Horizontal Rectangular Channel Research Articles

Investigation of fluid flow during flow boiling inside a horizontal rectangular channel with single-sided heating using particle image velocimetry

Subcooled flow boiling is a highly efficient cooling systems for thermal management systems. This study explores the intricate dynamics of subcooled flow boiling within a horizontal channel, investigating the impact of vapor generation on liquid-phase velocity using Particle Image Velocimetry (PIV) and advanced image processing techniques. Four mass flow rates ranging from 5–20 g/s with subcooled inlet conditions are investigated in a rectangular channel with single-sided heating. Three regions of interest along the heated channel are investigated for instantaneous PIV analysis. The PIV system captures detailed velocity profiles, illustrating the impact of varying mass flow rates and heat flux levels on flow behavior. Vapor masking techniques are introduced to enhance the precision of PIV data by mitigating interference from the vapor phase. Results demonstrate the influence of vapor bubbles on flow resistance, revealing non-uniform velocity distributions and turbulence near the liquid–vapor interface. The study emphasizes the critical role of inertia and buoyancy forces in shaping the velocity profiles. Moreover, the investigation sheds light on the effects of flow rates on the interfacial behaviors, hinting at a transition point between 10 and 15 g/s. In summary, this research contributes valuable insights into the nuanced dynamics of flow boiling, laying the foundation for future studies on turbulence, heat transfer, and phase-change phenomena in two-phase thermal management systems.

Slump-flow channel test for evaluating the relations between spreading and rheological parameters of sediment mixtures

Understanding debris flow phenomena and modeling them effectively requires accurate estimation of their rheological parameters. This study introduces a simple approach defined as the “slump-flow channel test”, which employs a horizontal rectangular channel to evaluate these parameters. The results of slump-flow channel tests indicate that the spreading parameters (spread length, angle of reach, and time to final spread) of sediment mixtures are strongly influenced by their sediment fractions and rheological properties. An empirical analysis of the temporal evolution of the spread length and spread velocity was carried out employing both experimental and simulation results. The numerical simulation of the slump-flow channel tests was performed using the Flow-3D software. Both experimental and simulation results demonstrate that the spreading and the rheological parameters of sediment mixtures exhibit strong correlations and this implies that the rheological parameters of sediment mixtures can be evaluated indirectly using a simple slump-flow channel test.

Determination of the surface roller length of hydraulic jumps in horizontal rectangular channels using the machine learning method

Determination of the surface roller length of hydraulic jumps in horizontal rectangular channels using the machine learning method

A heat transfer correlation of Poiseuille-Rayleigh-Bénard convection in the thermal entrance region of a horizontal rectangular channel

In order to understand heat transfer characteristics and obtain a heat transfer correlation of Poiseuille-Rayleigh-Bénard (P-R-B) convection in the thermal entrance region of a horizontal rectangular channel, we performed a series of the direct numerical simulations. The working fluid is water, and the spanwise aspect ratio of the rectangular channel ranges from 2 to 10. The results show that the thermal entrance length for the onset of buoyancy-driven convection extends with the decreasing Rayleigh number and the increasing Reynolds number. The average Nusselt number in the thermal entrance region increases with the increase of Rayleigh number and Reynolds number. Furthermore, a smaller aspect ratio and a shorter length of the channel contributes to enhanced heat transfer in the thermal entrance region. Based on the simulation results, the heat transfer correlation in the thermal entrance region is established, which can be used as a reference for the engineering design on P-R-B convection.

The Combined Effect of Coriolis Force and Double Diffusive for the Convention in a Rectangular Isotropic and Anisotropic Porous Channel

The combined effects of Coriolis force, heat, and mass diffusion for the convection in a horizontal rectangular channel filled with fluid in both isotropic and anisotropic porous channels is studied in the three-dimensional case for which the governing equations with the boundary conditions are derived with the help of the following assumptions: the fluid is incompressible; the flow is axisymmetric about the y-axis; the fluid is steady; thermal diffusion is larger than the viscous diffusion. With the help of the stream function, the resultant equations are made dimensionless, and non-dimension parameters like Rac, Rs along with anisotropic aspect ratio of permeabilities and thermal diffusivities are introduced. Later, the resulting linear partial differential equations are solved by the method of Fourier series analysis. The effect of the non-dimensional numbers plays a vital role in controlling parameters like velocity, temperature, and concentration for both isotropic and anisotropic cases. The expression for critical Rayleigh number has been established for both isotropic and anisotropic cases. Various computations are carried out in order to study the effects of velocity, temperature, concentration, and Critical Rayleigh number for different values of non-dimensional parameters. The obtained results are in good agreement with previous literary works and also have a wide application in the real world which can be seen in different industries.

Entropy generation of pure mixed convection from double circular cylinders rotating inside a confined channel

In this article, numerical investigations have been done on mixed convective laminar flow in a confined horizontal rectangular channel, considering air as the flowing fluid. The channel is provided with two hot solid cylinders rotating about their axes, placed vertically in a side-by-side configuration. A convection current is supplied by inducing a fully developed forced flow at a low temperature through the channel's inlet across the clockwise or counterclockwise rotating cylinders. Steady, two-dimensional Navier-Stokes and heat energy equations govern the transport phenomena within the flow domain. These equations have been simulated using the Galerkin finite element technique with appropriate boundary and interface conditions. Parametric studies have been conducted for Reynolds number based on the mean flow speed over a range of 31.62 ≤ Re ≤ 316.23, and Grashof number within the range of 103 ≤ Gr ≤ 105, while Richardson number is maintained unity (Ri = 1) indicating pure mixed convection. Variations of the geometrical configurations are considered in terms of the cylinders' blockage ratio (λ = 0.05, 0.1, 0.2) and gap ratio (γ = 0.25, 0.50, 0.75). The cylinders' rotational direction impacts are also analyzed by altering the rotational Reynolds number (Reω = 10, −10). Then, a configuration that maximizes the heat transfer rate is obtained by evaluating the flow and thermal properties and the accompanying entropy generation. It is found that maximum heat transfer and lower entropy generation occur when the cylinders rotate in opposite directions to each other. Moreover, the thermal performance criterion improves with a smaller cylinder size, and decreasing the gap ratio increases the Nusselt number and lowers entropy generation.

Experimental study on sub-regimes of air-water slug flow in a rectangular micro-channel

In mini/micro-channel two-phase flow, slug flow occurs easily because of the significant influence of surface tension and the low gravitational effect on the flow. Although an irregularity of slug flow has been reported, previous studies on mini/micro-channel slug flow have mainly concerned the slug flow with the alternate of film and liquid slug zones regularly. Therefore, the present study investigates sub-regimes of micro-channel slug flow with regular or irregular alternating film and liquid slug zones to understand their principal characteristics. Experiments are performed to visualize and simultaneously measure the transient local pressure of the air-water mixture flow in a horizontal rectangular channel with a 2 mm height and 1 mm width. Superficial Reynolds numbers for liquid and gas phases range from 56 to 1116 and 5.75 to 245, respectively. With the aid of visualization data, slug flow is categorized into two types of stable slug flow and four types of unstable slug flow. Present slug flow data is compared with previous correlations for predicting the regime of bubble formation mechanism, flow regime boundaries, and frictional pressure gradient. Measured temporal pressure records are analyzed using a fast Fourier transform and digital Butterworth filter, while a dominant frequency is identified from the normalized average power spectrum. Then, the local pressure fluctuation at the dominant frequency is examined for different types of slug flow using the visualization results. A morphological repetition is confirmed to be associated with the pressure fluctuation: the repeated film and liquid slug zones in both types of stable slug flow, the alternative between liquid-only flow and a group of gas bubbles and liquid slugs in type 3 unstable slug flow, and the periodic variation of bubble length in type 4 unstable slug flow. However, no correlation between morphological characteristics and pressure fluctuation is found in type 1 and 2 unstable slug flows.

Impact of thermal radiation and oriented magnetic field on the flow of two immiscible fluids through porous media with different porosity

ABSTRACT This work analyzes the impact of oriented magnetic fields and thermal radiation on the entropy generation of two non-miscible electrically conducting micropolar and Newtonian fluids in a horizontal rectangular porous channel. In this model, the walls of the duct are considered perfectly isothermal and the flow inside the porous channel takes place in the presence of an inclined magnetic field. Expressions for heat transformation, fluid flow velocity, Bejan number distribution, and entropy production characteristics are obtained with the help of a reliable method. To achieve the objective of the problem, the authors used the continuity of temperature distribution, thermal flux, shear stress, linear and angular velocity over the fluid–fluid interface and no-slip conditions at the fixed plates of the duct. The impact of various emerging parameters on the entropy optimization, Bejan number, heat transformation, and flow velocity is analyzed. Our findings are validated by the previously established results.

Experimental Study on Flow Condensation Heat Transfer in a Horizontal Rectangular Channel with Ellipse-shape Pin Fins

Experimental Study on Flow Condensation Heat Transfer in a Horizontal Rectangular Channel with Ellipse-shape Pin Fins

Transient Flow and Heat Transfer in a Horizontal Rectangular Channel Considering Thermal–Fluid–Structure Interaction

Abstract For the supercritical n-decane horizontally flowing in a rectangular channel of an active regenerative cooling system, a transient thermal–fluid–structure coupling method is employed to investigate the unsteady thermal-hydraulic characteristics and the wall deformation at a starting stage. The temperature distributions of the fluid domain and solid domain along the flow direction are investigated at fixed times as well as at a certain cross section. Streamlines in cross sections are employed to explain the temperature distribution. The velocity and pressure at a fixed point versus time are also given. Besides, the solid deformation is presented according to the uneven pressure distribution and temperature distribution. It is found that the response time is less than 30 s when the heat flux is less than 3.0 MW/m2. A larger heat flux contributes to promoting the steady state. The high-temperature part of the solid domain is close to the heated wall, but the situation is reversed for the fluid domain. This is because a bunch of dead-zone vortices appears in the vicinity of the upper wall of the channel. The maximum deformation is 0.132 mm for the condition of heat flux 3.0 MW/m2 and it is exacerbated by the uneven temperature and pressure distributions on the solid domain.

Supercritical Flow over a Submerged Vertical Negative Step

The transition from supercritical to subcritical flow around a fully submerged abrupt negative step in a horizontal rectangular open channel has been investigated. In a laboratory experiment the one-dimensional energy and the momentum conservation equations were studied by means of depth and pressure measurements by piezometers installed along the bottom and the step face. Froude number varied in the range 1.9 to 5.8 while the step height to critical depth ratio was in the range 1.34 to 2.56. The results are presented in dimensionless form using mainly a characteristic length scale that is the sum of critical depth and step height and the Froude number of the supercritical flow upstream. Five different types of rapidly varying flow are observed when the subcritical downstream tailwater depth varied. The supercritical water jet at the top of the step either strikes the bottom downstream of the step when the maximum pressure head is greater, or moves to the surface of the flow when it is lower than tailwater depth, and the separation of the two flow regimes occurs when the tailwater depth to the characteristic length scale is around 1.05. The normalized energy loss and a closure parameter for the momentum equation are presented in dimensionless diagrams for practical use by the design engineer. Finally, the one-dimensional equations of motion including Boussinesq terms are solved numerically and the results found are congruent to the experimental findings.

Reduction of skin friction and two-phase flow structure beneath wall in horizontal rectangular channel

From the viewpoint of the improvement of the air lubrication method for the ship's hull resistance reduction, an experimental study was conducted for two-phase flow in a horizontal rectangular channel with a length of 3.0 m, a gap of 0.05 m, and a width of 0.2 m, which simulates the external two-phase flow. The database on frictional drag and local two-phase flow parameters, including void fraction profile and gas chord length, was collected using a shear stress sensor and a double sensor probe. Measurement of two-phase flow structure was performed at three axial positions of z = 0.930, 1.43, and 1.93 m from the bubble injection port. The wall shear stress was obtained at z = 1.93 m. A total of 72 datasets are acquired a room temperature and at flow conditions of superficial liquid velocity <jf> ranging from 0.832 to 3.00 m/s and superficial gas velocity <jg> ranging from 0.0232 to 0.714 m/s. The effects of entry length, liquid and gas flow rates on the phase distribution characteristics beneath the wall were discussed. The bubble layer thickness was newly defined as the length scale. The bubble layer thickness was not so sensitive to the changes in the liquid flow rates and the entry length, and highly dependent on the gas flow rates in the present experimental conditions. The mean void fraction in the bubble layer was highly reliant on the liquid flow rate and decreased with the superficial liquid velocity. In contrast, the insignificant effect of gas flow rate on the mean void fraction was confirmed. A strong correlation between the drag reduction effect due to the air lubrication and the mean void fraction in the bubble layer was confirmed. The obtained data are expected to be used for the modeling of the interfacial area transport terms, development of the constitutive equations of the drift flux model, modeling of the drag reduction for the external two-phase flow and the benchmark tests of various CFD codes in the future study.

Stationary internal hydraulic jumps

This is a theoretical and laboratory study of stationary internal hydraulic jumps. These jumps are rapid transitions between internally supercritical flow, generated by placing a sill on the bed of a horizontal rectangular channel, and internally subcritical flow, generated by installing a downstream contraction. This contraction generates an approximately uniform flow downstream of the jump; thus mimicking barotropically driven two-layer flows, as found in tidally driven flows over underwater sills, and flows over mountain ranges driven by large-scale pressure gradients. Upstream of the jump a train of Kelvin–Helmholtz billows forms on the interface between the layers. Upper layer fluid is entrained into these billows, which are subsequently advected into the lower portion of the jump. These billows are broken down by the turbulence of the jump, and the entrained upper layer fluid is mixed with lower layer fluid. Downstream of the jump the upper layer remains homogeneous, the density step at the interface is weakened, the upper portion of the lower layer is approximately linearly stratified, and the lower portion of the lower layer is undisturbed. This altered density profile is the downstream conjugate state of the jump. When the contraction is narrowed the jump moves upstream and ‘drowns’ part of the train of billows, reducing the amount of entrainment. Thus, while the jump is responsible for mixing fluid from the upper layer into the lower layer, it is the position of the jump relative to the upstream train of billows that determines the amount of entrainment.

Numerical and experimental investigation of two phase flow geometrical characteristics

Abstract This paper presents an experimental and numerical analysis of the effect of the geometric parameter on the two-phase flow (white kerosene-water) flow pattern system. The investigation was carried out using three lengths (1, 2 and 3) m of rectangular horizontal smooth channel and three channel heights of (5, 7.5 and 10) cm respectively. The flow conditions for the input water velocity (0.2 m/s) and the input kerosene velocity (0.1 m/s) for both measurements have been investigated. Two-inlet techniques have been employed. Firstly, at the inlet, the kerosene was on top of the bath. Then, second, from the center, the kerosene inlets (water is above and below the kerosene). A numerical verification analysis was introduced using the ANSYS software using the method of volume of fluid (VOF) and mixture multiphase flow modeling coupled with the normal k-ε turbulence schemes. A collection of seven methods of CFD types is explored by running 224 instances. Comparisons were made between numerical and experimental works.

Investigation of the Perfect Hydraulic Jump in Horizontal Rectangular Channel

Accelerating the process of transition from supercritical to subcritical flow, by formation a forced hydraulic jump at the contract section (Forced perfect hydraulic jump), is one of the most important measures, in decreasing flow velocity, water energy dissipation and alleviation the scouring problem, leading to lessening the required protection length against the erosion issues in the bed of downstream of the channel. In the current study, physical model was prepared precisely at fluid mechanics laboratory in the faculty of Engineering/Alkhums at Elmergib University. Comprehensive experiments were conducted to evaluate measured and calculated characteristics of the perfect free jump, and consequently, the existence of the perfect hydraulic jump is investigated. Eventually, equation was derived that might be used to guarantee the existence of a free perfect jump, which is the limiting condition between both repelled and drowned jumps as well as, the limiting condition between both repelled and drowned jumps was graphically found.

How do the liquid properties affect the entrapment of bubbles in gas sheared liquid flows?

A large number of industries use fossil fuels for the purpose of cooling and lubrication utilizing a gas stream that acts as a shearing force on the liquid surface. Decreasing the carbon footprint of these processes needs an improved understanding of the effect of liquid properties. To this end this study investigates experimentally the effect of varying surface tension and liquid viscosity on the bubble generation and film statistics in a gas-sheared liquid flow. The experiments were conducted in a horizontal rectangular channel using high speed imaging in conjunction with the Brightness-Based Laser-induced Fluorescence technique (BBLIF) to measure film thickness over an area with a spatial resolution of 40 μm and a temporal resolution of 10 kHz. Two butanol–water solutions were used to give reduced surface tensions (namely 0.049 N/m and 0.04 N/m) compared to our previously-studied water only value. Also, two glycerol-water solutions were chosen to yield surface tension values closer to those of an oil of interest (namely 1.4 cP and 1.9 cP).The results show that compared to water, an increase in film thickness and a decrease in the disturbance wave velocity was observed with either the reduction in the surface tension or increase in the liquid viscosity. The frequency and size of the waves were found to be dominated by the liquid surface tension. Moreover, surface tension was found to have more of an effect on aeration as compared to viscosity. The bubble velocity was found to decrease with increase in viscosity, while it increases with decrease in surface tension. It is suggested that these changes would affect heat transfer and hence should be studied in more detail.

Effect of Aspect Ratio on Mixed Convection Heat Transfer from the Heated Bottom Wall in Horizontal Rectangular Channel

Effect of Aspect Ratio on Mixed Convection Heat Transfer from the Heated Bottom Wall in Horizontal Rectangular Channel

Characterization of the Pressure Drop during Condensation in Channels of Multi-Channel Cylinder Dryer Using Homogeneous and Separated Flow Models

The condensation resistance characteristics of steam flow in horizontal rectangular channels of multi-channel cylinder dryer (MCD) is a very important factor that affects the heat transfer, while it is not very clear due to the limited studies. In this paper, the frictional resistance characteristics of the two-phase flow (steam and water) in the rectangular small channels of MCD were investigated with deionized water as the working fluid, and the calculation models, homogeneous and separated flow models, of the two-phase flow pressure drop in the channel were verified and evaluated. It showed that the main part of the total pressure drop was the frictional pressure drop, which means that the calculation of frictional pressure drop was the key to the calculation of the pressure drop of the two-phase flow in the channel. Meanwhile, it was found that the homogeneous model was not suitable for the calculation of the frictional pressure drop and the separated flow model was completely in line with the experimental data. In this study, the converted coefficient of complete steam/liquid phase were concerned to calculate the frictional resistance using five separated flow models. It was found that the Chisholm B model showed better accuracy than prior correlations, which was greatly consistent with experimental data, and the average absolute percentage deviation (MAPE) was 24.9%.

A Novel Analytical Method for Evaluating the Characteristics of Hydraulic Jump at a Positive Step

We present a new method to evaluate the hydraulic jump characteristics in a horizontal rectangular channel with a positive step. We considered the flow curvature effect and the free surface’s small rise at the A-type hydraulic jump’s end. First, we present a novel method to give jump length estimation based on the similarity of the jump and the turbulent wall-jet, considering the pressure gradient. Then, considering the jump as a curvilinear flow and using a one-dimensional momentum equation, we present an accurate expression for the conjugate flow depth regarding the initial Froude number and step height. Finally, we compute the jump’s energy dissipation rate. Compared to the theoretical models for conjugate flow depth in a hydraulic jump, the proposed equation in this study fit the experimental data better, even for high steps and large initial Froude numbers. However, for low Froude numbers (F1 &lt; 5), the equation was less accurate in estimating the jump length. Regarding the jump’s energy dissipation rate, the results agreed well with the experimental data from previous investigations. However, it is noted that the increased energy dissipation rate dwindled in larger Froude numbers.

Coupling of pyrolysis and heat transfer of supercritical hydrocarbon fuel in rectangular minichannels

The coupling of pyrolysis and heat transfer of endothermic hydrocarbon fuels (EHFs) plays an important role in the design of cooling channels for advanced aircrafts. In this work, the convective heat transfer of EHFs with pyrolysis was experimentally investigated in horizontal rectangular channels under supercritical conditions (3.5 MPa, 700 °C) with different aspect ratios (λ = 1 ~ 5) by electrically heated tube test. CFD simulations with an updated kinetics were conducted and extensively validated to get detailed information of local flow, pyrolysis and heat transfer. The heat transfer is non-uniform in the cross-section with obvious temperature difference due to non-uniformity of boundary layer. Increasing λ is beneficial for heat transfer at topwall because of a relative lower heat flux and higher chemical heat absorption in bulk fluid. In addition, significant distribution of boundary layer along topwall and sidewall results in M-shape velocity distribution and subsequent high-degreed pyrolysis near sidewall region. This leads to dramatical variations of thermophysical properties and considerable decrease of chemical heat absorption, thus increasing the near-wall thermal resistances. Therefore, the local heat transfer is deteriorated at sidewall and corner, ascribed to a thicker boundary layer at the corner for increased fluid viscosity with secondary reactions, as well as the increased thermal resistances attributed to huge property gradient for pyrolysis distribution near sidewall.