Thermo-Fluid Optimization of a Solar Porous Absorber With a Variable Pore Structure

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
P. Wang ◽  
J. B. Li ◽  
K. Vafai ◽  
L. Zhao ◽  
L. Zhou
Keyword(s):  
Pressure Drop ◽  
Pore Structure ◽  
Pore Diameter ◽  
Evaluation Criteria ◽  
Poor Performance ◽  
Diameter Distribution ◽  
Maximum Deviation ◽  
Radiation Fields ◽  
Wide Range ◽  
Fluid Optimization

Optimization based on reconstruction of the velocity, temperature, and radiation fields in a porous absorber with continuous linear porosity or pore diameter distribution is carried out in this work. This study analyzes three typical linear pore structure distributions: increasing (“I”), decreasing (“D”), and constant (“C”) types, respectively. In general, the D type porosity (ϕ) layout combined with the I type pore diameter (dp) distribution would be an excellent pore structure layout for a porous absorber. The poor performance range, which should be avoided in the absorber design, is found to be within a wide range of porosity layouts (ϕi = ∼0.7 and ϕo > 0.6) and pore diameter layouts (di = 1.5–2.5 mm), respectively. With a large inlet porosity (ϕi > 0.8), the D type layout with larger porosity gradient (Gp) has a better thermal performance; however, the I type dp layout with a smaller inlet pore diameter (di < 1.5 mm) and a larger pore diameter gradient (Gdp) is recommended when considering the lower pressure drop. Different pore structure layouts (D type or I type) have a significant effect on the pressure drop, even with the same average ϕa and da, the maximum deviation can be up to 70.1%. The comprehensive performance evaluation criteria (PEC) value shows that the D type ϕ layout with a larger ϕa has an excellent thermopressure drop performance, and a part of PEC values for the I type dp layout are greater than unity.

Modeling and Analysis of an Efficient Porous Media for a Solar Porous Absorber With a Variable Pore Structure

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
P. Wang ◽  
K. Vafai
Keyword(s):  
Pore Structure ◽  
Radiative Heat ◽  
Pore Diameter ◽  
Heat Fluxes ◽  
Diameter Distribution ◽  
Loss Mechanism ◽  
Modeling And Analysis ◽  
Radiation Fields ◽  
Efficient Performance ◽  
Structure Layout

A theoretical mathematical model that considers the continuous linear porosity or pore diameter distribution is established to develop a novel porous absorber with variable pore structure, which will result in a thermopressure drop improvement. Efficient performance can be achieved based on reconstruction of the velocity, temperature, and radiation fields. Collimated and diffusive radiative heat fluxes and the heat loss mechanism from the irradiated surface are analyzed in the presence of the volumetric effect. This study analyzes three typical linear pore structure distributions: increasing (I), decreasing (D), and constant (C) types, respectively. In general, the D type porosity (φ) layout combined with the I type pore diameter (dp) distribution would be an excellent pore structure layout for a porous absorber.

Pore Structure Analysis on Hardened Paste of CaO-Al2O3-P2O5 Cement

2013 ◽  
Vol 591 ◽  
pp. 44-49 ◽  
Author(s):  
Xiao Dong Wang ◽  
Zhu Ding ◽  
Bi Qin Dong ◽  
Ming Zhang
Keyword(s):  
Pore Structure ◽  
Pore Diameter ◽  
Mercury Intrusion Porosimetry ◽  
Fractal Theory ◽  
Diameter Distribution ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
Hydraulic Cement ◽  
Pore Area ◽  
Curing Age

CaO-Al2O3-P2O5cementitious material (PAC) is a type of new developed hydraulic cement, which has excellent cementitious performance and mechanical property. In cement based materials, the pore structure of hardened cement paste has a significant effect on their performance, such like strength, permeability and durability. In the current paper, pore structure parameters of hardened PAC paste samples in five different curing stages were measured respectively by MIP (Mercury Intrusion Porosimetry). The pore fractal features (pore volume, pore area, porosity) were investigated with fractal theory. Results showed that the porosity of hardened PAC paste does not exactly decline with elongation of curing age and increase of compression strength. The PAC pastes pore structures have typical fractal nature which changes with curing age and pore diameter distribution. The fractal feather of hardened PAC paste can be effectively understood by using porosity fractal dimension.

Numerical Modeling of Multidirectional Flow and Heat Transfer in Graphitic Foams

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
S. A. Mohsen Karimian ◽  
Anthony G. Straatman
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pore Structure ◽  
Linear Models ◽  
A Priori ◽  
Experimental Results ◽  
Transfer Model ◽  
Thermal Dispersion ◽  
Wide Range ◽  
Graphitic Foam

To investigate the feasibility of the use of foams with an interconnected spherical pore structure in heat transfer applications, models for heat transfer and pressure drop for this type of porous materials are developed. Numerical simulations are carried out for laminar multidirectional thermofluid flow in an idealized pore geometry of foams with a wide range of geometry parameters. Semiheuristic models for pressure drop and heat transfer are developed from the results of simulations. A simplified solid-body drag equation with an extended high inertia term is used to develop the hydraulic model. A heat transfer model with a nonzero asymptotic term for very low Reynolds numbers is also developed. To provide hydraulic and heat transfer models suitable for a wide range of porosity, only a general form of the length-scale as a function of pore structure is defined a priori, where the parameters of the function were determined as part of the modeling process. The proposed ideal models are compared to the available experimental results, and the source of differences between experimental results and the ideal models is recognized and then calibrated for real graphitic foam. The thermal model is used together with volume-averaged energy equations to calculate the thermal dispersion in graphitic foam. The results of the calculations show that the linear models for thermal dispersion available in literature are oversimplified for predicting thermal dispersion in this type of porous material.

scholarly journals Mechanical Properties and Pore Structure Characteristics of Magnesium Oxychloride Cement Modified by Highland Barley Straw Ash

2021 ◽  
Author(s):  
Feng Cao ◽  
Hongxia Qiao ◽  
Penghui Wang ◽  
Weijia Li
Keyword(s):  
Mechanical Properties ◽  
Pore Structure ◽  
Pore Diameter ◽  
Barley Straw ◽  
Diameter Distribution ◽  
Magnesium Oxychloride ◽  
Magnesium Oxychloride Cement ◽  
Straw Ash ◽  
Highland Barley ◽  
Oxychloride Cement

Abstract Highland barley straw ash contains a large amount of silica, and the ash calcined and ground under certain conditions has a higher pozzolanic effect. In order to study the effect of HBSA added into magnesium oxychloride cement mortar (MOCM) on the mechanical properties and pore structure, the activity of highland barley straw ash was studied firstly through the macroscopic mechanical properties test. Nuclear magnetic resonance (NMR) and Brunner−Emmet−Teller (BET) were used to test the distribution of full pore and micropore for MOCM respectively. The microstructure of MOCM was characterized by scanning electron microscope (SEM). The results illustrate that the highest activity of HBSA was obtained by calcining at 600℃ for 2h and grinding for 2h. The addition of HBSA has a significant effect on the mechanical properties and pore diameter distribution of MOCM. A large amount of M-S-H gel was generated in MOCM added with 10% HBSA content, and had a consequence of decreased proportion of larger pores and the increased proportion of micropores as well as the better mechanical properties and pore structure.

Study on the Relationship Between Structure Parameters and Filtration Performance of Polypropylene Meltblown Nonwovens

2020 ◽  
Vol 20 (4) ◽  
pp. 366-371 ◽  
Author(s):  
Yuanxiang Xiao ◽  
Nazmus Sakib ◽  
Zhonghua Yue ◽  
Yan Wang ◽  
Si Cheng ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Pore Size ◽  
Pore Diameter ◽  
Fiber Diameter ◽  
Areal Density ◽  
Nonwoven Fabric ◽  
Filtration Efficiency ◽  
Structure Parameters ◽  
Nonwoven Fabrics ◽  
Wide Range

AbstractIn this study, polypropylene meltblown nonwoven fabrics with different structure parameters such as fiber diameter, pore size, and areal density were prepared by the industrial production line. The morphology of meltblown nonwoven fibers was evaluated by using scanning electron microscope, and the diameter of fibers was analyzed by using image-pro plus software from at least 200 measurements. The pore size of nonwoven fabric was characterized by a CFP-1500AE type pore size analyzer. The filtration efficiency and pressure drop were evaluated by TSI8130 automatic filter. The results showed that the pressure drop of nonwoven fabrics decreased with the increase in pore size; the filtration efficiency and the pressure drop had a positive correlation with the areal density. However, when the areal density is in the range of 27–29 g/m2, both filtration efficiency and pressure drop decreased with the increase of areal density; when the areal density was kept constant, the filtration efficiency decreased as the pore size decreased; when the pore size of the meltblown nonwoven fabric is less than 17 μm, the filtration efficiency increased as the pore diameter decreased; when the pore diameter of the nonwoven fabric is larger than 17 μm. In a wide range, the pressure drop decreased as the fiber diameter decreased.

Study on the influence on the formation of highly ordered porous anodic aluminia membrane

2017 ◽  
Author(s):  
O Pong-Sik ◽  
Ryang Se-Hun ◽  
Sin Gum-Chol ◽  
Hwang Guk-Nam ◽  
yongson hong
Keyword(s):  
Pore Diameter ◽  
Electrolyte Concentration ◽  
Aao Template ◽  
Alumina Template ◽  
Wide Range ◽  
Electrochemical Mechanism ◽  
Porous Anodic Alumina Template ◽  
Ordered Porous ◽  
Anodic Alumina Template ◽  
Scanning Electron

We have studied porous anodic alumina template through the second anodic oxidation of preparation. Observing the morphology of nanoscale AAO template using scanning electron microscope (SEM), the results indicate that the pores are orderly paralleled arranged with uniform pore diameter, perpendicular to the template surface. A detailed study of the influence of different oxidation conditions, such as different type of electrolyte, concentration, voltage and temperature on the template of alumina and its electrochemical mechanism were performed. By changing the oxidation voltage, electrolyte type, concentration, pore diameter and template thickness can be altered in a wide range such that we can obtain the desired aspect ratio. <br>

scholarly journals Mechanical and Microstructural Characteristics of Calcium Sulfoaluminate Cement Exposed to Early-Age Carbonation Curing

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3515
Author(s):  
Weikang Wang ◽  
Xuanchun Wei ◽  
Xinhua Cai ◽  
Hongyang Deng ◽  
Bokang Li
Keyword(s):  
Cement Paste ◽  
Pore Diameter ◽  
Performance Enhancement ◽  
Diameter Distribution ◽  
Early Age ◽  
Calcium Sulfoaluminate ◽  
Starting Point ◽  
And Performance ◽  
Curing Pressure ◽  
Carbonation Curing

: The early-age carbonation curing technique is an effective way to improve the performance of cement-based materials and reduce their carbon footprint. This work investigates the early mechanical properties and microstructure of calcium sulfoaluminate (CSA) cement specimens under early-age carbonation curing, considering five factors: briquetting pressure, water–binder (w/b) ratio, starting point of carbonation curing, carbonation curing time, and carbonation curing pressure. The carbonization process and performance enhancement mechanism of CSA cement are analyzed by mercury intrusion porosimetry (MIP), thermogravimetry and derivative thermogravimetry (TG-DTG) analysis, X-ray diffraction (XRD), and scanning electron microscope (SEM). The results show that early-age carbonation curing can accelerate the hardening speed of CSA cement paste, reduce the cumulative porosity of the cement paste, refine the pore diameter distribution, and make the pore diameter distribution more uniform, thus greatly improving the early compressive strength of the paste. The most favorable w/b ratio for the carbonization reaction of CSA cement paste is between 0.15 and 0.2; the most suitable carbonation curing starting time point is 4 h after initial hydration; the carbonation curing pressure should be between 3 and 4 bar; and the most appropriate time for carbonation curing is between 6 and 12 h.

scholarly journals Risk Factors and Prediction Models for Venous Thromboembolism in Ambulatory Patients with Lung Cancer

Healthcare ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 778
Author(s):  
Ann-Rong Yan ◽  
Indira Samarawickrema ◽  
Mark Naunton ◽  
Gregory M. Peterson ◽  
Desmond Yip ◽  
...  
Keyword(s):  
Risk Factors ◽  
Lung Cancer ◽  
Venous Thromboembolism ◽  
High Risk ◽  
Prediction Models ◽  
Poor Performance ◽  
Risk Models ◽  
Related Risk ◽  
Wide Range ◽  
Ambulatory Patients

Venous thromboembolism (VTE) is a significant cause of mortality in patients with lung cancer. Despite the availability of a wide range of anticoagulants to help prevent thrombosis, thromboprophylaxis in ambulatory patients is a challenge due to its associated risk of haemorrhage. As a result, anticoagulation is only recommended in patients with a relatively high risk of VTE. Efforts have been made to develop predictive models for VTE risk assessment in cancer patients, but the availability of a reliable predictive model for ambulate patients with lung cancer is unclear. We have analysed the latest information on this topic, with a focus on the lung cancer-related risk factors for VTE, and risk prediction models developed and validated in this group of patients. The existing risk models, such as the Khorana score, the PROTECHT score and the CONKO score, have shown poor performance in external validations, failing to identify many high-risk individuals. Some of the newly developed and updated models may be promising, but their further validation is needed.

scholarly journals Simulating the interstellar medium of galaxies with radiative transfer, non-equilibrium thermochemistry, and dust

2020 ◽  
Vol 499 (4) ◽  
pp. 5732-5748 ◽  
Author(s):  
Rahul Kannan ◽  
Federico Marinacci ◽  
Mark Vogelsberger ◽  
Laura V Sales ◽  
Paul Torrey ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Galaxy Formation ◽  
State Of The Art ◽  
Complex Function ◽  
Ionization State ◽  
Radiation Fields ◽  
Stellar Feedback ◽  
Wide Range ◽  
Dust Distribution ◽  
Non Equilibrium

ABSTRACT We present a novel framework to self-consistently model the effects of radiation fields, dust physics, and molecular chemistry (H2) in the interstellar medium (ISM) of galaxies. The model combines a state-of-the-art radiation hydrodynamics module with a H  and He  non-equilibrium thermochemistry module that accounts for H2 coupled to an empirical dust formation and destruction model, all integrated into the new stellar feedback framework SMUGGLE. We test this model on high-resolution isolated Milky-Way (MW) simulations. We show that the effect of radiation feedback on galactic star formation rates is quite modest in low gas surface density galaxies like the MW. The multiphase structure of the ISM, however, is highly dependent on the strength of the interstellar radiation field. We are also able to predict the distribution of H2, that allow us to match the molecular Kennicutt–Schmidt (KS) relation, without calibrating for it. We show that the dust distribution is a complex function of density, temperature, and ionization state of the gas. Our model is also able to match the observed dust temperature distribution in the ISM. Our state-of-the-art model is well-suited for performing next-generation cosmological galaxy formation simulations, which will be able to predict a wide range of resolved (∼10 pc) properties of galaxies.

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