Experimental Researches On Bubble Absorption Characteristics With Organic Working Fluids (R124-DMAC) In A Vertical Tube

Vapor absorption refrigeration systems(VARSs)are considered to have a wide application prospect because they can be driven by waste heat.Vehicle or ship engines will consume large quantity of fuel and exhaust vast waste heat to environment directly when they operate.If the waste heat can be recovered to drive VARS to meet cold energy demands for vehicles or ships,the energy consumption of those will be decreased.Under the support of National Natural Science Foundation of China(NSFC),an absorption-compression hybrid refrigeration cycle(ACHRC)driven by exhaust gases and power from vehicle engines was proposed by the research team in 2013,which had been verified the feasibility by theories and experiments.In the ACHRC,R124(2-chloro-1,1,1,2,-tetrafluoroethane)-DMAC(N',N'-dimethylacetamide)mixture as the working fluid was applied.However,few efforts about the heat and mass transfer performance and the air cooled finned bubble absorber which is a key device in the ACHRC had been made up to now.At present,the researches on organic working fluid bubble absorption processes under the condition of large volume flow rate ratio between gas and liquid are shortage,which brings a lot of difficulties and uncertainties for bubble absorber designing and miniaturization.Under the financial support by NSFC(Grant no.51376032),the research team continued to investigate on heat and mass transfer characteristics during R124-DMAC bubble absorption process in an air cooled absorber.Because of the defects of heat and mass couple transfer theories and the lack of basic data for the organic working fluids bubble absorption process,it was difficult to analyze the process with a fully theoretical method.Therefore,a visual and non-visual experimental platform for R124-DMAC bubble absorption in a vertical tube absorber was designed and built for this research.Based on the mainly experimental researches with theoretical analysis,the flow pattern characteristics,bubble absorption heights,the overall and local heat and mass transfer coefficients were studied,and the dimensionless correlations for heat and mass transfer coefficients were proposed.The bubble behaviors,flow pattern characteristics and distributions were observed and the bubble absorption heights were measured by using the visual bubble absorber.In general,three kinds of flow patterns,churn,slug and bubble flows,could be observed obviously when the gas liquid volumetric flow rate ratio reached a certain value.Slug flow was considered as an important flow pattern to be strengthened to decrease the bubble absorption height.A correlation for calculating bubble absorption height was proposed within the errors less than 20%.In addition,the nozzle orifice was a key parameter to affect bubble absorption height and flow pattern distribution.The orifice overall area was the main factor to bubble absorption height rather than orifice numbers.The non-visual bubble absorber was used to investigate on heat and mass transfer characteristics in the bubble absorption process.The results showed that increasing vapor and solution flow rate or decreasing the solution inlet temperature and concentration,cooling water inlet temperature and nozzle orifice diameter could enhance the heat and mass transfer performance of the absorber.Finally,correlations for calculating heat and mass transfer coefficients were proposed within the errors all less than 20%.A simplified distributed parameter model was established,in which the bubble absorption height,two-phase and single-phase distribution from visual experiments and the temperature distribution along with the absorber from non-visual experiments were considered as boundary and constraint conditions.The model could obtain the distribution of two-phase region,the two-phase convective heat transfer and volumetric mass transfer coefficients.Finally,new correlations of two-phase and single-phase convective heat transfer coefficients and two-phase mass transfer coefficient for R124-DMAC bubble absorption process in a vertical tubular bubble absorber were proposed within the errors all less than 15%.The research results could lay the foundation for studying organic working fluids bubble absorption process,compact air cooled finned bubble absorber and the practical application in mobile absorption refrigeration system driven by waste heat.