Mass and heat transfer characteristics of a single-high aspect ratio microchannel absorber

Yunshan Liu, Ebrahim Al Hajri

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Recently, study on a microscale-based absorption refrigeration system has sprung up motivated by the need of efficient energy utilization. Heat-driven absorption systems offer a possibility of generating both power and cooling with environment friendly refrigerants, such as ammonia/water and LiBr/water. However, these systems are often large in size and low in COP especially in single stage absorption systems. These characteristics of absorptions systems make them unattractive in most cases. This work introduces the utilization of micro-channel enhanced surfaces as heat exchangers to enhance the component and system performance, to reduce the system size and to reduce the cost of the system as well. In this work, a new concept of enhancing heat and mass transfer processes is applied in the absorber part of the absorption cycle by using a single micro-channel. Due to its merit of high area to volume ratio, microchannel technology has been well theoretically validated to be a very effective and potential choice for enhancing heat transfer performance. But there is a lack of research work on the mass transfer performance in micro-channels. This work investigated simultaneous mass and heat transfer characteristics of a novel microchannel absorber that uses LiBr/water as the working fluid. A microchannel with hydraulic diameter of 0.7mm is employed in this characterization study. Velocity distribution, pressure drop, concentration and temperature profile inside the microchannel as well as effects of the inlet absorbent concentration, flow rate and temperature together with the refrigerant flow rate on the heat/mass transfer are predicted. Investigations on the optimum inlet angle design of a single channel absorber are also presented in the end of this work. Feasibility of this novel absorber design was proved via this numerical simulation as the mass transfer taking place inside the mixing channel was observed to achieve the identical performance but with a size reduction by 1/27 compared to a conventional falling film absorber. A 7 times enhancement of the heat transfer coefficient was also achieved with the comparison of a macro-scale based absorber configuration.

Original languageBritish English
Title of host publicationASME 2012 International Mechanical Engineering Congress and Exposition, IMECE 2012
Pages1833-1846
Number of pages14
EditionPARTS A, B, C, D
DOIs
StatePublished - 2012
EventASME 2012 International Mechanical Engineering Congress and Exposition, IMECE 2012 - Houston, TX, United States
Duration: 9 Nov 201215 Nov 2012

Publication series

NameASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE)
NumberPARTS A, B, C, D
Volume7

Conference

ConferenceASME 2012 International Mechanical Engineering Congress and Exposition, IMECE 2012
Country/TerritoryUnited States
CityHouston, TX
Period9/11/1215/11/12

Keywords

  • Heat transfer
  • Libr/water
  • Mass transfer
  • Microchannel

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