It is well known that the adsorption chiller (ADC) utilizes theadsorbenteadsorbate characteristics to achieve useful cooling effectsat the evaporator by the amalgamation of two processesnamely ‘adsorption-triggered-evaporation’ and ‘desorption-activated-condensation’ [1]. The ADC works as a batch wise process i.e.adsorption and desorption occur alternatively in the adsorptionbed and is also time dependent [2e6]. So, the adsorption rate orkinetic equations are widely used to describe adsorption data atnon-equilibrium conditions, and are significant to investigate thebasic understanding of adsorption process that ranges from transientto the cyclic steady state. The simplest kinetics equation iscommonly expressed by dqt=dt ¼ aðq* qtÞ, where qt is the amountof adsorbate uptake at time t, q* is its value at equilibrium, and a isthe temperature dependent constant. This rate equation indeed isin line with the concept of LDF (linear driving force) model or thefirst order kinetic equation [7,8]. The basic mathematic model forthe diffusive transport of adsorbates within complex adsorbentstructures is the Fick's equations [9], and is difficult to solveanalytically under practical situation [9,10]. The LDF model [11]correlates experimental data in simple equation forms [11e13]employing data fitting parameters. The LDF model assumes thatthe adsorbent particle temperature is uniform, and its thermalconductivity is infinity, which means that the heat transfer effect isneglected. The LDF models also involve the intra-particle diffusionfor mass transfer process. The physical evidence of the LDF coefficientis obtained thermodynamically from Langmuirian kinetics. Itshould be noted here that the Langmuir kinetics [14e18] are used todescribe the non-equilibrium conditions of adsorbent þ adsorbatesystem. However, the Langmuir isotherm is limited to one site occupancyadsorption onto the homogeneous adsorbent surface.Moreover, the Langmuir isotherm gives inconsistency thermodynamicbehavior at higher pressure ranges [19].Bhatia et al. [9] gave a comprehensive theoretical perspective ofmolecular transport in nanopores with the proposal of an oscillatormodel and a distributed friction models. Sircar and Hufton [12]analyzed the connection between the linear driving force (LDF)model and the FD (Fickian Diffusion) model but the detailed characteristicsof local adsorption kinetic model are neglected duringintegrations. The Fick's differential equation is difficult to solveanalytically under practical situation, because the diffusivity,which considers sophisticate diffusion mechanisms within complex adsorbent structures, is highly computational time consuming todetermine its integration form over the complete time and spacedomain [12].Based on Langmuirian adsorption theory, Azizian [10] analyzedthe general analytical solution of two extreme cases theoreticallywith high initial concentration of adsorbate, and lower initialconcentration of solute, where the first one converts into a pseudofirst-order LDF model, while the latter follows a pseudo-secondorderequation. Liu and Shen [8] also gave a similar conclusion ofAzizian [10]. Employing Langmuir model, Marczewski [17] derivedthe integrated form of kinetics Langmuir equation (IKL), andcompared it with the nth-order, mixed 1, 2-order, and multiexponentialkinetic equations. Marczewski et al. [18] also proposeda generalization form of Langmuir kinetics (gIKL), and LF(LangmuireFreundlich) isotherm was applied to describe the nonidealbehavior of adsorption phenomena. Later, Azizian and Bashiri[13] developed the adsorption kinetics with SRT (statistical ratetheory) approach, and studied the solute adsorption at the solid/solution. The MPFO (modified pseudo-first-order) kinetic equation,proposed by Yang and Al-Duri [20], was interpreted theoretically[13]. By applying different adsorptive site energy distribution,Rudzinski and Panczyk [21] derived the power form of Elovichequation from LangmuireFreundlich and the Temkin isotherms.Corresponding to practical experimental conditions, Loh et al.proposed [22] a theoretical framework to describe the adsorptionkinetics for the non-isothermal system. Babrao and Jiang [23]investigated the transport diffusivities of CO2 and CH4 in silicalite,C168 schwarzite, and IRMOF-1 employing molecular dynamicssimulation, and it was found that the computational results matchwell with the MaxwelleStefan formulation for pure CO2 and CH4.To utilize the adsorption kinetics with adsorption chiller system,Aristov et al. [15,16] studied the water adsorption kinetics on silicagel (type Fuji RD) under real operating conditions with the optimizationof various loose grains silica gel configuration.Up to now, no significant attempts are established to explain thetheoretical origins of adsorption rate equations for a singlecomponent adsorbent þ adsorbate system in detai
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