A state of the art of required techniques for employing activated carbon in renewable energy powered adsorption applications

This paper reviews, for the first time, the measurement adsorption characteristics techniques to facilitate optimal testing of the validity of adsorbent materials in adsorption applications. Thermo-physical properties, adsorption characteristics and modelling techniques are presented. The characterisation of material thermo-physical properties includes true and bulk densities, specific heat capacity, surface area, pore volume distribution and thermal conductivity. The adsorption characteristics were categorized into adsorption isotherms and kinetics including experimental and theoretical equations. A range of models used in the simulation of adsorption cooling systems is presented and discussed. The paper highlights the conditions for which each measurement technique is most suitable and the limitations of modelling techniques, which is a vital element in the robust assessment of the performance of adsorption cooling units

Hybrid SC-Inductive Based Topologies for Low-volume High-efficiency Switched-mode Power Supplies

Switched-mode power supplies (SMPS) are widely used as the voltage or current regulators for electronic devices. The most commonly used SMPS are inductive converters based on conventional buck and boost converter topologies due to their simplicity and relatively high power density and efficiency. However, in applications with large voltage difference between their inputs and outputs, these converters suffer from excessive losses and increased volume due to more demanding filtering and also cooling requirements. Therefore strong and ever increasing demands for developing smaller and more efficient SMPS with high conversion ratios exist.In this work two new converter topologies suitable for applications with large input-to-output voltage difference are introduced for both input voltage step-down and step-up in two different types of applications, i.e. for dc-dc converters and rectifiers with power factor correction. These converters are developed based on the concept of merging Switched-capacitor (SC) and inductive based converter stages by means of newly emerged digital controllers, improving efficiency and reducing the overall volume of the converter. Hence, the benefits of high power density SC-based converters are exploited and at the same time the input-to-output voltage ratio for the inductive stage is reduced improving its power density and efficiency. Compared to two-stage solutions, by merging SC and inductive based stages, switches between two stages are shared, reducing conduction losses, intermediate/flying capacitors are eliminated and controllers are unified.The buck-based, voltage step-down solution combines a capacitive divider and an interleaved buck to reduce the volume of multi-phase step-down converters. Experimental results obtained with a 7V-to-1V, 10A, 1 MHz prototype demonstrate that the merged capacitor converter has 15% smaller inductor, 13% smaller output capacitor, up to 35% lower power losses and 15% shorter settling time after transients.In the boost-based voltage step-up solution, the improvements are achieved by replacing the output capacitor of the boost converter with a non-symmetric active capacitive divider, with a 2:1 division ratio, effectively providing four-level converter behavior. Experimental results obtained with a 350 W, 200 kHz, universal input voltage (85Vrms - 265Vrms) PFC prototype demonstrate 66% reduction of boost converter inductor and up to 10% improvement of efficiency.Ph.D

A 1-dimensional dynamic model for a sorption-compressor cell

Sorption-based cooler is considered as an excellent candidate for the vibration-free cooling at cryogenic temperature. In a such cooler, the sorption compressor is the most critical module. To design a sorption-compressor, effective numerical models are essential which allow one to simulate the details of the heat and mass transfer within the sorption-compressor cell, predict the system performance and optimize various parameters. This paper presents a 1-dimensional dynamic model for a sorption-compressor cell, which is based on extensive adsorption-isotherm measurements and realistic thermal properties of materials at low temperatures. This numerical model combines the mass and energy equations while the momentum equation is skipped. It assumes the pressure to be uniform within the cell. However, the convection term in the energy equation is evaluated in this model with proper approximation without calculating the velocity field. A typical simulation case is presented to understand the details during a sorption compression that occur in the sorption-compressor cell. Experiments based on helium and neon operating at 77 K (liquid nitrogen temperature) were carried out to validate this model. The measured compressor performance was deviated from the simulation about 18%, but that is a reasonable inaccuracy for design propose and is well reasoned. Such 1-D dynamic model is qualified to be further used to design sorption compressor