CFD modeling of humidification dehumidification distillation process

Abstract Exploring new methodologies to meet the growing demands for water and energy sources is an important step towards a sustainable future. HDH is a promising technology applied for both water desalination and industrial water treatment. However, due to the lower Gain Output Ratio (GOR) of HDH systems, its wide-ranging applications are restricted. This issue can be resolved solely by increasing the GOR of the HDH systems. The main principle of HDH systems considered in this study is the distillation of water under atmospheric condition by an air loop saturated with water vapor and driven by natural convection thus eliminating the need for pumping power. In this work, a numerical investigation is carried out for predicting the performance of a simple HDH cycle taking place in a rectangular enclosure (cavity) of different aspect ratios. The cavity has two horizontal adiabatic walls and two vertical isothermal walls; one of them is heated while the other one is cooled. The vertical hot wall is kept wet by maintaining a thin layer of water flowing downstream and the cavity is assumed long enough to justify the assumption of two-dimensional flow. A computational model is developed for predicting the velocity, temperature and concentration fields within the cavity as well as calculating the rate of water evaporating from the cavity hot side and condensing on its cold side. The model is based on numerical solution of the conservation equations of mass, momentum, energy and species considering the Boussinesq approximation. The model has been validated and the effect of aspect ratio on the performance of the HDH system is investigated. The results show that the aspect ratio of 1.5 produces the maximum heat and mass transfers. In addition, high convection rates tend to maximize the Nusselt number. The values of Nusselt based on latent heat exceed the Nusselt based on sensible heating.

[1]  Hwataik Han,et al.  Double diffusive natural convection in a vertical rectangular enclosure-!. Experimental study , 1991 .

[2]  Wei-Mon Yan,et al.  Mixed convection heat and mass transfer in vertical rectangular ducts , 1997 .

[3]  Li Ran,et al.  核磁気共鳴を用いたKH 3 (SeO 3 ) 2 単結晶の強弾性相転移の研究 , 2008 .

[4]  Yan Wei-Mon.  Effects of film evaporation on laminar mixed convection heat and mass transfer in a vertical channel , 1992 .

[5]  M. Engelhardt,et al.  Solarthermal seawater desalination systems for decentralised use , 1998 .

[6]  A. Hussein,et al.  Numerical simulation of three-dimensional double diffusive free convection flow and irreversibility studies in a solar distiller , 2012 .

[7]  J. Hyun,et al.  Double-diffusive convection in a rectangle with opposing horizontal temperature and concentration gradients , 1990 .

[8]  Amaresh Dalal,et al.  A numerical study of natural convection around a square, horizontal, heated cylinder placed in an enclosure , 2006 .

[9]  S. Ostrach,et al.  Experimental study of natural convection in shallow enclosures with horizontal temperature and concentration gradients , 1985 .

[10]  George N. Barakos,et al.  Natural convection flow in a square cavity revisited: Laminar and turbulent models with wall functions , 1994 .

[11]  Ruey-Jen Yang,et al.  Double diffusive natural convection in a partially heated enclosure with Soret and Dufour effects , 2009 .

[12]  Md. Abul Kalam,et al.  Double-diffusive natural convection in a triangular solar collector , 2012 .

[13]  M. J. Cunningham,et al.  Heat and moisture transfer by natural convection in a rectangular cavity , 1989 .

[14]  M. Sheremet,et al.  A numerical simulation of double-diffusive conjugate natural convection in an enclosure , 2011 .

[15]  G. Kefayati.  Simulation of double diffusive natural convection and entropy generation of power-law fluids in an inclined porous cavity with Soret and Dufour effects (Part II: Entropy generation) , 2016 .

[16]  Wei-Mon Yan,et al.  Mixed convection heat transfer enhancement through film evaporation in inclined square ducts , 2005 .

[17]  A. Kuznetsov,et al.  The Cheng–Minkowycz problem for the double-diffusive natural convective boundary layer flow in a porous medium saturated by a nanofluid , 2011 .

[18]  Gh.R. Kefayati,et al.  FDLBM simulation of entropy generation in double diffusive natural convection of power-law fluids in an enclosure with Soret and Dufour effects , 2015 .

[19]  J. Fourier.  Théorie analytique de la chaleur , 2009 .

[20]  Hwataik Han,et al.  Double diffusive natural convection in a vertical rectangular enclosureII. Numerical study , 1991 .

[21]  Ali J. Chamkha.  DOUBLE-DIFFUSIVE CONVECTION IN A POROUS ENCLOSURE WITH COOPERATING TEMPERATURE AND CONCENTRATION GRADIENTS AND HEAT GENERATION OR ABSORPTION EFFECTS , 2002 .

[22]  L. Burmeister.  Convective heat transfer , 1983 .

[23]  Numerical study of double-diffusion convection coupled to radiation in a square cavity filled with a participating grey gas , 2008 .

[24]  M. Engelhardt,et al.  Small-scale thermal seawater desalination simulation and optimization of system design , 1999 .

[25]  Brahim Benhamou,et al.  Effect of air humidity at the entrance on heat and mass transfers in a humidifier intended for a desalination system , 2011 .

[26]  S. Ostrach.  An analysis of laminar free-convection flow and heat transfer about a flat plate parallel to the direction of the generating body force , 1953 .