Mohanapriya Venkataraman
Department of Material Engineering Faculty of Textile Engineering
Prof. Ing. Jiri Miltky, CSc., EURING doc. Rajesh Mishra, Ph.D., B. Tech
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Background
Research Objectives
Materials & Methods
Results & Discussion
Conclusion
Future Direction
Research Outputs
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In extreme cold applications, the role of
the middle layer, in multilayer clothing, is
to protect the human body against
chilling.
Thermal insulation properties are
determined by the physical as well as
structural parameters of fabrics.
Heat transfer normally occurs through
three modes namely; conduction,
convection and radiation.
In general, the heat transport properties can be divided into two groups:
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Steady-state thermal
properties such as thermal
conductivity and resistance
which provide the
information on the warmth
of a fabric.
Transient-state thermal
properties such as thermal
absorptivity which provides
the information of warm–
cool feeling when fabric is
first handled.
Samples
No.
Sample
Description
Thickness
(mm)
Weight
(g/m2)
Density
(kg/m3)
S1
Silica aerogel treated
nonwoven fabrics
(Polyester +Polyethylene)
3.424 272.56 79.66
S2 6.212 499.46 80.42
S3 6.608 440.7 66.73
S4 8.06 535.1 66.39
S5 11.12 733.7 65.99
S6 13.8 942.7 68.33
H1 Needle punched
ROTIS nonwoven structure 9.336 402 43.06
H2 Needle punched
ROTIS nonwoven structure 8.048 407.5 50.64
M1 Elastic Gros Braun patent no. M123A2046
1.848 101.8 55.20
M2 POLARTEC with 100% polyester 1.522 104.1 68.384
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• “Mesoporous” refers to a material that contains pores ranging from 2 to 50 nm in diameter. Most of the pores in an Aerogel fall within this size range.
Aerogels exhibit somewhere between 90 to 99.8+% porosity and also contain a significant amount of microporosity (pores less than 2 nm in diameter).
An aerogel is an open-celled, mesoporous, solid foam that is composed of a network of interconnected nanostructures and that exhibits a porosity
(non-solid volume) of no less than 50%.
S. No. Properties Value range
1 Particle size range 0.1–0.7mm
2 Pore diameter ~20 nm
3 Particle density 120–140 kg/m3
4 Surface chemistry Fully hydrophobic
5 Thermal conductivity 0.012W/mK at 25oC
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Transparency allows use in lighting
Low thermal conductivity minimizes heat loss
Energy efficiency is an important path forward to helping solve our energy crisis
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The micro spacing between fibers is filled with aerogel
particles
Aerogel is covering surface of individual
fibers and is well distributed in the
structure
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Waves maker
Quasi-yarns maker
Input Output
Figure 2: Schematic diagram of a device for manufacturing products being
vertically pleated from thin nonwoven fabrics
2D 3D
PP web
(Top & Bottom layer)
Melt blown polyamide
nanofibres on both sides of
spunbond PP web (Middle layer)
Oldrich Jirsak, Thermo-Insulating Properties of Perpendicular-Laid Versus Cross-Laid Lofty Nonwoven Fabrics, Textile Research Journal February 2000 70: 121-128.
Particle Image Velocimetry
(PIV)
Custom Built Thermal
Measurement Instrument
Custom Built Thermal
Convection Instrument
P.K.Teknik Thermal
Manikin
KES Thermolabo II Alambeta C-Therm (TCi) Thermal
Conductivity Analyzer Air Permeability Tester
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Correlation of Thermal Conductivity Correlation of Thermal Resistance
Mohanapriya Venkataraman, Rajesh Mishra, Jiri Militky, Lubos Hes, Aerogel based nanoporous
fibrous materials for thermal insulation, Fibers and Polymers, Vol 15, No. 7, pp. 1444-1449, 2014,
(Impact factor: 0.881).
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Air permeability is related to porous
structure of the fabric and is directly
proportional to percentage of porosity
of the fabric.
When the pressure level increased, the
flow rate also increased. Irrespective of
different pressure levels.
Low air permeability may be attributed
to the layered structure and high
porosity.
Mohanapriya Venkataraman, Rajesh Mishra, Jiri Militky, Aerogel based nanoporous fibrous
materials for thermal insulation, Fibers and Polymers, Vol 15, No. 7, pp. 1444-1449, 2014
(Impact factor: 0.881).
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Schematic diagram of custom-built instrument for measuring thermal properties.
Schematic diagram of the newly fabricated instrument (single-plate method).
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Thermal conductivity Thermal resistance
Standard error for all the samples was not more than 0.0002 Confidence Ievel @ 95%
-25 -20 -15 -10 -5 0 5 10 15 20 250.018
0.024
0.030
0.036
0.042
0.048
0.054 S1
S2
S3
S4
S5
S6
H1
H2
Th
erm
al
co
nd
ucti
vit
y (
W.m
-1.K
-1)
Temperature (oC)
-25 -20 -15 -10 -5 0 5 10 15 20 25
160
180
200
220
240
260 S1
S2
S3
S4
S5
S6
H1
H2
Th
erm
al
resis
tan
ce (
m2.
K.
W-1
)
Temperature (oC)
Mohanapriya Venkataraman, Rajesh Mishra, Jakub Wiener, T M Kotresh, Jiri Militky, Miroslav
Vaclavik, Novel techniques to analyze thermal performance of aerogel treated blankets under
extreme temperatures, Journal of the Textile Institute, Accepted, June,
http://dx.doi.org/10.1080/00405000.2014.939808, 2014
(Impact factor: 0.722).
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Set Parameters Velocity of air – 2.5 m/s Climatic chamber temperature - -10oC Temperature of hot plate – 60oC
Mohanapriya Venkataraman, Rajesh Mishra, Guocheng Zhu, Jiri Militky, Dynamic heat flux
measurement for advanced insulation materials, Journal of Industrial Textiles (under review).
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Thermal manikin manufactured by P.K.Teknik systems are used to evaluate whole garments systems (or components of garment systems) for heat and moisture management related to garment insulation and breathability. The parallel method was used to calculate clothing insulation using insulation values from the individual segments operated in UST (Uniform skin temperature) mode.
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Linear model Poly 22:
f(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2
Goodness of fit: Coefficients (with 95% confidence bounds):
SSE: 6.798e-010
R-square: 1
Adjusted R-square: 1
RMSE: 1.844e-005
p00 = -0.002523 (-0.0151, 0.01005)
p10 = -7.515e-005 (-0.0005783, 0.000428)
p01 = 5.573 (5.483, 5.663)
p20 = -1.653e-006 (-1.086e-005, 7.556e-006)
p11 = 0.000316 (-0.00167, 0.002302)
p02 = -0.03054 (-0.1919, 0.1308)
Linear model Poly 22:
f(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2
Goodness of fit: Coefficients (with 95% confidence bounds):
SSE: 0.000474
R-square: 0.9137
Adjusted R-square:
0.6979
RMSE: 0.01539
p00 = 6.683 (-6.816, 20.18)
p10 = -0.09256 (-0.3402, 0.155)
p01 = -0.1301 (-0.3412, 0.08104)
p20 = 0.000412 (-0.00079, 0.001614)
p11 = 0.0007745 (-0.0009191, 0.002468)
p02 = 0.000713 (-0.0002566, 0.001683)
3D fit model (Thermal manikin) where x= Thickness (mm),
y=R-Value (m2.K/W) & z= Clo value
3D fit model (Thermal manikin) where x= Fabric density (kg/m3)
y=Heat flux (W/m2) & z= R-value (m2.K/W)
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Q-Q plot for residual normality check Q-Q Predicted Residuals
•The L-R plot is an influential scatter plot that is effective in distinguishing between high leverage points and outliers. •The L-R plot combines the leverage values and the residuals in a single scatter plot.
Mohanapriya Venkataraman, Rajesh Mishra, Guocheng Zhu, Jiri Militky, Dynamic heat flux
measurement for advanced insulation materials, Journal of Industrial Textiles (under review).
L-R Plot (Areal density, Heat flux & Thermal resistance)- Thermal manikin
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Image of wind column attached
during measurement
Components of KES Thermolabo II
Parameters
Room Temp.– 20oC, R.H – 65% B.T. Box – 30oC, 50 cm2, 10 gf/cm2
T Box – 25 cm2, 10gf/cm2
Velocity of air – 10 to 100 cm/s
Mohanapriya Venkataraman, Rajesh Mishra, T. M. Kotresh, Tomonori Sakoi, Jiri Militky, Effect of
compressibility on heat transport phenomena in aerogel treated nonwoven fabrics, Journal of
Textile Institute - accepted, 2015 (Impact factor: 0.722).
10 20 30 40 50 60 70 80 90 100
24
30
36
42
48
54
60
66
72
78 S1
S2
S3
S4
S5
S6
Th
erm
al
resis
tan
ce (
m2.K
/W)
Wind Velocity (cm/s)
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Thermal conductivity of fabrics (KES Thermolabo II & NT-H1)
Thermal resistance of fabrics (KES Thermolabo II & NT-H1)
10 20 30 40 50 60 70 80 90 100
0.010
0.012
0.014
0.016
0.018
0.020
0.022
0.024 S1
S2
S3
S4
S5
S6
Th
erm
al
co
nd
uc
tiv
ity
(W
/m.K
)
Wind Velocity (cm/s)
10 20 30 40 50 60 70 80 90 1000.010
0.012
0.014
0.016
0.018
0.020
0.022
0.024
0.026
0.028
S1
S2
S3
S4
S5
S6
Th
erm
al
co
nd
ucti
vit
y (
W/m
.K)
Wind Velocity (cm/s)
10 20 30 40 50 60 70 80 90 100
24
30
36
42
48
54
60
66
72
78
S1
S2
S3
S4
S5
S6
Th
erm
al
resis
tan
ce (
m2.K
/W)
Wind Velocity (cm/s)
10 20 30 40 50 60 70 80 90 100-2
-1
0
1
2Residuals
Linear: norm of residuals = 2.1666
10 20 30 40 50 60 70 80 90 10065
70
75
80
Air Velocity (cm/s)
Th
erm
al In
su
lati
on
Ra
te (
%)
y = 0.126*x + 64.6
data 1 linear Y = f(X)
Linear model Poly1: f(x) = p1*x + p2 Coefficients (with 95% confidence bounds): p1 = 0.1209 (0.09574, 0.1461) p2 = 64.85 (63.29, 66.41)
Goodness of fit: SSE: 7.859 R-square: 0.9388 Adjusted R-square: 0.9312 RMSE: 0.9911
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The PIV measurement technique allows obtaining information about the current distribution of velocities in two-dimensional array in a flowing fluid.
Basic Principle
Experimental setup
Conventional methods
• (HWA -Hot wire anemometry, LDV-
Laser doppler velocimetry)
• Single-point measurement
• Traversing of flow domain
• Time consuming
•Only turbulence statistics
Particle Image Velocimetry
•Whole-field method
•Non-intrusive (seeding)
• Instantaneous flow field
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Instantaneous measurement of 2 components in a plane
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• Particles appear from out of laser
plane
• Program assumes false interpolations
• Causes inaccurate vector field
Cross Flow
• Have many different velocities
• The vector field is very sensitive to
the dt choice
Seed particles
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If dt is too small, motion is not detected If dt is too large, the wrong motion will be detected
Look for small but noticeable bulk movement
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Figure 35. Vector and scalar maps for temperature gradient 51.0 C.
21.5 oC
23.8 oC
37.5 oC
51.0 oC
Vector and scalar maps for temperature gradient Distance and air velocity diagram.
Scalar maps are used to display the on-screen multiple data derived from the velocity fields. The x and y axis scales in vector and scalar maps illustrate the magnitude and direction of the out-of-plane velocity component.
Mohanapriya Venkataraman, Rajesh Mishra, Darina Jasikova, T M Kotresh, Jiri Militky,
Thermodynamics of aerogel treated nonwoven fabrics at subzero temperatures, Journal of
Industrial Textiles, doi:10.1177/1528083714534711, 2014 (Impact factor: 1.349).
0.1 0.2 0.3 0.40.0
0.1
0.2
0.3
0.4
Exp
eri
men
tal
valu
es (
m2.K
.W-1
)
Theoretical values (m2.K.W
-1)
0.1 0.2 0.3 0.4
0.07
0.14
0.21
0.28
0.35
Exp
eri
men
tal
valu
es (
m2.K
.W-1
)
Theoretical values (m2.K.W
-1)
Alambeta Custom built instrument
0.1 0.2 0.3 0.4
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Exp
eri
men
tal
valu
es (
m2.K
.W-1
)
Theoretical values (m2.K.W
-1)
TCi
Correlation between the theoretical and experimental values of thermal resistance were around R2 = 0.9 for the instruments.
It was concluded that the data generated
from the experiments are theoretically compatible.
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Reference - Oldrich Jirsak and Stanislav Petrik, Recent advances in nanofibre technology: needleless electrospinning, International Journal of Nanotechnology, http://dx.doi.org/10.1504/IJNT.2012.046756
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Equipment – Nanospider (needless electro spinning process) Solution Preparation – 18 wt.% PUR + aerogel , 2 hours stirring
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PUR nanofibre
PUR +Aerogel (powder) PUR +Aerogel (granular)
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Samples Sample description GSM Themal Conductivity
(W.m-1.K-1) Thermal resistance, r
(K.m2.W-1)
NA1 PUR 34.01 0.03362 7.68
NA2 PUR + aerogel (Powder) 33.11 0.03148 8.12
NA3 PUR + aerogel (Granular) 35.28 0.03204 8.88
NA4 PUR + aerogel (Powder) 35.29 0.03262 11.48
NA5 PUR + aerogel (Granular) 38.58 0.03222 11.44
Mohanapriya Venkataraman, Rajesh Mishra, Jaromir Marek, Jiri Militky, Electrospun
nanofibers from PUR and PVDF embedded with SiO2 Aerogel for Advanced Thermal
Properties, Textile Research Journal (under review).
AIR as Insulator | Stagnant Air Conditions
Aerogel as Insulator | Stagnant Air Conditions
The heat retention in the
nonwoven structure with
aerogel is 67% higher than in
the nonwoven structure
without aerogel implying that
aerogel hinders heat transfer,
thus keeping the body warmer.
No.of elements - 13,425
No.of nodes – 2522
Processing time – 6 hours
20 mins
Heat transfer through standard nonwoven without forced convection.
Heat transfer through standard nonwoven with forced convection.
Heat transfer through aerogel treated nonwoven without forced convection
Heat transfer through aerogel treated nonwoven without forced convection
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Aerogel-based fabric samples were found to have considerably lower thermal conductivity and higher thermal resistance even
at extreme temperatures and suitable for thermal insulation under extreme temperature conditions.
The newly fabricated and designed instruments were found to be suitable to measure conductivity and convection at sub-zero
temperatures and convenient for the measurement and evaluation of various temperature variations at different positions of
the fabric.
Electrospun nanofibrous layers from PUR and PVDF embedded with SiO2 Aerogel was found to have application as components
in hybrid battings with high bulk densities.
Simualted results correlated well with the experimental results.
Thermal properties
Thermal resistance
(Rct) of the fabric,
which depends on the
boundary layer of air,
was directly
proportionate to
fabric thickness.
Air permeability was
directly proportional
to percentage of
nanoporosity of the
aerogel based
composite structure.
Thermal insulation is
related to the weight
and compressional
properties of fabric.
High insulation is due
to layered structure
and higher thickness.
The fluid flow motion
accelerated according
to the increasing
temperature gradient.
Mohanapriya Venkataraman
Department of Material Engineering Faculty of Textile Engineering
Thank You