Abstract: The application of combustion technologies for thermal conversion of biomass and solid wastes to energy has been a major solution to the effective handling of wastes over a long period of time. Lab-scale biomass combustion systems have been observed to be economically viable and socially acceptable, but major concerns are the environmental impacts of the process and deviation of temperature distribution within the combustion chamber. Both high and low combustion chamber temperature may affect the overall combustion efficiency and gaseous emissions. Therefore, there is an urgent need to develop a control system which measures the deviations of chamber temperature from set target values, sends these deviations (which generates disturbances in the system) in the form of feedback signal (as input), and control operating conditions for correcting the errors. In this research study, major components of the feedback control system were determined, assembled, and tested. In addition, control algorithms were developed to actuate operating conditions (e.g., air velocity, fuel feeding rate) using ladder logic functions embedded in the Programmable Logic Controller (PLC). The developed control algorithm having chamber temperature as a feedback signal is integrated into the lab-scale swirling fluidized bed combustor (SFBC) to investigate the temperature distribution at different heights of the combustion chamber based on various operating conditions. The air blower rates and the fuel feeding rates obtained from automatic control operations were correlated with manual inputs. There was no observable difference in the correlated results, thus indicating that the written PLC program functions were adequate in designing the experimental study of the lab-scale SFBC. The experimental results were analyzed to study the effect of air velocity operating at 222-273 ft/min and fuel feeding rate of 60-90 rpm on the chamber temperature. The developed temperature-based feedback control system was shown to be adequate in controlling the airflow and the fuel feeding rate for the overall biomass combustion process as it helps to minimize the steady-state error.
Abstract: The swirl gripper is an electrically activated noncontact handling device that uses swirling airflow to generate a lifting force. This force can be used to pick up a workpiece placed underneath the swirl gripper without any contact. It is applicable, for example, in the semiconductor wafer production line, where contact must be avoided during the handling and moving of a workpiece to minimize damage. When a workpiece levitates underneath a swirl gripper, the gap height between them is crucial for safe handling. Therefore, in this paper, we propose a method to estimate the levitation gap height by detecting pressure at two points. The method is based on theoretical model of the swirl gripper, and has been experimentally verified. Furthermore, the force between the gripper and the workpiece can also be estimated using the detected pressure. As a result, the nonlinear relationship between the force and gap height can be linearized by adjusting the rotating speed of the fan in the swirl gripper according to the estimated force and gap height. The linearized relationship is expected to enhance handling stability of the workpiece.
Abstract: The numerical modeling is performed to study the effects of N2 addition to the fuel stream on the flame structure and temperature distribution of methane-air swirl diffusion flames with different swirl intensities. The Open source Field Operation and Manipulation (OpenFOAM) has been utilized as the computational tool. Flamelet approach along with modified k-ε model is employed to model the flame characteristics. The results indicate that the presence of N2 in the fuel stream leads to the flame temperature reduction. By increasing of swirl intensity, the flame structure changes significantly. The flame has a conical shape in low swirl intensity; however, it has an hour glass-shape with a shorter length in high swirl intensity. The effects of N2 dilution decrease the flame length in all swirl intensities; however, the rate of reduction is more noticeable in low swirl intensity.
Abstract: The objective of this paper is to observe the effects of injection conditions on flame structures in gas-centered swirl coaxial injector. Gaseous oxygen and liquid kerosene were used as propellants. For different injection conditions, two types of injector, which only differ in the diameter of the tangential inlet, were used in this study. In addition, oxidizer injection pressure was varied to control the combustion chamber pressure in different types of injector. In order to analyze the combustion instability intensity, the dynamic pressure was measured in both the combustion chamber and propellants lines. With the increase in differential pressure between the propellant injection pressure and the combustion chamber pressure, the combustion instability intensity increased. In addition, the flame structure was recorded using a high-speed camera to detect CH* chemiluminescence intensity. With the change in the injection conditions in the gas-centered swirl coaxial injector, the flame structure changed.
Abstract: Eddy viscosity models in turbulence modeling can be mainly classified as linear and nonlinear models. Linear formulations are simple and require less computational resources but have the disadvantage that they cannot predict actual flow pattern in complex geophysical flows where streamline curvature and swirling motion are predominant. A constitutive equation of Reynolds stress anisotropy is adopted for the formulation of eddy viscosity including all the possible higher order terms quadratic in the mean velocity gradients, and a simplified model is developed for actual oceanic flows where only the vertical velocity gradients are important. The new model is incorporated into the one dimensional General Ocean Turbulence Model (GOTM). Two realistic oceanic test cases (OWS Papa and FLEX' 76) have been investigated. The new model predictions match well with the observational data and are better in comparison to the predictions of the two equation k-epsilon model. The proposed model can be easily incorporated in the three dimensional Princeton Ocean Model (POM) to simulate a wide range of oceanic processes. Practically, this model can be implemented in the coastal regions where trasverse shear induces higher vorticity, and for prediction of flow in estuaries and lakes, where depth is comparatively less. The model predictions of marine turbulence and other related data (e.g. Sea surface temperature, Surface heat flux and vertical temperature profile) can be utilized in short term ocean and climate forecasting and warning systems.
Abstract: The matrix cooling channel was used for gas turbine blade cooling passage. The matrix cooling structure is useful for the structure stability however the cooling performance of internal cooling channel was not enough for cooling. Therefore, we designed the rib configurations in the matrix cooling channel to enhance the cooling performance. The numerical simulation was conducted to analyze cooling performance of rib configured matrix cooling channel. Three different rib configurations were used which are vertical rib, angled rib and c-type rib. Three configurations were adopted in two positions of matrix cooling channel which is one fourth and three fourth of channel. The result shows that downstream rib has much higher cooling performance than upstream rib. Furthermore, the angled rib in the channel has much higher cooling performance than vertical rib. This is because; the angled rib improves the swirl effect of matrix cooling channel more effectively. The friction factor was increased with the installation of rib. However, the thermal performance was increased with the installation of rib in the matrix cooling channel.
Abstract: The present paper expands details and confirms the transition mechanism between two subsequent polygonal patterns of the hollow-core vortex. Using power spectral analysis, we confirm in this work that the transition from any N-gon to (N+1)-gon pattern observed within a hollow-core vortex of shallow rotating flows occurs in two steps. The regime was quasi-periodic before the frequencies lock (synchronization). The ratios of locking frequencies were found to be equal to (N-1)/N.
Abstract: A 3C-2D PIV technique was applied to investigate the swirling flow generated by an axial plus tangential type swirl generator. This work is focused on the near-exit region of an isothermal swirling jet to characterize the effect of swirl on the flow field and to identify the large coherent structures both in unconfined and confined conditions for geometrical swirl number, Sg = 4.6. Effects of the Reynolds number on the flow structure were also studied. The experimental results show significant effects of the confinement on the mean velocity fields and its fluctuations. The size of the recirculation zone was significantly enlarged upon confinement compared to the free swirling jet. Increasing in the Reynolds number further enhanced the recirculation zone. The frequency characteristics have been measured with a capacitive microphone which indicates the presence of periodic oscillation related to the existence of precessing vortex core, PVC. Proper orthogonal decomposition of the jet velocity field was carried out, enabling the identification of coherent structures. The time coefficients of the first two most energetic POD modes were used to reconstruct the phase-averaged velocity field of the oscillatory motion in the swirling flow. The instantaneous minima of negative swirl strength values calculated from the instantaneous velocity field revealed the presence of two helical structures located in the inner and outer shear layers and this structure fade out at an axial location of approximately z/D = 1.5 for unconfined case and z/D = 1.2 for confined case. By phase averaging the instantaneous swirling strength maps, the 3D helical vortex structure was reconstructed.
Abstract: This paper presents a numerical investigation of electrically driven flow for enhancing convective heat transfer in a channel flow. This study focuses on the electrode arrangements, number of electrode and electrical voltage on Electrohydrodynamics (EHD) and effect of airflow driven on solid sample surface. The inlet airflow and inlet temperature are 0.35 m/s and 60 oC, respectively. High electrical voltage is tested in the range of 0-30 kV and number of electrode is tested in the range of 1-5. The numerical results show that electric field intensity is depended on electrical voltage and number of electrode. Increasing number of electrodes is increased shear flow, so swirling flow is increased. The swirling flows from aligned and staggered arrangements are affecting within the solid sample. When electrical voltage is increased, temperature distribution and convective heat transfer on the solid sample are significantly increased due to the electric force much stronger.
Abstract: Temperature distribution investigation in a conical diffuser fitted with helical screw-tape with and without center-rod is studied numerically. A helical screw-tape is inserted in the diffuser to create swirl flow that helps to enhance the temperature distribution rate with inlet Reynolds number 4.3 x 104. Three pitch lengths ratios (Y/L = 0.153, 0.23 and 0.307) for the helical screw-tape with and without center-rod are simulated and compared. The geometry of the conical diffuser and the inlet condition for both arrangements are kept constant. Numerical findings show that the helical screw-tape inserts without center-rod perform significantly better than the helical tape inserts with center-rod in the conical diffuser.
Abstract: This paper represents an experimental study of LPG
diffusion flame at elevated preheated air temperatures. The flame is
stabilized in a vertical water-cooled combustor by using air swirler. An
experimental test rig was designed to investigate the different
operating conditions. The burner head is designed so that the LPG fuel
issued centrally and surrounded by the swirling air issues from an air
swirler. There are three air swirlers having the same dimensions but
having different blade angles to give different swirl numbers of 0.5,
0.87 and 1.5. The combustion air was heated electrically before
entering the combustor up to a temperature about 500 K. Five air to
fuel mass ratios of 15, 20, 30, 40 and 50 were also studied. The effect
of preheated air temperature, swirl number and air to fuel mass ratios
on the temperature maps, visible flame length, high temperature region
(size) and exhaust species concentrations are studied. Some results
show that as the preheated air temperature increases, the volume of
high temperature region also increased but the flame length decreased.
Increasing the preheated air temperature, EINOx, EICO2 and EIO2
increased, while EICO decreased. Increasing the preheated air
temperature from 300 to 500 K, for all air swirl numbers used, the
highest increase in EINOx, EICO2 and EIO2 are 141, 4 and 65%,
respectively.
Abstract: Experimental investigations of the DC electric field effect on thermal decomposition of biomass, formation of the axial flow of volatiles (CO, H2, CxHy), mixing of volatiles with swirling airflow at low swirl intensity (S ≈ 0.2-0.35), their ignition and on formation of combustion dynamics are carried out with the aim to understand the mechanism of electric field influence on biomass gasification, combustion of volatiles and heat energy production. The DC electric field effect on combustion dynamics was studied by varying the positive bias voltage of the central electrode from 0.6 kV to 3 kV, whereas the ion current was limited to 2 mA. The results of experimental investigations confirm the field-enhanced biomass gasification with enhanced release of volatiles and the development of endothermic processes at the primary stage of thermochemical conversion of biomass determining the field-enhanced heat energy consumption with the correlating decrease of the flame temperature and heat energy production at this stage of flame formation. Further, the field-enhanced radial expansion of the flame reaction zone correlates with a more complete combustion of volatiles increasing the combustion efficiency by 3% and decreasing the mass fraction of CO, H2 and CxHy in the products, whereas by 10% increases the average volume fraction of CO2 and the heat energy production downstream the combustor increases by 5-10%
Abstract: Computational fluid dynamics analysis of the burning
of syngas fuels derived from biomass and plastic solid waste mixture
through gasification process is presented in this paper. The syngas
fuel is burned in gas turbine can combustor. Gas turbine can
combustor with swirl is designed to burn the fuel efficiently and
reduce the emissions. The main objective is to test the impact of the
alternative syngas fuel compositions and lower heating value on the
combustion performance and emissions. The syngas fuel is produced
by blending palm kernel shell (PKS) with polyethylene (PE) waste
via catalytic steam gasification (fluidized bed reactor). High
hydrogen content syngas fuel was obtained by mixing 30% PE waste
with PKS. The syngas composition obtained through the gasification
process is 76.2% H2, 8.53% CO, 4.39% CO2 and 10.90% CH4. The
lower heating value of the syngas fuel is LHV = 15.98 MJ/m3. Three
fuels were tested in this study natural gas (100%CH4), syngas fuel
and pure hydrogen (100% H2). The power from the combustor was
kept constant for all the fuels tested in this study. The effect of syngas
fuel composition and lower heating value on the flame shape, gas
temperature, mass of carbon dioxide (CO2) and nitrogen oxides
(NOX) per unit of energy generation is presented in this paper. The
results show an increase of the peak flame temperature and NO mass
fractions for the syngas and hydrogen fuels compared to natural gas
fuel combustion. Lower average CO2 emissions at the exit of the
combustor are obtained for the syngas compared to the natural gas
fuel.
Abstract: The comprehensive CFD models have been used to
represent and study the heterogeneous combustion of biomass. In the
present work, the operation of a global flue gas circuit in the sugarcane
bagasse combustion, from wind boxes below primary air grate
supply, passing by bagasse insertion in swirl burners and boiler
furnace, to boiler bank outlet is simulated. It uses five different
meshes representing each part of this system located in sequence:
wind boxes and grate, boiler furnace, swirl burners, superheaters and
boiler bank. The model considers turbulence using standard k-ε,
combustion using EDM, radiation heat transfer using DTM with 16
ray directions and bagasse particle tracking represented by Schiller-
Naumann model. The results showed good agreement with expected
behavior found in literature and equipment design. The more detailed
results view in separated parts of flue gas system allows observing
some flow behaviors that cannot be represented by usual
simplifications like bagasse supply under homogeneous axial and
rotational vectors and others that can be represented using new
considerations like the representation of 26 thousand grate orifices by
144 rectangular inlets.
Abstract: This paper presents a numerical investigation of two
horizontally mounted four-lobed swirl pipes in terms of swirl
induction effectiveness into flows passing through them. The swirl
flows induced by the two swirl pipes have the potential to improve
the efficiency of Clean-In-Place procedures in a closed processing
system by local intensification of hydrodynamic impact on the
internal pipe surface. Pressure losses, swirl development within the
two swirl pipe, swirl induction effectiveness, swirl decay and wall
shear stress variation downstream of two swirl pipes are analyzed and
compared. It was found that a shorter length of swirl inducing pipe
used in joint with transition pipes is more effective in swirl induction
than when a longer one is used, in that it has a less constraint to the
induced swirl and results in slightly higher swirl intensity just
downstream of it with the expense of a smaller pressure loss. The
wall shear stress downstream of the shorter swirl pipe is also slightly
larger than that downstream of the longer swirl pipe due to the
slightly higher swirl intensity induced by the shorter swirl pipe. The
advantage of the shorter swirl pipe in terms of swirl induction is more
significant in flows with a larger Reynolds Number.
Abstract: A comprehensive CFD model is developed to
represent heterogeneous combustion and two burner designs of
supply sugar-cane bagasse into a furnace. The objective of this work
is to compare the insertion and burning of a Brazilian south-eastern
sugar-cane bagasse using a new swirl burner design against an actual
geometry under operation. The new design allows control the
particles penetration and scattering inside furnace by adjustment of
axial/tangential contributions of air feed without change their mass
flow. The model considers turbulence using RNG k-, combustion
using EDM, radiation heat transfer using DTM with 16 ray directions
and bagasse particle tracking represented by Schiller-Naumann
model. The obtained results are favorable to use of new design swirl
burner because its axial/tangential control promotes more penetration
or more scattering than actual design and allows reproduce the actual
design operation without change the overall mass flow supply.
Abstract: Reburning is a useful technology in reducing nitric
oxide through injection of a secondary hydrocarbon fuel. In this paper,
an experimental study has been conducted to evaluate the effect of fuel
lean reburning on NOx/CO reduction in LNG flame. Experiments
were performed in flames stabilized by a co-flow swirl burner, which
was mounted at the bottom of the furnace. Tests were conducted using
LNG gas as the reburn fuel as well as the main fuel. The effects of
reburn fuel fraction and injection manner of the reburn fuel were
studied when the fuel lean reburning system was applied. The paper
reports data on flue gas emissions and temperature distribution in the
furnace for a wide range of experimental conditions. At steady state,
temperature distribution and emission formation in the furnace have
been measured and compared. This paper makes clear that in order to
decrease both NOx and CO concentrations in the exhaust when the
pulsated fuel lean reburning system was adapted, it is important that
the control of some factors such as frequency and duty ratio. Also it
shows the fuel lean reburning is also effective method to reduce NOx
as much as reburning.
Abstract: The most important part of modern lean low NOx combustors is a premixer where swirlers are often used for intensification of mixing processes and further formation of required flow pattern in combustor liner. Swirling flow leads to formation of complex eddy structures causing flow perturbations. It is able to cause combustion instability. Therefore, at design phase, it is necessary to pay great attention to aerodynamics of premixers. Analysis based on unsteady CFD modeling of swirling flow in production combustor swirler showed presence of large number of different eddy structures that can be conditionally divided into three types relative to its location of origin and a propagation path. Further, features of each eddy type were subsequently defined. Comparison of calculated and experimental pressure fluctuations spectrums verified correctness of computations.
Abstract: Combustion phenomenon will be accomplished
effectively by the development of low emission combustor. One of the
significant factors influencing the entire Combustion process is the
mixing between a swirling angular jet (Primary Air) and the
non-swirling inner jet (fuel). To study this fundamental flow, the
chamber had to be designed in such a manner that the combustion
process to sustain itself in a continuous manner and the temperature of
the products is sufficiently below the maximum working temperature
in the turbine. This study is used to develop the effective combustion
with low unburned combustion products by adopting the concept of
high swirl flow and motility of holes in the secondary chamber. The
proper selection of a swirler is needed to reduce emission which can be
concluded from the emission of Nox and CO2. The capture of CO2 is
necessary to mitigate CO2 emissions from natural gas. Thus the
suppression of unburned gases is a meaningful objective for the
development of high performance combustor without affecting turbine
blade temperature.
Abstract: Effects of insertion of coiled wire in juxtaposition with twisted tapes on heat transfer rate and solar radiation without disturbing the flow inside the riser tubes in a solar flat plate collector is experimentally reconnoitered in this present work. The wire coil used as a turbulator is placed inside the riser tube while the twisted tape is inserted into the wire coil to create a continuous swirling flow along the tube wall. The results of the heat transfer have been compared well with the available results. The heat transfer rate in the collector has been found to be increased by 18% to 70%. Solar water heaters having inserts in the flow tubes perform better than the conventional plain ones. It has been observed that heat losses are reduced consequently increasing the thermal performance about 30% over the plain water heaters under the same operating conditions. The effect of twisted tape with wire coils, flow Reynolds number, and the intensity of solar radiation on the thermal performance of the solar water heater has been presented. Effects of insertion of coiled wire in juxtaposition with twisted tapes on heat transfer rate and solar radiation without disturbing the flow inside the riser tubes in a solar flat plate collector is experimentally reconnoitered in this present work. The wire coil used as a turbulator is placed inside the riser tube while the twisted tape is inserted into the wire coil to create a continuous swirling flow along the tube wall. The results of the heat transfer have been compared well with the available results. The heat transfer rate in the collector has been found to be increased by 18% to 70%. Solar water heaters having inserts in the flow tubes perform better than the conventional plain ones. It has been observed that heat losses are reduced consequently increasing the thermal performance about 30% over the plain water heaters under the same operating conditions. The effect of twisted tape with wire coils, flow Reynolds number, and the intensity of solar radiation on the thermal performance of the solar water heater has been presented.