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To improve the permeate flux and to keep the advantage of the high thermal efficiency in air gap membrane distillation (AGMD) for desalination, the optimal design of countercurrent AGMD of the hollow fiber module (AGMD-HF) is proposed. The module is basically composed of hydrophobic porous fiber tubes for feed flow and nonporous tubes for cold flow. The set of mathematical model equations for the entire module is derived from rigorous mass, momentum, and energy balances of both the feed side and the cold side coupled with the simultaneous mass and heat transfer across the membrane. The temperatures across the membrane and along the length of the module are simulated. The sensitivity of the process performance to operating conditions along the fiber length is investigated over a range of temperature and the flow rate. It is found that in the AGMD-HF domain, air/vapor dominates the heat and mass transfer resistances, which are comparable with the available experimental results in the literature. An attempt is then made to adjust the packing density and the surface ratio of the hot porous fibers to the cold nonporous fibers in order to maximize the process performance. Based on the trade-off between productivity and the thermal efficiency under module parameters, optimal design of AGMD-HF using Pareto solutions and the genetic algorithm is finally carried out. The obtained optimal points show that productivity increases considerably at the cost of the higher thermal efficiency with the increase of both packing density of the module and the tube ratio of hot feed fibers to cold fibers, with the latter showing relatively complex effect.

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Objective: To investigate the maternal–neonatal outcomes of obstetric deliveries performed in negative pressure isolated delivery rooms (NPIDRs) during the coronavirus disease 2019 (COVID-19) omicron variant pandemic period in a single tertiary center in northern Taiwan. Methods: Confirmed positive and suspected-positive COVID-19 cases delivered in NPIDRs and COVID-19-negative mothers delivered in conventional delivery rooms (CDRs) in the period of 1 May 2022 to 31 May 2022 during the COVID-19 omicron variant pandemic stage were reviewed. The maternal–neonatal outcomes between the two groups of mothers were analyzed. All deliveries were performed following the obstetric and neonatologic protocols conforming to the epidemic prevention regulations promulgated by the Taiwan Centers for Disease Control (T-CDC). Multiple gestations, deliveries at gestational age below 34 weeks, and major fetal anomalies were excluded from this study. Results: A total of 213 obstetric deliveries were included. Forty-five deliveries were performed in NPIDRs due to a positive COVID-19 polymerase chain reaction (PCR) test (n = 41) or suspected COVID-19 positive status (n = 4). One hundred and sixty-eight deliveries with negative COVID-19 PCR tests were performed in CDRs. There was no statistical difference in maternal characteristics between the two groups of pregnant women. All COVID-19-confirmed cases either presented with mild upper-airway symptoms (78%) or were asymptomatic (22%); none of these cases developed severe acute respiratory syndrome. The total rate of cesarean section was not statistically different between obstetric deliveries in NPIDRs and in CDRs (38.1% vs. 40.0%, p = 0.82, respectively). Regardless of delivery modes, poorer short-term perinatal outcomes were observed in obstetric deliveries in NPIDRs: there were significant higher rates of neonatal respiratory distress (37.8% vs. 10.7%, p < 0.001, respectively), meconium-stained amniotic fluid (22.2% vs. 4.2%, p < 0.001, respectively) and newborn intensive care unit admission (55.6% vs. 8.3%, p < 0.001, respectively) in obstetric deliveries performed in NPIDRs than in CDRs. Maternal surgical outcomes were not significantly different between the two groups of patients. There was no vertical transmission or nosocomial infection observed in COVID-19 confirmed cases in this study period. Conclusions: Our study demonstrates that obstetric deliveries for positive and suspected COVID-19 omicron-variant cases performed in NPIDRs are associated with poorer short-term perinatal outcomes. Reasonable use of personal protective equipment in NPIDRs could effectively prevent nosocomial infection during obstetric deliveries for pregnant women infected with the COVID-19 omicron variant.