Increase In Liquid Height Research Articles

Experimental study on bubble dynamics and heat transfer of pool boiling at sub-atmospheric pressures

Pool boiling, as an efficient phase-change heat transfer method, has attracted extensive attention in recent years. However, the bubble dynamics behavior (BDB) and heat transfer characteristics of pool boiling at sub-atmospheric pressure (sub-ATM) are significantly different from those at or above standard atmospheric pressure (std-ATM). This paper presents experimental results of BDB and heat transfer characteristics of pool boiling at sub-ATM in the range of 30–120 kPa. High-speed backlight imaging technique was adopted. The results show that with the decrease of boiling pressure, the diameter and near circularity coefficient of bubble departure increase, and the frequency and aspect ratio decrease. With the decline in pressure, the critical heat flux (CHF) of pool boiling on the surface of the electric heater decreases. Specifically, the CHF at 120 kPa is 23.2% higher than that at 40 kPa. At sub-ATM, the boiling heat transfer coefficient (HTC) grows with the increase of liquid height. However, the HTC hardly changes with liquid height at std-ATM and higher.

A proposed method of bubble absorption-based deep dehumidification using the ionic liquid for low-humidity industrial environments with experimental performance

Liquid desiccant deep dehumidification (LDDD) is an excellent way to achieve low-carbon transformation of low-humidity industrial buildings. Currently, it is essential to improve its ability to produce lower humidity air (i.e., with a dew point below −10 °C). Functional ionic liquids (ILs) with extremely low vapor pressure, non-crystallization, and non-corrosion are ideal substitutes for high mass fraction aqueous inorganic solutions (e.g., LiCl, LiBr) in traditional liquid desiccant deep dehumidification. Meanwhile, the bubble absorption mode allows water vapor to condense on the huge contact surface between the bubbles and desiccant. Accordingly, it is expected to solve the low wettability and transfer unit number (NTUm) in falling-film absorption mode caused by the high viscosity of ILs. Thus, a new method of bubble absorption-based deep dehumidification using the IL is proposed. To validate it, the bubble absorption-based deep dehumidifier using a novel ionic liquid (BADD-IL) is developed and tested under different operating conditions. Besides, its moisture effectiveness is compared with those of falling film absorption-based dehumidifiers. The results show that increasing the liquid height, superficial velocity, as well as lowering the solution temperature, can strengthen the deep dehumidification performance, effectiveness and cooling ability to varying degrees. The increase of liquid height and superficial velocity promotes the gas-liquid interfacial area from different aspects, thus enhancing the transfer efficiency. Notably, the insufficient interfacial areas caused by low solution temperature cannot prevent better transfer efficiency dominated by high potential difference. Moreover, the NTUm of BADD-IL has a wide adjustment range (0.1–1.7), and the minimum supply air humidity ratio and maximum moisture effectiveness can reach 1.1 g/kgda and 81%, respectively. In overall, this study aims to further explore the deep dehumidification potential of ILs, and inform ideas for the LDDD development.

Experimental analysis of the humidification of air in bubble columns for thermal water treatment systems

The humidification-dehumidification process (HDH) for desalination is a promising technology to address water scarcity issues in rural regions. However, a low humidifier efficiency is a weakness of the process. Bubble column humidifiers (BCH) are promising for HDH, as they provide enhanced heat and mass transfer and have low maintenance requirements. Previous studies of HDH-systems with BCHs draw different conclusions regarding the impact of superficial air velocity and liquid height on the humidification. Furthermore, the impact of flow characteristics has never been investigated systematically at all. In this study, an optimized BCH test setup that allows for optical analysis of the humidifier is used and evaluated. Our test setup is validated, since the influence of water temperature on the humidification, which is exponential, is reproduced. Measurements with seawater show that the normalised system productivity is increased by about 56% with an increase in superficial air velocity from 0.5cm/s to 5cm/s. Furthermore, the system productivity is increased by around 29% with an increase in liquid height from 60mm to 378mm. While the impact of superficial air velocity can be traced back to temperature changes at the humidifier and dehumidifier outlets, the impact of liquid height is shown to be caused by a smaller heat loss surface in the humidifier with an increase in liquid height. For the impact of sieve plate orifice diameter, a clear influence on the humidification is not apparent, this parameter needs to be investigated further. Finally, our new test setup allows for analysing the humidification of air (1) in a systematic way, (2) in relevant measurement ranges and (3) in comparison with optical analyses of the flow characteristics.

Carbon dioxide removal by using Mg(OH)2 in a bubble column: Effects of various operating parameters

The present work includes the absorption of CO2 with Mg(OH)2 slurry in a bubble column reactor under semi-batch mode. To examine the effects of operating conditions on CO2 absorption performance, several important parameters including concentration of Mg(OH)2, inlet gas flow rate, and operating temperature on CO2 absorption behavior were studied. CO2 removal efficiency and absorption capacity (C:Mg ratio) were used to evaluate the absorption performance. Carbon dioxide removal efficiency increases with the increase of liquid height in the column, while the other parameters affect the efficiency in a more complex way. It is found that absorption capacity decreases with the increase of Mg(OH)2 concentration due to the interaction between Mg(OH)2 dissolution and MgCO3 precipitation. To observe the carbon transformation in solid phase, CHNS elemental analyzer was used to obtain the carbon mass percentage in solid samples. The carbon and magnesium speciation under equilibrium was modeled with MINEQL+. And the absorption capacity given by it conforms to the experimental data.

Dynamic Response Analysis of Vertical Cylindrical Storage Tanks Based on ADINA

Storage tanks after earthquake disaster may create the serious consequence, so their anti-seismic problems have drawn greater attention, and their seismic response become the focus of research. Considering the liquid-solid coupling and the interaction between foundation and storage tanks，three different volumes of storage tanks that have different liquid height were simulated under the earthquake using the software ADINA. The liquid sloshing wave height, peak acceleration of tank wall and hydrodynamic pressure were analyzed. The results show that the peak sloshing wave height shows a rising trend basically with the increase of liquid height, and the roofs of large tanks are more easier to be destroyed by liquid sloshing. With the increase of liquid height and tank volume, the response of peak acceleration is greater. The hydrodynamic pressure increases with the decrease of liquid height. Near the bottom of tank wall the value of hydrodynamic pressure is relatively large, so elephant foot buckling is easier to happen in that area.

Energy Dissipation and Shear Rate with Geometry of Baffled Surface Aerator

The geometric parameters of surface aeration systems govern the process phenomena. The dissipation rate of turbulent kinetic energy (e) and shear rate (γ) are the key process parameters for mixing in surface aerators. Present work by doing numerical computation by visimix® analyzes the effect of geometric parameters (impeller diameter, cross-sectional area of the tank, liquid height, width of the baffle, rotor blade length and immersion height) on e and γ. Analysis has been done by making the geometric parameters non-dimensionalized through rotor diameter. With an increase in liquid height and baffled width, there is an increase in the case of energy dissipation and shear rate values. In the case of tank area and blade length, it is vice versa. Energy dissipation and shear rate are not affected by the variation in immersion height of the impeller. Keywords: energy dissipation; mixing; shear rate; surface aerator DOI = 10.3329/cerb.v14i2.4910 Chemical Engineering Research Bulletin 14 (2010) 92-96

Variability of Energy Dissipation and Shear Rate with Geometry in Unbaffled Surface Aerator

The dissipation rate of turbulent kinetic energy () and shear rate (γ) are the key process parameters for mixing in surface aerators. At constant dynamic variables (rotational speed), both  and γ are greatly affected by the geometric parameters (impeller diameter, cross-sectional area of the tank, liquid height, rotor blade length and immersion height). By doing numerical computation by VISIMIX ®, present work analyzes the effect of non-dimensional (which is non-dimensionalized through rotor diameter) geometric parameters on e and g. With an increase in liquid height, there is an increase in the case of energy dissipation and shear rate values. In the case of tank area and blade length, it is vice versa. Energy dissipation and shear rate are not affected by the variation in immersion height of the impeller.

Variability of Energy Dissipation and Shear Rate with Geometry in Unbaffled Surface Aerator

mixing in surface aerators. At constant dynamic variables (rotational speed), both  and γ are greatly affected by the geometric parameters (impeller diameter, cross-sectional area of the tank, liquid height, rotor blade length and immersion height). By doing numerical computation by VISIMIX ®, present work analyzes the effect of non-dimensional (which is non-dimensionalized through rotor diameter) geometric parameters on e and g. With an increase in liquid height, there is an increase in the case of energy dissipation and shear rate values. In the case of tank area and blade length, it is vice versa. Energy dissipation and shear rate are not affected by the variation in immersion height of the impeller. © 2009 BCREC UNDIP. All rights reserved [Received: 17 October 2009, Revised: 12 December 2009, Accepted: 20 December 2009] [How to Cite : B. Kumar. (2009). Variability of Energy Dissipation and Shear Rate with Geometry in Unbaffled Surface Aerator. Bulletin of Chemical Reaction Engineering and Catalysis , 4(2): 55-60. doi:10.9767/bcrec.4.2.7110.55-60 ] [ How to Link/ DOI : http://dx.doi.org/10.9767/bcrec.4.2.7110.55-60 || or local: http://ejournal.undip.ac.id/index.php/bcrec/article/view/7110 ]

Entrainment and Maximum Vapour Flow Rate of Trays

This is a report on free entrainment measurements in a small (0.20 m × 0.20 m) air-water column. An adjustable weir controlled the liquid height on a test tray. Several sieve and valve trays were studied. The results were interpreted with a two- or three-layer model of the two-phase mixture on the tray. The top or spray layer is gas continuous: in the other layers, the liquid is continuous and contains small bubbles. Large bubbles erupt from the liquid-continuous phase, ejecting drops into the top layer. The distribution of the ejection velocities is taken to be Gaussian. The model allows prediction of the entrainment at different heights and for different gas velocities. As a result, a new equation for the maximum allowable vapour velocity can be presented. Two regimes were recognized: a ’low-liquid-height’ and a ‘high-liquid-height’regime. In the low-liquid-height regime, there are only two layers. Here the entrainment decreases with increasing liquid height and depends strongly on the type and geometry of the tray deck. At the transition, an intermediate liquid continuous layer develops. In the high-liquid-height regime, there are three layers. Here a further increase in liquid height causes the entrainment to increase. Moreover the entrainment is independent of the type and geometry of the tray deck. The results are compared with measurements from Fractionation Research Inc. on a large tray column. Similar conclusions can be drawn from these measurements, although there are differences owing to the difference in scale of the equipment. The model suggests that potentially large gains in the maximum allowable vapour rate of trays should be possible. A way of optimizing the vapour capacity of existing trays by an appropriate choice of the weir dimensions is presented.

Nonlinear hydroelastic vibration of a cylindrical tank with an elastic bottom containing liquid-analysis using harmonic balance method

Theoretical analyses and experimental studies have been carried out on the non-linear hydroelastic vibration of a cylindrical tank with an elastic bottom. In this paper, nonlinear axisymmetric free vibration analysis of the bottom plate of the tank, coupled with that of the liquid contained within it, is presented by means of the harmonic balance method. In the analysis, the effect of an in-plane force in the plate due to static liquid pressure is taken into account. The effect of the liquid on the non-linearity of the backbone curve of the super-harmonic and the sub-harmonic resonances as well as the principal resonance of both sloshing- and bulging-type responses was clarified, and it was found that with an increase of liquid height, the non-linearity with a hard-spring type of the bottom plate decreased in degree, and became close to linear characteristics. The influence of the bottom plate motions on the free surface response amplitude in the first bulging-type resonance region was also investigated.