Flow-related Parameters Research Articles

Experimental Study on Velocity Profiles with Different Roughness Elements in a Flume

The classical log law for velocity profile is applied to engineering practice. Field observations indicate that the composition of the bed materials obviously influences the shape of vertical velocity distribution. To clearly understand the roughness effect, six types of materials were laid separately at various depths for the investigation of the effects of roughness elements on the vertical velocity distribution. A down-looking 3D acoustic Doppler velocimeter was used to measure the velocity profiles. The experimental results showed that the curve characteristics of velocity profiles are strongly dependent on the roughness scale and related flow parameters. If d/R, Fr, and Re are larger than 0.15, 0.47, and 60 000, respectively, the velocity distribution may resemble an S-shape profile. The inflexion position Z*/H for a given S-shape profile was empirically deduced as Z*/H = −0.4481d/R + 0.3225. Otherwise, the velocity profile agrees well with the logarithmic law. The findings of this study are useful in engineering practice (i.e., depth-averaged velocity and flow rate estimate). Key words: velocity profiles, acoustic Doppler velocimeter, roughness elements, logarithmic law, S-shape curve.

Computed Tomography Angiography With High Flow Rates

The aims of this study were to test high-flow application of contrast media (CM) using novel high-flow needles and to assess injection- and flow-related parameters in a circulation phantom and in an in vivo population. A circulation phantom simulating physiological parameters was used. Preheated CM (300 mg/mL) was injected at flow rates varying between 5 and 15 mL/s through a novel 18-gauge high-flow intravenous injection needle. In addition, feasibility of these high-flow needles was tested with administration of flow rates of 9 mL/s in 20 patients referred for pre-transcatheter aortic valve implantation assessment. Injection parameters (eg, peak pressures, peak flow rates) in both phantom and in vivo setup were continuously monitored by a data acquisition program. Attenuation at predefined levels of the aorta (eg, aortic root to common femoral arteries) was measured in all patients to determine clinical applicability. In the phantom setup, injection rates up to 15 mL/s were feasible. An enhancement plateau was reached at 11 mL/s (464 [20] HU). In patients, no pressure- or flow-related complications (eg, extravasation) were recorded (mean [SD] peak pressure, 154 [8] psi; mean [SD] peak flow rate, 9.2 [0.1 mL/s; range, 9.1-9.6]). Diagnostic attenuation values were reached at all predefined levels of the aorta (330.8 [113.1] HU to 622.9 [81.5] HU). These results indicate that injections with 9 mL/s using high-flow injection needles are safe. The pressure limit of 325 psi was not reached, and the injections resulted in diagnostic attenuation values. Using this dedicated needle, high flow rates should not be considered a drawback for CM application in routine CT angiography examinations.

Statistical scaling of geometric characteristics in stochastically generated pore microstructures

We analyze the statistical scaling of structural attributes of virtual porous microstructures that are stochastically generated by thresholding Gaussian random fields. Characterization of the extent at which randomly generated pore spaces can be considered as representative of a particular rock sample depends on the metrics employed to compare the virtual sample against its physical counterpart. Typically, comparisons against features and/patterns of geometric observables, e.g., porosity and specific surface area, flow-related macroscopic parameters, e.g., permeability, or autocorrelation functions are used to assess the representativeness of a virtual sample, and thereby the quality of the generation method. Here, we rely on manifestations of statistical scaling of geometric observables which were recently observed in real millimeter scale rock samples [13] as additional relevant metrics by which to characterize a virtual sample. We explore the statistical scaling of two geometric observables, namely porosity (ϕ) and specific surface area (SSA), of porous microstructures generated using the method of Smolarkiewicz and Winter [42] and Hyman and Winter [22]. Our results suggest that the method can produce virtual pore space samples displaying the symptoms of statistical scaling observed in real rock samples. Order q sample structure functions (statistical moments of absolute increments) of ϕ and SSA scale as a power of the separation distance (lag) over a range of lags, and extended self-similarity (linear relationship between log structure functions of successive orders) appears to be an intrinsic property of the generated media. The width of the range of lags where power-law scaling is observed and the Hurst coefficient associated with the variables we consider can be controlled by the generation parameters of the method.

Geometric and flow features of type B aortic dissection: initial findings and comparison of medically treated and stented cases.

Uncomplicated acute type B aortic dissections are usually treated medically, but they can become acutely complicated by rapid expansion, rupture and malperfusion syndromes and in the longer term by chronic dilatation and aortic aneurysm formation. The objective of this study is to use computational fluid dynamics reconstructions of type B aortic dissections to compare geometric and haemodynamic factors between the cases selected for medical treatment and the cases selected for thoracic endovascular aortic repair (TEVAR), and to examine whether any of these factors are associated with the outcome of the medically treated group. This study includes eight type B dissection cases, with four in each group. Aortic flow analyses were carried out based on patient-specific anatomy at initial presentation before treatment. Comparisons between the two groups show that the false lumen to true lumen volume ratio is considerably higher in patients selected for TEVAR. Results from the four medically treated cases indicate that the size of the primary entry tear is the key determinant of the false lumen flow rate, which may influence the long-term outcome of medically treated patients. Potential relations between flow related parameters based on initial anatomy and subsequent anatomical changes in the medically treatment group were examined. Our initial findings based on the limited cases are that high relative residence time is a strong predictor of subsequent false lumen thrombosis, whereas pressure difference between the true and false lumen as well as the location of the largest pressure difference may be associated with the likelihood of subsequent aortic expansion.

Quantitative Magnetic Resonance Imaging of Pulmonary Hypertension

Pulmonary hypertension is a condition of varied etiology, commonly associated with poor clinical outcome. Patients are categorized on the basis of pathophysiological, clinical, radiologic, and therapeutic similarities. Pulmonary arterial hypertension (PAH) is often diagnosed late in its disease course, with outcome dependent on etiology, disease severity, and response to treatment. Recent advances in quantitative magnetic resonance imaging (MRI) allow for better initial characterization and measurement of the morphologic and flow-related changes that accompany the response of the heart-lung axis to prolonged elevation of pulmonary arterial pressure and resistance and provide a reproducible, comprehensive, and noninvasive means of assessing the course of the disease and response to treatment. Typical features of PAH occur primarily as a result of increased pulmonary vascular resistance and the resultant increased right ventricular (RV) afterload. Several MRI-derived diagnostic markers have emerged, such as ventricular mass index, interventricular septal configuration, and average pulmonary artery velocity, with diagnostic accuracy similar to that of Doppler echocardiography. Furthermore, prognostic markers have been identified with independent predictive value for identification of treatment failure. Such markers include large RV end-diastolic volume index, low left ventricular end-diastolic volume index, low RV ejection fraction, and relative area change of the pulmonary trunk. MRI is ideally suited for longitudinal follow-up of patients with PAH because of its noninvasive nature and high reproducibility and is advantageous over other biomarkers in the study of PAH because of its sensitivity to change in morphologic, functional, and flow-related parameters. Further study on the role of MRI image based biomarkers in the clinical environment is warranted.

Flow Pattern and Efficiency Changes of Squirrel Cage Fans due to Inlet Diffuser Diameter Changes - Using CFD Method and Experimental Validation

Inlet is one the basic elements of squirrel cage fans that has a significant effect on fan performance and efficiency. Recently using the CFD calculation methods with sufficient related tools for finding the flow pattern and related parameters, applying modifications and representing proper solutions, has being increased. In the present case study to study the effect of inlet diffuser diameter on the fan efficiency and flow pattern, using numerical simulations and experimental validations, three different inlet diffuser diameters are used as inlet instead of inlet nozzle. To simulate these cases some geometries with special additional element, proper mesh pattern and size and proper turbulence model was chosen.It is observed performance and efficiency curves of fans with respect to use of inlet nozzle are more flattened with higher magnitude. So fan operation around the best performance point is more stable without significant fluctuation of head pressure and efficiency.

Improved Paraffin-Deposition-Profile Estimation in Hydrocarbon Pipelines and Effective Mitigation Review

Summary Flow of paraffinic hydrocarbon liquids within extended pipeline networks orwells, where the environment/bulk temperature is below the cloud point orwax-appearance temperature (WAT), could result in precipitation of wax from thebulk fluid. Precipitated wax crystals from crudes deposits on the inner pipewall could lead to reduced flow area or even complete blockage and couldpresent a costly problem in the production and transportation of petroleumproducts. Timely removal of such deposits is extremely important to avoidassociated problems. This paper illustrates a numerical approach to estimatethe deposition profile and its effect on flow-related parameters. Later, theprocedure is validated with field data from a North Sea offshore productionfacility. This paper also seeks to propose a feasible solution to avoid suchflow-assurance issues; in doing so, current commonly practiced reduction andpreventive methods are reviewed. Previously, providing thermal insulation withaerogel foam had proved to be the most effective option in preventing wax fromprecipitating. A relatively new approach is discussed in this paper, whichallows for minimizing the usage of insulation material in an attempt to reducethe implementation cost of the proposed precaution. Theoretical implementationof the procedure was also conducted to identify its effectiveness, which waslater found to be elimination of the deposition completely.

USCOM—window to the circulation: utility of supra-sternal Doppler in an elderly anaesthetized patient for a robotic cystectomy

Supra-sternal Doppler (USCOM Ltd., Sydney, Australia) can be used during anaesthesia to measure cardiac output (CO) and related flow parameters. However, before the USCOM can be used routinely, its utility and limitations need to be fully understood and critical information about its use disseminated. In "Window to the Circulation" we use the example of an elderly man undergoing major urological robotic surgery to highlight the utility and limitations of intra-operative USCOM use. USCOM readings were verified against oesophageal Doppler. Despite the lack of major blood loss (<500 ml in 8-h), significant changes in haemodynamics were recorded. CO ranged from 3.2 to 8.3 l/min. The quality of USCOM scans and reliability of data was initially poor, but improved as CO increased as surgery progressed. When USCOM scans became acceptable the correlation with oesophageal Doppler was R(2) = 8.0 (p < 0.001). Several characteristic features of the supra-sternal Doppler scans were identified: Aortic and pulmonary flow waves, valve closure, E and A waves, false A-wave and aberrant arterial flow patterns. Their identification helped with identifying the main flow signal across the aortic valve. The USCOM has the potential to monitor changes in CO and related flow parameters intra-operatively and thus help the anaesthetist to more fully understand the patient's haemodynamics. However, achieving a good quality scan is important as it improves the reliability of USCOM data. The supra-sternal route is rich in flow signals and identifying the aortic valve signal is paramount. Recognizing the other characteristic waveforms in the signal helps greatly.

Optical coherence tomography platform for microvascular imaging and quantification: initial experience in late oral radiation toxicity patients

An optical coherence tomography (OCT) microvascular imaging platform, consisting of Doppler (DOCT) and speckle variance (svOCT) modalities, and microvascular image quantification tools are developed. The quantification methods extract blood flow-related parameters from DOCT images and vessel morphological parameters from svOCT images. This platform is used to assess the microvascular (DOCT and svOCT) images obtained during a clinical study on late oral radiation toxicity. This specific pathology was considered a suitable scenario for verifying the performance of the developed quantification platform because late oral radiation toxicity is known to involve microvascular damage. The derived parameters are compared between several DOCT and svOCT images from one patient and one healthy volunteer as proof-of-principle, and the significance of the observed differences is discussed. Given the low number of OCT clinical studies that measure and quantify microvascular images and considering the importance of such quantification in a number of pathologies, this newly developed platform can serve as a useful tool in studying diseases and treatments with microvascular involvement.

On the Damping in Tube Arrays Subjected to Two-Phase Cross-Flow

An experimental study was conducted to investigate the mechanism of damping in tube arrays subjected to two-phase cross-flow, mainly focusing on the influence of void fraction and flow regime. The model tube bundle had a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the homogeneous equilibrium model (HEM). Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate: the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods, due to the tube frequency shifting triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. A dimensional analysis was carried out to investigate the relationship between damping and two-phase flow related parameters. As a result, the inclusion of surface tension in the form of the capillary number appears to be useful when combined with the two-phase component of the damping ratio (interfacial damping). A strong dependence of damping on flow regime was observed when plotting the interfacial damping versus the void fraction, introducing an improvement over the previous results obtained by normalizing the two-phase damping, which does not exhibit this behavior.

Computational Fluid Dynamics Simulations of the Complex Geometry of a Technical Textile

The use of virtual prototypes for the prediction of relevant flow related parameters is well established in many industries such as the automotive industry. For the development of technical textiles an analogous approach is anticipated as being beneficial. However, so far the complex geometry of textiles consisting of a very large number of filaments has impeded this approach. We utilize this approach for the first time investigating a fabric, which is used during the paper forming process. The most challenging aspect for the simulation is the the process of geometry creation by use of single filaments together with the indispensable simplifications for a currently marketed fabric. Meshes of different sizes up 20 million cells have been generated and results from CFD calculations will be displayed together with an analysis of the numerical accuracy. The individual relevance of the simulation experiments will be discussed. Physical experiments at ambient temperature of laminar water flow through the same fabric under comparable conditions with a Reynolds Number of 15 based on pipe diameter of 9.0 mm and pipe volume flow rate averaged velocity magnitude of 0.00172 m/s were performed. The Reynolds Number based on the diameter of the different filaments of 0.2 mm up to 0.45 mm is approx. between 0.34 and 0.77. The experimental set up using Magnetic Resonance Imaging (MRI) will be explained. The use of this experimental approach as a means to validate the results of the simulation will be critically evaluated.

Abstract P6-11-12: Nanoparticle-enhanced chemotherapeutics delivery in drug-resistant triple-negative breast cancer

Abstract Chemotherapeutics delivery is generally poor in tumors characterized by rapid perfusion and low blood volume fraction. Systemically administered nanoparticles can be engineered to overcome abnormal flow conditions to act as intravascular drug depots for the localized delivery of high concentrations of chemotherapeutics. The feasibility of this approach was first demonstrated using melanoma, and is now being further investigated using well-characterized human triple-negative breast cancer biopsies implanted into mice. Intravital microscopy studies of human cancer-in-mice selected for differing vascular morphologies have yielded intriguing preliminary data regarding the role of tumor vascularity in drug and particle delivery. The first-pass perfusion of a 40kDa dextran tracer revealed that BCM-2665 tumors are perfused ∼6x more rapidly than BCM-4195 tumors (11.3 ± 2.3s vs. 67.6 ± 11.0) and contain ∼30% lower volume fraction of blood (0.046 ± 0.011 vs. 0.062 ± 0.015). Interestingly, flow parameters that adversely impact drug accumulation appear to favor plateloid particle accumulation. BCM-2665 xenografts receiving an i.v. injection of 1000×400 nm particles show ∼10x more particle accumulation than BCM-4195 tumors (24.8 ± 3.2 × 103/mm3 vs. 3.5 ± 0.4 × 103/mm3). The ability of these therapeutic particles to reach tumors appears to be primarily driven by flow-related parameters, which we characterize using a combination of intravital microscopy, computed tomography, and mathematical modeling. The total number of particles accumulated within a given tumor appears to be largely driven by the number of particles entering the tumor, since ∼65–70% of entering plateloid particles are retained by the tumor vasculature. This suggests that cytotoxic intravascular drug depots may be a promising strategy for increasing the efficiency of chemotherapeutics delivery to drug-resistant tumors and is the premise of ongoing therapeutic response studies. Clearly if more drugs can be delivered to the tumors, better outcomes can be expected for the patients. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-11-12.

Numerical Analysis of Flow Field and Performance Optimization of Axial-Flow Pressure Reducing Valve

In order to promote the technical progress of pressure reducing valve in nature gas transport system, a high pressure pilot operated axial-flow pressure reducing valve was designed and developed. The three-dimensional modeling of the natural gas pressure reducing valve internal flow passage was found by using Solidworks software. Import the flow channel model into meshing in CFD software based on the internal flow channel geometry and flow characteristics. The ideal gas compressible fluid model of natural gas and improved RNG k-Epsilon model were used to solve the pressure and velocity distribution as well as other flow related parameters of the natural gas pilot operated pressure reducing valve. The flow fields of the pressure reducing valve with different valve plug shape were analyzed. Changes of valve plug shape were made to improve the performance of the valve.

Flow-gated radial phase-contrast imaging in the presence of weak flow

To implement a flow-gating method to acquire phase-contrast (PC) images of carotid arteries without use of an electrocardiography (ECG) signal to synchronize the acquisition of imaging data with pulsatile arterial flow. The flow-gating method was realized through radial scanning and sophisticated post-processing methods including downsampling, complex difference, and correlation analysis to improve the evaluation of flow-gating times in radial phase-contrast scans. Quantitatively comparable results (R=0.92-0.96, n=9) of flow-related parameters, including mean velocity, mean flow rate, and flow volume, with conventional ECG-gated imaging demonstrated that the proposed method is highly feasible. The radial flow-gating PC imaging method is applicable in carotid arteries. The proposed flow-gating method can potentially avoid the setting up of ECG-related equipment for brain imaging. This technique has potential use in patients with arrhythmia or weak ECG signals.

Multi-variable sensitivity and identifiability analysis for a complex environmental model in view of integrated water quantity and water quality modeling

Environmental models are often over-parameterized. A sensitivity analysis can identify influential model parameters for, e.g. the parameter estimation process, model development, research prioritization and so on. This paper presents the results of an extensive study of the Latin-Hypercube-One-factor-At-a-Time (LH-OAT) procedure applied to the Soil and Water Assessment Tool (SWAT). The LH-OAT is a sensitivity analysis method that can be categorized as a screening method. The results of the sensitivity analyses for all output variables indicate that the SWAT model of the river Kleine Nete is mainly sensitive to flow related parameters. Rarely, water quality parameters get a high priority ranking. It is observed that the number of intervals used for the Latin-Hypercube sampling should be sufficiently high to achieve converged parameter rankings. Additionally, it is noted that the LH-OAT method can enhance the understanding of the model, e.g. on the use of water quality input data.

Failure to Unmask Pseudonormal Diastolic Function by a Valsalva Maneuver

Background— For the clinical assessment of patients with dyspnea, the inversion of the early (E) and late (A) transmitral flow during Valsalva maneuver (VM) frequently helps to distinguish pseudonormal from normal filling pattern. However, in an important number of patients, VM fails to reveal the change from dominant early mitral flow velocity toward larger late velocity. Methods and Results— From December 2009 to October 2010, we selected consecutive patients with abnormal filling with (n=25) and without E/A inversion (n=25) during VM. Transmitral, tricuspid, and pulmonary Doppler traces were recorded and the degree of insufficiency was estimated. After evaluating all standard echocardiographic morphological, functional, and flow-related parameters, it became evident that the failure to unmask the pseudonormal filling pattern by VM was related to the degree of the tricuspid insufficiency (TI). TI was graded as mild in 24 of 25 patients in the group with E/A inversion during VM, whereas TI was graded as moderate to severe in 24 of the 25 patients with pseudonormal diastolic function without E/A inversion during VM. Conclusions— Our data suggest that TI is a major factor to prevent E/A inversion during a VM in patients with pseudonormal diastolic function. This probably is due to a decrease in TI resulting in an increase in forward flow rather than the expected decrease during the VM. Thus, whenever a pseudonormal diastolic filling pattern is suspected, the use of a VM is not an informative discriminator in the presence of moderate or severe TI.

BLOOD PRESSURE LEVEL AND DURATION OF HYPERTENSION AS PARAMETERS ASSOCIATED WITH CEREBRAL HEMODYNAMICS IN HYPERTENSION: PP.8.323

Objective: To check, in a group of hypertensive patients the association between blood flow-related parameters of hemodynamics in middle cerebral artery (MCA) and systolic (SBP), diastolic (DBP) blood pressure and duration of hypertension (HT-time) and age. Design and Methods: The study was cross-sectional. Transcranial Doppler (TCD) examination was performed bilaterally. The MCAs were insonated through transtemporal window, and pulsatility (PI), resistance (RI) indexes and mean cerebral blood flow velocity (CBFV) were calculated. Blood pressures were measured conventionally in accordance with current guidelines. Results: Mean ± SD age of 96 patients was 58.7 ± 11.9 years. The group comprised 52.1% men, 18.9% smokers, 8.3% took nitrates (which in exploratory analyses were the only class of medications influencing PI and RI). Mean ± SD SBP/DBP was 142.6 ± 19.5/91.9 ± 12.6 mm Hg, mean PI was 0.97 ± 0.21, RI 0.59 ± 0.06 and CBFV 0.58 ± 0.17 m/s. The duration of hypertension averaged 9.5 ± 8.6 years. In multiple regression models adjusted for sex, age, smoking and use of nitrates, with SBP, DBP and HT-time forced into one model, neither duration of hypertension (p = 0.58) nor level of SBP(p = 0.60) or DBP (p = 0.58) were associated with CBFV. However, SBP (â = 0.003, p = 0.02), DBP (â = -0.007, p = 0.002), and HT-time (â = 0.006, p = 0.004) were significantly associated with PI. In similar analyses SBP (â = 0.0009, p = 0.03), DBP (â = -0.002, p = 0.004), and HT-time (â = 0.002, p = 0.006) were significantly associated with RI. After adjustment for the confounders listed above, HT-time independently explained 8.6% of variation in RI and 9.2% of variation in PI. When SBP or DBP were introduced separately, the percentage of variance in PI or RI explained by HT-time increased to over 11%. Conclusion: SBP and DBP influence PI and RI of middle cerebral artery, however, after adjustment for confounders, duration of hypertension plays a major role explaining about 10% (1/4 of the models' R-square) of variation in PI and RI. This underlines the importance of early adequate treatment of hypertension to protect against such cerebro-vascular complications as stroke or dementia.

Abstract 3985: New quantification tools for perfusion and VEGFR2 Expression in tumors

Abstract Microbubble contrast agents are used to enhance the visualization of the microcirculation in human and mouse tumors. Specifically, contrast agents allow for the relative quantification of tissue perfusion and vascular volume. The in vivo expression of endothelial cell surface markers can also be studied using targeted microbubbles. In this study a nonlinear contrast agent imaging technique, employing amplitude modulation on a linear array-based micro-ultrasound system was used to visualize and quantify time to peak enhancement (TP) and vascular volume (VV) in subcutaneous tumors, as well as to assess expression levels of VEGFR2. A Vevo 2100 high resolution ultrasound imaging system (VisualSonics Inc, Toronto, Canada) was used and all images were acquired with the MS-250 (center operating frequency of 20MHz, axial resolution 75um) probe. Tumor flow was assessed using MicroMarker contrast agents. A bolus delivery was employed to generate time-intensity curves of contrast wash-in; prototype analytical software was used to perform curve fit analysis and to generate parametric images visually depicting VV and TP as an overlay on the anatomical images. Additionally, Target-Ready MicroMarker contrast agents were conjugated to VEGFR2 antibodies to assess the expression level of this endothelial cell surface receptor. Again, prototype analytical software was used to quantify the relative expression of this target and to generate parametric images of its expression pattern within the tumor. All images were acquired from athymic nude mice implanted with hepatocellular carcinoma cells (Hep3B-Luc-C4) subdermally in the hind limb 4 to 5 weeks before imaging. Results showed heterogeneity in TP and VV in all tumors. TP ranged from 3.5 seconds in well perfused regions to 12 seconds in poorly perfused tumor regions. The graphical appearance of the associated parametric images readily revealed these differences. Assessment of VEGFR2 expression completed in 2D and 3D showed 2-3 times enhancement in VEGFR2 binding over that observed with the isotype control antibody. These results are consistent with previous methods using linear contrast processing. Overall this study shows the utility of nonlinear processing of contrast signals in assessment of various flow related parameters of the tumor microcirculation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3985.

Extension of the Mass Transfer Calculation for Three-Phase Distillation in a Packed Column: Nonequilibrium Model Based Parameter Estimation

Nonequilibrium (NEQ) modeling of three-phase (vapor-liquid-liquid) distillation in a packed column is still lacking of reliable correlations to calculate the interphase rate-based mass transfer. In this paper, extensions of the two most-used correlations [i.e., the Rocha correlation (Rocha, J. A.; Bravo, J. L.; Fair, J. R. Distillation Columns Containing Structured Packings: A Comprehensive Model for Their Performance. 2. Mass-Transfer Model. Ind. Eng. Chem. Res. 1996, 35, 1660) and the Billet and Schultes correlation (Billet, R.; Schultes, M. Prediction of Mass Transfer Columns with Dumped and Arranged Packings: Updated Summary of the Calculation Method of Billet & Schultes. Chem. Eng. Res. Des. 1999, 77, 498)] are proposed for mass transfer calculation of three-phase distillation in a packed column. Parameters used in the correlations are estimated on the basis of comprehensive experimental investigations on both two-phase (vapor-liquid) and threephase distillation. The experimental database contains 150 different experiments of the 1-butanol/water/ 1-propanol system for different packings (Montz-Pak B1-350, Raschig Super-Ring 0.3, Rombopak 9M). The parameter estimation with multiple data sets and multipacking turns out to be a large-scale optimization problem subjected to a large number of nonlinear model equations. To reduce the problem dimension and remove coupling among the parameters, a hierarchical estimation strategy is proposed. The parameters are classified into packing-related and flow-related parameters, which are estimated using two-phase and threephase distillation experimental data, respectively. In this way, the extension of mass transfer calculation for three-phase distillation is derived. Substantial improvements in the NEQ model prediction have been achieved. Compared with two-phase distillation, an increase of overall mass transfer ability is observed for the studied three-phase system. The extension of the mass transfer calculation can give a reasonable explanation for this observation, providing a better understanding of the intrinsic transfer phenomena inside three-phase packed columns.

A Novel Pulse Duplicator System: Evaluation of Different Valve Prostheses

The hemodynamic characteristics of different heart valve prostheses have been investigated in vitro with a novel pulse duplicator. A novel valved stent for transapical or percutaneous valve implantation has been compared with a native heart valve and mechanical heart valves. All experiments were designed to imitate both physiologic pressure ratios and flow characteristics in diastole and systole. After calibrating the system using a human aortic valve (primary orifice diameter: 22.0 mm), the following valves were studied under aortic pulsatile flow conditions: Hall-Kaster (Medtronic-Hall, 20.0 mm), St. Jude Medical (20.0 mm), a newly developed tricuspid valved stent (Tricumed TM4, 20.7 mm) and a newly developed biomechanical valve (Engage aortic valve Model 6000, 21.0 mm). All valves including the human aortic valve were assessed by videotape observation under pulsatile flow conditions. Measured flow-related parameters include in vitro mean transvalvular pressure, regurgitant volume, effective orifice area and performance index. The optical assessment of all five valves demonstrated a complete opening during systole and closing at the beginning of diastole. All valves were optically sufficient during diastole. Engage aortic valve Model 6000 showed the highest maximum transvalvular pressure (27.5 +/- 8.2 mmHg), whereas both Hall-Kaster (17.9 +/- 1.5 mmHg) and St. Jude Medical (16.7 +/- 0.7 mmHg) had a lower gradient than the native aortic valve (24.0 +/- 0.2 mmHg) and Tricumed TM4 (21.8 +/- 3.8 mmHg). The maximum effective orifice area of St. Jude Medical amounted to 258.7 +/- 3.4 mm(2), followed by Tricumed TM4 with an area of 222.1 +/- 1.9 mm(2) and the human aortic valve with 160.4 +/- 2.9 mm(2). Hall-Kaster and Engage aortic valve Model 6000 had an area of 198.9 +/- 1.6 mm(2) and 176.7 +/- 3.1 mm(2), respectively. The pulse duplicator proved to be highly accurate and yielded reproducible results. Since it has been calibrated with a human aortic valve, the hemodynamics of any heart valve prosthesis can be compared with the human valve. This system can evaluate and promote the development of new biological and mechanical heart valve prostheses.