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.

Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.

Pool boiling heat transfer enhancement on porous surface tube

The passive residual heat removal exchanger (PRHR HX),which is a key equipment of the passive residual heat removal system,is installed in an elevated pool.Its heat transfer performance affects security and economics of the reactor,and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded.The smooth tubes,which are widely used as heat transfer tubes in PRHR HX,can be replaced by some enhanced tubes to improve the boiling heat transfer capability.In this paper,the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source.Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer,and shortens the time significantly before reaching the liquid saturation temperature.Its boiling heat transfer coefficient increases from 68% to 75%,and the wall superheat decreases by 1.5oC.Combining effect of condensation inside tube with boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution.Based on these investigations,enhance mechanism of the porous surface tube is analyzed.

An Experimental Study of Porous Surface Tubes for Enhancement of Binary Liquid Mixture Pool Boiling Heat Transfer

Experiments have been conducted on the pool boiling of binary mixtures in JK tubeswith porous surface and ribbed channels,attempting to enhace the boiling heat transfer coefficientsinvolved.The binary mixtures used in this study are R113 and R11.The results show that the boilingfi1m heat transfer coefficients for the R113 and R11 binary mixtures in JK2 and JK1 tubes are 2—8tirnes and 2—5 times greater than those in smooth tubes respectively.Based on this experimentaldata and simple theoretical analysis,a correlation has been proposed to predict the boiling heattransfer coefficients for R113/R11 mixtures in a horizontal JK tube with a relative error of less than16%.

ENHANCED HEAT TRANSFER OF GLASS TUBE HEAT EXCHANGER

The enhancement of convective heat transfer in a glass tube heat exchanger was researched.A simple and efficient method using spiral wire turbulence promotors in the glass tube isrecommended.A series of experiments were conducted,and thetlon have been obtained.Performance evaluations Nr the enhanced heattrans比r In this heatexchanger are su门niii ed up and discussed Based on the vlewp01nt Of止berinodynaffi1CS,止he avaHableenergy lossof the heat transfer swtern Inside the tube Is analwed to determine and evaluate the over-all趴ct oQthe enhanced heat transfer,The mechanism ofenhanced heat transfer]n the glass tubeand the Influence of turbutlvlty In the fough tube are also analysed and discussed.

Theoretical Research on R245fa Condensation Heat Transfer inside a Horizontal Tube

Numerical simulation on R245fa condensation inside an inner diameter of 8 mm horizontal tube is researched in this paper. The effect of variation in velocity, condensation temperature and superheat of inlet steam and variation in cooling water temperature on heat transfer coefficient are investigated as a parametric study. Condensation process of steam has been successfully modeled by applying a user defined function (UDF) added to the commercial computational fluid dynamics (CFD) package. By analyzing the corresponding condensate contours and the curves of local heat transfer coefficient, the relationships between condensation heat transfer coefficient and various parameters of R245fa inside horizontal tube are obtained. It shows that the heat transfer coefficient increases by the increase in velocity, condensation temperature and superheat of inlet steam and the decrease in cooling water temperature. The errors between the heat transfer coefficient of simulation result and model of Wang and Shah are within ±30%. The parametric study will provide the basis for designing efficient heat exchangers of R245fa.

Heat Transfer and Flow Characteristics of Water Flow with Air Injection in Polyethylene Tube Placed over Metal Rods: Influence of Pitch Length and Tube Width

A polyethylene tube can be used as a heat exchanger for a low-running-cost?temperature control system. In this system, the flow of temperature-controlled?water in the tube is used as the heat source, and the tube is placed on the ceiling of a temperature-controlled space using a metal net. Owing to this structure, the tube is deformed by its weight. This deformation has a significant influence on heat transfer and flow characteristics. Therefore, an air injection method, in which air and water are injected simultaneously into the tube, is developed for preventing the deformation of the tube. In this study, bedding metal rods were used instead of a metal net. The influence of the pitch length of the metal rods (5 - 15 cm) and the width of the polyethylene tube 15, 20, 25, 30, and 35 cm was examined experimentally. The length of the polyethylene tube was 178 cm. The air flow rate was 9.5 × 10-5 m3/s. The water flow rates were 60, 80, 100, 120, and 140 mL/min. Results show that the thermal response improved because of air injection. In particular, the temperature at steady state increased, and steady state was attained approximately 1.2 - 3 times faster with air injection than without air injection. The optimum pitch length of the metal rods and the range of the optimum width of the polyethylene tube were 8 cm and 20 - 25 cm, respectively, with and without air injection.

Experimental study on convective boiling heat transfer in narrow-gap annulus tubes

Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are re- quired to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteris- tics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the tran- sition between various regimes. Some significant differences from unconfined forced convection boiling were found, and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.

In-Situ Preparation and Thermal Shock Resistance of Mullite-Cordierite Heat Tube Material for Solar Thermal Power

In order to improve the thermal shock resistance of solar thermal heat transfer tube material, the mullite-cordierite composite ceramic as solar thermal heat transfer tube material were fabricated by pressureless sintering using a-Al203, Suzhou kaolin, talc, and feldspar as starting materials. The important parameter for solar thermal transfer tube such as water absorption （W）, bulk density （Db）, and the mechanical properties were investigated. The phase composition and microstructure of the composite ceramics were analyzed by XRD and SEM. The experimental results show that the B3 sintered at 1 300 ℃ and holding for 3 h has an optimum thermal shock resistance. The bending strength loss rate of B3 is only 2% at 1 100℃ by air quenching-strength test and the sample can endure 30 times thermal shock cycling, and the water absorption, the bulk density and the bending strength are 0.32%, 2.58 g·cm-3, and 125.59 MPa respectively. The XRD analysis indicated that the phase compositions of the sample were mullite, cordierite, corundum, and spinel. The SEM images illustrate that the cordierite is prismatic grain and the mullite is nano rod, showing a good thermal shock resistance for composite ceramics as potential solar thermal power material.

Experimental study on thermo-hydraulic performances of nanofluids flowing through a corrugated tube filled with copper foam in heat exchange systems

Thermo-hydraulic characteristics of TiO_2-water nanofluids in thin-wall stainless steel test tubes(corrugated tube and circular tube) filled with copper foam(40 PPI) are experimentally investigated and compared with those in test tubes without copper foam. The effects of nanoparticle mass concentration on flow and heat transfer performances are investigated. In addition, the mutual restriction relationships between Reynolds number(Re), Nusselt number(Nu) and resistance coefficient(f) are discussed respectively. Also, the comprehensive coefficient of performance(CCP) between heat transfer and pressure drop is evaluated. The results show that core-enhancement region for heat transfer using experimental tubes filled with copper foam is notably different from that of tubes without copper foam. There is a corresponding Reynolds number(about Re = 2400) for the maximum CCP of each condition. And the heat transfer can be enhanced dramatically and sustained at 8000 ≤ Re ≤ 12000.

Experimental research on stabilities, thermophysical properties and heat transfer enhancement of nanofluids in heat exchanger systems

Stable TiO_2–water nanofluids are prepared by a two-step method, stabilities of nanofluids are investigated by precipitation method and transmittance method respectively, and thermal conductivities and viscosities are also measured. An experimental system for studying the heat transfer enhancement of nanofluids is established,and heat transfer and flow characteristics of TiO_2–water nanofluids in heat exchanger systems with a triangular tube and circular tube are experimentally studied. The effects of nanoparticle mass fractions(ω = 0.1 wt%–0.5 wt%) and Reynolds numbers(Re = 800–10000) on the heat transfer and flow performances of nanofluids are analyzed. Fitting formulas for Nusselt number and resistance coefficient of nanofluids in a triangular tube are put forward based on the experimental data. The comprehensive performances of nanofluids in a triangular tube are investigated. It is found that nanofluids in a triangular tube can significantly improve the heat transfer performance at the cost of a small increase in resistance coefficient compared with that in a circular tube, especially the resistance coefficients are almost the same between different nanoparticle mass fractions at turbulent flow. It is also found that the comprehensive evaluation index η decreases with Reynolds number at laminar flow but a critical maximum value appears at turbulent flow.

Numerical calculation of thermal field and heat transfer coefficient for 160 kA aluminum reduction cell

The principle of thermal flux being constant in heat flow tube and the principle of heat balance were applied to analyze and calculate the steady state thermal field and the electrolyte ledge heat transfer coefficient of aluminum reduction cell by finite element method. The calculated results show that the melt ledge heat transfer coefficient in the 160kA prebaked anode aluminum reduction cell of Guizhou Aluminum Smelter is higher than that of other cells of the same current. It is also found that the electrolyte and metal flow much faster, which may be the results of poor bus bar arrangements. Meanwhile, the calculated results of melt ledge heat transfer coefficient by heat flow tube method are almost in full agreement with the former works. This verifies the applicability of this method.

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.

Performance enhancement of water bath heater at natural gas city gate station using twisted tubes

Natural gas is transported from producing regions to consumption regions by using transmission pipelines at high pressures. At consumption regions, the pressure of natural gas is reduced in city gate stations(CGSs). Before the pressure reduction process, the temperature of natural gas is increased usually by using a water bath heater,which burns natural gas as fuel, to protect against freezing of natural gas. These types of heat exchangers have a low efficiency and consume a lot of fuel to generate the required heat. In the current study, the twisted configuration of the heating coil is proposed and investigated to enhance the heat transfer through a water bath heater with a nominal capacity of 1000 m^3·h^-1. Firstly, the implementation procedure is validated with data collected from the CGS of Qaleh-Jiq(located in Golestan province of Iran). A very good agreement is achieved between the obtained results and the real data. Then, three different twist ratios are considered to examine the twisting effects. The proposed technique is evaluated in the terms of velocity, temperature, and pressure variations, and the results are compared with the conventional case, i.e. straight configuration. It is found that both the heat transfer rate and the pressure drop augment as the twist ratio is raised. Finally, it is concluded that the twisted tubes can reduce the length of the gas coil by about 12.5% for the model with low twist ratio, 18.75% for the model with medium twist ratio, and 25% for the model with high twist ratio as compared to the straight configuration.

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.

三维变形管MVR蒸发器用于纤维素生产末端废水零排放项目

蒸发器的换热性能对机械蒸汽再压缩(MVR)系统投资及运行均有着重要影响。MVR蒸发器的管内传热与压降性能在基于三维变形管和直圆管的情况下存在明显差异。建立了考虑盐水浓度修正的三维变形管MVR蒸发器性能准则关联式,设计一套用于纤维素生产末端废水零排放项目的新型蒸发器。应用实践表明,相对于传统直圆管的MVR蒸发器,基于三维变形管的新型MVR蒸发器节材节能效果显著,其在节省29%换热面积的情形下仍能完全满足工程实际需要。在现场调研期间MVR系统处理每吨废水的压缩机耗电量在18.81~23.78 kW∙h之间,体现出新型蒸发器高能效的技术特性,极具应用推广价值。

基于响应面法的矿用翅片管空冷器参数优化

矿用空冷器是矿井降温系统常用的末端设备,优化矿用空冷器换热性能对提升矿井降温系统能效具有重要意义。采用Fluent建立了平直翅片管矿用空冷器模型,研究了翅片间距、翅片厚度、横向管间距和纵向管间距对传热因子、阻力因子和综合性能评价指标的影响规律;采用Box-Behnken响应面法,分析了双参数协同作用下传热因子、阻力因子和综合性能评价指标变化规律。结果表明:随着翅片间距、横向管间距的减小,以及翅片厚度增加,传热因子、阻力因子和综合性能评价指标逐渐增加;综合性能评价指标则随纵向管间距的增加而先增加后降低;横向管间距、翅片厚度是影响空冷器传热及流动性能最显著的两个参数,而翅片间距、纵向管间距的影响最小;得到了平直翅片管矿用空冷器的最优参数,传热因子提升16.3%、阻力因子增加26.3%、综合性能评价指标提升8.3%。研究结果可为矿用翅片空冷器设计参数优化提供指导。

变截面半圆通道内超临界二氧化碳热工水力性能研究

建立了不同半圆通道的数学和物理模型,并通过与实验数据的比较,验证了所建立模型的准确性。研究了超临界二氧化碳(S-CO_(2))在等截面半圆通道、渐扩型和渐缩型通道内的热工水力换热性能,并分析了不同通道和压力对S-CO_(2)在变截面半圆通道内的热工水力性能的影响。结果表明:相较于均匀截面半圆通道,渐扩型通道恶化传热,渐缩型通道强化传热;入口和出口半径比为1.0:0.5的渐缩型半圆通道的总体换热系数最大提升了39.93%,流动传热综合性能评价因子PEC最大为1.346;当压力越靠近临界压力或热通量较低时,传热性能越高。最后,从场协同性和湍动能分布的角度解释了渐缩型变截面通道强化传热的原因。研究结果可为S-CO_(2)循环系统冷却器的设计与优化提供新的思路和理论指导。

螺旋扭曲扁管传热流阻性能及工艺计算方法研究

螺旋扭曲扁管是一种非标换热管,成熟的热交换器计算商业软件,如HTRI、Aspen EDR等目前均尚未提供对应的计算模型,现有计算方法存在不统一、偏差大等问题。以螺旋扭曲扁管为对象,通过数值模拟计算、实验测试对其进行传热及流阻性能研究,综合利用HTRI传热计算软件,建立了一套螺旋扁管传热及流阻性能的通用化计算方法。进行了通用化计算结果、数值模拟分析数据、实验测试数据的对比,验证了通用计算方法的准确性,对螺旋扭曲扁管的工艺设计具有指导意义。

基于p阶线性模型的地埋管换热器流体温度分布研究

利用自主研发的分层热响应测试系统,获取沿深度方向上(竖向)管内流体温度实测数据,对比p阶线性分布模型计算结果和实测数据,研究两种典型工况条件下分层岩土介质中管内流体竖向分布规律和最佳p值。结果表明:恒热流工况时,p=-5阶线性分布模型能够准确预测管内流体温度分布;恒温工况时,最佳p值随流量的变化而变化,其关系为:|p|=7.361ln V+6.684。