash-coat technique. Oxygen storage capacity of LSCF was determined at 4465 μmol/g, using H2-TPR technique. H2O-TPSR and CO2-TPSR results suggested that a formation of surface hydroxyl group was the cause of H2O splitting favorable behavior of LSCF. Optimal operating reduction/oxidation temperature was found at 700 °C, giving 2266 μmol/g of H2, 705 μmol/g of CO, and 67% of solid conversion, when the H2O and CO2 ratio was 1 to 1, and WSHV was 186,000 mL/g.h. Activation energy of H2O spitting and CO2 splitting was estimated at 87.33 kJ/mol, and 102.85 kJ/mol The pre-exponential factor of H2O splitting and CO2 splitting was 595.24 s−1 and 698.79 s−1, respectively.

Kinetics of Fischer–Tropsch Synthesis in a 3-D Printed Stainless Steel Microreactor Using Different Mesoporous Silica Supported Co-Ru Catalysts

Fischer–Tropsch (FT) synthesis was carried out in a 3D printed stainless steel (SS) microchannel microreactor using bimetallic Co-Ru catalysts on three different mesoporous silica supports. CoRu-MCM-41, CoRu-SBA-15, and CoRu-KIT-6 were synthesized using a one-pot hydrothermal method and characterized by Brunner–Emmett–Teller (BET), temperature programmed reduction (TPR), SEM-EDX, TEM, and X-ray photoelectron spectroscopy (XPS) techniques. The mesoporous catalysts show the long-range ordered structure as supported by BET and low-angle XRD studies. The TPR profiles of metal oxides with H2 varied significantly depending on the support. These catalysts were coated inside the microchannels using polyvinyl alcohol and kinetic performance was evaluated at three different temperatures, in the low-temperature FT regime (210–270 °C), at different Weight Hourly Space Velocity (WHSV) in the range of 3.15–25.2 kgcat.h/kmol using a syngas ratio of H2/CO = 2. The mesoporous supports have a significant effect on the FT kinetics and stability of the catalyst. The kinetic models (FT-3, FT-6), based on the Langmuir–Hinshelwood mechanism, were found to be statistically and physically relevant for FT synthesis using CoRu-MCM-41 and CoRu-KIT-6. The kinetic model equation (FT-2), derived using Eley–Rideal mechanism, is found to be relevant for CoRu-SBA-15 in the SS microchannel microreactor. CoRu-KIT-6 was found to be 2.5 times more active than Co-Ru-MCM-41 and slightly more active than CoRu-SBA-15, based on activation energy calculations. CoRu-KIT-6 was ~3 and ~1.5 times more stable than CoRu-SBA-15 and CoRu-MCM-41, respectively, based on CO conversion in the deactivation studies.

The effect of operating conditions on acylation of 2-methylnaphthalene in a microchannel reactor

Abstract Acylation of 2-methylnaphthalene (2-MN) is a very important reaction in organic synthesis, and the effiency of the continuous reactor is more than one of the batch reactor. Considering that the Friedel–Crafts acylation is a rapid exothermic reaction, in this study, we perform the acylation of 2-MN in a stainless steel microchannel flow reactor, which is characterized by high mass and heat transfer rates. The effect of reactant ratio, mixing temperature, reaction temperature, and reaction time on product yield and selectivity were investigated. Under the optimal conditions, 2-methyl-6-propionylnaphthalene (2,6-MPN) was obtained in 85.8% yield with 87.5% selectivity. Compared with the conventional batch system, the continuous flow microchannel reactor provides a more efficient method for the synthesis of 2,6-MPN.

Preparation of monodisperse W/O emulsions using a stainless-steel microchannel emulsification chip

ABSTRACTIn this study, hydrophobically treated stainless-steel microchannel (MC) array chips were used for preparing monodisperse W/O emulsions. A water-saturated decane containing 5 wt% tetraglycerin monolaurate condensed ricinoleic acid ester was used as the continuous phase. A Milli-Q water containing 5 wt% polyethylene glycol (molecular weight 20,000) and 5 wt% NaCl was used as the dispersed phase. The stainless-steel MC array chips used for MC emulsification had a sufficiently high contact angle of the dispersed phase to their surface in the continuous phase. The resultant uniform-sized aqueous droplets with a coefficient of variation of <5% had average diameters of 100–300 µm, depending on the MC cross-sectional size. The maximum productivity of uniform-sized aqueous droplets reached higher than 1 mL h−1. The difference in the critical capillary number of the dispersed phase that flows in a 100-µm depth MC was 1.5 times greater than that in a 30-µm depth MC.

Analysis of Deep Drawing Process for Stainless Steel Micro-Channel Array.

The stainless steel bipolar plate has received much attention due to the cost of graphite bipolar plates. Since the micro-channel of bipolar plates plays the role of fuel flow field, electric connector and fuel sealing, an investigation of the deep drawing process for stainless steel micro-channel arrays is reported in this work. The updated Lagrangian formulation, degenerated shell finite element analysis, and the r-minimum rule have been employed to study the relationship between punch load and stroke, distributions of stress and strain, thickness variations and depth variations of individual micro-channel sections. A micro-channel array is practically formed, with a width and depth of a single micro-channel of 0.75 mm and 0.5 mm, respectively. Fractures were usually observed in the fillet corner of the micro-channel bottom. According to the experimental results, more attention should be devoted to the fillet dimension design of punch and die. A larger die fillet can lead to better formability and a reduction of the punch load. In addition, the micro-channel thickness and the fillet radius have to be taken into consideration at the same time. Finally, the punch load estimated by the unmodified metal forming equation is higher than that of experiments.

Correlation between structure, acidity and activity of Mo-promoted Pt/ZrO2-TiO2-Al2O3 catalysts for n-decane catalytic cracking

A series of Pt/MoO3/ZrO2-TiO2-Al2O3 composite oxides with various MoO3 contents were prepared by incipient wetness impregnation method, and coated on the inner wall of stainless-steel microchannels. Catalytic cracking of n-decane (as model molecule of hydrocarbon fuel) over such monolithic catalysts were investigated under high temperature and high pressure conditions. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS) and temperature programmed desorption of ammonia (NH3-TPD) techniques. The correlation between the catalytic performances of MoO3 modified catalysts and their structure as well as acidic property were observed. It was found that the conversion and heat sink of n-decane were obviously heightened compared with that obtained from thermal cracking. In particular, the catalyst which contains 7.0wt.% MoO3 exhibited the best catalytic cracking activity among the prepared catalysts, which is in well agreement with its highest amount of total acid sites and strong acid centers, along with the finely dispersed isolated and octahedral molybdenum species.

Catalytic cracking of RP-3 jet fuel over wall-coated Pt/ZrxTi0.9−xAl0.1O2 mixed oxides catalysts

This study involves a new series Pt-loaded ZrxTi0.9−xAl0.1O2 (PZTA) mixed oxides with different molar ratios of ZrO2:TiO2 (ZrO2:TiO2:Al2O3 = x:(0.9 − x):0.1, where x = 0, 0.225, 0.45, 0.675, 0.9) catalysts with high temperature resistant and large surface acidity for catalytic cracking of RP-3 jet fuel under high-temperature and high pressure conditions. PZTA catalysts were prepared by using a specially designed that co-precipitation technique subsequent incipient wetness impregnation, and were coated on the wall of stainless-steel microchannels. It was found that gas yield and heat sink of catalytic cracking over the as-prepared catalysts were noteworthy augmented compared with the thermal cracking. Furthermore, different molar ratios of ZrO2:TiO2 could greatly affect the catalytic cracking activities of RP-3 jet fuel. To be more specific, Cat3 (ZrO2:TiO2 = 0.45:0.45) performed the excellent cracking activity and high-temperature stability, which is in accordance with its bigger amount of strong acid, larger surface area and good dispersion effect of Pt. The gas yield, the alkenes content within the gas phase product and the heat sink of Cat3 at 700 °C are 40.7%, 51.5% and 3.41 MJ/kg. SEM/TEM measurements further demonstrated that the active phase (Pt) is fairly well dispersed with a particle size of 3–6 nm. The valuable information indicated in this work is that based on the special characters of PZTA, ternary composite oxides supported Pt, which should be an effective approach to maintain both catalytic activities and thermal stability.

A Novel Method to from Well-adhered γ-Al2O3 Coating in 316L Stainless Steel Microchannels

Abstract A method to enhance the adherence of Al 2 O 3 coating with AISI 316L metallic substrate was proposed in this study. The substrate was aluminized by pack cementation at 850°C for 10 h, and then oxidized at 900°C for 10 h, subsequently, the Al 2 O 3 whiskers formed uniformly. The suspension mixing 3 μm γ-Al 2 O 3 powder, alumina sol, PVA and water was directly applied to the microchannels pretreated by above mentioned aluminizing and oxidation method by dip coating. And then the sample was dried and calcined at 600°C for 2 h to form γ-Al 2 O 3 coating in the micochannel. The morphology and phase composition of the coating were characterized by X-Ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscope (SEM). The adhesion between the substrate and coating was tested by ultrasonic vibration. The results showed that aluminized treatment could effectively improve the adhesion, and the mass-loss rate of the coating was only 1.24%. The main pore size of the coating was between 30 A and 100 A. The coating has no cracks, and possessed with high specific surface area, 234 m 2 /g.

Hybrid Fabrication of Stainless Steel Channels for Microfluidic Application

This research develops a hybrid micromanufacturing technique by combining micromilling and electrochemical micropolishing to fabricate extremely smooth surface finish, high aspect ratio, and complex microchannel patterns. Milling with coated and uncoated ball-end micromills in minimum quantity lubrication is used to remove most materials to define a channel pattern. The milled channels are then electrochemically polished to required finish. A theoretical model accurately predicts surface finish in meso-scale milling, but not in micro-scale milling due to size effect. Electrochemical polishing using an acid-based electrolyte is applied to repeatedly produce stainless steel microchannels with average surface finish of 100 nm when measuring across grain boundaries and 10 nm within a single grain.