Experimental study of the ice slurry thermal-hydraulic characteristics in compact plate heat exchangers.

摘要

This study presents the results of an experimental work to characterize the fluid mechanical and heat transfer properties of ice slurries in compact plate heat exchangers. Both melting and ice slurry generation processes have been investigated.; In the first part of this study, the convective melting of ice slurry flowing vertically upward in an asymmetrically heated rectangular duct was investigated. Local ice slurry heat transfer coefficients and measurements of the mixture velocity, temperature and ice fraction distributions are reported for Re ∼2100 to 11,000, covering mean velocities from 0.06 to 0.90 m/s, average ice fractions by weight ranging from 0∼24%, two different heat flux conditions and two different channel gap-to-width aspect ratios of 1:12 and 1:8. Three factors were shown to elevate the heat transfer coefficients by 1.2 to 4 times in comparison to single-phase flow: (1) the average ice fraction, (2) thermally developing flow, and (3) the mixed convection and non-Newtonian flow characteristics experienced at low Reynolds numbers (Re 4000). The velocity profile measurements revealed that ice slurries display non-Newtonian flow characteristics even at low volume ice fractions (Φ_v > 2%). New heat transfer correlations are also proposed for the ice slurry heat transfer utilization in compact heat exchangers.; The second part of this study involved the scraped-surface heat transfer characteristics in a prototype compact plate ice slurry generator that was chilled by an evaporating R404A refrigerant. The chilled vertical surface was continuously scraped using a scraper-blade assembly to generate the ice slurry. The scraped-surface heat transfer coefficients are reported for both the chilling and ice slurry generation modes of operation for mass flow rates of 0.2∼1.2 kg/s, Reynolds numbers of 500∼4000, scraper frequency from 0 to 3 Hz and weight ice fractions from 0∼10%. The average heat transfer results suggested that the combined effects of agitation and phase change must be considered during the ice slurry generation process.; The results from this dissertation are useful for the development of compact heat exchangers for both the utilization and generation of ice slurry.