TY - JOUR
T1 - Rational design of sun and wind shaded evaporative cooling vests for enhanced personal cooling in hot and dry climates
AU - Rykaczewski, Konrad
N1 - Funding Information:
I would like to thank Dr. Kenneth Chad Manning and Dr. Akshay Phadnis from ASU for commenting on the manuscript and Pawel Lezanko for discussions about performance of evaporative vests used by bikers. I would also like to thank Agata and Stefan Rykaczewski for providing me the motivation to think about what the future in our desert might look like and how to make it little bit easier for them.
Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2020/5/5
Y1 - 2020/5/5
N2 - As heatwaves become more frequent and intense, personal cooling becomes increasingly important for maintaining outdoor activities and for individuals without access to air conditioning. For about one-third of the current global population living in drylands, evaporating water from clothing is the simplest method of augmenting natural thermoregulation. To cool off, one can simply wear a water-soaked cotton shirt or a highly water-absorbing commercial cooling garment. However, of the stored water, the vast majority is wasted if such apparel is exposed to solar radiation or even slow air flow. Here I show that this issue can be mostly mitigated by incorporating sun and wind shading elements over surface of the cooling garment. First, to enable rational design of these multifunctional shading elements, I develop and benchmark a comprehensive multiphysics finite element model. This model couples conductive, convective, evaporative, and radiative heat transfer with mass transport in natural or forced laminar flow. In the case of natural convection, the model accounts for air buoyancy induced by both temperature and water vapor concentration, which in conditions of interest have a competing effect that can induce flow reversal. Second, I use the model to quantify the impact of geometry and radiative properties of louver and slitted shades on the performance of an evaporative cooling vest in hot and arid conditions. Under natural convection conditions, wearer cooling and water usage efficiency are optimized by introducing about 1.5 cm ventilation gap between the vest surface and the shading structures. In forced convection conditions, however, such a gap results in excessive evaporation rates that are highly wind-speed dependent. Based on these results, I propose a slitted shade design with a collapsible ventilation gap that can provide nearly sun and wind independent moderate cooling rate. If required due to high wearer exertion rate, the intelligently shaded evaporative vest could also provide a higher cooling rate by maintaining the gap. This shaded evaporative vest design concept can minimize the weight of the water stored in the garment and/or significantly increase its cooling period.
AB - As heatwaves become more frequent and intense, personal cooling becomes increasingly important for maintaining outdoor activities and for individuals without access to air conditioning. For about one-third of the current global population living in drylands, evaporating water from clothing is the simplest method of augmenting natural thermoregulation. To cool off, one can simply wear a water-soaked cotton shirt or a highly water-absorbing commercial cooling garment. However, of the stored water, the vast majority is wasted if such apparel is exposed to solar radiation or even slow air flow. Here I show that this issue can be mostly mitigated by incorporating sun and wind shading elements over surface of the cooling garment. First, to enable rational design of these multifunctional shading elements, I develop and benchmark a comprehensive multiphysics finite element model. This model couples conductive, convective, evaporative, and radiative heat transfer with mass transport in natural or forced laminar flow. In the case of natural convection, the model accounts for air buoyancy induced by both temperature and water vapor concentration, which in conditions of interest have a competing effect that can induce flow reversal. Second, I use the model to quantify the impact of geometry and radiative properties of louver and slitted shades on the performance of an evaporative cooling vest in hot and arid conditions. Under natural convection conditions, wearer cooling and water usage efficiency are optimized by introducing about 1.5 cm ventilation gap between the vest surface and the shading structures. In forced convection conditions, however, such a gap results in excessive evaporation rates that are highly wind-speed dependent. Based on these results, I propose a slitted shade design with a collapsible ventilation gap that can provide nearly sun and wind independent moderate cooling rate. If required due to high wearer exertion rate, the intelligently shaded evaporative vest could also provide a higher cooling rate by maintaining the gap. This shaded evaporative vest design concept can minimize the weight of the water stored in the garment and/or significantly increase its cooling period.
KW - Evaporation
KW - Model-based design
KW - Multiphysics modeling
KW - Natural convection
KW - Personal cooling
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U2 - 10.1016/j.applthermaleng.2020.115122
DO - 10.1016/j.applthermaleng.2020.115122
M3 - Article
AN - SCOPUS:85080063167
SN - 1359-4311
VL - 171
JO - Journal of Heat Recovery Systems
JF - Journal of Heat Recovery Systems
M1 - 115122
ER -