University of Twente Student Theses


Micro-pump optimization for applications in CubeSats

Arendshorst, M.G. (2021) Micro-pump optimization for applications in CubeSats.

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Abstract:The general objective of this study is to optimize a piezoelectric powered micro-pump that has been developed by Royal Netherlands Aerospace Centre (NLR) such that the thermal challenges that are currently faced in CubeSats can be tackled. The current design consists of several plates that form the pump stack, with each plate having its own functionality. Among these plates, the piezo plate is the most important one because it holds the pump array. This pump array consists of five pump elements in parallel, each consisting of two pump units in series, leading to ten pump units in total. This was done to ensure that the pump does not fail completely when a single pump unit fails, but rather keeps operating at a slightly lower performance, i.e. with redundancy in mind. Despite the fact that the pump shows satisfactory performance, a better performance must be realized through optimization, such as a higher stroke volume of the piezoelectric elements, a lower pressure drop in the hydraulic channels and a lower pressure drop resulting from the valves. To this end a novel piezoelectric element actuation concept is proposed in the form of two piezo rings sandwiching a diaphragm, which utilizes a conventional bending mode as well as a bending & buckling mode to increase the maximum displacement of the piezoelectric element significantly. Since a greater maximum displacement results in a greater stroke volume, the pumps can potentially pump more fluid per stroke, leading to better pump performance. Unfortunately, integrating this concept into the micro-pump was not pursued. Furthermore, a valveless micro-pump concept in the form of a nozzle/diffuser system is evaluated and tested experimentally to potentially replace the passive dynamic valves in the current design of the micro-pump. A comparison between the pump curves from the nozzle/diffuser designs and the pump curves from individual pump elements in the piezo plate initially showed that the maximum flow rate in of the nozzle/diffuser plates is lower compared to the pump elements. In addition, the shut-off pressure in the nozzle/diffuser design is too low to be a considered as a feasible replacement for the current valves. Therefore, the current valves were used in the next phase of the research. In this next phase, a numerical model was built in Simulink to investigate and identify the bottlenecks in the hydraulic channels present in the piezo plate, such that a sensibility analysis can be performed quickly and cost-efficiently. With this numerical model, redesigns of the piezo plate can be simulated such that their performance can be compared to the current design of the piezo plate. In this way, only the most promising redesigns can be prototyped and tested experimentally. The numerical model was used to find a balance between the added mass and the pressure loss when the channel height is increased. However, this new piezo plate was not tested experimentally. Lastly, 3D printing is used to test the feasibility of using 3D printed plates in the pump stack to acquire a leak-tight pump stack and most importantly a working pump. In this way, new designs resulting from the numerical model can be tested experimentally through fast and cheap yet reliable prototyping. However, this was not done in this study. The pump curves from the 3D printed piezo plate are compared to the pump curves obtained from the original piezo plate that is made from stainless steel. Different pump curves are obtained, even though the exact same piezo elements and valve types haven been used. It was found that this difference is likely caused by the clamping of the piezo O-rings between the piezo plate and the backing plate. This suggests that the hydraulic resistances in the hydraulic channels are unlikely to be the biggest bottleneck, but rather the piezoelectric elements. The results from the 3D printed piezo plate are also compared to the nozzle/diffuser plates. An equally large maximum mass flow rate is found in the best performing pump element and the nozzle/diffuser plate, suggesting that the nozzle/diffuser plate could have been a replacement of the valves after all. However, the low shut-off pressure of the nozzle/diffuser pump only makes it a viable alternative if the loop outside the pump is small. Even though direct optimization was only done partially in the form of a suggested improvement to the piezo plate, a tool has been developed that can be used to optimize the micro-pump in the future.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:33 physics, 52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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