•Heat of a salinity-gradient solar pond is used for cogeneration of power and water in a new layout.•Two thermoelectric generators are used for power augmentation of the unit.•Thermodynamic and ...economic analysis and optimization are conducted.•Feasibility of the layout for the Urmia Lake in Iran was investigated.
This study aims at introducing a new layout for cogeneration of power and distilled water using thermal heat stored at the lower convective zone (LCZ) of a salinity-gradient solar pond (SGSP). The proposed system consists of a Kalina cycle (KC), a humidification-dehumidification (HDH) unit, and two thermoelectric generators (TEGs). The feasibility of the devised system at the base and optimal modes of operation under the steady-state assumption is carried out, using thermoeconomic and the rmodynamic tools. Later, a parametric study is carried out and the effects of important design factors on the system performance and cost metrics were investigated. The results of multi-objective optimization revealed that the energy utilization factor (EUF), exergy efficiency, and total unit cost of the product (TUCP) can be improved by 14.09%, 5.5%, and 27.93%, respectively, in comparison with the base case. The optimum EUF, exergy efficiency, and TUCP were achieved at 0.756, 27.7%, and 30.54 $/GJ, respectively, when the proposed power/desalination system was designed under the following design parameters: solar pond area of 15326 m2, LCZ thickness of 1.65 m, NCZ thickness of 1.35 m, UCZ thickness of 0.35 m, LCZ temperature of 370 K, the figure of merit of 2.45, desalination flow ratio of 2.45, the turbine inlet pressure of 2500 bar, the pump pressure ratio of 3, and ammonia concentration of 86%. The results of the case study showed that between 20 March and 20 April the system produces the minimum rate of freshwater, which is 0.152 m3/h. On the contrary, the maximum amount of distilled water can be obtained between 21 June and 21 July. Moreover, from 21 May to 21 August is the best time to run the system to produce simultaneous distilled water and electricity.
We searched the MEDLINE, CINAHL, and Cochrane Library databases for articles published between January 1990 and December 2011. The update of this clinical practice guideline is based on 184 clinical ...trials and systematic reviews, and 10 articles investigating humidification during invasive and noninvasive mechanical ventilation. The following recommendations are made following the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) scoring system: 1. Humidification is recommended on every patient receiving invasive mechanical ventilation. 2. Active humidification is suggested for noninvasive mechanical ventilation, as it may improve adherence and comfort. 3. When providing active humidification to patients who are invasively ventilated, it is suggested that the device provide a humidity level between 33 mg H(2)O/L and 44 mg H(2)O/L and gas temperature between 34°C and 41°C at the circuit Y-piece, with a relative humidity of 100%. 4. When providing passive humidification to patients undergoing invasive mechanical ventilation, it is suggested that the HME provide a minimum of 30 mg H(2)O/L. 5. Passive humidification is not recommended for noninvasive mechanical ventilation. 6. When providing humidification to patients with low tidal volumes, such as when lung-protective ventilation strategies are used, HMEs are not recommended because they contribute additional dead space, which can increase the ventilation requirement and P(aCO(2)). 7. It is suggested that HMEs are not used as a prevention strategy for ventilator-associated pneumonia.
Summary
A study of the performance enhancement of a humidification‐dehumidification (HDH) system integrated with multiple evaporators/condensers heat pump (HP) and heat recovery units is presented. ...The HP unit is intended to deliver necessary heating for humidifier and heating/cooling for dehumidifier in a new strategy. The proposed integrated system is capable to produce fresh water from the HDH system and HP unit. Four different configurations of the system formed by excluding/adding condensers and evaporators were investigated; mode‐A (seawater precooling and reheating), mode‐B (seawater reheating), mode‐C (seawater precooling and humid air reheating), and mode‐D (humid air reheating). Fresh water productivity, fresh water ratio, system water recovery, gain output ratio, specific work consumption, and fresh water production cost were used as performance measuring parameters of the system. The influences of operating parameters on the system performance were analytically studied and experimentally validated for different system configurations. The results indicate the enhancement of the systems' performance with increasing ambient air temperature and humidity, seawater and air flow rates, and with decreasing seawater temperature. The system configuration of mode‐B shows the best performance with fresh water production of 61.94 kg/h and gain output ratio of 4.97 which are higher than those of the other configurations by 13%, 55%, 85% and 11%, 48%, and 75%, respectively. Comparisons of the proposed configurations with the other HDH desalination systems available in the literature were presented and better performance of the proposed systems was noticed.
Improved humidification‐dehumidification integrated with modified heat pump desalination system was presented.
Four different alternative modes using multi condensers/evaporators were investigated.
The effects of the system controlling parameters on the system performance were studied.
The system productivity, gain output ratio, and specific work consumption were presented.
Maximum productivity was 61.94 kg/h and minimum fresh water cost was 0.0306 USD/kg.
•A Fresnel lens is used to focus sunlight into the desalination system.•Solar concentrating and bubbling technologies are combined into desalination system.•The accumulated yield can reach 5.61L/d/m2 ...under actual weather conditions.•System performance ratio is 0.69 under actual weather and 0.71 with electrical heater.
A bubbling humidification-dehumidification (HDH) desalination system directly heated by concentrated sunlight is presented in this work. Sending directly the concentrated sunlight into bubbling humidification chamber can save the circulation pipeline and solar receivers, and reduce the heat loss of the pipeline which simplifies the device's structure and adds its operation reliability. The HDH system consists of a Fresnel lens solar concentrator, a bubbling humidification chamber and a bubbling dehumidification chamber. The operating principle and the structural design of the bubbling chambers are explained. A cylindrical Fresnel lens is used to focus sunlight into the humidification chamber to directly heat the seawater. With air coming out from the perforated wall of the immerged pipe, bubbles will generate underwater to obtain sufficient heat and moisture transfer. Experimental tests under different conditions were carried out to verify the design and study the performance characteristics. The results that the maximum freshwater productivity is about 1.24L/h/m2 when the maximum solar irradiance is 980 W/m2. The accumulated yield can reach 5.61L/d/m2 with an average thermal efficiency about 69% for sunny weather conditions in October in Beijing. Besides, the average thermal efficiency is about 71% under steady-state condition. Compared to some published works, the proposed bubbling HDH desalination system has relatively higher freshwater productivity owing to its effective heat and moisture transfer enhancement by direct solar heating and bubbling. The economic analysis showed that the price of the produced water for the system is about 0.027$/L.
A psychrometric energy process desalination unit has been experimentally tested. The system is based on humidification and dehumidification process where seawater is heated and then sprayed to ...humidify the incoming air in the humidification chamber. The humidified air enters the dehumidification chamber and is cooled by the incoming cold seawater. The moisture is condensed out and the pure water is accumulated at the base of the chamber, and the dehumidified air is discharged to the outside. The seawater was heated to temperature between 60 - 90°C using a 2.4kW electric heater. Performance data on temperature, seawater mass flow rate, air flow rate and the amount of fresh water produced were obtained, and the maximum coefficient of performance (COP) of the system was calculated based on the data obtained. The result achieved indicates the system had a maximum fresh water production of 13kg/h with a maximum COP of 3.6. The initial test shows that the system has great potential with room for improvements and further optimisation.
•A new water desalination system using hybrid solar collector with two working fluids.•Eight thermoelectric cooling modules used to condense water vapor.•The productivity increases about 13% by using ...the thermoelectric cooling.•Daily productivity increases about 55% with increasing the flow rate of saline water.•Using 3-E analysis to show CO2 mitigation and system economic potentials.
In this study, a novel humidification–dehumidification desalination (HDD) system, consisting of a hybrid solar collector with two working fluids, air and ethylene glycol, is designed and tested under climatic condition of Tehran, Iran. In this design, air passes above the absorber plate, while ethylene glycol flows through the copper tubes located on the absorber plate. The dehumidification system is also equipped with thermoelectric cooling modules. The effects of different parameters including collector outlet air velocity, volumetric flow rates of ethylene glycol and saline water and the effect of thermoelectric cooling on the performance and exergy of the system have been investigated. The experimental results showed that the water production improves by 8% with increasing the collector outlet air velocity from 2.2 to 3 m/s, while it reduces by 17% when increasing the collector outlet air velocity in the range of 3 to 4.2 m/s. In addition, the daily productivity increases about 44% by increasing the volumetric flow rate of ethylene glycol in the collector in the range of 0.83 L/min to 2.24 L/min. Moreover, the daily productivity of the system improves about 55% by increasing the volumetric flow rate of saline water from 0.66 L/min to 3 L/min. Furthermore, the productivity improves about 4% as the distance between the glass cover and the absorber plate decreases from 27.25 mm to 14.75 mm. The results also show that the productivity increases about 13% by using the thermoelectric cooling system. Finally, the maximum hourly exergy efficiency and maximum daily exergy efficiency were measured as 12.75% and 8.78%, respectively. Economic analysis shows that the estimated cost of water production is 0.097 $/lit/m2 which is comparable with the other devices reported in the literature. Finally, the exergoeconomic and environmental analysis are analyzed and discussed to show CO2 mitigation and economic potential of the system.
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•A novel portable BBHDH coupled with a closed-loop pulsating heat pipe is designed.•Condensation latent heat is recovered in a closed-loop to improve energy efficiency.•The ...performance of the basin humidifier is better than the column humidifier.•The more the productivity, the greater is the heat recovery.•The maximum daily water productivity is 8.7 L/(day.m2).
The present work aims to enhance the performance of a solar energy-driven HDH desalination system. An experimental apparatus consisting of a novel closed-loop pulsating heat pipe (CLPHP) assisted by a bubble basin HDH system was investigated. To evaluate the productivity of the fresh water, tests have been properly designed and conducted in outdoor and indoor modes during June and July of 2020, under local weather conditions of Mashhad, Iran. A closed air-heated configuration is introduced into the HDH desalination system, to recover the condensation latent heat. The air leaving the dehumidifier is pre-heated and pre-humidified using CLPHP before entering the humidifier of the desalination unit. Also, an air injection system is used to enhance the mass and heat transfer rate by generating bubbles. In the experiments, the influence of the operating conditions such as radiation and air mass flow rate on the performance of the desalination unit was investigated. Furthermore, a comparison between the bubble basin and bubble column types was carried out. Based on the results, the bubble basin type presented a higher yield compared to the bubble column type that was obtained as 0.83 and 0.70 (kg/(hr.m2)), respectively. Besides, it was observed that by increasing the radiation and air mass flow rate, productivity is improved. The maximum obtained yield of the proposed system was achieved as 8.7 L/(day.m2).
•Three proposed solar powered humidification–dehumidification (HDH) water desalination systems are investigated and presented.•Parametric study of the hourly and daily systems performance is ...presented at various operating parameters.•Mathematical model of the HDH water desalination system is developed and solved numerically using EES software.•The performance of the proposed systems is maximized by changing between the open/closed mode of operations.
Transient performance analysis and investigation of three proposed solar powered humidification–dehumidification (HDH) water desalination systems: single stage (SS), double stages (DS) and modified double stages (MDS) systems are presented for hot and humid cities. Open/closed modes of operations of the systems are also investigated. A parametric study of the hourly and daily systems performance is presented at various operating parameters. The results reveal that: (i) inserting solar collectors in HDH systems for air and water heating substantially enhances the system’s performance; (ii) the fresh water productivity of all systems at open mode of operation increases with increasing the outdoor air temperature and humidity; (iv) at low outdoor humidity, the system’s performance at closed mode of operation is higher than those at open mode of operation and the opposite is true at high outdoor humidity; (v) comparing between the three systems, MDS system (open mode) can produce fresh water of 350 kg/day with GORday of 1.63 and its fresh water productivity enhances with 86.7% and 34% than SS and DS systems, respectively; and (vi) using control system, the performance of the proposed systems can be maximized by changing between the open/closed mode of operations according to the outdoor conditions.
•A quasi-2D transient model of PEMFC with anode recirculation is developed.•Anode recirculation leads to certain level of self-humidification.•Nitrogen accumulation causes performance decrease ...especially at anode downstream.•Current distribution non-uniformity of co-flow is improved by anode recirculation.•Anode recirculation avoids the severe fuel starvation compared to dead-ended anode.
Anode recirculation of proton exchange membrane fuel cell (PEMFC) is considered as an effective way for self-humidification and efficient hydrogen utilization, but nitrogen crossover presents a problem. To investigate the transient characteristics of PEMFC with anode recirculation, a comprehensive quasi-2D non-isothermal transient model is developed. The simulation results show that for a PEMFC initially operated with dry hydrogen, anode recirculation leads to certain level of performance increase in the beginning due to self-humidification effect, and then the performance decreases caused by nitrogen crossover, hydrogen dilution and the increase of anode activation loss. The nitrogen accumulation in anode downstream is severer than upstream, and the performance decline rate decreases with increasing cathode inlet velocity under the simulated operating conditions. The performance and current density distribution uniformity of counter-flow configuration is better than co-flow under low inlet humidity, but the difference becomes smaller with anode recirculation. Anode recirculation and dead-ended anode (DEA) operation both have self-humidification effect, and compared to DEA, the advantages of anode recirculation can be summarized as lower performance decline rate, less chance of local hydrogen starvation and better current density distribution uniformity.
•A novel heat pump coupled humidification-dehumidification system was proposed.•Heat pump evaporator was used as the air dehumidifier.•Sizes of the heat exchangers were obtained for fixed operational ...conditions.•System performance was balanced for fixed-size components at off-design conditions.•Characteristics method was utilized to study the system at off-design conditions.
In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design conditions resulting in changes in heat pump performance. Since the performance of a heat pump is a function of its refrigerant saturation temperatures, to examine the performance of the designed system at off-design conditions, the system performance balancing was carried out through the method of characteristics for a given set of fixed-size components. It was observed that the gained output ratio and hourly yield of the proposed system reach 2.476 and 0.91 kg/h, respectively. The economic analysis indicated that the cost per liter of the proposed system is 0.014 $/L.
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