Research Article  Open Access
Optimal Homotopy Asymptotic Solution for Exothermic Reactions Model with Constant Heat Source in a Porous Medium
Abstract
The heat flow patterns profiles are required for heat transfer simulation in each type of the thermal insulation. The exothermic reaction models in porous medium can prescribe the problems in the form of nonlinear ordinary differential equations. In this research, the driving force model due to the temperature gradients is considered. A governing equation of the model is restricted into an energy balance equation that provides the temperature profile in conduction state with constant heat source on the steady state. The proposed optimal homotopy asymptotic method (OHAM) is used to compute the solutions of the exothermic reactions equation.
1. Introduction
In physical systems, energy is obtained from chemical bonds. If bonds are broken, energy is needed. If bonds are formed, energy is released. Each type of bond has specific bond energy. It can be predicted whether a chemical reaction would release or need heat by using bond energies. If there is more energy used to form the bonds than to break the bonds, heat is given off. This is well known as an exothermic reaction. On the other hand, if a reaction needs an input of energy, it is said to be an endothermic reaction. The ability to break bonds is activated energy.
Convection has obtained growth uses in many areas such as solar energy conversion, underground coal gasification, geothermal energy extraction, ground water contaminant transport, and oil reservoir simulation. The exothermic reaction model is focused on the system in which the driving force was due to the applied temperature gradients at the boundary of the system. In [1–4], they proposed the investigation of RayleighBernardtype convection. They also study the convective instabilities that arise due to exothermic reactions model in a porous medium. The exothermic reactions release the heat, create density differences within the fluid, and induce natural convection that turn out the rate of reaction affects [5]. The nonuniform flow of convective motion that is generated by heat sources is investigated by [6–8]. In [9–13], they propose the two and threedimensional models of natural convection among different types of porous medium.
In this research, the optimal homotopy asymptotic method for conduction solutions is proposed. The model equation is a steadystate energy balance equation of the temperature profile in conduction state with constant heat source.
The optimal homotopy asymptotic method is an approximate analytical tool that is simple and straightforward and does not require the existence of any small or large parameter as does traditional perturbation method. As observed by Herişanu and Marinca [14], the most significant feature OHAM is the optimal control of the convergence of solutions via a particular convergencecontrol function and this ensures a very fast convergence when its components (known as convergencecontrol parameters) are optimally determined. In the recent paper of Herişanu et al. [15] where the authors focused on nonlinear dynamical model of a permanent magnet synchronous generator, in their study a different way of construction of homotopy is developed to ensure the fast convergence of the OHAM solutions to the exact one. Optimal Homotopy Asymptotic Method (OHAM) has been successfully been applied to linear and nonlinear problems [16, 17]. This paper is organized as follows. First, in Section 2, exothermic reaction model is presented. In Section 3, we described the basic principles of the optimal homotopy asymptotic method. The optimal homotopy asymptotic method solution of the problem is given in Section 4. Section 5 is devoted for the concluding remarks.
2. Exothermic Reactions Model
In this section, we introduce a pseudohomogeneous model to express convective driven by an exothermic reaction. The case of a porous medium wall thickness () is focused. The normal assumption in the continuity and momentum equations in the steadystate energy balance presents a nondimensional form of a BVP for the temperature profile [5, 13]: Here, is the temperature, the parameter is the maximum feasible temperature in the absence of natural convection, is the ratio of the characteristic time for diffusion of heat generator, and is the dimensionless activation energy. In the case of the constant heat source, (1) can be written assubject to boundary condition
3. Basic Principles of Optimal Homotopy Asymptotic Method
We review the basic principles of the optimal homotopy asymptotic method as follows.
(i) Consider the following differential equation:where is problem domain, , where , are linear and nonlinear operators, is an unknown function, and is a known function.
(ii) Construct an optimal homotopy equation aswhere is an embedding parameter and is auxiliary function on which the convergence of the solution greatly dependent. Here, are the convergencecontrol parameters. The auxiliary function also adjusts the convergence domain and controls the convergence region.
(iii) Expand in Taylor’s series about , one has an approximate solution: Many researchers have observed that the convergence of the series equation (6) depends upon , ; if it is convergent then, we obtain
(iv) Substituting (7) in (4), we have the following residual:If , then will be the exact solution. For nonlinear problems, generally, this will not be the case. For determining , , collocation method, Ritz method, or the method of least squares can be used.
(v) Finally, substituting the optimal values of the convergencecontrol parameters in (7) one can get the approximate solution.
4. Application of OHAM to an Exothermic Reaction Model
Applying OHAM on (2), the zeroth, first, and second order problems areWe consider , in the following manner:
4.1. Zeroth Order Problem
with boundary conditionsThe solution of (11) with boundary condition (12) is
4.2. First Order Problem
with boundary conditionsThe solution of (14) with boundary condition (15) is
4.3. Second Order Problem
with boundary conditionsThe solution of (17) with boundary condition (18) isThe final three terms solution via OHAM for isThe method of least squares is used to determine the convergence control parameters and in (20). In particular case for , , the values of the convergence control parameters are and .
By substituting the values of and in (20) and after simplification, we can obtain the second order approximate solution via OHAM. To check the accuracy of the OHAM solution, a comparison between the solutions determined by OHAM and numerical methods was made and is presented in Table 1. Graphical representation of the solution using finite difference technique [5], OHAM, and RungeKutta Fehlberg fourth fifth order method is shown in Figure 1; an excellent agreement can be observed. We can see that the OHAM gives a better accurate solution than the traditional finite difference technique of [5]. On the other hand, the OHAM gives a continuity solution, but the traditional finite difference technique gives a discrete solution. It follows that the solutions of the OHAM is easier to implement than the finite difference solutions.

In Figure 2, we exhibit the effect of different values of with fixed value of on temperature profile.
5. Concluding Remarks
In this paper, one has described an optimal homotopy asymptotic technique for obtaining the temperature profiles in porous medium. We can see that the temperature reduces to the end. The OHAM scheme for obtaining the model is convenient to implement. The OHAM gives fourth order accurate solutions. It follows that the method has no instability problem. The model should be considered in the case of nonconstant heat source.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This paper is supported by the Centre of Excellence in Mathematics, the Commission on Higher Education, Thailand. The authors greatly appreciate valuable comments received from Professor John D. Clayton and their reviewers.
References
 J. L. Beck, “Convection in a box of porous material saturated with fluid,” Physics of Fluids, vol. 15, no. 8, pp. 1377–1383, 1972. View at: Publisher Site  Google Scholar
 S. H. Davis, “Convection in a box: linear theory,” Journal of Fluid Mechanics, vol. 30, no. 3, pp. 465–478, 1967. View at: Publisher Site  Google Scholar
 Z. Gershuni and E. M. Zhukovitskii, Convective Stability of Incompressible Fluids, vol. 4, Israel Program for Scientific Translations, 1976.
 E. R. Lapwood, “Convection of a fluid in a porous medium,” Proceedings of the Cambridge Philosophical Society, vol. 44, pp. 508–521, 1948. View at: Google Scholar  MathSciNet
 N. Pochai and J. Jaisaardsuetrong, “A numerical treatment of an exothermic reactions model with constant heat source in a porous medium using finite difference method,” Advanced Studies in Biology, vol. 4, no. 6, pp. 287–296, 2012. View at: Google Scholar
 D. R. Jones, “The dynamic stability of confined, exothermically reacting fluids,” International Journal of Heat and Mass Transfer, vol. 16, no. 1, pp. 157–167, 1973. View at: Publisher Site  Google Scholar
 M. Tveitereid, “Thermal convection in a horizontal porous layer with internal heat sources,” International Journal of Heat and Mass Transfer, vol. 20, no. 10, pp. 1045–1050, 1977. View at: Publisher Site  Google Scholar  Zentralblatt MATH
 J. B. Bdzil and H. L. Frisch, “Chemically driven convection,” The Journal of Chemical Physics, vol. 72, no. 3, pp. 1875–1886, 1980. View at: Publisher Site  Google Scholar
 H. Viljoen and V. Hlavacek, “Chemically driven convection in a porous medium,” AIChE Journal, vol. 33, no. 8, pp. 1344–1350, 1987. View at: Publisher Site  Google Scholar
 H. J. Viljoen, J. E. Gatica, and H. Vladimir, “Bifurcation analysis of chemically driven convection,” Chemical Engineering Science, vol. 45, no. 2, pp. 503–517, 1990. View at: Publisher Site  Google Scholar
 W. W. Farr, J. F. Gabitto, D. Luss, and V. Balakotaiah, “Reactiondriven convection in a porous medium,” AIChE Journal, vol. 37, no. 7, pp. 963–985, 1991. View at: Publisher Site  Google Scholar
 K. Nandakumar and H. J. Weinitschke, “A bifurcation study of chemically driven convection in a porous medium,” Chemical Engineering Science, vol. 47, no. 1516, pp. 4107–4120, 1992. View at: Publisher Site  Google Scholar
 S. Subramanian and V. Balakotaiah, “Convective instabilities induced by exothermic reactions occurring in a porous medium,” Physics of Fluids, vol. 6, no. 9, pp. 2907–2922, 1994. View at: Publisher Site  Google Scholar  MathSciNet
 N. Herisanu and V. Marinca, “Accurate analytical solutions to oscillators with discontinuities and fractionalpower restoring force by means of the optimal homotopy asymptotic method,” Computers & Mathematics with Applications, vol. 60, no. 6, pp. 1607–1615, 2010. View at: Publisher Site  Google Scholar  MathSciNet
 N. Herisanu, V. Marinca, and G. Madescu, “An analytical approach to nonlinear dynamical model of a permanent magnet synchronous generator,” Wind Energy, 2014. View at: Publisher Site  Google Scholar
 F. Mabood and N. Pochai, “Asymptotic solution for a water quality model in a uniform stream,” International Journal of Engineering Mathematics, vol. 2013, Article ID 135140, 4 pages, 2013. View at: Publisher Site  Google Scholar
 V. Marinca and N. Herisanu, “Optimal homotopy perturbation method for strongly nonlinear differential equations,” Nonlinear Science Letters A, vol. 1, no. 3, pp. 273–280, 2010. View at: Google Scholar
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Copyright © 2015 Fazle Mabood and Nopparat Pochai. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.