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Numerical Heat Transfer And Fluid Flow

Although seawater is abundant, desalination is energy-intensive and expensive. Using the sun as an energy source is attractive for desalinating seawater; however, the performance of state-of-the-art passive devices is unsatisfactory when operated at less than one sun ($<$ $1$ $kW$ $m^{-2}$). Here, we present a completely passive, modular, and low-cost solar thermal distiller for seawater desalination. Each distillation stage is made of two opposed hydrophilic layers separated by a hydrophobic microporous membrane, and it does not require further mechanical ancillaries. Under realistic laboratory and outdoor conditions, we obtained a distillate flow rate of almost $3$ $L$ $m^{-2}$ $h^{-1}$ from seawater at less than one sun - twice the yield of recent passive device reported in the literature. In perspective, theoretical modelling suggests that the distiller has the potential to further doubling the peak flow rate observed in the current experiments. This layout can satisfy freshwater needs in isolated and impoverished communities, as well as realize self-sufficient floating installations or provide freshwater in emergency conditions.

Passive high-yield seawater desalination at below one sun by modular and low-cost distillation

Fresh water is an indispensable resource, which is getting contaminated. The shortage of freshwater has been identified as a crucial issue all around the world. Solar desalination is one of the options to produce fresh water from any type of contaminated water (brackish, contaminated and sea water) in a sustainable way. A solar still is a simple device used to purify the water using solar energy through evaporation and condensation processes. In general, the productivity of the conventional solar still (CSS) is about 2–5 l/m2/day. But this quantity is not sufficient for an individual to lead an adequate life. Hence either more than 1 m2 is required per person or better yet are modifications to improve the yield of the fresh water (likely more than 5 l/m2/day). In this work, an attempt has been made to categorize the different solar still designs with productivity exclusively more than 5 l/m2/day. Here, we identify as such efficient high productivity stills and discuss their novel modifications and heat transfer mechanism to arrive at useful conclusions. This comprehensive review will be a reference guide for future researchers who wish to concentrate only on efficient high productivity solar stills to improve the productivity further.

A review of efficient high productivity solar stills

Heat and mass transfer through thermal protective clothing – A review

A finite volume model was developed to simulate transient heat transfer in firefighters' protective clothing during flash fire exposure. The model domain consists of three layers of fire-resistant fabrics (outer shell, moisture barrier, and thermal liner) with two air gaps between the clothing layers, the human skin, and the air gap between the clothing and the skin. The model accounts for the combined conduction-radiation heat transfer in the air gaps entrapped between the clothing layers, and between the clothing and the skin. The variation in the air gap properties and energy content during both the exposure and the cool down periods was accounted for. Predictions were obtained for the temperature and heat flux distributions in the fabric layers, skin, and air gaps as a function of time. The influence of each air gap on the clothing performance was investigated as well. This article demonstrates the importance of accurately modeling the contributions of the air gaps in order to predict the protective c...

Numerical Simulation of Heat Transfer in Firefighters' Protective Clothing with Multiple Air Gaps during Flash Fire Exposure

A finite volume model was developed to simulate the transient heat transfer in a protective clothing system. The model domain consists of a fire-resistant fabric, the human skin, and the air gap between the fabric and the skin. The model uses a more sophisticated treatment of the air gap compared to previous models: it accounts for transient combined conduction-radiation heat transfer within the air gap and includes the variation in the air gap properties with temperature. Predictions were obtained for the temperature and heat flux distributions in the fabric, skin, and air gap as a function of time, as well as the time to receive skin burn injuries. The numerical model was used to explore the physics of heat transfer in protective clothing, which could potentially be used to improve the performance of this clothing. This study illustrates the dependence of the temporal behavior of the heat fluxes on the specific model assumptions, as well as the associated sensitivity of skin burn predictions to these as...

Numerical Simulation of Transient Heat Transfer in a Protective Clothing System during a Flash Fire Exposure

The motion of a person wearing protective clothing induces the clothing to move periodically towards the skin causing a cyclic variation in the air gap between the fabric and the skin. At the same time, the clothing movement causes cooling air to periodically flow into the air gap between the fabric and the skin. This paper uses a finite volume model to investigate these two effects and the resultant effect of the protective clothing movement on its performance during flash fire exposure. Special attention is drawn to the air gap model since it responds directly to the clothing movement. A parametric study is carried out to investigate the influence of a wider range of clothing movement. Specifically, the effect of the variation in the periodic movement frequency and amplitude on the clothing performance was investigated. The results show that increasing the movement frequency improves the clothing protective performance, while increasing the movement amplitude worsens the clothing performance.

Numerical simulation of the influence of fabric’s motion on protective clothing performance during flash fire exposure

A finite volume model was developed to simulate transient heat transfer in protective clothing during flash fire exposure. The model accounts for the combined conduction-radiation heat transfer in the air gap between the fabric and skin. The variation in the fabric and air gap properties with temperature and the thermochemical reactions in the fabric are also considered. This study investigates the influence of the air gap in protective clothing on the energy transfer through the clothing and hence on its performance. Different parameters that affect the conduction-radiation heat transfer through the air gap such as the air gap absorption coefficient and the air gap width were studied. Finally, the paper demonstrates that an innovative and potentially significant way to improve protective clothing performance is to reduce the emissivity on the backside of the fabric.

Influence of the air gap between protective clothing and skin on clothing performance during flash fire exposure

The analysis of the air gap between fire-protective clothing and the skin plays a crucial role in evaluating the protective performance of the clothing. However, the more accurate the analysis of the air gap, the more complex the air-gap model. This article introduces a novel air-gap model that stands halfway in terms of accuracy and complexity between other two models that already exist in the literature. A comparison between the performances of fire-protective clothing predicted by using the three air-gap models is discussed in this article. Different parameters that affect heat transfer within the air gap and hence the protective performance of the clothing were studied to assess the novel air-gap model compared with the other two models. Despite its simplicity, the novel air-gap model predicted the performance of fire-protective clothing as accurately as the most realistic model.

Ahmed Ghazy

Papers

Numerical Simulation of Transient Heat Transfer in a Protective Clothing System during a Flash Fire Exposure

Numerical Simulation of Heat Transfer in Firefighters' Protective Clothing with Multiple Air Gaps during Flash Fire Exposure

Numerical simulation of the influence of fabric’s motion on protective clothing performance during flash fire exposure

Influence of the air gap between protective clothing and skin on clothing performance during flash fire exposure

Numerical study of the air gap between fire-protective clothing and the skin: