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The implementation of heat sinks in high-power pulse electronic devices within hypersonic aircraft cabins has been facilitated by the emergence of innovative phase change materials (PCMs) characterized by excellent thermal conductivity and high latent heat. In this study, a representative material, layered porous media filled with paraffin wax, was utilized, and a three-dimensional numerical model based on the enthalpy-porosity approach was employed. A thermal response research was conducted on the Phase Change Heat Exchange Unit with Layered Porous Media (PCHEU-LPM) with different cooling methods. The results indicate that water cooling proved to be suitable for the PCHEU-LPM with a heat flux of 50,000 W/m2. Additionally, parametric studies were performed to determine the optimal cooling conditions, considering the inlet temperature and velocity of the cooling flow. The results revealed that the most suitable conditions were strongly influenced by the coolant inlet parameters, along with the position of the PCM interface. Finally, the identification of the parameter combination that minimizes temperature fluctuations was achieved through the Response Surface Analysis method (RSA). Subsequent verification through simulation further reinforced the reliability of the proposed optimal parameters.

The axial throughflow cooling is a realistic solution for the purpose of thermal management in the hydrodynamic gas foil bearings operating at ultra-high rotational speed and mini bearing clearance. In order to illustrate the effects of axial throughflow cooling within the fluid-solid coupled heat transfer mode on the aerodynamic and thermal behaviors of hydrodynamic gas foil journal bearing, a steady three-dimensional fluid-solid coupled numerical simulation is performed in the present study by assuming that the journal-bearing works in a steady-state condition with a fixed eccentricity ratio of 0.9. The results show that the shearing-induced circumferential flow is significantly dominant in the hydrodynamic air film layer. At both edges of the foil bearing section, local suction flow into the bearing clearance and local leakage flow out the bearing clearance happen simultaneously at different circumferential positions. The increase of axial throughflow mass flowrate plays an effective role on improving the cooling capacity. However, it should be noteworthy that the bleeding air pressure is prompted in a nearly quadratic relationship along with the increase of axial throughflow mass flowrate. Due to the non-uniformity nature of viscous-shearing heat generation inside the hydrodynamic gas foil bearing with a big eccentricity, the temperature on the shaft and top foil surfaces takes on a non-uniform distribution. The peak temperature generally has a 20 K–30 K difference with respect to the mean temperature.

A Plasma Synthetic Jet (PSJ) actuator is the promised equipment to produce a high-speed synthetic jet, which can be potentially applied to control the supersonic flow. Several researchers paid much attention to its application on Active Flow Control (AFC) in supersonic conditions, but the understanding of the flow field inner the cavity is extremely inadequate. This study aims to use experimental measurement and numerical simulation to reveal the variation of flow field during the issuing PSJ. The PSJ actuator driven by the capacitor group has been designed, and Large Eddy Simulation(LES) was conducted and verified by experimental data with high-resolution particle image velocimetry (PIV) and hot wire anemometer (HWA). The kinetic energy of the PSJ dominantly results from its thermal energy during the stage of plasma deposition, which makes the pressure and temperature of tiny volume near the electrode, increase sharply in microseconds. The electric discharge of the PSJ actuator is simulated by employing the energy input into the source term of the energy equation. The efficiency of the actuator was 20% is demonstrated in this study, which is consistent with the previous research. It is found that the high-pressure zone generated by plasma deposition shifts in a reciprocating way between the bottom and top of the cavity. The pressure inner the cavity and velocity of the PSJ attenuate while oscillating with the real-time. The geometry of the actuator paly a significant role in the performance of the PSJ. Keeping the cavity height constant, the frequency of the pressure is almost the same because the attenuating frequency is related to the cavity height. Increasing cavity height decreases attenuating frequency. The attenuation rate increases with the increase of orifice diameter and decreases of orifice height because of the leaking of gas from the cavity. The mathematic model is built and verified to describe the variation of pressure inner the cavity and the velocity of the PSJ.

Abstract Background Acupoint selection is a key factor in the treatment of diseases and has not been well studied. The aim of this trial is to explore the differences in efficacy between compatible acupoints and a single acupoint for patients with functional dyspepsia (FD). Methods This randomized controlled trial will be conducted in the First Affiliated Hospital of Changchun University of Chinese Medicine in China. Two hundred and sixteen FD patients will be randomly assigned to the compatible acupoints group, single acupoint group, or sham acupuncture group. This trial will include a 1-week baseline period, a 4-week treatment period, and a 4-week follow-up period. During the 4-week treatment period, patients will receive 20 sessions of acupuncture (weekly cycles of one session per day for 5 consecutive days followed by a 2-day break). The primary outcome will be a change in the Nepean Dyspepsia Life Quality Index from baseline to after the 4-week treatment period. Secondary outcome measures will include the dyspeptic symptom sum score, Overall Treatment Effect questionnaire, and 36-item Short Form survey. Adverse events also will be recorded. Ultraweak photon emission and metabolomics tests will be performed at baseline and at the end of treatment to explore the mechanisms of the differences between compatible acupoints and a single acupoint. Discussion The results of this trial will allow us to compare the difference in efficacy between compatible acupoints and a single acupoint. The findings from this trial will be published in peer-reviewed journals. Trial registration Acupuncture-Moxibustion Clinical Trial Registry, AMCTR-IPC-18000176, registered on 4 March 2019; Chinese Clinical Trial Registry, ChiCTR1900023983, registered on 23 June 2019.

Numerical simulations were performed to illustrate the influences effects of annular-cooler surface roughness on wind resistance and thermal environment in a high-speed centrifuge chamber, with the use of multi-reference-frame (MRF) method and classical roughness-modified model. In the present study, the absolute roughness height was specified in a range form 0.05 mm–2.5 mm. With respect to the clearance between rotating-arm tip and stationary-cooler surface, the relative roughness height was changed from 0.0014 to 0.07 accordingly. The results show that the flow field inside the centrifuge chamber is of highly three-dimensional feature. With the increase of surface roughness, the wind resistance is increased monotonously. With regard to the thermal environment, the maximum temperature inside the centrifuge chamber takes on a non-monotonous variation along with the surface roughness height, due to the two contrary influencing roles of surface roughness on the viscous dissipation heat generation and the heat removal capacity. In general, the use of roughed cooler-wall is a promising scheme for reducing the environmental temperature in a high-speed centrifuge chamber. Under the present research conditions, a more favorable relative roughness height is identified in term of a comprehensive factor that reflects the benefit of roughed surface on the reduction of maximum environmental temperature at the pay of aerodynamic penalty.

A simplified approach which utilizes an isotropic porous medium model has been widely adopted for modeling the flow through a compact heat exchanger. With respect to situations where the compact heat exchangers are partially installed inside a channel, such as the application of recuperators in an intercooled recuperative engine, the use of an isotropic porous medium model needs to be carefully assessed because the flow passing through the heat exchanger is very complicated. For this purpose, in this study the isotropic porous medium model is assessed together with specific pressure–velocity relationships for flow field modeling inside a rectangular channel with a built-in double-U-shaped tube bundle heat exchanger. Firstly, experiments were conducted using models to investigate the relationship between the pressure drop and the inlet velocity for a specific heat exchanger with different installation angles inside a rectangular channel. Secondly, a series of numerical computations were carried out using the isotropic porous medium model and the pressure–velocity relationship was then modified by introducing correction coefficients empirically. Finally, a three-dimensional (3-D) direct computation was made using a computational fluid dynamics (CFD) method for the comparison of detailed flow fields. The results suggest that the isotropic porous medium model is capable of making precise pressure drop predictions given the reasonable pressure–velocity relationship but is unable to precisely simulate the detailed flow features.

The turbulent fluid flow and convective heat transfer in counter-rotating disk cavity with central axial air inflow and radial air outflow are numerically studied based on the finite volume method. Efforts are focused upon the influence of the rotation number Rt on the flow structure, cooling performance, sealing effect, and surface tangential friction characteristics in the cavity. The stagnation point where the radial outward flow along the upstream disk driven by the rotation force meets the radial outward flow along downstream disk driven by the combination of rotation force and inflow inertial force moves from upstream disk wall to the shroud with increasing Rt . At the Rt far smaller than 1, the fluids in the core region between two disks rotate with the upstream disk like a rigid body, and the tangential velocity of the rotating core decreases with the increase of the disk cavity radius, which is different from the Batchelor-type flow. At the Rt larger than 1, the fluids on the upstream disk side rotate like the Batchelor-type flow, while the sandwich rotation disappears in the fluid on the downstream disk side. The temperature on the upstream disk wall increases and then decreases with increasing values of Rt , and the critical value of Rt for the change of temperature variation is assessed to be at about Rt = 0.69. The temperature and radial temperature gradient of the downstream disk wall decrease with increasing Rt . With increasing Rt by increasing the disk rotation rate, the pressures near the downstream disk decrease, while the frictional moments on rotating disks increase. Due to the effect of flow structure, the frictional moment on the upstream disk is smaller than that on the downstream disk.

The turbulent flow between shrouded contra-rotating disks was numerically studied with a two-layer turbulence model and a modified Launder–Sharma low-Reynolds number k - ε model. The dissipation rate decrease caused by solid body rotation was considered in the second model. The comparisons of the effectiveness between these two turbulence models for capturing the critical radius of flow structure transition and reproducing the flow velocity measurements data were presented. For the flow between shrouded disks rotating at the same speed but in opposite senses, that is, the angular velocity ratio of the two disks equals to −1, the Stewartson-type flow structure is found in the cavity. For the flow with one disk rotating more slowly than the other, Stewartson-type flow coexists with Batchelor-type flow, that is, Batchelor-type flow occurs radially outward of the stagnation point where two opposing boundary layer flows meet, and Stewartson-type flow occurs radially inward. The stagnation points near the slower disk move radially outward as the angular velocity ratio decreases toward −1. Theory of rotating fluids with the presence of centrifugal and Coriolis forces stemming from the disk rotation is employed to manifest the flow structure transition mechanisms as the rotation ratio of the disks is varied. The source of the earlier transition to turbulent flow in counter-rotating disk cavity compared with rotor-stator disk cavity is also explained through the research of instability of the flowing free shear layer formed by the counter secondary circulations. With the aid of the numerical results obtained from the two turbulence models, it is found that a more turbulent flow in the core can destroy the Batchelor-type flow and creates a larger Stewartson-type flow region.

Film cooling enhancement by incorporating an upstream sand-dune-shaped ramp (SDSR) to the film hole exit was numerically investigated on a flat plate under typical blowing ratios ranging from 0.5 to 1.5. Three heights of SDSRs were designed: 0.25D, 0.5D, and 0.75D. The results indicated that the upstream SDSR effectively controlled the near-wall primary flow and subsequent mutual interaction with the coolant jet, which was the main mechanism of the film cooling enhancement. First, a pair of anti-kidney vortices was formed at the trailing ridges of the SDSR, which helped suppress the kidney vortex pair due to the interaction between the coolant jet and the primary flow. Second, a weak separation and a low pressure zone were induced behind the backside of the SDSR, which caused the coolant jet to spread around the film cooling hole and improve the lateral film coverage. With respect to the baseline cylindrical film cooling holes, the effect of the upstream SDSR was distinct under different blowing ratios. Under a low blowing ratio, the upstream SDSR shortened the streetwise film layer coverage in the vicinity of the film hole centerline but increased the span-wise film layer coverage. A relatively optimal ramp height seemed to be 0.5D. Under a high blowing ratio, both the streamwise and span-wise film layer coverages improved in comparison with the baseline case. The film cooling effectiveness improved gradually with increasing ramp height.

In this paper, the thermal performance of the corrugated surfaces cooled with a piezoelectric fan was studied. A total of 25 corrugated surfaces with different wave shapes have been tested under different Re and gap heights (G). The results showed that only the corrugated surface with the A/WPF of 0.167 and T/WPF of 0.533 produces the highest Nuarea values for all conditions, which is approximately 50% higher than that of a flat surface. It is confirmed that the corrugated shape is not only conducive to promoting the development of the vortex structure but also beneficial to increase the effective heat transfer area so that the overall heat transfer is optimal. An empirical correlation for estimating Nuarea on the hot corrugated surfaces was developed which has a mean absolute deviation of 11.0% and a mean relative deviation of 0.2%, predicting 75.9% of the entire database within a ±20% band. In addition, a corresponding simulation on the flow field revealed that the gap distance between adjacent wave crests is the key to balance the increasing effective heat transfer area and promoting the development of the vortex structure. [ABSTRACT FROM AUTHOR]