Power Consumption and Mixing Efficiency in Agitation

Overview:

Agitation and mixing experiment, showing terminal box with ribbon cable to A/D board in computer, Servodyne stirrer motor controller on shelf, Cole-Parmer conductivity meter connected to conductivity probe in tank at bottom, variable speed DC stirrer motor on ball-bearing slide, fiberglass shaft with downward-driving impeller, 20 liter polycarbonate tank with tracer injection funnel, lamp and optical bead sensor.

Detailed Description:

The apparatus involves of a variable speed stirrer.  The stirrer controller allows students to set the RPM in a range of 60 to 2000 RPM, and also to read the torque.  Three polycarbonate tanks with removable baffles are supplied, as are a number of turbines and propellers of various sizes. The tanks can be mounted on a roller bearing based torque table equipped with a load cell connected to an Omega panel meter.  Thus torque can be measured in two ways.  The 20 liter tank is equipped with a conductivity cell mounted near the bottom and connected to a Cole-Parmer conductivity meter driving an RTD A/D board mounted in a 486 or Pentium computer (computer supplied as an option).  The tank is also equipped with an optical sensor and lamp assembly designed to detect the approach of small plastic beads suspended in the tank.  Finally we supply a resistance heated aluminum cylinder equipped with a temperature sensor and driven by a variable transformer.  This is used to determine the effect of stirred speed and impeller and baffle design on the heat transfer coefficient.

The experiment operates in four modes, namely:

The students select a tank, impeller, baffle presence, and liquid (either water, Karo corn syrup, or catsup).  Then the stirrer RPM is varied over a range, and the torque vs. RPM data are collected and plotted and compared to correlations in the literature.  The data for a single torque vs. RPM run are obtained quite rapidly, but the many combinations of tank size, baffle presence, impeller design, and fluid type allow for extensive studies.

Using water in the 20 liter tank, the students set an RPM and inject about 30 ml of salt solution using a funnel mounted at the top of the tank.  As the tracer is dispersed, the transient conductivity at the bottom of the tank is digitized and recorded.  Then a nonlinear regression program is used to determine two parameters of a six-pool model of the flow pattern in the tank.  One of the parameters is the circulation rate in the tank, from which the mixing time can be calculated.  Ten or more tracer injection runs can be made before refilling the tank.

Several hundred plastic beads are added to the 20 liter tank, and the optical sensor is mounted on the side of the tank under the halogen lamp.  A BASIC program acquires the sensor data, identifies bead entries into the illuminated region, and computes the entry interval distribution.  This is typically a Poisson distribution, with characteristics that depend on stirrer speed.

The aluminum heat transfer probe is mounted in the 20 liter tank, the probe power is set, and the temperature of the probe is determined as a function of stirrer speed.  From these data the heat transfer coefficient can be calculated and compared to the literature.

Membrane Air Separation

Description: 

Membrane air separation experiment, showing air filter and pressure regulator, two Permea membrane modules with valving to permit series or parallel operation, Omega pressure transducer with panel meter, needle valve for flow control, Sierra mass flow meters on tube side (low O2) and shell side (high O2) flows, Engineered Systems oxygen meters on tube and shell side streams.  Air source is a standard cylinder of dry compressed air.

Detailed Overview:

The apparatus consists of two Permea air separation modules, connected by stainless tubing and valves.  Each module contains hundreds of polymeric tubes, the walls of which are more permeable to oxygen than to nitrogen.  Dry air from a standard cylinder passes through a filter to a pressure regulator, which permits setting the operating pressure at which the modules operate.  Air flow through the tube side (fiber lumen side) of the membrane modules can be parallel or series.  Effluent air from tube sides of the modules is combined and passes to a needle valve used to control the total tube side flow rate.  It then flows to a Sierra mass flow meter and an Engineered Systems electrochemical. 

The basic data for each run thus consists of the flow configuration (parallel or series), operating pressure, tube side flow rate and oxygen n level, and shell side flow rate and oxygen level.  A typical run takes about one minute, and consumes little air.  The data can be processed  to produce values for the oxygen and nitrogen permeability coefficients of the module fibers.

The apparatus typically operates at room temperature. 

Diamond-studded electrode: a cure to paralysis

A diamond is forever, not only on your ring, but also inside your body-- implants made from these shiny stones can cure paralysis. Two Case Western Reserve University researchers are building implants made of diamond and flexible polymer that are designed to identify chemical and electrical changes in the brain of patients suffering from neural disease, or to stimulate nerves and restore movement in the paralyzed.

The work of Heidi Martin, a professor of chemical engineering, and Christian Zorman, a professor of electrical engineering and computer science, is years from human trials but their early success has drawn interest worldwide. 

Unlike standard electrodes, diamonds don't corrode. Diamond is so hard and rigid, however, that an entire implant made of the stuff would quickly damage surrounding tissue and the body would seal off the implant as if it were a splinter. The key is to use just enough diamond i. e. just the amount of diamond at the biological interface - where the device connects with a nerve

The real diamond is grown as a film - under high temperature, in a vacuum. By adding impurities  properties of diamond is changed. For electrodes, boron is added, turning the diamond blue. Blue diamonds, including the famous Hope Diamond at the Smithsonian, conduct electricity. Because diamond is made at 800 to 900 degrees celsius, a temperature that would melt the polymer base. Diamond is first selectively grown  in a series of tiny squares of diamond film on silicon dioxide, the stuff of sand and quartz.

Then it is laid in a thin flexible polymer that fills in the gaps between diamonds, followed by a layer of metal that connects to the back of the diamonds and will conduct electricity.
Lastly, he adds a thick layer of flexible polymer base. Then device is dropped in hydrofluoric acid, which eats away the silicon dioxide and frees the probe. 


Small, cortical probes that measure chemical changes at a location in the brain or along a nerve have two diamond contacts affixed. These probes are designed to assist health researchers who are trying to understand the role of chemicals in stimulating nerves or communicating within the brain. Recent research has found, for example, a link between a deficiency in the neurotransmitter dopamine and Parkinson's disease. Lab tests have shown one diamond-coated electrode can monitor chemical and electrical signals as well as stimulate nerves.

Aerosols....

From Chemical Engineering point of view it is basically a suspension of solid particles or liquid droplets in gas. Few examples can be smog, haze, smoke etc. The aerosol product consists of the following components: Propellant, Container,  Valve and Actuator and Product concentrate.

Propellant: The propellant is generally regarded as the heart of the aerosol package. It is responsible for development of pressure within the container, supplying the necessary force to expel the product when the valve is opened. The propellant also acts as a solvent and as a diluent and has much to do with determining the characteristics of the product as it leaves the container. Examples of propellants include Chloro fluro carbons (CFCs), Hydro fluoro alkanes (HFA)and Fluorinated hydrocarbons

Containers: Different materials are used for the manufacture of aerosol containers. The materials must be inert, non-toxic and must withstand pressure as high as 140 to 180 psig at 130ºF. Examples include aluminum containers, glass etc.

Valves: Valve must be multifunctional in that it is capable of being easily opened and easily closed and capable of delivering the contents in the desired form. Also in case of metered dose inhaler aerosol, the valve is expected to deliver a given amount of medication.

Applications of Dimethyl Ether

1.   Dimethyl ether (DME) has been increasingly used as a propellant in aerosol formulations to replace chlorofluorocarbons (CFCs), which are found to destroy the ozone layer of the atmosphere. DME is nontoxic and easily degrades in the troposphere. Several aerosol-based household products include colognes, hair sprays and dyes, personal care mousses, antiperspirants, and room air fresheners.

2.   DME has very promising uses as an ultra-clean transportation fuel as well as a fuel for power generation. DME has a high cetane value of about 55-60 and can be directly and effectively used for DME diesel engines. Burning DME in diesel engines results in a lower NOx with no SOx, thus also contributing to the societal air quality. The advantages of using DME are not only ultralow emissions of nitrogen oxides (NOx), but also, reduced engine noise or quiet combustion, practically soot-free or smokeless operation and high diesel thermal efficiency.

3.   DME is a useful intermediate for the preparation of many important chemicals, including methyl sulphate and dimethyl sulphate is an important commercial commodity as a solvent and also as an electrolyte in high energy density batteries. 

4.  Dimethyl ether is also an essential intermediate in the synthesis of hydrocarbons from coal or natural gas derived syngas (synthesis gas). Lower olefins like ethylene and propylene or higher molecular weight compounds such as gasoline range boiling hydrocarbons are produced from syngas using dimethyl ether as an intermediate. A variety of specialty industrial chemicals such as oxygenates, acetaldehyde, acetic acid, ethylene glycol etc. can be formed using dimethyl ether as a feedstock.

5.  Dimethyl ether is a low-temperature solvent and extraction agent, applicable to specialised laboratory procedures. Its usefulness is limited by its low boiling point (−23 °C), but the same property facilitates its removal from reaction mixtures. Dimethyl ether is the precursor to the useful alkylating agent, trimethyloxonium tetrafluoroborate.

Introduction to Dimethyl Ether

Dimethyl ether (DME) also known as methyl ether, methyl oxide and wood ether, is the organic compound with the formula CH3OCH3. The simplest ether, it is a colourless liquid or compressed gas that is a useful precursor to other organic compounds and an aerosol propellant. DME consists of two methyl groups bonded to a central oxygen atom, as expressed by its chemical formula CH3-O-CH3. It has been used in a variety of consumer applications viz., personal care (e.g., hairspray, shaving creams, foams and anti perspirants), household products, automotive, paints, food products, insect control, animal products and other related applications. It is commonly used in organic synthesis as a reaction solvent for systems requiring volatile polar solvents and is also promising as a clean-burning hydrocarbon fuel.

DME can be produced from natural gas—providing an alternative way of its utilization, in competition to such technologies as Fischer-Tropsch synthetic fuels—as well as from other carbon-containing feed stocks, including coal and biomass. DME has replaced CFC gases (freons) as an environmentally friendly and safe aerosol propellant, which is one of its major current applications. Potential future uses of DME include an alternative automotive fuel, a substitute for other fuels in power generation and in the household and a source of hydrogen for fuel cells. Worldwide DME production grew from 100,000-150,000 tons per annum in the 1990s to some 200,000 tons in the mid-2000s.

With the chemical structure somewhat similar to methanol, DME contains oxygen and no carbon-carbon bonds, thus seriously limiting the possibility of forming carbonaceous particulate emissions during combustion. However, unlike methanol, DME has a high enough cetane number to perform well as a compression-ignition fuel. Also unlike methanol, DME is a gas at ambient temperature and pressure, so it must be stored under pressure as a liquid similar to LPG (liquefied petroleum gas). When used as a diesel fuel, DME provides reduced PM (Particulate Matter) and NOx emissions.

The physical properties of DME (density, viscosity, etc.) are so different from the diesel fuel that the entire fuel system must be redesigned. It seems clear that DME, like perhaps some other alternative fuels, would be able to produce many larger emissions reductions than it is possible with diesel fuel. Therefore, from today’s perspective, the DME fuel is more likely to be used in certain niche applications, rather than provide a wide-scale alternative to liquid diesel fuels.