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

abdrahim@upm.edu.my

2Department of Mechanical Engineering, Hassan

Usman Katsina Polytechnic

Katsina, Nigeria

ibrahimmuhd1980@gmail.com,

3Department of Mechanical Engineering, College of

Engineering, Universiti of Anbar, Anbar, IRAQ

kafelazeez@yahoo.com

4Faculty of Information Science and Engineering,

Management & Science University, University Drive,

Seksyen 13, 40100 Shah Alam, Selangor, MALAYSIA

minadiir@gmail.com

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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