Experimental investigation of laminar turbulent intermittency in pipe flow

In shear flows turbulence first occurs in the form of localized structures (puffs/spots) surrounded by laminar fluid. We here investigate such spatially intermittent flows in a pipe experiment showing that turbulent puffs have a well defined interaction distance, which sets the minimum spacing of puffs as well as the maximum observable turbulent fraction. Two methodologies are employed here. Starting from a laminar flow puffs can be created by locally injecting a jet of fluid through the pipe wall. When the perturbation is applied periodically at low frequencies, as expected, a regular sequence of puffs is observed where the puff spacing is given by the ratio of the mean flow speed to the perturbation frequency. On the other hand, at large frequencies puffs are found to interact and annihilate each other. Varying the perturbation frequency an interaction distance can be determined. In the second set of experiments, the Reynolds number is reduced suddenly from fully developed turbulence to the intermittent regime.The resulting flow reorganizes itself to a sequence of constant size puffs which, unlike in Couette and Taylor Couette flow are randomly spaced. The minimum distance between the turbulent patches is identical to the puff interaction length. The puff interaction length is found to be in excellent agreement with the wavelength of regular stripe and spiral patterns in plane Couette and Taylor-Couette flow. We propose that the same interaction mechanism is present in these flows

Air Treatment Techniques for Abatement of Emissions from Intensive Livestock Production

Intensive livestock production is connected with a number of environmental effects, including emissions of ammonia (NH3), greenhouse gases (CH4 and N2O), odour, and particulate matter (PM10 and PM2.5). Possible strategies for emission reduction include feed management, adaptation of housing design, and, in case of mechanically ventilated animal houses, the application of end-of-pipe air treatment, viz acid scrubbers and bioscrubbers. Air treatment techniques can achieve very high emission reductions (up to 100% ammonia removal for acid scrubbers). Furthermore, air treatment offers the possibility to achieve removal of not just one compound but of a combined removal of a variety of pollutants (ammonia, odour and particulate matter) at the same time. The successful application of scrubbers is of increasing importance as intensive livestock operations have to comply with ever stricter regulations and emission limits. Research is needed to address topics such as reduction of costs (both investment and operational costs), improvement of process control to guarantee stable removal efficiencies, decrease of N2O production in bioscrubbers, and increase of odour removal efficienc

PERFORMANCE OF A NEW PACKING ELEMENT FOR PACKED COLUMN USING AIR-WATER SYSTEM

Packed tower is a continuous contact equipment widely used for gas absorption, distillation and liquid-liquid extraction. It consists of a cylindrical shell filled with a suitable packing material to provide a large interfacial area of contact between the phases. Since its inception, packing has shown great progress and improvement in its design and performance. The aim of this experiment is to develop a new type of packing element for packed tower. The design concept for the new packing is by making a rigid structure that holds the soft, flexible structure. This flexible structure should be fine and thin in order to give maximum mass transfer area while the rigid structure is to provide the strength to the packing element. The new packing is developed by using simple apparatus consist of plastic tightener attached to a metal rod. The metal rod provides the strength to the packings while the plastic tightener provides the mass transfer area. Physical characteristics of the developed packing were measured and used to calculate the geometric surface area, void fraction and equivalent spherical diameter. After the new packing is completed, experiments were carried on self-developed pilot plant using air and water as the medium. Water is fed from the top of the column while air is fed from the bottom. Air and water will counter-currently in contact. Two methods were used to analyze the pressure drop and mass transfer performance; pressure drop and mass transfer test. For pressure drop, two test was conducted, the dry pressure drop and the wet pressure drop. The mass transfer performance was analyzed by evaluating the change in moisture content of the outlet gas. The entire test was set against the result of same experiment for 10 spherical marbles as reference. For the experiment set-up, air-water counter current flow system that replicates a real packed column was constructed to test the new packing element using pipe. The packing characteristics of the developed packing such as geometric surface area, void fractions, and equivalent spherical diameter of packing particle was compared with other packing elements used in the industry. Data from experiments conducted shows that packing is able to gives low pressure drops and increase mass transfer. Based on these results, it can be concluded that the developed has potential for further research

High pressure gas filter system Patent

Developing high pressure gas purification and filtration system for use in test operations of space vehicle

The crossover from single file to Fickian diffusion

The crossover from single-file diffusion, where the mean-square displacement scales as ~t^(1/2), to normal Fickian diffusion, where ~t$, is studied as a function of channel width for colloidal particles. By comparing Brownian dynamics to a hybrid molecular dynamics and mesoscopic simulation technique, we can study the effect of hydrodynamic interactions on the single file mobility and on the crossover to Fickian diffusion for wider channel widths. For disc-like particles with a steep interparticle repulsion, the single file mobilities for different particle densities are well described by the exactly solvable hard-rod model. This holds both for simulations that include hydrodynamics, as well as for those that don't. When the single file constraint is lifted, then for particles of diameter \sigma and pipe of width$L$ such that (L- 2 \sigma)/\sigma = \delta_c << 1 the particles can be described as hopping past one-another in an average time t_{hop}. For shorter times t << t_{hop} the particles still exhibit sub-diffusive behaviour, but at longer times t > t_{hop}, normal Fickian diffusion sets in with an effective diffusion constant D_{hop} ~ t_{hop}^(1/2). For the Brownian particles, t_{hop} ~ 1/\delta_c^(2) when \delta << 1, but when hydrodynamic interactions are included, we find a stronger dependence than \delta_c^{-2}. We attribute this difference to short-range lubrication forces that make it more difficult for particles to hop past each other in very narrow channels

How to Get the Best from Your Kerosene Range

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Optional Soil Moisture Sensor Protocol

The purpose of this resource is to measure the water content of soil based on the electrical resistance of soil moisture sensors. Students install soil moisture sensors in holes that are 10 cm, 30 cm, 60 cm, and 90 cm deep. They take daily readings of soil moisture data by connecting a meter to the sensors and using a calibration curve to determine the soil water content at each depth. Educational levels: Middle school, High school

Production Practices and Sample Costs for a Diversified Organic Vegetable Operation on the Central Coast of California

Organic vegetable farms on the Central Coast region of California are generally intensive operations. That is, two and sometimes three crops may be harvested off the same acreage each year. Many approaches exist for rowing and marketing organic vegetables. This publication describes the range of soil management practices, pest management, crop rotations, cover crops, and harvest and packing methods currently used by organic growers on the Central Coast of California. Marketing options and state and federal regulations governing organic commodities are also discussed. A general sequence of operations, equipment requirements, resource use, costs, yield and return ranges are presented for thirteen vegetable crops and two cover crops. The vegetables included are cabbage, cauliflower, cucumbers, garlic, lettuce (leaf and romaine), onions (red and yellow), snap peas, snow peas, bell peppers (green and red), sweet corn, and winter squash (large and small varieties). Barley and vetch are the two cover crops detailed.Crop Production/Industries,