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

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.

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

2008 ◽  
Vol 273-276 ◽  
pp. 782-788 ◽  
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.

Characterising the Differences between the Adsorption and Desorption Processes in a Desiccant Layer by Detailed Numerical Modelling

2012 ◽  
Vol 326-328 ◽  
pp. 690-695
Author(s):  
C.R. Ruivo ◽  
J.J. Costa ◽  
A.R. Figueiredo
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Channel Wall ◽  
Water Adsorption ◽  
Sorption Isotherms ◽  
Transfer Coefficients ◽  
Desorption Process ◽  
Adsorption And Desorption ◽  
Adsorption Desorption ◽  
Simultaneous Heat

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.

Heat Transfer on Nanofluid Flow With Homogeneous–Heterogeneous Reactions and Internal Heat Generation

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Raj Nandkeolyar ◽  
Peri K. Kameswaran ◽  
Sachin Shaw ◽  
Precious Sibanda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Generation ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Heterogeneous Reactions ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Fluid Properties

We investigated heat and mass transfer on water based nanofluid due to the combined effects of homogeneous–heterogeneous reactions, an external magnetic field and internal heat generation. The flow is generated by the movement of a linearly stretched surface, and the nanofluid contains nanoparticles of copper and gold. Exact solutions of the transformed model equations were obtained in terms of hypergeometric functions. To gain more insights regarding subtle impact of fluid and material parameters on the heat and mass transfer characteristics, and the fluid properties, the equations were further solved numerically using the matlab bvp4c solver. The similarities and differences in the behavior, including the heat and mass transfer characteristics, of the copper–water and gold–water nanofluids with respect to changes in the flow parameters were investigated. Finally, we obtained the numerical values of the skin friction and heat transfer coefficients.

An engineering model for coupled heat and mass transfer analysis in heated concrete

2002 ◽  
Vol 216 (2) ◽  
pp. 213-222 ◽  
Author(s):  
L y Li ◽  
J A Purkiss ◽  
R T Tenchev
Keyword(s):  
Mass Transfer ◽  
Mass Transport ◽  
Heat And Mass Transfer ◽  
Liquid Water ◽  
Gaseous Mixture ◽  
Sorption Isotherms ◽  
Engineering Model ◽  
Water Saturated ◽  
Mass Transport Equation ◽  
Heated Concrete

In this paper an engineering model for coupled heat and mass transfer in heated concrete is proposed. The model considers the heat transfer and mass transport of liquid water and gaseous mixture. The evaporation of liquid water is assumed to be related to the imbalance pressure between liquid water and water vapour controlled by the ideal gaseous mixture pressure and water saturated pressure. Thus, the content of liquid water is determined directly from its mass transport equation rather than through assumed sorption isotherms as in most existing models. Numerical results for temperature, pore pressure and contents of liquid water and gaseous mixture are presented. Some important features are highlighted through the discussion of results.

The Experimental Investigation of Steam Condensation With Non-Condensable Gas Under Natural Convection

2018 ◽  
Author(s):  
Xizhen Ma ◽  
Wen Fu ◽  
Haijun Jia ◽  
Peiyue Li ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
High Pressure ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Vertical Wall ◽  
Experimental System ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Calculation Results

The non-condensable gas is used to keep the pressure stable in the steam-gas pressurizer. The processes of heat and mass transfer during steam condensation in the presence of non-condensable gas play an important role and the thermal hydraulic characteristics in the pressurizer is particularly complicated due to the non-condensable gas. The effects of non-condensable gas on the process of heat and mass transfer during steam condensation were experimental investigated. A steam condensation experimental system under high pressure and natural convection was built and nitrogen was chosen in the experiments. The steam and nitrogen were considered in thermal equilibrium and shared the same temperature in the vessel under natural convection. In the experiments, the factors, for instance, pressure, mass fraction of nitrogen, subcooling of wall and the distribution of nitrogen in the steam, had been taken into account. The rate of heat transfer of steam condensation on the vertical wall with nitrogen was obtained and the heat transfer coefficients were also calculated. The characteristics curve of heat and mass transfer during steam condensation with non-condensable gas under high pressure were obtained and an empirical correlation was introduced to calculated to heat transfer coefficient of steam condensation with nitrogen which the calculation results showed great agreement with the experimental data.

Numerical Simulation of Heat and Mass Transfer Enhancement in Absorption Process With Double-Side Film-Inversion

2008 ◽  
Author(s):  
Ya-Ping Chen ◽  
Chen-Jie Shi ◽  
Ming-Heng Shi ◽  
Chen-Min Ling
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Vertical Plane ◽  
Mathematic Model ◽  
Absorption Process ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Plane Plate ◽  
Before And After ◽  
Calculation Results

Film-inversion is an effective way recently developed to enhance heat and mass transfer in absorbers. However, only one-side of round or rectangular tube i.e. half of the total heat transfer area is used to form film-inverting configuration in the published literature. The paper presents a double-side film-inverting scheme, which consists of two plate bundles and a set of comb shaped conjunction guiders between them for leading solution film from both-sides of each couple of the upper plate bundle to the opposite sides of the bottom ones. A two-scale crosswise corrugation plate bundle, which has vertical large corrugations and horizontal small ones, is suggested instead of the plane plate bundle. The horizontal small corrugation can make the film turbulent and film distribution uniform before and after inversion with surface tension effect, thus increasing the heat and mass transfer coefficients of the absorption process. A mathematic model for heat and mass transfer in absorption process with aqueous Li-Br solution falling film-inverting on two sequential vertical plane plates was established and solved numerically. The distributions of dimensionless velocity, temperature and concentration of liquid film profile before and after film-inverting were obtained. The influence of the number of inversion on heat and mass transfer characteristics was analyzed. The calculation results show that the heat and mass transfer coefficients of the once-film-inverting scheme have about 58% and 73% increment respectively over these of the none film-inverting scheme.

Lyon-Type Integral Forms of Wall Friction, Heat- and Mass Transfer Closure Relationships for Non-Equilibrium Two-Phase Flows: Generalization for Annular and Rod Cluster Geometries

2013 ◽  
Author(s):  
Yuri Kornienko
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Constitutive Relations ◽  
Wall Friction ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Friction Heat ◽  
Integral Forms ◽  
Substance Transfer

The main goal of this paper is to describe new approach to constructing generalized closure relationships for pipe, annular and sub-channel transfer coefficients for wall friction, heat and mass transfer. The novelty of this approach is that it takes into account not only axial and transversal parameter distributions, but also an azimuthal substance transfer effects. These constitutive relations, which are primordial in the description of single- and two-phase one-dimensional (1D) flow models, can be derived from the initial 3D drift flux formulation. The approach is based on the Reynolds flow, boundary layer, and substance transfer generalized coefficient concepts. Another aim is to illustrate the validity of the “conformity principle” for the limiting cases. The method proposed in this paper is founded on the similarity theory, boundary layer model, and a phenomenological description of the regularity of the substance transfer (momentum, heat, and mass) as well as on an adequate simulation of the flow structures. With the proposed generalized approach it becomes possible to develop an integrated in form and semi-empirical in maintenance structure analytical relationships for wall friction, heat and mass transfer coefficients.

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