Flow In Tube Research Articles

Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets

An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (NuR) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ1 = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (PR = 1.0) and height (BR = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ1 = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ1, the entropy generation (S˙′gen) was reduced to a lower value and the maximum exergy efficiency (ηEx) was obtained for the LPTW at α = 60° and θ1 = 0° The peak thermal performance around 2.5 together with NuR = 4.68 was found at a= 60°, θ1 = 45° and the lowest Re. However, the optimal condition at α= 60°, θ1 = 30° was preferable because it provides the greatest NuR = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.

The characteristics of laminar film condensation of pure vapor flow in a vertical tube

In this study, we investigate the characteristics of laminar film condensation of pure vapor flow in a vertical tube, taking into account (i) the vapor flow rate reduction owing to condensation, (ii) the finiteness of the vapor boundary-layer thickness, (iii) the curvature of the vapor layer, and (iv) the pressure variation. An approximate integral two-phase boundary-layer equation model is derived, and a condition that pressure recovery occurs is determined from the asymptotic analysis around the tube inlet. Furthermore, the present model is further simplified to obtain an analytical solution if the degree of subcooling is sufficiently large. The asymptotic solution for sufficiently large degrees of subcooling gives a good approximation to the numerical solution. The tube length of complete condensation is estimated. Comparison with vertical plane condensation demonstrates that the film thickness and the Nusselt number increased and decreased, respectively, by the vapor flow reduction for large degrees of subcooling.

Poiseuille-Type Approximations for Axisymmetric Flow in a Thin Tube with Thin Stiff Elastic Wall

An asymptotic ansatz for the solution of the axisymmetric problem of interaction between a thin cylindrical elastic tube and a viscous fluid filling the thin interior of the elastic tube was recently introduced and justified by G. Panasenko and R. Stavre. The thickness of the elastic medium (ε) and that of the fluid domain (ε1) are small parameters with ε<<ε1<<1, while the scale of the longitudinal characteristic size is of order one. At the same time, the magnitude of the stiffness and density of the elastic tube may be large or finite parameters with respect to the viscosity and density of the fluid when the characteristic time is of order one. This ansatz can be considered as a Poiseuille-type solution for the fluid–structure interaction problem. Its substitution to the Stokes fluid–elastic wall coupled problem generates a one-dimensional model. We present a numerical experiment comparing this model with the solution of the full-dimensional fluid–structure interaction problem.

Practical implications of the erroneous treatment of exposure time in the Eulerian hemolysis power law model.

Eulerian and Lagrangian power-law formulations are both widely used for computational fluid dynamics (CFD) to predict flow-induced hemolysis in blood-contacting medical devices. Both are based on the same empirical power-law correlation between hemolysis and the shear stress and exposure time. In the Lagrangian approach, blood damage is predicted by tracking both the stress and exposure time along a finite number of pathlines in the domain. In the Eulerian approach, a scalar transport equation is solved for a time-linearized damage index within the entire domain. Previous analytical work has demonstrated that there is a fundamental problem with the treatment of exposure time in the Eulerian model formulation such that the only condition under which the model correctly represents the true exposure time is in a flow field with no streamwise velocity variation. However, the practical implications of this limitation have yet to be thoroughly investigated. In this study, we demonstrate the inaccuracy of Eulerian hemolysis power-law model predictions due to the erroneous treatment of exposure time by systematically considering four benchmark test cases with increasing degrees of flow acceleration: Poiseuille flow through a straight tube, inclined Couette flow, and flow through a converging tube with two different convergence ratios. Compared with Lagrangian predictions, we show that, as flow acceleration becomes more pronounced, the resultant inaccuracy in the Eulerian predictions increases. For the inclined Couette flow case, there is a small degree of flow acceleration that yields a discrepancy in the range of 10% between Lagrangian and Eulerian predictions. For flows with a larger degree of acceleration, as occurs in the converging tube flow cases, the discrepancy is considerably larger (up to 257%). The inaccuracy of hemolysis predictions due to the erroneous treatment of exposure time in the Eulerian power-law model can be significant when there is streamwise velocity variation in the flow field. These results may partially explain the extremely large variability in CFD hemolysis predictions reported in the literature between Lagrangian and Eulerian models.

Evaluation of Spatial Gas Temperature and Water Vapor Inhomogeneities in TDLAS in Circular Multipass Absorption Cells Used for the Analysis of Dynamic Tube Flows.

The use of optical circular multipass absorption cells (CMPAC) in an open-path configuration enables the sampling free analysis of cylindrical gas flows with high temporal resolution and only minimal disturbances to the sample gas in the pipe. Combined with their robust unibody design, CMPACs are a good option for many applications in atmospheric research and industrial process monitoring. When deployed in an open-path configuration, the effects of inhomogeneities in the gas temperature and composition have to be evaluated to ensure that the resulting measurement error is acceptable for a given application. Such an evaluation needs to consider the deviations caused by spectroscopic effects, e.g., nonlinear effects of temperature variations on the intensity of the spectral line, as well as the interaction of the temperature and concentration field with the characteristic laser beam pattern of the CMPAC. In this work we demonstrate this novel combined evaluation approach for the CMPAC used as part of the tunable diode laser absorption spectroscopy (TDLAS) reference hygrometer in PTB's dynH2O setup for the characterization of the dynamic response behavior of hygrometers. For this, we measured spatially resolved, 2D temperature and H2O concentration distributions, and combined them with spatially resolved simulated spectra to evaluate the inhomogeneity effects on the line area of the used H2O spectral line at 7299.43 cm-1. Our results indicate that for dynH2O, the deviations caused by the interaction between large concentration heterogeneities and the characteristic sampling of the beam pattern of the CMPAC are three orders of magnitude larger than deviations caused by small temperature heterogeneity induced spectroscopic effects. We also deduce that the assumption that the "path-integrated" H2O concentration derived with the open-path CMPAC setup represents an accurate H2O area average in the flow section covered by the CMPAC in fact shows significant differences of up to 16% and hence does not hold true when large H2O concentration gradients are present.

Interphase Mechanical Energy Transfer of Gas-Liquid Flow in Variable Cross-Section Tubes

The use of gas energy includes a wide range of applications to directly accelerate the liquid in a pipeline without the aid of mechanical equipment, such as marine gas-liquid jet propulsion. To clarify the characteristics of energy transfer by interphase forces for gas-liquid flows in variable cross-section tubes, two-fluid models of annular flow, bubbly flow and homogeneous flow were adopted, respectively, along with four newly elaborated coefficients, which are the work factor of gas fg, reflecting the relative ability of gas to power liquid, the interface work transfer coefficient kg (representing the relative magnitude of mechanical work received by liquid from gas), the interphase work-to-energy conversion coefficient kl (denoting the capability of energy transfer through work performed by interphase forces) and the interphase mechanical efficiency ηw. The results reveal the interphase work transfer is strongly influenced by the structural parameters of the tubes (or nozzles), and an optimized design is necessary to improve the performance. The higher the degree of gas dispersion in the liquid, the more advantageous the conversion of gas work into the liquid’s mechanical energy. Of these three flow patterns, annular flow has the lowest kl and ηw (kl = 0.0797, ηw = 0.9885 in present example), while homogeneous flow displays the limit of interphase mechanical energy conversion because the gas-liquid momentum coupling reaches the maximum (kl = 0.9979, ηw = 1).

Entropy generation analysis of turbulent flow in conical tubes with dimples: a numerical study

Minimizing the entropy generation rate is one of the key performance indicators for enhancing the thermal design of heat exchangers. This paper introduces a comprehensive numerical entropy generation analysis of turbulent water flow inside—newly proposed—conical tubes with dimples subjected to a constant heat flux. The effect of different tube diameter ratios (DR = 1, 1.5, 2, 3, and 5) and flow modes (convergent and divergent tube configurations) on the thermal, viscous, and total entropy generation rates is investigated within Reynolds number (Re) range of 3 × 103–40 × 103 using ANSYS-Fluent package. Realizable k-ε (RKE) turbulence model is adopted in this study. A well-validated 3D model was adopted to estimate the dimensionless indices: Bejan number (Be), enhanced entropy generation ratio (Ns,en), and the irreversibility distribution ratio ({phi }_{mathrm{s}}) to characterize the entropy generation performance and to compare conical dimpled tubes to smooth ones. The results showed that total entropy production rate values for dimpled tube geometries are lower than those for the corresponding smooth ones, especially for convergent dimpled tubes. Convergent dimpled tubes with DR in the range of 1.5–3 achieved the lowest total entropy production values over the whole Re range, with an average value of 0.20 W K−1, as compared to an average value of 0.34 W K−1 for the smooth configurations. The average Ns,en values for dimpled convergent tubes with DR = 1.5–3 are 0.46 and 0.80 at Re = 3000 and 40,000, with reductions of 50.54% and 3.61% at both Re values, respectively. The study also showed that the entropy generation analysis could provide an effective tool to highlight the optimal design of tube heat exchangers based on the minimum entropy generation and the enhanced entropy generation ratio.

Numerical Evaluation of the Hydrothermal Process in a Water-Surrounded Heater of Natural Gas Pressure Reduction Plants

The gas pressure in the main network of transmission lines is about 700 to 1000 psi (4826.33 to 6894.76 kPa), which is reduced to 250 psi (1723.69 kPa) at the entrance station of a city. This reduction process, which occurs in the regulator, causes a severe drop in gas temperature. The drop in the gas temperature produces hydrates and even causes the water vapor in the gas to freeze. As a result, there is a possibility that the passage of gas in the regulator is blocked and the gas flow is cut off. By employing heaters (indirect water heaters), the temperature of the gas entering the regulator can be preheated to eliminate the possibility of freezing in the regulator. This heater is fueled with natural gas and it operates for 24 hr a day, especially in the cold seasons. Therefore, one of the main challenges in using this type of heater is its high fuel consumption. Consequently, researchers are looking for a solution to reduce the fuel consumption (natural gas) of gas heaters. In this paper, the heat transfer and fluid flow in a heater of a natural gas pressure reduction plant, the Aliabad Power Plant (Iran), are numerically investigated using a commercial Computational Fluid Dynamics (CFD) code, ANSYS FLUENT 18.2. The considered heater consists of three parts, including (i) gas coils, (ii) a water bath (shell), and (iii) a fire tube. The indirect heat transfer process takes place between the hot liquid flow in the fire tube (combustion exhaust) and the cold liquid flow (natural gas) using the natural convection flows generated in the water bath. Numeric modeling is performed for four different gas mass flows, including 6 × 104, 8 × 104, 1 × 105, and 12 × 105 standard cubic meters per hour (or 16.67, 22.22, 27.78, and 33.33 m3/s). The results indicate that the natural gas outlet temperature achieved to a temperature higher than required. By installing a regulator on the burner, the gas consumption can be reduced, resulting in station cost savings, and also reducing the environmental impacts. The outcomes depict that the maximum possible reductions in monthly gas consumption and economic savings in the proposed system are 67,500 m3 and IRR 25 million at a gas mass flow rate of 60,000 SCMH.

MiR-95-3p/EPM2A/MMP2 contributes to the pathogenesis of severe preeclampsia through the regulation of trophoblast biological behaviour

ObjectivePreeclampsia (PE) is a maternal multisystem disease with an unclear mechanism. Data showed that MiR-95-3p promoted cell migration, invasion and proliferation, leading to the occurrence and development of many cancers, and placental trophoblasts and tumor cells had similar migration, invasion and proliferation abilities. Meanwhile we found that MiR-95-3p was differentially expressed in PE and normal placenta. Therefore, this article aimed to explore the biological function and mechanism of miR-95-3p in PE. MethodsThe expression of miR-95-3p in PE and normal placental tissue was explored by high-throughput sequencing and qRT–PCR. The effects of miR-95-3p on trophoblast migration, invasion, proliferation, angiogenesis and apoptosis were investigated by Transwell migration and invasion assays, cell viability assay, tube formation assay and flow cytometry in two trophoblast cell lines (HTR-8/SVneo and JAR). The miR-95-3p target gene EPM2A was identified and verified by unique identifier mRNA next-generation sequencing and dual-luciferase reporter gene experiments. Rescue experiments were conducted to investigate whether miR-95-3p regulated EPM2A to participate in trophoblast migration and invasion. Finally, the effects of miR-95-3p and EPM2A on the expression of angiogenic factors and inflammation-related factors were investigated by ELISA. ResultsWe found that miR-95-3p was expressed at low levels in the placental tissue of patients with PE and was negatively correlated with EPM2A expression. In vitro upregulation of miR-95-3p and downregulation of EPM2A promote trophoblast migration, invasion and proliferation. Furthermore, EPM2A was confirmed as a target mRNA of miR-95-3p. Upregulation of EPM2A mitigated miR-95-3p-mediated promotion of trophoblast migration and invasion and vice versa. Finally, both miR-95-3p and EPM2A regulate the expression of trophoblast angiogenesis-related factors and inflammation-related factors. ConclusionOur findings demonstrated that miR-95-3p promoted the migration and invasion of trophoblast cells by targeting EPM2A to inhibit the occurrence and development of PE.

A time-relaxed Monte Carlo method preserving the Navier-Stokes asymptotics

In this paper, a new time-relaxed Monte Carlo (TRMC) method is proposed for the inhomogeneous Boltzmann equation. Compared to the standard TRMC scheme, the proposed method performs the same convection operator, however, divides the collision operator by a micro-macro decomposition. The continuous part of the collision operator is constructed based on the first-order Chapman-Enskog expansion and solved by an explicit second-order scheme, while the numerical solution of the rest nonequilibrium part is still provided by the standard TRMC scheme. In this way, the new TRMC method demonstrates the same accuracy as the standard TRMC scheme in the kinetic limit, however, preserves Navier-Stokes asymptotics and the second-order accuracy in the fluid limit. Several numerical cases of inhomogeneous flows, such as the one-dimensional Poiseuille flow, Sod tube flow, the shock wave and two-dimensional hypersonic flow past a cylinder, are calculated and compared with direct simulation Monte Carlo (DSMC) or Navier-Stokes solutions. It is noted that the new TRMC scheme is more accurate and efficient than the standard TRMC and DSMC methods for simulations of multi-scale gas flows.

Numerical Evaluation of Novel Curved Rib Turbulators for Thermal Performance Improvement in Circular Geometries

Internal heating/cooling using roughness elements such as ribs are a promising passive heat-transfer enhancement technique for many thermal applications. The curved ribs are roughness elements that boost the fluid residence time and enhance the thermal-hydraulic performance of the system. In the present study, curved ribs of different cross-sections were fitted at the inner wall of the circular tube to intensify convection heat transfer to the fluid flowing through it. Novel curved ribs of inline configurations of different shapes and geometrical parameters were numerically studied for convection heat transfer using a three-dimensional computational model. The finite volume method discretizes the tube fluid flow domain’s mass, momentum, and energy equations. The local heat transfer enhancement over the tube surface is 2.75 times the smooth tube flow, with Reynolds numbers ranging from 10,000 to 50,000. The cost-effectiveness of this heat transfer enhancement method was quantified using a thermohydraulic performance evaluation factor. This factor accounts for the increased heat transfer at the same pumping power and the same available surface area for heat dissipation. The average heat transfer enhancement at the same Reynolds number and pumping power was found to be 120% to 450% and 98% to 260% of the smooth tube flow.

Analysis of Mixed Convection and Free Convection in a Reduced Solar Collector Using a Nanofluid as Heat Transfer Fluid

A three-dimensional investigation of mixed convection which occurs from Al2O3-water nanofluid flow in tube of a reduced solar collector and free convection in air gap situated between cover of solar collector and its absorber was investigated. Heat transmission by conduction in absorber and cover as well as thermal losses to exterior expressed in form of a convective flux have also been taken into account. The different transport equations were solved using CFD-Fluent software which is founded on finite volume method and Boussinesq’s law was introduced to take into account of buoyancy effects. In this investigation, thermal efficiency of solar collector was evaluated and use of nanofluids allows to increase this parameter which is generally low for this kind of thermal systems. Length of thermal regime established in the tube is proposed and this investigation is extended relative to other works developed in this research field. Results obtained gave an idea about the flow structure of the fluid under consideration in a tube of a solar collector and heat transmission mechanisms in air gap and in other elements of the solar collector. These results can facilitate design of this thermal system.

Analysis of Flow-Induced Vibrations in a Heat Exchanger Tube Bundle Subjected to Variable Tube Flow Velocity

Analysis of Flow-Induced Vibrations in a Heat Exchanger Tube Bundle Subjected to Variable Tube Flow Velocity

Optimization and numerical investigation of the effect of using phase change material and two-phase nanofluid flow in a V-shaped tube mounted in a thermal solar panel

BackgroundThis article presents a numerical analysis and optimization of the cooling of a thermal solar panel due to the place of renewable energies in the future energy supply. The panel is one of a set of panels in a solar system. For this purpose, a 10 W panel with a V-shaped copper tube is simulated. Laminar and homogeneous water/copper nanofluid (NFD) flows in the tube. MethodsThe temperature of the panel (TPL), the value of PCM volume fraction, and the outlet temperature of the nanofluid (TNF) are determined in an hour. The flow of NFD is modeled using the two-phase method, and COMSOL software is employed to simulate the flow of NFD and PCM phase change. Significant findingsThe results demonstrate that enhancing the tube diameter (TUD) reduces the TPL and the outlet TNF, enhancing the PCM's phase change time. The TPL and the outlet TNF are reduced with the FLR of the NFD. Optimization of the geometry and flow parameters showed that the maximum outlet temperature occurred at the lowest pressure drop in the diameter of 6 mm and the FLR of 0.76 lit/min.

Comparison of Standalone and Hybrid Machine Learning Models for Prediction of Critical Heat Flux in Vertical Tubes

Critical heat flux (CHF) is an essential parameter that plays a significant role in ensuring the safety and economic efficiency of nuclear power facilities. It imposes design and operational restrictions on nuclear power plants due to safety concerns. Therefore, accurate prediction of CHF using a hybrid framework can assist researchers in optimizing system performance, mitigating risk of equipment failure, and enhancing safety measures. Despite the existence of numerous prediction methods, there remains a lack of agreement regarding the underlying mechanism that gives rise to CHF. Hence, developing a precise and reliable CHF model is a crucial and challenging task. In this study, we proposed a hybrid model based on an artificial neural network (ANN) to improve the prediction accuracy of CHF. Our model leverages the available knowledge from a lookup table (LUT) and then employs ANN to further reduce the gap between actual and predicted outcomes. To develop and assess the accuracy of our model, we compiled a dataset of around 5877 data points from various sources in the literature. This dataset encompasses a diverse range of operating parameters for two-phase flow in vertical tubes. The results of this study demonstrate that the proposed hybrid model performs better than standalone machine learning models such as ANN, random forest, support vector machine, and data-driven lookup tables, with a relative root-mean-square error (rRMSE) of only 9.3%. We also evaluated the performance of the proposed hybrid model using holdout and cross-validation techniques, which demonstrated its robustness. Moreover, the proposed approach offers valuable insights into the significance of various input parameters in predicting CHF. Our proposed system can be utilized as a real-time monitoring tool for predicting extreme conditions in nuclear reactors, ensuring their safe and efficient operation.

Non-symmetric distributions of solids deposition for solid-water stratified flow in deviated tubing strings

Dynamic performance on solids flow with water in deviated tubing is essential for the reliability of pump and normal operation of horizontal and directional wells. Compared with coal-water flow in vertical tubing and sand-oil flow with high production in deviated tubing, solids deposition with water shows obvious non-symmetric distributions in deviated tubing from simulations and experiments. The mathematical model of two phase flow was developed under coupling conditions of deviated tubing, low flow rate and viscosity based on the kinetic theory of granular flow and first-order discrete scheme. The results show that solid-water stratified flow in deviated tubing can be divided into two zones of suspension bed and the moving bed throughout the flow field. The solid flowing velocity with water is negative and particles slide down at the bottom of moving bed zone. The process of solids flow with water in deviated tubing will produce pressure loss and consume the kinetic energy. The thickness of deposited layer and the flowing velocity of solids flow downward with water at the moving bed zone enhance with the decreased inlet flow rate and the increased particle size, tubing inside diameter (ID) and inclination angle. Solids are easier into suspension from the upper part of moving bed zone to suspension bed zone and more solid particles flow with water towards the tubing outlet with the increase of inlet flowing velocity. The decision is made to reduce the screen width, tubing ID and inclination angle to maintain to be greater than critical deposition velocity in order to prevent solids settling. And it provides the theoretical basis and technical reserves for solid control and offers an effective approach to enhance tubing cleaning in deviated strings.

Highly sensitive single tube B-lymphoblastic leukemia/lymphoma minimal/measurable residual disease test robust to surface antigen directed therapy.

Measurement of minimal/measurable residual disease (MRD) in B-lymphoblastic leukemia/lymphoma (B-ALL) has become a routine clinical evaluation tool and remains the strongest predictor of treatment outcome. In recent years, new targeted anti-CD19 and anti-CD22 antibody-based and cellular therapies have revolutionized the treatment of the high-risk B-ALL. The new treatments raise challenges for diagnostic flow cytometry, which relies on the presence of specific surface antigens to identify the population of interest. So far, reported flow cytometry-based assays are developed to either achieve a deeper MRD level or to accommodate the loss of surface antigens post-target therapies, but not both. We developed a single tube flow cytometry assay (14-color-16-parameters). The method was validated using 94 clinical samples as well as spike-in and replicate experiments. The assay was well suited for monitoring response to targeted therapies and reached a sensitivity below 10-5 with acceptable precision (coefficient of variation < 20%), accuracy, and interobserver variability (κ = 1). The assay allows for sensitive disease detection of B-ALL MRD independent of CD19 and CD22 expression and allows uniform analysis of samples regardless of anti-CD19 and CD22 therapy.

A method for real-time mechanical characterisation of microcapsules

Characterising the mechanical properties of flowing microcapsules is important from both fundamental and applied points of view. In the present study, we develop a novel multilayer perceptron (MLP)-based machine learning (ML) approach, for real-time simultaneous predictions of the membrane mechanical law type, shear and area-dilatation moduli of microcapsules, from their camera-recorded steady profiles in tube flow. By MLP, we mean a neural network where many perceptrons are organised into layers. A perceptron is a basic element that conducts input–output mapping operation. We test the performance of the present approach using both simulation and experimental data. We find that with a reasonably high prediction accuracy, our method can reach an unprecedented low prediction latency of less than 1 millisecond on a personal computer. That is the overall computational time, without using parallel computing, from a single experimental image to multiple capsule mechanical parameters. It is faster than a recently proposed convolutional neural network-based approach by two orders of magnitude, for it only deals with the one-dimensional capsule boundary instead of the entire two-dimensional capsule image. Our new approach may serve as the foundation of a promising tool for real-time mechanical characterisation and online active sorting of deformable microcapsules and biological cells in microfluidic devices.

An optimized delayed equilibrium model for predicting the pressure profile of the critical flow in a slit

The mass flux and pressure profile of the critical flow in a slit are connected to the original diameter and concentration of radioactive aerosols in leak-before-break monitoring in nuclear power plants. The Delayed Equilibrium Model (DEM), although accurate for mass flux and pressure prediction of critical flow in a circular tube, suffers from underprediction of the pressure drop for critical flow in the slit. In this study, an optimized DEM considering the shape effect of flash boiling is proposed by changing the saturated phase mass flow rate fraction gradient and two-phase friction coefficient multiplier in the DEM. Two novel equations for the new coefficients, C4 and C5, are introduced in the optimization. The relative error of the critical flow pressure in the slit can be reduced using the optimized DEM. In addition, a sensitivity analysis of the original critical flow model is conducted and the mass flux and critical pressure of the critical flow model are found to be most sensitive to the inlet temperature. The effectiveness of the optimization proves that the shape effect of the velocity of achieving thermal equilibrium in flash boiling is critical for the critical flow in a slit.

Application of CFD-DSMC coupling method in H2 flow and heat transfer in microtube

In the research of porous media and the interior of microelectronic devices, fluids frequently shuttle among pores and wall cracks, therefore it is of great significance to explore the influence of media wall on fluid flow and heat transfer. In this paper, CFD-DSMC coupled iterative algorithm is first used in the research of the flow and heat transfer of gas near the wall in the porous media, which simplified into the flow and heat transfer in micron-scale tube with smooth and rough wall conditions. It is found that compared with the pure CFD method, the velocity field obtained by the coupled method is quite different in the region close to the wall, and this will affect the flow field in the mainstream region, that is, with the higher roughness of the wall, the velocity in the central region will be smaller. There is no significant difference in the temperature distribution in the microtube before and after coupling, but the temperature in the mainstream decreases with the increase of the roughness of the wall. In addition, the temperature jump was found from some of the coupling results close to the wall. The results will contribute to a deeper understanding of the influence of rough surfaces on gas flow and heat transfer near the wall, and provide guidance for the regulation of flow and heat transfer in porous media.