Comprehensive Thermal Characteristic Investigations on Hemp-and Jute-Based Nature Fibre-Reinforced Composites for Engineering Applications through Coupled and Verified Engineering Approaches

low-cost nature. Tis paper focuses on the thermal application of NFRPs, which have shown great potential due to their good thermal insulation properties. In this study, the fabrication of jute and hemp fbre-reinforced composites, experimental testing, comparison, validation by using computational method, and proposed hemp NFRPs insulated exhaust pipe in place of conventional steel pipe. However, challenges such as moisture absorption and limited thermal properties on high thermal load still need to be addressed to enable the full-scale commercialization of NFRPs in thermal applications. For these comprehensive investigations, coupled and verifed engineering approaches have been imposed. Fluid-thermal coupling has been executed in ANSYS workbench associated with conventional test outcomes. Trough this approach, the low weight and low cost-based thermal load resisting material has been proposed for various engineering applications.


Introduction
Natural fbre has grown in popularity in recent years due to its low cost, abundance, nontoxic, and environmentally benefcial character.It is created by combining natural fbres such as jute, hemp, kenaf, cotton, silk, sisal, and others with a matrix material such as resin to form a material with stronger and additional mechanical and thermal qualities than the preceding raw materials.Natural fbre reinforcement polymers (NFRPs) have the ability to minimize energy consumption by reducing the work performed by the thermal system to recover the heat pulled out, as well as greenhouse gas emissions and encourage sustainable development.In lower thermal loads, NFRPs provide a sustainable alternative to other insulation materials such as asbestos, polystyrene, and so on.Te typical representation of prepared natural composite is revealed in Figure 1.
Natural fbre-reinforced composites are made by combining natural fbre in the reinforcing phase with a synthetic or bio-based polymer-based matrix in the matrix phase.
Because it has a direct efect on the property of a composite product and renders it unsuitable for the desired use, the mixture would take place in the right proportion.Because of their advantages, such as being easily decomposable and ecofriendly, NFRPs will be used in thermal insulation in future industries such as aerospace, automobile, and chemical.
In the context of thermal systems such as exhaust, manifold insulation in vehicle sectors gives numerous benefts in terms of engine performance.Te heat produced by the engine can be retained by insulating the exhaust pipe.Tis can help to raise the temperature of exhaust gases, where enhances gas fow out of the engine, particularly at lower RPMs.Exhaust gas temperature for varied petrol is taken from [1] and shown in Figure 2.
According to Arnau et al., insulation will aid in the combustion of unburned hydrocarbons emitted by the engine and thus minimize emissions [2].Exhaust gas velocity is also boosted by retaining heat and lowering back pressure in the engine, which can result in improved performance and efciency.However, it is dependent on the design of the bike engine.
Natural fbre composites have lesser thermal stability when compared to various types of synthetic fbres, and fbre deterioration owing to high thermal load will render NFRPs unsuitable for high temperature withstanding applications, particularly in higher cc bikes.Processing processes that include fame retardants have an efect on high thermal loads and thermal degradation.
1.1.Related Works.Muthukumar et al. investigated the usage of natural fbres such as banana, pineapple, and jute in various density combinations.60% of the combinations used banana fbre, whereas the remaining 40% only used pineapple fbre.Te increase in composite fbre thickness has an inverse relationship with the heat conductivity of the fbre combination.Maximum thermal resistance and lowest thermal conductivity were obtained when (C05) 60% banana, 32% pineapple, and 8% jute fbres were combined.Termal conductivity and resistance of six combination fbre composites were investigated, and they demonstrated good insulation properties [3].
Venkatesan and Kadiresh produced a new jute reinforced composite material by combining three synthetic resins known for reduced thermal conductivity values of polymeric materials ranging from 0.1 to 0.5 W/mK with general-purpose resin, vinyl ester, isophthalic polyester, and cardanol.It has a few advantages over commonly used metals, including low density, high corrosion resistance, and inexpensive production costs.Te efect of modifying each parameter was explored, and a regression equation was developed to identify whether composite material has good thermal properties.Termal conductivity test results for the manufactured composite materials are range from 0.125 to 0.16 W/mK [4].
Debnath researched jute fbre, which is less priced, yearly renewable, and commercially available than any other natural fbre crop.Jute farming is well known in Bangladesh and India.Hessian, carpet backing, and packaging (sacks) are a few well-known applications for fbre.Because of their lower cost and faster manufacturing method, synthetic fbres gradually surpassed traditional jute textiles in market share.It possesses thermal, electric, and acoustic resistant properties in various insulating forms [5].
Abedom investigated the fabrication of composite materials employing bamboo charcoal and bagasse fbre for technical uses by combining their diverse mechanical and thermal insulating capabilities.Five hybrid composites with various bagasse fbre/bamboo charcoal mixes are created using the compression molding procedure.ASTM techniques were used to evaluate the mechanical properties of the composite materials.Te morphological test is used to analyze binding properties, internal fssures, and alignments.Tensile properties of natural fbre composites were found to be the same as those of artifcial fbre composites.Te insulating qualities of the natural fbre manufactured from bamboo with 30/70 charcoal were greater than those of other artifcial fbres.Te fndings indicate the potential for employing these materials in component systems for automotive interiors [6].
Martin et al. used thermo gravimetric analysis, diferential scanning calorimetry, and nitrogen and air atmospheres to investigate the thermal properties of raw and defatted sisal fbre.Te atmosphere was a critical aspect in the DSC experiments that indicated the deteriorating process.In an inert environment, the DSC curve revealed distinct peaks for sisal fbres and their components.In the case of the air environment, all of the components' thermal curves displayed two exothermic peaks.In an inert environment, cellulose degrades via endothermic reactions, while in an atmosphere with air, it declines via exothermic processes.Te elimination of lignin, as confrmed by TGA 2 Journal of Engineering tests, resulted in cellulose and hemicelluloses occurring at lower thermal loads than the raw form of sisal fbre [7].Zhang et al. investigated the heat distribution and insulation behavior of a multilayered passive thermal protection system (MPTPS).Te problem is that when exposed to high temperatures, the carbon-phenolic combination pyrolyzes, altering its thermal properties.Te devolatilization of phenolic resin generates heat, which is absorbed by the carbon-phenolic compound.Tube furnace heating and Py-GC-MS experiments were used to investigate the pyrolysis properties of carbon-phenolic composites.Te transient heat conduction process and many numerical computations supported the investigation of the efects on the insulating behavior of the passive system by negative heat source.Te carbon-phenolic materials were pyrolyzed at 200 °C, and the mass-loss rate increased to 25% when the heating temperature was raised to 900 °C.Temperature rising point is delayed by increasing the wall thickness and negative heat source of the phenolic-carbon composited and has a large impact on outer wall temperature [8].
Awoyera et al. investigated the insulating and structural qualities of cement mortar supplemented with diferent mineral wool and fbre extracted from rice straw.Te purpose was to see if adding mineral wool and rice straw would improve the thermal insulating qualities of Portland cement mortar.Te mortar samples with dimensions of 40 × 40 × 160 mm were reinforced with varied mineral wool and fbre from rice straw varying in bulk from 0% to 50% of weight.Water absorption, fexural and compressive strength, and thermal conductivity tests were performed on samples with and without the addition of mineral wool and rice straw.SEM was used to examine the microstructure of mortars.Te heat conductivity of mortars decreased for reinforced mortars compared to cement with sand only.Te inclusion of fbres delayed the mechanical characteristics of mortar, although the delay was not signifcant or fell short of acceptable standards [9].
Yusaf et al. evaluated the efect of methanol mixing ratios on engine performance.Te mixing ratios were 10%, 20%, and 30% methanol.At various engine speeds, the performance of a four-stroke diesel engine was improved by altering the methanol mixture with fuel, and the reported exhaust temperature of a diesel-only engine was lower when compared to a blended fuel engine with improved performance.According to this study, adding 10% methanol to diesel fuel can have a considerable impact on both the environment and engine performance [1].Saravanan et al. developed jute, pineapple, and banana fbre-based composites with diferent weight percentages.Composites with two fbres of equal weight percentage and diferent thicknesses of 5 mm, 10 mm, and 15 mm are utilized to insulate the generator exhaust pipe.Tis study was conducted normally, and the thermal characteristics of the insulated pipe were enhanced over the noninsulated pipe [10].
Kandylas and Stamatelos summarized the current state of knowledge about heat transport phenomena in vehicle exhaust systems.Experiment data from steady-state transient heat transfer measurements in automotive exhaust systems are provided and analyzed using a comprehensive transient computer model that covers the exhaust pipe by single wall and double wall with air flled confguration.Tis study hypothesized that insulating the exhaust gas pipes and manifolds would raise the temperature of the exhaust gas [11].Krishnara et al. used FEM methods to analyze the exhaust manifold for several designs.Te inclination of the manifold structure causes pressure drop and temperature loss, resulting in a low power output from the engine.Reduced tilt greatly increases temperature and pressure from the preceding structure and power delivery from the engine [12].Arnau et al. investigated exhaust thermal insulation using transient analysis.Exhaust ports and manifolds are insulated using various approaches.And it was concluded that insulation reduces fuel pollutants and CO emissions by 20% while increasing exhaust gas enthalpy [2].

Methodologies
Heat transfer rate and conductivity properties must be examined to build the NFRP in a thermal feld.A heat fow meter is used to investigate thermal conductivity and resistivity, as well as moisture absorption qualities.Validate the experimental results and the computational analysis performed on the experimental test specimen.Based on the low error percentage, a computational analysis on the exhaust pipe is performed, and a grid convergence study is performed to improve the accuracy of the results [2,[13][14][15][16][17][18][19][20][21][22][23][24][25][26]. 1, it can be observed that Kenaf, Sisal, and cotton fbres have much lower thermal conductivity values in comparison to the other types of fbres.However, the availability, fabric preparation, and extraction cost of these fbres are signifcantly elevated.

Test Material Preparation.
Te raw jute and hemp fbres have a diameter of 10 microns and 25 microns, respectively, and are treated and woven into a sort of bidirectional fabric.Jute has a layer thickness of 0.84 mm, while hemp has a thickness of 0.89 mm.If there were 8 layers of hemp fabric, the total thickness would be 7.12 mm, and if there were 9 layers of jute fabric, the total thickness would be 7.56 mm.Te results of a mixture of epoxy resin and aromatic amine hardener with the proportion of 10 : 2 as weighted shown in Figure 6 are presented.
Te ratio of fbre to resin in the mixture is exactly 50/50.Te conventional method of hand-layup is utilized throughout the production of test materials.Te mold is prepared for the frst time for the insertion of the fbres.Te resins are then subjected to an impregnation process, during which rollers, brushes, or several other types of impregnators are utilized.After going through this procedure, the laminates that were created are subsequently cured using    meter, the testing material is sliced into pieces of 300 by 300 mm with a user-specifed thickness of 12 mm before being placed in a heat fow meter apparatus consisting of a heated plate and temperature sensors that were in contact with the testing material.Te thermal conductivity and resistance of the test material are both determined by making use of the diference in temperature that is measured between the two sensors [2, 13-26].
2.1.4.Moisture Absorption Test.Te method that is given in ASTM D 579-99 procedures is used to determine the moisture absorption capabilities of hemp and jute fbre reinforced composites.Te relationship of water absorption is expressed in the following equation: From the composite, test specimens with the dimensions of 25.4 × 76.2 mm 2 and a thickness of 12 mm are cut, and the results of the measurements taken are presented in Figure 8. Te samples are then promptly dried before being weighed.In order to get an accurate reading of the water absorption, test materials are submerged in water for varied amounts of time while their restored weights are recorded [2,[13][14][15][16][17][18][19][20][21][22][23][24][25][26].

Test Results
. HFM is used to conduct tests on a fabricated jute and hemp fbre reinforced composite with dimensions of 300 mm × 300 mm and a thickness of 12 mm in order to examine heat convection.Te test is carried out with a temperature diference of 10 degrees Celsius and a constant temperature of 80 degrees Celsius.Based on the fndings, the thermal conductivity and resistivity of jute NFRP have been determined to be 0.14873 W/mK and 0.08119 m 2 /mK.Similarly, for hemp NFRP, the thermal conductivity and resistivity values are found as 0.122702 W/mK and 0.098422 m 2 /mK.Te comprehensive experimental test based outcomes of thermal conductivity and resistivity are revealed in Figure 9 [2, [13][14][15][16][17][18][19][20][21][22][23][24][25][26].
Utilizing equation ( 1), a determination can be made on the percentage of moisture absorbed by the test specimen.Figure 10 presents a plot of the fndings of the experiment.
Te NFRP of hemp can absorb up to 0.99% of its body weight, while the NFRP of jute can absorb up to 5.39% of its body weight.

Computational Termal Analysis
2.2.1.Computational Plate Model.Te composite plate constructed of jute and hemp fbre is the physical representation of this problem in the computational model.Figure 11 depicts a composite plate that measures 300 mm on each side and has a thickness of 12 mm.For the purpose of designing the computational model, the Ansys Design-Modeler workbench is utilized [27][28][29][30].
After the model has been created, the material properties of the hemp and jute are derived from the experimental data reported in Table 2 and then supplied into the model as material input data.

Discretization.
Te continuous domain is discretized using either fnite elements or discrete elements when computational models are used.Structured meshing takes the place of adaptive meshing when it is applied to a surface that has been subdivided into a grid of square elements.Te generation of a mesh that has sufcient density to faithfully depict the plate's overall heat fux is the objective of the discretization process.Te underlying mesh structure of the plate is shown in Figure 12 [27][28][29][30].

Boundary Condition.
Te Dirichlet boundary condition is applied, and both the starting and ending temperatures are held at a constant value across the boundaries.One side of the material has a thermal load of 80 degrees Celsius applied to it, while the other side has a thermal load of 70 degrees Celsius applied.In addition, the state of the remaining faces is maintained to be adiabatic.Figure 13 illustrates the model with the boundary condition added in [27][28][29][30].

Solver Data and Equations. Te convection-difusion
equation is an equation that conserves both energy and mass and is responsible for governing the convective heat transfer.Te equation for the general form of energy conservation in convective heat transfer is as follows: where z(ρc T )/zT is the time rate change of energy within the domain, T is the temperature of the medium, ∇ is denoted as divergence factor, v is the velocity vector of the fuid, ∇ * (ρc T u) is represented as convective term that accounts the amount of heat transported by convection, ∇ * (k.∇T) is represented as difusive term that accounts the amount of heat transported by difusion, ∆T is the temperature difference between the boundaries, and Q is denoted as the source/sink term [27][28][29][30].

Result and Validation.
Te fndings of the thermal analysis performed on the composite plates for the experimental boundary condition are withheld.Figure 14 where Q is the heat transferred amount, k is denoted as thermal conductivity in W/mK, ∆T is the temperature diference between the two surfaces, A is the cross-sectional area, and D is represented as thickness of the specimen [27][28][29][30].
Heat transferred for jute NFRPs can be calculated as follow, the values of jute NFRPs are k � 0.14 W/mK, ∆T � 283 k, D � 0.12 m, and A � 0.036, where For hemp NFRPs k � 0.12, where Q � 0.12 * 283 * 0.036 0.12 � 10.18 W. ( It would appear that the error percentage while validating experimental and computational data is less than 10%.Tis suggests that the experimental test specimen may have discontinuity, inappropriate resin fbre contact, and poor resin fbre fusion, all of which vary according to the preparation and curing method.Te insulation of the realworld problem can be solved by using the solutions that were collected and validated [27][28][29][30].triangular and tetrahedral parts.Figure 18 demonstrates how the meshed structure of the computational model may be seen [27][28][29][30].

Boundary Conditions.
For discretized model, inlet velocity is found by using volumetric fow rate from the engine cylinder as follow.
Given the specifcations of a Honda CB 200's 200cc motorcycle engine, namely, a stroke length of 63mm and a bore diameter of 61mm, operating at a rotational speed of 6000 RPM, we can analyse the performance characteristics of this four-stroke engine.Tis implies that there are 3000 exhaust strokes occurring within a minute.
Volumetric fow rate of exhaust gas is calculated as 0.0100 m 3 /sec.
At 6000 RPM, piston completes 12000 strokes per minute, velocity can be found by using the following equation: Te bore diameter of cylinder is 61 mm.Area at cylinder exit is as follows: Diameter at exhaust exit tip is 31.5 mm and the area is calculated by using the following equation: By using continuity equation, exit velocity can be calculated as follows:

Journal of Engineering
Te inlet of the discretized model is the velocity inlet, and the average exhaust gas temperature from [1] of 393 k is fed as boundary condition for the inlet.Te outlet of the model is a pressure outlet, and the magnitude of pressure is 101325 Pa.Conditions for the wall are no slip, stationary wall equipped with convective heat transfer of default thermal conductivity value of steel as 16.27 W/mK, and ambient temperature of 288.16K [27][28][29][30].

Solver Data and Equations.
For fuid analysis through the domain of the exhaust, working fuid is chosen as air treated as ideal gas.
where ρ is denoted as the density of working fuid, p p is denoted as operating pressure, p is denoted as static pressure, R is represented as universal gas constant, M is represented as molecular weight of air, and T 0 is denoted as local temperature [27][28][29][30].
Viscosity depends on temperature to consider this, Sutherland's law and its models is employed as follows: where μ 0 , μ 1 , T 1 , and S are denoted as viscosity of working liquid, reference viscosity, reference temperature at sea level, and Sutherland constant, respectively.Te three coefcient of Sutherland's law default values for air is as follows: Te governing equation of continuity, momentum, and energy relation for this case is as follows: where v → , τ, E, k eff , and S H are represented as velocity vector, stress tensor, internal energy, efective conductivity of the fuids, and energy source term [27][28][29][30].
Turbulence efects are included by deploying k − ε model.Governing equation for k − ε model is provided as follows: where

Results from Computational Study. Because of this work,
NFRPs can now be used as an insulating material in bike exhaust systems.Te heat transfer to the surrounding environment is investigated using jute and hemp NFRPs as well as traditional steel exhaust pipes for comparison.Figures 24 and 25 present the fndings that were obtained when the specifed boundary condition was applied.
Te results from the fuent are input into the steady state thermal model in order to calculate the quantity of heat transmitted and the heat fux. Figure 26 presents the imported results of temperature measurements taken from the fuid domain.Tis can be carried out in accordance with the manner described in Section 2.2.

Journal of Engineering 13
In addition, steel is incorporated so that the results may be compared with those of NFRP materials made of jute and hemp.Figure 27 illustrates the heat fow that was imported from a model containing steel's characteristics.Figure 28 presents the heat fux that is disclosed by the hemp NFRPs properties-imposed model.Figure 29 illustrates the heat fux that is caused by the properties-imposed model for jute NFRPs.
In comparison to steel and jute NFRPs, the quantity of heat that is transferred by convection through hemp NFRPs is much lower.Figure 30      Journal of Engineering heat fux that occurs between NFRPs made of steel, jute, and hemp.

Conclusion
Hemp and jute are selected with the assistance of a literature review on the basis of their availability, the cost of processing, and their thermal performance.It is possible to successfully manufacture composite material that is reinforced with jute and hemp fbres.Te constructed model is put through a thermal test in steady state, and observed thermal load transfer is carried out.When subjected to a moisture absorption test in order to determine the capability of capturing moisture, the results showed that hemp NFRPs had a lower level of moisture absorption in comparison to jute NFRPs.Additionally, the heat transmission in hemp NFRPs was quite low.Te use of computational tools allows for this assertion to be properly confrmed.
Te exhaust model is evaluated computationally to ensure that there is minimal error based on the results of the computations.Te velocity and temperature of exhaust gas are estimated using an analytical approach and reviews of the relevant literature.For the sake of computational investigation, these values are employed.A grid convergence research is carried out in order to guarantee the precision of the CFD.Te fndings from the jute and hemp NFRPs were compared with those from typical steel pipes, and it was discovered that the hemp NFRPs are best suited for lower thermal loads and have lower heat transfer values.
Te primary focus of future study will be on the development of composites, namely, by altering the fbre-toresin ratio and combining fbre pavement with alkaline materials in an efort to improve the thermal resistance of NFRP composites.In terms of the insulation, the analysis would need to be carried out in a transient state in order to monitor the thermal performance of the composite brought about by varying fow parameters using computational methods.
Te commercialization of hemp natural fbre reinforced plastics (hemp NFRPs) in low thermal environments involves the study of additional characteristics such as thermal deterioration and the treatment of fbres prior to manufacture in order to increase thermal behavior.

Figure 2 :
Figure 2: Exhaust gas temperature for varying fuel mixture.

Figure 4 :
Figure 4: Jute fabric for experimental test specimen preparation.

Figure 5 :
Figure 5: Hemp fabric for experimental test specimen preparation.

Figure 6 :
Figure 6: Measurements of epoxy-resin for experimental test specimen.

Figure 11 :
Figure 11: Computational plate model for testing.

Figure 14 :
Figure 14: Applied thermal load 80 with a temperature gradient of 10 °C.

Figure 15 :
Figure 15: Uniform distribution of heat fux over the jute NFRPs properties imported computational model.

Figure 16 :
Figure 16: Uniform distribution of heat fux over the hemp NFRPs properties imported computational model.

Figure 19 :
Figure19: Grid convergence study for varying element size and maximum temperature is plotted.

Figure 20 :
Figure 20: Grid convergence study for varying element size and minimum temperature is plotted.

Figure 22 :
Figure 22: Meshed structure and temperature results for 562650 mesh elements.

Figure 24 :
Figure 24: Temperature of fuid created for exhaust pipe.

Figure 25 :
Figure 25: Velocity of fuid domain created for exhaust pipe.
.2. Author Observation.Te authors discovered that natural composites have poorer thermal conductivities than other metals such as steel and aluminim due to the presence of microstructures such as pores and voids.Tese microstructures cause thermal resistance and signifcantly impair heat transmission rate.Peak deterioration occurs in natural fbres at maximum temperatures ranging from 150 °C to 360 °C depending on fbre reinforcement.Natural composites with higher fbre content have lower thermal conductivity values because fbres have lower thermal [1,[3][4][5][6][7][8][9]ility and maximum temperature capability can be improved by treating fbre with alkaline solution, fller materials, curing process, and reinforcing procedures.Table1displays the results of research papers[1,[3][4][5][6][7][8][9]that reported thermal conductivity values for several types of available fbre.Authors concluded that NFRPs are mostly ft for lower thermal load applications.Te detailed procedure involved in this work is revealed in Figure3.

Table 1 :
Termal conductivity values for varying density and matrix phase.
standard atmospheric conditions.In a manner analogous, six layers of hemp are utilized in order to achieve a composite thickness of 12 mm.Te fully constructed model of a square plate made of hemp may be shown in Figure7[2, 13-26].2.1.3.Test Apparatus-HFM.In accordance with ISO 8301 : 1991, a heat fow meter can be used to determine the thermal properties of the test material, such as the thermal conductivity and thermal resistivity of the material.According to the instructions provided by the heat fow

Table 2 :
Properties of the materials.
[27][28][29][30]turbulence kinetic energy, k is denoted as turbulence dissipation rate, G k and G b are the turbulence kinetic energy created due to velocity gradients and buoyancy, Y M is represented as dilation fuctuation in compressible turbulence to overall dissipation rate, μ t , σ k , and σ ε are the eddy viscosity and turbulent Prandtl number for k and ε, S k and S ε are the source terms, and C 1ε , C 2ε , and C 3ε are the constants[27][28][29][30].2.3.4.Grid Convergence Study.Te study of grid convergence ofers a clearer comprehension of how the results of computations are infuenced by the size of their constituent elements.Tere are eight distinct situations, each consisting of a diferent element size, capturing proximity with or without the element, curvature size functions, minimizing element size, and doing analysis.Te maximum temperature and the minimum temperature are the two factors that are taken for the computational model which is taken for the study.Taking these two parameters helps enhance accuracy and provides a dependable output.Te results are presented in the form of a graph, which can be found in Figures19 and 20, respectively.Figures19 and 20show the highest and minimum temperatures at which saturation occurs for a range of element sizes.Saturation is reached at 850958 elements and the results are analyzed for the steel, hemp, and jute properties-imposed model.At 850958 elements, saturation is achieved.Te maximum temperature at saturation is 393.329K, and the minimum is 363.299K.
Figure 21: Meshed structure and temperature results for 443593 mesh elements.
depicts a plot of the diference in Figure 23: Meshed structure and temperature results for 2013664 mesh elements.
Figure 27: Heat fux for steel properties-imposed model.
MinFigure 26: Imported load from the fuid domain.B: Steady-State Thermal