Techno-Economic Assessment of an Air-Multiple PCM Active Storage Unit for Free Cooling Application

A latent energy storage (LES) unit is presented in this paper for free space cooling and ventilation application. The unit includes multiple phase change materials (PCM) to advance the thermal performance of common LES units. It is composed by metallic rectangular panels containing commercial paraffins with melting temperatures ranging among 20 °C and 25 °C and surrounded by air channels. The average cooling load of the unit corresponds to approximately 1 kW over 8 h. It fulfils the peak ventilation cooling load during summer of an office building in Portugal. The study provides a techno-economic analysis and the environmental benefits of the LES technology compared to a traditional air conditioning (AC) unit for the cooling and ventilation of an office building. During daytime, the air-multiple PCM unit allows reducing the energy consumption by nearly 200 kWh. The full charging of the PMs during nighttime, requires significant energy consumption due to the high air flowrate demand for full solidification. The competitiveness of such units can be achieved by introducing fins into the panels, allowing double the energy savings. In an overall perspective, the unit presents several benefits such as lower initial cost and reduced maintenance requirements (non-use of refrigerants and batteries) that also allows better personal health issues when related to traditional ACs.

Lossy mode resonances in photonic crystal fibers

The interaction effect of the fundamental mode in a special photonic crystal fiber (PCF) with a thin-film absorbing coating deposited on a surface of a fiber cladding on the optical transmission of the PCF is theoretically studied. It is shown that the transmission has a multi-peak spectrum that is determined by the resonance capture of the fundamental PCF mode energy by the coating. In some cases, this capture is explained by a resonance coupling between the fundamental core mode and leaky modes of the coating, or between the fundamental PCF mode and cladding modes located between PCF air channels and the coating. Examples are presented of using this effect to develop fiber-optic sensors of refractive index or pressure, and to sense a nanoscale adsorption layer of ammonia molecules deposited on a coating surface contacting air.

Highly Efficient Piezoelectrets through Ultra-Soft Elastomeric Spacers

Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N–1) and dynamic (7500 pC N–1) coefficients were achieved. The isothermal stability of the coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic coefficient on seismic mass and acceleration showed high coefficients, even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static coefficients of the suggested structure indicating a potential for further optimization.

A bioinspired scaffold for rapid oxygenation of cell encapsulation systems

Inadequate oxygenation is a major challenge in cell encapsulation, a therapy which holds potential to treat many diseases including type I diabetes. In such systems, cellular oxygen (O2) delivery is limited to slow passive diffusion from transplantation sites through the poorly O2-soluble encapsulating matrix, usually a hydrogel. This constrains the maximum permitted distance between the encapsulated cells and host site to within a few hundred micrometers to ensure cellular function. Inspired by the natural gas-phase tracheal O2 delivery system of insects, we present herein the design of a biomimetic scaffold featuring internal continuous air channels endowed with 10,000-fold higher O2 diffusivity than hydrogels. We incorporate the scaffold into a bulk hydrogel containing cells, which facilitates rapid O2 transport through the whole system to cells several millimeters away from the device-host boundary. A computational model, validated by in vitro analysis, predicts that cells and islets maintain high viability even in a thick (6.6 mm) device. Finally, the therapeutic potential of the device is demonstrated through the correction of diabetes in immunocompetent mice using rat islets for over 6 months.

Energy-based performance analysis of a double pass solar air collector integrated to triangular shaped fins

In this paper, the performance of a double pass solar air collector with triangular integrated fins was investigated experimentally at Hungarian University of Agriculture and Life Sciences in Gödöllő, Hungary. The focus of this research is on energy-based performance evaluation. The thermal efficiency of the collector has been compared by testing two collectors that had the same design, with and without fins. The effect of the collector's air mass flow rate on thermal performance was investigated under various environmental situations. The results revealed that the temperature difference is always higher through the finned collector and the higher variation temperature between the inlet and outlet temperature leads to higher useful heat. The daily thermal efficiency of the finned collector was 56.57%, 59.41%, and 61.42%, while for the un-finned collector was 51.04%, 53.28%, and 57.08% for the mass flow rate 0.0081, 0.0101, and 0.0121 kg/s. The finned double pass solar air collector improved the thermal efficiency by 4.3–6.1% over the un-finned one. The efficiency of the finned collector is always higher than the un-finned one regardless of the mass flow rate. The presence of the fins to the top air channels significantly increases collector efficiency, owing to the increased absorbing surface area, which is responsible for increasing the internal thermal convective exchanges. Moreover, it creates a turbulence airflow, meaning that the air will be in good contact with the absorber plate and penetrate all regions, reducing the dead zones contributing to increased heat transfer.

Numerical analysis of the effect of trapezoidal baffles inside fuel and air channels on the performance of a planar-type Solid Oxide Fuel Cell

The present paper investigates the effect of trapezoidal baffles inside a planar-type solid oxide fuel cell. To achieve the objective, four cases are proposed: 1) simple planar geometry as base case, 2) trapezoidal baffles inside the fuel channel, 3) trapezoidal baffles inside the air channel and 4) trapezoidal baffles in both fuel and air channels. The height of the trapezoidal baffles inside the channels of the solid oxide fuel cell increases along the direction of the fluid flow. The numerical investigation is based on a three-dimensional computational fluid dynamics (CFD) model that takes into account the phenomenon of mass transfer, heat transfer, species transport and electrochemical reactions. A detailed comparison of the performance between the four cases of the fuel cell is provided in terms of power density, fluid flow, species concentration, temperature distributions and electric fields at a variable current density and a fixed power density of 3000 W/m2. The results show that the power density, the velocity, the availability of the hydrogen and oxygen species on the electrodes-electrolyte interfaces increases for the case 2, case 3 and case 4, respectively, in comparison to the case 1. Finally, the average temperature of the electrode-electrolyte interface is reduced with the baffles and it is concluded that the configuration with baffles inside air channel (case 3) shows better results in terms of the increment of the power density and the decrement of the average temperature.

Design of Thermal Insulation Materials with Different Geometries of Channels

Investigating the large number of various materials now available, some materials scientists promoted a method of combining existing materials with geometric features. By studying natural materials, the performance of simple constituent materials is improved by manipulating their internal geometry; as such, any base material can be used by performing millimeter-scale air channels. The porous structure obtained utilizes the low thermal conductivity of the gas in the pores. At the same time, heat radiation and gas convection is hindered by the solid structure. The solution that was proposed in this research for obtaining a material with porous structure consisted in perforating extruded polystyrene (XPS) panels, as base material. Perforation was performed horizontally and at an angle of 45 degrees related to the face panel. The method is simple and cost-effective. Perforated and simple XPS panels were subjected to three different temperature regimes in order to measure the thermal conductivity. There was an increase in thermal conductivity with the increase in average temperature in all studied cases. The presence of air channels reduced the thermal conductivity of the perforated panels. The reduction was more significant at the panels with inclined channels. The differences between the thermal conductivity of simple XPS and perforated XPS panels are small, but the latter can be improved by increasing the number of channels and the air channels’ diameter. Additionally, the higher the thermal conductivity of the base material, the more significant is the presence of the channels, reducing the effective thermal conductivity. A base material with low emissivity may also reduce the thermal conductivity.

Structural Analysis of Gas Turbine Blade

A turbine blade is a machine component which makes up the turbine section of a gas turbine. These blades are responsible for extracting energy from the high temperature, high pressure gas produced by the combustor. The turbine blades are often the limiting component of the gas turbine. To survive in this difficult environment , turbine blades often use exotic materials like super alloys and many different methods of cooling , such as internal air channels and thermal barrier coatings. A common failure mode for turbine machine is high cycle of fatigue of compressor and turbine blades due to high dynamic stress caused by blade vibration and temperature has significant effect on gas turbine blades. The stresses with detrimental effect to the nozzle and blade were principally of thermal type, developed due to high temperature gradients across the air foil wall. These generate thermal fatigue mechanism and high steady state load leading to creep mechanism. In this project, a turbine blade is designed and modelled in NX Unigraphics software which is an advanced high-end CAD/CAE/CAM. The design is modified by changing the base of the blade to increase overall efficiency. Since the design of turbo machinery is complex and efficiency is directly related to material performance and material selection is of prime importance. In this project few materials are considered for turbine blade –titanium alloy and Nickel alloy. Optimisation will be done by varying the materials by performing structural analysis and thermal analysis on the turbine blades for both the designs