Discharge improvement of a phase change material-air-based thermal energy storage unit for space heating applications using metal foams in the air sides

This study examines the energy discharge of a phase-changing material (PCM)-based air heat exchanger using a metal foam inside the heat transfer fluid (HTF) channel. Such systems have various potential applications in the heating space and building ecosystem. Thermal energy storage (TES) often utilizes air as the HTF, which limits the heat transfer performance due to the low thermal conductivity. This paper aims to address this drawback via incorporating a metal foam into the HTF channel to enhance the thermal performance between the heat transfer fluid (air) and the PCM, which is considered as the novel side of this study. The combined system is mathematically modeled with an symmetrical, three-dimensional computational fluid dynamics method for various flow rates and inlet temperatures of the HTF with different geometric parameters of the metal foam. This study indicates the advantage of utilizing the porous medium in the air channel. The results show the HTF flow rate has a great influence on the discharging rate. The presence of the porous medium in the system improves the discharging process by 116% compared with a non-porous medium system at the same flow rate. The discharging time decreases by increasing the porosity, and the value of 90% is found as the best porosity value at the flow rate of 0.005 kg/s in this system. The solidification rate is proportional to the pore density because of the surface area impacts of the porous medium, also the pressure-drop and the pumping required are highly affected by the mentioned dependent parameters.     

Pectic acid–graphene oxide nanocomposite as an adsorbent in vortex-assisted dispersive solid-phase extraction for preconcentration of copper ion followed by flame atomic absorption spectrometry

Polymer Bulletin - An efficient, green, novel and rapid vortex-assisted dispersive solid-phase extraction (VADSPE) technique was used for the preconcentration and determination of trace levels of...     

On the design of a reject band filter for antennas mutual coupling reduction

In this article, a novel concept for mutual coupling reduction between antenna elements is proposed at 2.45 GHz for Wi‐Fi applications. A reject band filter (RBF) is used in order to reduce the mutual coupling between two monopoles for multi‐input multi‐output (MIMO) systems. The proposed RBF inclusions are developed to have zero refractive index response over a specific frequency band. The inclusions considered here are composed of open‐loop resonators; each one with the same iteration level of Minkowski‐like pre‐fractal structures coupled with an open‐stub transmission line to increase the band selectivity. The inclusions are inserted between λ/2‐spaced monopole elements at 2.45 GHz. A significant mutual coupling reduction is realized by incorporating only two RBF cells. Such effective response is attributed to the electromagnetic wave cloaking at 2.45 GHz using the developed RBF inclusions. An extensive theoretical study using both numerical and analytical methods is invoked to obtain the best performance of the proposed MIMO antenna structure. Finally, the experimental and numerical results are agreed excellently.     

Numerical modeling of time-dependent deformation and induced stresses in concrete pipes constructed in Queenston shale using micro-tunneling technique

Effects of time-dependent deformation (TDD) on a tunnel constructed using the micro-tunneling technique in Queenston shale (QS) are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids (LFs) used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio (K_o), and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining. The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.     

Seasonal design and multi-objective optimization of a novel biogas-fueled cogeneration application

Switching from fossil fuels to biofuels is an effective option for small-scale power production and cogeneration systems. The target of the current study is to propose and investigate a novel seasonal combined cycle driven by a biogas-fueled gas turbine from thermodynamic and economic viewpoints. Regarding the high-temperature of the turbine's exhaust gases, an integration of Rankine and ejector refrigeration cycles is configured. The bottoming cycle is designated for winter and summer conditions, independently. Hence, a combined cycle capable of operating as a cogeneration system producing electricity/heating or electricity/cooling, individually, is designed. Moreover, a parametric study based on assessing the impact of key parameters on the essential variables and a multi-criteria optimization trough a genetic algorithm are performed to attain the facilities of the proposal. According to the results, the capability of the whole system in winter conditions is significantly higher than that for summer conditions due to the higher heating capacity. Also, the evaluated variables are more affected by change in the environment temperature in both seasons. Additionally, the optimal overall energy, exergy and levilized cost of products are calculated as 79.2%%, 45.6%, and 21.7 $/GJ for summer and 70.7%, 37.0%, and 17.6 $/GJ for winter, respectively.     

Anycast tree-based routing in mobile wireless sensor networks with multiple sinks

A routing scheme for wireless sensor networks with mobile sensors and mobile multiple sinks is proposed and studied. The scheme is based on expanding ring search, anycast messaging and reactive mode with maintaining route state information in sensors. As a result of a successful routing request issued by the sensor, it becomes a member of a routing tree with some sink as a root. Anycast messaging is used only at the stage of establishing a path from a sensor to a sink. Replies from sinks are always forwarded in unicast mode. This considerably reduces network traffic and, as a result, energy consumption by sensors. To take into account routing conditions for network nodes in receiving messages from different directions, the receiving area of each node is assumed to consist of a number of sectors, considered as independent links with random change of link states in time. The proposed routing scheme was investigated with the use of a detailed simulation model, implemented in terms of a class of extended Petri nets. In simulation the following performance metrics were investigated versus time-to-live value: response ratio, relative network traffic and relative energy consumption. These metrics were considered for a number of combinations of parameters, such as the number of sinks, sensor availability and link availability. The results of simulation were compared with published characteristics of a similar model, in which sensors do not maintain any routing state information, and is proved to outperform it.     

Joint network-host based malware detection using information-theoretic tools

In this paper, we propose two joint network-host based anomaly detection techniques that detect self-propagating malware in real-time by observing deviations from a behavioral model derived from a benign data profile. The proposed malware detection techniques employ perturbations in the distribution of keystrokes that are used to initiate network sessions. We show that the keystrokes’ entropy increases and the session-keystroke mutual information decreases when an endpoint is compromised by a self-propagating malware. These two types of perturbations are used for real-time malware detection. The proposed malware detection techniques are further compared with three prominent anomaly detectors, namely the maximum entropy detector, the rate limiting detector and the credit-based threshold random walk detector. We show that the proposed detectors provide considerably higher accuracy with almost 100% detection rates and very low false alarm rates.