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Numerical Analysis of heat and mass transfer in Heat and Moisture Exchanger (HME)

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 Vincent’s Hospital, Melbourne. Contents. Significance

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Numerical Analysis of heat and mass transfer in Heat and Moisture Exchanger (HME)

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  1. Numerical Analysis of heat and mass transfer in Heat and Moisture Exchanger (HME) Pezhman Payami1 Supervisors: Masud Behnia1, Barry Dixon2 1 Fluid Dynamics Group, School of Mechanical Engineering, 2 Saint Vincent’s Hospital, Melbourne

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

  3. Significance • 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

  4. Significance • 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

  5. General Classification of HMEs • 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

  6. Problem Specification 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 Patient side (T=34ºC, RH=100%) • The flow is considered incompressible/ steady/ laminar

  7. Heat Transfer Mechanisms

  8. Methodology

  9. Net rate of flow of  out of fluid element (convection) Rate of increase of  of fluid element Rate of increase of  due to diffusion Rate of increase of  due to sources + = + Methodology • 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 Darcy’s law is governed by • A computational fluid dynamics package, ANSYS CFX 13, is used to simulate fluid flow and heat transfer in the HME

  10. 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. • KayaAhmet, AydinOrhan, 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 • 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

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