We investigate the joint uplink-downlink configuration of an intelligent reflecting surface (IRS) for multi-user frequency-division-duplexing (FDD) and time-division-duplexing (TDD) systems. This is ...motivated in FDD since uplink and downlink transmissions occur simultaneously and hence an IRS must be jointly configured for both transmissions. In TDD, while a joint design is not strictly necessary, it can significantly reduce feedback overhead, power consumption, and configuration periods associated with updating the IRS. To compute the trade-off between uplink and downlink rates achieved by a joint design, a weighted-sum problem is formulated and optimized using a developed block-coordinate descent algorithm. The resulting uplink-downlink trade-off regions are investigated by numerical simulation to gain insights into different scenarios. In all FDD scenarios and some TDD scenarios, the jointly optimized design significantly outperforms the fixed-uplink (fixed-downlink) heuristic of using the IRS configuration optimized for uplink (downlink) to assist downlink (uplink) transmissions. Moreover, the joint design substantially bridges the gap to the individual design upper bound of allowing different IRS configurations in uplink and downlink. Otherwise, in the remaining TDD scenarios, the fixed-uplink and fixed-downlink designs nearly achieve the individual design performance and substantially reduce overhead and/or complexity compared to the optimized joint design and individual design.
Adsorption technology offers a potential in vital applications like energy storage, cooling and heating, and water desalination which can be driven by low-grade or renewable heat sources leading to ...significant reduction in CO2 emissions. The adsorbent material is a key element in adsorption heat pump systems determining the performance, size and cost of such technology. Metal-organic frameworks (MOFs) are class of adsorbents with superior water uptake, high pore volume and surface area. This study describes the experimental testing of adsorption heat pumps using aluminium fumarate, CPO-27(Ni) and MIL-100(Fe) for various adsorption applications. Results showed that energy storage density of 1200 W h kg−1 was achieved using MIL-100(Fe) regenerated at 95°C, and cycle time of 90 min. For cooling applications, MIL-100(Fe) showed high specific cooling power of 226 W kg−1 at 95°C while aluminium fumarate produced 136 W kg−1 specific cooling power (SCP) at 90°C. Regarding water desalination, MIL-100(Fe) showed high water production rate specific daily water production (SDWP) of 19 m3 ton−1 day−1. For power generation, including a turbine in the adsorption system can increase the effective coefficient of performance (COP) of the adsorption cooling system by 22%. Integrating the adsorption cooling system with Organic Rankine Cycle (ORC) can produce an effective COP of 0.8.
Although many adsorbent materials have been used in adsorption systems, only silica-gel was tested experimentally for desalination applications. This work experimentally and numerically investigates ...the use of CPO-27(Ni) an advanced Metal Organic Framework-MOF adsorbent material in a 1-bed adsorption system for water desalination and cooling applications. Operating parameters as switching time, half cycle time, evaporator and condenser water inlet temperatures were studied to investigate their effects on cycle water production and cooling. Moreover, a mathematical simulation model is developed, validated and used to predict cycle outputs at other operating conditions. Results showed that as evaporator temperature increases and condenser temperature decreases, cycle outputs increase. Also, it was shown that adsorption desalination cycles can work with condenser pressure lower than evaporator pressure as the cycle is an open loop one (i.e. no refrigerant is flowing back from condenser to evaporator). A water production of 22.8m3/tonne·ads/day was achieved using 40°C evaporator temperature, 5°C condenser temperature and 95°C desorption temperature. Similar water production can be achieved using 30°C condensing temperature but at 120°C desorption temperature. For space cooling applications (Tevap<20°C), cycle cooling produced was found to be 65Rton/tonne·ads. This work highlights the potential of using advanced MOF materials for water desalination/ cooling applications.
•Experimental - numerical study of CPO-27Ni MOF for adsorption desalination/cooling•Effects of Condenser and evaporator water inlet temperatures are studied.•Simulink model is developed, validated and used to study other operating conditions.•CPO-27Ni produced water and cooing of 23m3/day & 216Rton per ton·ads, respectively.
Although many water desalination techniques have been introduced decades ago, there are still areas around the world suffering from fresh water shortages. The widespread of desalination technologies ...is limited due to their high energy consumption, cost and adverse environmental impact. Recently, adsorption technology for water desalination has been investigated showing potential of using low temperature waste heat (50–85°C) thus reducing energy consumption and CO2 emissions. This work mathematically investigates the performance of 4 bed adsorption cycle using two different adsorbents, silica-gel and an advanced zeolite material AQSOA-Z02, produced by Mitsubishi-plastics for fresh water production and cooling. The work studied effects of evaporator and heat source temperatures on water production rate and cooling capacity. Results showed that at low chilled water temperatures below 20°C, AQSOA-Z02 outperforms silica-gel with water production of 6.2m3 of water/day and cooling of 53.7Rton/tonne of AQSOA-Z02 compared to 3.5m3 of water/day and 15.0Rton/tonne of silica-gel. While, at chilled water temperatures above 20°C, AQSOA-Z02 and silica-gel have comparable performance with around 7m3 of water/day and 60Rton of cooling. Since cooling applications require chilled water temperature less than 20°C, therefore AQSOA-Z02 is more suitable for applications where cooling and fresh water are needed.
•4 bed adsorption desalination/refrigeration system is modeled.•Two adsorbent materials are compared AQSOA-Z02 to silica-gel.•For cooling applications, below 20°C AQSOA-Z02 outperforms silica-gel.•For higher evaporator temperatures above 20°C, silica-gel is recommended.•Evaporator water temperature change considerably affects silica-gel performance.
•Comprehensive investigation of various parameters affecting geyser phenomenon inside thermosiphon.•The occurrence of geyser boiling highly depends on the fill ratio and inclination at every heat ...input.•Period of geyser boiling is sensitive to the fill ratio, orientation and heat load.•Effect of coolant mass flow rate and inlet temperature on geyser boiling depends on inclination and fill ratio.
Geyser boiling is a complex phenomenon which may occur in heat pipes causing high temperature and pressure oscillation leading to noticeable vibration. Therefore, understanding of such process is essential to improve heat pipes thermal performance and avoid damage. In this experimental study, a comprehensive investigation of several parameters on the characteristics of the geyser boiling has been conducted during the operation of two-phase closed thermosiphon (TPCT) using water as the working fluid. The effect of different inclination angles (90, 60, 30 and 10°) at various fill ratios defined as volume of liquid in the evaporator to the volume of the evaporator (25%, 65% and 100%) on the geyser boiling has been investigated at a broad range of heat load and for various mass flow rates and inlet temperatures of the cooling water. These important parameters have been examined to report the occurrence and period of the geyser effect at each heat input. The results showed that the orientation and the liquid charge have a significant impact on the occurrence and period of the geyser boiling at low and high heat inputs. For example, at a fill ratio of 100%, the geyser boiling occurs at a lower heat input compared with that for fill ratios 25%, 65% at all inclination angles, while it happens at a higher heat load at a low inclination 10° compared with other angles at all fill ratios. In addition, at high input energies, it almost disappears at orientations of 90 and 60° for all liquid charges. Also, comparing with fill ratios of 25% and 65%, a shorter period is observed for a fill ratio of 100% at angles of 90, 30 and 10°, whereas it is longer at 60° and low heat inputs. This work highlights the effects of the operating conditions on geyser boiling in heat pipes.
The diagnostic of magnetized radio frequency complex plasma via probing techniques and spectroscopy is challenging. However, a self-excited dust ion acoustic waves (DIAWs) have been observed ...employing laser scattering. Inspired by the current high enthusiasm for the theoretical description of complex plasma, we study the propagation of DIAWs in a three-dimensional collisional and magnetized dusty plasma medium. We consider the fluid model for dust and ion particles, while we neglect the inertia of electrons considering the Boltzmann distribution. A linear dispersion relation is obtained and a nonlinear modified Zakharov-Kuznetsov equation is derived utilizing the reductive perturbation technique. The effects of ion-neutral and dust-neutral collisions on the dynamics of the nonlinear DIAWs are considered. The phase portrait analysis and numerical illustration of a rarefactive DIA cnoidal waves and solitons are also presented. Our findings agree with experimental observations by Choudhary M, Bergert R, Mitic S, and Thomas MH. Influence of external magnetic field on dust acoustic waves in a capacitive rf discharge. Contrib Plasma Phys. 2020;60:e201900115 as the growth of nonlinear periodic waves is recorded when the magnetic field is roughly 0.05 T and vanishes when the magnetic field is close to 0.1 T. Moreover, the model reveals that the electrostatic cnoidal and soliton waves propagate with low frequencies up to 140 Hz.
The global transmission of SARS-COV-2 constitutes a highly challenging situation for long-term care facilities, especially with the lack of standardized and approved procedures. Residents in these ...facilities are at high risk for contamination due to proximity, and to morbidity and mortality given their advanced age and critical baseline health conditions. This paper exposes the experience and outcomes of a COVID-19 outbreak in a long-term facility in Jeddah, Saudi Arabia, which occurred after admission of a new resident despite high baseline level of alertness including systematic isolation and screening of all newly admitted residents. We highlight the challenges for case detection and application of protective measures, and describe the adaptive management strategies implemented to contain the outbreak.
The availability of potable water and cooling are becoming increasingly important to ensure good sustainability and quality of life. In this work, a new multi-cycle adsorption desalination and ...cooling system using AQSOA-Z02 has been developed for high water production and cooling rates using renewable and waste heat sources. It consists of two 2-adsorber bed cycles linked with integrated evaporator/condenser, one cycle uses the integrated evaporator/condenser as evaporator (upper) and the second one uses it as a condenser (lower). In this system low condensing temperatures can be achieved using the cooling effect from the evaporator of the lower cycle and the integrated evaporator/condenser thus enhancing the system performance. Also, the adsorber beds of the upper and lower cycles are heated in series during the desorption process using the same heat source. This system can operate in three modes depending on the desalinated water and cooling capacity requirements. Results showed that the specific daily water production ranges from 6.64 to 15.4m3/tonne adsorbent/day while the cooling capacity reaches up 46.6Rton/tonne adsorbent at evaporator temperature of 10°C. The new cycle offers potential of simultaneously producing large amounts of desalinated water and cooling capacity (at 10°C) compared to other cycles.
•A 4 bed combined adsorption desalination and cooling cycles is modelled.•Effect of Condenser temperature is studied.•3 operating modes can produce various amounts of water & cooling according to needs.•Can produce more water than any system along with cooling at low evap. temp. (10°C).
Adsorption heat pumps can be used for generating heating, cooling, seasonal energy storage and water desalination applications. Metal-organic frameworks (MOFs) are hybrid porous materials with high ...surface area and superior adsorption characteristics compared to conventional adsorbents. MIL-101(Cr) has a large pore size with water vapour adsorption capacity up to 1.5 gH2O gads−1 and high cyclic stability, and thus has the potential to be used in adsorption heat pumps. This work investigates the enhancement of the thermal conductivity and water adsorption characteristics of MIL-101(Cr) using hydrophilic graphene oxide. Two methods have been used to develop MIL-101(Cr)/GrO composites. The first method was through the physical mixing of GrO and MIL-101(Cr) while the other was through incorporating the GrO during the synthesis process of MIL-101(Cr). The composites and neat MIL-101(Cr) were characterized in terms of their structure, water adsorption uptake, BET surface area, particle size, thermal gravimetric analysis, SEM images and thermal conductivity measurements. Results showed that introducing low amounts of GrO (2%) to the neat MIL-101(Cr) enhanced the water adsorption characteristics at high relative pressure but enhanced the heat transfer properties by 20–30% while using more than 2% of GrO reduced the water adsorption uptake but significantly enhanced the thermal conductivity by more than 2.5 times.
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•Composites MIL-101(Cr)/Graphene oxide were synthesized with different GrO content.•The 2%GrO_synthesis composite showed enhanced water adsorption characteristics.•MIL-101/GrO showed higher thermal conductivity than parent material.•MIL-101/GO is a promising candidate for adsorption heat pump applications.
The current study investigates the solvability conditions and the general solution of three symmetrical systems of coupled Sylvester-like quaternion matrix equations. Accordingly, the necessary and ...sufficient conditions for the consistency of these systems are determined, and the general solutions of the systems are thereby deduced. An algorithm and a numerical example are constructed over the quaternions to validate the results of this paper.
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