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The motion and interaction of a bubble pair in a non-Newtonian fluid (xanthan gum solution) were numerically simulated using volume of fluid (VOF) method, in which the continuous surface tension model and the power-law model were adopted to represent surface tension and rheological properties of non-Newtonian fluids, respectively. The effects of initial horizontal bubble interval, oblique alignment and rheological properties of non-Newtonian fluids on a pair of bubbles rising side-by-side were evaluated in this study. The results indicated that for the case with non-dimensional initial horizontal interval of bubble h* = 4.0, the interaction between the bubbles shows a minimum repulsive effect. Moreover, for the oblique angle alignment a greater repulsive force between the bubbles was seen when the angle was reduced.However, oblique coalescence occurred due to the higher attraction between the bubbles at higher angle, which is independent of flow index It is also found that the repulsion effect as well as the variation of the bubble shape from spherical to wobbling are more significant at a lower flow index (n < 0.5) due to the shear-thinning effect as well as the differences of their flow field structures.

The experimental analysis of base pressure in a high-speed compressible flow is carried out. The flow is made to expand abruptly from the nozzle into an enlarged duct at fifteen sonic and supersonic Mach numbers. The analysis is made for variation in the nozzle pressure ratio (NPR), length to diameter ratio, and area ratio. The effect of active micro-jets on the base and wall pressure is assessed. The data visualization of the huge experimental data generated is performed using heat maps. For the first time, six back-propagation neural network models (BPMs) are developed based on input and output possibilities to predict the pressure in high-speed flows. The experimental analysis revealed that depending upon the type of expansion, the base pressure changes. A jet of air blown at the base using micro-jets is found to be effective in increasing the base pressure during the under-expansion regime, while the wall pressure remains unaffected. The data visualization provided an insight into the highest impact on the base pressure by the NPR. The six BPMs with two hidden layers having four neurons per layer are found to be most suitable for the regression analysis. BPM 5 and BPM 6 accurately predict the highly non-linear data of the base and wall pressure.

Bubble coalescences have a significant role in petroleum and chemical industries for proper mixing, good heat and mass transfer between the gas and liquid phases. In this study, the volume of fluid method has been used to model for investigation of co-axial bubble coalescence dynamic evolution in stagnant fluid. The CSF method was incorporated as a source term in the momentum equation to track the motion of the bubble and liquid interface. The effects of Bond number ranges, Bo~4.09-50 (variation of the surface tension) and Reynolds number range, Re~0.98-120 (variation of the liquid viscosity) were investigated. Significant effects were observed in the process of bubble coalescence on the shape of bubbles when the viscosity ratio (μ r ), and density ratio (ρ r ) were kept constant. The changes in bubble shape with progressing time were validated by the experimental observation of available literature. For low Bo and Re, the late coalescence of the bubbles was found, whereas the shape of the succeeding bubbles had changed significantly. The same ratio of Bo/μ r and Bo/Re does not affect the bubble coalescence process, if Bo, μ r and Re is reduced to 82%. By the study of co-axial coalescence of three bubbles, it is found that the liquid-film rupture and bubble breakup between the middle and third bubble occurs faster for both low and high Re. Figure 4. Predicted two co-axial bubble coalescence for (a) Re = 12, Bo = 50, r = 1000, r = 100 (Case 2) and (b) Re = 10, Bo = 50, r = 850, r = 100 (Chen et al. [16] ).Asia-Pacific Journal of Chemical Engineering NUMERICAL STUDY OF CO-AXIAL BUBBLE COALESCENCE 675 Bo = 5 ; (1st) Bo = 5 ; (2nd) Bo = 5 ; (3rd) Bo = 50 ; (1st) Bo = 50 ; (2nd) Bo = 50 ; (3rd) Figure 9. Effect of Bond number on three co-axial bubble rising history for Re = 12, r = 1000 and r = 100. Figure 10. Predicted three co-axial bubbles coalescence for r = 1000 and r = 100. (a) Re = 1.2, Bo = 50. (b) Re = 120, Bo = 50. MD. T. ISLAM ET AL. Asia-Pacific Journal of Chemical Engineering 678

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Summary In an electric vehicle, energy storage is in the form of electrochemical batteries, which are prone to thermal runaway and capacity fading if not maintained below safe temperature limits. An efficient battery cooling system is necessary for safer usage of electric cars during their life cycle. The current work presents a novel design that allows the coupling of liquid channels to a phase change material container in cylindrical batteries. The channeling approach allows heat dissipation from the phase change material container to both circulating media and convecting air. The design also helps to operate the cooling system without the circulation of liquid media in case of low ambient conditions. The comparison of the proposed system with a noncoupled liquid channel system is also presented to underline the merits of the system. The cooling media at a supply temperature of 30°C and the flow rate of 30 mL/min is adequate during the high ambient temperature of 40°C. The coupling of liquid channels to phase channel containers resulted in lowering the battery temperature well below 41.2°C even at an extremely high ambient temperature of 40°C.

The adsorption of MB dye from aqueous solution onto HCl acid treated water-hyacinth (H-WH) was investigated by carried out batch sorption experiments. The effect of process parameters such as pH, adsorbent dosage, concentrations and contact time, and ionic strength were studied. Adsorption of MB onto H-WH was found highly pH dependent and ionic strength shows negative impact on MB removal. To predict the biosorption isotherms and to determine the characteristic parameters for process design, Langmuir, Freundlich, Temkin, and Halsey isotherms models were utilized to equilibrium data. The adsorption kinetics was tested for pseudo-first-order (PFO), pseudo-second-order (PSO), intraparticle diffusion (IPD), and Bangham’s kinetic models. The Langmuir isotherm model showed the goodness-of-fit among the tested models for equilibrium adsorption of MB over H-WH and indicated the maximum adsorption capacity as 63.30 mg/g. Higher coefficient of determination (R2>0.99) and better agreement between the qe (experimental) andqe(calculated) values predicted that PSO kinetic model showed the goodness-of-fit for kinetic data along with rate constant1.66×10-3,4.42×10-3, and3.57×10-3 mg·g-1min⁡-1/2⁡, respectively, for the studied concentration range. At the initial stage of adsorption, the overall rate of dye uptake was found to be dominated by external mass transfer, and afterwards, it is controlled by IPD mechanism.

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