Effects of flashing on spray characteristics of splashplate nozzles

TAPPI Journal ◽  
2013 ◽  
Vol 12 (5) ◽  
pp. 21-27
Author(s):  
REZA KARAMI ◽  
ARI KANKKUNEN ◽  
NASSER ASHGRIZ ◽  
HONGHI TRAN
Keyword(s):  
Mass Flow Rate ◽  
Mass Distribution ◽  
Droplet Size ◽  
Flow Rate ◽  
Laboratory Experiments ◽  
Black Liquor ◽  
Small Scale ◽  
Excess Temperature ◽  
The Mean ◽  
Actual Size

The effects of flashing on black liquor spray patterns were investigated by analyzing numerous spray images obtained from laboratory experiments using small scale splashplate nozzles with water and experiments using actual size splashplate nozzles with black liquor. The results showed that flashing produces small droplets and increases droplet velocity. The liquor mass flow rate varies with direction: the rate is higher at the center than at the sides of the spray sheet, particularly at a lower excess temperature. At a higher excess temperature, however, the mass distribution becomes more uniform across the spray sheet. Criteria were developed for predicting the onset of flashing and for estimating the mean droplet size of the black liquor spray under flashing conditions.

Leakage Prediction in Mechanical Seals Under Hydrostatic Operating Condition

2007 ◽  
Author(s):  
S. Elhanafi ◽  
K. Farhang
Keyword(s):  
Closed Form ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rough Surfaces ◽  
Mechanical Seals ◽  
Operating Condition ◽  
Form Equation ◽  
Macro Scale ◽  
The Mean

This paper considers leakage in mechanical seals under hydrostatic operating condition. A contact model based on the Greenwood and Williamson contact of rough surfaces is developed for treating problems involving mechanical seals in which both the micron scale roughness of the seal face and its macro scale profile are used to obtain either a closed-form equation or a nonlinear equation relating mean plane separation to the mass flow rate. The equations involve the micron scale geometry of the rough surfaces and physical parameter of the seal and carriage. Under hydrostatic condition, it is shown that there is an approximate closed-form solution in which mass flow rate in terms of the mean plane separation, or alternatively, the mean plane separation in terms of the leakage mass flow rate is found. Equations pertaining to leakage in nominally flat seal macro profile is considered and closed form equation relating to leakage flow rate to pressure difference is obtained that contain macro and micron geometries of the seal.

Air Blowing Into Boundary Layer Of A Flat Plate With Length-Dependent Permeability

2016 ◽  
Vol 11 (3) ◽  
pp. 16-26
Author(s):  
Vladimir Kornilov ◽  
Andrey Boiko ◽  
Ivan Kavun ◽  
Anatoliy Popkov
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Skin Friction Coefficient ◽  
Air Blowing ◽  
The Mean

A generalized analysis of the results of numerical and experimental studies of air blowing into a turbulent boundary layer through finely perforated surface consisting of alternating permeable and impermeable sections of varying length providing a sudden change in the flow conditions at the boundaries of these sections is presented. The air blowing coefficient Cb determined by the mass flow rate per unit area of the active perforated sample varied in the range from 0 to 0.008. It is shown that as Cb grows, the maximum reduction in the mean surface skin-friction coefficient CF, which is the value through the permeable area of perforated sample, reaches about 65 %. When keeping the equal mass flow rate Q for all tested combinations, the mean skin-friction coefficient remains constant, independent of geometrical parameters of permeable and impermeable sections. Increasing the length of the last permeable section leads to the growth of relaxation region which is characterized by the reduced skin friction values on the impermeable part of the flat plate.

scholarly journals Simulation and Optimization of Municipal Solid Waste Combustion: A Case Study of a Fixed Bed Incinerator

2020 ◽  
pp. 5-19
Author(s):  
Arthur M. Omari ◽  
John P. John ◽  
Baraka Kichonge
Keyword(s):  
Municipal Solid Waste ◽  
Solid Waste ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Fixed Bed ◽  
Small Scale ◽  
Waste Incinerator ◽  
Simulation And Optimization

In this study, a Computational Fluid Dynamics (CFD) technique was used to develop a model for the simulation and flow conditions of the incinerator. The CFD technique are based on subdividing the volume of interest, i.e., the combustion chamber (or other parts of the plant) into a grid of elementary volumes. The relevant equations of conservation (mass, momentum, energy) are then applied to each of those elements, after defining all inputs, outputs and boundary conditions. The resulting system is then integrated from start to finish, after introducing momentum, mass and heat transfer. The objective of the study was to evaluate and optimize the performance of locally available incinerators in Tanzania. The small scale municipal solid waste incinerator modelling was done by using a fluent solver. The case study of the existing incinerator at a Bagamoyo hospital in Tanzania was used as a model and the obtained values were compared with simulated results and other publications for validation. The design optimization using CFD techniques to predict the performance of incinerator showed the deviation of input air by 14%, the mass flow rate by 26.5%, the mass fraction of carbon dioxide by 10.4% and slight deviation of nitrogen dioxide and carbon monoxide. The study suggested removing the ash during the incineration process by using a moving grate mechanism to minimize the possibility of formation of NOX. The study found the maximum mass flow rate capacity of incinerator to be 68kg/h with input air A1 as 0.03639 kg/s, input air A2 as 0.03046 kg/s and input air A3 as 0.03409 kg/s. The findings indicated that as capacity is scaled up, the available momentum declines relative to the dimensions of the furnace.

Dynamic Behavior and Off-Design Performance Analysis of Solar Driven ORC Using Scroll Expanders

2019 ◽  
Author(s):  
Ying Zhang ◽  
Arun Kumar Narasimhan ◽  
Mengjie Bai ◽  
Li Zhao ◽  
Shuai Deng ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
System Level ◽  
Working Fluid ◽  
Small Scale ◽  
Solar Insolation ◽  
Design Performance ◽  
Fluid Mass

Abstract Solar driven ORC system is a possible solution for small-scale power generation. A scroll expander is considered due to its better suitability among other positive displacement expanders for small-scale power outputs. This work conducted a test of an ORC system with an expansion valve by varying the working fluid mass flow rate in two scenarios. A dynamic system-level model of ORC was developed and validated with experimental data. The validated model was used to predict the ORC performance considering off-design conditions of expander and solar insolation. The experimental data showed that pressures and temperatures exhibited the same trend as that of the working fluid mass flow rate, of which the evaporation pressure was the most sensitive to this variation. The simulation results are in good agreement with the experimental results. Results from the dynamic model showed that the ORC power output was underestimated by up to 54.7%, when off-design performance of expander was not considered. Considering the expander off-design performance and solar insolation, a highest thermal efficiency of 7.6% and an expander isentropic efficiency of 80.6% were achieved.

Experimental Study on a New Small-Scale Absorption System: Response Surface and Inverse Analyses

2021 ◽  
pp. 1-41
Author(s):  
Gaurav Singh ◽  
Ranjan Das
Keyword(s):  
Response Surface ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Load ◽  
Driving Factors ◽  
Hot Water ◽  
Small Scale ◽  
Absorption System ◽  
Multi Objective

Abstract In this paper, a new small-scale lithium bromide (LiBr)-water absorption system consisting water-cooled evaporator and air-cooled condenser is experimentally studied. For compactness, water-cooled heat exchangers for evaporator, absorber and generator are made helical-coiled type, whereas, based on the water availability and load requirements, condenser is air-cooled. Accurate empirical correlations for thermal load and evaporator temperature against system driving factors concerning a have been reported. Thereafter, response surface analysis of the developed performance parameters are studied with respect to LiBr concentration, temperature of generator and mass flow rate of hot water. Using experimental data, estimation of overall heat transfer coefficient (U) and its variation with system driving factors is quantified. The error margin between theoretical and actual pressure loss is limited within 5 %. Next, a multi-objective inverse analysis of the developed system is done to simultaneously retrieve the required LiBr concentration, mass flow rate of hot water, and vapor generator temperature to derive a desired cooling performance demand from the system. The obtained U values for all the components are found to be in line with the standard data. The physics related to salt concentration and generator temperature in governing U values are reported. Apart from the developed correlations, it can be established that the necessary operational parameters can be predicted by the present multi-objective inverse method to meet the necessary thermal load and temperature demands within an accuracy level of 6 % and 5 %, respectively.

scholarly journals A Model for Igniter Mass Flow Rate History Evaluation for Solid Rocket Motors

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Yanjie Ma ◽  
Futing Bao ◽  
Weihua Hui ◽  
Yang Liu ◽  
Yijie Gao
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Large Scale ◽  
Rocket Motor ◽  
Small Scale ◽  
Solid Rocket Motor ◽  
Combustion Gas ◽  
Proposed Model ◽  
Solid Rocket

This paper describes a zero-dimensional model for evaluating the mass flow rate history of a solid rocket motor igniter. Based on the results of an igniter-firing experiment, in which the igniter is the only source of combustion gas and no propellant is ignited, the proposed model can be used to compute the mass flow rate of the igniter. Different species and temperature-dependent properties, such as the specific heat for each species, are considered. The coupling between the flow field variables in the combustion chamber and the heat transfer at the gas-solid interface is computed in a segment way. Calculations are performed for different species and properties, and the errors are discussed. Using the computed igniter mass flow rate as a boundary condition, a two-dimensional calculation is performed for validation purposes. The results are in good agreement with experimental data. The proposed model can be used to provide reasonable boundary conditions for solid rocket motor simulations and to evaluate the performance of igniters. Although derived on the basis of a small-scale solid rocket motor, the model has the potential to be used in large-scale systems.

Obtaining Time-Varying Pulsatile Gas Flow Rates With the Help of Dynamic Pressure Difference and Other Measurements for an Orifice-Plate Meter

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
A. Narain ◽  
N. Ajotikar ◽  
M. T. Kivisalu ◽  
A. F. Rice ◽  
M. Zhao ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Difference ◽  
Dynamic Pressure ◽  
Orifice Plate ◽  
Absolute Pressure ◽  
Time Varying ◽  
Flow Rates ◽  
The Mean

Use of a conventional orifice-plate meter is typically restricted to measurements of steady flow rates. For any gas flowing within a duct in a pulsatile manner (i.e., large amplitude mass flow rate fluctuations relative to its steady-in-the-mean value), this paper proposes a new and effective approach for obtaining its time-varying mass flow rate at a specified cross section of an orifice meter. The approach requires time-varying (dynamic) pressure difference measurements across an orifice-plate meter, time-averaged mass flow rate measurements from a separate device (e.g., Coriolis meter), and a dynamic absolute pressure measurement. Steady-in-the-mean turbulent gas flows (Reynolds number ≫2300) with low mean Mach numbers (<0.2) exhibit effectively constant densities over long time-durations and are often made pulsatile by the presence of rotary or oscillatory devices that drive the flow (compressors, pumps, pulsators, etc.). In these pulsatile flows, both flow rate and pressure-difference fluctuation amplitudes at or near the device driver frequency (or its harmonics) are large relative to their steady mean values. The time-varying flow rate values are often affected by transient compressibility effects associated with acoustic waves. If fast Fourier transforms of the absolute pressure and pressure-difference measurements indicate that the predominant frequency is characterized by fp, then the acoustic effects lead to a nonnegligible rate of change of stored mass (associated with density changes) over short time durations (∼ 1/fP) and modest volumes of interest. As a result, for the same steady mean mass flow rate, the time variations (that resolve these density changes over short durations) of mass flow rates associated with pulsatile (and turbulent) gas flows are often different at different cross sections of the orifice meter (or duct). Together with the experimental measurements concurrently obtained from the three recommended devices, a suitable computational approach (as proposed and presented here) is a requirement for effectively converting the experimental information on time-varying pressure and pressure-difference values into the desired dynamic mass flow rate values. The mean mass flow rate measurement assists in eliminating variations in its predictions that arise from the use of turbulent flow simulation capabilities. Two independent verification approaches establish that the proposed measurement approach works well.

Characteristics of Mean Droplet Size Produced by Spinning Disk Atomizers

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Mahmoud Ahmed ◽  
M. S. Youssef
Keyword(s):  
Droplet Size ◽  
Flow Rate ◽  
Liquid Flow ◽  
Liquid Flow Rate ◽  
Sauter Mean Diameter ◽  
Disk Diameter ◽  
Downstream Distance ◽  
Spinning Disk ◽  
Mean Diameter ◽  
The Mean

Characteristics of mean droplet size of spray produced by spinning disk atomizers were experimentally investigated. The phase-doppler particle analyzer (PDPA) was used to measure the droplet size of water spray in the downstream distance along the spray trajectory. Effects of various operating conditions on the mean diameter had been studied. The studied variables were: the rotational speed in the range of 838 to 1677 rad/s (8,000–16,000 rpm), the liquid flow rate in the range of 0.56 to 2.8 × 10−6 m3/s (2–10 L/h), the disk diameter in the range of 0.04 to 0.12 m, and the downstream tangential distance along the spray trajectory of up to 0. 24 m. The Sauter mean diameter (d32) was used to represent the mean of generated spray droplet sizes. The results indicated that the Sauter mean diameter can be correlated with dimensionless groups, such as the Reynolds number, Weber number, flow coefficient, and the ratio of downstream distance to disk diameter. Based on this correlation, it was found that the Sauter mean diameter (d32) increases as the downstream tangential distance, and liquid flow rate increase. Similarly, a decrease of rotational speed and disk diameter results in an increase in the Sauter mean diameter (d32). A comparison between the developed correlation and correlations obtained by other researchers has been presented and discussed in detail.

Numerical Simulation of Capillary Tube for Selected Refrigerants Using Homogeneous Equilibrium Model

2019 ◽  
Vol 27 (01) ◽  
pp. 1950001 ◽  
Author(s):  
Praveen Alok ◽  
Debjyoti Sahu
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equilibrium Model ◽  
Capillary Tube ◽  
Tube Length ◽  
Mean Deviation ◽  
Choked Flow ◽  
Homogeneous Equilibrium ◽  
The Mean

In this work, a set of computational investigation results of two-phase refrigerant flow through adiabatic capillary are presented. There are various sizes of capillary tubes that can be selected related to commercially available copper tubes. Earlier refrigerants and new refrigerants like R12, R22, R134a, R410A and R32 are used for the flow analysis. Homogeneous-equilibrium model is employed with user-defined properties of the refrigerants for computation using ANSYS CFX. Several important parameters can be predicted rapidly and accurately using this method such as refrigerant mass flow rate, vapor mass fraction, local Mach no. etc. The mean deviation in mass flow rate is found to be [Formula: see text]1.18% for the same length of capillary tube and the mean deviation of tube length is found to be [Formula: see text]1.48% for the same experimental mass flow rate with choked flow condition.

Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations

2011 ◽  
Author(s):  
M. Kivisalu ◽  
N. Gorgitrattanagul ◽  
S. Mitra ◽  
R. Naik ◽  
A. Narain
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rectangular Cross Section ◽  
Pressure Fluctuations ◽  
Inlet Pressure ◽  
Bottom Surface ◽  
Exit Pressure ◽  
Condensing Flows ◽  
The Mean

The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the bottom surface (316 Stainless Steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or exit) pressure, and wall cooling conditions. It has been reported elsewhere that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or exit) pressure, and wall cooling condition held at quasi-steady values, there is a very strong sensitivity to certain impositions of pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these impositions, it was found that the mean exit (or inlet) pressure changes to significantly affect mean test-section pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).

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