ABSTRACT
Condensation frosting usually causes a negative influence on heat exchangers employed in engineering fields. As the relationships among the first three typical condensation frosting stages in the edge regions of cold plates are still unclear, an experimental study on the localized condensation frosting characteristics in the edge region of a cold plate was conducted. The edge effects on the water droplet condensation (WDC), water droplet frozen (WDF) and frost layer growth characteristics were quantitatively investigated. The results showed that the number of droplets coalescing in the edge-affected regions was around 50% greater than in the unaffected regions. At the end of the WDC stages, the area-average equivalent contact diameter and coverage area ratio of water droplets in the edge-affected regions were 2.69 times and 11.6% greater than those in the unaffected regions under natural convection, and the corresponding values were 2.24 times and 9.9% under forced convection. Compared with the unaffected regions, the WDF stage duration in the edge-affected regions decreased by 63.6% and 95.3% under natural and forced convection, respectively. Additionally, plate-type and feather-type frost crystals were, respectively, observed in natural and forced convection. The results of this study can help in the better understanding of the condensation frosting mechanism on a cold plate, which provides guidelines for optimizing the design of heat exchanger structures and system control strategies facing frosting problems.
ABSTRACT
As the human excreta, urine is often used as one of the test materials in medical research due to its composition and content directly reflecting the health status of the body. Considering that the substances in urine may show different effects on its freezing process, solidification characteristics of sessile urine droplets on a horizontal cold plate surface under natural convection were experimentally investigated by comparing with those of water droplets under same conditions. To make the conclusion analysis more reasonable, the urine of a human without any diseases, especially metabolic diseases, was treated and used. The characteristics include nucleation location, dynamic variation of droplet color, and temperatures at different heights inside the droplet, and so forth. It was found that, similar to that of a water droplet, the solidification process of a urine droplet also experiences the following four stages: supercooling, recalescence, freezing, and cooling, in chronological order. Differently, the urine droplet changes from transparent to blur white at the supercooling stage due to the precipitation of inorganic salts. For nucleation locations, 46.67% cases are at the bottom, while others are at the top and middle of urine droplets. For a 10 µL droplet on a surface of -30 °C, urine has a 0.95 s freezing duration shorter than water, and a 5.31 °C lower phase-transition temperature. Results of this study are expected to reflect the content of substances in urine and thus provide references for urinalysis of patients with metabolic diseases.
Subject(s)
Convection , Water , Freezing , Humans , Phase Transition , Transition TemperatureABSTRACT
The interaction parameters between two components need to be first determined to obtain the thermophysical properties of the binary mixtures. In this paper, the research progresses of the binary interaction parameter for CO2 and hydrocarbons (HCs) and their related mixtures are illustrated. Aiming at the physical property prediction of CO2/alkanes (C1-C10) binary mixtures in pseudocritical regions, the experimental data of CO2/alkanes (C1-C10) in the pseudocritical region available in the open literature are collected. Besides, the calculation of k ij is carried out by five typically accepted correlations selected from the literature. The effects of temperature, pressure, carbon number, and acentric factor on k ij are investigated. By researching the influence of the above five factors on k ij , it reveals that temperature is the most important one. Considering the influence of the critical temperatures of mixtures, a simple correlation is proposed to evaluate k ij for light HC mixtures in the pseudocritical region.
