Dynamic Response of a Centrifugal Blower to Periodic Flow Fluctuations

1986 ◽  
Vol 108 (1) ◽  
pp. 77-82 ◽  
Author(s):  
A. N. Abdel-Hamid

Experimental investigation of the dynamic response of a centrifugal blower to periodic flow rate modulations was carried out at different blower operating conditions. For modulation frequencies in the range of 0.0085–0.085 of the shaft rotation frequency, the fluctuating pressures at inlet, discharge, and across a flow orifice were simultaneously measured and analyzed in the time and frequency domains. Measurements of the amplitude and phase of the transfer function between the blower static pressure rise and the discharge flow rate fluctuations indicated that the quasi-steady approximation should be limited to frequencies lower than 0.02 of the shaft rotation frequency. For the same average flow rate, the static pressure rise progressively lagged the discharge flow rate fluctuations as the frequency was increased. The trend was similar to that of the inertia effects of a fluctuating flow in a pipe. For the same frequency these inertia effects increased as the average flow rate through the blower was decreased. Applications of the results to on-line measurements of the slope of the characteristic curve and improved dynamic modeling of centrifugal compressors and blowers are discussed.

1987 ◽  
Vol 109 (2) ◽  
pp. 150-155 ◽  
Author(s):  
M. P. Malkin ◽  
S. A. Klein ◽  
J. A. Duffie ◽  
A. B. Copsey

A modification to the f-Chart method has been developed to predict monthly and annual performance of thermosyphon solar domestic hot water systems. Stratification in the storage tank is accounted for through use of a modified collector loss coefficient. The varying flow rate throughout the day and year in a thermosyphon system is accounted for through use of a fixed monthly “equivalent average” flow rate. The “equivalent average” flow rate is that which balances the thermosyphon buoyancy driving force with the frictional losses in the flow circuit on a monthly average basis. Comparison between the annual solar fraction predited by the modified design method and TRNSYS simulations for a wide range of thermosyphon systems shows an RMS error of 2.6 percent.


1983 ◽  
Vol 245 (4) ◽  
pp. H553-H559
Author(s):  
M. B. Maron

The possibility that histamine may cause the fluid and protein content of lymph to be altered during passage through the lymph node was evaluated using the canine perfused popliteal lymph node preparation. This preparation enables nodal perfusion via an afferent lymphatic (all other afferents are ligated) with artificial lymph of known composition and collection of the total efferent effluent for analysis of potential changes in volume and composition. In 11 dogs, the node was perfused at an average flow rate of 0.229 ml/min with artificial lymph containing 3.71 g/100 ml albumin. Under base-line conditions, there was no significant modification of the lymph as it passed through the node. The addition of histamine to the infusate (2-4 micrograms base/ml) caused the efferent lymph flow to increase to 0.295 ml/min (35.3% increases, P less than 0.05), the efferent protein concentration to increase to 4.32 g/100 ml (15.2% increases, P less than 0.05), and the efferent protein flux to increase from 8.40 to 12.86 mg/min (58.0% increases, P less than 0.05). The appearance of Evans blue dye-tagged protein and plasma protein fractions, not originally present in the lymph, in the efferent lymph at this time further indicated that the source of the added fluid and protein was the nodal vasculature. Mass balance calculations indicated that the addition of a fluid with a protein concentration of approximately 90% that of plasma to the lymph could account for the observed increases in efferent lymph flow and protein concentration.(ABSTRACT TRUNCATED AT 250 WORDS)


1980 ◽  
Vol 58 (11) ◽  
pp. 1295-1318 ◽  
Author(s):  
Robert G. Sheath ◽  
Beverly J. Hymes

Ten taxa of freshwater red algae have been observed in a survey of 62 streams and rivers within southern Ontario, Canada, over a period of 3 years. Five species are additions to the flora of Canada, Chroodactylon ramosum, Boldia erythrosiphon, Sirodotia tenuissima, Batrachospermum densum, and B. ectocarpum. In addition to these algae, Audouinella violacea, Sirodotia suecia, and Tuomeya fluviatilis are new observations within Ontario.Most of the Ontario red algae are restricted to streams or rivers with a minimum average flow rate of 10 m min−1. Audouinella violacea, B. moniliforme, and Lemanea fucina occur in a large number of streams which have a wide pH and conductivity range whereas S. tenuissima and B. ectocarpum are confined to one of the sites examined.Ultrastructural findings are reported concerning the cell organization of Boldia as well as the relationship between Batrachospermum plants and the "chantransia" stage. A key to the 10 taxa is included plus descriptions and a list of epiphytes of each alga are presented.


Author(s):  
C. Hariharan ◽  
M. Govardhan

AbstractThe present work reports the effect of inlet clearance on the performance of a centrifugal blower, with parallel wall volute, over its full operating range. For a particular impeller configuration, four volutes based on constant angular momentum principle, have been designed and analysed numerically for varying inlet clearances ranging from 0 mm (ideal clearance) to 5 mm. The computational methodology is validated using experimental data. The results indicate that as the clearance increases, the impeller performance in terms of both static and total pressure rise deteriorate. Further, the stage performances deteriorate in terms of efficiency and specific work for all mass flow rates. However, the performance of volute improves at lower mass flow rates compared to the Best Efficiency Point (BEP). A set of correlations have been developed to predict the change in stage performance as a function of clearance ratio. The non-dimensional values of change in specific work, isentropic efficiency and static pressure are found to be same irrespective of the shape of the volute.


2004 ◽  
Vol 286 (6) ◽  
pp. H2416-H2424 ◽  
Author(s):  
Andrew W. Bowman ◽  
Sándor J. Kovács

Although modeling the four-chambered heart as a constant-volume pump successfully predicts causal physiological relationships between cardiac indexes previously deemed unrelated, the real four-chambered heart slightly deviates from the constant-volume state by ventricular end systole. This deviation has consequences that affect chamber function, specifically, left atrial (LA) function. LA attributes have been characterized as booster pump, reservoir, and conduit functions, yet characterization of their temporal occurrence or their causal relationship to global heart function has been lacking. We investigated LA function in the context of the constant-volume attribute of the left heart in 10 normal subjects using cardiac magnetic resonance imaging (MRI) and contemporaneous Doppler echocardiography synchronized via ECG. Left ventricular (LV) and LA volumes as a function of time were determined via MRI. Transmitral flow, pulmonary vein (PV) flow, and lateral mitral annular velocity were recorded via echocardiography. The relationship between the MRI-determined diastolic LA conduit-volume (LACV) filling rate and systolic LA filling rate correlate well with the relationship between the echocardiographically determined average flow rate during the early portion of the PV D wave and the average flow rate during the PV S wave ( r = 0.76). We conclude that the end-systolic deviation from constant volume for the left heart requires the generation of the LACV during diastole. Because early rapid filling of the left ventricle is the driving force for LACV generation while the left atrium remains passive, it may be more appropriate to consider LACV to be a property of ventricular diastolic rather than atrial function.


2009 ◽  
Author(s):  
Raman Chadha ◽  
Gerald L. Morrison ◽  
Andrew R. McFarland

High efficiency air blowers to meet future portable aerosol sampling applications were designed, fabricated, and their performance evaluated. A preliminary blower design based on specific speed was selected, modeled in CFD, and the flow field simulated. This preliminary blower size was scaled in planar and axial directions, at different rpm values, to set the Best Efficiency Point (BEP) at a flow rate of 100 L/min (1.67×10−3 m3/s @ room conditions) and a pressure rise of 1000 Pa (4″ WC). Characteristic curves for static pressure rise versus air flow rate through the impeller were generated. Experimentally measured motor/blower combination efficiency (ηEXP) for the preliminary design was around 10%. The low value was attributed to the low efficiency of the D.C. motor used (Chadha, 2005). CFD simulations using the κ–ε turbulent model and standard wall function (non-equilibrium wall functions) approach overpredicted the head values. Enhanced wall treatment under-predicted the head rise but provided better agreement with experimental results. The static pressure rise across the final blower is 1021 Pa at the design flow rate of 100 L/min. Efficiency value based on measured static pressure rise value and the electrical energy input to the motor (ηEXP) is 26.5%, a 160% improvement over the preliminary design.


2013 ◽  
Vol 305 (12) ◽  
pp. H1709-H1717 ◽  
Author(s):  
Samira Jamalian ◽  
Christopher D. Bertram ◽  
William J. Richardson ◽  
James E. Moore

Any disruption of the lymphatic system due to trauma or injury can lead to edema. There is no effective cure for lymphedema, partly because predictive knowledge of lymphatic system reactions to interventions is lacking. A well-developed model of the system could greatly improve our understanding of its function. Lymphangions, defined as the vessel segment between two valves, are the individual pumping units. Based on our previous lumped-parameter model of a chain of lymphangions, this study aimed to identify the parameters that affect the system output the most using a sensitivity analysis. The system was highly sensitive to minimum valve resistance, such that variations in this parameter caused an order-of-magnitude change in time-average flow rate for certain values of imposed pressure difference. Average flow rate doubled when contraction frequency was increased within its physiological range. Optimum lymphangion length was found to be some 13–14.5 diameters. A peak of time-average flow rate occurred when transmural pressure was such that the pressure-diameter loop for active contractions was centered near maximum passive vessel compliance. Increasing the number of lymphangions in the chain improved the pumping in the presence of larger adverse pressure differences. For a given pressure difference, the optimal number of lymphangions increased with the total vessel length. These results indicate that further experiments to estimate valve resistance more accurately are necessary. The existence of an optimal value of transmural pressure may provide additional guidelines for increasing pumping in areas affected by edema.


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