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Subject: search.filters.subject.mass transfer

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Now showing 1 - 5 of 5
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    Item type:Item,
    A refined model for ozone mass transfer in a bubble column
    (1998-01-01)
    Huang, WH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Lee, SJ
    ;
    Yu, YH
    The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
  • Thumbnail Image
    Item type:Item,
    Dynamic model of ozone contacting process with oxygen mass transfer in bubble columns
    (2002-11-01)
    Chen, YH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Huang, WH
    ;
    Yu, YH
    The dynamic process of the dissolution of ozone in a countercurrent bubble column is studied for model establishment. Bubble columns have been used widely for ozone contacting in the plant and laboratory. Ozone is produced by oxygen-enriched gas through an ozone generator, and introduced into the bottom of the column equipped with the gas diffuser. The ozone contacting system proceeds for a temporary and unsteady period before reaching steady state. The available ozone dissolution models employed for the description of the dissolved ozone profiles were commonly developed for the steady state. Moreover, oxygen mass transfer is usually neglected in the preceding ozone dissolution models. However, this information is desirable for proper operation of ozone dissolution in a bubble column. Thus, the objective of this study is to model and investigate the dynamic ozone dissolution process in a bubble column with the oxygen mass transfer. The dynamic axial dispersion model proposed is employed to predict the variations of ozone and oxygen concentrations along the column, and the amount of off-gas. The validity of the model is demonstrated by comparing the predicted results with the experimental data. The dynamic model of ozone dissolution is useful and referable for proper prediction of the variables of the ozone contacting system in a bubble column.
  • Thumbnail Image
    Item type:Item,
    NUMERICAL ANALYSIS OF MASS TRANSFER ON THE MELTING PHENOMENON FROM A VERTICAL PLATE IN A LIQUID-SATURATED POROUS MEDIUM
    (2012)
    Cheng, W. T.
    ;
    Lin, C. H.
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    An analysis is performed to investigate the mass transfer on the melting phenomenon from a vertical plate in a liquid-saturated porous medium. The governing partial differential equations are reduced to nonlinear ordinary differential equations by using appropriate dimensionless variables. The final resulting boundary value problem is then solved by means of the Runge-Kutta-Gill method associated with Newton's iteration. As shown in the results, the melting process is highly affected by mass transfer effect. With increasing the strength of the buoyancy ratio, the melting effect may be inhibited because the heat flux is removed by stronger convection. The Lewis number has a more notable effect on the local mass transfer rate than it does on the local heat transfer rate at the solid-liquid interface. Additionally, the Lewis number may affect the melting phenomenon when the mass transfer is considered in the system. The little change for the melting effect can make a great influence on the local mass transfer rate, which is significant when the system is dominated by mass transfer for a larger Le.
  • Thumbnail Image
    Item type:Item,
    A refined model for ozone mass transfer in a semibatch stirred vessel
    (1997-11-01)
    Chiu, CY
    ;
    Chang, CY
    ;
    Huang, WH
    ;
    Lee, SJ
    ;
    Yu, YH
    The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas-liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGi), and the outlet gas in the free volume above the liquid surface (C-AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E-r with C-ALb, which changes with time during the course of gas-liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.
  • Thumbnail Image
    Item type:Item,
    A refined model for ozone mass transfer in a bubble column
    (1998-01-01)
    Huang, WH
    ;
    Chang, CY
    ;
    Chiu, CY
    ;
    Lee, SJ
    ;
    Yu, YH
    The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.