Design of Concept

Working Enviroment
A resistive magnet will be used to produce a variable magnetic field in which to grow the yeast. With this constraint, a better understanding of the magnet was necessary. Below is the schematic for the magnet that will be used in this experiment. The maximum magnetic field strength of this magnet is 20 tesla. The axial location of the center of this field is 81.93 cm below the top of the magnet and it remains constant for approximately 3.00 cm above and below the center point. The radial field decreases exponentially with respect to the distance away from the axis of the bore. The operating temperature inside the bore of the magnet is approximately 8 degrees Celsius and the diameter of the bore is 19.56 cm. The magnet is stored in cell #4 at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida.

Resistive Magnet/Working Enviroment

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Material Selection

A vital decision in our design process involved the selection of the proper materials. Selecting the material for the shell casings and the tubing of the device included several constraints due to the working environment. The casings required a material with particular properties such as: nonmagnetic, low density, high ultimate tensile strength, low cost and low thermal conductivity. The three possibile materials chosen for this application were stainless steel, aluminum, and copper. In determining the inner tubing, many attributes were taken into consideration. The primary concern was preventing oxidation of the tubing and contamination to the medium. From the table below aluminum was chosen to be the most practical for the shells. Stainless steel was chosen for the oxygen inlet tube because of its high corrosion resistance. The external water tubing requirements consisted of flexibility, low cost and high thermal resistivity. The tubing selected for this application was a polymer material (garden hose), which will be easily obtained from any hardware store. The growth container, which sits inside the inner casing, requires Spectrosil grade silica (transparent) and an optically flat base. The size of the container must not exceed 4-cm diameter with maximum durability. From these constraints a beaker made from Pyrex was chosen to be most suitable. This concludes the material selection portion of the design of concept.

Material Properties

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Thermal Analysis

Final Calculations

Intial Calculations

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Components
Components were researched individually and chosen depending on the design constraints. A critical obstacle in selecting the components was adjusting theoretical component parameters to the existing manufacturer specifications. Extensive research and analysis produced the most feasible solution for each element of the design. Below is a list of selected components and the reasoning behind their selection.

Shell Casings: Initially the design incorporated a quadruple aluminum casing. The two outer and inner casings were filled with insulation, which allowed a space between the two to create a water jacket. The dimensions of the shells were optimized using the thermal and bore constraints. However the casings with the determined dimensions are not commonly manufactured. This led to modifications in shell dimensions. The new dimensions of the design were based upon availability of the shell casing and the revised thermal calculations. See thermal calculations in Appendix D, E and engineering drawings in Appendix G.

Pump: Thermal calculations were preformed with various mass flow rates in order to determine the one most efficient for the system. Results from the calculations proved the desired mass flow rate to be 400 gph. Three companies that manufactured a pump, which met this requirement, were Pondmaster, Rena, and Aqua Master. From these Pondmaster provided the simplest, cheapest pump with a five-year warranty. This pump has a half-inch diameter inlet and outlet and costs around $80.

Insulation: Constraining factors for choosing the insulation were the workability and R value. There were four reasonable types, which includes a fiberglass blanket, loose fill fiberglass, perlite and the spray polyurethane foam. Due to the greatest R value and the easy method of application, the spray Polyurethane foam was preferred. The manufacturer of this foam is "Great Stuff" and costs $3.75 a can at the local hardware store. The approximate amount of cans required is 5.

Beaker: The beaker, which sits inside the inner casing, requires Spectrosil grade silica (transparent) and an optically flat base without producing contamination to the yeast medium. The size of the container must not exceed 4-cm diameter and must also provide durability. From these constraints a beaker made from Pyrex was chosen to be most suitable.

Thermocouple: Two models were examined for the design's environmental temperature measuring device. The thermister and thermocouple, which provide basically the same function, was researched to decide the most feasible unit for the design. Through observation of the two models, the primary factor in this decision was cost. The Iron-Constantan thermocouple, manufactured by Scientific Instrument Inc., had the lowest cost and also provided the ability to measure temperatures to 800 degrees C. The main difference between the thermocouples was the wire diameter. The smaller the diameter of the wire the faster primarily an equilibrium temperature condition, a thermocouple with a wire diameter of .005 in. was chosen for the design.

Data Recording System: An approach to acquire system data was necessary for performing the yeast experiment. The sponsor proposed two systems for data acquisition, manual and automatic. The manual method is the least desired because of an abundance of equipment, constant supervision and less accuracy. For these reasons the automatic method was selected for the data recording system. Lab View is the desired software for this function because of its accessibility and help benefits from experienced personal. This method is more complicated to set up however once implemented the experiment will run much smoother, the error associated with the experiment will be significantly decreased, and the operation of the experiment will become more convenient.

Photon Multiplier (PM tube): A PM tube is required to perform this experiment as a way of measuring luminescence emission produced by the yeast. The selected PM tube must have high cathode sensitivity near 75 micro amps and low dark current close to 0.5 nano amps. Other requirements include magnetic shielding and a sensitivity wavelength between 200-630 nano meters.

Fiber Optics: Constraints discussed previously directed the design to incorporate fiber optics as a tool for transporting the light from the yeast medium to the PM tube. The optic cable must be reasonably flexible for ensured perseverance under stressful situations, be fairly priced and be shielded from outside interference. In deciding the length of the cable the distribution of the magnetic field was taken into account. This was accounted for because the PM tube can only operate correctly under a magnetic field less than 20 gauss. Running the experiment with a 20 tesla field will require the PM tube to be at least four meters away from the magnet. From Appendix F the required distance from the magnet can be extrapolated.

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Engineering Drawings

The purpose of generating the engineering drawings was to insure the feasibility of the system and provide help to the machinist in developing the components. By producing the drawings it will also give a better visual conceptualization of the system design. The drawings were created using ProE.

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Last Revised: 2000-12-20