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General Secretary Xi Jinping pointed out that in a country, if the youth is strong, the country would be strong and if sport is a strong entity in China, the country will be strong as well. In regard to that, promoting the continuous development of sports in China is an important aspect of the great rejuvenation of the Chinese nation. The “Healthy China 2030” plan is a program in the creation of a “healthy China.” With the current state of physical education in higher vocational colleges, three aspects are included in the innovative thinking of higher vocational physical education which are strategies for the challenges and impacts faced by physical education teachers in higher vocational colleges, achieving exquisite indicators in physical education as the ultimate goal of vocational colleges, as well as piquing the interest of higher vocational colleges for learning in regard to physical education courses.

Thermal entrainment is an integral feature of free-shear flows involving temperature changes, including fountains (negatively buoyant jets). The understanding of thermal entrainment is essential for applications involving thermal stratification such as that in a solar water storage tank. In this study, thermal entrainment in the core regions of transitional plane fountains in linearly-stratified ambient fluids is studied numerically over a range of the Froude number, Reynolds number, and dimensionless thermal stratification parameter. The results show that thermal entrainment has a negligible effect on the inner core region, but is significant in the outer core region, particularly at the interfaces among the upflow, downflow, and ambient fluid, and the thermal entrainment parameter, which quantifies the extent of thermal entrainment, decreases with height or in a stronger stratification, but increases with increasing Froude number or Reynolds number. Several numerical relations are obtained with the numerical results for the thermal entrainment parameter.

Solar collector with horizontal double-row all-glass evacuated tubes has been extensively implemented in the solar water heating system engineering. The temperature distribution and stratification of horizontal double-row all-glass evacuated tube collector with 24 evacuated tubes have been studied. Validation of instantaneous efficiency under different declination angle qm were studied by means of experiments. Moreover, numerical simulations are carried out for four different declination angle qm (0/2/4/6). The results showed that the declination angle qm has significant effect on energy conversion efficiency, flow patterns and stratification inside evacuated tubes. When qm > 0, with the declination angle increased, the instantaneous efficiency also increased, nevertheless, the temperature stratification weakened and the heat loss coefficient demonstrated no significant change. Declination angle 6 allowed to achieve significant higher temperatures, nevertheless, along with inactive area at the bottom of evacuated tubes appears. If declination angle qm < 0, inversion phenomenon appears. With the increase of |qm|, more heat is trapped in the sealed end of the evacuated tube, which is not conducive to the flow heat transfer in evacuated tube solar collector.

Scalings for the thicknesses of the thermal and velocity boundary layers, the plate temperature, and the maximum vertical velocity in a homogeneous Pr > 1 fluid are validated against numeri...

The unsteady natural convection boundary layer (NCBL) on a vertical wall heated by time varying flux in initially quiescent homogeneous fluid with a small Prandtl number (Pr) was studied. Scalings for the parameters typifying NCBL behavior, including plate temperature, maximum vertical velocity, thermal boundary-layer thickness, and velocity boundary-layer thickness, at different development stages, and the time for the transition from the start-up stage to the quasi-steady state, were developed by scaling analysis. The obtained scalings were compared to and validated by the numerical results with different values of Pr, the Rayleigh number Ra and the dimensionless time-varying heat flux frequency fn, over 106 ≤ Ra ≤ 109, 0.01 ≤ Pr ≤ 0.5, and 0.001 ≤ fn ≤ 0.025. It is also found that the development of the boundary layer at the start-up stage is one-dimensional and but becomes two-dimensional at the quasi-steady state.

A linear temporal stability analysis is conducted for inviscid sheared convective boundary layer flow, in which the sheared instability with stable stratification coexists with and caps over the thermal instability with unstable stratification. The classic Taylor–Goldstein equation is applied with different stratification factors Js and Jb in the Brunt–Väisälä frequency, respectively. Two shear-thermal hybrid instabilities, the hybrid shear stratified (HSS) and hybrid Rayleigh–Bénard (HRB) modes, are obtained by solving the eigenvalue problems. It is found that the temporal growth rates of the HSS and HRB modes vary differently with increased Jb in two distinct wavenumber ([Formula: see text]) regions defined by the intersection point between the stability boundaries of the HSS and HRB modes. Based on [Formula: see text] where the temporal growth rate of the HSS and HRB are equal, a map of the unique critical boundary, which separates the effective regions of the HSS and HRB modes, is constructed and found to be dependent on Js, Jb, and [Formula: see text]. The examinations of the subordinate eigenfunctions indicate that the shear instability is well developed in the HSS mode, in which the large vortex structures may prevail and suppress the formation of convective rolls; the shear instability in the HRB mode is either “partly developed” when [Formula: see text] or “undeveloped” when [Formula: see text], thus only plays a secondary role to modify the dominant convective rolls, and as Jb increases, the eigenfunctions of the HSS mode exhibit different transitional behaviors in the two regions, signifying the “shear enhancement” and “shear sheltering” of the entrainment of buoyancy flux.

Thermal stratification can lead to the damping of turbulence, which reduces the mixing of solutes in a fluid body. A series of direct numerical simulation (DNS) solutions sweeping through a range of four different meandering channel curvatures, from a sharp to mild curvature range, are obtained to investigate the effect of curvature on stratification in meandering thermally stratified turbulent open channel flow with an internal heat source that models radiative heating from above. Based on the DNS results, the present paper addresses two issues. First, the influence of changing curvature on the complex bi-cellular pattern of the secondary flow is investigated, including the distribution of the temperature field. Second, the effects of changing curvature on the degree of stratification are analyzed. Stratification can be characterized by the friction Richardson number [Formula: see text] and the bulk Richardson number Rib. Stratification can also be viewed in terms of the transfer of energy from mean flow kinetic energy to potential energy via buoyancy fluxes. We study the effect of curvature on stratification by investigating its effect on the friction and bulk Richardson numbers. We also study the transfers between the global potential and kinetic energy reservoirs, including the global available Ea, background Eb, and total potential energy Ep, and the domain-averaged mean kinetic and turbulent kinetic energy. It is found that, in meandering channels, with the increase in curvature, Ep increases and [Formula: see text] and Rib decrease, indicating that increasing curvature leads to a decrease in the level of stratification. On the other hand, we also find that a low curvature meandering channel has a higher level of stratification than a straight channel.

The transient conjugate natural convection heat transfer in a differentially-heated cavity with a partition of finite thickness and thermal conductivity are investigated numerically over the range of the Rayleigh number from 103 to 108, the thermal conductivity ratio of partition to that of fluid from 0.1 to 1000, and the dimensionless partition thickness from 0.05 to 0.2. An analysis of the obtained temperature contours and profiles, the time for the onset of stratification and the Nusselt number shows that the thermal conductivity ratio effect is significant only over the range of 0.1–10, when the role played by the partition changes, whereas the effect becomes negligible as the thermal conductivity ratio is very large (100 or beyond). It is also found that the scaling relations developed for the non-partitioned cavity are found to be applicable for the partitioned cavity. The results further show that the effect of the partition thickness on heat transfer is significant mainly when the thermal conductivity ratio is small.

Multicolor-tunable materials have attracted extensive interest due to their unique advantages in applications of lighting and displays. In this paper, energy transfer from Ce3+ to Tb3+ occurred and the effective energy transfer efficiency (ηETE) of Ce3+-Tb3+ has been calculated to be as high as 36%. To obtain multicolor-tunable emissions, Eu3+ ions were successfully introduced into Ce3+–Tb3+ codoped Sr3La6(SiO4)6 samples. Furthermore, an energy transfer process from Ce3+ to Eu3+ ions has also been demonstrated by an energy transfer bridge of Tb3+. Meanwhile, we achieved the precise adjustment of purple, green, orange and red emissions of Sr3La6(SiO4)6: Ce3+, Tb3+, and Sr3La6(SiO4)6: Ce3+, Tb3+, Eu3+. In addition, Sr3La6(SiO4)6: Ce3+, Tb3+, Eu3+ phosphors exhibited a good thermal stability: their integrated emission intensities at 450 K still kept more than 90% of their initial intensity at room temperature. Therefore, these results might provide a novel multicolor-tunable phosphor for lighting and display application.

Numerical simulations are used to investigate the entrainment for forced turbulent fountains over a range of Reynolds numbers and Froude numbers, with ranges based on the fountain source properties. Other fountain properties such as height and width are also examined to provide information on the general structure of the fountains. The results show that the fountains have minimal Reynolds number dependency, while they have a strong linear relation with the Froude number for the cases considered in this study. The entrainment coefficient is obtained as well as scaling constants for height and width in terms of the Froude number. References G. Abraham. Jets with negative buoyancy in homogeneous fluid. J. Hydraul. Res., 5(4):235248, 1967. doi:10.1080/00221686709500209. W. D. Baines, J. S. Turner, and I. H. Campbell. Turbulent fountains in an open chamber. J. Fluid Mech., 212:557592, 1990. doi:10.1017/S0022112090002099. L. J. Bloomfield and R. C. Kerr. A theoretical model of a turbulent fountain. J. Fluid Mech., 424:197216, 2000. doi:10.1017/S0022112000001907. H. C. Burridge and G. R. Hunt. Entrainment by turbulent fountains. J. Fluid Mech., 790:407418, 2016. doi:10.1017/jfm.2016.16. I. H. Campbell and J. S. Turner. Fountains in magma chambers. J. Petrol., 30(4):885923, 1989. doi:10.1093/petrology/30.4.885. P. D. Friedman, V. D. Vadakoot, W. J. Meyer, and S. Carey. Instability threshold of a negatively buoyant fountain. Exp. Fluids, 42(5):751759, 2007. doi:10.1007/s00348-007-0283-5. D. D. Gray and A. Giorgini. The validity of the Boussinesq approximation for liquids and gases. Int. J. Heat Mass Tran., 19(5):545551, 1976. doi:10.1016/0017-9310(76)90168-X. N. B. Kaye and G. R. Hunt. Weak fountains. J. Fluid Mech., 558:319328, 2006. doi:10.1017/S0022112006000383. B. P. Leonard and S. Mokhtari. Beyond first-order upwinding: The ultra-sharp alternative for non-oscillatory steady-state simulation of convection. Int. J. Numer. Meth. Eng., 30(4):729766, 1990. doi:10.1002/nme.1620300412. T. J. McDougall. Negatively buoyant vertical jets. Tellus, 33(3):313320, 1981. doi:10.3402/tellusa.v33i3.10718. T. Mizushina, F. Ogino, H. Takeuchi, and H. Ikawa. An experimental study of vertical turbulent jet with negative buoyancy. Warme Stoffubertrag., 16(1): 1521, 1982. doi:10.1007/BF01322802. B. R. Morton. Forced plumes. J. Fluid Mech., 5(1):151163, 1959. doi:10.1017/S002211205900012X. S. E. Norris. A parallel NavierStokes solver for natural convection and free surface flow. PhD thesis, University of Sydney, 2000. J. S. Turner. Jets and plumes with negative or reversing buoyancy. J. Fluid Mech., 26(4):779792, 1966. doi:10.1017/S0022112066001526. N. Williamson, N. Srinarayana, S. W. Armfield, G. D. McBain, and W. Lin. Low-Reynolds-number fountain behaviour. J. Fluid Mech., 608:297317, 2008. doi:10.1017/S0022112008002310. N. Williamson, S. W. Armfield, and W. Lin. Forced turbulent fountain flow behaviour. J. Fluid Mech., 671:535558, 2011. doi:10.1017/S0022112010005872. H. Zhang and R. E. Baddour. Maximum penetration of vertical round dense jets at small and large Froude numbers. J. Hydraul. Eng., 124(5):550553, 1998. doi:10.1061/(ASCE)0733-9429(1998)124:5(550).

Research hotspots about Ce3+-Tb3+ and Ce3+-Mn2+ codoped multicolor-tunable materials, has grown rapidly and is still growing. However, few feasible strategies can be employed to achieve the multicolor-tunable luminescence under the premise of maintaining high QE. In this paper, KSrLu(PO4)2:0.25Ce presents a high luminescence efficiency with approximately 78% quantum efficiency. Furthermore, Ce3+-Tb3+ and Ce3+-Mn2+ codoped optimal samples give a green and red luminescence, which corresponds to a high 61% and 55% quantum efficiency due to a high energy transfer efficiency of Ce3+→Tb3+ and Ce3+→Mn2+. Besides, we achieved the precise adjustment of blue, green, orange and pink emissions of KSrLu(PO4)2:Ce3+, Tb3+, Mn2+ samples. Meanwhile, KSrLu(PO4)2:Ce3+, Tb3+ and KSrLu(PO4)2:Ce3+, Mn2+ phosphors present a weak thermal quenching: their integrated emission intensity at 500K still keep more than 80% of their initial intensity at room temperature. Therefore, the results might provide a novel multicolor-tunable phosphor for backlight display application.

The transient natural convection boundary-layer flow adjacent to a vertical plate heated with a time-dependent heat flux in an initially linearly stratified ambient fluid with Prandtl numbe...

Solar selective absorber coating (SSAC) is one of the key components of a solar collector, with its optical properties having a significant impact on the collector’s thermal performance. The key parameters characterizing the optical properties of an SSAC are the solar absorptance (absorptance of solar radiation) and the thermal emittance (emittance for long-wave radiation). However, some of high-performing SSACs suffer from some drawbacks, such as lower durability, lower resistance to corrosion and abrasion, which is particularly harmful for SSACs, as, for example, chlorides in the atmosphere have become a main contributor to corrosion in coastal areas with the increasing trend of global warming. In this paper, salt spray tests have been conducted on the SSACs manufactured by three common manufacturing technologies, i.e., the anode oxidation (AO) technology, the vacuum magnetron sputtering (VMS) technology, and the black chromium plating (BCP) technology, over the testing durations of 12 h, 24 h, 36 h, and 48 h, respectively, to examine the effect of the salt spray testing on the optical properties of SSACs manufactured by different manufacturing technologies. The salt spray testing is an accelerated aging testing method for evaluating the SSAC’s resistance to corrosion when it is under an extended exposure to a saline, or salted, spray (fog). The experimental results show that, in general, the SSACs manufactured by the BCP technology have excellent resistance to salt spray (i.e., to corrosion) and those manufactured by the AO technology have only reasonable resistance to corrosion, whereas the SSACs manufactured by the VMS technology have very poor resistance to corrosion. The results also demonstrate that there are noticeable differences in the optical properties of the SSAC samples even manufactured by the same technology but by different manufacturers, with some having significant differences. The causes for the differences have been further examined through the inspection of the physical appearance of the selected SSAC samples and the experimentally measured distributions of the monochromatic reflectance of solar radiation of the samples over the solar spectrum before and after the salt spray testing over different durations.

The article aims to explore the new concepts and their enlightenment to school physical education curriculum management based on the concept of transformative curriculum leadership. The study found that transformational curriculum leadership is an educational concept that conforms to the trend of the times and produces a courage to criticize and reflect. It is practice-oriented and implementation-oriented, and faces the complexity and irreducibility of school education. Although it is not as clear as the traditional curriculum leadership view, it is closer to the real education situation, which has revolutionary inspiration for the transformation of school physical education curriculum management. Its enlightenment to the management of physical education curriculum in our country mainly includes the following three points: (1) Re-propose a new definition of the concept of leadership in physical education curriculum; (2) Combine sports and health to show new art; (3) Combine school sports culture with local characteristics Establish harmonious school public relations.

Heat sink can effectively dissipate heat in a range of thermal applications for improved performance and reliability. Thermally conductive polymer composites show great promise in solving the overheating issue in electronic devices. This experimental study investigates the thermal performance and the flow characteristics of straight and oblique finned heat sinks made of thermally conductive polymer composites under forced convection conditions over 7450

Direct numerical simulation (DNS) results for turbulent open-channel flow through an idealized sine-generated meander with and without an internal heat source that models radiative heating from above are used to analyze the effect of a very sharp meander configuration and thermal stratification on the turbulence structure in the channel with friction Reynolds number [Formula: see text]. Spatial distributions of temperature, mean velocities, vorticity, mean-flow kinetic energy, and turbulent kinetic energy (TKE) are presented. In both cases, the cross-sectional motion is characterized by three circulation cells: a center-region cell and two weaker outer bank and inner bank cells. However, there is also a small cell observed near the corner of the channel bed inner bank at the channel outlet and the channel bed outer bank at the channel inlet. The tri-cellular cross-stream motions control the distributions of temperature and kinetic energy. In the stratified case, two separated shear layers (SSLs) are found: the first one is formed before the bend apex, and the second one is observed in the wake after the bend apex. In the neutral case, only the first SSL is observed. Turbulent amplification can be seen in both cases; however, in the stratified case, the second SSL stretches out to the channel outlet and is introduced back to the channel inlet by an anti-symmetric periodic boundary condition and then follows the outer bank line. The two SSLs converge in the region before the bend apex and amplify the turbulence more strongly there than in the neutral case. The turbulence kinetic energy budget terms for the stratified case are analyzed to determine the characteristics of production, dissipation and transport of TKE in thermally stratified meandering flow.

The stability features of the inviscid, homogenous, and free cross sheared flow, with base flow velocities [Formula: see text] in the primary direction, which is unstable, and [Formula: see text] in the orthogonal direction, which is stable, are thoroughly examined with linear temporal stability analysis, where z is the transverse coordinate perpendicular to the flow and ξ is the cross shear ratio which is the ratio of the characteristic magnitudes of V to U. The map of the unstable regions directly related to [Formula: see text] is obtained, where ([Formula: see text]) is the ratio between the orthogonal and primary wavenumbers. Further examination of the eigenfunctions shows that the eigenfunction structures divide into the orthogonal wavenumber (OW) mode where ([Formula: see text]) dominates and the cross shear (CS) mode where ξ dominates. The cross shear is found necessary for stabilization in spite of different fashions for the OW and CS modes. The transition from the OW mode to the CS mode shows that the developments of the two modes inherently compete with each other, so that when [Formula: see text] decreases the enhanced cross shear needs to deteriorate the OW mode before it helps the growth of the CS mode. Based on the magnitudes of the associated eigenfunctions in the enstrophy budget, the map of the OW, CS, and hybrid modes, which includes the mixed features of both the OW and CS modes, is produced and discussed.

Indoor thermal comfort in primary classrooms is important to students' learning and health. The studies focusing on it, especially under the subtropical plateau monsoon climate, are scarce. In this study, the indoor thermal comfort surveys and parameter measurements were made over the period from October 2018 to December 2018 in Kunming, China. A series of indoor thermal comfort and outdoor parameters were measured each 1 h and subjective questionnaire surveys were performed on the selected 20 students every week except on holidays. A series of three-dimensional numerical simulations were carried out using ANSYS Fluent. Keywords: Indoor thermal comfort, PMV, PPD, Primary school classrooms, Field study

A wet scrubber is an air pollution removal device that eliminates particulate matter and acid gases from a diesel engine. The exhaust gas enters the scrubber beneath the liquid surface, causing a reduction in gas temperature and increases the relative humidity of the scrubber outlet. In this study, a wet scrubber was investigated experimentally based on a transient heat loss and steady-state heating process. A transient heat loss experiments were performed to estimate the heat loss from the scrubber surface. The steady-state heating process was investigated separately with various inlet gas temperatures and flow rates. The experimental results confirmed that the scrubber effectively reduces the inlet gas temperature from 650 oC to about 50oC. However, the outlet gas relative humidity increased due to the high liquid evaporation rate. A thermodynamic analysis estimated the outlet gas relative humidity and compares it with the measured values. The contribution of this study is: heat loss estimation methodology and relative humidity calculations.

Numerical simulations have been carried out to investigate the unsteady natural convection flow in a cavity subjected to a sidewall heat flux varying sinusoidally with time. With all walls non-slip and the upper and lower boundaries and one sidewall adiabatic, the heating and cooling on the other sidewall produces an alternating direction natural convection boundary layer that discharges hot fluid to the top and cold fluid to the bottom of the cavity, generating a strong and time-varying thermal stratification in the cavity interior. The thermal stratification is shown to be strongly dependent on the forcing frequency.

In this paper, high-speed cameras and flow visualization techniques are used to investigate the behavior of the ‘fountain filling box’ flow resulted from releasing a round fountain in a homogeneous quiescent fluid in a cylindrical container over the ranges of 1.0 ⩽ Fr ⩽ 20.0 , 102 ⩽ Re ⩽ 1502 , and 27.9 ⩽ λ ⩽ 48.75 , where Fr , Re and λ are the Froude number, the Reynolds number, and the dimensionless radius of the container, respectively, with λ non-dimensionalized by the fountain source radius. The results show the transition of the flow behavior of the fountain and its secondary flows (i.e., the intrusion, reversed flow and stratification) from laminar to turbulent with increasing Fr, and turbulence of the flow strengthened with increasing Re. For intermediate (e.g., Fr = 3.0 ) and forced turbulent fountains (e.g., Fr = 5.0 , 8.0, 15.0) with a specific λ , the non-dimensionalized time-scale for the intrusion front to impinge upon the sidewall, τ w , is nearly constant for Re ≳ 500 . This is because the secondary intrusion flow is dominated by the wall-jet and buoyancy-inertial regimes where the non-dimensionalized intrusion front velocity, v i , is only time-dependent ( v i ~ τ - 1 / 2 ) or time-dependent but also under the influence of Fr ( v i ~ Fr - 1 / 2 τ - 1 / 4 ). However, τ w for the fountains of Re ≲ 204 is significantly different, which may result from the change in the dominant regime for the intrusion or the interaction between the upflow, downflow of the fountain and the ambient fluids. Furthermore, it is found that the non-dimensionalized quasi-steady development rate of the stratification, v s , increases with Fr, but decreases with Re, since the diffusion effect is suppressed with decreasing Fr or increasing Re.

In this study, a series of three-dimensional direct numerical simulations were carried out for transitional round fountains in a linearly-stratified fluid over the ranges of 100 ≤ Re ≤ 400, 1 ≤ Fr ≤ 8 and 0.0 ≤ s ≤ 0.3, where Fr, Re and s are the Froude, Reynolds, and dimensionless temperature stratification parameters, respectively, to examine, both qualitatively and quantitatively, the effect of these parameters on their transition to asymmetry and the asymmetric behavior. It is found that the transition to asymmetry are well represented and quantified by azimuthal velocity, with non-zero or noticeable azimuthal velocity indicating asymmetry. The results show that when Fr or Re are small, a fountain remains axisymmetric for all time; however, when Fr or Re are increased to be sufficiently large, the fountain will be axisymmetric initially, before becoming asymmetric and unsteady, ultimately reaching a fully developed quasi-steady stage when each quantity fluctuates over a constant, time-average, value. The stratification is found to play a positive role to stabilize the flow and to reduce or even to eliminate the asymmetric behavior. The numerical results were also used to develop the scaling for the time for transition to asymmetry, which is found to be strongly dependent on Fr and s, while only weakly dependent on Re.

In this study numerical results for conjugate natural convection flow and heat transfer in a differentially-heated square cavity divided by a partition with finite thickness and thermal conductivity are presented. A series of numerical simulation is carried out using the finite volume method over a wide range of the Rayleigh number (105–109), with three dimensionless partition thicknesses (0.05, 0.1 and 0.2) and three dimensionless partition positions (0.25, 0.5 and 0.75), both are non-dimensionalized by the cavity width. The results show that the average Nusselt number increases with the Rayleigh number but decreases with partition thickness. It is also found that the partition position has a negligible effect on the average Nusselt number for the whole range of Rayleigh number considered.

The transition to asymmetry of transitional fountains is further complicated by the stratification of the ambient fluid. In this study, a series of three-dimensional direct numerical simulations were carried out for transitional round fountains in linearly-stratified fluids over the ranges of 100 ≤ Re ≤ 400, 1 ≤ Fr ≤ 8 and 0.0 ≤ s ≤ 0.3, where Fr, Re and s are the Froude, Reynolds, and dimensionless temperature stratification parameters, respectively, to examine, both qualitatively and quantitatively, the effect of these parameters on their axisymmetric transition and their maximum penetration heights. The results show that when Fr or Re are small enough, a fountain remains axisymmetric for all time; however, when Fr or Re are increased sufficiently, the fountain will be axisymmetric initially, before becoming asymmetric and unsteady, ultimately reaching a fully developed quasi-steady stage when the maximum fountain penetration height fluctuates over a constant, time-average, value. The stratification is found to play a positive role to stabilize the flow and to reduce or even to eliminate the asymmetric behavior. The numerical results were also used to develop a series of scaling relations, in conjunction with the scalings obtained with dimensional analysis, for the initial and time-averaged fountain penetration heights, and the time for the fountain to attain the initial penetration height. It is further found that in general these characteristic parameters are strongly dependent on Fr and s, while only weakly dependent on Re.

In this paper, a scaling analysis using a simple three-region structure was used to develop scalings for the unsteady natural convection boundary layer (NCBL) of a homogeneous Newtonian fluid with Pr>1 adjacent to a finite vertical plate evenly heated with a time-varying sinusoidal temperature, where Pr is the Prandtl number. Three distinct sub-stages are identified in the heating stage, i.e., a start-up stage, a transitional stage, and a quasi-steady stage. After the heating stage, there is a very short cooling stage, in which a double thermal boundary layer structure is developed, which leads to a new, thinner thermal boundary layer adjacent to the plate co-existing with the original thermal boundary layer. A series of scalings are developed for the thermal and viscous boundary thicknesses, the maximum vertical velocity within the boundary layer, and the Nusselt number which are the major parameters representing the flow behavior, in terms of the governing parameters of the flow, i.e., the Rayleigh number Ra, Pr, and the dimensionless natural frequency of the time-varying sinusoidal temperature at various flow development stages. These scalings are tested by full numerical solutions of the governing equations and are shown to, in general, provide an accurate description of the flow.

In this study, the PIV and flow visualization techniques and three-dimensional direct numerical simulation are used to investigate the behavior of triple transitional round fountains, which are aligned along a straight line, interacting with each other in a homogeneous fluid over the ranges of 1 ≤ Fr ≤ 10 and 100 ≤ Re ≤ 1000, at a fixed spacing of D / X 0 = 6 , where Re and Fr are the Reynolds and Froude numbers, D is the spacing between the two neighbouring fountain sources, and X0 is the radius of orifices at the fountain source, respectively. The results show that the interaction behavior of triple transitional round fountains, over the ranges of Re and Fr studied, is dominated by the bobbing and flapping motions, and is either steady, or unsteady weakly multi-modal, or unsteady strongly multi-modal. In a steady interaction, the bobbing-flapping motions are only present in its initial development stage and the interaction will attain a steady state in the later stage in which the bobbing-flapping motions are no longer present. In contrast, in an unsteady interaction, the interaction remains unsteady all the time and the bobbing-flapping motions are present at all stages. Among all cases considered, a steady interaction occurs at Re ≤ 300 with F r = 1 and at R e = 100 with Fr ≤ 5; an unsteady weakly multi-modal interaction occurs at R e = 100 with 6 ≤ Fr ≤ 10, at 200 ≤ Re ≤ 300 with 2 ≤ Fr ≤ 10, and at R e = 400 with F r = 1 ; and an unsteady strongly multi-modal interaction occurs at 600 ≤ Re ≤ 1000 with F r = 1 and at 400 ≤ Re ≤ 1000 with 2 ≤ Fr ≤ 10. Such interaction behavior is found to be similar to that of twin transitional round fountains over comparable ranges of Re and Fr, as discovered by us in an earlier study. It is also found that the two interaction regions formed by the three fountains have essentially symmetrical behavior about the middle fountain for all cases considered. Furthermore, the maximum fountain penetration heights and the maximum thicknesses of the interaction regions of the triple transitional round fountains are quantified with the experimental and numerical results and compared to the available scalings for single fountains at comparable Fr and Re values. Several scaling relations are then developed for these parameters over the ranges of Fr and Re considered.

Research hotspots about Ce

When a fountain is injected into a linearly stratified fluid, its behavior will be governed by the stratification of the ambient fluid, represented by the dimensionless temperature stratification parameter (s), in addition to the Reynolds number (Re) and the Froude number (Fr). In this study, a series of three-dimensional direct numerical simulations (DNS) were carried out using ANSYS Fluent for transitional plane fountains in linearly-stratified fluids with Re, F r and s over the ranges 28 ≤ Re ≤ 300, 3 ≤ F r ≤ 10, and 0.1 ≤ s ≤ 0.5 to study the effects of these governing parameters on the characteristics of such unsteadiness. Empirical correlations to quantify the effects of F r, Re and s over the studied ranges on the characteristics of the unsteadiness are also obtained and compared to the relevant scaling relations developed for weak plane fountains. Keywords: Direct numerical simulation, Plane fountain, Stratification, Transitional flow, Unsteadiness.

Heat sink can effectively dissipate heat in a range of thermal applications for improved performance and reliability. Thermally conductive polymer composites show great promise in solving the overheating issue in electronic devices. This experimental study investigates the heat dissipation performance of straight and oblique fin heat sinks made of thermally conductive polymer composites under forced convection conditions over 7.45 × 10 4 ⩽ Re ⩽ 3.60 × 10 5 , where Re is the Reynolds number. The heat sinks were 3D printed using Ice9 Flex (carbon filled polymer), copper filled filament (polylactic acid with 80 wt% copper particles) and bronze filled filament (polylactic acid with 80 wt% bronze particles), respectively. Oblique fins were found to effectively reduce the thermal resistance of heat sinks, increase the convective heat transfer and the inner-fin velocity which results in lower pressure drop, in comparison to straight fins. The carbon-filled polymer (Ice9 Flex) heat sink was shown to have much superior heat dissipation capability compared to metal filled filament heat sinks.