Alexandra Cheng's Individual Contribution Page
Stock Tank Mixing Team
Spring 2014 Contributions
Team goals this semester will focus on re-designing the stock tank pump to achieve optimal efficiency and energy input usage.
Two main designs were fabricated and tested on the small scale: a shallow bucket with small holes in the bottom and a plate (each attached to a handle) that were pumped up and down in the stock tank. The bucket design was meant to physically bring dense solution located at the bottom of the tank to the top of the tank while the plate design created turbulence and jets to encourage mixing. Both designs achieved full mixing with the same number of pump cycles, but the plate design requires less time because when the plate reaches the surface height, it is immediately plunged back down to the bottom of the tank. The bucket design, meanwhile, requires waiting for the fluid to drain out before being plunged back to the bottom. Full-scale designs will be based on the plate mixer.
Another design tested to decrease required input injected water into the bottom of the dense solution in the stock tank. Initial tests showed water injection was incredibly effective in mixing the majority of the stock solution, and any additional required mixing was achieved by the plate mixer.
Fall 2013 Contributions
Team goals this semester included purchasing non-lab environment appropriate (e.g. not easily breakable) hydrometers or other suitable measurement tools for PACl and chlorine stock solutions, testing and confirming the PACl concentration-density relationship, and designing and fabricating a centrifugal pump to be used in the stock tank to ensure complete mixing of stock solutions.
Hydrometer
The $74 Krackeler Scientific 1.000-1.220 polycarbonate hydrometer was deemed the most appropriate model for measuring typical AguaClara PACl solutions and three were purchased and sent to Honduras with the team in January 2014. Chlorine solutions pose a more complicated problem - the specific gravity range required is very small, and thus a hydrometer with a small range was required. Currently, no polycarbonate hydrometers with an appropriately small specific gravity range are commercially available. The $33.50 Cole Parmer 1.000-1.050 glass hydrometer was purchased to determine if a hydrometer is an accurate enough tool for chlorine solutions, and further evaluation determining a field appropriate tool should be performed.
Utilizing PACl from Honduras, the team performed tests to determine the concentration-density relationship of PACl; this relationship is important in giving actual meaning behind SG readings from the purchased hydrometer. The relationship was found to be Density.PACl = 0.492*Concentration.PACl + Density.Water
Centrifugal Pump
Previous teams' pumps were scaled down to allow for design evaluation and adjustment. The test setup utilized a 1/2" PVC plate screwed to a base tee joint to secure the bottom of the pump, with a wood plank with three holes clamped to the test tank to secure the top of the pump. The two holes located on the ends of the plank provided a surface for clamping and the pump itself was stabilized by being threaded through the middle hole. The pump had a rotating arm located just below the water surface that was meant to bring dense solution from the bottom of the tank to the top via the pressure gradient created during rotation. Sugar solutions of various concentrations were dyed with Red Dye #40 and a stratified solution was created in the tank to allow visualization of fluid movement. Through numerous tests, it was determined that the current design has large inefficiencies resulting from the major loss of input power due to drag on the arm.