EXPERIMENTAL INVESTIGATION OF FLOW PATTERN IN A SPRAY DRYER

1nvest.igation of flow pattern in a cocurrent disk spray dryer by means of measurement, of the kernel function is described. The obtained measurement results not only inform on the air flow type but ran be directly applied as input in the integral equation based simulation of heat and mass transfer.     

OBSERVATIONS OF FLOW PATTERNS IN A SPRAY DRYER

ABSTRACT

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anticlockwise and chaotic behaviour.     

OBSERVATIONS OF FLOW PATTERNS IN A SPRAY DRYER

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anticlockwise and chaotic behaviour.     

EXPERIMENTAL INVESTIGATION ON FLOW AND DRYING CHARACTERISTICS OF A VERTICAL AND SEMI-CYCLIC COMBINED IMPINGING STREAMS DRYER

Abstract

Flow characteristics of a vertical and semi-cyclic combined impinging streams dryer(VSCIS) was investigated. Results show that centrifugation and gravity have obvious influences on pressure drop and on momentum commutation between gas and particles in impingement zones. The effects of various operating parameters on water removal from particles have been studied experimentally. It is found that initial hot air temperature Tin, μ and initial moisture content of particles X₀ play important roles on water removal from particles. Based on the experimental data, dimensionless correlations for flow and drying characteristics in the system were obtained. VSCIS has shown to be a good way to overcome the shortcomings of single configuration of either vertical or semi-cyclic impinging streams. It can take full advantages of both arrangement to remove more water from particles.     

FLOW VISUALISATION AND INSTANTANEOUS VELOCITY MEASUREMENTS OF SPRAY DRYER GAS AND SPRAY FLOWS USING PARTICLE IMAGE VELOCIMETRY

The technique of particle image velocimetry has been used to produce good quality instantaneous velocity maps of the gas and spray phases within a pilot plant co-current spray dryer. Good quality flow visualisation data provided by the use of the laser sheet as an intense source of illumination has indicated that the air and spray flows were characterised by an offset central jet with down flowing (right hand side) and up flowing (left hand side) wall streams. This is significantly different from what would normally be expected and it was suggested that this was possibly due to a maldistribution of the air phase on inlet to the dryer.     

FLOW VISUALISATION AND INSTANTANEOUS VELOCITY MEASUREMENTS OF SPRAY DRYER GAS AND SPRAY FLOWS USING PARTICLE IMAGE VELOCIMETRY

ABSTRACT

The technique of particle image velocimetry has been used to produce good quality instantaneous velocity maps of the gas and spray phases within a pilot plant co-current spray dryer. Good quality flow visualisation data provided by the use of the laser sheet as an intense source of illumination has indicated that the air and spray flows were characterised by an offset central jet with down flowing (right hand side) and up flowing (left hand side) wall streams. This is significantly different from what would normally be expected and it was suggested that this was possibly due to a maldistribution of the air phase on inlet to the dryer.     

EXPERIMENTAL INVESTIGATION ON FLOW AND DRYING CHARACTERISTICS OF A VERTICAL AND SEMI-CYCLIC COMBINED IMPINGING STREAMS DRYER

Flow characteristics of a vertical and semi-cyclic combined impinging streams dryer(VSCIS) was investigated. Results show that centrifugation and gravity have obvious influences on pressure drop and on momentum commutation between gas and particles in impingement zones. The effects of various operating parameters on water removal from particles have been studied experimentally. It is found that initial hot air temperature Tin, μ and initial moisture content of particles X₀ play important roles on water removal from particles. Based on the experimental data, dimensionless correlations for flow and drying characteristics in the system were obtained. VSCIS has shown to be a good way to overcome the shortcomings of single configuration of either vertical or semi-cyclic impinging streams. It can take full advantages of both arrangement to remove more water from particles.     

AIR FLOW, TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

AIR FLOW,TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

ABSTRACT

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

喷干塔五种燃煤方式的综合分析

本文根据实际使用效果,分析介绍了喷干塔五种燃煤方式的工作原理及特点,并从粉料工艺性能,燃煤适应性,操作及控制,建设投资,运行成本等方面进行了综合分析。     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

碟片填料旋转床气阻与气液传质实验研究

实验测量了超重力旋转床气液传质反应器在采用同心环波纹碟片填料的时的气相压降和气液传质特性,对不同转速,气流量,液流量条件下的气相阻力与气液传质性能进行了实验研究和分析,结果表明干床的气相压降是相同状态下采用金属丝网填料的气相压降的６０％左右。     

SIMULATION OF SPRAY DRYING OF A SOLUTION ATOMIZED IN A PULSATING FLOW

Spray drying of NaCl solution was carried out under an intense oscillating flow field generated by a pulse combustor. A pulse combustion spray drying system was constructed. An optical analyzer was used to measure the particle diameter distribution of droplets atomized by a pulsating flow. The momentum, heat and mass transfer in both gaseous and particulate phases during spray drying inside the drying chamber were simulated using the computational fluid dynamics method. The simulated profiles of flow field, temperature and humidity of the gaseous phase, as well as the particulate phase, in the drying chamber were presented. The simulation showed changes of the flow field and particle trajectories in the drying chamber during one pulsating period. A large-scale vortex was observed in the upper part of the drying chamber because of the unstable state of flow field and particle trajectories. Short drying time and large evaporation rate are characteristics of pulsating spray drying. The influence of gas stream pulsation frequency on the drying process is also analyzed.     

滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量     

垂直下降管内油水乳状液流动特性的研究

对垂直下降管内油包水型和水包油型油水乳液的流动特性进行了深入的实验研究,根据实验结果分析得出了一个新的油水乳状表观粘度的表达式;同时也得出了一个新的油水乳状液发生相转变的判别式,并提出了采用Ｒｅ和摩擦阻力系数的关联式计算摩擦阻力的方法,也得到了判别油水乳状液为牛顿流体和非牛顿流体的方法。     

浸入式顶吹气流在熔池中穿透行为的实验研究

利用摄像法对浸入式顶吹气流在不同液体中的穿透深度进行了实验研究．在实验基础上，通过量纲分析，得出了气流无量纲穿透深度与修正弗鲁德数的经验式．     

周边式二沉池流态数值模拟

利用改进的RNG两方程湍流模型,借助大型计算流体力学软件FLUENT,对不同回流比情况下的周边进水周边出水二次沉淀池进行了数值模拟。结果表明：由于周边式沉淀池出水口和进水口在同侧距离较近,会发生短流,沉淀池容积利用率也较低,导致沉淀效率下降。随着回流比的增加,短流和死区会减少,但始终不能消除,周边式二沉池内不存在理想的设计流态。     

EXPERIMENTAL INVESTIGATION OF HIGHLY EFFECTIVE COOLING WITH AN EVAPORATING ANNULAR FLOW IN A SMALL VERTICAL TUBE

An experimental study was performed to investigate the heat transfer characteristics of the non-boiling annular two-phase flow of nitrogen gas and subcooled water through a small vertical heated tube with uniform wall heat flux. The experimental results were compared with the numerical calculations based on the two-phase flow boundary layer model. The experimental data show that the annular two-phase flow of nitrogen gas and subcooled water in a small vertical tube can provide quite high heat transfer ability, while wall temperatures lie in a low range even if at quite high wall heat fluxes. In particular, the highest values of the wall temperatures are insensitive to the change of flowing and heating conditions. This characteristic is quite suitable for highly effective cooling of polymer electrolyte membrane fuel cells.     

EXPERIMENTAL INVESTIGATION OF HIGHLY EFFECTIVE COOLING WITH AN EVAPORATING ANNULAR FLOW IN A SMALL VERTICAL TUBE

An experimental study was performed to investigate the heat transfer characteristics of the non-boiling annular two-phase flow of nitrogen gas and subcooled water through a small vertical heated tube with uniform wall heat flux. The experimental results were compared with the numerical calculations based on the two-phase flow boundary layer model. The experimental data show that the annular two-phase flow of nitrogen gas and subcooled water in a small vertical tube can provide quite high heat transfer ability, while wall temperatures lie in a low range even if at quite high wall heat fluxes. In particular, the highest values of the wall temperatures are insensitive to the change of flowing and heating conditions. This characteristic is quite suitable for highly effective cooling of polymer electrolyte membrane fuel cells.