Chamber Inlet Research Articles

Membrane-based sample inlet for centrifugal microfluidic cartridges

Centrifugal microfluidics enables the rapid execution of complex blood sample analyses in a fully automated manner at the point of care. However, during blood sample addition, the cartridge is at rest and centrifugal forces are not present to allocate the sample in a controlled way. We present a versatile approach for the user-friendly, well-controlled and safe sample addition into a centrifugal microfluidic cartridge for use in serology. It features a commercial (plasma separation) membrane stacked into the inlet chamber of the cartridge. This combination of sample inlet and plasma separation in one structural unit brings the advantage of reducing footprint in highly integrated point-of-care testing. By using a pipette the user may add a blood sample (90μL) to the membrane holding the liquid by capillary forces. Flowing across the membrane, cells separate from blood plasma. The blood plasma releases into the downstream structure upon centrifugation. The mean plasma recovery rate was 57.3 (±4.7) % and mean plasma purity 99.5 (±0.6) % from samples of varying hematocrit (36%–59%). Furthermore, the analyte C-reactive protein (CRP) did not significantly adsorb to the membrane. This was concluded, since CRP immunoassay results with plasma from spiked whole blood, obtained from membrane-based plasma separation and from plasma separation on a standard laboratory centrifuge, did not significantly differ. Thus, the suggested approach is promising for simultaneous application as sample inlet holding the sample by capillary forces and as a plasma separation module for centrifugal microfluidics. Potential future applications may include other sample matrices. The use with further blood transfer devices (capillary, directly from fingertip) seems possible, yet requiring further evaluation.

Pro-oxidative effects of spray drying orange oil in a bench top dryer

ABSTRACTThe influence of potential heat exposure during spray drying on the oxidative stability of spray dried orange oil was studied. The design of some of the table top spray driers expose dried product to dryer exit air temperatures in the powder collection chamber or on the walls of the dryer if there is an accumulation of material on the drying chamber walls. This heat exposure may accelerate oxidation of the product in subsequent storage. To determine the potential for heat damage to affect oxidation of the powders produced, an orange oil infeed emulsion (carrier material - modified starch) was prepared and spray dried using the sample collection chamber supplied by the manufacturer as standard equipment. The spray dryer was then modified to extend the collection chamber inlet such that the product remained cooler than in the standard collection chamber. In this study, the spray dryer was operated for 1 h (inlet air temperature; 180°C and an exit air temperature; 100°C). Thus, the spray dry product could have been exposed to as much as 1 h of heating in the collection chamber (potentially at temperatures as high as the exit air temperature). In the case of spray drying with a collection chamber extension, the collected product was maintained at ca. room temperature. This would approximately mimic the heat exposure powders receive in an industrial spray dryer. Powders produced using both equipment designs were taken from both the collection and drying chambers, adjusted in water activity (0.33) under a nitrogen environment, and then put into storage in an incubator maintained at 35°C for 4 weeks (exposed to air). The ratio of limonene oxide to limonene was used to monitor oxidation using gas chromatography. This study showed a substantial increase in rate of oxidation of the spray dried powder from the table top spray dryer with the standard commercial collection chamber and much less in case of an extended collection chamber. The powder from the respective drying chamber also showed a higher rate of oxidation in comparison to its collection chamber. Thus, we urge researchers studying heat damage (e.g., oxidation) of powders produced on the table top dryers to be conscious of overestimating heat damage during drying.

Investigations of flow structures and heat transfer in a swirl chamber with different inlet chambers and various aerodynamic parameters

This paper numerically compares the flow structures and thermal performance in a swirl chamber with three different inlet chambers. The cross section of inlet chambers are constant, convergent, and divergent along the streamwise direction, respectively. Parametric studies involve Reynolds number and the temperature ratio between cooling air and the wall of swirl chamber. Results indicate that shear layer vortices, corner vortices, and large-scale vortices appear in different sections of swirl chamber. Besides, Görtler vortices appear in convergent inlet chamber. The alternation of the inlet chamber changes more than the value of the Nusselt number. It also changes the flow structures and the distribution of Nusselt number. In comparisons, the swirl chamber with convergent inlet chamber possesses the highest thermal performance coefficient. With the increase of Reynolds number, the intensity of heat transfer is significantly enhanced. Different from former research, the rise of temperature ratio leads to relatively high Nusselt number due to the addition of multiple jet nozzles and the inlet chamber. In addition, empirical correlation among global average Nusselt number, Reynolds number, and temperature ratio is obtained to assist relevant research and design.

Effects of injection nozzle exit width on rotating detonation engine

A series of numerical simulations of RDE modeling real injection nozzles with different exit widths are performed in this paper. The effects of nozzle exit width on chamber inlet state, plenum flowfield and detonation propagation are analyzed. The results are compared with that using an ideal injection model. Although the ideal injection model is a good approximation method to model RDE inlet, the two-dimensional effects of real nozzles are ignored in the ideal injection model so that some complicated phenomena such as the reflected waves caused by the nozzle walls and the reversed flow into the nozzles can not be modeled accurately. Additionally, the ideal injection model overpredicts the block ratio. In all the cases that stabilize at one-wave mode, the block ratio increases as the nozzle exit width gets smaller. The dual-wave mode case also has a relatively high block ratio. A pressure oscillation in the plenum with the same main frequency with the rotating detonation wave is observed. A parameter σ is applied to describe the non-uniformity in the plenum. σ increases as the nozzle exit width gets larger. Under some condition, the heat release on the interface of fresh premixed gas layer and detonation products can be strong enough to induce a new detonation wave. A spontaneous mode-transition process is observed for the smallest exit width case. Due to the detonation products existing in the premixed gas layer before the detonation wave, the detonation wave will propagate through reactants and products alternately, and therefore its strength will vary with time, especially near the chamber inlet. This tendency gets weaker as the injection nozzle exit width increases.

Counter-current flow limitation for air-water and steam-water flows in a PWR hot leg geometry

Steady state counter-current flow limitation (CCFL) experiments were conducted in a 1:3 scaled flat model of the hot leg and part of the steam generator inlet chamber of a German Konvoi pressurized water reactor. The experiments include air-water tests at 1 and 2bar as well as steam-water tests at 10, 25 and 50bar. Flooding characteristics are obtained in dependency on the dimensionless gas and liquid flow rates (Wallis-parameter). They showed a slight, but clear dependency on pressure – with increasing pressure more liquid can flow in counter-current to the gas in case of partial CCFL. Also the dimensionless gas flow rate for zero penetration slightly increases with pressure. Beside the flooding characteristics also slug frequencies were analyses basing on pressure measurements along the horizontal part of the test section. Finally, comprehensive video material was obtained which is suited for extracting quantitative data on the local flow structure. This can contribute to the further CFD-code development and validation.

In-situ measurement of residence time distributions in a turbulent oxy-fuel gas-flame combustor

For improving the design of combustors, the knowledge of residence-time distributions (RTD) is important as they influence exhaust gas compositions. Measuring RTDs in combustors is challenging, due to high temperatures, chemical reactions, the presence of particles or corrosive species as well as high turbulence levels. This paper presents a technique for the in situ measurement of RTDs in combustors. Based on tunable diode laser absorption spectroscopy (TDLAS), the temporal evolution of the concentration of tracers is tracked simultaneously at the combustion chamber inlet and outlet. Using either air or mixtures of oxygen and carbon dioxide (oxy-fuel atmosphere) as oxidants, the method is applied to reacting and non-reacting operating conditions in a 20-kWth methane combustor. For reacting conditions, hydrogen chloride is used as a tracer, whereas for non-reacting conditions methane was chosen. Depending on the tracer, for a repetition rate of approximately 2 kHz detection limits of 16–40 ppmV are achieved. For deriving RTDs, low-pass filtering is compared to reactor network modeling. Different RTDs observed for varying operating conditions are discussed.

Discharge source-dependent variation in the densities of active species in the flowing afterglows of N2 RF and UHF plasmas

With a potential application to surface modification of oxide materials in mind, active species in RF and microwave (UHF) N2 afterglows were analyzed in our newly designed flowing reactors. For both plasma systems, discharge of N2 was generated in a long quartz tube with a small diameter (dia. 5–6 mm) and then was directly injected into a chamber with a large diameter of 15–20 cm. The discharge condition was set to be similar between the two systems; the gas pressure, flow rate and the applied power were 6 Torr, 0.6 slm and 100 W, respectively. Under this condition, the residence time at the chamber inlet was (1–3) x 10−3 s. The RF and UHF afterglows were formed in the chamber with luminous jets from the end of the discharge tube. However, we found that the densities of active species were quite source-dependent; N and N2(A) densities were higher in UHF than in RF in spite of more O-atoms impurity. The origin of such difference is also attributed to the inherent difference in the nature of excitation between the two plasma sources; RF is more vibrational and is longer than UHF.

Simulation of 3D Flow Field on Pneumatic Butterfly Valve System for Sequential Turbocharging Diesel Engine

Sequential turbocharging is the most effective method to improve the performance for high pressure diesel engine at low load. Pneumatic butterfly valve system is an important part of diesel engine. A three-dimensional flow field numerical simulation mode was established based on FLUENT software for pneumatic butterfly valve system, which provides a theoretical basis for the analysis of pneumatic butterfly valve performance. Research results show that the air rate in exhaust chamber is larger than inlet chamber, the velocity in the electromagnetic valve throttle of inlet pipe is maximum, and inlet throat velocity variation is not obvious. When the fluid flow from the inlet pipe through into the inlet throat and chamber, the flow velocity take on a spurting shape of the throat as a vertex. Along with the increase of pressure in the intake cylinder, the pressure differential is reduced between the throttle and throat, flow speed obviously showed a trend of slowing down.

Co-production of cement and carbon nanotubes with a carbon negative footprint

C2CNT (CO2 to carbon nanotube) cement plants are introduced and analyzed with a significant economic incentive to eliminate current plant CO2 greenhouse gas emissions. The exhaust from partial and full oxy-fuel cement plant configurations are coupled to the inlet of a C2CNT chamber in which CO2 is transformed by electrolysis in a molten carbonate electrolyte into CNTs at a steel cathode and pure oxygen at a nickel anode that is looped back in improving cement line energy efficiency and production rate. A partial oxy-fuel process looping O2 back through the plant calcinator has been compared to a full process in which it enters through the plant kiln. The first provides easier retrofit; the second maximizes efficiency by minimizing N2 throughput. Providing an economic impetus to carbon dioxide removal, per ton CO2 avoided the C2CNT cement plant consumes $50 electricity, emits no CO2, and produces $100 cement and ∼$60,000 of CNTs.

Effect of gas flow rates and nozzle throat width on deposition of α-alumina films of granule spray in vacuum

Deposition of α-alumina film by spraying alumina granules in a vacuum at room temperature was performed using a modified aerosol deposition system that had a supplemental gas flow line in addition to the carrier gas flow line. The pressure difference between the nozzle inlet and deposition chamber was increased by increasing the supplemental gas flow rate or by decreasing the nozzle throat width. For the same nozzle, the alumina film thickness per granule consumption increased as the pressure difference was increased. However, the film obtained by using the wide throat nozzle was thicker than that by using the narrow throat nozzle in spite of the smaller pressure difference except for the case without using the supplemental gas. The deposition behaviors according to the supplemental gas flow rate and the nozzle throat width were explained in part by the friction-affected layer near the nozzle throat wall and a critical granule velocity for film deposition. Alumina granules and films were characterized by scanning electron microscopy, X-ray diffractometry, surface profilometry, and transmission electron microscopy to assess and correlate the film quality to the deposition conditions.

Experimental stand for investigation of fluid flow in heat exchangers with cross-flow arrangement

The operation analysis of high-performance heat exchanger with tubes elliptical indicated that the heat exchangers can be subject to damage. The reason for this is probably improper distribution of working fluid in tubular space of heat exchanger. Therefore, a part of the tubes may be improperly cooled and subject to compressible stresses. The paper presents an experimental stand allowing to confirm the given assumption. The experimental investigation enables to examine the mass flow rate in heat exchanger tubes. Also, it is possible to assess the impact of the construction of inlet, intermediate and outlet chambers on the flow distribution within the heat exchanger tubes.

Preliminary study of the primary nozzle position of a supersonic air ejector with a constant-area mixing chamber

This work aims at investigating the primary nozzle position in a proposed supersonic air ejector device. The ejector is primarily made up of a supersonic primary nozzle, which is located in the axis of the ejector, a suction chamber or secondary stream inlet, a mixing chamber and a diffuser. The ejector design allows to translate the primary nozzle in the axis direction and fix it in a chosen distance from the beginning of the mixing chamber and hence influence the secondary mass flow rate. In a limit case, it is possible to set the nozzle to such a position where no secondary flow occurs. If we ignore the case where no secondary flow occurs, five different nozzle distances have been investigated in this paper. Some cases seem to be alike and there are no significant dissimilarities between them. Courses of relative back-pressure ratio are carried out against the entrainment ratio and transition between on-design and off-design regimes is determined. Measurements of the mixed flow based on the standard ISO 5167 are performed by means of orifice plate method. In addition, a comparison between experiments and simulations performed by Ansys Fluent software is presented in order to indicate further improvements to the numerical model.

Air-Based Dynamic Structure for On-chip Cell Seeding and Culture

This paper reports a novel method of using air column to temporarily change microfluidic structure for cell seeding and culture in a microfluidic chamber. In conventional on-chip culture system, the medium flow has to be carefully controlled to prevent from excessive shear stress that washes out cells. We propose a method to directly seed cells into a stagnation area so that the cells can be stably cultured inside a microfluidic chamber without being affected by the flow. Air column is intentionally introduced during the seeding, and it forms a virtual wall, which temporarily changes the flow pattern. The changed flow allows the cell to flow into the stagnation area for seeding. The idea has been experimentally tested, and cells are successfully seeded and cultured in a single inlet chamber.

CFD Simulation of Ejector in Steam Jet Refrigeration

In this study CFD technique was employed to investigate the effect of divergent angle of primary nozzle, NXP (NXP = Distance between the nozzle exit to mixing chamber inlet) and throat of the ejector on the performance of ejector using the steam jet refrigeration cycle. In all these cases, only one fixed mixing chamber with different divergent primary nozzle, NXP and throat of an ejector was investigated numerically using the commercial CFD package, the effect of primary fluid pressure mass flow rate and mach numbers were observed and analyzed. The velocity contour lines were used to explain the happening of process inside the ejector it was found that the throat diameter, NXP and diverging angle of primary nozzle plays a crucial role in the steam jet refrigeration.

Study on Design of Pressure Chamber in a Linear-Jet Type Air Curtain System for Prevention of Smoke Spread

Death toll by smoke in fire is estimated at 70% which emphasizes the importance of smoke control system to deal with the fire smoke. In advanced countries, the studies on method to prevent smoke spread by forming the air curtain using high velocity jet flow are underway now. In this study, a linear-jet type air curtain system is proposed to prevent the smoke spread and analysis of flow characteristics of pressure chamber, which is the core component, is conducted through numerical analysis and experimental approach. Consequently, the pressure was increased in 2D functional way to input air flowrate and about 595 Pa pressure was formed at pressure chamber inlet in response to 30 m/s nozzle jet velocity.

유동분배판에 의한 원통-다관형 열교환기의 성능 특성에 관한 수치해석적 연구(II): 전열특성

The flow pattern inside the inlet chamber of the tube side is one of the key parameters influencing on the performances of the shell-and-tube type of heat exchangers(STHE). In order to improve the flow distribution, the baffle shaped as the porous plate is installed in the inlet chambers. In the present study, numerical simulation has been performed to investigate the flow features of the tube side of the STHE in sense of the hydraulic performances. The flow fields have been analysed by the three-dimensional Navier-Stokes solvers with the proper turbulent models. Computational domain is ranged in the whole of the tube side of the STHE. The numerical results showed that the presence of the baffles improves the redistribution of the flow injecting to the tube bundels. The good agreements of the numerical results with the experimental results of PIV measurements have been shown for the validation of the numerical methods adopted in the present papers.

Effect of geometry and speed on the temperatures estimated by CFD for an isothermal model of a gamma configuration low temperature differential Stirling engine with Flat-shaped heat exchangers

In the temperature distribution in a hot-side displacer chamber of a low temperature differential Stirling engine, a relation between the inlet temperature, average temperature and heat exchanger temperature is calculated by CFD and is expressed by the ratio of temperatures. The parameters of the CFD are the inlet velocity; the sizes of the inlet, heat exchanger and displacer; the positions of the inlet, heat exchanger and displacer chamber wall; and the temperatures of the inlet and heat exchanger. The calculation result and the estimated regenerator efficiency produce the temperature difference in the working fluid, which can be utilized for isothermal model analysis. In the Schmidt cycle, only a phase angle and the dimensionless value introduced here dominate the shape of the P-V diagram. The maximum fluctuation of the ensemble averaged working fluid temperatures (MFEAWFTs) is utilized to evaluate a P-V diagram. When the analyses are compared with experimental results, estimated MFEAWFTs are approximately 80% of the experimental results. In comparing the calculation results, a higher engine speed causes a lower average temperature on the hot side of a displacer chamber and the larger indicated power. A wider inlet reduces the difference between inlet temperature and average temperature. The longer stroke of displacer motion makes the indicated work larger to some extent.

The effects of compressor blade roughness on the steady state performance of micro-turbines

The aim of this work is to study the effects of the compressor blade roughness on the Off-Design performance of a microturbine. Compressor fouling is the most important factor of gas turbines performance deterioration and its main effect is compressor blade roughness growth. Hence understanding of microturbine behavior in case of blade roughness increment is an important step in gas turbine’s health monitoring. In current study a model is presented to simulate Off-Design performance of a Microturbine. The model is validated against experimental data. Characteristic map of a radial compressor in clean state and three different surface roughness has been employed in mentioned Off-Design model to calculate Effects of roughness growth on microturbine performance and determine sensitive parameters. This simulation’s results show blade roughness increment induces new condition which improves recuperator performance and micro turbine thermal efficiency in constant speed. But in this condition turbine inlet temperature is raised and exceeded from allowed temperature. So allowable output power fall significantly (about 8%). Results show that in constant power, combustion chamber inlet temperature with 2.8% and turbine exhaust temperature with 2.7% rise are most sensitive parameters to roughness changes while compressor discharge temperature has negligible sensitivity to roughness increment.

Design and Analysis of Solar Dryer for Mid-Latitude Region

In this study, an indirect natural convection updraft solar dryer was designed and fabricated with objectives to; suit mid-latitude applications, determine its performance efficiency, analyze air properties by use of psychrometric chart and assess the quality of dried product. The dryer was fabricated using low cost and locally available materials. For mid-latitude regions, zenith angle is dependent on latitude, solar declination angle, time of the year and of the day. Based on these changing parameters, the solar dryer was designed to suit the conditions. The main parts of the dryer are; hinged flexible angled solar collector, drying chamber consisting of three drying trays, updraft chimney with metallic absorber plate. The experiments were carried out to dry sliced apples of 2.5 mm thickness spread over the drying trays. Temperature and relative humidity of airflow were taken at the collector inlet, drying chamber inlet and drying chamber outlet to chimney using data loggers. Airflow inlet to solar collector and from drying chamber was determined using hot wire anemometers, irradiation in W/m2 was measured by radiation meter. Drying characteristics such as the collected solar energy to evaporated moisture, average drying rate, moisture content, etc., were determined. Natural convectional flow was adopted with an advantage of utilizing updraft air chimney to induce thermo-siphoning effect hence improving efficiency. In our current study, fresh apples of 886.64 grams with moisture content of 86% were dried to moisture content of 8.12% (wet basis) within 9 hours 20 minutes at an average irradiance of 534.45W/m2. The overall dryer efficiency was estimated to be 17.89%. The possibility of formation of water droplets within the drying chamber, which is a challenge to most direct solar dryers was considered to be minimal. This was based on analysis of the dew-point of drying chamber inlet air in comparison to outlet air properties. This design is simple; it can easily be replicated elsewhere in the world, products can be dried in one day and has capability to dry products at commercial scale while retaining the color, flavor and nutrients.

Predicting Flashback Limits of a Gas Turbine Model Combustor Based on Velocity and Fuel Concentration for H2–Air Mixtures

This study investigates the influence of the fuel injection strategy on safety against flashback in a gas turbine model combustor with premixing of H2–air mixtures. The flashback propensity is quantified and the flashback mechanism is identified experimentally. The A2EV swirler concept exhibits a hollow, thick-walled conical structure with four tangential slots. Four fuel injector geometries were tested. One of them injects the fuel orthogonal to the air flow in the slots (jet-in-crossflow injector (JICI)). Three injector types introduce the fuel almost isokinetic to the air flow at the trailing edge of the swirler slots (trailing edge injector (TEI)). Velocity and mixing fields in mixing zone and combustion chamber in isothermal water flow were measured with high-speed particle image velocimetry (PIV) and high-speed laser-induced fluorescence (LIF). The flashback limit was determined under atmospheric pressure for three air mass flows and 673 K preheat temperature for H2–air mixtures. Flashback mechanism and trajectory of the flame tip during flashback were identified with two stereoscopically oriented intensified high-speed cameras observing the OH* radiation. We notice flashback in the core flow due to combustion-induced vortex breakdown (CIVB) and turbulent flame propagation (TFP) near the wall dependent on the injector type. The flashback resistance (FBR) defined as the ratio between a characteristic flow speed and a characteristic flame speed measures the direction of propagation of a turbulent flame in the flow field. Although CIVB cannot be predicted solely based on the FBR, its distribution gives evidence for CIVB-prone states. The fuel should be injected preferably isokinetic to the air flow along the entire trailing edge in order to reduce the RMS fluctuation of velocity and fuel concentration. The characteristic velocity in the entire cross section of the combustion chamber inlet should be at least twice the characteristic flame speed. The position of the stagnation point should be tuned to be located in the combustion chamber by adjusting the axial momentum. Those measures lead to safe operation with highly reactive fuels at high equivalence ratios.