Thermal Fluid Group Meeting: Nano-engineered Porous Materials' Heat Fluxes, Lab Reports of Materials science

Download Thermal Fluid Group Meeting: Nano-engineered Porous Materials' Heat Fluxes and more Lab Reports Materials science in PDF only on Docsity! Thermal-Fluid Sciences Group Meeting: Fridays 11 am 12 noon in UNTRP B140 – Dr. Matthew J. Traum Assistant Professor, MEE Department © 2008 Matthew J. Traum Thermal Fluid Sciences Group @ UNT Today’s Agenda 1. Assign TFS Group Officer Positions 2. Seminar by Dr. Traum: L h fl h hatent eat uxes t roug nano- engineered porous materials Thermal Fluid Sciences Group @ UNT Research Objectives 1. Big Picture: self cooling protective garment 2 Study heat and mass transport. enabled by membranes with nano- and micro-scale pores 3. Create engineering correlations to inform design of future systems Thermal Fluid Sciences Group @ UNT Setting the Scene: Soldier Thermal Load Baghdad, Iraq summer desert conditions: 120 °F (49 °C) at 10 - 50 % relative humidity Heat Sources: Metabolic: 400 watts/m2 (jogging) Solar Insolation: 1000 watts/m2 Inward Conduction From Ambient Environment Ab 1400 / 2 b d fout watts m must e remove rom the soldier system to maintain thermal equilibrium, and Tambient > TsoldierThermal Fluid Sciences Group @ UNT Inspirational System – The Camel Micro-pores with hydrophobic surface coatings enable control of Body BodyA B evaporation front location; porous barrier materials behavior like camel fur. A S S’ Evaporation At Skin Surface Evaporation At Fur Surface Air Air Camel Other Mammal Thermal Fluid Sciences Group @ UNT Adapted from original in Schmidt-Nielsen (1979) Study of Pore Size Hytrel® is a polyester elastomer, formed by condensation of polybutylene terephthalate (PBT) and terathane (polyether) The PBT . blocks form the hard segment and the polyether blocks form the soft segment. 50 Nominally 13μm effective diameter pores μm Nucrel® is a random copolymer of ethylene and methacrylic acid. The membranes used contain 12% methacrylic acid by weight. Nominally 1.2μm effective diameter pores5μm Kapur, DuPont, 2005 Thermal Fluid Sciences Group @ UNT Nucrel Membrane – Straight Through Pores Normal to the Membrane Face Sample was prepared by microtome slicing, and was imaged under SEM Thermal Fluid Sciences Group @ UNT Properties Important to Heat and Mass Transfer Overlay Membrane Thickness, L Membrane Porosity, εv Ave. Pore Area, Ap Effective Pore Diameter, de [ ] [μm] [%] [μm2] [μm] Nucrel A 112 ± 3 7.6 ± 2.5 0.8 ± 0.3 1.0 ± 0.2 Nucrel B 119 ± 4 7.5 ± 3.3 1.6 ± 0.5 1.4 ± 0.2 Hytrel A 113 ± 3 11.2 ± 3.1 161 ± 36 14.2 ± 1.6 Hytrel B 123 ± 3 8.6 ± 2.7 126 ± 31 12.6 ± 1.5 Latex 141 ± 3 0 N/A N/A 2 1 2 ⎟⎟ ⎞ ⎜⎜ ⎛ = p A d ⎠⎝ π e Thermal Fluid Sciences Group @ UNT Deep Evaporation Chamber 33 mm 121 mm Thermal Fluid Sciences Group @ UNT Buoyancy-Driven Flows Within Chamber RH 0%≈ Critical Ra Number = 1708 Critical Ra Number = 1101 chirality demonstrated by experimental tracers Circulation’s Crucial Benefits 1. Head space circulation assures water-saturated air reaches membrane 2. Liquid circulation allows majority of input heat to enter the liquid, where evaporation can occur 3000 Rayleigh Numbers Define Operational Envelope 2500 Head Space Rayleigh NumberWater Charge Rayleigh Number 2000 m be r Critical Head Space Ra # = 1708 1500 yl ei gh N um Critical Water Charge Ra # = 1101 1000 R ay Operating Range Too Much LiquidToo 500Little Liquid 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Charge Mass [grams] Micro-porous Membranes Facilitate Significant Cooling 55.0 Θ=0 Fra 40 0 45.0 50.0 C ] Nucrel Membrane Closed Chamber 13.4 ± 2.4°C 14.0 ± 2.0°C actional A cΘ=0 4 30.0 35.0 . e - T am b) [o C Hytrel Membrane 35.2 ± 1.3°C ccom plishe . 20.0 25.0 ra tu re (T ba se ed C ooling,Θ=1 5 0 10.0 15.0 Δ T em pe r Open Chamber , Θ -5.0 0.0 . 0 25 50 75 100 125 150 175 200 225 250 275 300 Time [minutes] Traum, M.J. et al., ASME J. Heat Transfer, Recommended for Publication Pending Revisions (submitted 7/31/2006). 5 5 6 Pore Diameter [1-15μm] Does Not Impact Mass Transport Membrane volume flux Nucrel (1.0μm) 4.5 5 . m s] rates are consistent with human sweat rates: 2.1 L/(m2-hr) vs. Open Chamber Sample B 3.5 4 gr am s] s L os t [ gr am 0.5 – 1.5 L/(m2-hr) Hytrel (14.2μm) Sample A 2.5 3 as s L os t [ g at iv e M as s Nucrel (1.4μm) Sample A 1 1.5 2M a C um ul a Hytrel (12.6μm) Sample B 0 0.5 Closed Chamber 0 25 50 75 100 125 150 Time [minutes] Traum, M.J. et al., ASME J. Heat Transfer, Recommended for Publication Pending Revisions (submitted 7/31/2006). Comparison of Experimental DH2O,air to Canonical Model ( ) ( ) drrdrrrrrm r r chamber∫ ∫ = = ⎪ ⎬ ⎫⎪ ⎨ ⎧ ⎥ ⎤ ⎢ ⎡ −⋅ = 0 0 )()(12 ρρρρπ& ( ) ( ) ( ) ( ) ( )rRrRrRrvrrRrRr ambient r downstreamBLmembraneupstreamBLmembranedownstreamBL ave o o ⎪⎭⎪⎩ − ⎥⎦⎢⎣ + − + ,,, )()(δ membrane b LR = vairOH mem rane D ε⋅,2 Knudsen Transition Apparatus-ind. Overlay Number (λ/de) Theory DH2O,air Experimental DH2O,air % Difference 2 2[ ] [ ] [m /s] [m /s] [%] Nucrel, Sample A 0.099 2.12E-05 1.95E-05 -9 Nucrel, Sample B 0.071 2.18E-05 2.68E-05 19 Hytrel, Sample A 0.007 2.33E-05 1.68E-05 -38 Hytrel, Sample B 0.008 2.36E-05 1.68E-05 -40 Latent Heat Fluxes Through Nano- engineered Porous Materials Backup Slides Follow Matthew J. Traum mtraum@unt.edu Thermal Fluid Sciences Group @ UNT ●ASHRAE Fundamentals Handbook, Published by the American Society of Heating, Refrigerating and References Air-Conditioning Engineers, 2005. ● Holt, J.K., Park, J.G., Wang, Y., Stadermann, M., Artyukhin, A.B., Grigoropoulos, C.P., Noy, A., Bakajin, O., “Fast Mass Transport Through Sub–2-Nanometer Carbon Nanotubes”, Science, Volume 312, Pages 1034-1037, May 2006. ● Kapur, V., DuPont, personal e-mail communication (10/4/2005). ● Lechner, N., Heating, Cooling, Lighting: Design Methods for Architects, John Wiley & Sons, Inc., 2001. ● Marshal, S.L.A., The Soldier’s Load, The Marine Corps Association, Quantico, VA., First Published 1950. ● Mills, A. F., Basic Heat & Mass Transfer, 2nd Edition, Prentice Hall, Inc., Upper Saddle River, NJ, 1999. ● Mills, A. F., Basic Heat Transfer, 2nd Edition, Prentice Hall, Inc., Upper Saddle River, NJ, 1999. ● Nellis, G., Evans, J., Klein, S., Albrecht, S., “Updated Assessment of Microclimate Cooling Options for the Individual Soldier”, U.S. Army Soldier & Biological Chemical Command, Technical Report, February 2003. ● Ring, E.F.J., “Quantitative Thermal Imaging”, Physical Physiology Measurements, Vol. 11, Supplement A, Pages 87 – 96, 1990. ● Schmidt-Neilsen, Knut, Desert Animals: Physiological Problems of Heat and Water, Dover Publications, 1979. ● Traum, M.J., Griffith, P., Thomas, E.L., Peters, W.A., “Latent Heat Fluxes Through Nano-engineered Porous Materials”, ASME Journal of Heat Transfer, Accepted and in press, anticipated April 2008. ● Tritton, D.J., Physical Fluid Dynamics, Van Nostrand Company, Ltd., Wokingham, England, 1977. ● Ullal, C.K., Maldovan, M., Thomas, E.L., Chen, G., Han, Y., Yang, S., “Photonic crystals through holographic lithography: Simple cubic, diamond-like, and gyroid-like structures”, Applied Physics Letters, Vol. 84, No. 28, June 2004. Soldier Thermal Load – Human Body Hot Spots Thermography a branch of physiology that relates skin temperature to injury in which infrared cameras are used to measure temperature variations on the surface of the body http://www.miditherm.com The upper chest and back Human Desert Sweat Rates of the neck are potential human body “hot spots” f i i h d Long term sweat rates of 0.5 – 1.5 liters/m2-hr o nterest; r g t un er the soldier’s body armor Ring (1990) Schmidt-Neilsen (1979) Deep Chamber Heat and Mass Transport Experimental Apparatus Thermal Fluid Sciences Group @ UNT Begin with a mass continuity balance on a fluid element in the vicinity of the upstream membrane face. The Derivation of Mass Transfer Model Equation element is a cylindrical shell of radius r, width Δr, and height δ(r), approximated as the boundary layer thickness. The top surface of the element is the upstream membrane face, and the element follows the fluid flow from the outer radius of the evaporation chamber, ro, towards the chamber center, r = 0, through incremental reductions in its radius by Δr. By mass continuity, the water vapor contained within the element must equal the mass entering minus the mass leaving the element: dt dm dt dm rrdA dt rd outin −=)()()( δρ B di th l ft h d id i T l S i d li lik t t dt dm t dt dm rrrdA dr rd outin Δ−Δ=Δ )()()( δρ y expan ng e e an s e n a ay or er es an cance ng e erms, )()()( r dmrdmrrrdArd outin Δ−Δ=Δ δρ To put the fluid element in a Eulerian reference frame, a substitution is made for Δt to give: )()( rvdtrvdtdr Recognizing that the mass flows in and out of the fluid element are governed respectively by diffusion (in) through the boundary layer on the upstream membrane face and diffusion (out) through the membrane and downstream boundary layer the following substitutions are made )( )( , rdA R r dt dm upstreamBL chamberin ρρ −= )( )( , rdA RR r dt dm downstreamBLmembrane ambientout + − = ρρ , , Derivation of Mass Transfer Model Equation (continued) 0≈ambientρ ⎥ ⎤ ⎢ ⎡ −− bi th b rrrd )()(1)( ρρρρρ due to a cross flow of dry nitrogen. Finally, combining the previous expressions and canceling like terms, the desired result is obtained: Boundary Condition: ⎥⎦⎢⎣ + −= downstreamBLmembrane am en upstreamBL c am er RRRrvrdr ,,)()(δ Both boundary layer resistances are calculated as described in the following slides. All of these equations can be ( ) ( )2Trr sato ρρ == drdr RR r R r RR rm r ambient r chamber ave ∫ ∫ = = ⎪ ⎪ ⎬ ⎫ ⎪ ⎪ ⎨ ⎧ − ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ + − − + ⋅ = 0 0 )()( )()( 12 ρρ ρρ δ π & combined to create the following complete canonical expression: rvrr r downstreamBLmembraneupstreamBLmembranedownstreamBLo o ⎭⎩ ,,, which was solved numerically via MATLAB for the unique combination of Rmembrane and ρ(r) that satisfies the boundary condition.