Experimental and Numerical Investigation of the Performance of Turbulent Heat Transfer in Tubes with Different Cross-Sectioned Wire Coils

The thermal-hydraulic performance of plain tubes with and without wire coils in turbulent regimes is investigated experimentally and numerically.The effects of wire coil distribution(circular cross section)within the tube were explored experimentally,and water was employed as the working fluid.The numerical simulation was carried out using software programmer ANSYS Fluent 2019 R3 using the finite-volume approach.In the turbulent regime,six cross-sectionedwire coilswere analyzed,including:circular,rectangular,hexagonal,square,star shape,and triangle.The utilization of a tube with a wire coil has been shown to increase heat transfer rate and pump consumption.The results indicate a high level of concurrence,as the deviations are all below 8%.Compared with plain tube,the wire coils,according to the arrangement(TWD),gave the best PEC.The heat transfer enhancement ability of different cross sections follows the following order:StCS>RCS>HCS>SqCS>CCS>TCS.Also,the sequence of pump consumption for each cross section is as follows:RCS>StCS>SqCS>HCS>CCS>TCS.

Performance Simulation of a Double Tube Heat Exchanger Based on Different Nanofluids by Aspen Plus

A heat exchanger’s performance depends heavily on the operating fluid’s transfer of heat capacity and thermal conductivity.Adding nanoparticles of high thermal conductivity materials is a significant way to enhance the heat transfer fluid’s thermal conductivity.This research used engine oil containing alumina(Al_(2)O_(3))nanoparticles and copper oxide(CuO)to test whether or not the heat exchanger’s efficiency could be improved.To establish the most effective elements for heat transfer enhancement,the heat exchangers thermal performance was tested at 0.05%and 0.1%concentrations for Al_(2)O_(3)and CuO nanoparticles.The simulation results showed that the percentage increase in Nusselt number(Nu)for nanofluid at 0.05%particle concentration compared to pure oil was 9.71%for CuO nanofluids and 6.7%for Al_(2)O_(3)nanofluids.At 0.1%concentration,the enhancement percentage in Nu was approximately 23%for CuO and 18.67%for Al_(2)O_(3)nanofluids,respectively.At a concentration of 0.1%,CuO nanofluid increased the LMTD and overall heat transfer coefficient(U)by 7.24 and 5.91%respectively.Both the overall heat transfer coefficient(U)and the heat transfer coefficient(hn)for CuO nanofluid at a concentration of 0.1%increased by 5.91%and 10.68%,respectively.The effectiveness(εn)of a heat exchanger was increased by roughly 4.09%with the use of CuO nanofluid in comparison to Al_(2)O_(3)at a concentration of 0.1%.The amount of exergy destruction in DTHX goes down as Re and volume fractions go up.Moreover,at 0.05%and 0.1%nanoparticle concentrations,the percentage increase in dimensionless exergy is 10.55%and 13.08%,respectively.Finally,adding the CuO and Al_(2)O_(3)nanoparticles improved the thermal conductivity of the main fluid(oil),resulting in a considerable increase in the thermal performance and rate of heat transfer of a heat exchanger.

Investigate the Impact of Dimple Size and Distribution on the Hydrothermal Performance of Dimpled Heat Exchanger Tubes

In this study,the primary objective was to enhance the hydrothermal performance of a dimpled tube by addressing areas with low heat transfer compared to other regions.To accomplish this,a comprehensive numerical investigation was conducted using ANSYS Fluent 2022 R1 software,focusing on different diameters of dimples along the pipe’s length and the distribution of dimples in both in-line and staggered arrangements.The simulations utilized the finite elementmethod to address turbulent flowwithin the tube by solving partial differential equations,encompassing Re numbers spanning from 3000 to 8000.The study specifically examined single-phase flow conditions,with water utilized as the cooling fluid.The results of the investigation indicated that increasing the Reynolds number resulted in higher average Nusselt numbers,pressure drops,the overall performance criterion,and a reduction in average thermal resistance across all models analyzed.Notably,both proposedmodels demonstrated improved heat transfer when compared to the conventional model.Out of all the models evaluated,the tube featuring staggered dimples(Model B)demonstrated the most notable improvement in the Nu number.It exhibited an enhancement of approximately twice the value compared to the conventional model.The mean thermal resistance for the tube with dimples in the staggered arrangement(Model B)is 0.0057 k/W,compared to 0.0118 k/W for the traditional model.The maximum overall performance criterion for Model-A-and Model-Bis 1.22 and 1.33,respectively.

Effect of Streamlined Nose Length on the Aerodynamic Performance of a 800 km/h Evacuated Tube Train

The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.

Research on seismic performance of shear walls with concrete filled steel tube columns and concealed steel trusses

In order to further improve the seismic performance of RC shear walls, a new composite shear wall with concrete filled steel tube （CFT） columns and concealed steel trusses is proposed. This new shear wall is a double composite shear wall; the first composite being the use of three different force systems, CFT, steel truss and shear wall, and the second the use of two different materials, steel and concrete. Three 1/5 scaled experimental specimens： a traditional RC shear wall, a shear wall with CFT columns, and a shear wall with CFT columns and concealed steel trusses, were tested under cyclic loading and the seismic performance indices of the shear walls were comparatively analyzed. Based on the data from these experiments, a thorough elastic-plastic finite element analysis and parametric analysis of the new shear walls were carried out using ABAQUS software. The finite element results of deformation, stress distribution, and the evolution of cracks in each phase were compared with the experimental results and showed good agreement. A mechanical model was also established for calculating the load-carrying capacity of the new composite shear walls. The results show that this new type of shear wall has improved seismic performance over the other two types of shear wails tested.

The Hot Corrosion Performance of NiCr-Cr_3C_2 Cermet Coating to Boiler Tube

Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler tube steel, FeCrAl, NiCrTi, Ni50Cr and NiCrAlMoFe-Cr 3C 2 coatings, which are widely used at present for protection of boiler tubes. Meanwhile,the influence of sealer on the hot corrosion resistance of various coatings and the mechanisms of coating corrosion were explored.

Performance enhancement of filled-type solar collector with U-tube

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube(HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little.Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

Two Phase Pressure Drop Performance of Refrigerant in a Small Horizontal Smooth Tube with 2.5 mm inside Diameter

Two-phase flow pressure drop measurements were made during the phase change heat transfer process of R22 in a small horizontal smooth tube with 2.5 mm inside diameter. Conclusions can be drawn that the quality corresponding to the pressure gradient peak value of small tubes became higher than that of large tubes. The effect of quality to pressure drop becomes weak as the mass flux increases. The experiment data were compared with the predicated values of the state-of-the-art correlations from the open literature. The comparisons between the data and the predictions indicate that most of the state-of-the-art correlations fails to predict the experimental data. Chisholm model shows a relatively better predictive ability than the other empirical correlations although it has a mean deviation of 26.7%. But the predicated values of Chisholm model are lower by 50% than the experimental data when the quality becomes larger.

Effects of Heat Exchange Tube Structural Parameters on Performance of Vehicle Radiator

In order to improve the performance of vehicle radiators, a two-dimensional heat transfer steady-state model of the radiator was set up. The influence of the structural parameters (axial ratio) of the heat exchange tube on the windward side on the heat transfer performance of the radiator was studied. With the increase of the axial ratio of the heat exchange tube on the windward side, the heat exchange capacity of the heat exchange tube surface slightly decreases. The heat exchange area increases significantly, which increases the total heat exchange of the radiator and improves the heat transfer performance of the radiator. When the axial ratio increases from 1.0 to 2.0, the average surface heat transfer capacity decreases from 5664.16 W/m2 to 5623.57 W/m2.

Time-domain CFD computation and analysis of acoustic attenuation performance of water-filled silencers

The multi-dimensional time-domain computational fluid dynamics(CFD) approach is extended to calculate the acoustic attenuation performance of water-filled piping silencers. Transmission loss predictions from the time-domain CFD approach and the frequency-domain finite element method(FEM) agree well with each other for the dual expansion chamber silencer, straight-through and cross-flow perforated tube silencers without flow. Then, the time-domain CFD approach is used to investigate the effect of flow on the acoustic attenuation characteristics of perforated tube silencers. The numerical predictions demonstrate that the mean flow increases the transmission loss, especially at higher frequencies, and shifts the transmission loss curve to lower frequencies.

Preparation and Performance of Corona-proof Conductive Composite Coatings

Because of its merits,acrylic resin was chosen to improve the mechanical,conductive and hydrophobic properties.Carbon fiber powders (CF),carbon nanotubes (MWCNT),and nano-TiO_(2) were incorporated into the acrylic resin to prepare the corona-proof conductive composite coatings.The incorporation of CF and MWCNT may improve the conductivity and mechanical strength of the coatings.However,the addition of nano-TiO_(2) may increase the hydrophobicity of the coatings.Thus,the effects of different additives on the mechanical properties,conductivity,hydrophobicity and heat resistance of the conductive film were studied.The experimental results show that the incorporation of carbon fiber powders and multi walled carbon nanotubes can significantly improve both the conductivity and mechanical properties of the conductive coatings,and the addition of nano titanium dioxide can improve the hydrophobicity of the conductive film.

INVESTIGATION ON NEW TYPE OF DOUBLY BLENDING ABRASIVE WATER JET NOZZLE SYSTEM WITH HIGHER PERFORMANCE

Based on the two existing abrasive water-jet（AWJ） systems, the dia-jet （or pre-jet） and the post-jet, a new type of abrasive water-jet system is put forward, which combines the dia-jet＇s advantage, low operating system pressure, slender stream jet, and more concentrative abrasive in the blended stream, with merits of post-jet, the less sophisticate apparatus, successive supply of abrasives. The theoretic analysis is brought out in detail, and the nozzle system structure is concisely illustrated. Its relevant experiment results are demonstrated, proving that this new system is effective in various aspects, enlarging penetrating capability without raising system pressure, saving machining power supply, lessening energy loss, etc.

Performance Assessment of Heat Exchangers for Process Heat Integration

Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.

新型浆锚连接方钢管混凝土拼接柱抗震性能试验研究

为进一步提高用于钢-混凝土组合结构的柱构件的装配效率,并改善其抗震性能,降低生产成本,提出一种新型浆锚连接方钢管混凝土拼接柱设计方法。通过对缩尺比例为2的5个拼接柱构件和1个整浇柱构件开展拟静力试验,获得不同配筋率、配筋形式和柱-柱节点拼接部位的新型拼接柱的抗震性能。试验结果表明:新型拼接柱构件在低周期反复荷载下的破坏过程及其形态与整浇柱构件相似,其滞回曲线饱满,耗能能力、抗承载力退化和抵抗变形(刚度)能力均比整浇柱构件更加优良,特别是将柱-柱节点拼接部位设于柱间反弯点区域的P类型构件变形能力最佳,证明了该新型拼接柱设计方法的科学性,并对提高钢-混凝土组合框架结构的整体抗震性能具有应用潜力。

Torsional Behavior Design of UHPC Box Beams Based on Thin-Walled Tube Theory

This study proposed a prediction formula for the torsional strength enabling to reflect the tensile strength of ultra high performance concrete (UHPC) beams based upon the thin-walled tube theory. The remarkable ductile behavior of UHPC can also be attributed to the steel fiber reinforcement. This feature must be considered to provide rational explanation of the torsional behavior of UHPC structures. In this study, the proposed torsional design adopts a modified thin-walled tube theory so as to consider the tensile behavior of UHPC. And torsion test was conducted on thin-walled UHPC box beams to validate the proposed formula through comparison of the predicted torsional strength with the experimental results. The comparison of the predicted values of the cracking torque and torsional moment resistance with those observed in the torsional test of UHPC verified the validity of the design method. The contribution of the steel fibers to the torsional strength and cracking load was larger than that of the stirrups, but the stirrups appeared to contribute additionally to the torsional ductility. Accordingly, it is recommended that design should exploit effectively the contribution of the steel fiber rather than arrange a larger number of stirrups in UHPC structures subjected to torsion.

A comprehensive comparison on vibration and heat transfer of two elastic heat transfer tube bundles

Elastic heat transfer tube bundles are widely used in the field of flow-induced vibration heat transfer enhancement. Two types of mainly used tube bundles, the planar elastic tube bundle and the conical spiral tube bundle were comprehensively compared in the condition of the same shell side diameter. The natural mode characteristics, the effect of fluid-structure interaction, the stress distribution, the comprehensive heat transfer performance and the secondary fluid flow of the two elastic tube bundles were all concluded and compared. The results show that the natural frequency and the critical velocity of vibration buckling of the planar elastic tube bundle are larger than those of the conical spiral tube bundle, while the stress distribution and the comprehensive heat transfer performance of the conical spiral tube bundle are relatively better.

Numerical Simulation and Optimization of Perforated Tube Trolley in Circular Cooler

Three symmetrically perforated tubes were arranged in the circular cooler trolley as auxiliary cooling inlet to improve the cooling performance of the sintered body during the production process. Fluent 15.0 has been used to simulate the process;the study shows that the perforated tube structure trolley has changed the temperature field within the sintering area, thereby improving the sintering area of the cooling effect and uniformity, also greatly reducing the cooling time. Compared with the traditional trolley, the best structure of the porous tube trolley has reduced 41% cooling time and increased 50% waste heat recovery.

基于PERFORM-3D的筒中筒结构弹塑性时程分析与性能评估

采用PERFORM-3D软件及纤维剪力墙单元,通过对一14层筒中筒结构试验模型进行弹塑性时程分析,并与试验结果对比,验证了软件模型的合理性。通过结构在不同烈度情况下的变形分析,具体研究了该结构的层间位移角分布,并参考美国性能规范ASCE41—06,对结构在弹塑性阶段的性能进行评估。得出在高烈度地震动下结构底部剪力墙出现较大塑性变形,以耗散大部分能量,同时给出相应的设计建议,为同类高层结构弹塑性分析提供参考。

Techno-economic analysis of single U-tube and double U-tube heat exchangers in Chongqing area

On the basis of practical projects in Chongqing,the thermal performance of heat exchangers (single U-tube type and double U-tube type) of the ground-source heat pump (GSHP) system in the hot summer was obtained and analyzed. The data obtained from test could match with the result deduced from theoretical calculation. From the test results,the cooling capacity of double U-tube is 1.6 times that of single U-tube. Taking cost per depth per watt Clq as the evaluation standard,Clq of single U-tube is 4.69 RMB$/W,and Clq of double U-tube is 3.14 RMB$/W. The double U-tube heat exchangers usage should be prioritized.