Heat and Mass Transfer in Hygroscopic Rotor During Adsorption and Desorption Process

In this paper, the performance of a channel element of a hygroscopic matrix is evaluated by detailed numerical modeling. The adopted physical model takes into account the gas-side and solid-side resistances to heat and mass transfer, as well as the simultaneous heat and mass transfer occurring simultaneously with the water adsorption/desorption process in the desiccant porous channel wall domain. The desiccant medium is silica gel RD, the equilibrium being characterized by sorption isotherms. Appropriate convective transfer coefficients are taken into account for the calculation of the heat and mass transfer phenomena between the airflow and the channel wall. The response of the channel element to a step change in the airflow states is simulated, the results enabling the investigation of some differences between the adsorption and desorption processes.

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Numerical Modelling of the Heat and Mass Transfer in a Channel with Hygroscopic Walls

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.273-276.782 ◽

2008 ◽

Vol 273-276 ◽

pp. 782-788 ◽

Cited By ~ 1

Author(s):

C.R. Ruivo ◽

J.J. Costa ◽

A.R. Figueiredo

Keyword(s):

Mass Transfer ◽

Porous Medium ◽

Numerical Modelling ◽

Heat And Mass Transfer ◽

Sorption Isotherms ◽

Physical Modelling ◽

Desorption Process ◽

Strongly Coupled ◽

Two Phases ◽

Adsorption Desorption

In this paper the numerical modelling of the behaviour of a channel of a hygroscopic compact matrix is presented. The heat and mass transfer phenomena occurring in the porous medium and within the airflow are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption/desorption processes. The adopted physical modelling takes into account the gas side and solid side resistances to heat and mass transfer, as well as the simultaneous heat and mass transfer together with the water adsorption/desorption process in the wall domain. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms. The airflow is treated as a bulk flow, the interaction with the wall being evaluated by using appropriated convective coefficients. The model is used to perform simulations considering two distinct values of the channel wall thickness and different lengths of the channel. The results of the modelling lead to a good understanding of the relationship between the characteristics of the sorption processes and the behaviour of hygroscopic matrices, and provide guidelines for the wheel optimization, namely of the duration of the adsorption and desorption periods occurring in each hygroscopic channel.

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Numerical Investigation of Heat and Mass Transfer During the Desorption Process of a LaNi5–H2 Reactor

Journal of Heat Transfer ◽

10.1115/1.4033056 ◽

2016 ◽

Vol 138 (9) ◽

Cited By ~ 1

Author(s):

Fatma Bouzgarrou ◽

Faouzi Askri ◽

S. Ben Nasrallah

Keyword(s):

Mass Transfer ◽

Heat And Mass Transfer ◽

Dynamic Behavior ◽

Heating Temperature ◽

Applied Pressure ◽

Computer Code ◽

Desorption Process ◽

Time Space ◽

Simple Implementation ◽

Volume Method

In this paper, coupled heat and mass transfer during the desorption process of a metal–hydrogen reactor (LaNi5–H2) is numerically investigated. To predict the dynamic behavior of this reactor, a new algorithm based on the lattice Boltzmann method (LBM) is proposed as a potential solver. Based on this algorithm, a computer code is developed using fortran 90. This algorithm is validated successfully by comparison with experimental data reported in the literature and results obtained by finite volume method (FVM). Using the developed code, the time–space evolutions of the temperature and the hydride density within the reactor are presented. In addition, the effect of some parameters (applied pressure, heating temperature, and overall heat transfer coefficient) on the dynamic behavior of the reactor is evaluated. Compared to the FVM, the proposed algorithm presents simple implementation on a computer and with reduced CPU time.

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Effectiveness Parameters for the Heat and Mass Transfer in a Desiccant Wheel

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.312-315.205 ◽

2011 ◽

Vol 312-315 ◽

pp. 205-210

Author(s):

C.R. Ruivo ◽

J.J. Costa ◽

A.R. Figueiredo

Keyword(s):

Mass Transfer ◽

Heat And Mass Transfer ◽

Sorption Isotherms ◽

Channel Length ◽

Transfer Coefficients ◽

Desorption Process ◽

Strongly Coupled ◽

Desiccant Wheel ◽

Cyclic Behaviour ◽

Two Phases

The desiccant wheel is the key component in a solid-desiccant system for air dehumidification. The heat and mass transfer phenomena occurring within the porous channel walls of the wheel and with the airflow are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption/desorption processes. The dynamic analysis of such devices integrated in non-conventional HVAC&R systems can be easily done by a project designer using the NTU-effectiveness method, provided that appropriate correlations for two independent effectiveness parameters are available. In this work, the performance of a desiccant wheel was evaluated by numerical modelling the cyclic behaviour of a representative channel of the hygroscopic matrix. The physical model adopted takes into account the gas-side and solid-side resistances, as well as the simultaneous heat and mass transfer coupled with the water adsorption/desorption process in the channel wall domain. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms. The desiccant medium considered is silica gel RD. In the numerical model, the airflow is treated as a bulk flow, and its interaction with the wall channel matrix is represented by appropriate convective heat and mass transfer coefficients. Two independent effectiveness parameters were defined. A set of cases was numerically simulated and the results were analysed to assess the dependence of those effectiveness parameters on the process and regeneration airflow rates and on the channel length. As a conclusion, novel empirical correlations are here purposed.

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