A simplified thermodynamic analysis of a LiBr-H2O vertical tube absorber

Rogdakis, ED; Papaefthimiou, VD

dc.contributor.author	Rogdakis, ED	en
dc.contributor.author	Papaefthimiou, VD	en
dc.date.accessioned	2014-03-01T02:42:03Z
dc.date.available	2014-03-01T02:42:03Z
dc.date.issued	2002	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/30755
dc.relation.uri	http://www.scopus.com/inward/record.url?eid=2-s2.0-78249285599&partnerID=40&md5=368641e1c4e6c212adbcbcaf1bc7a0bc	en
dc.relation.uri	http://www.scopus.com/inward/record.url?eid=2-s2.0-0346781697&partnerID=40&md5=987137d27fa9082ffd8ab137347df1bd	en
dc.subject	Absorption	en
dc.subject	Effectiveness	en
dc.subject	Heat of absorption	en
dc.subject	Partial enthalpy	en
dc.subject	Real gas	en
dc.subject.other	Absorption process	en
dc.subject.other	Absorption system	en
dc.subject.other	Aqueous solutions	en
dc.subject.other	Binary solutions	en
dc.subject.other	Coolant temperature	en
dc.subject.other	Effectiveness	en
dc.subject.other	Energy differences	en
dc.subject.other	Falling film	en
dc.subject.other	Heat and mass transfer coefficients	en
dc.subject.other	Heat of absorptions	en
dc.subject.other	Heat of dilution	en
dc.subject.other	Ideal gas	en
dc.subject.other	Initial treatment	en
dc.subject.other	Liquid solution	en
dc.subject.other	Liquid water	en
dc.subject.other	Lithium bromide	en
dc.subject.other	Mass exchange	en
dc.subject.other	Mass flow rate	en
dc.subject.other	Mass fraction	en
dc.subject.other	Mass transfer coefficient	en
dc.subject.other	Mass transfer rate	en
dc.subject.other	Partial enthalpies	en
dc.subject.other	Pump system	en
dc.subject.other	Pure substances	en
dc.subject.other	Real gas	en
dc.subject.other	Saturated water	en
dc.subject.other	Solution interactions	en
dc.subject.other	Solution temperature	en
dc.subject.other	Spatial variations	en
dc.subject.other	Superheated steam	en
dc.subject.other	System of ordinary differential equations	en
dc.subject.other	Theoretical result	en
dc.subject.other	Thermo dynamic analysis	en
dc.subject.other	Thermo-physical property	en
dc.subject.other	Transport phenomena	en
dc.subject.other	Tube absorbers	en
dc.subject.other	Vertical tube	en
dc.subject.other	Water vapour	en
dc.subject.other	Binary mixtures	en
dc.subject.other	Bromine compounds	en
dc.subject.other	Differentiation (calculus)	en
dc.subject.other	Enthalpy	en
dc.subject.other	Gas absorption	en
dc.subject.other	Gases	en
dc.subject.other	Laminar flow	en
dc.subject.other	Lithium	en
dc.subject.other	Mass transfer	en
dc.subject.other	Mechanical engineering	en
dc.subject.other	Ordinary differential equations	en
dc.subject.other	Pumps	en
dc.subject.other	Solutions	en
dc.subject.other	Steam	en
dc.subject.other	Temperature	en
dc.subject.other	Thermoanalysis	en
dc.subject.other	Tubes (components)	en
dc.subject.other	Water treatment	en
dc.subject.other	Water absorption	en
dc.title	A simplified thermodynamic analysis of a LiBr-H2O vertical tube absorber	en
heal.type	conferenceItem	en
heal.publicationDate	2002	en
heal.abstract	One of the most important components of an absorption air-conditioning/heat pump system is the absorber, where the refrigerant water vapour is absorbed into the liquid solution. While absorption systems have been in use for several years, the complex transport phenomena occurring in the absorber are not fully elucidated yet. Thus, an attempt is made to model the absorption process of water vapour in aqueous solutions of lithium bromide considering a falling-film, vertical-tube absorber. The proposed analysis is based on the formulation of four differential equations describing the spatial variation (parallel to the tube-axis) of solution mass, temperature, mass fraction and coolant temperature. The system of ordinary differential equations is numerically solved using a non-stiff numerical method. Thermophysical properties and especially, heat and mass transfer coefficients are calculated using widely-accepted and reliable relationships, which are extracted from the literature using recently published information on wavy-laminar flows. In the present study, the questionable assumption of treating the water vapour as an ideal gas is heavily modified utilizing. Consequently, the hypothesis of saturated water vapour at the steam-solution interaction surface is revised by introducing an energy difference between the superheated steam and the liquid water within the binary solution. The last correction encouraged us to compare theoretical results for solution temperature, mass fraction and mass flow rate, which were obtained using both assumptions. It was proved that the initial treatment causes an underestimation of the absorbed steam mass and correspondingly, an underestimation of solution temperature and mass fraction at the mass exchange interface. An attempt is made also to identify the effect of mass transfer coefficient on the effectiveness of the absorption process and on the energy differences between the superheated steam and the liquid water either as pure substance or as component of the binary mixture. It was shown that the increase of mass transfer coefficient leads to an increase of steam mass transfer rate and to a corresponding decrease of solution temperature slope at the entrance of a tube. Correspondingly, the increase of mass transfer coefficient results in an increase of heat of absorption and heat of dilution at the same variation range of the solution mass fraction. Copyright © 2002 by ASME.	en
heal.journalName	ASME International Mechanical Engineering Congress and Exposition, Proceedings	en
dc.identifier.volume	42	en
dc.identifier.spage	455	en
dc.identifier.epage	462	en