Design and developement of energy efficient miniature devices for energy harvesting, thermal management and biomedical applications

Official URL: http://192.168.1.20/record=b1558963 (Table of Contents)

This thesis aims to make contributions to the literature in the field of energy efficient miniature devices for energy harvesting, thermal management and biomedical applications. In the first part, experimental results related to energy harvesting capability of a miniature power reclamation device based on external liquid flows are represented. The device’s reclamation principle depends on the conversion of mechanical energy into electrical energy. The mechanical energy in the device was generated by capturing vibrations caused by external liquid flows via the device’s tails, which were designed by taking inspiration from the body shape of the black ghost knife fish, apteronotus albifrons. The reclaimed power was obtained through magnetic polarization, which was generated by rotating circular waterproof magnet structures as a result of rotating movements of the mentioned tails and is transferred to 3.76 V (Ni-Mg) batteries. Power reclamation was also simulated using COMSOL 4.2 software in order to compare the maximum reclaimable theoretical energy harvesting capacity to the experimental results. Experimental tests were performed within a range of flow velocities (1.0 m/s ~ 5.0 m/s) for various fluid densities (plain water, low-salt and highsalt water) in order to obtain extensive experimental data related to the device in response to external fluid flows. According to experimental results, the device could generate powers up to 17.2W. On the other hand, the maximum reclaimable power was obtained as 25.7W from COMSOL Multiphysics 4.2 simulations. Promising energy harvesting results imply that the output from this device could be used as a power source in many applications such as in lighting and GPS (Global positioning system) devices. In the second part of the thesis, a miniature system was used for flow boiling in mini/microtubes. Flow boiling was investigated with surface enhancements provided by crosslinked polyhydroxyethylmethacrylate (pHEMA) coatings, which were used as a crosslinker coating type with different thicknesses (~50 nm, 100 nm and 150 nm) on inner microtube walls. Flow boiling heat transfer experiments were conducted on microtubes (with inner diameters of 249 μm, 507 μm and 908 μm) coated with crosslinked pHEMA coatings. pHEMA nanofilms were deposited with the initiated chemical vapor deposition (iCVD) technique. De-ionized water was utilized as the working fluid. Experimental results obtained from coated microtubes were compared to their plain surface counterparts at two different mass fluxes (5,000 kg/m2s and 20,000 kg/m2s), and significant enhancements in Critical Heat Flux (up to 29.7 %) and boiling heat transfer (up to 126.2 %) were attained. The enhancement of boiling heat transfer was attributed to the increase in nucleation site density and incidence of bubbles departing from surface due to porous structure of crosslinked pHEMA coatings. The underlying mechanism was explained with suction-evaporation mode. Moreover, thicker pHEMA coatings resulted in larger enhancements in both CHF and boiling heat transfer. In the third part, a platform for gene delivery via magnetic actuation of nanoparticles was developed. The importance of high transfection efficiency has been emphasized in many studies investigating methods to improve gene delivery. Accordingly, non-viral transfection agents are widely used as transfection vectors to condense oligonucleotides, DNA, RNA, siRNA, deliver into the cell, and release the cargo. Polyethyleneimine (PEI) is one of the most popular non-viral transfection agents. However, the challenge between high transfection efficiency and toxicity of the polymers is not totally resolved. The delivery of necessary drugs and genes for patients and their transport under safe conditions require carefully designed and controlled delivery systems and constitute a critical stage of patients’ treatment. Compact systems are considered as the strongest candidate for the preparation and delivery of drugs and genes under leak free and safe conditions because of their low energy consumption, low waste disposal, parallel and fast processing capabilities, removal of human factor, high mixing capabilities, enhanced safety, and low amount of reagents. Motivated by this need in the literature, The use of PEI-SPION (Super paramagnetic iron oxide nanoparticles) as transfection agents in in-vitro studies was investigated with the effect of varying magnetic fields provided by a special magnetic system design, which was used as a miniature magnetic actuator device offering different magnet's turn speeds in the system. Experimental results obtained from experimental magnetic actuator systems were compared to the experiments without magnetic actuation, and it was observed that significant enhancements in transfection efficiency (up to 25-30 %) in MCF-7 and PC-3 cells were attained.