Comparison of Transport Equation-Based Cavitation Models and Application to Industrial Pumps with Inducers

This paper investigates and compares four commonly used flow transport equation-based cavitation models and their applicability to predict the cavitation performance and bubble dynamics of an industrial centrifugal pump with a helical inducer. The main purpose of this study is to identify the most appropriate cavitation model and the associated empirical constants for calculating the cavitation performance of centrifugal pumps with inducers. Each cavitation model is reviewed in detail and the uniqueness of each model is outlined. These cavitation models are incorporated in a computational fluid dynamics code to study the vaporization and condensation transport rate of the fluid. Experimental tests are conducted on the pump to determine the true cavitation performance in terms of Net Positive Suction Head (NPSH). Experimental results are compared to simulation results for different cavitation models to validate accuracy and assumptions of each model, along with the empirical constants. Lastly, bubble formation, cavitation inception, and bubble growth predicted by each cavitation model are compared with the experimental results. A sensitivity analysis is conducted in order to determine the impact of each set of empirical constants to the condensation and the vaporization rate in the centrifugal pump. Results show that two of the cavitation models exhibit high dependency on the empirical constants in terms of change in vaporization rate. Modifications to empirical constants for two of the four cavitation models are suggested to obtain agreement with the experimentally observed cavitation behavior and better predict NPSH performance for the industrial pump studied.

A numerical study on capillary-evaporation behavior of porous wick in electronic cigarettes

A mathematical model based on heat and mass transfer processes in the porous wick of electronic cigarettes was established to describe the atomization of e-liquids according to max liquid temperature, vaporization rate and thermal efficiency in a single puff. Dominant capillary-evaporation effects were defined in the model to account for the effects of electrical power, e-liquid composition and porosity of the wick material on atomization and energy transmission processes. Liquid temperature, vaporization rate, and thermal efficiency were predicted using the mathematical model in 64 groups, varying with electrical power, e-liquid composition and wick porosity. Experimental studies were carried out using a scaled-model test bench to validate the model’s prediction. A higher PG/VG ratio in the e-liquid promoted energy transfer for vaporization, and the e-liquid temperature was comparatively reduced at a relatively high power, which was helpful to avoid atomizer overheating. Compared with the other factors, wick porosity affected the thermal efficiency more significantly. The vaporization rate increased with a higher wick porosity in a certain range. The modelling results suggested that a greater wick porosity and a higher PG ratio in e-liquids helped to improve the overall thermal efficiency.

Exploring the Acetone Evaporation and Airborne Neurotoxicity Bioassay against Adult Mosquito in the Enclosed Environment of Peet Grady Chamber

Mosquito has comprehensive and sensitive olfactory neuro-sensory located at antenna utilized for detecting airborne organic compounds in search of blood host. Mosquito is also known to have similar neurotransmitters function with human at neural synapses e.g. acetylcholinesterase, esterases and oxidases enzymes. Thus, there is potential use mosquito in predicting neurotoxicity of exogenic volatile organic compounds (VOC) e.g. manufactured acetone. Hence, the study evaluates the suitability to conduct bioassay of VOC neurotoxicity against mosquito in Peet Grady chamber that is commonly used for insecticidal bioassay. Acetone as the representative of VOC is easily evaporized at laboratory temperature of 26 to 29 °C without heating. The acetone evaporation profile on liquid surface and porous solid surface under the Peet Grady chamber is studied to ascertain the consistency of vaporization rate with homogenized distribution. The study showed the acetone has shown consistent vaporization rate of 23 mg/min from liquid surface and 116.3 mg/min from porous surface (filter paper) without heating, in a linear regression of very high positive correlation (r = 1.000) between time and mass of acetone vaporized. However, the non-homogenized distribution of acetone vapours in the Peet Grady chamber directly affected the accuracy to elucidate the neurotoxicity bioassay against mosquito in term of mosquito knockdown. The study suggests the positioning of mosquitoes in the Peet Grady chamber should be lower than the point of acetone vaporization, whereby the mosquitoes are knockdown by acetone vapours within the 20th minute upon reaching concentration of 170.3 to 196.1 ppm.

Oxidation Behavior of Si-B-C-N Multiphase Ceramic

Si-B-C-N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane and polyborazine due to their mutual solubility. The pyrolysis behavior of Si-B-C-N precursor was analyzed by TG-DSC-FTIR-MS coupling technique. The oxidation behavior was studied through static oxidation test. Results showed that oxidation rate of Si-B-C-N multiphase ceramic was greater than that of SiC ceramic obviously, which promoted forming the liquid B2O3 or stable borosilicate glass. The generated glass state oxides acted as a protective layer which could heal the cracks and reduce oxidation rate due to lower vaporization rate and smaller oxygen diffusivity. Furthermore, Si-B-C-N multiphase ceramic shows excellent oxidation resistance and can be kept in service in a long time at 1200°C