•Chevron-hydroformed manifold of evacuated heat pipe solar collector was designed.•Heat transfer characteristics and hydrodynamic behavior characterized via CFD.•Thermal performance and pressure drop ...were evaluated experimentally.•Use of stainless-steel based hydroformed manifold in solar heating is feasible.
A manifold is an essential component of an evacuated tube heat pipe solar collector (ETHPSC) that directly influences the thermal efficiency of a solar heating system. This study aimed to develop and assess the use of a stainless-steel based chevron-hydroformed manifold in ETHPSCs as an alternative to conventional copper-based welded manifolds, which have a high manufacturing cost and short life span and are easily corroded. In the present study, the physical design of the proposed chevron-hydroformed manifold was elucidated. Numerical simulation using computational fluid dynamics was performed to characterize the hydrodynamic behavior of fluid flow through the chevron-hydroformed channels. The thermal characteristics and frictional pressure drops of a smooth-hydroformed and a chevron-hydroformed manifolds were experimentally investigated. The experimental results showed that the convective heat transfer coefficient of the chevron-hydroformed manifold was greater than the smooth-hydroformed manifold by approximately 29.0 %. However, the proposed chevron pattern of the proposed hydroformed manifold resulted in a larger pressure drop compared to the conventional manifold by approximately 17.7 %. Field experiments were conducted to compare the performance of the stainless-steel based chevron-hydroformed manifold with that of a conventional copper-based welded manifold. The feasibility of employing the stainless-steel based hydroformed manifolds in ETHPSCs in solar heating applications was examined.
We report on the study of binary collisions between quantum droplets formed by an attractive mixture of ultracold atoms. We distinguish two main outcomes of the collision, i.e., merging and ...separation, depending on the velocity of the colliding pair. The critical velocity v_{c} that discriminates between the two cases displays a different dependence on the atom number N for small and large droplets. By comparing our experimental results with numerical simulations, we show that the nonmonotonic behavior of v_{c}(N) is due to the crossover from a compressible to an incompressible regime, where the collisional dynamics is governed by different energy scales, i.e., the droplet binding energy and the surface tension. These results also provide the first evidence of the liquidlike nature of quantum droplets in the large N limit, where their behavior closely resembles that of classical liquid droplets.
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•The complete ML-optimization of injector and injection parameters for GCI Engine.•Spray angle (SA) and start of injection (SOI) are the most important design parameters.•Two optimum SOI regimes at ...part-load and two preferable SAs at high-load were found.•10.7% reduction in fuel consumption at part-load and 7.5% at high-load were achieved.•The improvements by optimization were mainly caused by the increased air utilization.
In this study, computational fluid dynamics (CFD) and machine learning (ML) were used to investigate the effects of and optimize the injector design parameters for light-duty gasoline compression ignition (GCI) engine. This study was performed at part- (6 bar) and high-load (22 bar) indicated mean effective pressure (IMEP) conditions. The effects of number of nozzles (nNoz), spray angle (SA) and plume angle (PA) while maintaining total nozzle area (TNA) and start of injection (SOI) were first investigated. The increased nNoz and PA enhanced fuel/air mixing, especially in the bowl region, by even spray distribution at part-load condition, but the effects are negligible at high-load mixing-driven combustion due to high in-cylinder temperature and pressure at the time of main injection. On the other hand, SA had significant effect on the air utilization and hence engine performance and emissions at both part- and high-load conditions. The best design from this manual parametric study produced a balanced air utilization between piston bowl and squish region resulting from the fuel spray targeting the upper lip of the bowl. The second phase of this study focused on the optimization of the injector and injection parameters including nNoz, SA, nozzle hole diameters (dNoz) and SOI using design of experiment (DoE) approach. 32 DoE cases were generated and best design was selected at each load point. It was found that the SA and SOI are the most influential injection parameters. Specifically, two optimum SOI regimes at part-load conditions have been identified. These are a) early injection resulting in retarded combustion and low pressure rise rate and b) late injection yielding high combustion efficiency and low hydrocarbon emission. At high-load condition, SOI right before top dead center (TDC) is most preferable and early injection should be avoided to minimize pressure rise rate. The narrow SA (90 degrees (deg) in this study) as well as wide SA were found to produce optimum performance. Subsequently, ML algorithm was used to further optimize the injector and injection parameters. As a result of this optimization study, 10.7% reduction of fuel consumption at part-load and 7.5% reduction at high-load were achieved.
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•Simulation of ozonolysis model for OzBiONY® reactor using COMSOL Multiphysics®.•Reaction kinetic parameters are estimated via Sparse Nonlinear Optimizer (SNOPT).•Larger biomass ...particle confers faster delignification rate (k1 = 2.23 m3/mol∙s).•Higher ozone concentration is simulated on the surface of larger biomass particle.•Lignin degradation of 78 wt% is achieved using OzBiONY® ozonolysis reactor.
Pre-treatment is the key step in biorefinery for enhancing cellulose accessibility from lignocellulosic biomass (LB) such as empty fruit bunch (EFB), which contains highly valuable cellulose. Ozonolysis pre-treatment appears as a promising green alternative for isolation of EFB to cellulose. This study develops the diffusion–reaction model of EFB ozonolysis inside a well-mixed novel OzBiONY® ozonolysis reactor at lab scale production. The mathematical model is numerically solved using COMSOL Multiphysics® software. Kinetic reaction parameters are computationally estimated via gradient-based Sparse Nonlinear Optimizer (SNOPT) method with sequential quadratic programming (SQP) algorithm. The evolution of ozone velocity and concentration profiles inside the reactor are simulated by computational fluid dynamics (CFD) method to study the effect of biomass particle sizes. The larger particle size consumes higher ozone (k1 = 2.23 m3/mol∙s) compared to the smaller particle size (k1= 0.09 m3/mol∙s). This reveals that larger biomass particle confers faster delignification rate and a much higher degradation of insoluble lignin. The simulation results demonstrate ozone velocity at the surface of larger particle is lower, but the surface concentration of ozone is higher. The diffusion–reaction model of EFB ozonolysis elucidates the plausible reaction pathway of lignin degradation via ozonolysis pre-treatment with minimum objective function (Z) of 1.41 × 10−3. From experimental results, the highest lignin degradation is 78 wt.% and the highest glucose yield is 12 wt.%. The outcomes of this research will contribute to the development of smart biorefinery technology and systems for sugar production in a sustainable and circular economy.
Thermal fluid dynamics and experiments have been used to study the evolution of pores during selective laser melting of Ti-6Al-4V. Scanning electron micrographs show that the morphology of pores ...changed from near-spherical to elongated shape as the laser scan speed increased. Computational fluid dynamics suggests that this is caused by the change of flow pattern in the melt pool which is dictated by forces such as vapour pressure, gravitational force, capillary and thermal capillary forces exerted on the metallic/gaseous interface.
•Microchannel heat sink with triangular ribs on sidewalls.•Triangular ribs can significantly improve the heat transfer performance.•Different arrangement leads to different thermohydraulic ...characteristics.•Geometry of rib exerts significant influence on thermohydraulic performance.•New pressure drop and heat transfer correlations are proposed.
Triangular ribs mounted in the microchannel heat sink generally result in higher heat transfer coefficient, but are usually accompanied by higher pressure drop per unit length. In order to obtain some insight into the effect of geometry parameters of triangular ribs on laminar flow and heat transfer characteristics, three-dimensional conjugated heat transfer models taking account of the entrance effect, viscous heating and temperature-dependent thermophysical properties are conducted, and four non-dimensional variables related to the width, height, converging-diverging ratio and spacing of the triangular rib for both aligned and offset arrangements are designed. Effects of the geometry and arrangement of triangular ribs on thermohydraulic performance are examined by the variations of average friction factor and Nusselt number for Reynolds number (Re) ranging from 187 to 715. The studied microchannels have the same width (Wc) of 0.1 mm and same depth (Hc) of 0.2 mm in the constant cross-section region. The geometric parameters of aligned or offset triangular ribs are ranged in 0.025–0.4 mm for width (Wr), 0.005–0.025 mm for height (Hr), 0.2–5 mm for spacing (Sr) and 0–1 for the width ratio of converging region to a single rib (Wcon/Wr). Based on the total 660 computational cases of the microchannel heat sinks with triangular ribs, the correlations of average friction factor and Nusselt number are proposed, respectively for aligned and offset arrangements. For the studied Reynolds number range and geometry parameters of flow passage, the microchannel heat sinks with aligned triangular ribs present 1.03–2.01 times higher of average Nusselt number and 1.06–9.09 times larger of average friction factor, and those with offset triangular ribs show 1.01–2.16 times higher of average Nusselt number and 1.04–7.43 times larger of average friction factor, compared with the reference straight microchannel heat sink. Proposed heat transfer and friction factor correlations show good agreements with the computational results for the microchannel heat sinks within the parameter ranges of 187 ≤ Re ≤ 715, 0.25 ≤ Wr/Wc ≤ 4, 0.05 ≤ Hr/Wc ≤ 0.25, 0 ≤ Wcon/Wr ≤ 1, and 2 ≤ Sr/Wc ≤ 50.
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