Conventional Absorbing Materials Research Articles

Experimental and numerical analysis of the thermal performance of pebble solar thermal collector

In this work, pebbles of higher specific heat than the conventional absorber materials like aluminium or copper are proposed as a absorber in the solar flat plate collector. The proposed collector are integrated into the building design and constructed with masonry. Tests were conducted by varying the operating parameters which influence its performance, like the flow rate of the heat-absorbing medium, and the tilt of the collector using both coated and uncoated pebbles. The maximum temperature difference that could be measured for a conventional absorber was approximately 8 °C for a flow rate of 0.6 L/min. While for a coated and uncoated absorber, it was 7 °C and 5.5 °C respectively. This difference decreased with an increase in flow rates from 0.6 L/min to 1.2 L/min. For all the flow rates, it was observed that the average difference in efficiency between the coated and the conventional absorber collector is 5.82 %, while the difference between the coated and uncoated absorber collector is 15.68 %. Thus, it is very much evident that by replacing the conventional absorber with the proposed coated pebble absorber, the overall loss in efficiency is just 5.82 %, but the advantages are enormous. Along with the experimental study, numerical analysis was also carried out with CFD modeling. The numerical results agreed well with experimental results with the least error. Therefore, CFD simulation can be further used to optimize the design of the collector.

Investigation on acoustical performances of micro-perforated panel with soft boundary backing cavity

Low-frequency noise control is still an issue due to its characteristic of having a long wavelength. Therefore, attenuation requires a bulky noise control component, including an acoustic absorber. Conventional absorber materials, such as micro-perforated panels (MPP), are a candidate to circumvent such a problem. However, the requirement of backing cavity depth causes the MPP to work under a quarter wavelength constraint. Eventually, the bulky characteristic of the absorber is persistent. Therefore, this study introduces a soft boundary condition to the MPP to enable the system to work at a lower frequency while the associated dimensions reduce. Open gaps between the backing cavity and rigid surface realize the soft boundary conditions and double-layer MPP is considered to test such a system. The experimental result shows that the soft boundary can enhance at low frequencies (<250 Hz) by 0.3-0.6 points. At the same time, the open gap can slightly increase the resulting absorption performance deficiency at mid-frequency.

Combination of artificial materials with conventional pyramidal absorbers for microwave absorption improvement

This article addresses the combination of an artificial and conventional absorber materials in order to enhance its absorption properties and compactness. We demonstrate an increase of the absorption performance of the pyramidal absorbers by integrating a metamaterial layer. The latter is composed of two unit cells with multi resonance behavior between 2GHz and 18GHz. The simulation results of the hybrid material predict absorption for normal and oblique incidence of the electromagnetic wave at low and high frequencies depending on the wave polarization.Hybrid materials (metamaterial+conventional pyramidal absorbers) have been achieved using two pyramidal absorbers; the first one is a commercial absorber APM12/SIEPEL and the second one is the same material but with reduced dimensions. These absorbers are made of polyurethane foam loaded with carbon particles. The measurements show an increase of the absorption performance compared to the pyramidal absorber alone, even for the absorber with reduced dimensions.

Hybrid crystalline sp2[sbnd]sp3 carbon as a high-efficiency solar cell absorber

Carbon is a versatile element that has allotropes with both sp2 (graphene) and sp3 (diamond) bonding. However, none of the allotropes can be used as light-absorber materials in solar cells due to either too large or too small band gap. Here, we propose a novel concept that enables a tunable band gap of carbon phases with sp2 carbon atoms within a sp3 carbon structure. The tunability is due to the quantum confinement effect. By embedding the sp2 atoms within the sp3 structure, we can design new carbon allotropes with ideal optical properties for optoelectronic applications. Five carbon allotropes incorporated this structural feature were identified by combining this new concept with our freshly developed multi-objective inverse band structure design approach. They all have proper band gaps for optical absorption, and the simulated photovoltaic efficiency of C10-C is even higher than conventional absorber materials such as GaAs, which indicates that C10-C with mixed sp2sp3 hybridization may have potential application as light-absorber material in electronic and optoelectronic devices.

Semitransparent polymer-based solar cells with aluminum-doped zinc oxide electrodes.

With the use of two transparent electrodes, organic polymer-fullerene solar cells are semitransparent and may be combined to parallel-connected multijunction devices or used for innovative applications like power-generating windows. A challenging issue is the optimization of the electrodes, to combine high transparency with adequate electric properties. In the present work, we study the potential of sputter-deposited aluminum-doped zinc oxide as an alternative to the widely used but relatively expensive indium tin oxide (ITO) as cathode material in semitransparent polymer-fullerene solar cells. Concerning the anode, we utilized an insulator-metal-insulator structure based on ultrathin Au films embedded between two evaporated MoO3 layers, with the outer MoO3 film (capping layer) serving as a light coupling layer. The performance of the ITO-free semitransparent polymer-fullerene solar cells was systematically studied as dependent on the thickness of the capping layer and the active layer as well as the illumination direction. These variations were found to have strong impact on the obtained photocurrent densities. We performed optical simulations of the electric field distribution within the devices using the transfer-matrix method, to analyze the origin of the current density variations in detail and provide deep insight into the device physics. With the conventional absorber materials studied here, optimized ITO-free and semitransparent devices reached 2.0% power conversion efficiency and a maximum optical transmission of 60%, with the device concept being potentially transferable to other absorber materials.