Semicircular Cross Section Research Articles

Modeling and manufacturing of solar modules of different designs for energy supply of biogas plant

The article presents a description of the modeling and manufacturing of solar modules of photovoltaic, thermal and photovoltaic thermal designs intended to supply energy to a biogas plant intended for the production of biohydrogen and biomethane. Mathematical modeling of the photovoltaic module was carried out and the calculated temperature of the photovoltaic converters was determined, and also the photovoltaic module was manufactured using the process of sealing the photovoltaic converters with a two-component polysiloxane compound. Mathematical modeling of a solar thermal collector with water radiators in the form of a round copper tube, an oval copper tube, as well as a rectangular water cooling channel (“water jacket”) was also carried out, in which pressure losses and the amount of water heating were assessed. The distances between the rectangular channels of the water-cooling radiator for uniform heat removal were determined, and mathematical modeling of the thermal state of a solar thermal collector with a semicircular cross-section of the water-cooling radiator channel was carried out, after which the solar thermal collector was manufactured. Mathematical modeling of the total displacements of the components of a photovoltaic thermal module, the values of which do not exceed acceptable limits, was carried out, after which a photovoltaic thermal module was manufactured using the process of sealing photovoltaic converters with a two-component polysiloxane compound.

Investigation of numerical phase transition of nano-enhanced SiC/paraffin wax PCM in solar-assisted water desalination system

Adding nanoparticles in phase change material (PCM) is a new trend for enhancing their thermal energy-storing ability as well as thermal conductivity. From this point of view, a numerical study is carried out to examine the addition of silicon carbide nanoparticles in paraffin wax PCM, used as heat energy storing material in a semi-cylindrical solar water desalination system. The PCM temperature is maintained at 52 °C and the semi-cylindrical tubular section has a wall temperature of 85 °C. The top plane section of the tubular solar collector is made up of graphite material. A semi-circular cross-section is selected for numerical analysis. A finite volume solver is used for solving thermal and fluid flow governing equations. A pressure staggering option algorithm is applied for pressure–velocity coupling. The temporal parameters like temperature, velocity contours, melting fraction, enthalpy, and entropy of nano silicon embedded paraffin wax PCM are widely discussed. The results clearly show that the phase transition of solid PCM to fluid PCM is greatly influenced by nanoparticle addition and enhances the rate of heat transfer. Initially for the first 60 min the melting fraction and temperature of PCM remain uniform as the time step increases above 60 min the behavior of PCM changes abruptly which clearly indicates the random distribution of nanoparticles within the PCM. A critical time and temperature limit exists for nanoparticles-based PCM beyond which, the thermal efficiency of the solar water desalination system gets influenced.

Numerical investigation of supercritical flow and heat transfer mechanism in printed circuit heat exchanger (PCHE) channels

A numerical study is conducted to investigate supercritical hydrogen flow and heat transfer mechanisms and characteristics in printed circuit heat exchanger (PCHE) channels. The impact of large variations of the thermal-physical properties due to a wide range of operating temperatures have been studied and analyzed in detail. The heat transfer mechanisms of supercritical hydrgen under horizontal and vertical flow conditions are studied numerically. In addition, the influence of different cross-section shapes of the channel is also analyzed. The results show that asymmetrical fluid temperature distributions near the top wall and bottom wall due to the buoyancy effect result in heat transfer deterioration. Spiral flow occurs in the heat transfer deterioration region, which further confirms that the heat transfer deterioration is related to the spiral flow effect caused by the buoyancy effect. The heat transfer coefficient without gravity is lower than that with gravity, indicating that the buoyancy effect enhances the overall heat transfer in the horizontal circular channel. Furthermore, the fluid temperature in the vertical upflow channel decreases slowly from the near wall to the core area, while the fluid temperature in the vertical downflow channel changes sharply, which directly leads to the difference in the temperature gradient near the wall. Compared with the square cross-section channel and semicircular cross-section channel, the supercritical hydrogen can achieve greater heat transfer performance in the circular cross-section channel.

Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels.

This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrates increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.

Modeling of the flow and heat exchange in pipes with turbulators of viscous heat carriers in the laminar region, as well as in the transition to turbulent flow

Objective. Mathematical modeling of heat transfer in pipes with turbulators for viscous heat carriers at Reynolds numbers characteristic of laminar and transient flow regimes is carried out by the calculation method. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multiblock computing technologies based on the solution of the Reynolds equations (closed for the transient mode using the Menter shear stress transfer model) and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method (FCOM) was considered.Method. The calculation was carried out on the basis of a theoretical method based on the solution of the Reynolds equations, closed for transient modes using the Menter shear stress transfer model, and the energy equation on multiscale intersecting structured grids (FCOM), by a factorized finite-volume method.Result. Both local and averaged characteristics of the flow and heat exchange in pipes with turbulators for a viscous coolant for laminar and transient flow modes of the coolant were obtained using the FCOM method in the work, which made it possible to determine for these modes the levels of heat exchange intensification that satisfactorily correlate with the existing experiment.Conclusion. The calculated relative hydraulic resistance for low turbulators increases quite slightly, and for medium-altitude turbulators reaches 2÷2.5 to the critical Reynolds number, and subsequently it increases up to 3 times; for high turbulators, the relative hydraulic resistance increases up to 4 times even before the transition flow regime is reached, after which it increases up to 4.5 times. The calculated relative isothermal intensified heat exchange under the laminar flow regime of a viscous coolant for relatively high turbulators increases almost 2 times; for relatively medium heights of turbulators — almost one and a half, and for low relative heights, the intensification of heat exchange is insignificant.

Investigation on the thermal hydraulic characteristics of sodium-supercritical CO2 in compact heat exchange channel

Sodium-cooled fast reactor coupled with supercritical CO2 Brayton cycle has broad development prospects owing to the high thermal efficiency, smaller components and compact footprint. As one of the key components, sodium-supercritical CO2 compact heat exchanger plays a vital role in improving the operation performance of coupled power systems. In this paper, a numerical model for coupling heat transfer of sodium-supercritical CO2 in a straight-channel compact heat exchange channel is established and the prediction accuracy of the model is verified with experimental results. The influence of structural parameters and flow parameters on the resistance characteristics and heat transfer performance of cold and hot channels is systematically analyzed. The results show that the structure of semi-circular cross-section with an ABAB layout performs best in heat transfer performance. For the sodium channel, performance evaluation criteria gradually grow with the increase of sodium inlet velocity and slowly decline with the supercritical CO2 inlet velocity. For the supercritical CO2 channel, performance evaluation criteria decrease with the increase of sodium inlet velocity and increase with the supercritical CO2 inlet velocity. Reducing the supercritical CO2 inlet temperature could effectively improve the thermal hydraulic performance of the sodium-supercritical CO2 compact heat exchange channel.

Micro segment analysis of supercritical methane thermal-hydraulic performance and pseudo-boiling in a PCHE straight channel

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleate-boiling-like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a film-boiling-like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE.

A Theoretical Study of the Energy‐Harvesting Properties of Nontracking Semicircular Concentrating Troughs

The objective of this paper is to give a theoretical appraisal of the light harvesting attributes of nontracking concentrating troughs of a simple semicircular cross section. Emphasis is placed on the importance of the geometry of the caustic exhibited by reflection from a semicircular surface. The efficacy of various placings of the absorber tube is assessed using the method of ray tracing calculations. Utilization of the caustic geometry leads to troughs of optimized width which can capture 100% of the incident radiation normal to the fixed trough aperture. Troughs of different optimized widths (in units of the diameter of planar or cylindrical absorbers) are examined. The major results are to show that these troughs, with fixed concentration ratios, have universal properties which scale with the absorber size and that a favorable comparison is made with the ubiquitous compound parabolic concentrator of the same order of magnitude in size. This work suggests that there is further scope for the optimized design and testing of semicircular troughs.

Optimization analysis of multi-layered microchannel heat sink

Microchannel heat sinks with a large specific surface area are widely applied to the heat dissipation of microelectronic devices. In this work, a multi-layered microchannel heat sink with a size of was proposed based on the microchannel of the Printed Circuit Heat Exchanger (PCHE). The thermal resistance network model was established for the multi-layered heat sink with a semi-circular cross-section microchannel. Then, the Genetic Algorithm(GA) was employed to optimize the structure and operation parameters of the heat sink based on the thermal resistance network model. The optimized parameters and the corresponding thermal resistance under various power consumption were obtained. The optimization results show that the thermal resistance decreases rapidly with the increase of power consumption. When the power consumption is large, the trend of thermal resistance reduction is gradually flat. When the power consumption increases to 0.8 W, the optimal value of channel layers is up to 12, and the thermal resistance of the heat sink is 0.322 °C/(W/cm2). As the power consumption further increases from 0.8 W, the optimal value of layers remains constant at 12, and the ratio of the channel radius to the plate thickness remains at about 0.56. Three-dimensional numerical simulation is performed to verify the thermal resistance network model, and the results of the thermal network model agree well with the simulation.

Dieless blanking using noncylindrical micropunches

Dieless blanking/punching are useful for piercing microholes because removing the die makes it possible to overcome the difficulty in piercing a small-sized die hole and assembling a die set. However, only cylindrical punches had been employed in previous studies on dieless blanking/punching. Piercing holes using noncylindrical micropunches was therefore attempted. The workpiece was backed up with adhesive tape instead of the die. Stainless-steel sheets were blanked using cemented tungsten carbide micropunches fabricated by electrical discharge machining. Blanking was successfully carried out in a 5-μm-thick sheet using micropunches with a rectangular cross section of 18 μm on the long side and 16 μm on the short side and a semicircular cross section of 20 μm in diameter. Corners of the pierced holes were finely processed, especially at the hole entrances. This result demonstrates that noncircular microholes can be pierced as well as circular ones by dieless blanking. An investigation into the relationships between blanking conditions and blanking characteristics showed that the punch stroke must be at least 30 μm for micropunches to penetrate a 5-μm-thick sheet at a punch feed speed of 50 μm/s. Furthermore, the maximum punch load increased with increasing punch feed speed for semicylindrical micropunches and was almost the same for quadrangular-prism micropunches. Rotating micropunches were also used and circular microholes were successfully pierced, indicating that noncylindrical micropunches can be employed for piercing both circular and noncircular holes. In addition, the punch load decreased with increasing punch rotation speed, likely because the cutting action by the peripheral edges of micropunches facilitated punch penetration.

Modeling of a Soft Actuator With a Semicircular Cross Section Under Gravity and External Load

Compared to rigid robotic actuators, soft actuators based on fibre-reinforced elastomeric actuators (FREAs) have great potential for use in exploring complex terrain, medical operations, and flexible capture of targets. However, it is still challenging to model the mechanical behaviour of soft actuators because of the large deformation and nonlinear characteristics of elastic materials. This paper proposes an analytical model to predict the shape of a soft actuator to better describe the relationship between its deformation and input pressure, gravity, and other external forces. We first derive the relationship between soft actuator deformation and pressure using volume maximisation and the principle of virtual work. We further use Euler–Bernoulli beam theory to investigate the influence of self-gravity and external forces on the soft actuator configuration. The model is verified by fabricating a soft actuator prototype via mold casting. Finally, we perform a series of experiments to evaluate the accuracy of our proposed model. The longest total time to solve the model is 0.035 s. Experimental results show that the model's maximum error rate is between 2.89% and 9.75%. This indicates that the model can effectively predicts the deformation of soft actuators considering gravity and other external forces.

Mathematical Modelling of Heat Transfer in Pipes with Turbulators in the Laminar Region and in the Transition to Turbulent Flow

The article presents an analysis of mathematical modeling of heat transfer in pipes with turbulators at low Reynolds numbers characteristic of laminar and transient flow modes of heat carriers. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multi-block computing technologies based on the solution of Reynolds equations closed using the Menter shear stress transfer model and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method is considered. Both local and averaged characteristics of the flow and heat transfer to a pipe with a system of turbulators were obtained, which made it possible to determine the levels of heat exchange intensification for these regime ranges.

3D-printed chemiluminescence flow cells with customized cross-section geometry for enhanced analytical performance

Low force stereolithography is exploited for the first time for one-step facile fabrication of chemiluminescence (CL) flow-through cells that bear unrivalled features as compared to those available through milling or blowing procedures or alternative 3D printing technologies. A variety of bespoke cross-section geometries with polyhedral features (namely, triangular, square, and five-side polygon) as well as semicircular cross-section are herein critically evaluated in terms of analytical performance against the standardcircular cross-section in a flat spirally-shape format. The idea behind is to maximize capture of elicited light by the new designs while leveraging 3D printing further for fabrication of (i) customized gaskets that enable reliable attaching of the active mixing zone of the CL cell to the detection window, (ii) in-line 3D-printed serpentine reactors, and (iii) flow confluences with tailorable shapes for enhancing mixing of samples with CL reagents. Up to twenty transparent functional cells were simultaneously fabricated without inner supports following post-curing and surface treatment protocols lasting less than 5 h. In fact, previous attempts to print spirally-shaped cells in one-step by resorting to less cost effective photopolymer inkjet printing technologies were unsuccessful because of the requirement of lengthy procedures (>15 days) for quantitative removal of the support material. By exploiting the phthalazinedione-hydrogen peroxide chemistry as a model reaction, the five-side irregular pentagon cell exhibited superior analytical figures of merit in terms of LOD, dynamic range and intermediate precision as compared to alternative designs. Computational fluid dynamic simulations for mapping velocities at the entry region of the spiral cell corroborated the fact that the 5-side polygon cross-section flow-cell with Y-type confluence permitted the most efficient mixing of reagents and sample while enabling larger flow velocities near the inlet that contribute to a more efficient capture of the photons from the flash-type reaction. The applicability of the 3D-printed 5-side polygon CL cell for automatic determination of hydrogen peroxide using a computerized hybrid flow system was demonstrated for the analysis of high matrix samples, viz., seawater and saliva, with relative recoveries ranging from 83 to 103%.

Heat transfer coefficient of boiling flows in minichannels with a semicircular cross-section

The boiling heat transfer characteristics of vertically upward flows in small-diameter semicircular channels heated with hot water were experimentally investigated to characterize the influences of channel cross-section and thermal diffusivity of a heat transfer wall on heat transfer characteristics. The inlet subcooling degree was set to 10 K at a saturated temperature of 30 °C with a mass flux of 100–400 kg/(m2 s). Two types of hydraulic channels (stainless steel and copper) with diameters of 1.04 and 0.55 mm were used with refrigerant R-245fa. Moreover, the average heat transfer coefficient was evaluated considering the fin efficiency of the heat transfer wall. As a result, the heat transfer coefficient for high mass flux increased with the outlet quality owing to the nucleate boiling in the channel corners, causing a strong fluctuation of the gas–liquid interface. For the 0.55-mm channel, as the liquid film was thicker in the corners than in other regions due to surface tension, the increase in thermal resistance at the corners promoted nucleate boiling. A new correlation equation was derived to express the heat transfer coefficient for semicircular minichannels considering the fin efficiency; the mean absolute error between the experimental data and calculated values was 11.3 %.

Thermal and hydraulic performance of a large scale printed circuit heat exchanger (PCHE)

In present work, a printed circuit heat exchanger (PCHE), which was expected to be capable of heat exchange of 200 kW, was designed and manufactured, and its performance was evaluated by conducting experiments using nitrogen. Microchannels with a semi-circular cross section and a diameter of 2 mm were etched in the form of ‘N’ and ‘reverse N (RN)’ types on heat transfer plates made of STS316L and manufactured by diffusion bonding. Liquid nitrogen was vaporized and fed as gaseous state in hot side, and it was fed by pressurizing liquid nitrogen to the cold side. The mass flow rates were from 1531.8 to 2513.7 kg/h and from 407.2 to 980.5 kg/h in hot and cold side, respectively. The operating pressures were ranged from 0.51 MPa to 0.76 MPa and from 1.69 MPa to 9.38 MPa in hot and cold sides. Inlet temperature of nitrogen gas was ranged from 7.0 to 11.5 °C in hot side, and those of liquid nitrogen were from −165.9 to 178.3 °C. The phase change heat transfer coefficients of the cold side were calculated using the measured temperature and pressure values and compared with the existing correlation equations. The comparison showed a large discrepancy, so a new correlation equation, Nu = 0.09Re th 0.79 Pr v 0.33 (μ v /μ w ) 0.5 , was developed and proposed. Also, through the measured pressure drop, the pressure coefficient, K value was calculated since the pressure drops appearing outside the main micro channel of the core is proportional to the square of the velocity, and it was confirmed that R 2 = 0.99 when pressure coefficient, K was 15.7.

An Analysis of Semicircular Channel Backscattering Interferometry through Ray Tracing Simulations.

Recent backscattering interferometry studies utilise a single channel microfluidic system, typically approximately semicircular in cross-section. Here, we present a complete ray tracing model for on-chip backscattering interferometry with a semicircular cross-section, including the dependence upon polarisation and angle of incidence. The full model is validated and utilised to calculate the expected fringe patterns and sensitivities observed under both normal and oblique angles of incidence. Comparison with experimental data from approximately semicircular channels using the parameters stated shows that they cannot be explained using a semicircular geometry. The disagreement does not impact on the validity of the experimental data, but highlights that the optical mechanisms behind the various modalities of backscattering interferometry would benefit from clarification. From the analysis presented here, we conclude that for reasons of ease of analysis, data quality, and sensitivity for a given radius, capillary-based backscattering interferometry affords numerous benefits over on-chip backscattering interferometry.

Comparative study of solar air heater (SAH) roughened with transverse ribs of NACA 0020 in forward and reverse direction

Experimental and Numerical investigation of heat transfer and fluid flow characteristics is carried out for SAH duct (aspect ratio, W/H = 10:1) with transverse ribs of different cross-sections (square, semi-circular and symmetric half NACA 0020 in both forward and reverse orientations) on one of its broad wall. Solutions are obtained using SIMPLE algorithm for coupling of pressure and velocity, while for discretization of momentum and energy equations upwind scheme of second order is used in commercial ANSYS software. Nusselt number ( Nu ) and friction factor (f) are evaluated for Reynolds number (Re) ranging from 6000 to 18000, fixed relative roughness pitch (P/e = 12) and relative roughness height (e/D = 0.05). The highest value of ( Nu ) is found for ribs of semi-circular cross-section while minimum (f) is observed for forward oriented symmetric half NACA 0020. The highest thermo-hydraulic performance parameter is achieved at Re = 6000 with symmetric half NACA 0020 rib roughness when used in reverse orientation. Contours plots of temperature, velocity streamlines and pressure variation yielded important results for understanding the physical phenomenon inside the SAH. The numerical outcomes are validated with experimental results.

Compression waves in semi-circular channel

Partially filled pipe flows are commonly observed in urban hydraulics, sewers and road crossings. The occurrence of a compression wave in the confined space may result from flash flooding, transient operation or accidental blockage, inducing explosive conditions. In this study, the propagation of a compression wave was studied in a relatively large laboratory flume of semi-circular cross-section. The unsteady flow properties were recorded to understand how the circular cross-sectional shape impacted the surging water propagation. Both free-surface and velocity data indicated a marked impact of the compression wave passage, with large instantaneous fluctuations comparable to and sometimes larger than observations of compression waves in rectangular channels.

Corrigendum to “Pressure drop and flow patterns of boiling flows in Mini-channels with Semi-Circular Cross-Section” [Appl. Therm. Eng. 194 (2021) 117096

Corrigendum to “Pressure drop and flow patterns of boiling flows in Mini-channels with Semi-Circular Cross-Section” [Appl. Therm. Eng. 194 (2021) 117096

Free convection heat transfer from a semi-circular cylinder inside a square enclosure: Orientation effects

The numerical investigation has been carried out for the buoyancy driven flow (free convection) from a cylinder of semi-circular cross-section at three orientation angles (i.e., φ=0°,45°and90°) to stagnant power-law fluids inside a square cavity. The coupled governing equations were solved for the given range of the pertinent dimensionless parameters of Rayleigh number (102⩽Ra⩽105), Prandtl number (10⩽Pr⩽100), and power-law index (0.3⩽n⩽1.8). At different orientation angles of the semi-circular cylinders, the numerical results were visualized in terms of velocity and temperature profiles near the cylinder and, gross engineering parameters (e.g., average Nusselt numbers). If all other factors are equal, the rate of heat transfers from a semi-circular cylinder at φ=90° is higher than for the other orientations. The rate of heat transfer can also be increased by increasing the value of Ra and decreasing the value of Pr. In the power-law fluids, the heat transfer rate is always higher in shear-thinning fluids under the same condition. In the end, the average Nusselt number for different orientation angles of the cylinder has been correlated by simple expression.