High Flow Resistance Research Articles

Investigation of force-assisted suction reed valves in hermetic reciprocating compressors

Reed valves are widely used in hermetic reciprocating compressors and are responsible for a major share of thermodynamic losses. The suction valve in particular, which is opened for almost the entire suction phase, has a very significant improvement potential. Suction valves in hermetic reciprocating compressors are usually opened only by the pressure difference created by the moving piston and should be closed before the compression phase starts, in order to avoid a reversed mass-flow through the valve. The valves are thus preloaded, which, on the other hand, results in a higher flow resistance. In this work, a force-assisted suction valve is investigated. An electromagnetically actuated spring generates an additional force acting on the conventional suction reed valve. This force leads to a completely different valve movement and a significant reduction of the losses caused by the suction valve. A conventional suction valve flutters during the suction phase. Thus, it hits the valve seat several times which has, beside an increased flow resistance, negative influences on the reliability of the reed valve and noise emissions. With the help of the additional force, it is able to overcome the opening delay due to the preload and the oil ‘stiction’ effect. Furthermore, the suction valve can be held open during the whole suction phase, and it closes smoothly in time near the bottom dead centre of the piston. The investigation of the force-assisted suction valve is done by numerical simulations as well as by experiments. Results show an improvement of the coefficient of performance by approximately 0.7%–1.6% depending on the operating conditions.

High Permeability of Boron along the Transverse Direction of Wood under High-Voltage Electrostatic Field (HVEF) Treatment

Permeability of wood preservative is one of the most significant factors for protection of wood construction. Anisotropic flow permeability was involved in different directions of wood with higher flow resistance in the transverse and lower longitudinal directions. In this study, boron acid solution was brushed onto the tangential section of air-dried wood cubes and boron penetration along wood transverse direction was investigated under free diffusion, vacuum and HVEF treatments. Multi-scale boron distribution, FTIR measurement, leaching property, mechanical properties and fungistatic characteristic were investigated for free diffusion, vacuum and HVEF treated samples respectively. The results revealed that boron exhibited high permeability along the transverse direction with the penetration depth of ≈35 mm for HVEF treated samples and ≈1 mm for free diffusion and vacuum treated samples. For HVEF treated samples, no significant decrease of hardness, compression modulus of elasticity and strength were found in the treated samples. Better fungistatic characteristic was showcased in HVEF treated samples exposed to white rot fungi. Thus, HVEF treatment has a positive effect on boron permeability and the improvement of penetration depth of preservatives hence playing a significant role in wood protection and prolonging the service life of wood construction.

MORPHOFUNCTIONAL PECULIARITIES OF THE PLACENTA IN WOMEN WITH UNDIFFERENTIATED CONNECTIVE TISSUE DYSPLASIA SYNDROME.

The aim: The impact of undifferentiated connective tissue dysplasia on the formation of the placenta. Materials and methods: The morphostructure of 50 placentas with the undifferentiated connective tissue syndrome and 50 placentas of women with physiological pregnancy and absence of connective tissue pathology was studied. Results: The results of morphological studies have shown that the main pathogenetic link of placental dysfunction with highly resistant blood flow in the umbilical arteries in pregnant women with undifferentiated connective tissue dysplasia syndrome is a disorder of functional differentiation of the villous tree.In these cases the dominats were large and medium-sized villi with narrowed lumen in arterial, venular and capillary vessels and arterial spasm and venous plethora, as well as with numerous chaotically sclerosed villi, indicating stage I and II of placental. There is a large amount of fibrins in intervillous space which narrows it and leads to violation of microcirculation and placenta tissue hypoxia. Conclusions: The morphological basis of high flow resistance in the umbilical artery with the undifferentiated connective tissue dysplasia syndrome in pregnant women is a pathological immaturity of the placental villous tree. Morphological study of the architecture of the stem and intermediate placental villi revealed a violation of the structure of collagen fibers in the form of lack of crosslinks of bundles of collagen fibers.

Modelling the Effects of Nanomaterial Addition on the Permeability of the Compacted Clay Soil Using Machine Learning-Based Flow Resistance Analysis

Impermeable base layers that are made of materials with low permeability, such as clay soil, are necessary to prevent leachate in landfills from harming the environment. However, over time, the permeability of the clay soil changes. Therefore, to reduce and minimize the risk, the permeability-related characteristics of the base layers must be improved. Thus, this study aims to serve this purpose by experimentally investigating the effects of nanomaterial addition (aluminum oxide, iron oxide) into kaolin samples. The obtained samples are prepared by applying standard compaction, and the permeability of the soil sample is experimentally investigated by passing leachate from the reactors, in which these samples are placed. Therefore, Flow Resistance (FR) analysis is conducted and the obtained results show that the Al additives are more successful than the Fe additive in reducing leachate permeability. Besides, the concentration values of some polluting parameters (Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), and Total Phosphorus (TP)) at the inlet and outlet of the reactors are analyzed. Three different models (Artificial Neural Networks (ANN), Multiple Linear Regression (MLR), Support Vector Machine (SVM)) are applied to the data obtained from the experimental study. The results have shown that polluting parameters produce high FR regression similarity rates (>75%), TKN, TP, and COD features are highly correlated with the FR value (>60%) and the most successful method is found to be the SVM model.

Developmental respiratory physiology.

Various developmental aspects of respiratory physiology put infants and young children at an increased risk of respiratory failure, which is associated with a higher rate of critical incidents during anesthesia. The immaturity of control of breathing in infants is reflected by prolonged central apneas and periodic breathing, and an increased risk of apneas after anesthesia. The physiology of the pediatric upper and lower airways is characterized by a higher flow resistance and airway collapsibility. The increased chest wall compliance and reduced gas exchange surface of the lungs reduce the pulmonary oxygen reserve vis‐à‐vis a higher metabolic oxygen demand, which causes more rapid oxygen desaturation when ventilation is compromised. This review describes the various developmental aspects of respiratory physiology and summarizes anesthetic implications.

Optimization on the gradually varied pore structure distribution for the irradiated absorber

An optimization method for the gradually varied porous absorber is proposed. The Monte Carlo Ray Tracing method based on the acceptance-rejection sampling is established to obtain the absorption distribution of irradiation in the gradually varied porous absorber. The fluid flow, convection, and thermal radiation in the porous absorber are evaluated. Combined with the genetic algorithms, the distribution of porosity and pore size of the porous absorber could automatically adjust to match the non-uniform radiation flux in both radial and axial directions. Moreover, the internal flow layout could be regulated by an optimized radial pore distribution that directs more fluid enters the high heat flux zone. The optimization results demonstrate that the gradually varied porous absorber with porosity ranging from 0.95 to 0.90 and pore size ranging from 2.5 mm to 1.5 mm could achieve high thermal efficiency and low flow resistance. Compared with the standard model of the uniform porous absorber, the thermal efficiency of the optimal gradually varied porous absorbers could be further increased by 1.23%–9.76%, while the pressure drop could be reduced by 7.88%–55.73%.

Influence of particle size on powder rheology and effects on mass flow during directed energy deposition additive manufacturing

Metal powders used in directed energy deposition additive manufacturing are subjected to particle-particle and particle-gas interactions not captured through traditional powder characterization. Variations in powder performance were identified through mass flow rate measurements of lean (UNS S32101), standard (UNS S32205), and super (UNS S32750) duplex stainless steel powders specified for directed energy deposition on three commercial powder feeders. Across these different systems, the lean grade consistently displayed the lowest mass flow rates. Differences between the three powders were only identified with advanced powder and rheological characterization tools, which linked particle characteristics and rheological properties to powder flow and performance. A slight shift to a larger size distribution in the lean grade produced a higher percentage of larger particles with higher masses that resisted motion and increased flow resistance. Higher flow resistance was captured through higher cohesion strength and fluidization measurements during rheological testing.

The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

This review describes the world of edges in submerged vegetated marine canopies (seagrasses, saltmarshes, and seaweeds) where an edge is a boundary with a frontal area separating the vegetation from the adjacent non-vegetated zones. Plants within the vegetation are made of flexible elements pronating in the direction of the flow and oscillating back and forth in response to wave forcing. Some of them also occupy the full height within the water body. The analysis focuses on both the canopy- and local-patch scales to acquire knowledge about the hydrodynamics and the biophysical interactions in the structural shallows and deep limits of the canopies as well as on the structural edges of vegetation patches and the edges in the gaps within the canopies. The spatial arrangements of both canopy and patch edges are not only well imposed through the modification of hydrodynamics, but so too through small-scale interactions from internal structural causes and modifications. The continuous fragmentation of coastal marine habitats has reduced their structural complexity, thus making habitat edges a prevalent seascape feature, including in the shallow (or upper) and deep (or lower) limits of the canopies, the patch edges, and the edges in the gaps within the canopies. Canopy patches represent a region of high flow resistance where flow deflects and accelerates above and/or next to the canopy, resulting in an increase in water velocity and turbulence, especially at the edges of the patch. At the edges, energy transfer is found in spectral wave velocities from the longer to shorter wave period components. Likewise, at the edges, the net deposition of sediments decreases over a distance to a certain length, relative to the bare bed, which is associated with a region of vertical updraft and elevated turbulent kinetic energy. The edge effects also relate to the influence that a patch edge can have on determining species composition and predation risk, which is additionally mediated by the effect the edges have on habitat complexity within the vegetated patch. Organism feedback within the edges does not simply follow the canopy and local features and, in fact, the intricate interaction between biogeophysical processes is key in explaining the complexity of coastal submerged canopy landscapes. For example, proximity to patch edges has a greater influence on epifaunal density and community structure than structural complexity or predation do. The extent to which edges reduce predation risk depends on the extent to which they support higher structural complexities compared to patch interiors. The canopies’ shallow limits and their position in the underwater beach profile are mostly limited by light availability, the intensity of the wave action, and the local nearshore hydrodynamics, but they also depend on the local structural conditions at the vegetated side. The deep limits of the canopies, however, mainly depend on the availability of light and research findings support migration both to the deeper and shallower layers. All structural edges face changes caused by increasing nutrient inputs, development of coastal zones and the increasing impact of climate change. A considerable challenge to managing, restoring, and conserving coastal marine ecosystems stems from understanding how the canopies are able to cope with these natural and anthropogenic disturbances.

Sinuous bar fingers of digitate shallow‐water deltas: Insights into their formative processes and deposits from integrating morphological and sedimentological studies with mathematical modelling

AbstractThis paper helps to address the growing need to resolve the severe loss of deltaic lands by providing a new understanding for shallow‐water digitate delta growth. The integration of satellite image analysis of modern deltas, field studies of the Ganjiang Delta in the Poyang Lake and ‘Delft3D’ simulations further results in improved facies models for shallow‐water digitate deltas. These analyses show that shallow‐water digitate delta bar fingers are sinuous in contrast to the straight deep‐water digitate delta bar fingers. These differences are assigned to the effect of water depth on outflow hydraulics, where friction‐dominated shallow‐water delta effluents promote mouth bar deposition that then divert flow around the mouth bar, resulting in the formation of sinuous bar fingers. These effects are further strengthened by the meandering of the shallow‐water jet that increases lateral sediment transport, and by the higher flow resistance and lower gradient of the shallow‐water outflows. Our data and analyses further show differences in the morphology and deposits of the shallow‐water sinuous bar fingers, where some bar fingers develop sinuous and others meandering (with point bars) distributary channels. Lateral channel migration and point bar formation (meandering) occur as a secondary process that does not change the shape or width of the bar fingers themselves, and is suggested to be a function of slight initial differences in channel sinuosity. These differences in distributary channel morphology have a strong effect on bar finger facies distribution. Sediment cohesion is another important control on bar finger bending processes, because high cohesion promotes formation of enclosed bays, where their bank strength exceeds the centrifugal force of water flow. Lower sediment cohesion results in sinuous bar fingers without formation of enclosed bays. This work provides insights into natural and artificial shallow‐water digitate delta growth and provides new quantitative facies models for shallow‐water digitate deltas.

Liquid lead flow-accelerated corrosion testing with the rotating cage set-up: A CFD optimisation

In this study the rotating cage setup, a simple laboratory methodology extensively used for flow-accelerated corrosion and erosion-corrosion testing, is optimized via CFD simulations for flow-accelerated corrosion testing with liquid lead for lead-cooled nuclear reactors. In the rotating cage, samples manufactured from the material of interest are rotated in a bath of corrosive liquid to mimic the shear flow conditions found in actual applications such as pipes, heat exchangers and pumps. The optimized rotating cage design presented here allows circumventing the high flow resistance associated with the high density of liquid lead, and yields a more uniform flow around the testing samples that better reproduces actual pipe/channel flow conditions, which is instrumental to clearly and univocally associate the observed corrosion rates with the fluid shear.

Prediction of Hardness in Friction Stir Processing by Artificial Neural Networks

This research focuses on the use of Artificial Neural Network (ANN) for the prediction of the microhardness of friction stir processed aluminium based metal matrix composite (AA6061+Al2O3). Different specimens were obtained by using rotating speeds of 1100, 1210, 1320 and 1430 rpm and travelling speeds of 36, 48, 60, 72 mm/min. The microhardness value (HV) of the processed surface of each of the samples was measured and the data collected from the specimens was used as learning data for ANN. Higher rotational speed and lower transversal speeds resulted in higher hardness value since processing at higher tool rotational speed causes high material flow and good resistance to the tool pin profile. A uniform increase in microhardness was observed up to 1320 RPM and a subsequent decrease on any further increments of tool rotational speed. Subsequently, the highest values of microhardness were observed with a square mandrel at 1320 RPM and 36 mm/min. The calculated results were satisfactorily compliant with the measured data and the ANN model was successful in predicting the microhardness.

Numerical Study of Heat Transfer Intensification in a Circular Tube Using a Thin, Radiation-Absorbing Insert. Part 1: Thermo-Hydraulic Characteristics

The presented paper, which is the first of two parts, shows the results of numerical investigations of a heat exchanger channel in the form of a cylindrical tube with a thin insert. The insert, placed concentrically in the pipe, uses the phenomenon of thermal radiation absorption to intensify the heat transfer between the pipe wall and the gas. Eight geometric configurations of the insert size were numerically investigated using CFD software, varying its diameter from 20% to 90% of the pipe diameter and obtaining the thermal-flow characteristics for each case. The tests were conducted for a range of numbers Re = 5000–100,000 and a constant temperature difference between the channel wall and the average gas temperature of ∆T = 100 °C. The results show that the highest increase in the Nu number was observed for the inserts with diameters of 0.3 and 0.4 of the channel diameter, while the highest flow resistance was noted for the inserts with diameters of 0.6–0.7 of the channel diameter. The f/fs(Re) and Nu/Nus(Re) ratios are shown on graphs indicating how much the flow resistance and heat transfer increased compared to the pipe without an insert. Two methods of calculating the Nu number are also presented and analysed. In the first one, the average fluid temperature of the entire pipe volume was used to calculate the Nu number, and in the second, only the average fluid temperature of the annular portion formed by the insert was used. The second one gives much larger Nu/Nus ratio values, reaching up to 8–9 for small Re numbers.

Numerical Study of Heat Transfer Intensification in a Circular Tube Using a Thin, Radiation-Absorbing Insert. Part 2: Thermal Performance

This article is the second part of the work under the same title, which is based on the results of the research presented in the previous article: “Numerical study of heat transfer intensification in a circular tube using a thin, radiation-absorbing insert. Part 1: Thermo-hydraulic characteristics”. Part 1 presents an analysis of pressure drops and heat transfer intensification in a round tube with an insert, using the phenomenon of radiation absorption. In this paper, an analysis of the tested insert’s thermal performance (PEC) is presented, taking into account the criterion of equal pumping power. The tests were carried out for the range of Re = 5000–100,000 numbers, for various insert diameters (from 20% to 90% of the pipe diameter) and a constant temperature difference between the wall and the gas ∆T = 100 °C. The highest Nu numbers were observed for inserts with dimensionless diameters of 0.3 and 0.4, while the highest flow resistance was observed for inserts with diameters of 0.6 and 0.7 of the channel diameter. The thermal efficiency was calculated in two ways, as was the associated Nu number. These results significantly differed from each other: the maximum PEC values for method (I) reached 2, and for method (II) to 8. The common feature for both calculation methods was the fact that the maximum values of the Nu number and the thermal efficiency were observed for small Re numbers; however, as the Re number increases, PEC and Nu number decrease strongly.

Thermal energy storage technology to control rheological properties of drilling fluid

This paper deals with the experimental investigation on the impact of nanoparticles for the increased thermal energy storage to minimize cooling effects on rhelogical properties of drilling fluids. In deepwater oil and gas drilling, drilling fluids thicken with temperature decrease, causing serious problems as lost circulation and high flow resistance. Hybrid nanoparticles assembly was developed via multi-steps to form a Fe3O4@SiO2@Ag multilayer structure with heat storage property. It allows the capture of high-density thermal energy stored in the deep earth to be used in lower temperature zones during the drilling fluid circulation. The synthesized materials were characterized by IR-ATR, UV–Vis, VSM and DLS. The required and promising heat storage capacity of the Fe3O4@SiO2@Ag nanoparticles was demonstrated by DSC and a proposal bench test with temperature and time control. The interaction of bentonite clay and Fe3O4@SiO2@Ag nanoparticles was evaluated by Zeta Potential. Finally, it was demonstrated that the generated nanoparticles provided yield stress reduction in almost 80% at 4 °C by thermal exchange and electronic effect as function of pH value. Therefore, the pioneer and efficient rheological control method proposed in this study can be useful to design water-based drilling fluids to be employed at low temperatures.

Pressure drop in fibrous filter – Representative domain size and effect of fibre orientation

Clean air or gas is critical e.g. in many industrial or health applications. Various filtration processes are employed to ensure that liquid droplets and/or solid particles, i.e. so–called aerosols, are removed efficiently and at low costs from the respective gas streams. Fibrous filters are often used in this context, because of their low cost, their high capture efficiency, and their low pressure drop. Hence, the performance of fibrous filter materials is judged based on their pressure drop and capture efficiency. A generalized model to describe and predict these two parameters would be helpful in developing optimal filter material.In the current work, numerical investigations using the commercial CFD tool ANSYS CFX are engaged to predict the pressure drop caused by multiple randomly–oriented fibres in a 3D domain. The fibres are randomly generated until the desired filter solidity is met. Hereby, the generation algorithm ensures that no fibres intersect. The implementation is based on a fictitious–domain approach, which has the great advantage to perfectly decouple the mesh from the fibre generation, as fibres are implemented as volumes of infinitely–high flow resistance in the fixed mesh. Hence, there is no need for a case–specific and body–fitted mesh. The effect of the domain size is particularly investigated and we find that a domain size of more than 45 times the fibre diameter in all three directions, proves to give domain–size–independent results for the pressure drop. The boundary conditions are also carefully analyzed, and we find that particularly the symmetry planes parallel to the mean flow direction are not appropriate as the representative domain is cut out of the filter layer. Here, the introduction of a pseudo–plane proves to minimize non–physical flow fields. Moreover, using scanning microscopy, a sample fibrous filter is analysed to characterize the (random) fibre orientation. It is found, that within the filter plane an evenly–distributed fibre orientation angle α can be observed, while out of the filter plane the orientation angle β appears rather limited. This limitation is also implemented into the model. Finally, several simulations are performed for various operating conditions to infer an empirical correlation to predict the pressure drop. This correlation is validated using experimental data.

Enhanced photovoltaic performance of dye-sensitized solar cells-based Carica papaya leaf and black cherry fruit co-sensitizers

Natural dye sensitizers are attractive as an alternative to expensive and rare organic sensitizers in dye-sensitized solar cells. The partial absorption of solar spectrum by solar cell-based natural dye negates its usefulness as the power conversion efficiency (PCE) is poor. Co-sensitization of two or more natural dyes with variant absorption spectra could be a feasible solution. Herein, Carica papaya leaf (P) and black cherry (B) fruit dye extracts were prepared and used as co-sensitizers at different volume concentration ratios (B:P=1:3, B:P=1:1 and B:P=3:1). The optical performance analysis shows that the light-harvesting ability of the device optimized after the co-sensitization at B:P=3:1 significantly improved. The DSSCs-based B and P show PCEs of 0.25% and 0.29%, respectively. The DSSC-based B:P=3:1 shows the highest PCE of 0.56%. Further investigation using cyclic voltammetry (CV) shows that DSSC-based B:P=3:1 has the smallest electron-injection barrier (ΔEe) among all the fabricated DSSCs while DSSC-based B has the highest ΔEe. Also, electrochemical impedance spectroscopy (EIS) reveals that the DSSC-based B:P=3:1 has the least charge flow resistance, thereby reducing charge recombination in the device. Meanwhile, the radius of the DSSCs-based B arc is the largest depicting presence of high charge flow resistance thereby increasing charge recombination in the device. The co-sensitizer, (B:P=3:1), compensates for absorption defects of single dye ((B or P) and improves the photo-response current. Also, it suppresses the charge recombination in the device and improves the PCE of the device.

Thermo-hydraulic performance of a circular microchannel heat sink using swirl flow and nanofluid

Increasing the power and reliability of microelectronic components requires heat sinks with greater heat transport performance. This study investigates the hydraulic and heat transport performance of a silicon heat sink under a constant heat flux of 100 W/cm2 with liquid coolant running through parallel microchannels. The coupled heat transfer through the silicon walls and the coolant, modelled as a single-phase fluid, is examined over the Reynolds number range 100≤Re≤350 for micro-channels of circular cross-section, with a straight tape, and with a twisted tape that induces swirl in the flow. Al2O3 nanofluid at nanoparticle volume fractions ϕ = 0, 1, 2 and 3% is used as the coolant. The microchannel heat sink with swirl flow and with the highest nanoparticle volume fraction concentration provides the lowest thermal resistance and contact temperature. Whilst it has a higher flow resistance than the micro-channel with no tape cooled by pure water, it has a positive trade-off between the gains in cooling performance and in flow resistance. This makes these configurations attractive for designing more performing heat sinks for temperature limited or temperature sensitive micro-electronics.

Hemodynamic Assessment of Hollow-Fiber Membrane Oxygenators Using Computational Fluid Dynamics in Heterogeneous Membrane Models.

Extracorporeal membrane oxygenation (ECMO) has been used clinically for more than 40 years as a bridge to transplantation, with hollow-fiber membrane (HFM) oxygenators gaining in popularity due to their high gas transfer and low flow resistance. In spite of the technological advances in ECMO devices, the inevitable contact of the perfused blood with the polymer hollow-fiber gas-exchange membrane, and the subsequent thrombus formation, limits their clinical usage to only 2-4 weeks. In addition, the inhomogeneous flow in the device can further enhance thrombus formation and limit gas-transport efficiency. Endothelialization of the blood contacting surfaces of ECMO devices offers a potential solution to their inherent thrombogenicity. However, abnormal shear stresses and inhomogeneous blood flow might affect the function and activation status of the seeded endothelial cells (ECs). In this study, the blood flow through two HFM oxygenators, including the commercially available iLA® MiniLung Petite Novalung (Xenios AG, Germany) and an experimental one for the rat animal model, was modeled using computational fluid dynamics (CFD), with a view to assessing the magnitude and distribution of the wall shear stress (WSS) on the hollow fibers and flow fields in the oxygenators. This work demonstrated significant inhomogeneity in the flow dynamics of both oxygenators, with regions of high hollow-fiber WSS and regions of stagnant flow, implying a variable flow-induced stimulation on seeded ECs and possible EC activation and damage in a biohybrid oxygenator setting.

Enhancing the flow resistance and sound absorption of open-cell metallic foams by creating partially-open windows

Metallic foams with high flow resistivity are of high interest as practical sound absorption materials. Herein, we report the novel open-cell metallic foams associated with a partially-open window morphology between interconnected pores for improved flow resistivity and sound absorption coefficient. Such a microstructure was produced through exploiting the shear thinning behavior of the metal slurry during the template replication fabrication process. A new microstructural model for permeability simulation is also developed for the new foam to account for the increased specific surface area from the windows. Input parameters to the model include cell geometries that are accessible via morphological characterization. Results showed that metallic foams with the window morphology have significantly increased flow resistivity (1.5 times) with little loss in porosity (< 2.3%). Impedance tube acoustic measurements confirmed such increments to improve the sound absorption coefficient (averaged as 0.2) throughout the entire frequency range. The concept explored in this study demonstrates a generic approach for the design of microstructure-specific foams with simultaneously increased flow resistance and a fully open-celled microstructure associated with high porosity (between 93%~97%). The proposed fluid model also has excellent potential to be adopted in a diverse range of applications for design and characterization.

Optimization on the Gradually Varied Pore Structure Distribution for the Irradiated Absorber

An optimization method for the gradually varied porous absorber is proposed. The Monte Carlo Ray Tracing method based on the acceptance-rejection sampling is established to obtain the absorption distribution of irradiation in the gradually varied porous absorber. The fluid flow, convection, and thermal radiation in the porous absorber are evaluated. Combined with the genetic algorithms, the distribution of porosity and pore size of the porous absorber could automatically adjust to match the non-uniform radiation flux in both radial and axial directions. Moreover, the internal flow layout could be regulated by an optimized radial pore distribution that directs more fluid enters the high heat flux zone. The optimization results demonstrate that the gradually varied porous absorber with porosity ranging from 0.95 to 0.90 and pore size ranging from 2.5mm to 1.5 mm could achieve high thermal efficiency and low flow resistance. Compared with the standard model of the uniform porous absorber, the thermal efficiency of the optimal gradually varied porous absorbers could be further increased by 1.23% to 9.76%, while the pressure drop could be reduced by 7.88% to 55.73%.