Annular flow pressure drop model for pease–anthony‐type venturi scrubbers

Abstract

An annular flow pressure drop model has been developed and compared with experimental data obtained on a pilot-plant-size Pease-Anthony-type venturi scrubber. Droplet and film accelerations as well as wall friction, based on the two-phase Lockhart-Martinelli correlation, are considered. Excellent agreement with experimental data is demonstrated for a wide range of throat gas velocities, liquid to gas ratios, and film flow rates for a single scrubber geometry. Venturi scrubbers have been recognized widely for their high particulate matter collection efficiencies. Fine-particle collection generally requires elevated pressure drops. The primary objective of this study was to develop a realistic mathematical model for prediction of pressure drop in a PeaseAnthony venturi scrubber.Flow losses are predicted by accounting for frictional effects and acceleration of liquid drops and the liquid films flowing on the walls. Recovery in the diffuser is also considered. Model validation involved measurement of pressure gradients, film flow rates, liquid to gas ratios, and throat gas velocities for a pilot-plant-scale venturi. A comparison is made among three widely used correlations using experimental data taken from the pilot-plant-scale venturi scrubber. CONCLUSIONS AND SIGNIFICANCEAn annular flow model is developed for accurate prediction of pressure drops in Pease-Anthony venturi scrubbers. This model-which considers the primary design parameters of liquid to gas ratio, throat gas velocity, venturi geometry, and liquid film flow rate-accurately predicted the measured pressure gradients and overall energy losses.The Hesketh (1974) correlation underestimated pressure drops at all liquid to gas ratios and throat gas velocities tested. The Calvert modified model (Yung et al., 1977a) predicted overall pressure drops lower than those experimentally measured for liquid to gas ratios below 8.0 X lod4 m3 liquid/m3 air, and greater magnitudes for liquid to gas ratios exceeding 1.3 xThe region of good agreement was achieved in spite of the neglect of wall friction, converging section losses, and diffuser pressure recovery when these effects compensated each other.Boll 's model (1973) consistently overpredicted the experimental pressure drops. The deviation increased with increasing liquid to gas ratios. Since film flow was not considered, the droplet acceleration component was always overestimated. The frictional losses, which were predicted using a homogeneous model (Wallis, 1969), were overestimated.

Modelagem E Simulação De Lavador Venturi Utilizando Fluidodinâmica Computacional

“…As simulações realizadas foram comparadas com os modelos de Boll (1973), dado pela Equação 1, e de Viswanathan (1985), dado pela Equação 2, utilizando as vazões de líquido e de gás referentes a cada simulação e com diâmetro de gota igual para todas (Item 2.1.2). O coeficiente de atrito usado nos modelos foi calculado supondo as paredes do lavador como totalmente lisas e a velocidade das gotas na direção do escoamento do gás como nulas.…”

“…As perdas de pressão total no equipamento, para um comprimento de 0,4 m da secção de saída, foram próximas aos obtidos nas simulações em comparação com o modelo de Viswanathan (1985), o qual superestimou no caso das duas vazões de líquido maiores e subestimando no caso da vazão menor. Comparando-se os dados de queda de pressão para a maior vazão de gás do modelo de Viswanathan (1985) com as simulações realizadas, pode-se perceber pela Figura 10, que a adequação ocorre para a região convergente e da garganta, assim como ocorrido nos casos anteriores.…”

Graphical Analysis of the Performance of Venturi Scrubbers for Particle Abatement. Part I: Rapid Collection Efficiency Evaluation

“…Their approach provides an elegant insight into the mechanisms at work, accounting, inter alia, for the presence of liquid film on the venturi walls, continual atomization and re-deposition of the liquid on the walls, and boundary layer growth and separation. A similar approach has also been followed by Viswanathan (1985) to develop an annular flow pressure drop model.…”

Film fraction in a vertical circular Venturi scrubber

“…In any case it is necessary to ensure that all the film (and only the film) was extracted. ABCM The variation of film fraction with axial distance from the injection point was measured by Viswanathan et al (1985Viswanathan et al ( , 1997, in a Venturi with a rectangular cross section and liquid injected as jets, and by Azzopardi (1993), in a circular Venturi with liquid injected as a film upstream the convergence (this injection arrangement is called "wetted approach"). These authors used a porous wall to remove the film (by an applied pressure difference).…”

“…The film can be extracted by making the film flow out of the equipment through either a porous wall (Viswanathan et al, 1985;Azzopardi, 1993;Viswanathan et al, 1997) or a slot (Gonçalves et al, 2004). In any case it is necessary to ensure that all the film (and only the film) was extracted.…”