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AEROGEL APPLICATION ON FIRE CERTIFICATION TECHNIQUES AND
HEAT TRANSFER
A R Abu Talib1, I Mohammed
2, K A Mohammed
3
and N Bheekhun4
1Aerodynamic, Heat Transfer and Propulsion Research
Group (AHTP), Department of Aerospace Engineering
Faculty of Engineering, Universiti Putra Malaysia,
Serdang, Selangor, MALAYSIA
2Department of Mechanical Engineering, Hassan
Usman Katsina Polytechnic
Katsina, Nigeria
3Department of Mechanical Engineering, College of
Engineering, Universiti of Anbar, Anbar, IRAQ
4Faculty of Information Science and Engineering,
Management & Science University, University Drive,
Seksyen 13, 40100 Shah Alam, Selangor, MALAYSIA
Abstract—The study investigates the experimental fire
certification and numerical simulation of heat transfer of silica
aerogel application. The aim of the study is to evaluate the
performance of different types of silica aerogel used for fire
certification and heat transfer application. The fire
certification of aerogel was performed experimentally by
coating the aluminium alloy 2024-T3 with polymer-aerogel and
burn-through according to ISO2685 standard. While the heat
transfers application of the aerogel was conducted by
numerical simulation on different types of channels. From the
result obtained based on fire certification test GEATM 0.125
silica aerogel composite produces less thermal conductivity
than the other two composites with 10.9% and 25.2% greater
than Enova® IC3100 and Hamzel® respectively. Also, the result
of heat transfer shows that 4% concentration of Hamzel®
Produce higher heat exchange than 1%, likewise, trapezoidal
step facing channel produces a better result than the other
three channels. Conclusively, the study indicates that the nano-
fluid silica aerogel can be used in fire certification application
and heat transfer applications with better performance since it
is lightweight in nature and environmentally friendly.
Keywords-flame temperature; fire certification; heat
transfer; nano-fluid; silica aerogel.
I. INTRODUCTION
Global warming, climate change and other related energy issues lead various government agencies, researchers and industrial sectors for an alternative solution with an efficient and lightweight material. A renewable energy source that is greener was chosen to be used in thermal insulation of various components in aircraft and in building structures which is aerogel. Aerogel was used in a different form such as powdered aerogel doped paint, aerogel-based blanket, aerogel fillers in vacuum packed insulation sheets and translucent aerogel pellets [1-3]. Also, the aerogel can be applied in mortar coating or coating by hand lay-up method
when mixed with epoxy or other bonded paint [4, 5]. The aerogel was used in an aeronautical application for thermal spray coating due to its non-carbon dioxide (CO2) gas emission, lightweight and save more space. Silica aerogel was prepared locally by liquefying a rice husk ash in aqueous sodium hydroxide, adding sulphuric acid to the solution, and by developing the gel skeletal in aging process, evacuating the water using alcohol to get alcogel and drying the solution by replacing the alcohol with CO2 gas (replacing the liquid phase with gaseous phase), therefore, the aerogel was produced with little or no shrinkage on the gel.
Silica aerogel was first developed in 1931 by a scientist Samuel Kistler, it is one of the lightest nano-structured material developed on earth surface after graphene aerogel [6]. The aerogel is a gel that its solid network is been conserved with less or no shrinkage after a gas replaces the liquid phase of the aerogel [7]. The following were among the properties of silica aerogel; a low sound velocity of 100m/s, low thermal conductivity of approximately 0.012 W/mK, melting point temperature of 1400⁰C, optical transparency of visible spectrum of approximately 99%, low dielectric constant of approximately 1.0 to 2.0, refractive index of approximately 1.05 and an ultralow bulk density of 0.003 g/cm
3. Manufacturing cost and brittle nature of the
aerogel affect the development and commercialising the aerogel product at its early developing age, but nowadays, the research on the development and application of aerogel is growing very fast due to its nature that concern about its weight, environmental issues and the thermal behaviour of its granular and when used in a composite, also the flexible aerogel-based was introduced by Aspen Aerogel
® for high
temperature and thermal protection [8-11]. The aerogel can be applied in various sectors such as in
biomedical and aerospace industries due to its thermal and acoustical insulation. National Aeronautics and Space Administration (NASA) uses aerogel for aeronautical
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operations in thermal insulation and hypervelocity particle capture in block structures. As reported by Kumar and Kandasubramanian [12]; Longo [13] aerogel was used to protect some components of a gas turbine engine against high flame fire temperature, corrosion and wear when used as thick thermal spray coating on the components. Various types of materials undergo an aerogel thermal spray coating and were deposited on the materials such as metals and their alloys, ceramics and reinforced fibres that change the brittle aerogel to the flexible thermal insulating material [14]. Aspen Aerogel
® accomplishes a study of assessing the
flammability of some component of fire designated zone of an aircraft engine that include electronic engine control (EEC), wires and pipes; whereby the study revealed that it withstand a high temperature of 1100⁰C for 15 minutes using a thickness of 7 mm, while the rear face received a temperature of around 150⁰C within the 15 minutes time. Also, a study was conducted by Mohammed et al. unpublished [5] whereby three types of silica aerogel (Hamzel
®, Enova
® IC3100 and GEA
TM 0.125) were used to
coat an aluminium alloy 2024-T3 and two of the aerogel (Enova
® IC3100 and GEA
TM 0.125) proved to be fireproof
composite, withstand 15 minutes for a flame fire temperature of 1100⁰C ± 80⁰C and a heat flux of 116 kW/m
2 ±10 kW/m
2.
Among the companies that produce powdered silica aerogel used worldwide were Cabot Corporation produces Enova
® Aerogel that uses tetraethyl orthosilicate (TEOS)
drying at ambient temperature, Green Earth Aerogel Technology produces green Earth AerogelTM (GEA
TM) that
uses rice husk ash (RHA) dry at ambient, Maerotech Sdn Bhd produces Hamzel
® that uses rice husk ash and dried
using carbon dioxide (CO2) gas, and JIOS Aerogel produces AeroVa
® Aerogel uses water-glass and dried at ambient.
Also, the other companies were Aerogel Poland Nanotechnology, Aspen Aerogel Inc., BASF SE, Nano High Technology Co. Ltd, Svenska Aerogel AB among others. The use of aerogel in an industrial sector is expected to rise in the coming years as forecasted by Global Aerogel Market [15], whereby oil and gas sectors produce the highest percentage of aerogel usage followed by thermal and acoustic insulation. Effect of nano-fluid was investigated by many researchers among were those focusing on heat transfer across an engine, the performance of microchannel heat sink [16]. The heat transfer across the micro-channel was studied by Koo and Kleinstreuer [17], while Hussein et al., [18] evaluate the performance of SiO2 nano-fluids for automobile radiator where the results indicate a great improvement in the heat transfer.
Different types of silica aerogel were used in this study to certify the fire resistance and heat transfer application of these nanomaterials. The main objective of the study is to evaluate the application of aerogel on fire certification technique and on heat transfer. The aerogel was dissolved in a polymer by stirring and by using ultrasonic bath machine to dissolve all the pores of the aerogel in epoxy resin to form a fused polymer-aerogel, which is used to coat an aluminium alloy 2024-T3 for fire certification. Also, the Hamzel
® silica
aerogel was evaluated by numerical simulation using various channels for heat transfer application. The composite
fabricated was used as a thermal insulator and a firewall blanket in a fire designated zone.
II. MATERIALS AND METHODS
The three types of silica aerogel available in Propulsion Laboratory, Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia were Hamzel
®,
Enova® IC3100 and GEA
TM 0.125. This types of aerogel
were used for experimental fire certification and numerical simulation of heat transfer in the Propulsion Laboratory. Also, a characterisation test of the types of silica aerogel was conducted at Material Characterisation Laboratory at Universiti Putra Malaysia.
Fire certification was conducted on two sheets of aluminium alloy of 1 mm thickness each and the mixture of silica aerogel with epoxy resin/hardener. A 250 mm x 300 mm x 2.5±0.2 mm aluminium alloy sheets was used as the metal alloy, while the mixture of silica aerogel with epoxy resin/hardener was made by dissolving one percent of silica aerogel in an epoxy resin using a mechanical stirrer and an ultrasonic bath machine to dissolve all the pores of the aerogel in the epoxy resin to form a fuse polymer-aerogel. Later after the mixture of epoxy and aerogel cool to room temperature, hardener was added to the mixture and mix using mechanical stirrer. Aluminium alloy sheets were prepared by cleaning its surface with acetone to remove dirt on the surface, whereby the mixture of fused polymer-aerogel was sprayed on the surface of the aluminium sheet by hand lay-up method using a brush. The fabricated composite was compressed using a compression machine and cured for twenty-four hours. Fire test was conducted on the fabricated samples for fifteen minutes using a propane-air burner according to ISO2685 standard (flame temperature of 1100°C ± 80°C, the heat flux of 116 kW/m
2 ± 10 kW/m
2,
with 3-inches distance between the samples and burner face) [19]. The average result of each composite was recorded accordingly using a data logger. The thermal conductivity of the three composite was evaluated using (1).
K = (W x D)/(A x ∆T) (1) where K = is thermal conductivity of the composite plate (W/mK)
W = heat flow (W) D = Thickness of samples (m) A = Area (m
2), and
∆T = Temperature difference. Also, the three types of silica aerogel were used to
determine the thermal diffusivity of each nanofluid. NETZSCH LFA 457 MicroFlash
® laser flash apparatus with
3 replicates were used to evaluate the thermal diffusivity of all the three nano-powders. The measurements were conducted in line with heat source probe at 25.0, 39.8, 59.8, 79.8 and 99.9°C. The laser voltage is ~2,978.0 V and the pulse width is 0.50 ms. It is used to determine the thermal diffusivity and specific heat capacity of materials. The front surface of a plane-parallel sample is heated by a short energy light pulse, as shown in Fig. 1. The thermal diffusivity and specific heat capacity can be determined simultaneously based on the temperature excursion of the rear face measured using an infrared (IR) detector. The latter parameter can be
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measured provided that a reference specimen is used. The thermal conductivity of the material can be determined by knowing these thermo-physical properties and the density value using (2):
λ(T) = a(T) • Cp(T) • ρ(T) (2) where: λ = thermal conductivity of silica aerogel (W/(m•K))
a = thermal diffusivity (mm²/s) Cp = specific heat (J/(g•K)) ρ = bulk density (g/cm
3)
Figure 1. Laser flash technique used to heat the sample.
Fig. 2 shows the thermal diffusivity of the three aerogels
(Hamzel®, Enova
® IC3100 and GEA
TM 0.125). It is apparent
that the Hamzel® silica aerogel nanopowder has the highest
thermal diffusivity, followed by GEATM
0.125, and least of
all, the Enova® IC3100 silica aerogel nanopowder. Based on
the thermal diffusivity measurements, the Hamzel® silica
aerogel nanopowder was chosen for the numerical
simulations. The GEATM
0.125 and Enova® IC3100 silica
aerogel nanopowders are not chosen because of their lower
thermal diffusivity and moreover, these nanopowders tend
to dissolve in water, which will alter their physical
properties [20]. The lightweight and low density of the
Hamzel®
silica aerogel nanopowder compared with the
other types of nanopowders (i.e. Al2O3, ZnO, CuO, and
SiO2) unpublished [21] will reduce pumping power, which
in turn, decreases the pressure drop and skin friction
coefficient. This is highly desirable since the volume
fraction of the Hamzel® silica aerogel nano-powder can be
increased in order to significantly enhance heat transfer of
the heat exchanger.
Figure 2. Measured thermal diffusivity of the Hamzel®, Enova® IC3100
and GEATM 0.125 silica aerogel nanopowders.
III. RESULT AND DISCUSSION
The results of the investigation were reported in two-part, viz fire certification and heat transfer. The fire certification part result was obtained after calibrating the burner according to ISO2685 standard. The average result obtained from the rear face temperature of the composite of three K-type thermocouples was presented in Table 1, while the composite characteristic result was presented in Table 2.
TABLE I. FACE AVERAGE TEMPERATURE OF THE COMPOSITES
Time (min) Temperature (ºC) of Composites
Hamzel® Enova
® IC3100 GEA
TM 0.125
1 73 67 64
2 125 117 112
3 197 176 173
4 265 249 242
5 324 291 285
6 374 334 326
7 420 383 375
8 492 431 423
9 523 469 463
10 631 495 487
11 672 541 532
12 718 569 561
13 - 630 619
14 - 669 657
15 - 723 710
TABLE II. BURN-THROUGH RESPONSES OF THE COMPOSITES
Behaviour Composite
Hamzel® Enova
®
IC3100
GEATM
0.125
Burn-through Time (min)
12:37 seconds
˃ 15 ˃ 15
Property Fire resistant Fireproof Fireproof
As observed from the two tables Hamzel® composite
burned before the standard time, therefore it is fire resistant composites since it passes five minutes. While the other two composites were fireproof composite, withstand a standard
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flame for fifteen minutes, with GEATM
0.125 having the lowest percentage of flame penetration. The thermal conductivity of the three composites was evaluated using equation 1 as indicated in Fig. 3.
Figure 3. The thermal conductivity of aerogel composites.
The silica aerogel used in the composites has lightweight properties, non-toxic and increases the thermal resistance of the composites. The aerogel is an excellent thermal insulator and saves space that required less layered as used in thermal coating for fire protection application. The used of aerogel on the fire zones is to safeguard lives and properties from chances of detecting and preventing the hazard that will be caused by fire. Also, the aerogel was used to fulfil the certification requirement of the fire designated zone of different components used on different devices as it withstands a high temperature using a less layered metal; it reduces the tendency of delamination of the metals.
The second part of the results was based on heat transfer enhancement and fluid flow characteristics of the novel nanofluid Hamzel
® silica aerogel-water nano-fluid. The
performance of nanoparticle concentration on the average Nusselt number (Nu), pressure drop, and skin friction coefficient of Hamzel
® silica aerogel-water nano-fluid in the
laminar flow region was numerically simulated; whereby the aerogel nano-particles was dispersed in distilled water at various volume fractions (0, 1, and 4%). The average nanoparticle diameter is 25 nm. Fig. 4 indicates the effect of aerogel nano-particle concentration on the average Nu of the aerogel-water nano-fluid for the flat channel, backward-facing step channel, and triangular and trapezoidal facing step channels in the laminar flow region. The amplitude height and wavelength of the corrugated wall is fixed at 4 mm and 2 cm, respectively.
Figure 4. Effect of nanoparticle concentration on the average Nu of the
Hamzel® silica aerogel-water nano-fluid in the laminar flow region.
The most encouraging finding here is that the average Nu
increases significantly as the Re is increased, regardless of the type of channel, which is due to higher temperature gradients at the channel walls. It can also be observed that for a given Re, the average Nu increases with an increase in the nanoparticle concentration since the addition of the silica aerogel nano-particles into the base fluid improves the thermal conductivity of the working fluid, which leads to a higher heat transfer rate. Indeed, the distilled water has the lowest average Nu due to its poor thermal conductivity. It also indicates that in Fig. 4(c) and (d) when Re increase over 250 sudden increase occur in the Nu this is due to the double effect of step and the corrugated wall led to more distribute of fluid motion led to increasing Nu.
Fig. 5 shows the effect of nanoparticle concentration (0, 1, and 4%) on the pressure drop of the Hamzel® silica aerogel-water nano-fluid for the four types of channel investigated in this research. The Re is varied from 100 to 1,500, indicating that the flow is in the laminar region. It can be seen that there is an increase in the pressure drop with an increase in the Re, and the pressure drop is most apparent for the nano-fluid containing 4% of Hamzel® silica aerogel nano-particles. The increase in pressure drop is due to the increase in the fluid viscosity at higher nanoparticle concentrations. When the nanoparticle diameter is kept constant, the effective viscosity increases when the volume fraction of nanoparticles is increased, which increases the pressure drop penalty. It is known that fluids with a higher
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viscosity will increase the shear stress between the fluid and channel walls as well as between the fluid layers.
Figure 5. Effect of nanoparticle concentration on the pressure drop of the
Hamzel® silica aerogel-water nano-fluid in the laminar flow region.
Skin friction coefficient of Hamzel® silica aerogel-water
nanofluid for all the channels as shown in Fig. 6 that shows the effect of nanoparticle concentration (0, 1, and 4) in the laminar flow region. It is apparent that the skin friction coefficient decreases with an increase in the Re. The nano-fluid containing 4% of Hamzel
® silica aerogel nano-particles
has the highest skin friction coefficient among all of the working fluids, which is due to higher fluid viscosity, which leads to higher pressure drop. There is a slight difference in the skin friction coefficient between the nano-fluid with a volume fraction of 4% and that with a volume fraction of 1% and 0%. This difference is even more apparent for the backward-facing step channel, and triangular and trapezoidal corrugated facing step channels. In general, the difference in the skin friction coefficient values is caused by the pressure drop, which is different for each volume fraction. The distilled water has the lowest skin friction coefficient, as expected.
Figure 6. Effect of nanoparticle concentration on the skin friction of the
Hamzel® silica aerogel-water nano-fluid in the laminar flow region.
Fig. 7 shows the effect of channel type on the average
Nu, pressure drop, and skin friction coefficient of the Hamzel
® silica aerogel-water nano-fluid containing 4% of
Hamzel® silica aerogel nano-powder. The nanoparticle
diameter is 25 nm. The amplitude height and wavelength is fixed at 4 mm and 2 cm, respectively. The Re range is 100–1,500 nm. It is evident from the results that there is a significant increase in the average Nu with an increase in Re, particularly for the triangular and trapezoidal corrugated facing step channels. This is indeed expected since the fluid velocity and temperature gradients at the channel walls increase, which improves the heat exchange between the channel walls and the working fluid.
Figure 7. Effect of channel type on the average Nu and pressure drop of
the Hamzel® silica aerogel-water nano-fluid in the laminar flow region.
The trapezoidal corrugated facing step channel has the highest average Nu since this channel design significantly enhances fluid mixing, whereby large recirculation regions
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are generated in the diverging sections of the corrugated facing step channel. As expected, the flat (smooth) channel has the lowest average Nu due to poor fluid mixing. The trend is similar for the pressure drop, whereby there is a significant increase in the pressure drop as the Re is increased, and this increase is most pronounced for the triangular and trapezoidal corrugated facing step channels.
The average Nusselt number (Nu) enhancement ratio (i.e. heat transfer enhancement ratio) of the Hamzel
® silica
aerogel-water nano-fluid in the laminar flow region result was shown in Fig. 8. The results of three channels (backward, triangular and trapezoidal facing step channels). The nanoparticle concentration is 1 and 4%. In general, the average Nu enhancement ratio varies, depending on the type of channel, Re, and volume fraction of the nanoparticles. The highest average Nu enhancement ratio is obtained for the trapezoidal corrugated facing step, followed by triangular corrugated facing step channel and backward-facing step channel. The highest average Nu enhancement ratio is achieved when the volume fraction of the Hamzel
® silica
aerogel nanoparticles is 4%.
Figure 8. Average Nu enhancement ratio of the Hamzel® silica aerogel-
water nano-fluid in the laminar flow region.
Fig. 9 present the result based on the comparison between Hamzel
® silica aerogel-water and SiO2-Water for
the Nuav. The silica aerogel-water gives best Nuav compared with SiO2. This is due to the high thermal conductivity of Hamzel
® silica aerogel-water compared with SiO2-Water.
Also, we can refer to when Re increase over 250 sudden increase occurs in the Nu this is due to the double effect of step and the corrugated wall led to more distribute of fluid motion led to increasing Nu.
Figure 9. Comparison average Nu and Pa of the Hamzel® silica aerogel-
water and SiO2- water nano-fluids.
The performance evaluation criteria (PEC) of Hamzel®
silica aerogel-water and SIO2-Water nano-fluids was compared in which Hamzel
® silica aerogel-water has greater
values (high thermal performance). Therefore, the two nano-fluids considered shows that there is an improvement in heat transfer than the increase in pressure drop and friction factor since they all have a value of PEC greater than 1. Fig.10 shows the Performance evaluation criteria for Hamzel
® silica
aerogel-water is better than the SIO2-Water nano-fluids. This is due to the high thermal conductivity of Hamzel
® silica
aerogel-water compared with SiO2-Water.
Figure 10. Performance evaluation criteria of combined nano-fluids with
corrugated facing wall for 4% Hamzel® silica aerogel-water and 4% SiO2- water.
Among the properties of the aerogel composites used in
this study were less weight, high melting temperature, good
thermal conductivity between 1.3 and 1.6 W/mK, high heat
transfer, low density, environmentally friendly, negligible
smoke production during fire test, lower production cost and
simple manufacturing process. The newly developed
composite was lightweight in nature, produces less layered
composites that overcome the problem of delamination of
composite layered during the fire and other tests. The
aerogel also produces a lower thermal diffusivity between
0.02 to 0.58 mm2/s.
IV. CONCLUSION
The investigation conducted was based on developing new, lightweight, greener and environmentally friendly materials for fire certification and heat transfer applications. The objective of the study was achieved as the materials used to compete with the existing materials and even has a greater performance than it. The results obtained from fire certification shows that the nanoparticles silica aerogel can withstand a high temperature within a specified time, whereby GEA
TM 0.125 composite recorded the highest flame
resistant and least thermal conductivity than the other two types. The result shows that GEA
TM 0.125 has a higher flame
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resistance of 5.6% and 10.4% than Enova® IC3100 and
Hamzel® with also 10.9% and 25.2% respectively in terms of
thermal conductivity. In terms of heat transfer, the numerical simulations show
the effect of Hamzel® silica aerogel nano-particle
concentration (0, 1, and 4%), nano-particle diameter is 25 nm based on different channel shape on the average Nu and pressure drop for a novel nano-fluid (Hamzel
® silica aerogel-
water nano-fluid) in the laminar flow region. The result obtained for 4% concentration shows that the nano-fluid is promising working fluid for heat exchangers, more especially on the trapezoidal corrugated facing step channel; which gives the best heat transfer enhancement. The Nusselt number enhancement ratio reached to 80% and 85% when using Hamzel
® silica aerogel-water in the trapezoidal-
corrugate at Nanoparticle concentrations of 1% and 4% respectively. The trapezoidal-corrugate provides the highest thermal-hydraulic performance at amplitude height of 4 mm and 2 cm wavelength flowed by a triangle having the same property.
The future research to be carried out on fire certification is by reducing the thickness of the composite, whereby the thickness of aluminium alloy will be reduced and increasing the percentage of silica aerogel in the polymer.
ACKNOWLEDGMENT
The authors would like to thank the Universiti Putra Malaysia for providing the financial support through the IPS Grant scheme no. 9538500.
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