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.

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.

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.

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.

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.

The characterization and preparation of porous low dielectric films using various cyclodextrins as template materials

2003 ◽  
Vol 766 ◽  
Author(s):  
Jin-Heong Yim ◽  
Jung-Bae Kim ◽  
Hyun-Dam Jeong ◽  
Yi-Yeoul Lyu ◽  
Sang Kook Mah ◽  
...  
Keyword(s):  
Thin Film ◽  
Mechanical Properties ◽  
Dielectric Constant ◽  
Pore Structure ◽  
Pore Diameter ◽  
Dielectric Films ◽  
Low Dielectric Constant ◽  
Cyclodextrin Derivatives ◽  
Low Dielectric ◽  
Low K

AbstractPorous low dielectric films containing nano pores (∼20Å) with low dielectric constant (<2.2), have been prepared by using various kinds of cyclodextrin derivatives as porogenic materials. The pore structure such as pore size and interconnectivity can be controlled by changing functional groups of the cyclodextrin derivatives. We found that mechanical properties of porous low-k thin film prepared with mCSSQ (modified cyclic silsesquioxane) precursor and cyclodextrin derivatives were correlated with the pore interconnection length. The longer the interconnection length of nanopores in the thin film, the worse the mechanical properties of the thin film (such as hardness and modulus) even though the pore diameter of the films were microporous (∼2nm).

Experimental Studies of Hydrodynamics and Heat Transfer in Channels With High-Porous Cellular Materials in Single-Phase Forced Convection and Flow Boiling of Working Fluids

1999 ◽  
Author(s):  
Yury F. Gortyshov ◽  
Igor A. Popov ◽  
Konstantin E. Gulitsky
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Pore Diameter ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Internal Heat ◽  
Cellular Materials ◽  
Heat Fluxes ◽  
Working Fluids ◽  
Resistance Surface

Abstract In this paper we consider experimental studies of hydraulic resistance, surface heat transfer, internal heat exchange and critical heat fluxes for the flow of single-phase and boiling working fluids in channels with high-porous inserts. Experiments were carried out with more than 40 samples of high-porous cellular materials with the porosity 0.8...0.98 and mean pore diameter 0.62...4 mm and with more than 10 samples of regular porous inserts and porosity ε = 0.512...0.86 and mean pore diameter 1.5...3.5 mm. These samples were made of porcelain, invar, nichrome, bronze and copper.

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