Analytical and Numerical Investigation on Effective Thermal Conductivity of Polymer Composites Filled with Conductive Hollow Particles

The thermal behavior of hollow conductive particles filled in epoxy resin has been investigated using 3D finite element computation. The effect of the filler concentrations associated with the particle/matrix interfacial resistance on the effective thermal conductivity of the composites was considered. The relationship between the out-of-plane effective thermal conductivity, the wall thickness of the hollow particles, and the ratio of the thermal conductivities of the filler to the matrix material were also taken into account. The numerical results show an increase of the effective thermal conductivity with increasing wall thickness of the hollow particles. However, for a large contact resistance and/or for a high effective thermal conductivity, it is shown that the contact resistance has a dominant influence on the effective thermal conductivity of the composites. The numerical results were also compared to some well-known analytical effective thermal conductivity models.     

Treatment of dairy wastewater by electrocoagulation process: Advantages of combined iron/aluminum electrodes

ABSTRACT

The objective was to assess the efficiency of electrode material in an electrocoagulation (EC) process for wastewater treatment by comparing the efficiency of aluminum (Al–Al), iron (Fe–Fe) and combined Fe–Al electrodes. The treatment of synthetic dairy wastewater, characterized by high levels of 5-day biological oxygen demand (BOD₅) and chemical oxygen demand (COD), was used to compare electrode materials. Experimental results showed that all electrodes materials achieved the same final removal yield in the range of current studied (55% COD, 60% total organic carbon, 90% total nitrogen, and nearly 100% turbidity) when equilibrium was achieved. But at fixed current density and initial concentration of dairy waste, the Al–Al assembly exhibited the fastest elimination, whereas the slowest removal rate was observed with the Fe–Fe electrodes, even though adsorption was always the main removal mechanism. Finally, an Fe–Al system using an Fe anode with an Al cathode emerged as a techno-economic trade-off because of the low price of iron: both metals contributed to the removal of dairy waste, and the treatment time to achieve equilibrium values was closer to the Al–Al assembly at fixed current density. Moreover, experimental results proved the additivity of the mechanisms reported for Al–Al and Fe–Fe systems with Fe–Al.     

Design of variable structure voltage regulator using poleassignment technique

In a power system, the role of a generator voltage regulator is to ensure that the output voltage is maintained within an acceptable threshold. In this paper a voltage regulator is proposed. The design of this regulator is based on both variable structure control theory and a pole assignment technique. The performance of the proposed regulator has been compared to that of the realistic regulator system proposed by the IEEE Committee on Excitation Systems. The results are discussed, and the pertaining recommendations are given     

Visible light induced hydrogen evolution on new hetero-system ZnFe2O4/SrTiO3

The physical properties and photoelectrochemical characterization of the spinel ZnFe₂O₄, elaborated by chemical route, have been investigated for the hydrogen production under visible light. The forbidden band is found to be 1.92 eV and the transition is indirectly allowed. The electrical conduction occurs by small polaron hopping with activation energy of 0.20 eV. p-type conductivity is evidenced from positive thermopower and cathodic photocurrent. The flat band potential (0.18 V_SCE) determined from the capacitance measurements is suitably positioned with respect to H₂O/H₂ level (−0.85 V_SCE). Hence, ZnFe₂O₄ is found to be an efficient photocatalyst for hydrogen generation under visible light. The photoactivity increases significantly when the spinel is combined with a wide band gap semiconductor. The best performance with a hydrogen rate evolution of 9.2 cm³ h⁻¹ (mg catalyst)⁻¹ occurs over the new hetero-system ZnFe₂O₄/SrTiO₃ in Na₂S₂O₃ (0.025 M) solution.