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Pezhman Payami1 Supervisors: Masud Behnia1, Barry Dixon2

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Presentation on theme: "Pezhman Payami1 Supervisors: Masud Behnia1, Barry Dixon2"— Presentation transcript:

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 Upper airways and nose structure
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 HME as an artificial nose in mechanically ventilated patients
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 HMEs Hygroscopic Hydrophobic Composite (Hygroscopic/Hydrophobic) 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
Conduction Inside/between porous material and the casing Convection Between gas phase and solid portion of porous material Between the casing and the ambient air Radiation Radiation heat transfer across the domain (could be neglected)

8 Methodology Porous Fluid Flow Heat transfer Mass transfer
Modified N-S equations using Darcy’s 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 N-S equations Energy equation for fluid phase by considering porosity effect in the porous zone

9 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 Rate of increase of  of fluid element Net rate of flow of  out of fluid element (convection) of  due to diffusion sources = +

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 , 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 , 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 , 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 , 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: , InTech, Available from: 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 , 2004. ANSYS, ANSYS CFX-Solver Theory Guide. 2010, Canonsburg, PA

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