Local Stagnant Air Flow Indicator (Reverse-flow Rate Index) and Effects of Structural Shape

In order to evaluate effects of operational parameters on the removal efficiency of trichloroethylene and 1,1,1-trichloroethene from water, lab-scale experiments were conducted using a novel hollow-fibre gaspermeable membrane system, which has a very thin gas-permeable membrane held between microporous support membranes. The permeation rate of chlorinated hydrocarbons increased at higher temperature and water flow rate. On the other hand, the effects of the operational conditions in the permeate side were complex. When the permeate side was kept at low pressure without sweeping air (pervaporation), the removal efficiency of chlorinated hydrocarbon, as well as water permeation rate, was low probably due to lower level of membrane swelling on the permeate side. But when a very small amount of air was swept on the membrane (air perstripping) under a low pressure, it showed a higher efficiency than in any other conditions. Three factors affecting the permeation rate are: 1) reduction of diffusional boundary layer within the microporous support membrane, 2) air/vapour flow regime and short cutting, and 3) the extent of membrane swelling on the permeate side. A higher air flow, in general, reduces the diffusional boundary layer, but at the same time disrupts the flow regime, causes short cutting, and makes the membrane dryer. Due to these multiple effects on gas permeation, there is an optimum operational condition concerning the vacuum pressure and the air flow rate. Under the optimum operational condition, the residence time within the hollow-fibre membrane to achieve 99% removal of TCE was 5.25 minutes. The log (removal rate) was linearly correlated with the average hydraulic residence time within the membrane, and 1 mg/L of TCE can be reduced to 1 μg/L (99.9% removal).

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Model of thermal buoyancy in cavity-ventilated roof constructions

Journal of Building Physics ◽

10.1177/1744259120984189 ◽

2021 ◽

pp. 174425912098418

Author(s):

Toivo Säwén ◽

Martina Stockhaus ◽

Carl-Eric Hagentoft ◽

Nora Schjøth Bunkholt ◽

Paula Wahlgren

Keyword(s):

Analytical Model ◽

Flow Rate ◽

Numerical Study ◽

Air Flow ◽

Wind Pressure ◽

Air Flow Rate ◽

Test Set ◽

Air Cavity ◽

Thermal Buoyancy ◽

The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

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Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements

Designs ◽

10.3390/designs5010004 ◽

2021 ◽

Vol 5 (1) ◽

pp. 4

Author(s):

Dillon Alexander Wilson ◽

Kul Pun ◽

Poo Balan Ganesan ◽

Faik Hamad

Keyword(s):

Water Flow ◽

Flow Rate ◽

Cfd Simulation ◽

Air Flow ◽

Bubble Diameter ◽

Diameter Ratio ◽

Experimental Measurements ◽

Cfd Model ◽

Flow Rates ◽

Throat Diameter

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study.

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Modeling and optimization of radish root extract drying as peroxidase source using spouted bed dryer

Scientific Reports ◽

10.1038/s41598-021-93563-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Shahrbanoo Hamedi ◽

M. Mehdi Afsahi ◽

Ali Riahi-Madvar ◽

Ali Mohebbi

Keyword(s):

Kinetic Parameters ◽

Flow Rate ◽

Air Flow ◽

Cost Effective ◽

Industrial Applications ◽

Interactive Effects ◽

Root Extract ◽

Air Flow Rate ◽

Spouted Bed ◽

Radish Root

AbstractThe main advantages of the dried enzymes are the lower cost of storage and longer time of preservation for industrial applications. In this study, the spouted bed dryer was utilized for drying the garden radish (Raphanus sativus L.) root extract as a cost-effective source of the peroxidase enzyme. The response surface methodology (RSM) was used to evaluate the individual and interactive effects of main parameters (the inlet air temperature (T) and the ratio of air flow rate to the minimum spouting air flow rate (Q)) on the residual enzyme activity (REA). The maximum REA of 38.7% was obtained at T = 50 °C and Q = 1.4. To investigate the drying effect on the catalytic activity, the optimum reaction conditions (pH and temperature), as well as kinetic parameters, were investigated for the fresh and dried enzyme extracts (FEE and DEE). The obtained results showed that the optimum pH of DEE was decreased by 12.3% compared to FEE, while the optimum temperature of DEE compared to FEE increased by a factor of 85.7%. Moreover, kinetic parameters, thermal-stability, and shelf life of the enzyme were considerably improved after drying by the spouted bed. Overall, the results confirmed that a spouted bed reactor can be used as a promising method for drying heat-sensitive materials such as peroxidase enzyme.

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Laser-Doppler Velocimetry Measurements Inside a Backward Curved Centrifugal Fan

International Journal of Rotating Machinery ◽

10.1155/s1023621x01000161 ◽

2001 ◽

Vol 7 (3) ◽

pp. 173-181

Author(s):

Tong-Miin Liou ◽

Meng-Yu Chen

Keyword(s):

Flow Rate ◽

Turbulence Intensity ◽

Laser Doppler Velocimetry ◽

Reverse Flow ◽

Flow Region ◽

Design Flow ◽

Laser Doppler ◽

Centrifugal Fan ◽

Doppler Velocimetry ◽

Flow Rates

Laser-Doppler velocimetry (LDV) measurements are presented of relative mean velocity and turbulence intensity components inside the impeller passage of a centrifugal fan with twelve backward curved blades at design, under-design, and over-design flow rates. Additional LDV measurements were also performed at the volute outlet to examine the uniformity of the outlet flow for the three selected flow rates. Complementary flow visualization results in the tongue region are further presented. It is found that the number of characteristic flow regions and the average turbulence level increase with decreasing air flow rate. For the case of under-design flow rate, there are a through-flow region on the suction side, a reverse flow region on the pressure side, and a shear layer region in between. The corresponding average turbulence intensity is as high as 9.1% of blade tip velocity.

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Method to Determine an Optimal Air-Flow Rate in Solar Collectors

Journal of Energy ◽

10.2514/3.62444 ◽

1979 ◽

Vol 3 (6) ◽

pp. 357-362

Author(s):

H. C. Hewitt ◽

E. I. Griggs

Keyword(s):

Flow Rate ◽

Air Flow ◽

Solar Collectors ◽

Air Flow Rate

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A Meanline Model for Impeller Flow Recirculation

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-51349 ◽

2008 ◽

Cited By ~ 10

Author(s):

Xuwen Qiu ◽

David Japikse ◽

Mark Anderson

Keyword(s):

Flow Rate ◽

Recirculation Zone ◽

Reverse Flow ◽

Low Flow ◽

Suction Surface ◽

Blade Loading ◽

Flow Recirculation ◽

Impeller Outlet ◽

Active Flow ◽

Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

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