Narrow Channel Walls Research Articles

Numerical and experimental study of abnormal enhancement of separated turbulent flow and heat transfer in inclined oval-trench dimples on the plate and on the narrow channel wall

The numerically found abnormal enhancement of separated flow and heat transfer in inclined oval-trench dimples (OTDs) on the plate and on the wall of the narrow channel was experimentally confirmed at the stands of the Research Institute of Mechanics (Lomonosov Moscow State University), the Kazan Scientific Center RAS, and the Kazan State Research Technical University – the Kazan Aviation Institute. The measured static pressure drops in a single OTD at Re = 6.7 × 104 and 16.7 × 104, the velocity profiles of accelerating laminar (Re = = 1000) and turbulent (Re = 4300) flows in the narrow channel with two rows of 26 OTDs, the estimate of Nusselt numbers on the channel wall with single-row OTDs are in good agreement with the numerical predictions within the RANS approach.

Abnormal separated flow intensification and heat transfer enhancement in single-row inclined oval-trench dimples on the narrow channel wall

Intensification of turbulent separated air flow and heat transfer enhancement at the hydrodynamic stabilization length on the periodic section of the narrow channel with inclined one-row oval-trench dimples (OTDs) is analyzed. The periodic section of the channel of height equal to 1, length – 8, and width – 9 is considered at Re=104. The inclined OTD 0.5 in width, 7.05 in length, and 0.25 in depth is located in the center of the heated isothermal wall. The rounding radius of the dimple edge is 0.21. The OTD inclination angle varies from 0° to 52.5°. It is found that the optimal inclination angles in terms of thermal and hydraulic performance (THP) are equal to 45° and 30°. It is observed that at large inclination angles the minimum value of relative friction decreases many times (up to-3.5).

Study of solar irradiation distribution in narrow channel of desiccant rotor

The objective of this paper is to present experimental results on distribution characteristics of solar irradiation absorbed by the narrow channel wall of desiccant rotor. Experiments are performed with the channel made by the silica gel and the poly propylene (PP). Energy absorption rate is measured in conditions of different channel lengths, incident irradiation angles, air temperatures, and humidity. The result of the present measurement for silica gel is equal to that of the previous study [J. Li, Y. Hamamoto, and H. Mori, Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers 32(2), 149–154 (2015)], which is conducted using laser light as a source. It is confirmed the previous prediction model of laser light is suitable for this solar light system. Moreover, the previous model is improved, because the rate of laser for PP is larger than that of solar. These models are applicable to predict desorption rate of the water vapor in a desiccant rotor heated directly by the concentrated solar irradiation. The results show that the absorption rates of solar irradiation and red laser are equal to each other in the silica gel channel. The absorption rates of the laser irradiation are larger than that of the solar irradiation for PP materials. It is clear that the solar irradiation absorption rate cannot be influenced by the ambient humidity and temperature. The prediction model of the absorption efficiency based on the laser for silica gel channel can reproduce well the absorption efficiency of experiment based on solar irradiation. In the case of PP, the difference between the prediction and the measurement is observed.

Special Issue on Precision Surface Finishing

Precision surface finishing plays an important role in product quality owing to its direct effects on product appearance. As a result, automated precision surface finishing processes (APSFPs) are key technologies for industrial products and molds for forming and shaping processes. APSFPs can be divided into three main categories, namely, mechanical processes, electrochemical processes, and high energy beam processes. The objective of this special issue is to collect the cutting-edge research works focused on APSFPs. This issue includes 11 papers on APSFPs covering the following topics: ===danraku===- Review of ultraprecision surface finishing processes. ===danraku===- Ultraprecision surface machining and finishing with compensated feeding mechanisms. ===danraku===- Ultrasonic assisted cutting of unidirectional wetting surfaces and polishing of mold steels. ===danraku===- Vibration-assisted polishing of glass lenses. ===danraku===- Magnetic-assisted polishing of mirror surfaces. ===danraku===- Chemical-mechanical polishing of single-crystal SiC and GaN wafers. ===danraku===- Direct transfer of smoothing Au surfaces. ===danraku===- Plasma surface finishing of narrow channel walls of X-ray crystal monochromators. ===danraku===- Analysis and characterization of finished surfaces. It is expected that this issue will be helpful for readers to understand the recent developments in APSFPs and will lead to further research on APSFPs. We deeply appreciate the contributions of all authors and thank the reviewers for their incisive efforts.

Abnormal enhancement of separated turbulent air flow and heat transfer in inclined single-row oval-trench dimples at the narrow channel wall

New shapes of surface vortex generators are proposed which allow improving the energy performance of channels of propulsion devices and contribute towards the safety of space flights. Abnormal enhancement of heat transfer and separated turbulent air flow in oval-trench dimples of depth 0.3 inclined at an angle of 45о to the incoming flow and located in-line at the heated wall of the narrow channel is accompanied by a four-fold growth of relative negative friction and an almost five-fold increase of relative heat transfer in the separation zone. At the same time, a maximum secondary flow velocity in the vicinity of the dimple reaches a maximum flow velocity in the plane-parallel channel. A reason for the onset of this phenomenon (ultra intensification of transport processes) caused by the formation of a high pressure drop between closely spaced stagnation zones on the windward side of the dimple and a low pressure on the entrance spherical portion of the dimple is disclosed.

Microfluidic on-chip immunohistochemistry directly from a paraffin-embedded section.

We present here a novel microfluidic platform that can perform microfluidic on-chip immunohistochemistry (IHC) processes on a formalin-fixed paraffin-embedded section slide. Unlike previous microfluidic IHC studies, our microfluidic chip made of organic solvent-resistant polyurethane acrylate (PUA) is capable of conducting on-chip IHC processes consecutively. A narrow channel wall structure of the PUA chip shows effective sealing by pressure-based reversible assembly with a section slide. We performed both on-chip IHC and conventional IHC processes and compared the IHC results based on the immunostaining intensity. The result showed that the effects of the on-chip deparaffinization, antigen retrieval, and immunoreaction processes on the IHC result were equivalent to conventional methods while reducing the total process time to less than 1/2. The experiment with breast cancer tissue shows that human epidermal growth factor receptor 2 (HER2) classification can be performed by obtaining a clearly distinguishable immunostaining intensity according to the HER2 expression level. We expect our on-chip microfluidic platform to provide a facile technique suitable for miniaturized, automated, and precise diagnostic devices, including a point-of-care device.

Mathematical modeling of longitudinal oscillations tapered narrow channel wall under pulsating pressure of highly viscous liquid

Mathematical modeling of longitudinal oscillations tapered narrow channel wall under pulsating pressure of highly viscous liquid

Thermal performance of a meso-scale liquid-fuel combustor

Combustion in small scale devices poses significant challenges due to the quenching of reactions from wall heat losses as well as the significantly reduced time available for mixing and combustion. In the case of liquid fuels there are additional challenges related to atomization, vaporization and mixing with the oxidant in the very short time-scale liquid-fuel combustor. The liquid fuel employed here is methanol with air as the oxidizer. The combustor was designed based on the heat recirculating concept wherein the incoming reactants are preheated by the combustion products through heat exchange occurring via combustor walls. The combustor was fabricated from Zirconium phosphate, a ceramic with very low thermal conductivity (0.8 W m −1 K −1). The combustor had rectangular shaped double spiral geometry with combustion chamber in the center of the spiral formed by inlet and exhaust channels. Methanol and air were introduced immediately upstream at inlet of the combustor. The preheated walls of the inlet channel also act as a pre-vaporizer for liquid fuel which vaporizes the liquid fuel and then mixes with air prior to the fuel–air mixture reaching the combustion chamber. Rapid pre-vaporization of the liquid fuel by the hot narrow channel walls eliminated the necessity for a fuel atomizer. Self-sustained combustion of methanol–air was achieved in a chamber volume as small as 32.6 mm 3. The results showed stable combustion under fuel-rich conditions. High reactant preheat temperatures (675 K–825 K) were obtained; however, the product temperatures measured at the exhaust were on the lower side (475 K–615 K). The estimated combustor heat load was in the range 50 W–280 W and maximum power density of about 8.5 GW/m 3. This is very high when compared to macro-scale combustors. Overall energy efficiency of the combustor was estimated to be in the range of 12–20%. This suggests further scope of improvements in fuel–air mixing and mixture preparation.

Problems of simulating tornado-like heat transfer in turbulent flow past a dimpled relief on a narrow channel wall

This paper analyzes the state of the art of numerical and partly physical simulation of convective heat transfer in the vicinity of dimpled reliefs on one of the walls of narrow plane-parallel channels. We show that there is a mismatch and spread of the results of these investigations, their conclusions lack substantiation, and there are “white spots” in the problems under consideration and in the methods of their investigation. Several physical experiments have been analyzed, and the correlation between the calculated predictions and measurement data has been discussed. In conclusion, the thermohydraulic characteristics of various dimpled reliefs are compared, and the advantage of oval dimples over spherical ones is demonstrated.

Simulation of the Flow around Spacer Filaments between Narrow Channel Walls. 1. Hydrodynamics

Insights into the effect of spacer filaments in membrane systems on the flow pattern were obtained using a computational fluid dynamics code. The flow patterns were examined for a single filament adjacent to the wall and centered in the channel and for three different spacer configurations, the cavity, zigzag, and submerged spacers, with variations in both the mesh length and filament diameter for Reynolds numbers ranging from 90 to 768. Large recirculation regions were formed behind the filaments, and the flow around the filament increased the shear stress on the wall. For an identical Reynolds number and filament diameter, a single filament adjacent to a membrane wall produced a larger recirculation region than a single filament in the center of the channel. For the cavity and submerged spacers, above a critical Reynolds number or mesh length, the recirculation regions between sequential filaments influenced each other and merged to form one large recirculation region between sequential filaments. In co...