Water Adsorption In Zeolites Research Articles

Experimental investigation of an adsorptive thermal energy storage

A zeolite-water adsorption module, which has been originally constructed for an adsorption heat pump, has been experimentally investigated as an adsorptive thermal energy storage unit. The adsorber/desorber heat exchanger contains 13.2 kg of zeolite 13X and is connected to an evaporator/condenser heat exchanger via a butterfly valve. The flow rate of the heat transfer fluid in the adsorber/desorber unit has been changed between 0.5 and 2.0 l min−1, the inlet temperature to the evaporator between 10 and 40°C. It turned out that the higher the flow rate inside the adsorber/desorber unit the faster and more effective is the discharge of heat. However, at lower flow rates higher discharge temperatures are obtained. Storage capacities of 2.7 and 3.1 kWh have been measured at the evaporator inlet temperatures of 10 and 40°C, respectively, corresponding to thermal energy storage densities of 80 and 92 kWh m−3 based on the volume of the adsorber unit. The measured maximum power density increases from 144 to 165 kWh m−3 as the flow rate in the adsorber increases from 0.5 to 2 l min−1. An internal insulation in form of a radiation shield around the adsorber heat exchanger is recommended to reduce the thermal losses of the adsorptive storage. Copyright © 2006 John Wiley & Sons, Ltd.

06/02220 Design and performance prediction of a novel zeolite-water adsorption air conditioner: Wang, D. C. et al. Energy Conversion and Management, 2006, 47, (5), 590–610.

The geometric structures and fractal dimensions of fractal tree-like branched networks have the significant influence on the efficiency of physiological, communication and transport processes. We analyze the heat conduction through symmetric fractal tree-like branched networks. We obtain the expression of thermal conductivity in the networks and analyze the relationship between the effective thermal conductivity (ETC) and the geometric structures of the networks. We have found that the ETC of the networks is always less than that of a single channel, and the value of the thermal conductivity of the network can tend to zero under certain conditions; as long as the branching number N is fixed, the heat conduction reaches the fastest rate at the same diameter ratio βm which is corresponding to the fractal dimension Dd = 2.0. We have also found that the heat conduction in the networks is rather different from Murray’s law both for laminar regime (2−1/3) and for turbulent flow regime (2−3/7).

The influence of periodic operation on the characteristics of adsorption devices

Abstract In this paper, we elaborate on the improvement of the design of adsorption heat pump cycles by combining economic and thermodynamic information. A method is used, which results in a relation between the performance and the specific cost of the device. The performance, of course, is given in terms of COP. The cost is approximated by a figure for the required area for heat exchange, which includes all the cost for the heat exchange equipment that is required to exchange heat with the environment (hot and cold heat source, heat sink). Because these costs represent a major part of the investment cost for the device, we use it our calculations. The resulting relation between the COP and the area cost is representative for the specific device. It is represented in the “optimal operational plot”, which is the maximal efficiency (COP) against the required heat exchange area. The study is performed on a standard, single stage, zeolite–water adsorption device with two adsorbers and an internal heat recovery. Usually, continuously operating devices perform better than discontinuously operating ones. The cyclic behaviour has some consequences, e.g. same design for adsorber and desorber, thermal cycling of adsorbers, importance of inactive thermal mass and different approaches to internal heat recovery. The effect of these items on the optimisation results is presented in this study. It is shown how the periodic operation results in a decrease in COP and an increase in the specific heat exchange area, i.e. the cost. The increase in exchange area depends mainly on the duration of the phase, where no cooling energy is produced, while the decrease in COP depends mainly on the inactive thermal mass.

Design and performance prediction of a novel zeolite–water adsorption air conditioner

Abstract A novel adsorption air conditioner is designed that supplies 8–12 °C chilled water for the fan coil in the locomotive operator cabin. Different from other two-bed adsorption cooling systems, this system has two adsorption/desorption chambers. One adsorber, one condenser and one evaporator are housed in one and the same adsorption/desorption chamber. There are no valves installed in the vacuum side. So, the reliability of the system is improved greatly. This machine uses zeolite and water as the working pairs. This system is driven by 350–450 °C exhaust gas generated by the internal combustion engine of the locomotive. The designed refrigerating power and COP (coefficient of performance) are 5 kW and 0.25, respectively, according to the requirements for the refrigeration output in the locomotive operator cabin and the waste heat provided by the engine. In this paper, a model for this system is described, and the simulation results are discussed. The model is validated in principle by limited experimental data. According to the calculation results, the refrigerating power of the machine is up to 10 kW with gas inlet temperature of 450 °C and evaporating temperature of 6.5 °C. The adsorber can be heated from 97 °C to 423 °C or cooled from 423 °C to 97 °C in 1320 s. Therefore, the heat and mass transfer performance of the adsorber is improved greatly. A few experimental data prove these conclusions.

Framework dynamics including computer simulations of the water adsorption isotherm of zeolite Na-MAP

Computer simulations of the water adsorption isotherm of zeolite Na-MAP have been performed. Both grand canonical molecular dynamics and a combination of Monte Carlo calculations and lattice relaxations (pseudodynamic simulations) have been used to account for the lattice dynamics of the zeolite framework during water adsorption. A number of different force fields have been evaluated to find the force field best suited for this kind of study. It is shown that the augmented CVFF is the only force field which is currently able to predict water adsorption in zeolites in a reasonable and affordable manner. The water adsorption isotherm of Na-MAP can be correctly predicted qualitatively. To reach quantitative agreement with experiment the way the excess chemical potential is determined has to be improved. An explanation of the reasons for the shape of the isotherm based on energetics is provided.

Regenerative adsorption heat pumps: Optimization of the design

The optimization of the design of a zeolite-water adsorption heat pump is presented, using a recently published model. Attention has been focused on the optimization of the energy fluxes between the machine components and the user. A modification of the system is proposed to achieve a constant heat flux from the external heat exchanger. The influence of several parameters, including the global bed heat transfer coefficient, on the performance of the system was analyzed. It was shown that by optimizing the design of the heat pump system, good improvements in performance can be achieved. A constant power of 18.6 kW released during 70% of the cycle time with a COP of 1.4 can be obtained with a two reactor regenerative system using 152 kg of zeolite in total. On the way to more efficient and economic regenerative systems, future research attention should be focused on improving the heat transfer inside the machine.

Shape-Selective Assemblies of Charge-Transfer Complexes as Molecular Probes for Water Adsorption in Zeolites

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTShape-Selective Assemblies of Charge-Transfer Complexes as Molecular Probes for Water Adsorption in ZeolitesK. B. Yoon, T. J. Huh, and J. K. KochiCite this: J. Phys. Chem. 1995, 99, 18, 7042–7053Publication Date (Print):May 1, 1995Publication History Published online1 May 2002Published inissue 1 May 1995https://doi.org/10.1021/j100018a042RIGHTS & PERMISSIONSArticle Views263Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Dynamic simulation of a recuperative adsorption heat pump

We present a method for dynamic simulation of a two-reactor adsorption heat pump. The operating principle of the system is described and the governing equations are derived, taking into account the efficiencies of the various components. A non-dimensional form of the model shows the important parameters which influence system performance. The resulting set of nonlinear differential equations is solved numerically using an iterative method. The model is tested using the zeolite-water adsorption pair and design data from the literature.

Experimental investigation on an adsorption system for producing chilled water

This paper describes a zeolite-water adsorption refrigeration system for producing chilled water, in which zeolite-13X-H 2O is used as a working pair and the exhaust gas from a diesel engine is utilized as a heat source. The system is to be used on a fishing boat for preserving aquatic products. The design of the system is given. The adsorption unit consists of many adsorption elements. The dynamic curve of the elements has been measured in a laboratory. A medium-size prototype of the adsorption chiller has been made, and its preliminary operating performance with an associated diesel engine is given. Further testing of its application is underway.

Identification of zeolites for heat transformer, chemical heat pump and cooling systems

Among the gas-solid adsorption processes the zeolite water adsorption seems to be very interesting for use in thermodynamic systems such as chemical heat pump, heat transformer and cooling systems. This work evaluates theoretically the best type of zeolite for use in each system on the basis of the adsorption data of zeolites using prefixed operative conditions. Results obtained indicate that thermodynamically a given zeolite type achieves better results than the others for each of the abovementioned systems. Methodology and criterion of comparison used can be applied to other gas-solid processes aiming at realizing chemical heat pump, heat transformer and cooling systems.