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Numerical Analysis of heat and mass transfer in Heat and Moisture Exchanger (HME) Pezhman Payami 1 Supervisors: Masud Behnia 1, Barry Dixon 2 1 Fluid Dynamics Group, School of Mechanical Engineering, 2 Saint Vincents Hospital, Melbourne

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Contents Significance General Classification of HMEs Problem Specification Heat Transfer Mechanisms Methodology References 2

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Significance 3 Normal breathing and nose function To warm and humidify inspired air in upper airways to reach the alveoli as saturated vapour at the core temperature To maintain core body temperature within an appropriate range To prevent drying of the tracheal mucosa and other structures causing respiratory mucosal dysfunction and hypothermia Upper airways and nose structure

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Significance 4 Mechanically ventilated patients When the upper airways are bypassed by oral or nasal endotracheal intubation it is essential to seek an alternative way to heat and humidify inspiratory gases HME is an artificial nose (passive humidifier) that traps expiratory heat and moisture in a medium and returns a portion of it to the next inspiration HME as an artificial nose in mechanically ventilated patients

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General Classification of HMEs 5 HMEs Hygroscopic Hydrophobic Composite (Hygroscopic/Hydrophobic) Composed of plastic foam, wool or paper condensation surfaces with a low thermal conductivity Impregnated with a hygroscopic chemical such as Calcium Chloride to improve moisture conserving properties Large pleated surface composed of ceramic fibres Covered by a synthetic resin that repels the water Felt filter layer such as polypropylene non- woven fibre subjected to an electrical field to improve filtration efficiency Moisture exchange component of polyurethane open-cell foam or cellulose fibre (either cotton or wood pulp) impregnated with Calcium Chloride

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Problem Specification 6 Patient side (T=34ºC, RH=100%) Ventilator side Peak airway pressure: less than 30 cmH2O Flow rate: 30 l/min Frequency: 12-16 times per minute Temp and RH: room air conditions could be assumed for the first run The flow is considered incompressible/ steady/ laminar

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Heat Transfer Mechanisms 7

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Methodology 8 Porous Flow Modified N-S equations using Darcys law Linear directional loss defined by streamwise and transverse permeabilities Heat transfer Energy equation for solid phase Interfacial heat transfer between the fluid and solid considering overall heat transfer coefficient between the fluid and the solid Mass transfer Mass concentration of each component according to ideal gas equation of state Fluid Flow N-S equations Heat transfer Energy equation for fluid phase by considering porosity effect in the porous zone Interfacial heat transfer between the fluid and solid considering overall heat transfer coefficient between the fluid and the solid Mass transfer Mass concentration of each component according to ideal gas equation of state

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Methodology 9 General transport equation Where is a general variable that can be replaced with macroscopic properties of the fluid such as pressure, velocity components or temperature to describe the behavior of the flow In the porous zone the Darcys law is governed by A computational fluid dynamics package, ANSYS CFX 13, is used to simulate fluid flow and heat transfer in the HME Rate of increase of of fluid element Net rate of flow of out of fluid element (convection) Rate of increase of due to diffusion Rate of increase of due to sources =++

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References Tariku F, Kumaran M.K., Fazio P., Transient Model for Coupled Heat, Air and Moisture Transfer Through Multilayered Porous Media, International Journal of Heat and Mass Transfer, 53, pp. 3035-3044, 2010. Baggio P., Bonacina C., Schrefler B.A., Some Considerations on Modelling Heat and Mass Transfer in Porous Media, Transport in Porous Media, 28, pp. 233-251, 1997. Kaya Ahmet, Aydin Orhan, Dincer Ibrahim, Numerical Modelling of Heat and Mass Transfer During Forced Convection Drying of Rectangular Moist Objects, International Journal of Heat and Mass Transfer, 49, pp. 3094-3103, 2006. R. Younsi R., Kocaefe D., Poncsak S., Kocaefe Y., Gastonguay L., CFD Modelling and Experimental Validation of Heat and Mass Transfer in Wood Poles Subjected to High Temperatures: a Conjugate Approach, International Journal of Heat and Mass Transfer, 44, pp. 1497-1509, 2008. Eva Barreira, João Delgado, Nuno Ramos and Vasco Freitas (2010). Hygrothermal Numerical Simulation: Application in Moisture Damage Prevention, Numerical Simulations - Examples and Applications in Computational Fluid Dynamics, Lutz Angermann (Ed.), ISBN: 978-953-307-153-4, InTech, Available from: http://www.intechopen.com/articles/show/title/hygrothermal-numerical-simulation-application-in-moisture- damage-prevention http://www.intechopen.com/articles/show/title/hygrothermal-numerical-simulation-application-in-moisture- damage-prevention Dellamonica J., Boisseau N., Goubaux B., Raucoules-Aime M., Comparison of Manufacturers Specifications for 44 Types of Heat and Moisture Exchanging Filters, British Journal of Anaesthesia, 93 (4), pp. 532-539, 2004. ANSYS, ANSYS CFX-Solver Theory Guide. 2010, Canonsburg, PA 10

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