Home About us Contact
|
Home About us Contact | ||
|
|
||
Optimal Flow Rate (optimal + flow_rate)
Selected AbstractsMineral precipitation associated with vertical fault zones: the interaction of solute advection, diffusion and chemical kineticsGEOFLUIDS (ELECTRONIC), Issue 1 2007CHONGBIN ZHAO Abstract This article is concerned with chemical reactions that occur between two interacting parallel fluid flows using mixing in vertical faults as an example. Mineral precipitation associated with fluid flow in permeable fault zones results in mineralization and chemical reaction (alteration) patterns, which in turn are strongly dependent on interactions between solute advection (controlled by fluid flow rates), solute diffusion/dispersion and chemical kinetics. These interactions can be understood by simultaneously considering two dimensionless numbers, the Damköhler number and the Z -number. The Damköhler number expresses the interaction between solute advection (flow rate) and chemical kinetics, while the Z -number expresses the interaction between solute diffusion/dispersion and chemical kinetics. Based on the Damköhler and Z -numbers, two chemical equilibrium length-scales are defined, dominated by either solute advection or by solute diffusion/dispersion. For a permeable vertical fault zone and for a given solute diffusion/dispersion coefficient, there exist three possible types of chemical reaction patterns, depending on both the flow rate and the chemical reaction rate. These three types are: (i) those dominated by solute diffusion and dispersion resulting in precipitation at the lower tip of a vertical fault and as a thin sliver within the fault, (ii) those dominated by solute advection resulting in precipitation at or above the upper tip of the fault, and (iii) those in which advection and diffusion/dispersion play similar roles resulting in wide mineralization within the fault. Theoretical analysis indicates that there exists both an optimal flow rate and an optimal chemical reaction rate, such that chemical equilibrium following focusing and mixing of two fluids may be attained within the fault zone (i.e. type 3). However, for rapid and parallel flows, such as those resulting from a lithostatic pressure gradient, it is difficult for a chemical reaction to reach equilibrium within the fault zone, if the two fluids are not well mixed before entering the fault zone. Numerical examples are given to illustrate the three possible types of chemical reaction patterns. [source] Effects of water flow rate on growth rate, mortality and biomass return of abalone in slab tanksAQUACULTURE RESEARCH, Issue 6 2010Matthew Wassnig Abstract The capital-intensive nature of land-based abalone farming demands that infrastructure be fully utilized. This study investigated whether the negative impact of high stocking density in shallow raceway tanks could be ameliorated by optimizing water flow. We quantified the effect of flow rate (87,246 L min,1) on the performance of 2-year-old hybrid abalone (Haliotis laevigata and Haliotis rubra) held at two stocking densities (11400 and 7600 tank,1). A 50% higher density yielded a 27% increase in biomass gain, despite a 10% growth reduction and 3% higher mortality. At the lower density, there was an optimal flow rate of approximately 200 L,1, at which biomass gain was 474 kg and the feed conversion ratio (FCR) was 1.31. At the higher density, biomass gain (max = 658 kg) and FCR (min = 1.41) improved linearly with increasing flow, suggesting that an optimal flow rate exists at 246 L,1 or beyond those tested. Increased oxygen availability with increasing flow is thought to have enhanced abalone performance, although flows greater than 200 L min,1 may have reduced performance at low density due to feed washout and nutrient leaching. Overall, greater financial return per tank was favoured by the combination of high stocking density and high water flow. [source] Role of nutrient supply on cell growth in bioreactor design for tissue engineering of hematopoietic cellsBIOTECHNOLOGY & BIOENGINEERING, Issue 7 2005Pragyansri Pathi Abstract In the present study, a dynamic mathematical model for the growth of granulocyte progenitor cells in the hematopoietic process is developed based on the principles of diffusion and chemical reaction. This model simulates granulocyte progenitor cell growth and oxygen consumption in a three-dimensional (3-D) perfusion bioreactor. Material balances on cells are coupled to the nutrient balances in 3-D matrices to determine the effects of transport limitations on cell growth. The method of volume averaging is used to formulate the material balances for the cells and the nutrients in the porous matrix containing the cells. All model parameters are obtained from the literature. The maximum cell volume fraction reached when oxygen is depleted in the cell layer at 15 days and is nearly 0.63, corresponding to a cell density of 2.25 × 108 cells/mL. The substrate inhibition kinetics for cell growth lead to complex effects with respect to the roles of oxygen concentration and supply by convection and diffusion on cell growth. Variation in the height of the liquid layer above the cell matrix where nutrient supply is introduced affected the relative and absolute amounts of oxygen supply by hydrodynamic flow and by diffusion across a gas permeable FEP membrane. Mass transfer restrictions of the FEP membrane are considerable, and the supply of oxygen by convection is essential to achieve higher levels of cell growth. A maximum growth rate occurs at a specific flow rate. For flow rates higher than this optimal, the high oxygen concentration led to growth inhibition and for lower flow rates growth limitations occur due to insufficient oxygen supply. Because of the nonlinear effects of the autocatalytic substrate inhibition growth kinetics coupled to the convective transport, the rate of growth at this optimal flow rate is higher than that in a corresponding well-mixed reactor where oxygen concentration is set at the maximum indicated by the inhibitory kinetics. ©2005 Wiley Periodicals, Inc. [source] Cell Detachment Model for an Antibody-Based Microfluidic Cancer Screening SystemBIOTECHNOLOGY PROGRESS, Issue 5 2006Swapnil P. Wankhede We consider cells bound to the floor of a microfluidic channel and present a model of their flow-induced detachment. We approximate hydrodynamic force and cell elastic response using static finite-element simulation of a single cell. Detachment is assumed to occur when hydrodynamic and adhesive forces are roughly equal. The result is extended to multiple cells at the device level using a sigmoidal curve fit. The model is applied to a microfluidic cancer-screening device that discriminates between normal epithelial cells and cells infected with human papillomavirus (HPV), on the basis of increased expression of the transmembrane protein ,6 integrin in the latter. Here, the cells to be tested are bound to a microchannel floor coated with anti ,6 integrin antibodies. In an appropriate flow rate range, normal cells are washed away while HPV-infected cells remain bound. The model allows interpolation between data points to choose the optimal flow rate and provides insight into interaction of cell mechanical properties and the flow-induced detachment mechanism. Notably, the results suggest a significant influence of cell elastic response on detachment. [source] Extracorporeal photopheresis with permanent subcutaneous right atrial cathetersJOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 12 2007Hartmut Ständer Summary Background: Adequate peripheral venous access is crucial for successful extracorporeal photopheresis (ECP). As this approach is not always feasible in older patients and patients with graft-versus-host disease, central venous catheters play an increasing role in providing long-term vascular access for ECP.However, not all catheters are able to deliver the minimum flow rate of 7 ml/min for ECP. Patients and Methods: Eight different permanent subcutaneous right atrial catheters were connected in vitro to the UVAR® -XTSÔ photopheresis system and median flow rates were determined. In addition, in vivo flow rates of patients who received ECP, using either peripheral or central venous access, were determined. Results: Hemodialysis catheters with an internal diameter of 2.0 or 1.5 × 3.5 mm and a length up to 48 cm provided in vitro flow rates of 27,28 ml/min, almost identical to a peripheral access needle. Central venous catheters with a length of over 90 cm reached flow rates below 7 ml/min and are impractical for ECP. The analysis of 308 ECP collection cycles with peripheral vascular access revealed an average flow rate of 31.5 ± 6.4 ml/min. Only permanent subcutaneous right atrial catheters made for hemodialysis provided similar flow rates (Quinton PermCath Dual Lumen) (33.7 ± 4.7 ml/min, n = 198). Conclusions: Permanent subcutaneous hemodialysis catheters with a length of maximally 48 cm achieve optimal flow rates for ECP. They represent therefore the central venous access of choice in patients with inadequate peripheral vascular access. [source] Optimal Pressure Regulation of the Pneumatic Ventricular Assist Device With Bellows-Type DriverARTIFICIAL ORGANS, Issue 8 2009Jung Joo Lee Abstract The bellows-type pneumatic ventricular assist device (VAD) generates pneumatic pressure with compression of bellows instead of using an air compressor. This VAD driver has a small volume that is suitable for portable devices. However, improper pneumatic pressure setup can not only cause a lack of adequate flow generation, but also cause durability problems. In this study, a pneumatic pressure regulation system for optimal operation of the bellows-type VAD has been developed. The optimal pneumatic pressure conditions according to various afterload conditions aiming for optimal flow rates were investigated, and an afterload estimation algorithm was developed. The developed regulation system, which consists of a pressure sensor and a two-way solenoid valve, estimates the current afterload and regulates the pneumatic pressure to the optimal point for the current afterload condition. Experiments were performed in a mock circulation system. The afterload estimation algorithm showed sufficient performance with the standard deviation of error, 8.8 mm Hg. The flow rate could be stably regulated with a developed system under various afterload conditions. The shortcoming of a bellows-type VAD could be handled with this simple pressure regulation system. [source] | ||||||||||||||||