Bio-based synthesis of a sustainable Nano drag reducing agent for sprinkler irrigation systems

High-grade silica Nano particles were extracted from rice husk using a straightforward thermochemical method. The specifications of the isolated Nano particles were verified using a variety of material characterization techniques. Siloxane and silanol groups were notably visible in the spectra obtained using Fourier transform infrared spectroscopy. Scanning Electron Microscopy images revealed main Nano particles alongside secondary Micro particles. The size of the particles varied from 14.56 to 33.72 nm. The drag reduction experiments were took place in a facility that uses a forced closed loop. The extracted Nano silica was mixed with faucet water at a weight concentration of 50 to 400 mg/l to reduce drag. Records of pressure loss were obtained along a 186 cm carbon steel tube with internal diameters of 1.6 and 2.7 cm and variable flow rates of solutions at a comfortable temperature of 25 °C. The friction factor values were found to be around Blasuis asymptote for pure water but they were found to be near maximum drag reduction asymptotes when using the Nano material. A maximal drag reduction of nearly 68 % was achieved by using 400 ppm of Nano silica. It was observed that there is a crucial Reynolds number around 96000 that should not be surpassed since any additional increase results in a drop in drag reduction. Furthermore, a relationship between wall shear stress and velocity of the fluid was established.


Introduction
The reduction of drag impact is incredibly intriguing from a factual perspective.Pipelines carry the majority of liquids, thus reducing frictional drag offers significant cost savings and increased transport efficiency.Irrigation systems, transport of oil through pipelines, cooling and heating systems, firefighting, sewage productivity and other commercial applications of drag-reduction have all been successful.
Many researchers have proposed a variety of approaches for lowering drag for a wide range of applications.One of these methods relies on the use of baffles of various heights in the turbulent flow zone to suppress turbulent eddies [1].Other methods include oily materials or bubble layers to decrease skin friction [2].However, adding minute amount of chemical agents to fluids delivered through pipes is the most effective method of reducing drag [3].
Polymers were utilized first as drag reduction additives to lower frictional drag in turbulent water flow.The friction factors of viscoelastic fluids in turbulent flow regions are substantially lower than those of pure viscous fluids.Alternative additives were investigated since polymeric solution is severely influenced by mechanical and thermal breakdown, which could lead to a reduced lifetime of drag reduction effectiveness.Therefore, surfactants were used to lower frictional drag since they are less susceptible to thermal, mechanical, and chemical deterioration.But, they simply experience impermanent deterioration when a specific crucial wall shear stress is surpassed [4].Scientists reported recently the utilization of Nano fluid in the drag reduction process.Nano fluids have the benefits of high tolerance to salinity, extreme operation temperatures, prolonged durability, and minimal clogging.The use of silica, titanium, graphene, and aluminum oxides Nano particles to enhance the viscoelastic and rheology characteristics of solutions has been described in several investigations [5].
However, silica Nano particles are the most extensively employed in drag reduction applications since it is the primary compound of sand, which is the most prevalent substance on the planet.Moreover, they are simple to manufacture, and their chemical behavior may be easily adjusted for specific purposes by surface modification [6].
Previous studies have described the preparation of silica materials utilizing a variety of extraction processes, including thermochemical redox process, sol gel process, precipitation of solutions, and so on [7].Despite substantial studies on silica nanoparticles, there are still some obstacles in the sector due to cost and large environmental issues.Where, all aforementioned methods are energy intensive and release greenhouse gases such as CO 2 [7][8].
Researchers have become more interested in finding alternate sources of silica and the technique of extracting it in recent years.Bio-based substances have recently sparked attention in a variety of disciplines due to their abundance, inexpensive, and harmless nature [9].Rice husk is a waste of farming practices that is plentiful in the world's top rice-producing countries.Rice husk produces a large volume of rice husk ash when used as a fuel.Furthermore, disposal of both husk from rice and its ash is a major challenge.As a result, there have been numerous attempts to use this husk and its ash to produce Nano silica.Hossain et al. [10] reviewed and explored several procedures for producing Nano silica from them.
This research pushes the boundaries of knowledge by extracting Nano silica from rice husk and assessing them for drag reduction applications in sprinkler irrigation systems that used in rice farms.The size distribution of the extracted silica Nano particles was examined, as well as their physical and chemical characteristics.Moreover, the effect of silica Nano particles on the decrease of drag for water flowing in carbon steel pipes was investigated.In order to give actual utility, the inflow statuses and instrumentations were picked out from careers done in the irrigation systems.

Experimental work
Silicon oxide Nano particles from rice husk ash were synthesized utilizing a two stages acidic-basic reaction procedure according to Fernandes et al. [11].Rice husk was received from Al-Mishkhab rice peeling factory, Al-Najaf, Iraq.It was leached with 1 M hydrochloric acid and calcificated at 600 °C to make rice husk ash.Many authors deduced that pretreatment of peels with hydrochloric acid is an efficient technique to remove the majority of contaminated minerals [12].30 g of the rice husk ash was placed in a vial and 160 cc of 30% soda ash solution was thereafter added to the container.The mixture was vigorously stirred and boiled for 4 hours in reflux circumstances.Then, it was filtrated and the filtered solid was rinsed with warm distilled water.The material was transferred to an autoclave where 6% polyethylene glycol is added while it was being stirred.The reactor was supplied with mixed gases including N 2 /CO 2 .After carbonation for 60 minutes, the resultant slurry is allowed to age for 3 hours at ambient temperature before being filtered.The precipitate was rinsed with distilled water before being dried for 24 hours at 120 °C.The resulting material was tested using SEM, AFM and FTIR to examine the morphology and composition of produced silica.
The drag reduction runs were conducted in a circulatory compelled closed loop flow system.Figure 1 depicts the schematic diagram of the system.A twin concentric pipe experimental section permits us to operate the runs at adiabatic situations because the liquid runs via the inside carbon steel pipe and the fixed temperature reconditioning fluid passes through the annular gap.This has been done because of the considerable influence of temperature on pressure drop [13].A U manometer has been used to measure the pressure loss throughout a 186 cm pipe length with diameters of 1.6 and 2.7 cm.The gravitational and acceleration effects were neglected.The liquid was flowed through the apparatus via a pump (Viva, QB 60, Italy) with a maximum capacity of 2.1 m 3 /h.Variable area Rota meters were used to monitor and control the flow rates (Liquatec, PMF 0505).To acquire completely confirmed drag reductions, it is fundamental to determine the pressure difference among the pressure probes in the zone of flow that is fully developed.A tripping ring was put in the tube at a depth of 1 cm from the pipe entry to speed up the transition to turbulence.The tripping ring creates an abrupt reduction of the tube spacing in the flow orientation.However, the entry length for turbulence of Newtonian liquids is quite short and 40 tube radiuses are ordinarily appropriate [14].As a result, the pressure tapes for both pipes were placed at an entrance length of 55 cm.
The surface tension was measured using an automatic liquid surface tension meter (VTSYIQI, BZY-203) with a sensitivity of 0.01 mN/m.Furthermore, Vortex-fading period tests were carried out to provide an approximate estimation of the solutions viscoelastic properties.100 cm 3 of solution was put in a flask.The flask was wrapped with a thin PVC film and positioned on a magnetism-heating mixer (Vevor, SH-3ABEII).The mixer was activated and left to run for 10 minutes and then it was immediately shut off.A timer was set once the stirring rod had stopped rotating.The timer was paused when the liquid started to rebound.This is assigned as the vortex-fading period.Fluids with low vortex-fading periods are predominating high drag reduction.750 liters of solution was made for every group of experiments.Dried Nano silica was mixed with snug deionized water for 10 hours by a powered mixing machine (Meakida, MD-7001).The solution was forced to circulate throughout the system after being poured into the reservoir.Then the tests are started after adjusting the liquid flow to the appropriate values.The solution rate of flow is gradually raised and enough time was given to attain equilibrium before collecting the data.The readings of pressure are calculated using the temporal average of one minute's worth of data, since the fluctuations are usually small.Pressure difference data from experimental setup were required to determine the drag reduction percentage.It expresses mathematically as [15]: Where ΔP o and ΔP n are pressure drops for pure solvent and drag reducing solution, respectively.In addition, drag reduction percentage could be quantified as: The friction factor (f) was calculated by employing the formula [16]: Where τ w is the wall shear stress, V is the bulk mean fluid velocity and ΔP corr is the corrected pressure drop.The fanning friction factor is an expression for Reynolds number at fully developed flow of liquid.Blasius correlation is the basic function between fanning friction factor and Reynolds number for pure fluid [17]: The asymptote of ultimate drag reduction determines the utmost reduction of drag that could be attained by a liquid with drag reducer.Virk [18] proposed the widely applicable asymptote for polymer solution: A considerable number of data assured this asymptote, which not depends on pipe dimensions, amount of additive or its molecular weight, etc.
There is nearly unanimity that the asymptote of ultimate drag reduction for surfactant must be greater than that of polymeric solutions [19].Zakin et al. [20] proposed the renowned maximal drag reduction asymptote for diluted surfactant solutions: However, equations or correlations that describe the efficiency of nanomaterial as a drag reduction additive are rarely mentioned in the literature.Therefore, there is a pressing need to continue research in this field for better understanding and increase the efficiency of this process.

Results and Discussion
The prepared Nano silica FTIR spectrograph is shown in figure 2. RHA-Silica was predominant by the functional groups (Si-O-H) and (Si-O-Si).The hydroxyl group is responsible for the bend at 3450 1/cm and the vibrating bent of the H 2 O molecule within Si-O-H group is responsible for the bend at 1635 1/cm.The peaks show asymmetrical spreading vibration of siloxane unit at 1100 1/cm.The symmetrical spreading vibration of the Si-O bonding causes the wave numbers at 801 1/cm.Silanol units are generated by solubilizing sodium silicate with hydrochloric acid, whereas siloxane units are created via condensation [22].
Figure 3 shows SEM and AFM images for prepared SiO 2 Nano particles.Spherical with homogeneous surface characteristics were identified in the sample with some aggregation.Furthermore, the figure shows the three dimensional pictures of the AFM analysis that revealed a continual and permeable surface morphology of the silica specimen.In order to confirm that the experimental setup performance operates in an acceptable manner, faucet water data was gathered over the pertinent limits and shown in figure 5.The friction factor was calculated using the measured pressure drop data and contrasted with the mathematical predictions of Blasius SEM AFM equation.The experimental and theoretical forecasts are on 5% mean differences.The experimental and theoretical outcomes are in good agreement when the measurement inaccuracy is taken into account and the experimental set up may be regarded to be performing satisfactorily.The experiential inaccuracy for the dimensions of the tubes were determined to be 186 ± 0.2 cm for length and 1.6 ± 0.03 cm and 2.7 ± 0.05 cm for the pair diameters.The fluid temperature and pressure drop measurement are uncertain by 2 °C and 1%, respectively.There is 0.01 to 0.08 m 3 /h uncertainty in the volumetric rate of flow, which depends on rate of flow values.Any residual discrepancy between theoretical and experimental findings could be referred to minor machining defects in the experimental parts.The nanomaterial solutions friction factor values measured in the two pipes (1.6 and 2.7 cm) and additive concentration (50, 100, 200 and 400 mg/l) were shown with respect to the solvent-based Reynolds number.The maximal drag reduction asymptotes for Virk and Zakin as well as the friction factor line relating to Newtonian turbulent flow for Blasius were presented as references.In the present labor, Reynolds number was computed based on the solvent viscosity.Since, it is highly challenging to forecast the appropriate viscosity from rheometric observation for such solutions in turbulent flow because of time dependents rheological substance characteristics in the shear-induced structures.
The testing data demonstrates that the friction factors are gradually decreased as Reynolds number increasing, although the inclination of the friction factor reduction lines increase with increasing of the solutions concentrations.This is a typical outcome since higher additives concentrations leads to higher nanoparticle concentrations within the solution, which serves as the key component in drag reduction phenomenon.Furthermore, table 1 demonstrates the distinct interplay of additives concentrations and interfacial tension of solutions.The interfacial tension of the solutions reduces as additive concentration rises.This causes the resistance to fluid motion to diminish, which in turn causes the values of the friction factor and pressure drop to decrease, since the interfacial tension acts mainly as impedance to the movement of the droplet when it is being pumped over a solid surface.However, in zone of turbulence, both of the aforementioned elements as well as several others may have an impact on the solution's viscoelastic properties.Numerous investigations in the literature show that viscoelastic fluids have substantially lower friction factors than Newtonian or pure viscous fluids [16].Additionally, size of tube influence on the lines of friction factor versus Reynolds number may be noticed by contrasting figures 5a and 5b.The friction coefficient quantities start increasing after attaining a lower limit at a specific Reynolds number called "Critical Reynolds number".Since fluid degradation is typically correlated with an increase in friction factor values, different diameter pipes with the same Reynolds number may have different fluid properties.The critical Reynolds number magnitude rises as pipe size increases.This is because that as tube diameter rises, the bulk average velocity and as a result, shear stress reduces which drove the critical Reynolds number value to increase.
Percent of drag reduction is depicted as a function of shearing velocity in figure 6.According to these graphs, all experimental data appear to be closely related to four distinct lines related to four solution concentrations.These figures suggest that there exists a single critical shear velocity of 0.2 m/s for every concentrations and tube diameters.This amount relates to a wall shear stress of 70 kg/m.s 2 and a bulk average liquid velocity of 6.8 m/s.This crucial velocity should not ever be achieved in practical systems because the advantage of adding nanomaterial to water starts to decline as the velocity increases from this significance threshold.This may be understood in light of the intriguing stress-controlled drag reduction effect found in nanomaterial solutions.
Drag reduction increases as shear stress increases up until a threshold value.Behind this value, there was no longer any difference between the drag reduction of the nanomaterial solutions and that of the nanomaterial-free solutions.The commencement drag reduction in this instance happened at a reasonably high Reynolds number.However, it can be inferred that neither additive amounts nor tubes diameters have a significant impact on the critical zone for reducing drag.It relies primarily on velocity of the fluid.Under any operating circumstances, it is forbidden to surpass this critical velocity when utilizing the Nano silicate aqueous solution pumping method because any additional acceleration of the velocity causes the reduction of drag to fall, which in turn lowers the flow rate of the pump.The relationship of wall shear stress versus bulk mean fluid velocity is shown in figure 7.These graphs suggest that there is a distinct linear relation among wall shear stress and average liquid velocity in logarithm scale for different solution concentrations and tube sizes.Furthermore, it may be demonstrated that this linear relationship is sufficiently close to be expressed by a single line for every concentration of solutions and tube sizes.In the current study, the relation was established as:

Figure 1 .
Figure 1.Flowchart for the testing equipment.

Figure 2 .
Figure 2. FTIR spectra of prepared silica from rice husk ash.

Figure 4
Figure4shows particle size frequency distributions.The mean size of the SiO 2 Nano particles obtained from rice husk ash was 26.8±9.4nm.The presence of only few minor micro-particles might be attributable to the aggregation impact.

Figure 3 .
Figure 3. SEM and AFM graphs of prepared silica from rice husk ash.

Figure 4 .
Figure 4. Particle size frequency distributions of prepared silica from rice husk ash.

Figure 5 .
Figure 5. Friction factor versus solvent-based Reynolds number with different concentration of solution for tube diameter equals to (a) 15.8 mm; (b) 26.6 mm.

Figure 6 .
Figure 6.Drag reduction percent versus shear velocity with various solution concentrations for pipe diameter equals to (a) 15.8 mm; (b) 26.6 mm.
The mean standard deviation was investigated and determined to be 9.54%.

Figure 7 .
Figure 7. Wall shear stress versus bulk mean fluid velocity with various solution concentrations for pipe diameter equals to (a) 15.8 mm; (b) 26.6 mm.

Table 1 .
Surface tension of Nano materials solutions.