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The study presents an experimental and numerical investigation to determine the role of adiabatic lame temperature on controlling the operability of a micromixer-based gas turbine model combustor holding premixed CH4/CO2/O2 non-swirl jet flame for carbon capture. The experimental test rig consists of a mixing pipe and multihole/micromixer-like burner of 61 tubes. The numerical aspect of the study is achieved using the computational fluid dynamic (CFD) approach. Models of the ansys Fluent are used to solve elliptical governing equations involved in the combustion system. Since flames under consideration are jet premixed releasing into a quiescent atmosphere, the partially premixed combustion of species model is used. Large eddy simulation (LES) is used as the turbulence model while radiative transfer equation (RTE) is solved using discrete ordinate (DO). A good agreement between experimental and numerical results is achieved. Results indicated that adiabatic flame temperature (Tad) controls the flame macrostructure, oxygen fraction (OF) controls the peak of the product formation rate rather than Tad, and positions of OH radical reaffirmed that Tad controls the flame macrostructure and increasing the OF leads to reaction rate dominancy and, hence, increases the Damkohler number.

This paper presents the results of an experimental investigation of combustion characteristics of nonswirl CH₄/CO₂/O₂ flames under atmospheric pressure in a lean-premixed multihole burner’s gas-turbine model combustor. The CO₂ and O₂ are well premixed and then channeled to a test rig, which is made up of a 2 in. diameter 1 m long pipe to premix the fuel and oxidizers before getting to the multihole burner. The burner consists of main holes and subholes that prevent flashbacks that may lead to rig explosion. The burner imparts jet to the premixed measured composition of CH₄/CO₂/O₂. The results indicated that the adiabatic flame temperature (Tₐd) is a strong controlling parameter in quantifying the stability map and combustor flame shape; variation in oxygen fraction and equivalence ratio influence the flame shape, whereas the equivalence ratio (ϕ) is the major controlling parameter of temperature distribution within the combustor. The results also indicated that the stability map does not follow the lines of constant power density, mass flow rate of the mixture (mₘᵢₓ), and Reynolds number (Re).

The published literature on natural circulation in package boilers lacks a model that performs calculations for each circuit and determines circulation parameters for all circuits. This study presents a developed computational procedure capable of sizing and analyzing the performance of natural circulation package boilers to meet a specific load. Also; the study identifies the most critical circuit of a package boiler and determines the impact of heat flux, friction factor and tube plugging on the circulation ratio and wall temperature. The model was validated by comparing its results with experimental data. The results revealed that the Circuit 3 (The D-Tubes) is the most critical circuit. Plugging some of these tubes reduces the circulation ratio and increases the tube wall temperature significantly. The results indicate that the circulation ratio decreased by 20% and the wall temperature increased by 9.6% as a result of increase in the heat flux by 24%.

Header tube arrangements are commonly used in the heat exchangers. This arrangement is used to distribute the flow from the header into several tubes to achieve the required heat exchange. The flow mal-distribution within the tubes occurs due to the development of vena-contracta at the inlet to the tubes. In order to reduce the flow mal-distribution in the header tube arrangement, two approaches are presented in this study and solved numerically. In the first approach, the actual tube inlet is reduced by the introduction of an orifice. The results of the present study indicate that, by using orifice approach, flow mal-distribution can be reduced by approximately 12 times the original. However, the pressure drop from the heat exchanger increases by 7.8% compared to the case without orifices. In the second approach, the actual tube inlet is increased by the introduction of a nozzle. The results of the present study indicate that, by using nozzle approach, flow mal-distribution can be reduced by approximately 7.5 times the original. However, the pressure drop from the heat exchanger decreases by 9.8% compared to the case without nozzles.

Thepredictionofflowratesatwhichthevibration- induced instability takes place in tubular heat exchangers due to cross flow is of major importance to the performance and service life of such equipment. In this paper, the semi- analytical model is developed and utilized to study the tri- angular tube patterns. The developed mathematical model is tuned with the experimentally measured fluid-elastic force coefficients. An experimental setup with water channel and instrumentedtestsectionisconstructed.Inthisinvestigation, two test sections are constructed for both the normal trian- gular and the rotated triangular tube arrays. The developed scheme is utilized for predicting the critical flow velocities at the inception of flow-induced instability in the two trian- gular tube arrays. The results are compared to those obtained for two other bundle configurations, namely the square and rotated square arrays. The results of the two tube patterns are viewed in light of TEMA predictions. The comparisons demonstrated that TEMA predictions provided more conser- vative guidelines for all the configurations considered. Field application of the obtained results was successful in extend

Flow maldistribution in heat exchanger tubes can significantly affect its performance. In this work, 16 tubes are connected between the inlet and the exit headers forming the heat exchanger. The feed nozzle is connected to the inlet header, and its connection point can be altered. The influences of inlet flow Reynolds number, nozzle diameter, number of nozzles and nozzle location on the flow maldistribution are experimentally investigated. Water is chosen to be the working fluid inside the heat exchanger set of tubes. At lower flow rates, the results showed that the flow Reynolds number has a significant effect on the flow maldistribution inside the heat exchanger set of tubes; however, at higher flow rates, this effect was insignificant. Locating the nozzle at the center of the inlet header resulted in about 25–30% reduction in the standard deviation (STD) of the flow rate inside the tubes. Increasing the number of inlet nozzles resulted in an insignificant effect on the flow maldistribution. Increasing the nozzle diameter resulted in increased STD of the flow rate distribution among the tubes and pressure drop across the tubes at the considered heat exchanger geometry and water flow rate.

This study aims to investigate experimentally the natural convection flow over an array of discrete surfaces mounted on a flat vertical substrate. The investigation covers the case where the discrete surfaces/substrate unit forms a wall of a closed cavity. Experimental measurements of the flow and thermal fields were conducted. The experimental study is aimed at investigating the influence of the Rayleigh number on the velocity and thermal fields inside the cavity. Two cases of heat source distribution were considered: uniform heat source distribution and non-uniform heat source distribution. Measurements of vertical and horizontal velocity components were obtained for three heating values: 10, 15, and 20 W corresponding to Rayleigh number values of Ra = 9.06 × 109, Ra 1.19 × 1010, and Ra 1.41 × 1010. For each case, the velocity measurements were conducted at three different vertical locations, located at the middle of each of the three heaters. Velocity measurements were also obtained for non-uniform ...

Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location, nozzle geometry, nozzle diameter, inlet flow velocity and the incorporation of a second header on the flow maldistribution inside the tubes of an air-cooled heat exchanger were investigated using a 3-D computational method. The results are presented in terms of the standard deviations of the mass flow rate and static pressure in addition to the distributions in the static pressure inside the inlet header of the air-cooled heat exchanger. The results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the flow maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. Fifty percent decrease in the standard deviation is achieved as a result of incorporation of a second header of 7 holes. The results indicate that the mass flow rate and the static pressure distributions become uniform at the inlet of the second pass.

This paper presents the fluid flow characteristics of natural convection flow in an anti-symmetrically heated parallel-plate vertical channel using the Particle Image Velocimetry (PIV) system. The channel walls were subjected to uniform temperature conditions, with one wall heated above ambient and the opposing wall maintained below ambient temperature. Velocity measurements were conducted at three different sections on the horizontal plane to validate two-dimensionality of the flow and at three different heights in the vertical plane to establish vertical mean velocity profiles. The results indicate that the flow recirculation in the channel exhibits a similar character to that of a closed cavity and the induced flow rate is much lower than the one for a channel with both walls heated. A correlation for the dimensionless flow rate is developed.

The present paper provides correlations of flow maldistribution parameters in air-cooled heat exchangers. The flow field in the inlet header was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The results were obtained for different number of nozzles of 2–4, different inlet flow velocities of 1–2.5m/s and different nozzle geometries in addition to incorporation of a second header. The results are presented in terms of mass flow rate distributions in the tubes of the heat exchanger and their standard deviations. The results indicate that the inlet flow velocity has insignificant influence on maldistribution while the nozzle geometry shape has a slight effect. Also, the results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. A 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. A 50% decrease in the standard deviation is achieved as a result of incorporation of a second header of seven holes. It is also found that the hole-diameter distribution at the exit of the second header has a slight influence on the flow maldistribution. Correlations of the flow maldistribution in terms of the investigated parameters are presented. Copyright © 2007 John Wiley & Sons, Ltd.

Erosion in the tube entrance region of a typical air-cooled heat exchanger is numerically predicted. The erosion rates are obtained for different flow rates and particle sizes assuming low particle concentration. The erosion prediction is based on using a mathematical model for simulating the fluid velocity field and another model for simulating the motion of solid particles. The fluid velocity model is based on the solution of the time-averaged governing equations of 3-D turbulent flow while the particle-tracking model is based on the solution of the governing equation of each particle motion taking into consideration the viscous and gravity forces as well as the effect of particle rebound behavior. The computational model was validated against available experimental data and the comparison resulted in a good agreement. The investigation covered particle sizes from 10 to 350 μm and inlet flow velocities from 0.18 to 4.5 m/s. The results show that the location and number of eroded tubes depend mainly on the particle size and flow velocity at the header inlet. The total rate of erosion was found to increase exponentially with flow velocity. At high flow velocities, the maximum total erosion rate results from large particles and the effect is reversed at low velocities. Similarly, the tube penetration rate was found to increase with the increase of flow velocity for all particle sizes. At the typical velocity of 1.1 m/s, the minimum tube lifetime was caused by the 350 μm particles and the maximum was caused by the 200 μm particles. Based on the obtained results, it is well established that erosion cannot be totally avoided so long as solid particles are present in the fluid. However, the threshold velocity below which erosion is negligible can be accurately defined if an acceptable lifetime (or penetration rate) is defined.

The problem of buoyancy driven turbulent flow in parallel-plate channels is investigated. The investigation is limited to vertical channels of uniform cross-section with different modes of heating. The details of the flow and thermal fields are obtained from the solution of the conservation equations of mass, momentum, and energy in addition to equations of the low Reynolds number turbulence model. The study covers Rayleigh number ranging from 105 to 107 and focuses on the effect of channel geometry on the characteristic of the flow and thermal fields as well as the local and average Nusselt number variation. A Nusselt number correlation has been developed in terms of a modified Rayleigh number and channel aspect ratio for the cases of symmetrically heated isothermal and isoflux conditions.

This paper presents the results of velocity measurements of natural convection in symmetrically heated vertical channel using the particle image velocimetry (PIV) system. Velocity measurements were conducted at three different sections on the horizontal plane to validate the flow two-dimensionality and at three different heights in the vertical plane to establish vertical mean velocity profiles. The results indicate a considerable influence of the Rayleigh number and aspect ratio on the mean velocity profile. The results also indicate significant diffusion rates of the vertical mean velocity component and normal Reynolds stresses towards the center of the channel.

This paper deals with erosion prediction in a pipe with sudden contraction for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration. The pipe axis was considered vertical and the flow was either in direction of gravity (downflow) or against it (upflow). The mathematical models for the calculations of the fluid velocity field and the motion of the solid particles have been established and an erosion model was used to predict the erosion rate. The fluid velocity (continuous phase) model was based on the time-averaged governing equations of 3-D turbulent flow and the particle-tracking model (discrete phase) was based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behavior. The effects of flow velocity and particle size were investigated for one contraction geometry considering water flow in a steel pipe. The results showed the strong dependence of erosion on both particle size and flow velocity but with little dependence on the direction of flow. The effect of flow direction was found to be significant only for large particle size and moderate flow velocity. The erosion critical area was found to be the inner surface of the tube sheet (connecting the two pipes) in the region close to the small pipe. The results also indicated the presence of a threshold velocity below which erosion is insignificant for all particle sizes.

PurposeIn oil and gas industries, the presence of sand particles in produced oil and natural gas represents a major concern because of the associated erosive wear occurring in various flow passages. Erosion in the tube entrance region of a typical shell and tube heat exchanger is numerically predicted.Design/methodology/approachThe erosion rates are obtained for different flow rates and particle sizes assuming low particle concentration. The erosion prediction is based on using a mathematical model for simulating the fluid velocity field and another model for simulating the motion of solid particles. The fluid velocity (continuous phase) model is based on the solution of the time‐averaged governing equations of 3D turbulent flow while the particle‐tracking model is based on the solution of the governing equation of each particle motion taking into consideration the viscous and gravity forces as well as the effect of particle rebound behavior.FindingsThe results show that the location and number of eroded tubes depend mainly on the particle size and velocity magnitude at the header inlet. The rate of erosion depends exponentially on the velocity. The particle size shows negligible effect on the erosion rate at high velocity values and the large‐size particles show less erosion rates compared to the small‐size particles at low values of inlet flow velocities.Originality/valueIn oil and gas industries, the presence of sand particles in produced oil and natural gas represents a major concern because of the associated erosive wear occurring in various flow passages. The results indicate that erosion in shell and tube heat exchanger can be minimized through the control of velocity inlet to the header.

Corrosion in deadlegs occurs as a result of water separation due to the very low flow velocity. This work aims to investigate the effect of geometry and orientation on flow field and oil/water separation in deadlegs in an attempt for the development of a deadleg criterion. The investigation is based on the solution of the mass and momentum conservation equations of an oil/water mixture together with the volume fraction equation for the secondary phase. Results are obtained for two main deadleg orientations and for different lengths of the deadleg in each orientation. The considered fluid mixture contains 90% oil and 10% water (by volume). The deadleg length to diameter ratio (L/D) ranges from 1 to 9. The results show that the size of the stagnant fluid region increases with the increase of L/D. For the case of a vertical deadleg, it is found that the region of the deadleg close to the header is characterized by circulating vortical motions for a length l≈3 D while the remaining part of the deadleg occupied by a stagnant fluid. In the case of a horizontal deadleg, the region of circulating flow extends to 3–5 D. The results also indicated that the water volumetric concentration increases with the increase of L/D and is influenced by the deadleg orientation. The streamline patterns for a number of cases were obtained from flow visualization experiments (using 200 mW Argon laser) with the objective of validating the computational model.

Steady two-dimensional natural convection in an inclined parallel-walled channel was investigated numerically. The full elliptic forms of conservation equations were solved together and the velocity vectors, temperature contours and local and average Nusselt number distribution were obtained. The comparisons of local and average Nusselt number with published experimental and numerical results indicate very good agreement. Results are presented for a single aspect ratio, L/b=24, over the range of Rayleigh number of 3–1000 and angle of inclination 0–90°. The results indicate that the overall channel average Nusselt number is reduced as the inclination angle is increased. Significant reductions in the overall Nusselt number are exhibited at high angle of channel inclination. Copyright © 2005 John Wiley & Sons, Ltd.

Deadlegs are defined as the inactive portion of the pipe where the flow is stagnant. Corrosion in deadlegs occurs as a result of water separation due to the very low flow velocity. The present work provides an investigation of the effect of deadleg geometry and average flow velocity on flow field and oil/water separation in deadlegs. The investigation is based on the solution of the mass and momentum conservation equations of an oil/water mixture together with the volume fraction equation for the secondary phase. A fluid flow model based on the time-averaged governing equations of 3-D turbulent flow has been developed. An algebraic slip mixture model is utilized for the calculation of the two immiscible fluids (water and crude oil). The model solves the continuity and momentum equations for the mixture, and the volume fraction equation for the secondary phase utilizing an algebraic expression for the relative velocity. Flow visualization experiments were conducted in order to validate the numerical procedure. Good agreement was obtained between the calculated and measured flow patterns. Results are obtained for different lengths of the deadleg. The considered fluid mixture contains 90% oil and 10% water (by volume). The inlet flow velocity ranges from 0.2 to 10 m/s and the deadleg length to diameter ratio (L/D) ranges from 1 to 10. The results showed that the size of the stagnant fluid region increases with the increase of L/D and decreases with the increase of inlet velocity. The results also indicated that the water volumetric concentration increases with the increase of L/D and influenced by the deadleg geometry.

Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd.

Heat transfer characteristics to turbulent pulsating pipe flows under a wide range of Reynolds number and pulsation frequency were experimentally investigated under uniform heat flux condition. Reynolds number was varied from 8462 to 48540 while the frequency of pulsation ranged from 1 to 29.5 Hz. The results showed that the relative mean Nusselt number is strongly affected by both pulsation frequency and Reynolds number. Enhancements in mean Nusselt number of up to 50% were obtained at medium pulsation frequency between 4.1 and 13.9 Hz for Reynolds number range of 8462 to 14581. An enhancement of up to 50% in mean Nusselt number was obtained at high pulsation frequency range between 13.9 and 29.5 Hz, specially as Reynolds number is close to 15000, while a reduction was observed at higher Reynolds number more than 21200. This reduction, at high Reynolds number, increased as pulsation frequency increased. Also, there was a reduction in mean Nusselt number of up to 20% that obtained at low pulsation frequency range between 1 and 4.1 Hz for Reynolds number range of 8462 to 48543. A significant reduction in mean Nusselt number of up to 40% was obtained at medium pulsation frequency between 4.1 and 13.9 Hz for Reynolds number range of 21208 to 48543. Empirical equations have been developed for the relative mean Nusselt number that related to Reynolds number and dimensionless frequency with about uncertainty of 10% rms.

A numerical investigation aimed at understanding the flow and heat transfer characteristics of pulsating turbulent flow in an abrupt pipe expansion was carried out. The flow patterns are classified by four parameters; the Reynolds number, the Prandtl number, the abrupt expansion ratio and the pulsation frequency. The influence of these parameters on the flow was studied in the range 1044, 0.7

This paper presents the results of velocity measurements of natural convection in symmetrically and asymmetrically heated vertical channels. In the first case of symmetrical flow, the two channel plates were both kept at a constant temperature higher than the ambient. In the second case of asymmetrical flow, one plate was kept at a temperature higher than the ambient temperature while the other plate was kept at a temperature lower than the ambient temperature. The velocity measurements were performed using a Laser Doppler Anemometer. In the case of symmetrical flow, the results indicate a reverse flow region located at the center of the channel close to its exit. In the case of asymmetrical flow, the results show that the flow accelerates up the hot plate and decelerates down the cold plate. The results also indicate that cooling one of the two plates below ambient influences the flow pattern significantly and results in the formation of a small reversed vortex at the center of the channel.

Experimental and numerical investigations were carried out to study the effect of weld parameters on the temperature-time history at the back of a tubesheet (adjacent to the gasket) of a shell-and-tube heat exchanger. Experiments were conducted to validate one of the cases simulated (second case in Table 1). The simulated case is called the base case. The predictions obtained for the base case agree well with experimental results. Moreover, parametric studies based on numerical results are carried out for different weld parameters. These parameters include weld duration, weld temperature, tube-sheet size, tubesheet material and sequence of welding. The results indicate that the weld duration has a significant effect on the magnitude of the maximum temperature at the back surface of the tubesheet adjacent to the gasket. Doubling the weld duration increases the maximum temperature by more than 40 per cent. An increase of more than 20 per cent in the peak value of temperature at the back of the tubesheet near the gasket is predicted for five consecutive welds with a time gap of 10 s, whereas a 7.4 per cent increase is predicted for alternate welds.

Empirical correlation has been developed for local and average Nusselt numbers in the thermal entrance region of steady and pulsating turbulent air-flows in a pipe. The correlation was based on experimental data obtained from experiment carried out on a pipe heated under uniform heat flux conditions. The rate of flow was periodically varied at frequencies ranging from 1 Hz to 13 Hz while the average Reynolds number varied from 6400 to 42000.

Lasers find wide applications in industry due to their precision operation and low cost. Laser machining processes exhibit common characteristics such as heating, melting and evaporation. Modelling of the heating process may enhance understanding of the laser machining process, which in turn minimizes the optimization cost. This study is conducted to explore the laser heating process including evaporation through the electron-kinetic theory approach. The basis in examining the problem using the kinetic theory approach is to describe the transport of energy through electron–phonon and molecule–phonon collisions. A numerical scheme is introduced to solve the resulting coupled-energy equations, since the governing equations are in the form of integro-differential equations. To obtain the material response to the heating pulse, three different heating pulses are employed, consequently, the resulting temperature distributions inside and at the surface of the substances are computed. The study is extended to include first and second law efficiencies of the melting process, which in turn provides the pulse shape giving the improved melting efficiency. It is found that the temperature distribution in the vicinity of the surface depends on the electron distribution and number of collisions taking place in this region. The Fourier theory results, obtained from the previous study, gives a lower surface temperature than that predicted from this study.