Serpentine Channel Research Articles

Insights on the interaction of serpentine channels and gas diffusion layer in an operating polymer electrolyte fuel cell: Numerical modeling across scales

Three-dimensional direct numerical simulations were performed for investigating the flow in a serpentine channel and the under-laying porous gas diffusion layer (GDL) of a micro polymer electrolyte fuel cell (PEFC). The flow field comprised three straight sections and two U-turns. The geometry was acquired with high-resolution (2.9 μm) in situ X-ray tomographic measurements on an operating cell. Simulations considered the GDL under dry and partially saturated conditions, whereby saturation was established via electrochemically produced water. A lattice Boltzmann (LB) methodology was adopted for simulating the single-phase (gas) transport in the actual 3D channel and porous GDL geometry. The global pressure drop in the dry GDL was dominated by the turns in the gas channel, while the pressure drops were quite small along the straight channel sections. In the wet GDL case, however, the pressure drop was mainly dictated by the neck-shaped passages created by the large water clusters inside the channel. Owing to the water blockage, the local accumulated cross-flows along the serpentine channel length, when normalized by the inlet channel flow, were substantially higher in the wet GDL, reaching local values up to 45% compared to 18% for the dry GDL. The implications are that in an electrochemically operating cell, the GDL under the rib would receive more gas (and thus O2). The creation of cross-flows through the porous GDL would enhance cell performance under the ribs since diffusion will not be the main driving mechanism for oxygen transport and water evaporation. The analysis indicated that the flow field, although designed as serpentine, behaved like half-interdigitated (with a rib of 1.5 mm, half-serpentine flow field, depending on the state of channel flooding).

Numerical investigation of effects of different flow channel configurations on the 100 cm2 PEM fuel cell performance under different operating conditions

The supply of species gases and removal of liquid water in a PEM fuel cell are performed through gas flow channels. Therefore, optimising the flow channel configurations is critical for maximising performance of fuel cells. In this paper, the ANSYS PEM Fuel Cell Module is used to simulate a PEM fuel cell with an active area of 100 cm2 and four different flow channel configurations: single-channel serpentine, two-channel serpentine, three-channel serpentine, and parallel channel with headers under two set of different operating conditions. Under both sets of operating conditions, the simulation results indicated that 3-channel serpentine configuration has the best performance due to uniform distribution of species gases over the catalyst layer. It was concluded from the simulation results that the pressure-drop along the 3-channel serpentine configuration is less compared to other serpentine channel configurations, which will require less power for the blowing in of the species gases. The results obtained from simulation under more optimal operating conditions (set 2) used by Hwang’s URFC, predicted increase in the performance of all the four channel configurations compared to the set 1 operating conditions due to higher cell temperature and stichometry of inlet gases. Under set 2 operating conditions, the values of pressure drop across all the channel configurations have increased substantially due to higher flow rates of inlet gases.

Numerical study of a photovoltaic thermal (PV/T) system using mono and hybrid nanofluid

Photovoltaic thermal systems (PV/T) are system that simultaneously turn solar energy into electricity and thermal energy. Through the working fluids (water, ethylene glycol) used in the solar collector, PV/T systems aiming to reduce solar cell temperature come to the fore with increase in electrical efficiency. In recent years, the use of mono nanofluid with superior to heat transfer properties comparison conventional fluids as working fluid in photovoltaic thermal systems has become widespread. The main purpose of this study is to investigate the improvements in the use of hybrid and mono nanofluid on the performance of sheet and tubes based PV/T systems compared to water. In numerical analysis, different velocity inlet (0.02–0.08 m/s) of base fluid, CuO + Fe/water and CuO/water (50:50) are investigated via ANSYS Fluent 18.2 software. The three dimensional geometry used includes serpentine channel, absorber plate and solar cells to examine heat transfer mechanisms via conduction and convection. The results indicate that increase in inlet fluid velocity positively affects the thermal efficiency, but also increases pressure drop. However, there is no significant effect in terms of electrical efficiency. The increase after 0.06 m/s velocity gradually decrease and a more stable value is reached. The maximum increase of electrical and thermal efficiency for (φ = 2%) hybrid nanofluid is 2.14% and 5.4% comparison to water. While this value for mono nanofluid is 1.32% and 3.33%. Using hybrid nanofluid, the pressure drop was 214.78 Pa. As a consequence of the study, it is determined that the using hybrid nanofluid improves the PV/T system performance.

Microstructure and rheological properties of a semisolid A356 alloy with erbium addition

The effects of erbium addition on the rheological properties and microstructure of a semisolid A356 alloy were studied. The semisolid slurries were prepared through the serpentine channel technique before they were thixoformed using parallel-plate compression with cylindrical discs. The grain and globule size decreases as the Er content increases, resulting in an improved and uniform distribution of spherical primary α-Al phase within the semisolid slurry. The addition of the Er modifies the grain morphology and size of the α-Al grains, resulting in a better and more uniform distribution of spherical primary α-Al phase within the semisolid slurry. As a result, rheocast quality index increases with the addition of Er, which is suitable for the thixoforming process. The A356 alloy without Er has the highest viscosity herein. The viscosity decreases, and the flow characteristics of the semisolid feedstock are expected to improve when Er is added as a result of the refinement of primary α-Al and modification of eutectic silicon. Furthermore, the refined semisolid A356 alloys with Er show a slightly larger fraction of high-angle grain boundaries compared to that for the unrefined alloy.

Inertial microfluidics in contraction-expansion microchannels: A review.

Inertial microfluidics has brought enormous changes in the conventional cell/particle detection process and now become the main trend of sample pretreatment with outstanding throughput, low cost, and simple control method. However, inertial microfluidics in a straight microchannel is not enough to provide high efficiency and satisfying performance for cell/particle separation. A contraction-expansion microchannel is a widely used and multifunctional channel pattern involving inertial microfluidics, secondary flow, and the vortex in the chamber. The strengthened inertial microfluidics can help us to focus particles with a shorter channel length and less processing time. Both the vortex in the chamber and the secondary flow in the main channel can trap the target particles or separate particles based on their sizes more precisely. The contraction-expansion microchannels are also capable of combining with a curved, spiral, or serpentine channel to further improve the separation performance. Some recent studies have focused on the viscoelastic fluid that utilizes both elastic forces and inertial forces to separate different size particles precisely with a relatively low flow rate for the vulnerable cells. This article comprehensively reviews various contraction-expansion microchannels with Newtonian and viscoelastic fluids for particle focusing, separation, and microfluid mixing and provides particle manipulation performance data analysis for the contraction-expansion microchannel design.

Cylindrical battery thermal management based on microencapsulated phase change slurry

The present study focuses on application of microencapsulated phase change material (MEPCM) slurry in cooling electric cars' batteries. These materials, benefiting from their high latent heat property, are especially capable of heat absorption while they impose excessive pressure drop to the system. This study aims to establish a trade-off between the cooling efficiency and pressure drop of the system. 186 batteries whose model is 18,650 with a serpentine arrangement, similar to that of Tesla car model S, are considered. The maximum temperature inside the battery, the maximum temperature difference of the battery pack and the coolant pressure drop are investigated as the critical parameters. Moreover, the temperature variation along the serpentine channel is also studied. In order to examine the thermal performance of the system, the maximum temperature limit of 313 K and maximum temperature difference of 5 K are considered for the batteries. The studied variables are discharge rate (3C and 5C), concentration of the MEPCM slurry (10% and 20%), and fluid velocity (up to 0.4 m/s). Results show that, for a specified velocity, application of MEPCM slurry reduces maximum temperature and the maximum temperature difference with respect to water. However, when the velocity rises, this effect diminishes which means that the application of the proposed material results in higher pressure drop and more energy consumption. Results also indicated that for the discharge rate of 3C, by the application of 10% MEPCM slurry at 0.1 m/s, the minimum thermal requirements are fulfilled bringing about the least pressure drop. These conditions for the 5C discharge rate are 20% concentration and 0.2 m/s fluid velocity.

Three-dimensional simulation of different flow fields of proton exchange membrane fuel cell using a multi-phase coupled model with cooling channel

A suitable cooling flow field design for proton exchange membrane fuel cell (PEMFC) improves the cell's net generated power, besides achieving steady cell performance and a longer lifespan. The innovation in this work lies in the simultaneous simulation of electrochemical and cooling models while accounting for both thermal and electrical contact resistance between the gas diffusion layer and bipolar plates. In this study, flow field designs including straight parallel channels (Case A), straight parallel channels filled with metal foam (Case B), multi-channel serpentine (Case C), novel serpentine channels (Case D), and integrated metal foam (Case E) used for both gas channels and cooling channels are numerically simulated. Results show that the highest uniformity of temperature in the catalyst layer-gas diffusion layer interface is obtained in Case D, which has the largest pressure drop compared to Cases B, C, and E. However, due to the uniform distribution of reactant flows, the maximum temperature observed in the catalyst layer of this flow field was the lowest compared to the rest of the cases. Furthermore, the maximum power density of 0.75 Wcm−2 was observed in Case D at a corresponding voltage of 0.6 V, which reduced when the effect of high pressure drop was taken into account. Following the conclusion of the simulation and analysis, Case D displayed the best cooling performance while Case E produced the maximum net power output.

Reduction of threading dislocations in GaN grown on patterned sapphire substrate masked with serpentine channel

Gallium nitride (GaN) is a promising semiconductor for the fabrication of a wide range of electronic and optoelectronic devices. For GaN grown on widely used sapphire substrate, bundles of threading dislocations (TDs) are induced by thermal and lattice mismatch. These TDs intersect the surface of GaN and degrade the internal quantum efficiency (IQE) of GaN-based devices. To address this issue, two innovative techniques are proposed for effective filtration of TDs. First, a novel design of serpentine channel pattern sapphire substrate (SCPSS) is applied for effective filtration of TDs at the interface. Transmission electron microscopy (TEM) indicated that SCPSS plays an effective role in the filtration of TDs; however, cathodoluminescence (CL) revealed that many TDs still intersect the surface of GaN. To further optimize the growth of GaN, the temperature was ramped down to the intermediate level and an interlayer (IL) of InGaN was introduced near the window of SCPSS. CL analysis indicated that additional use of InGaN-IL further reduced the TDs. Raman microscopy showed that incorporation of IL lead to drastic reduction in compressive stress. Atomic force microscopy (AFM) confirmed the achievement of excellent surface topography with InGaN-IL. Moreover, it is observed that growth of GaN by SCPSS is better than conventional growth because of improved surface morphology and low TDs. The reduction of TDs by SCPSS and InGaN-IL is an effective approach for the growth of high-quality GaN towards efficient devices.

Response of a proton exchange membrane fuel cell to step changes in mass flow rates

AbstractTransient regime effects are particularly important in fuel cells designed for vehicles. Three‐dimensional modeling of a proton exchange membrane fuel cell with a serpentine channel is presented, and the response of the fuel cell to a step‐change in the mass flow rates is analyzed by using the computational fluid dynamics techniques. After a validation study of the mathematical and numerical model, step increases of 20% in mass flow rates are applied to the inlet boundary conditions, and time dependent power and current density responses of the fuel cell are analyzed. Polarization curves are generated for the assessment of the fuel cell performance, and their variations in time are presented. The results show that current and power densities increase with time at low cell voltage values due to concentration losses; however, increases in power and current are negligible at high voltages.

An easy-fabricated and disposable polymer-film microfluidic impedance cytometer for cell sensing

We report here an easy-fabricated and disposable polymer-film microfluidic impedance cytometer (PMIC) integrated with inertial focusing and parallel facing electrodes for cell sensing. The cells are first focused in an asymmetric serpentine channel, and then their impedance signals are measured when passing through the electrode region. The proposed PMIC device is the first impedance cytometer that is fabricated into a flexible sheet (with a thickness of 0.45 mm) by using the materials of commonly-available ITO-coated polymer films and double-sided adhesive tapes, the whole fabrication process is shortened from traditional 3–4 days to less than 5 min by using UV laser cutting. To verify the feasibility of our device for cell sensing, we explore the focusing behaviors of three differently sized particles and two types of tumor cells, and analyze their impedance signals. The results show that our device is capable of obtaining impedance information on numbers, diameters, and longitudinal positions of cells. We envision that our PMIC device is promising in label-free cell sensing owning to the advantages of low cost, small footprint, and simple fabrication.

Heat dissipation optimization for a serpentine liquid cooling battery thermal management system: An application of surrogate assisted approach

Lithium-ion batteries are currently the primary source of power for electric vehicles (EVs), but the batteries are sensitive to temperature changes. Excessively high or low temperatures will affect the batteries performance, causing thermal runaway and safety accidents. The battery thermal management system (BTMS) can maintain the batteries within a safe temperature range. This paper studied a liquid cooling BTMS incorporating serpentine microchannels. Firstly, we studied the arrangement of the inlet direction of serpentine microchannel cooling plates. The research demonstrated that for plan 3 (i.e., inlet and outlet are staggered), the BTMS has the best cooling performance. The maximum temperature of plan 3 is 311.2592 K, which is 0.6892 K lower than plan 1. Then, we selected plan 3 as the baseline. The surrogate assisted approach was conducted to parameterize and model the selected scheme. After that, the multi-objective genetic algorithm (MOGA) was used to optimize the parameters of the serpentine channel and water flow velocity. The optimization results indicated that the maximum temperature of the battery module dropped from 311.2592 K to 308.6067 K, the maximum pressure decreased from 578.9111 Pa to 502.0554 Pa, the average temperature decreased from 308.7952 K to 306.0020 K. After optimization, the temperature uniformity of the battery module is significantly improved, which provides guidance for improving the heat dissipation performance of the serpentine liquid cooling BTMS. Especially, the maximum pressure decreased by 13.28%, which can reduce the pumping power of the cooling water in the channel, and the consumption of energy of the EVs.

Multiplexed serpentine microchannels for high-throughput sorting of disseminated tumor cells from malignant pleural effusion

Accurate isolation and detection of disseminated tumor cells from the malignant pleural effusion (MPE) is of significant clinical importance. Cytology is a routine diagnostic tool for the analysis of MPE. However, its sensitivity is limited by the existence of a significant number of contaminating blood cells and relatively small and even rare number of target tumor cells in the effusion. To address this limitation, we proposed and developed multiplexed inertial microfluidic devices for fast and efficient isolation and purification of tumor cells from a large volume (> 50 mL) of pleural effusion sample in a label-free way. The rare tumor cells were separated from blood cells relying on the mechanism of size-based differential inertial focusing. The inertial focusing and separation performance of the single serpentine channel was characterized using polystyrene beads and cancer cells lines (A549 and MCF-7) spiked in blood. Subsequently, the multiplexed devices were developed by parallelizing serpentine channels in both planar and vertical directions (e.g., 8 and 24 parallel channel) and the separation was evaluated by the spiked tumor cells (recovery ratio ∼ 80 % for the 8-channel device). Finally, we validated the performance of the multiplexed device using the clinical pleural effusion samples. Malignant tumor cells (MTCs) with a concentration of 49–4806 counts/mL were detected in all 5 pleural effusion samples, with an average purity of ∼30 %. We envision that the multiplexed device is a promising disposable tool towards the clinical applications, given the superiorities of simple structure, high throughput, low cost and good efficiency.

(Invited) Multi-Scale Analysis of Transport in Dry and Partially-Saturated Porous Media

Improvements in imaging techniques, such as micro- and nano-computer tomography (CT) and focus ion beam scanning electron microscopy (FIB-SEM), have enabled the reconstruction of complex porous media that can then be analyzed by computer simulation to estimate effective transport properties, e.g., ref. [1, 2]. Experimental setups have also been developed to measure dry and partially-saturated gas diffusivity and permeability of gas diffusion layers (GDLs) and catalyst layer (CLs), e.g., ref. [3, 4]. Based on the available literature, a comparison between micro-scale simulation results and experimental data must be performed to assess the accuracy of direct numerical simulation CT image analysis for dry and partially-saturated transport property estimation. In the later case, the validity of computational methods to predict water intrusion, such as full morphology/morphological image opening [1] and watershed segmentation [5], should also be assessed by comparing mercury intrusion experiments to numerical predictions, and by direct comparison of numerical results to CT images. Finally, these transport properties should be integrated into complete fuel cell models where volume-averaging techniques are used to properly estimate channel-porous media interactions. Such interactions however are seldom studied in literature.The proposed contribution aims at first studying the validity of two popular methods for numerical estimation of effective transport properties from three-dimensional reconstructed porous media, i.e., direct numerical simulation (DNS) and pore network modeling (PNM). Two fuel cell gas diffusion media and an electrolyzer porous transport layer are analyzed by CT and characterized by measuring mercury intrusion porosimetry (MIP), and dry permeability and diffusivity. A comparison of numerical and experimental results shows that DNS tools in OpenFCST [6] are capable of accurately predicting intrusion, and transport properties without using any fitting parameters. Accurate predictions are also achieved with the PNM implementation in OpenPNM [7] when the inscribed diameter method is used to estimate the pore size distribution, and the equivalent diameter is used to estimate pore transport properties. These tools open an avenue for computational design of porous materials.Effective transport properties must be integrated into volume-averaged fuel cell models where porous media-channel interactions are of paramount importance. These interactions however, as well as the method used for volume averaging fuel cell equations, are seldom studied in detail. Therefore, the second contribution of the talk aims at analyzing channel-porous media interactions by developing a compressible volume-averaged channel-porous media model in OpenFCST, and validating it with respect to permeability and diffusion bridge experiments in the literature. Comparison of numerical and experimental results show that, depending on the volume-averaging methodology used, experimentally obtained transport properties do not correspond to the input parameters needed in volume-averaged models. Finally, the numerical model is used to estimate flow by-pass in serpentine and inter-digitated channels, as well as compressibility effects [8].

Effect of divider wall-to-end wall distance on the vortical structures and heat transfer characteristics of two-pass channel using topological analysis

PurposeThis study aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis and critical points principles of three-dimensional vortex flow.Design/methodology/approachThis aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis as well as critical points principles of three-dimensional vortex flow.FindingsThe endwall heat transfer in the narrow spacing passage is significantly stronger than that in a wide spacing channel. As the gap clearance is kept at 0.87 times of the hydraulic diameter, the endwall heat transfer and thermal performance can be accordingly enhanced with low pressure drops, which is because a relatively strong concentrated impingement flow for the medium gap clearance helps to restrain the downstream fluid flow and enhance the shear effect of the secondary flow.Practical implicationsThe numerical results can be applied in designing sharp turn of serpentine channel in heat exchangers, heat sinks, piping system, solar receiver and gas turbine blades.Originality/valueThe evolution mechanism of the vortices in the turning region under different gap clearance was analyzed, and thermal enhancement characteristics were predicted innovatively using topological analysis method.

Numerical analysis of heat dissipation performance of heat sink for IGBT module depending on serpentine channel shape

Numerical analysis of heat dissipation performance of heat sink for IGBT module depending on serpentine channel shape

Effects of the membrane thickness and ionomer volume fraction on the performance of PEMFC with U-shaped serpentine channel

A three-dimensional, multi-component, single-phase model is applied for analyzing the electrochemical performance of the proton exchange membrane fuel cell (PEMFC) with U-shaped channel using COMSOL Multiphysics software. To validate the numerical model, the results are compared with the experimental data available in the literature. This work numerically investigates the effects of convection and diffusion under the rib, membrane thickness, ionomer content, and current density distribution at an interface between the gas diffusion layer and the catalyst layer. These effects were not studied for a U-shaped single serpentine channel despite having several benefits such as uniform reactant distribution through convection and diffusion under the rib and the resulting uniform current generation. A total of three membranes with 2, 3.5, and 5 mil thicknesses are analyzed, and an improvement of 17% in PEMFC performance with 2 mil thickness is observed owing to a decrease in internal resistance compared to 3.5 and 5 mil. Furthermore, an ionomer volume fraction in the catalyst layer is varied from 0.3 to 0.6, and the performance enhancement of 7% is reported at 0.5 volume fraction.

RETRACTED: Numerical studies of effect of integrated through-plane array flow field on novel PEFC performance using BWO algorithm under uncertainties

One of the essential mechanisms for polymer electrolyte FCs (PEFCs) is the flow-field plates. Two types of flow fields are serpentine channels and incorporating parallel, which is the most common models. The main objective of this paper is to model and analyse the thermodynamic performance of a novel FC. In this paper, a novel kind of PEFC is proposed, which is a new flowing field known as the through-plane array (TPA). Furthermore, a novel application of the Black Widow Optimization Algorithm (BWO) is implemented to gain unidentified parameters of the novel PEFC model. Developing a precise PEFC model is the final goal of the current work that prepares real modelling and simulation results of desired FCs. The various curves of the PEFC such as I–V, I–P, I–P–V, and I-T-Voltage are obtained via the BWO algorithm. This problem is a nonlinear model, in which the sum of the squared errors of FC. BWO algorithm is applied for objective function minimization. The predicted PEFC model is verified using measured results, which are obtained under different conditions of pressure and temperature uncertainty. Finally, a comparison between the TPA model and the other two models based on the BWO is accomplished and the superiority of the proposed technique is proved.

Flow Field Effect on the Performance of Direct Formic Acid Membraneless Fuel Cells: A Numerical Study

The performance of both air-breathing and air-feeding direct formic acid membraneless fuel cells (DFAMFCs) possessing different flow fields were numerically investigated in this study at given concentration and flow rate for both fuel and electrolyte. Single serpentine, stepwise broadening serpentine, multi-serpentine and parallel channel were tested as liquid flow field, while single serpentine, stepwise broadening serpentine, multi-serpentine and pin channel were tested as air flow field. The channel width was either 0.8 mm or 1.3 mm. The simulation results showed that the air-breathing DFAMFC having identical flow field for both fuel and electrolyte yielded highest cell output. The air-breathing DFAMFC having SBS liquid flow field yielded a maximum power density of 10.5 mW/cm2, while the air-breathing DFAMFC having S(1.3) liquid flow field produced an open circuit voltage of 1.0 V owing to few formic acid penetration into the cathode. Concerning the air-feeding DFAMFCs, the DFAMFC having SBS liquid flow field and MS(0.8) air flow field yielded highest peak power density, 12 mW/cm2, at an airflow rate of 500 sccm. Considering the power generated by the DFAMFCs together with the power consumed by the air pump, DFAMFC having SBS liquid flow field and Pin(0.8) air flow field could be the preferred design.

Experimental Study of Outflow Effects in a Rotating Turbulated Channel

Abstract The three-pass turbulated serpentine channel has many applications in internal turbine blade systems. However, the studies on the effects of the outflow ratio are lacking, which decreases the thermal analysis accuracy in such a model. To fill this gap, outflow-ratio experiments are conducted on the Nusselt number distributions of a three-pass turbulated channel. The current experimental results can guide and optimize the turbine blade internal cooling system. The results show with the mass flow of the lateral outlet increasing, the low-heat transfer region on the lateral-outflow passage gradually expands. Increasing the mass flow of the lateral outlet heightens the spanwise-averaged Nusselt number of the lateral-outflow passage, especially under the static condition. In the lateral-outflow passage, the rotation significantly improves the Nusselt number uniformity, particularly at the high mass flowrate of the lateral holes; the rotation shows slight effects on the spanwise-averaged Nusselt number of the lateral-outflow passage at low rotation numbers, whereas the profound influence is observed for the spanwise-averaged Nusselt number under high rotation-number condition. The rotation can profoundly increase the pressure coefficient leading to a reduced pressure loss with the rotation number increasing from 0.03 to 0.06.

Highly efficient exosome purification from human plasma by tangential flow filtration based microfluidic chip

Abstract Exosomes play an important role in microenvironmental regulation, cellular communication, tumor progression/metastasis and prognosis. A key challenge in the study of exosomes is the isolation and purification of exosomes from contaminants. In this study, we develop a size-dependent microfluidic chip to isolate and purify exosomes from human blood by tangential flow filtration. The microfluidic chip combines symmetrically two polymethyl methacrylate (PMMA) layers with serpentine channels and a nanoporous polycarbonate track etched (PCTE) membrane in between. Due to the uniform pore size (∼100 nm in diameter) of the nanoporous PCTE membrane, protein contaminants can be cleaned with high efficiency (> 97 %), and exosomes trapped in the microfluidic chip can be collected by reverse elution with high recovery (> 80 %). The collected exosomes are subjected to matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) analysis. Based on the fingerprint peaks of exosomes, it is demonstrated that plasma proteins are largely cleaned and only exosome proteins dominate the mass spectra. Compared to ultracentrifugation (UC) that is considered as the “gold standard” for exosome isolation and purification, the size-dependent microfluidic chip-based protocol shows higher protein cleaning efficiency and exosome recovery rate. The whole process takes