The paper presents a computationally efficient method for solving the time dependent diffusion equation in a granule of the Li-ion battery's granular solid electrode. The method, called Discrete Temporal Convolution method (DTC), is based on a discrete temporal convolution of the analytical solution of the step function boundary value problem. This approach enables modelling concentration distribution in the granular particles for arbitrary time dependent exchange fluxes that do not need to be known a priori. It is demonstrated in the paper that the proposed method features faster computational times than finite volume/difference methods and Padé approximation at the same accuracy of the results. It is also demonstrated that all three addressed methods feature higher accuracy compared to the quasi-steady polynomial approaches when applied to simulate the current densities variations typical for mobile/automotive applications. The proposed approach can thus be considered as one of the key innovative methods enabling real-time capability of the multi particle electrochemical battery models featuring spatial and temporal resolved particle concentration profiles.
COBISS.SI-ID: 13847835
We tested several established hydrodynamic cavitation models on the problem of cavitation on ultrasonic horn transducers, but none of them was able to correctly predict the flow features. As a specific characteristic of such acoustic cavitation problems lies in the rapidly changing driving pressures, we present an improved approach to cavitation modeling, which does not neglect the second derivatives in the Rayleigh-Plesset equation. Comparison with measurements of acoustic supercavitation at an ultrasonic horn of 20kHz frequency revealed a good agreement in terms of cavity dynamics, cavity volume and emitted pressure pulsations. The newly developed cavitation model is particularly suited for simulation of cavitating flow in highly fluctuating driving pressure fields such as cavitation in fuel injection nozzles and cavitation development during the startup of the rocket fuel turbopump - the new model was a basis for awarding us a new contract from the European Space Agency (ESA).
COBISS.SI-ID: 13644827
Innovative lignocellulosic biofuel, obtained through solvolysis of spruce wood in multifunctional alcohols was tested in an experimental turbine engine with different primary air temperatures. Variation of primary air temperature was used to emulate two types of microgas turbine generators - fully recuperated and simple cycle setups resulting in different temperatures of combustion chamber intake air. Results indicate that different temperatures, velocities, and flow conditions in primary one of combustion chamber strongly influence on droplet penetration depth and rate of mixture formation as well as emissions formation. For the innovative lignocellulosic biofuel emission trends of CO and THC were found to be significantly higher in simple cycle mode, whereas no influence of operation mode was observed for baseline diesel fuel. NO emissions of innovative biofuel generally increased in regenerative cycle mode and also became sensitive on turbine inlet temperature, with similar trends being observed with diesel fuel. In the case of innovative fuel, deposits of char and polymerized fuel were observed on the combustor walls after operation in simple cycle mode, whereas in regenerative cycle mode, only small amounts of ash deposits were found on hot path surfaces, indicating beneficial influence of high primary air temperatures on combustion efficiency of innovative fuel. The study therefore presents the key finding in case of utilization of presented innovative fuel in microturbines. The utilization of this principle of operation is unavoidable as it enables durable and low emission operation.
COBISS.SI-ID: 13804059
This is an invited paper for a special issue of the journal Ultrasonics Sonochemistry "Cleaning with bubbles". We show our most recent work using hydrodynamic cavitation for removal of pharmaceuticals, toxic cyanobacteria, green microalgae, bacteria Legionella pneumophila and viruses from water and wastewater. It is shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants. The work presented in this paper manifested itself in several patents (one in Germany and one pending in USA) and an award for the best innovation of the University of Ljubljana.
COBISS.SI-ID: 3649871
A hybrid energy system, based on renewable energy sources and with hydrogen storage, can become an alternative for stand-alone electricity and heat supply. The objective of this work is to evaluate the feasibility of a completely renewable supply of power and heat for an isolated household, and a comparison to reference and alternative energy supply scenarios. In this paper, an energy system using fossil and renewable energy sources is compared to a system using only renewable energy sources (solar and wind) with hydrogen-based energy storage technologies. A reference household in Slovenia's coastal region was used for modelling and numerical simulation. Simulations and optimal energy system identification were conducted by considering the geographical location and availability of energy sources, load dynamics, and components' technical and economical characteristics. A household with electricity consumption of 11 kWh/day, hourly peak power demand of 3.8 kW and 660 L of oil-equivalent yearly heat demand was considered as the stand-alone load. The results show that 100% renewable electricity and heat supply of a reference household is technically feasible and is more cost-effective, compared to systems utilising fossil heat.
COBISS.SI-ID: 13637147