Average Pressure Drop Research Articles

Hydrothermal characteristics of fluid flow in a circular tube fitted with free rotating axial-turbine-type swirl generators: Design, swirl strength, and performance analyses

The effect of inserting free rotating axial-turbine-types swirl generators (ATTSGs) in a circular tube is numerically investigated for convective heat transfer enhancement. Different types of ATTSGs with different blade designs are placed inside the tube, which are rotating freely around their axis depending on the velocity of the fluid flowing in the tube. The moving reference frame (MRF) method is used to model the fluid rotation in the zones containing the ATTSGs and the source terms arising from the transformation of stationary to rotating reference frame. Free rotational speed of the ATTSGs is estimated at different Reynolds numbers by systematically analysing the net torque applied on the ATTSGs in terms of their angular velocity. The local and average convective heat transfer and pressure drop are investigated for the cases with ATTSGs and the case of a plain tube. Considerable enhancement in the convective heat transfer is observed for all the ATTSGs, with the maximum of around 75%. To investigate the efficiency of the ATTSGs in terms of heat transfer enhancement, the intensity of the vortex structures generated by the ATTSGs is represented by the Q-criterion iso-surfaces. The ATTSGs which generate stronger swirling effect at the vicinity of the heated wall cause greater heat transfer enhancement. Inserting the ATTSGs leads to an increase in the pressure drop. Performance evaluation criterion (PEC) is introduced and evaluated for different ATTSGs to identify configurations that enhance the convective heat transfer at the lowest pumping power. The highest PEC of 1.4 is reported for the ATTSG with trapezoid twisted blade design.

OBSERVED EFFECTS OF BODY MASS INDEX ON BLOOD PRESSURE DIPPING PATTERN, IN A PRIVATE HOSPITAL IN ABUJA, NIGERIA

During a normal 24-hour ambulatory blood pressure monitoring (ABPM), there should be a more than 10% drop in average nighttime blood pressure (BP), compared to the average daytime BP. This is called the normal ABPM dipping pattern. Abnormal dipping patterns occur when the average night-time blood pressure drop is lower than 10%. A high body mass index has been described as a contributing factor for unusual ABPM dipping patterns, which predisposes an individual to a higher likelihood of developing cardiovascular disease. The goal of this research was to assess the link between the body mass index (BMI) and the dipping pattern during ABPM in the adult population who underwent ABPM at Cardiocare Abuja. Anthropometric data from 100 patients who had done ABPM were used, together with data obtained from the CONTEC ABPM50 device. The BMI was calculated with the weight and height, and they were grouped into weight classes using their BMI. The proportions of the various dipping patterns were then determined within each class. Majority of the participants involved in the study had BMI between 30-39 kg/m2. Those who presented with higher BMI classes were also discovered to have unusual dipping patterns, indicating a link with relation to the BMI and the ABPM dipping pattern. In the morbidly obese class, with BMI >40 kg/m2 there was a trend of the reverse dipping. It concluded that ABPM should be done routinely for persons with a high BMI for early detection of unusual dipping patterns and prompt intervention.

Effects of Experimental Parameters on Condensation Heat Transfer in Plate Fin Heat Exchanger

This study aims to provide an experimental investigation and comparison of the condensation heat transfer characteristics in a plate–fin heat exchanger (PFHE). The heat flux, mass flux, and saturation pressure were adjusted as experimental parameters to verify the effects on the condensation heat transfer. In addition, condensation heat transfer correlation of two-stream PFHEs was provided based on the experimental data for utilization as a design reference for the heat exchanger. The turbulence is the most influential in heat transfer. One of the ways to foster turbulence is to increase shear stress. The higher flow velocity results in the higher shear stress. That was why increasing mass flux or the flow with higher vapor quality showed the higher heat transfer coefficient (HTC). Refrigerant properties such as viscosity and specific volume of vapor changed according to the saturation pressure. It is expected they affect the degree of turbulence too in similar manners. The mass flux was more influential than the heat flux and saturation pressure. Thus, the equivalent mass flux of the refrigerant is dominant in the derived correlation model. The average difference between experimental and calculated HTC from correlations was about 6.5%. Multi-stream PFHE comprises an additional heat transfer surface, which implies a more active droplet formation. The average pressure drop in the multi-stream is 15% larger than that of the two-stream.

Application of hybrid nanofluid and a twisted turbulator in a parabolic solar trough collector: Energy and exergy models

The impact of a twisted turbulator in a parabolic solar collector on the improvement of thermal–hydraulic performance (THP), as well as energy and exergy Efficiency of MgO-Cu/water hybrid nanofluid (HNF) is numerically evaluated. The main goal of this study is to use a twisted turbulator with pitch ratios (γ) of 1, 1.5, 2, and 2.5 for Reynolds numbers (Re) of 8000 to 32,000 and volume fractions (ϕ) of 1, 2, and 3% of MgO and Cu nanoparticles. Numerical simulation findings are reported in the form of graphs of average Nusselt number (Nuave), pressure drop (Δp), THP, energy Efficiency (ηc), and exergy Efficiency (ηex). It can be concluded that Nuave and Δp depends on ϕ and Re and augments linearly with their values. Moreover, Nuave and Δp increases significantly by increasing the pitch ratio of the turbulator. The results revealed that the maximum values of augmentation of ηc and ηex are respectively 23.79% and 21.15% by raising Re from 8000 to 32000. In a SC with a turbulator with γ = 2 and ϕ = 3%, ηc is raised by 24.16% by increasing Re from 8000 to 32000; while, in the case of γ = 2.5 and ϕ = 3%, ηc is enhanced by 18.2%.

Flow and Heat Transfer Simulation Analysis of 3D Compact Heat Exchanger

Compact heat exchangers (CHEs) are one of the most commonly used heat exchangers in the industry due to their superior advantages over other types of heat exchangers. Various geometric (fin spacing, tube inclination angle, etc) and process (such as flow velocity, temperature, etc) parameters affect the performance of such compact HEs. This research aims to examine the effects of fin spacing, tube inclination angle, and airflow velocity on heat transfer and pressure drop performance of CHE in both inline and staggered configurations. A three-dimensional (3D) numerical method with the aid of Ansys FLUENT software was carried out for the laminar flow condition. Based on the obtained results, the highest average heat transfer coefficient was observed at 120° for both tube arrangements while the lowest average pressure drop penalty is at 30°. Therefore, the recommended inclination angle when high heat transfer is needed is at 120° while if the pumping power is the major problem, 30 °or 150° is recommended. based on the London area goodness factor (j/f), 30° and 150° show the highest value for both configurations. The j/f factor decreases with the increase of Reynolds number for both configurations. In addition, 120° shows the lowest j/f which can be due to the high pressure drop.

Aerodynamic port-aligned fins to enhance thermal-hydraulic performance of jet impingement arrays

Jet impingement arrays with interspersed fluid extraction ports can suffer degraded heat transfer near outlets due to flow separation. This study explores the potential to integrate aerodynamic port-aligned fins on the impingement surface to maintain wall-jet attachment and increase heat transfer area. Such fins may also enhance local transport under inlet nozzles. Laminar-flow conjugate heat transfer simulations are performed for a range of Reynolds numbers and geometries to characterize this concept for slot jet impingement arrays. The simulation methodology is validated with conventional slot jet data from the literature and demonstrated to achieve mesh convergence. Overall flow characteristics are evaluated for a representative geometry, and results show a significant increase in relative average Nusselt number (Nu∗‾)and a reduction in peak temperature of the cooled surface. Conjugate heat transfer effects are evaluated, and are found to be significant for lower conductivity fin materials. Parametric studies are performed to generate performance maps for relative average Nusselt number and pressure drop as functions of Reynolds number, fin height, base width, and tip radius. Pareto curves are generated for the geometries that optimally trade heat transfer enhancement and pressure drop penalty to guide design. Teardrop shaped fins are found to be optimal for low Re, whereas continuously narrowing fins are preferable for higher Re. This jet impingement enhancement is shown to deliver up to 25% enhancement in Nu∗‾ at baseline pressure drop.

Experimental quantification of air-side row-by-row heat transfer coefficients on fin-and-tube heat exchangers

• Mass transfer experimental method to visualize and quantify local air-side HTCs. • Local and averaged HTCs on real-scale HX aluminum fin surfaces. • HTC comparison between fin-and-tube HXs with inline and staggered tube arrangement. • Row-by-row HTC degradation of plain fin-and-tube HXs at various Re. • Correlations of averaged HTC and pressure drop on measured HX fin geometry. An absorption-based mass transfer method has been employed in the current study to obtain two-dimensional HTC distributions on two different 8-row fin-and-tube heat exchangers. The method utilizes a color change coating material and a tracer gas to quantify local mass transfer on the fin surfaces and then employs the heat and mass transfer analogy to calculate local air-side HTCs. The accuracy and robustness of the method were validated in previous studies. The current study focuses on investigating the row-by-row HTC degradation by increasing the number of tube rows. The local HTC measurements of the current study ranged from 0.5-4.8 ms −1 face airflow velocity using dry fin surfaces. The two 8-row fin-and-tube heat exchangers have the same tube diameter, tube pitch, fin pitch, and fin shape. The only difference is the staggered vs. inline arrangement of the tube bundle. Averaged HTCs of each row are quantified and compared. The results show HTC degradation is related to the tube arrangement, airflow velocity, and row number. The heat exchanger with inline tube arrangement shows a more substantial HTC degradation than the heat exchanger with the staggered tube arrangement. The maximum HTC decline is observed on the second row with 40% compared to the first row while flow velocity is below 1 ms −1 . The row-by-row HTC degradation becomes less significant for higher flow velocities. HTC degradation appears to be negligible past the 5 th row. The current study provides a method that can be used to predict air-side HTCs of fin-and-tube heat exchangers with multiple rows.

Study on turbulent flow in wave wall tube heat exchanger

The traditional straight wall tube heat exchanger has low heat exchange efficiency, in order to solve this problem, the turbulent flow in wave wall tube heat exchanger was studied by numerical simulation. It is found that the unique corrugated structure of the heat exchange tube in the wave wall tube heat exchanger can improve the flow state of the fluid in the heat exchanger. The average pressure drop of heat exchanger gradually increases with the increase of Reynolds number Re. Under the same conditions, the average pressure drop of wave wall tube heat exchanger is lower than that of straight wall tube heat exchanger. The improvement of heat exchange performance of heat exchanger can not be realized only by increasing the inlet flow of heat exchanger. The wave wall tube heat exchanger can strengthen the heat exchange of the fluid in the heat exchanger.

Design and development of a novel additively manufactured geothermal heat exchanger

The existing geothermal heat exchangers pose a complex installation process and occupy large spaces which can potentially be cost-prohibitive to many potential users. In the present study, an additively manufactured heat exchanger was designed and developed to address this issue. The designed heat exchanger can be integrated with conventional geothermal heating and cooling systems for improved efficiency and easy installation. The additively manufactured heat exchanger developed in the present study eliminates the current need to excavate the soil and install the long piping as conventionally required for the existing geothermal systems. The prototype of the proposed geothermal heat exchanger was designed using CREO software and fabricated using the direct metal laser sintering technique (DMLS) to be integrated into a heat pump to exchange heat between a constant temperature of a water bath circulator and a water heat sink. Furthermore, the support structure model generated for metal printing of the proposed geothermal heat exchanger was exposed and discussed. Two customized geothermal heating and cooling modes were separately developed to evaluate the heat transfer performance of the heat exchanger analytically and numerically. Using the analytical approach, the system sizing was designated based on the metal additive manufacturing and thermal considerations, and then average heat transfer coefficients and pressure drops were estimated for a range of mass fluxes lying in the transitional and turbulent regimes. The distributions of wall temperature, fluid's bulk temperature, and fluid's velocity along the helically-coiled channel of the heat exchanger was also investigated numerically using the COMSOL-Multiphysics. Lastly, a detailed cost analysis was conducted to estimate the total cost per part for the prototype fabricated using the DMLS technology. Novelty Statement A novel ground-source heat exchanger was additively fabricated using the direct metal laser sintering (DMLS) technique. The unique compact screw-type design eliminates the need of excavating soil and features easy installation with less maintenance costs. Heat transfer characteristics of the proposed design were evaluated analytically and numerically. The proposed geothermal heat exchanger contributes effectively to the deployment of sustainable energy systems.

Design of control valve with low energy consumption based on Isight platform

The pressure drop of a control valve is directly associated with the energy consumption of the control system. The conventional design method of a control valve results in high energy consumption, while the control ability deviates from the design goal. Additionally, repeated corrections via flow experiments are inefficient. To efficiently design a low-energy-consumption control valve that satisfies control requirements, a novel design method is proposed herein. It is parametrically defined in Sculptor software based on the conventional valve spool. Various software packages are integrated using script files in the Isight platform. An approximate model is constructed using sample points generated based on the design of experiments; subsequently, it is solved using an optimization algorithm. Simulation results indicate that the output pressure of the pump and the average pressure drop of the control valve decrease by 4.38% and 5.51%, respectively, under the same flow rate. The working flow characteristics curve exhibits high linearity, implying that energy conservation is realized while the control ability is improved. Moreover, the force on the valve spool decrease by 1.36% on average, while the pressure and velocity in the flow field are reduced.

Numerical Study on Effects of Pipeline Geometric Parameters on Release Characteristics of Gas Extinguishing Agent

In order to guide the optimization design of the pipeline network of the aircraft-fixed gas fire extinguishing system and improve its fire extinguishing performance, FLUENT software was used to simulate the influence of pipeline parameters such as diameter, length, and roughness on the release characteristics of the fire extinguishing agent. It can be found that the extinguishing agent can be divided into liquid and vapor extinguishing agents in the fire extinguishing pipeline system during the release. The spatial distribution and proportion of the liquid and vapor extinguishing agents are asymmetric. Results show that the peak value of the pressure drop rate (dPmax) has a good quadratic function relationship with the pipeline diameter (D) and the functional relationship is dPmax=−22.224+2.782D+0.089D2, which means that the peak value increased significantly with the increase in the pipeline diameter. Moreover, when the pipeline diameter is 25 mm, the average pressure drop rate of the vessel is about 35.02 MPa/s, which is 5.97 times the value of the average pressure drop rate when the pipeline diameter is 10 mm. With the increase in the pipeline diameter, the release time decreases significantly, the mass flow rate increases obviously, while the gasification ratio decreases rapidly at first and then increases slightly. The pipeline length also has a significant influence on the release characteristics of the extinguishing agent. With the increase in the pipeline length, the release time and the gasification ratio increase linearly, while the mass flow rate decreases linearly. Compared with the pipeline diameter and pipeline length, the influence of the pipeline roughness on the release characteristics of the extinguishing agent is weak. With the increase in the pipeline roughness, the release time and the gasification ratio of the extinguishing agent increases slowly, while the mass flow rate decreases slowly.

Simulation of a parabolic trough solar collector containing hybrid nanofluid and equipped with compound turbulator to evaluate exergy efficacy and thermal‐hydraulic performance

AbstractThis research is mainly aimed at investigating the numerical modeling of thermal‐hydraulic and exergy efficiencies of parabolic trough solar collectors (P‐SCs) filled with magnetic hybrid nanofluid. The k‐epsilon turbulence, S2S, and mixture models were used to simulate the turbulence equations, radiation, and two‐phase nanofluid, respectively. The experiments were run using magnetic nanofluid in Reynolds numbers of 5000‐20 000, the volume fractions of 1%‐3%, and the ratios of pitch (ROPs) of 1, 2, and 3 of the combined turbulator. According to the results, there is a significant increase in average Nusselt number (Nu) and pressure drop (ΔP) with increasing Reynolds number, nano‐additive concentration, and ROP. Moreover, the use of the hybrid magnetic turbulator and hybrid nanofluid increased the thermal performance of the P‐SC. It was also found that the Reynolds number of 20 000 and volume fraction of 3% of nanoparticles resulted in the optimal exergy efficiency mode in using a hybrid turbulator.

Impact of mechanical tripping on cuttings transport in large-diameter horizontal directional drilling applications

In horizontal directional drilling (HDD), both drilling performance and drilling efficiency are affected by the downhole condition, i.e. the presence of cuttings. Previous research has focused on cuttings transport during drilling; however, less effort has gone into investigating the effect of the movement of the bottom hole assembly (BHA) for downhole cleaning, possibly due to the lack of downhole annular pressure data. In HDD, mechanical trips are the movement of the drillhead from the cutting face towards the borehole entry point, and back again. In the current work, any movement of the BHA of a length greater than ten drill stem segments (towards the entry point) during the drilling process is defined as mechanical tripping. Based on the downhole annular pressure data from a large-scale HDD project, an initial analysis of the pressure drop due to six trips was determined for drilling the pilot bore. The average pressure drop observed for these six mechanical trips is 69%. This difference in annular pressure before and after tripping indicates that, in practice, this is a potential method to remove cuttings from the borehole.

Heat Transfer and Friction Factor Characteristics of Turbulent Flow through a Conical Heat Exchanger

In this present energy demand scenario, the use of a waste heat recovery device like regenerator, recuperator, reheaters in the industrial processes is gaining much more importance due to improvement in thermal efficiency, and consequently reduction in thermal pollution. In the power plant, the waste heat carried by hot flue gases through the chimney remains untapped which can be recovered through the use of a conical heat exchanger at the inner portion of the chimney. Also, few customized designs of the conical coil heat exchanger can have the potential to be used to recover the waste heat in other industrial processes like chemical reactors, electrical contractors, HVAC applications, condenser, boiler, and evaporator, etc. In the present study, different arrangements of the conical coil heat exchanger are analyzed using a numerical technique. A conical coil of different geometrical configurations viz. at three different cone angles 45°, 90°and 135°, and at three different pitches 20 mm, 25 mm, and 30 mm are considered. The results for heat transfer and friction factor are presented for the flow of fluid of different Reynolds numbers. The impact of geometrical parameters as well as flow parameters on pressure drop and heat transfer under constant wall heat flux conditions are presented. The average heat transfer and pressure drop values are observed to be 175 to 225% more than the smooth tube values with increased pressure drop. Also, the results indicate that there is a nonlinear increase in both Nusselt number and friction factor with the increase in cone angle and pitch of conical coil.

Experimental study on heat transfer and pressure drop characteristics utilizing three types of water based nanofluids in a helical coil under isothermal boundary condition

• Three types of nanofluids TiO 2 /water, ZnO /water and Ag /water through helical coils are experimentally investigated. . • Increasing the coil pitch reduces both Nusselt number and pressure drop. • Nusselt number enhancement up to 28.7 %, 17.8 % and 11.8 % was achieved for TiO 2 /water, ZnO /water and Ag /water respectively. • Pressure drop increasing up to 28.5%, 23.5% and 25.4% was observed for TiO 2 /water, ZnO /water and Ag /water respectively. • Novel correlations are introduced for Nusselt number and pressure drop. Nanofluids are an innovative attractive challenging field suitable for many heat transfer applications. The helical coil is preferred due to compactness and additional curvature flow disturbance. Heat transfer and pressure drop characteristics of Ag, ZnO and TiO 2 water based nanofluids through helical coil tubes under isothermal boundary conditions are experimentally investigated with 0.25% nanoparticles volume concentration Ag /water, ZnO /water and TiO 2 /water nanofluids. Five coils are constructed with different coil pitches of 2, 4, 6, 8 and 10 cm. The flow rate of the nanofluid varies between 1 to 3.5 L/min with inlet temperature from 30 °C to 60 °C. The results showed that increasing the coil pitch reduces Nusselt number and pressure drop. The nanofluids have a positive impact on the enhancement of heat transfer but with a pressure drop penalty. Average Nusselt number enhancement up to 11.8 %, 17.8 % and 28.7 % was achieved at Ag /water, ZnO /water and TiO 2 /water with average pressure drop increasing up to 25.4%, 23.5% and 28.5% respectively. The results showed that an increase in coil pitch decreases hydrothermal performance index ( HTPI) and utilizing nanofluids increases HTPI for all types of nanofluids Ag /water, ZnO /water and TiO 2 /water. Novel correlations were developed to predict Nusselt number and pressure drop. Graphical Abstract .

Heat transfer and pressure drop in turbulent nanofluid flow in a pin-fin heat sink: Fin and nanoparticles shape effects

In this paper, the turbulent flow of a nanofluid in a channel is simulated in the presence of a pin-fin heatsink. Pin fins have different shapes, including hexagonal, circular, square, and triangular that are considered in two different arrangements. Constant heat flux is applied to the heatsink from its bottom due to the operation of an electronic chip. The nanoparticles suspended in water are alumina, which are in different shapes such as blades, bricks, cylinders, and plates. Their shape effect is investigated. The nanofluid enters the channel at a constant velocity in the range of 1–3 m/s and a constant volume percentage of 2%, and exits after cooling the pin-fin heatsink. The standard k-ε turbulence model is used to model turbulent flow, and the SIMPLEC method is employed to linearize the equations. The variables include fin type, fin arrangement, nanoparticle shape, and nanofluid velocity. Their effect on the maximum and average heatsink temperature and pressure drop (ΔP) is studied. The results show that increasing the velocity leads to a reduction in heatsink temperature, and the use of brick-shaped nanoparticles and circular fin results in the best cooling performance. Also, the use of circular fin and brick nanoparticles requires less ΔP than other cases.

Heat transfer augmentation for turbulent flow in circular tubes using inserts with multiple curved vortex generator elements

Measurements of local heat transfer coefficients on the circumference of a circular tube, fitted with two modified versions of an already existing axially inline curved Vortex Generator (VG) element insert are reported in this study. Measurements for average pressure drop are also presented and the air was used as the working fluid. The first modified insert is manufactured with a pair of two VG elements spaced symmetrically 180° apart but with the subsequent pairs along the axis staggered at an angle of 90°. The geometric features for the staggered insert were identical to the optimal one for the existing inline one. The staggered insert gives a more uniform circumferential and axial Nusselt number distribution. The ratio of the highest and lowest Nusselt number values for the staggered and inline case is equal to approximately 1.3 and 1.6 respectively. The average Nusselt number ratio at constant Reynolds number (10,000 < Re < 45,000) and constant pumping power however remained the same at about 2.6 and 1.5 respectively. The second modified insert was manufactured with three vortex generators placed symmetrically 120°apart at each axial location with all subsequent locations in line with one another. Two angles of attack 30°and 45° were used for the vortex generator elements and the pitch to projected length ratio of the VGs was varied between 1.6 and 12.2. The average heat transfer coefficient augmentation ratio using this insert at the equal Reynolds number and constant pumping power was obtained in the range of 1.5–5.5 and 1.0 - 1.8, respectively. The experimental data is presented in the form of empirical correlations for Nusselt number, and friction factor as a function of tube flow parameters, and non-dimensional geometrical parameters of VG inserts, which predict the data with an accuracy equal to ±20 %.

Numerical Investigation of Hydraulic-Thermal Performance for a Double-Pipe Heat Exchanger Equipped with 45°-Helical Ribs

In this paper, the hydraulic-thermal performance of a double-pipe heat exchanger equipped with 45°-helical ribs is numerically studied. The ribbed double-pipe heat exchanger is modelled using three heights (H = 0, 2.5, 3.75, 5 mm) of 45°-helical ribs. Two numbers (4-ribs and 8-ribs) of 45°-helical ribs are attached on the outer surface of the inner pipe of the counter-flow double-pipe heat exchanger and compared with a smooth double-pipe heat exchanger. Three-Dimensional computational fluid dynamics (CFD) model for a laminar forced annular flow is performed in order to study the characteristics of pressure drop and convective heat transfer. In addition, the influence of rib geometries and hydraulic flow behaviour on the thermal performance is system-atically considered in the evaluations. The annular cold flow is investigated with the range of Reynolds numbers from 100 to 1000, with three heights of ribs at the same width (W = 2 mm) and inclined angles of (θ = 45°).The results illustrate that the average Nusselt number and pressure drop increase with an in-creasing number of ribs, the height of ribs and Reynold number, while the friction factor decreas-es with increasing Reynolds numbers. The percentage of averaged Nusselt number enhancement for three rib heights (H = 2.5, 3.75 and 5 mm) at 4-ribs is (34%, 65% and 71%), respectively, While for 8-ribs the enhancement percentage is (48%, 87% and 133%) as compared with the smooth double-pipe heat exchanger at Re = 100. The best performance evaluation criteria of (PEC) at (8-ribs, and H = 5 mm) is 2.8 at Re = 750. The attached 45-helical ribs in the annulus path can generate kind of secondary flows, which enhance the fluid mixing operation between the hot surface of the annular gap and the cold fluid in the mid of the annulus, which lead to a high-temperature distribution. Increasing the height of 45°-helical ribs lead to an increase in the sur-face area subjecting to convective heat transfer.

Topology optimization for spider web heat sinks for electronic cooling

• The topology optimization method is firstly employed for bionic heat sinks. • The performance of the heat sinks are studied by numerically and experimentally. • Different optimization goals for temperature uniformity can lead to different results. • The optimal heat sinks is superior to the conventional heat sinks in terms of the performance. • The CFD results agree well with the experimental results. In this paper, topology optimization method is applied to bionic domain, and in order to improve the thermal performance of heat sinks, two topological heat sinks are obtained under two objectives. One objective is minimize the temperature difference and pressure drop, and another is minimize the average temperature and pressure drop. The topological heat sink designed by topology optimization with the minimum temperature difference and the pressure drop as a goal is named as M2, while that designed with the minimum average temperature and the pressure drop as a goal is called M3. The flow and thermal performance of these two topological flow channel heat sinks are investigated numerically. The results show that for Re = 2056.8, the temperature difference of the topological heat sink M2 is reduced by 57.35% compared to conventional spider web heat sink M1, while that of the topological heat sink M3 is reduced by 10.64% compared to M1. In addition, the thermal resistance of the topological heat sinks are smaller than the conventional spider web heat sink. Through analysis, it can be known that M2 has the best comprehensive heat dissipation capacity. In order to verify the correctness of the numerical simulation, M2 is manufactured, and the heat transfer performance of M2 is investigated experimentally. The experimental results of the optimal heat sink agree well with the calculated results.

Comprehensive mechanics‐based virtual model of NHERI@UCSD shake table—Uniaxial configuration and bare table condition

AbstractA mechanics‐based virtual model of the NHERI@UCSD large high‐performance outdoor shake table (LHPOST) in its uniaxial configuration and under bare table condition is presented. The virtual model includes: (i) a reprogrammed version (i.e., virtual replica) of the actual controller, (ii) a servovalve model including servovalve spool dynamics and two independent servovalve flow nonlinearities for each of the four servovalves of the system, (iii) an actuator model for each of the two single‐ended actuators, (iv) two accumulators modeling the average supply pressure drop at the entrance of the servovalves, and (v) a one‐degree‐of‐freedom mechanical subsystem model. Based on forced vibration test results for the foundation block, it was found that the soil‐foundation compliance effects do not need to be included in the virtual model of the LHPOST. The virtual model presented is able to predict accurately the actual shake table platen response under narrow and broadband inputs with the controller gains set to the same values as on the actual shake table. Moreover, the fourth stage spool displacements and actuator driving force from actual tests are reproduced accurately by the virtual model. The mechanics‐based virtual model presented in this article can be coupled with FE models of specimens to be tested on the LHPOST and can be used to improve the signal reproduction fidelity of the LHPOST and to develop more advanced model‐based shake table controllers.