The parameters that control the stability of ZnO-nanoparticles suspensions and their deposition by electrophoretic deposition were studied, so as to organize the assembly and compaction of nanoparticles. The addition of cationic polyelectrolyte - Polyethylenimine (PEI) - with different molecular weights was investigated, in order to study their effectiveness and the influence of the molecular weight of the organic chain on suspensions dispersion. It was found that PEI with the highest molecular weight provided better dispersion conditions. Cathodic EPD was performed under previously optimized suspensions conditions and over electropolished stainless steel substrates. Experimental results showed that the EPD process in these conditions allows obtaining dense transparent ZnO thin films. Deposition times and intensities were optimized by analyzing the resulting thin films characteristics. Finally, the deposits were characterized by FE-SEM, AFM, and different spectroscopic techniques.

ZnO films have been grown on different substrates by using a variety of fabrication techniques. In the present work, we discuss the results on the preparation of ZnO films by electrophoretic deposition (EPD) starting from synthetic flake-shaped nanoparticles. The critical parameters related to the preparation of aqueous colloidal suspensions have been analyzed. Dispersing conditions have been evaluated in terms of particle/cluster morphology, electrokinetic properties, i.e., particle size distribution and cationic surface functionality, and zeta potential. EPD parameters for film assembly have been selected. Depending on both the particle morphology and the solid’s concentration in the colloidal system, different orientation effects have been observed in the built structure. For a low ZnO concentration, independent clusters arrive at the Ni substrate where the large dimension of the ZnO flakelike nanoparticles align with the surface of the substrate. When the solid’s concentration increases, such ordering is not observed. The electrical resistivity measured by the four-point probe method evidences the presence of a ZnO film with unusually high electrical resistivity for undoped ZnO.

No abstract

Adsorption systems driven by engine waste heat are one of the possible alternatives to the conventional automobile air conditioning in terms of energy savings and environmental issues. Assessment of this issue are carried in a two-part study. In this first part I, theoretical and experimental investigations were performed on a two bed, silica gel adsorption chiller for automotive applications. A prototype adsorption system with a total weight of about 86 kg was developed and tested to driven by low-grade waste heat. The single adsorbent bed consisted of three plate-fin heat exchangers connected in parallel. An improved nonequilibrium lumped parameter model was developed to predict the transient performance of the system. The model is fully dynamic and takes into account the mass transfer resistance and pressure drop for each component of the system. The results showed that the model is able to accurately predict the dynamic performance of the system under different operating conditions and configuration modes with a short calculation time. The tested chiller was able to produce an average cooling capacity of about 2.1 kW with a COP of 0.35 at the rated operating conditions. Heat recovery system results in increasing the COP by 43% and the cooling power by 4%.