The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Alfred T. Hodgson - One of the best experts on this subject based on the ideXlab platform.
-
modeling the reversible diffusive Sink Effect in response to transient contaminant sources
Indoor Air, 2002Co-Authors: Dongye Zhao, John C Little, Alfred T. HodgsonAbstract:A physically based diffusion model is used to evaluate the Sink Effect of diffusion-controlled indoor materials and to predict the transient contaminant concentration in indoor air in response to several time-varying contaminant sources. For simplicity, it is assumed the predominant indoor material is a homogeneous slab, initially free of contaminant, and the air within the room is well mixed. The model enables transient volatile organic compound (VOC) concentrations to be predicted based on the material/air partition coefficient (K) and the material-phase diffusion coefficient (D) of the Sink. Model predictions are made for three scenarios, each mimicking a realistic situation in a building. Styrene, phenol, and naphthalene are used as representative VOCs. A styrene butadiene rubber (SBR) backed carpet, vinyl flooring (VF), and a polyurethane foam (PUF) carpet cushion are considered as typical indoor Sinks. In scenarios involving a sinusoidal VOC input and a double exponential decaying input, the model predicts the Sink has a modest impact for SBR/styrene, but the Effect increases for VF/phenol and PUF/naphthalene. In contrast, for an episodic chemical spill, SBR is predicted to reduce the peak styrene concentration considerably. A parametric study reveals for systems involving a large equilibrium constant (K), the kinetic constant (D) will govern the shape of the resulting gasphase concentration profile. On the other hand, for systems with a relaxed mass transfer resistance, K will dominate the profile.
-
Predicting the emission rate of volatile organic compounds from vinyl flooring
Environmental Science & Technology, 2002Co-Authors: John C Little, Alfred T. HodgsonAbstract:A model for predicting the rate at which a volatile organic compound (VOC) is emitted from a diffusion-controlled material is validated for three contaminants (n-pentadecane, n-tetradecane, and phenol) found in vinyl flooring (VF). Model parameters are the initial VOC concentration in the material-phase (C{sub 0}), the material/air partition coefficient (K), and the material-phase diffusion coefficient (D). The model was verified by comparing predicted gas-phase concentrations to data obtained during small-scale chamber tests, and by comparing predicted material-phase concentrations to those measured at the conclusion of the chamber tests. Chamber tests were conducted with the VF placed top side up and bottom side up. With the exception of phenol, and within the limits of experimental precision, the mass of VOCs recovered in the gas phase balances the mass emitted from the material phase. The model parameters (C{sub 0}, K, and D) were measured using procedures that were completely independent of the chamber test. Gas- and material-phase predictions compare well to the bottom-side-up chamber data. The lower emission rates for the top-side-up orientation may be explained by the presence of a low-permeability surface layer. The Sink Effect of the stainless steel chamber surface was shown to be negligible.
Vera A Khokhlova - One of the best experts on this subject based on the ideXlab platform.
-
ultrasound guided tissue fractionation by high intensity focused ultrasound in an in vivo porcine liver model
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Tatiana D Khokhlova, Yaknam Wang, Julianna C Simon, Bryan W Cunitz, Frank Starr, Marla Paun, Lawrence A Crum, Michael R Bailey, Vera A KhokhlovaAbstract:The clinical use of high intensity focused ultrasound (HIFU) therapy for noninvasive tissue ablation has been recently gaining momentum. In HIFU, ultrasound energy from an extracorporeal source is focused within the body to ablate tissue at the focus while leaving the surrounding organs and tissues unaffected. Most HIFU therapies are designed to use heating Effects resulting from the absorption of ultrasound by tissue to create a thermally coagulated treatment volume. Although this approach is often successful, it has its limitations, such as the heat Sink Effect caused by the presence of a large blood vessel near the treatment area or heating of the ribs in the transcostal applications. HIFU-induced bubbles provide an alternative means to destroy the target tissue by mechanical disruption or, at its extreme, local fractionation of tissue within the focal region. Here, we demonstrate the feasibility of a recently developed approach to HIFU-induced ultrasound-guided tissue fractionation in an in vivo pig model. In this approach, termed boiling histotripsy, a millimeter-sized boiling bubble is generated by ultrasound and further interacts with the ultrasound field to fractionate porcine liver tissue into subcellular debris without inducing further thermal Effects. Tissue selectivity, demonstrated by boiling histotripsy, allows for the treatment of tissue immediately adjacent to major blood vessels and other connective tissue structures. Furthermore, boiling histotripsy would benefit the clinical applications, in which it is important to accelerate resorption or passage of the ablated tissue volume, diminish pressure on the surrounding organs that causes discomfort, or insert openings between tissues.
Chi Yung Jim - One of the best experts on this subject based on the ideXlab platform.
-
air conditioning energy consumption due to green roofs with different building thermal insulation
Applied Energy, 2014Co-Authors: Chi Yung JimAbstract:On hot days, green roofs could reduce heat flux into indoor space and air-conditioning energy use. Most thermal-benefit studies estimate energy saving based on temperature measurements. A field experiment on the roofs of two residential buildings in subtropical Hong Kong was designed to measure air-conditioning electricity consumption in relation to three factors: (1) building thermal insulation (BTI): omitted at Block 1 and installed at Block 2; (2) green-roof type: each block had a bare (Control) and two extensive green-roof plots, namely simple Sedum and more complex herbaceous Peanut vegetation; and (3) three summer weather scenarios: sunny, cloudy, and rainy. Air-conditioning electricity consumption of six vacant apartments below the experimental plots was monitored by precision energy loggers. Under all weather conditions, the unshielded Control imposes high cooling load at Block 1, but BTI at Block 2 cuts heat ingress. Sedum reduces more energy consumption than Control at both blocks, with Block 2 better than Block 1. The best Effect occurs on sunny day, followed by cloudy and rainy. Sedum roof with BTI enhances thermal benefit. Without BTI, Sedum roof consumes more energy, hence the simple green roof cannot substitute BTI function. Under three weather scenarios, Peanut uses more electricity at Block 2 than Block 1, indicating the joint operation of green-roof heat-Sink Effect (GHE) and building heat-Sink Effect (BHE) at Block 2. Thicker substrate with higher moisture-holding capacity generates GHE. Added BTI material layers create BHE, with thermal resistance reduced by moisture penetration and elevated temperature. Their joint Effect has raised thermal mass and thermal capacity. A rather steep thermal gradient is formed to induce thermal-insulation breaching to push heat into indoor space. At Block 1, Peanut roof can partly compensate for omission of BTI. At Block 2, however, Peanut coupled with BTI can synergistically increase cooling load. The findings can inform policies and design of green roof and associated BTI in cities with hot summer.
-
heat Sink Effect and indoor warming imposed by tropical extensive green roof
Ecological Engineering, 2014Co-Authors: Chi Yung JimAbstract:Abstract The study evaluates diurnal cooling Effect of two herbs on tropical green roofs, C3 broadleaved Perennial Peanut (Arachis pintoi) and CAM succulent Mexican Sedum (Sedum mexicanum) with contrasting photosynthesis-transpiration physiology. The holistic outdoor-substrate-indoor vertical temperature profile is evaluated. Control, Sedum and Peanut experimental plots were established on a residential building in Hong Kong, each equipped with temperature sensors at 7–11 vertical positions. On summer sunny day, Control plot displays conspicuous daytime heating at roof surface and 15 cm and 150 cm above it. Indoor air and ceiling temperatures with soil > Sedum surface > drainage > 150 cm > tile. Sedum surface is heated to a maximum of 35.4 °C, merely 1–2 °C lower than adjacent soil and 15 cm air, indicating daytime CAM stomata closure to restrict transpiration cooling. Contrary to expectation, sensible heat stored in Sedum roof generates green-roof heat-Sink Effect (GHE), driving downward heat flux throughout the day to raise indoor temperature by 1–2 °C. Peanut plot's vertical thermal sequence is: 150 cm > 15 cm > soil > rockwool > Peanut surface > drainage > tile. Peanut surface is significantly cooled by C3 transpiration to 28.8 °C, and it remains the coolest among outdoor positions throughout the day. Slightly less heat than Sedum is fluxed downwards to raise indoor temperature. Cooling due to Effective C3 transpiration and thicker vegetation and substrate layers is offset by more intensified GHE. The green roofs demonstrate opposite proximal thermal impact which is limited to near-ground (15 cm) air, with warming at Sedum but cooling at Peanut. Both vegetated plots show less heat ingress into indoor space in daytime, but more in nighttime. On summer cloudy and rainy days, both green roofs with GHE brought more heat flux to indoor space throughout the day. Contrary to findings outside the tropics, the tropical extensive green roofs cannot bring net cooling to indoor environment in summer.
J S Huang - One of the best experts on this subject based on the ideXlab platform.
-
flow and heat transfer over an unsteady stretching surface with non uniform heat source
International Communications in Heat and Mass Transfer, 2008Co-Authors: R Tsai, K H Huang, J S HuangAbstract:Abstract The non-uniform heat source/Sink Effect on the flow and heat transfer from an unsteady stretching sheet through a quiescent fluid medium extending to infinity is studied. The boundary layer equations are transformed by using similarity analysis to be a set of ordinary differential equations containing three parameters: unsteadiness parameter (S), space-dependent parameter (A⁎) and temperature-dependent parameter (B⁎) for heat source/Sink. The velocity and temperature fields are solved using the Chebyshev finite difference method (ChFD). Results showed that the heat transfer rate, − θ′(0) and the skin friction, − f″(0) increase as the unsteadiness parameter increases whereas decrease as the space-dependent and temperature-dependent parameters for heat source/Sink increase.
Krishna M. Pillai - One of the best experts on this subject based on the ideXlab platform.
-
variations in unsaturated flow with flow direction in resin transfer molding an experimental investigation
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Hua Tan, Tonmoy Roy, Krishna M. PillaiAbstract:Abstract The dual-scale nature of fiber preforms due to the presence of large continuous gaps between fiber tows gives rise to the unsaturated flow in resin transfer molding (RTM) process which is characterized by a droop in the injection pressure history due to the delayed absorption of fiber tows (the ‘Sink’ Effect). In this study, we experimentally investigate the Effect of change in flow direction on the unsaturated flow in three anisotropic dual-scale fiber mats. A series of 1-D mold-filling experiments involving a constant flow rate were conducted for a unidirectional woven fiber-mat, a biaxial stitched mat, and a triaxial stitched fiber-mat along with a reference single-scale random mat. In the case of the unidirectional mats, the droop in the inlet-pressure history, signifying the strength of the Sink Effect, is found to be strongest for flow along the micro-channels aligned with fiber tows. The droop, and hence the Sink Effect, is observed to weaken progressively for flow-directions at 45° and 90° to this principal direction. In the case of the biaxial and triaxial mats, the situation is more complex due to the multi-layer construction of such mats: maximum droop is found when mats are oriented at a 45° angle with respect to the fiber-mat coordinate, and it weakens in the 0° and 90° directions. The unsaturated flow Effect is also quantified by measuring percentage deviation in the area under the experimental curve from that of the predicted curve. A clear correlation between the droop (through the percentage deviation) and the permeability along a flow direction in the unidirectional mats is observable, though such a relationship eludes the triaxial mat. The Effect of unsaturated flow on liquid-front progress during the 1-D experiment was also studied. In contrast to the reference single-scale random mat where the observed front progress closely follow the prediction based on the single-scale physics, a small difference was observed between the observed and predicted front progress for the three dual-scale mats considered. However the difference was too small to yield any significant correlation with the flow direction.
-
investigation of unsaturated flow in woven braided and stitched fiber mats during mold filling in resin transfer molding
Polymer Composites, 2001Co-Authors: J Slade, Krishna M. Pillai, Suresh G AdvaniAbstract:In Resin Transfer Molding (RPM), which is a process to manufacture polymer composites, the impregnation of fibrous reinforcement In the form of mats by a thermosetting resin is modeled as the flow of a Newtonian liquid through a single length-scale porous medium. While this approach is sufficiently accurate for random fiber-mats, it can lead to appreciable errors when applied to woven, braided, or stitched fiber-mats that contain two length scales. This work investigates the primary factors governing the isothermal unsaturated flow through such dual-scale porous media. Two studies were conducted to better understand this phenomenon: the first experimenatally investigated the flow, while the second theoretically modeled the flow and identified important parameters affecting such a flow with the help of dimensionless analysis. In the first study, one-dimensional constant injection rate experiments were performed using various fiber mats. The unsaturated flow behavior of various mats was characterized using a constant “Sink” term in the continuity equation. Results indicated that for a given fiber-mat, the magnitude of the Sink Effect was a function of the capillary number. In the second study, a numerical model was developed to describe flow through dual-scale preforms in which the two flow domains, the inter- and intra-tow regions, were coupled. We identified a dimensionless number called the Sink Effect index ψ that characterizes the magnitude of liquid absorption by the tows and is a function of the relative resistance to flow in the tow and inter-tow regions, and the packing density of the tows. The parametric study of this index with the help of numerical simulations reveals its influence on the flow and identifies the distinct transient and steady-state flow regimes.
