Exit Plate Research Articles

Investigation of heat transfer enhancement inside developing gravity-driven films along a vertical permeable plate subject to nonuniform suction

Flow and heat transfer through the boundary layers of a falling liquid film on a vertical permeable plate subject to nonuniform suction flow are analyzed in this work. The continuity, momentum, and energy equations are transformed to nonsimilar equations and solved using a validated implicit and iterative finite difference method. Increases in the Froude number, Galilei number, and the dimensionless average suction velocity are found to increase the skin friction coefficient, the Nusselt number, and the heat transfer enhancement ratios. These enhancement ratios are noticed to increase at the plate exit as the suction velocity power-law index increases. The Froude number for uniform suction case required to attain the same enhancement ratios due to nonuniform distribution of this suction flow is found to increase as the Galilei number, average suction velocity, and power-law index increase. It is found that the upper most values of the enhancement factors in heat transfer and Froude number are [Formula: see text] folds when the suction power-law index is equal to [Formula: see text]. This work demonstrated that significant heat transfer enhancement inside developing gravity-driven liquid films is attainable when properly distributing the suction velocity along the plate.

Numerical study of solidification of A356 aluminum alloy flowing on an oblique plate with experimental validation

Molten A356 aluminum alloy flowing on an oblique plate is water cooled from underneath. The melt partially solidifies on plate wall with continuous formation of columnar dendrites. These dendrites are continuously sheared off into equiaxed/fragmented grains and carried away with the melt by producing semisolid slurry collected at plate exit. Melt pouring temperature provides required solidification whereas plate inclination enables necessary shear for producing slurry of desired solid fraction. A numerical model concerning transport equations of mass, momentum, energy and species is developed for predicting velocity, temperature, macrosegregation and solid fraction. The model uses FVM with phase change algorithm, VOF and variable viscosity. The model introduces solid phase movement with gravity effect as well. Effects of melt pouring temperature and plate inclination on hydrodynamic and thermo-solutal behaviors are studied subsequently. Slurry solid fractions at plate exit are 27%, 22%, 16%, and 10% for pouring temperatures of 620 °C, 625 °C, 630 °C, and 635 °C, respectively. And, are 27%, 25%, 22%, and 18% for plate inclinations of 30°, 45°, 60°, and 75°, respectively. Melt pouring temperature of 625 °C with plate inclination of 60° generates appropriate quality of slurry and is the optimum. Both numerical and experimental results are in good agreement with each other.

Influence of plate length and plate cooling rate on solidification and microstructure of A356 alloy produced by oblique plate

A356 alloy melt solidifies partially when it flows down on an oblique plate cooled from bottom by counter flowing water. Columnar dendrites are continuously formed on the plate wall. Because of the forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously by producing semisolid slurry at plate exit. Plate cooling rate provides required extent/amount of solidification whereas plate length enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained is solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets are also heat-treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets are compared. The effects of plate length and plate cooling rate on solidification and microstructure of billets produced by using oblique plate are illustrated. Three different plate lengths (200 mm, 250 mm, 300 mm) associated with three different heat transfer coefficients (1000, 2000 and 2500 W/(m2·K)) are involved. Plate length of 250 mm with heat transfer coefficient of 2000 W/(m2·K) gives fine and globular microstructures and is the optimum as there is absolutely no possibility of sticking of slurry to plate wall.

Visualisation of plane shock wave diffraction from the curved exit of a shock tube

There have been numerous studies of the diffraction of a plane shock wave from the normal exit of a shock tube, including studies of tubes with square, lenticular, or other irregular exit shapes. However, in considering the practical case in which such diffraction may spontaneously occur (e.g. the propagation of a blast wave through climate conditioning ducts or of a shock wave through a tuned motor vehicle exhaust system), the more likely geometric boundary condition would be of a curved exit diffraction surface. The current study explored the diffraction of a plane shock wave from the curved exit of a shock tube with a boundary plate to remove the characteristic length of the shock tube thickness. The cases tested all had: separations between the axis of the curved plate and the shock tube axis of between 0.5 and 2.5 shock tube internal diameters; radius ratios of the exit surface to the shock tube inner diameter of 3 or 5; and Mach numbers ranging between 1.2 and 1.6. The flow field was visualised using a high-speed camera operating at 75 kfps capturing schlieren images. It was found that for the case of the exit surface tangent to the inner surface of the shock tube a vortex loop is not formed but rather a horseshoe vortex which convects downstream bound by the tangent exit plate. For higher Mach numbers it seems that the horseshoe vortex may close into a loop, but this cannot be definitely concluded from the available images. An additional feature was noted which is suspected of being the tangent view of a complex shock wave reflection due to the curved edge diffraction.

Influence of melt pouring temperature and plate inclination on solidification and microstructure of A356 aluminum alloy produced using oblique plate

The preparation of semisolid slurry of A356 aluminum alloy using an oblique plate was investigated. A356 alloy melt undergoes partial solidification when it flows down on an oblique plate cooled from underneath by counter flowing water. It results in continuous formation of columnar dendrites on plate wall. Due to forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously to produce semisolid slurry at plate exit. Melt pouring temperature provides required condition of solidification whereas plate inclination enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained was solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets were heat treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets were analyzed. Effects of melt pouring temperature and plate inclination on solidification and microstructure of billets produced using oblique plate were described. The investigations involved four different melt pouring temperatures (620, 625, 630 and 635 °C) associated with four different plate inclinations (30°, 45°, 60° and 75°). Melt pouring temperature of 625 °C with plate inclination of 60° shows fine and globular microstructures and it is the optimum.

Large eddy simulations of a circular orifice jet with and without a cross-sectional exit plate

The effect of a cross-sectional exit plane on the downstream mixing characteristics of a circular turbulent jet is investigated using large eddy simulation (LES). The turbulent jet is issued from an orifice-type nozzle at an exit Reynolds number of 5×104. Both instantaneous and statistical velocity fields of the jet are provided. Results show that the rates of the mean velocity decay and jet spread are both higher in the case with the exit plate than without it. The existence of the plate is found to increase the downstream entrainment rate by about 10% on average over the axial range of 8–30de (exit diameter). Also, the presence of the plate enables the formation of vortex rings to occur further downstream by 0.5–1.0de. A physical insight into the near-field jet is provided to explain the importance of the boundary conditions in the evolution of a turbulent jet. In addition, a method of using the decay of the centreline velocity and the half-width of the jet to calculate the entrainment rate is proposed.

Energy modeling of photovoltaic thermal systems with corrugated unglazed transpired solar collectors – Part 1: Model development and validation

Building-integrated photovoltaic–thermal (BIPV/T) systems with unglazed transpired solar collectors (UTCs) can provide a key solution for on-site electricity and thermal energy generation. Although the energy saving potential of this technology is significant, no systematic thermal analysis model has been developed for optimal system design and integration with building operation. This paper is the first of two companion papers focused on modeling and performance analysis of BIPV/T systems with UTC. In Part 1, energy models are presented for two configurations: UTC only and UTC with PV panels, to predict the cavity exit air temperature and plate surface temperature with weather (incident solar radiation, ambient air temperature, dew point temperature and wind speed) and design (airflow rate or suction velocity and geometry) parameters used as inputs. Nusselt number and effectiveness correlations, representing both the exterior and interior convective heat transfer processes, have been obtained from experimentally validated, three-dimensional, Reynolds-Averaged Navier–Stokes (RANS), Computational Fluid Dynamics (CFD) simulations, using high resolution grids and the ReNormalization Group Methods k–ε (RNG k–ε) turbulence closure model. The energy models were validated with measurements in an outdoor test-facility. Good agreement was observed between the model prediction and the experimental data, with the root mean square error (RMSE) being within 1°C for the UTC-only model and within 2°C for the model of UTC with PV modules. In the companion paper, Part 2, the effects of important parameters on system performance are demonstrated based on information from the literature and simulations using CFD and energy models. The optimal geometry is investigated for both configurations and the performance curves, under different levels of solar radiation, wind speed and suction velocity, are presented to provide guidelines for system design.

Onset of cellular flame instability in adiabatic CH4/O2/CO2 and CH4/air laminar premixed flames stabilized on a flat-flame burner

This paper presents numerical and experimental studies on the onset and evolution of laminar cellular flames of CH4/O2/CO2 (oxy-fuel) and CH4/air mixtures under adiabatic conditions, stabilized in the proximity of a flat-flame burner at atmospheric pressure. In the numerical simulations, a two-dimensional domain with periodicity at the transverse far field boundaries is resolved using a high accuracy finite difference method and employing a detailed chemical kinetic mechanism and detailed transport properties. In the experiments a specially designed adiabatic flat-flame burner, a so-called heat flux burner, is employed. A key parameter, the standoff distance between the flame front and the burner exit plate, is identified. A critical standoff distance is found, above which cellular flame instability is observed. It is shown that the critical standoff distance is closely related to the density ratio and the laminar flame thickness for each flame studied. The observed onset of cellular flames is governed by the hydrodynamic instability mechanism, which is generally suppressed by the burner when the flame is very close to the burner plate. Diffusive-thermal effects play an important role in the flame instability when the flame is far from the burner. The critical standoff distance has no clear correlation with the Lewis number, indicating a less significant effect of diffusive-thermal instability on the flames near the burner.

Ultralightweight Compact Heat Sinks With Metal Foams Under Axial Fan Flow Impingement

Experimental results of ultralightweight compact heat sinks with open-celled copper (Cu) foams under the impingement of axial fan flows are presented. The thermal resistance of the system and the pressure coefficient on heat sink base plate were measured, focusing on the influences of foam height (Hf ) and impinging distance between fan exit and base plate (H). With the impinging distance fixed at H/D = 0.5 (D being the fan diameter), it is demonstrated that an optimum foam height exists at Hf /D = 0.22, providing the lowest thermal resistance. Furthermore, with the foam height fixed at Hf /D = 0.22, reducing the impinging distance to the foam height level reduces the thermal resistance further. In comparison with conventional aluminum (Al) plate-fin heat sinks under identical flow conditions, the Cu foam heat sinks require only 30% of the weight and 50% of the volume to achieve a similar level of heat dissipation performance.

물성치 적용 기법에 따른 하이브리드 풍력 블레이드 동적특성 해석에 관한 연구

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single 60° inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

경사 충돌 제트 열전달 실험에서 정상 상태와 천이 TSP 기법의 비교 연구

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single 60° inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

Improving quantitative gas chromatography–electron ionization mass spectrometry results using a modified ion source: Demonstration for a pharmaceutical application

Gas chromatography–mass spectrometry is a well established analytical technique. However, mass spectrometers with electron ionization sources may suffer from signal drifts, hereby negatively influencing quantitative performance. To demonstrate this phenomenon for a real application, a static headspace-gas chromatography method in combination with electron ionization-quadrupole mass spectrometry was optimized for the determination of residual dichloromethane in coronary stent coatings. Validating the method, the quantitative performance of an original stainless steel ion source was compared to that of a modified ion source. Ion source modification included the application of a gold coating on the repeller and exit plate. Several validation aspects such as limit of detection, limit of quantification, linearity and precision were evaluated using both ion sources. It was found that, as expected, the stainless steel ion source suffered from signal drift. As a consequence, non-linearity and high RSD values for repeated analyses were obtained. An additional experiment was performed to check whether an internal standard compound would lead to better results. It was found that the signal drift patterns of the analyte and internal standard were different, consequently leading to high RSD values for the response factor. With the modified ion source however, a more stable signal was observed resulting in acceptable linearity and precision. Moreover, it was also found that sensitivity improved compared to the stainless steel ion source. Finally, the optimized method with the modified ion source was applied to determine residual dichloromethane in the coating of coronary stents. The solvent was detected but found to be below the limit of quantification.

SDF1 Regulates Leading Process Branching and Speed of Migrating Interneurons

Cell migration is required for normal embryonic development, yet how cells navigate complex paths while integrating multiple guidance cues remains poorly understood. During brain development, interneurons migrate from the ventral ganglionic eminence to the cerebral cortex within several migratory streams. They must exit these streams to invade the cortical plate. While SDF1 (stromal cell-derived factor-1) signaling is necessary for normal interneuron stream migration, how they switch from tangential stream migration to invade the cortical plate is unknown. Here, we demonstrate that SDF1 signaling reduces interneuron branching frequency by reducing cAMP levels via a G(i) signaling pathway using an in vitro mouse explant system, resulting in the maintenance of stream migration. Blocking SDF1 signaling or increasing branching frequency results in stream exit and cortical plate invasion in mouse brain slices. These data support a novel model to understand how migrating interneurons switch from tangential migration to invade the cortical plate in which reducing SDF signaling increases leading process branching and slows the migration rate, permitting migrating interneurons to sense cortically directed guidance cues.

Characterization and Improvement of Signal Drift Associated with Electron Ionization Quadrupole Mass Spectrometry

Quadrupole mass spectrometry with electron ionization (EI-QMS) is a very popular detection technique in combination with gas chromatography. It is deployed for the analysis of volatile and semivolatile analytes in many industry domains. Although a very important factor for quantitative analysis, little is known about the stability of ion source performance. Only a few papers and patents report possible signal instabilities due to sample adsorption, degradation, or insulating deposits on the hot stainless steel surface of the ion source. In this study, a conventional stainless steel ion source was used to investigate possible signal drifts. It was observed that the EI-QMS instrument indeed suffered from continuous signal instability. It was found that the key parts which are responsible for the signal instabilities are those that regulate the ion beam toward the mass analyzer: the repeller, exit plate, and focusing lenses. The voltage of the repeller was found to have a major influence on the signal stability. The surface of the repeller, exit plate, and focusing lenses was modified by applying a gold coating. It was demonstrated that the signal stability of the MS dramatically improved when using the gold-coated parts. The contribution of each part to the stability improvement was quantitatively determined and compared with the standard stainless steel source performance. It was assumed that the signal drift observed with the stainless steel EI source originated from charge buildup on the surfaces. This hypothesis was supported by software simulations.

G0600-2-4 衝突噴流群を用いた流路内の流動および熱移動解析(熱工学部門一般講演(2):伝熱(2))

This paper shows the influence of flow behavior of multiple impingement jets on characteristics of heat transfer of narrow spaces. The jets were set a 5×5 nozzles of sharp edged orifice type with D=5 mm in diameter. The jet-to-jet space is 10 mm. The experiments were performed for the separation distance, H, between jet exit and impingement plate ranging from H/D=1 to 3, at Reynolds number 1600〜3300. The time and spatial temperature profiles over the impingement plate were measured using at infrared camera (TVS-8500, Avio) with a two-dimensional array of Indeum-Antimony (In Sb) sensors. To clarify the influence of the flow behavior on heat transfer fields, we visualized a smoke flow field by means of a laser light sheet method (LLS). Based on these experimental data, the relationships between the fluid flow and the heat transfer characteristics were clarified.

Experimental and Theoretical Analysis of Heat Transfer Characteristics in a Rectangular Duct with Jet Impingement

The heat transfer characteristics are analyzed in a rectangular cross section duct where impingement jet technique is applied for the purpose of heating and cooling. Heat transfer characteristics on surfaces are calculated using commercial CFD software, Fluent. Numerical results are compared with the experimental results obtained through a transient liquid crystal technique. To better present the heat transfer results, different cross-sectional size geometric models are used. The geometric models are of six in-line circular jets housed in a confined rectangular channel. As the jet temperature varies with time during a transient test, a time-depended solution method was selected in Fluent. One of the primary varying parameters in the present study is the magnitude of spacing between the jet exit and target plate. The jet Reynolds numbers range from 14,000 to 40,000 for every geometry. The effects of crossflow on the overall flow characteristics in the housed channel and heat transfer distributions on both target surface and jet-issuing plate are investigated. Comparison was made between the present numerical results and experimental data obtained earlier by the lead author, Uysal et al. [1]. The companion experimental study was based on the transient thermochromic liquid crystal (TLC) measurements on detailed local heat transfer distributions on both the target surface and jet-issuing surface.

Sonic hedgehog induces response of commissural axons to Semaphorin repulsion during midline crossing

Pathfinding axons change responses to guidance cues at intermediate targets. During midline crossing, spinal cord commissural axons acquire responsiveness to class 3 Semaphorins and Slits, which regulate their floor plate exit and restrict their post-crossing trajectory into a longitudinal pathway. We found that Sonic Hedgehog (Shh) could activate the repulsive response of pre-crossing axons to Semaphorins. Blocking Shh function with a monoclonal antibody to Shh, 5E1, in 'open-book' explants or by expressing a dominant-negative form of Patched-1, Ptch1(Delta loop2), or a Smoothened (Smo) shRNA construct in commissural neurons resulted in severe guidance defects, including stalling and knotting inside the floor plate, recrossing, randomized anterior-posterior projection and overshooting after crossing, reminiscent of Neuropilin-2 mutant embryos. Enhancing protein kinase A activity in pre-crossing axons diminished Shh-induced Semaphorin repulsion and caused profound midline stalling and overshooting/wandering of post-crossing axons. Therefore, a morphogen, Shh, can act as a switch of axon guidance responses.

Emissions Reductions in Diesel and Kerosene Flames Using a Novel Fuel Injector

A SPRAY serves as the heart of almost every type of liquidfueled combustion system. Ideally, to promote combustion withmaximumefficiency andminimumharmful emissions, an injector should deliver a fuel spray that rapidly disperses and evaporates to yield a homogeneousmixture of gaseous fuel and air. Characteristics of an ideal injector include good atomization over a wide range of either steady or transient fuel flow rates, unaffected by flow instabilities, low power requirements, scalability, resistant to blockages, and delivery of a fine spray [1,2]. Reviews by McDonell and Samuelsen [3], Razdan [4],Mansour [5], andNakamura et al. [6] deal with fuel sprays optimized for lean combustion. Pressure atomization, air-assist and air-blast atomization, and effervescent atomization [7] are commonly used techniques for a variety of injector applications. In the current study, we are exploring the so-called flow-blurring injector of Ganan-Calvo [8] in a combustion system. As illustrated in Fig. 1, the flow-blurring (FB) concept consists of a liquid nozzle and an orifice plate situated downstream of the nozzle. The nozzle’s wall is tapered at the outlet, and the sharpened edge of the orifice plate is the same diameter as the inner diameter of the nozzle (d). When the axial distance between the nozzle exit and orifice plate (H) is small (i.e., H=d < 0:25), some of the gas flowing into the lateral cylindrical passageway between the nozzle exit and orifice plane is forced upstream a short distance into the nozzle carrying the liquid. The backflow of gas causes vigorous combination of turbulent mixing and effervescing, or the so-called flow-blurring, which results in a spray with very fine droplets. Simmons et al. [9] conducted cold-flow visualization experiments for a range of geometric and flow conditions to demonstrate the high efficiency of the FB injector concept. To the best of our knowledge, the FB injector concept has never been applied to combustion systems. The objective of this study is to experimentally characterize emissions performance of the FB injector in a liquid-fueled combustor operated at atmospheric pressure. Experiments using diesel and kerosene fuels are performed for fixed fuel and total airflow rates, and the atomizing airflow rate is varied. The FB injector performance (NOx and CO emissions) is compared with that of a commercial air-blast (AB) injector. II. Experimental Setup

Stem Cell Factor Functions as an Outgrowth-Promoting Factor to Enable Axon Exit from the Midline Intermediate Target

Commissural axons are attracted to the midline intermediate target by chemoattractants, but upon crossing the midline they switch off responsiveness to attractants and switch on responsiveness to midline repellents, which expel the axons from the midline and enable them to move on. Here we show that midline exit also requires the stimulation of axon outgrowth by Stem Cell Factor (SCF, also known as Steel Factor). SCF is expressed by midline floor plate cells, and its receptor Kit, a receptor tyrosine kinase, is expressed by commissural axons. In Steel and Kit mutant mice, the majority of commissural axons line up transiently at the contralateral edge of the floor plate, showing a delay in midline exit. In vitro, SCF selectively promotes outgrowth of postcrossing, but not precrossing, commissural axons. Our findings identify SCF as a guidance cue in the CNS, and provide evidence that exiting intermediate targets requires activation of outgrowth-promoting mechanisms.

A numerical simulation of the hole-tone feedback cycle based on an axisymmetric discrete vortex method and Curle's equation

An axisymmetric numerical simulation approach to the hole-tone self-sustained oscillation problem is developed, based on the discrete vortex method for the incompressible flow field, and a representation of flow noise sources on an acoustically compact impingement plate by Curle's equation. The shear layer of the jet is represented by ‘free’ discrete vortex rings, and the jet nozzle and the end plate by bound vortex rings. A vortex ring is released from the nozzle at each time step in the simulation. The newly released vortex rings are disturbed by acoustic feedback. It is found that the basic feedback cycle works hydrodynamically. The effect of the acoustic feedback is to suppress the broadband noise and reinforce the characteristic frequency and its higher harmonics. An experimental investigation is also described. A hot wire probe was used to measure velocity fluctuations in the shear layer, and a microphone to measure acoustic pressure fluctuations. Comparisons between simulated and experimental results show quantitative agreement with respect to both frequency and amplitude of the shear layer velocity fluctuations. As to acoustic pressure fluctuations, there is quantitative agreement w.r.t. frequencies, and reasonable qualitative agreement w.r.t. peaks of the characteristic frequency and its higher harmonics. Both simulated and measured frequencies f follow the criterion L / u c + L / c 0 = n / f where L is the gap length between nozzle exit and end plate, u c is the shear layer convection velocity, c 0 is the speed of sound, and n is a mode number ( n = 1 2 , 1 , 3 2 , … ) . The experimental results however display a complicated pattern of mode jumps, which the numerical method cannot capture.