Showing papers on "Pressure drop published in 2013"

Heat transfer and fluid flow analysis of solar air heater: A review of CFD approach

Abstract: The objective of this article is to present a detailed review of the literature that deals with the application of CFD in the design of solar air heater. Solar air heater is one of the basic equipment through which solar energy is converted into thermal energy. CFD is a simulation tool which uses powerful computer and applied mathematics, to model fluid flow situations for the prediction of heat, mass and momentum transfer and optimal design in various heat transfer and fluid flow processes. The quality of the solutions obtained from CFD simulations are largely within the acceptable range proving that CFD is an effective tool for predicting the behavior and performance of a solar air heater. One of the great challenges in the design of a solar air heater using CFD approach is the selection of appropriate turbulence model. The decision about a suitable turbulence model chosen in a CFD computation is not easy. In this article a CFD investigation is also carried out to select best turbulence model for the design of a solar air heater. A modern CFD code ANSYS FLUENT v12.1 is used to simulate fluid flow through a conventional solar air heater. A two-dimensional flow is assumed. The influences of the five different turbulence models on the quality of the obtained results are tested. It appears from the performed calculations that the Renormalization-group k–e model yields the best results for two-dimensional flow through conventional solar air heaters.

A microfluidic platform for generating large-scale nearly identical human microphysiological vascularized tissue arrays

Abstract: This paper reports a polydimethylsiloxane microfluidic model system that can develop an array of nearly identical human microtissues with interconnected vascular networks. The microfluidic system design is based on an analogy with an electric circuit, applying resistive circuit concepts to design pressure dividers in serially-connected microtissue chambers. A long microchannel (550, 620 and 775 mm) creates a resistive circuit with a large hydraulic resistance. Two media reservoirs with a large cross-sectional area and of different heights are connected to the entrance and exit of the long microchannel to serve as a pressure source, and create a near constant pressure drop along the long microchannel. Microtissue chambers (0.12 μl) serve as a two-terminal resistive component with an input impedance >50-fold larger than the long microchannel. Connecting each microtissue chamber to two different positions along the long microchannel creates a series of pressure dividers. Each microtissue chamber enables a controlled pressure drop of a segment of the microchannel without altering the hydrodynamic behaviour of the microchannel. The result is a controlled and predictable microphysiological environment within the microchamber. Interstitial flow, a mechanical cue for stimulating vasculogenesis, was verified by finite element simulation and experiments. The simplicity of this design enabled the development of multiple microtissue arrays (5, 12, and 30 microtissues) by co-culturing endothelial cells, stromal cells, and fibrin within the microchambers over two and three week periods. This methodology enables the culturing of a large array of microtissues with interconnected vascular networks for biological studies and applications such as drug development.

Variability of computational fluid dynamics solutions for pressure and flow in a giant aneurysm: the ASME 2012 Summer Bioengineering Conference CFD Challenge.

Abstract: Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline. For phase II, a physical model of the geometry was constructed, from which pressure and flow rates were measured. Groups repeated their simulations using a geometry reconstructed from a micro-computed tomography (CT) scan of the physical model with the measured flow rates and fluid properties. Phase I results from 25 groups demonstrated remarkable consistency in the pressure patterns, with the majority predicting peak systolic pressure drops within 8% of each other. Aneurysm sac flow patterns were more variable with only a few groups reporting peak systolic flow instabilities owing to their use of high temporal resolutions. Variability for phase II was comparable, and the median predicted pressure drops were within a few millimeters of mercury of the measured values but only after accounting for submillimeter errors in the reconstruction of the life-sized flow model from micro-CT. In summary, pressure can be predicted with consistency by CFD across a wide range of solvers and solution strategies, but this may not hold true for specific flow patterns or derived quantities. Future challenges are needed and should focus on hemodynamic quantities thought to be of clinical interest.

Magnetic resonance measurement of turbulent kinetic energy for the estimation of irreversible pressure loss in aortic stenosis.

Abstract: ObjectivesThe authors sought to measure the turbulent kinetic energy (TKE) in the ascending aorta of patients with aortic stenosis and to assess its relationship to irreversible pressure loss.Backg ...

Flow boiling in micro-scale channels – Synthesized literature review

Abstract: This paper presents a synthesized review on the recent literature concerning micro-scale flow boiling. The topics covered are macro- to micro-scale transition, flow patterns, pressure drop, heat transfer coefficient, critical heat flux, superficial void fraction and liquid entrainment. The analyses revealed some characteristics common to micro-scale two-phase flow, i.e. absence of stratified flow, predominance of annular flow over all saturated region, uniform liquid film thickness during horizontal flows, reduced liquid entrainment, high heat transfer coefficients and pressure drops. Despite the importance of liquid entrainment and void fraction in predictive methods, there is a lack of experimental results for these parameters in the micro-scale literature. Important accomplishments concerning the investigation of micro-scale flow boiling have been obtained over the last two decades, but some aspects, including local physical mechanisms related to heat transfer, onset of dryout and flow boiling instabilities still remain unclear.