Analysis of Collapse in Flattening a Micro-grooved Heat Pipe by Lateral Compression

The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element（FE） analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.

A coupled thermo-mechanical peridynamic model for fracture behavior of granite subjected to heating and water-cooling processes

Thermal damage and thermal fracture of rocks are two important indicators in geothermal mining projects.This paper investigates the effects of heating and water-cooling on granite specimens at various temperatures.The laboratory uniaxial compression experiments were also conducted.Then,a coupled thermo-mechanical ordinary state-based peridynamic(OSB-PD)model and corresponding numerical scheme were developed to simulate the damage of rocks after the heating and cooling processes,and the change of crack evolution process was predicted.The results demonstrate that elevated heating temperatures exacerbate the thermal damage to the specimens,resulting in a decrease in peak strength and an increase in ductility of granite.The escalating occurrence of thermal-induced cracks significantly affects the crack evolution process during the loading phase.The numerical results accurately reproduce the damage and fracture characteristics of the granite under different final heating temperatures(FHTs),which are consistent with the test results in terms of strength,crack evolution process,and failure mode.

Heat dissipating upper body compression garment:Thermoregulatory,cardiovascular, and perceptual responses

Purpose:The aim of the present study was to determine the effects of an upper body compression garment(UBCG)on thermoregulatory responses during cycling in a controlled laboratory thermoneutral environment(~23℃).A secondary aim was to determine the cardiovascular and perceptual responses when wearing the garment.Methods:Sixteen untrained participants(age:21.3±5.7 years;peak oxygen consumption(V02 peak):50.88±8.00 mL/min/kg;mean±SD)performed 2 cycling trials in a thermoneutral environment(~23℃)wearing either UBCG or control(Con)garment.Testing consisted of a 5-min rest on a cycle ergometer,followed by 4 bouts of cycling for 14-min at ~50%VO2 peak,with 1-min rest between each bout.At the end of these bouts there was 10-min of passive recovery.During the entire protocol rectal temperature(Trec),skin temperature(Tskin),mean body temperature(Tbody),and heat storage(HS)were measured.Heart rate(HR),VO2,pH,hematocrit(Hct),plasma electrolytes,weight loss(Wloss),and perceptual responses were also measured.Results:There were no significant differences between garments for Tskin,HS,HR,VO2,pH,Hct,plasma electrolyte concentration,Wloss,and perceptual responses during the trial.Trec did not differ between garment conditions during rest,exercise,or recovery although a greater reduction in Trec wearing UBCG(p=0.01)was observed during recovery.Lower Tbody during recovery was found when wearing UBCG(36.82℃±0.30℃ vs.36.99℃±0.24℃).Conclusion:Wearing a UBCG did not benefit thermoregulatory,cardiovascular,and perceptual responses during exercise although it was found to lower Tbody during recovery,which suggests that it could be used as a recovery tool after exercise.

Entropy Analysis of NH_3/H_2O Absorption-Compression Heat Pump

The absorption-compression heat pump (ACHP) has been considered as an effective approach to recover and utilize low-grade heat sources. In the present study, the first and second law thermodynamic analyses of the ACHP with NH3/H2O as working fluid were performed. Thermodynamic properties of each point and heat transfer rate of each component in the cycle under basic operation conditions were calculated from the first law analysis. Following the second law of thermodynamics, the entropy generation of each component and the total entropy generation of the system were obtained. The effects of the heating temperature, heat source temperature, and compression ratio on the coefficient of performance (COP) and the total entropy generation (STot) of the system were examined. The results show that the increase in COP corresponds to a decrease in STot, and vice versa; besides, for certain operating conditions, an optimum compression ratio in the NH3/H2O ACHP exists.

Analytical solutions to a compressible boundary layer problem with heat transfer

The problem of momentum and heat transfer in a compressible boundary layerbehind a thin expansion wave was solved by the application of the similarity transformation and theshooting technique. Utilizing the analytical expression of a two-point boundary value problem formomentum transfer, the energy boundary layer solution was represented as a function of thedimensionless velocity, and as the parameters of the Prandtl number, the velocity ratio, and thetemperature ratio.

Effect of High Pressure Heat Treatment on Microstructure and Compressive Properties of Low Carbon Steel

The effect of high pressure heat treatment on microstructure and compressive properties of low carbon steel were investigated by optical microscope,transmission electron microscope,hardness tester and compression test methods.The results show that martensite appears in low carbon steel at 1-5GPa GPa and 950°C for 15 minutes treatment,high pressure heat treatment can improve the hardness and compressive properties of the steel,the yield strength of the steel increases with increasing pressure,and its compressive properties are better than that treated under normal pressure quenching.

A BLOW-UP CRITERION FOR COMPRESSIBLE VISCOUS HEAT-CONDUCTIVE FLOWS

We study an initial boundary value problem for the Navier-Stokes equations of compressible viscous heat-conductive fluids in a 2-D periodic domain or the unit square domain. We establish a blow-up criterion for the local strong solutions in terms of the gradient of the velocity only, which coincides with the famous Beale-Kato-Majda criterion for ideal incompressible flows.

A BLOW-UP CRITERION FOR 3-D NON-RESISTIVE COMPRESSIBLE HEAT-CONDUCTIVE MAGNETOHYDRODYNAMIC EQUATIONS WITH INITIAL VACUUM

In this paper,we prove a blow-up criterion of strong solutions to the 3-D viscous and non-resistive magnetohydrodynamic equations for compressible heat-conducting flows with initial vacuum.This blow-up criterion depends only on the gradient of velocity and the temperature,which is similar to the one for compressible Navier-Stokes equations.

某油田联合站污水余热利用研究

原油集输系统中的热化学沉降脱水,需要将原油温度升高,这一过程将消耗大量能源,其燃料主要为天然气,加热产生大量的CO_(2)。文中通过对某油田联合站生产流程研究分析,同时结合站内用热情况,确定采用压缩式热泵替代现有燃气加热炉技术路线,用于冬季采暖和一段原油加热。项目实施后,每年可节能源8932×10^(4) MJ,折合标煤减少3481.8 t,减少CO_(2)排放2024.5 t,每年可节省能源消耗费用651.8万元,节能减排效果显著,该研究对油田联合站清洁能源替代,减少CO_(2)排放具有重要意义。

基于朗肯热力循环模型修正的热电厂热耗改进分析与实践

朗肯循环是热力发电厂的典型热力循环之一,主要包括等熵压缩、等压加热、等熵膨胀以及等压冷凝4个热力过程。在分析朗肯循环的基础上,结合实际工程案例,对4个热力过程进行优化和修正,提高了发电厂朗肯循环的效率,并结合《ASME PTC46电厂整体性能试验标准》,运用简单的Excel软件开发了机组效率分析软件,对发电厂蒸汽循环过程进行了详细的分析诊断,找出机组效率折损点以及优化提升方向。通过检修工作逐一落实热耗改进方案,实现了机组高效运行,节省热耗支出约2263万美元。

压缩空气储能地下储气库热力学改进模型研究

【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过多的不足。本文在全面分析地下储气库热力学模型理论基础合理性的前提下,先分析储气库热量计算偏差的形成根源;再提出改进模型。【结果】研究结果表明:现有的热力学计算解析模型忽略了CAES地下储气库在运行过程中温度分布的不均匀性,这种温度分布的不均匀导致储气室洞壁与压缩空气之间的对流换热模型失真,导致温度计算结果偏差大。考虑混合对流换热的改进模型二可以较好地解决储气阶段温度计算结果与真实结果之间偏差过大的问题。算例分析证明了改进模型二的合理性。【结论】本文的改进模型二可为CAES地下储气库容积优化设计与效率分析提供计算依据。

大温升蒸汽压缩式热泵系统优化研究进展

在“双碳”战略的背景下,大温升热泵技术不仅低碳节能,而且能够有效利用更低品位热能,向更高温领域发展。本文概述了大温升蒸汽压缩式热泵系统(大温升系统)优化的研究进展,从制冷剂、组件、循环优化、示范验证四个方面详细分析了大温升系统可行的优化手段。分析表明:当前大温升系统实践工程的常用制冷剂仍以R134a、R245fa等高GWP制冷剂为主;而在大温升制冷剂筛选方面,自然纯制冷剂中二氧化碳(R744)适用温度范围广泛,性能表现优异;水(R718)是大温升系统突破超高温(150℃)限制的潜力制冷剂之一;有机纯制冷剂发展迅速,R1234ze(Z)、R1336mzz(Z)等具有极低的GWP与优异的热力学性质;制备R32基、HFOs基、CO_(2)基混合制冷剂低GWP的混合制冷剂是当前具有前景的思路;在组件优化方面,压缩机变频技术等成熟技术为大温升系统组件优化提供了现行方案;磁悬浮轴承技术工业产品走向成熟,可有效降低大温升系统摩擦损失;线结构换热器技术等新兴技术为大温升系统提供了新的组件优化思路;在循环优化方面,补气/补液增焓与多级压缩等成熟技术为大温升系统循环优化提供了现行方案;喷射技术与涡流管技术等研究成果对大温升系统具有优化效果,但受到工程实践经验缺少、机理研究不明等方面限制;结合示范验证部分,补气增焓技术是目前适用范围最宽泛、工业运用最成熟的大温升系统优化技术,一定条件下可提高大温升系统性能系数20%以上;串联多级压缩技术与复叠式压缩技术是提高系统温升范围、保障低温供暖的有力手段。

硫黄硫化体系对天然橡胶性能的影响研究

以促进剂CBS用量作为变量,研究硫黄硫化体系对天然橡胶(NR)性能的影响。结果表明:促进剂CBS用量增大,混炼胶的F_(max)和F_(max)-F_(L)增大,t_(10)和t_(90)缩短,硫化胶的压缩生热降低,压缩变形减小;促进剂CBS用量为2.5份的有效硫黄硫化体系硫化胶的拉伸性能最好,促进剂CBS用量为3份的有效硫黄硫化体系硫化胶的tanδ峰值最小;在90℃以上,促进剂CBS用量为2和2.5份的半有效硫黄硫化体系硫化胶的热导率较高。

纤维素复合气凝胶的制备及保温隔热性能研究

利用化学交联和冷冻干燥技术制备了绿色环保的羧甲基纤维素钠(CMC)/明胶(GL)-戊二醛(GA)复合气凝胶(CL-A);研究不同比例的羧甲基纤维素钠(CMC)、明胶(GL)和不同含量的戊二醛(GA)对气凝胶微观结构、热稳定性、力学强度以及保温隔热等性能的影响。实验结果表明,羧甲基纤维素钠(CMC)与明胶(GL)比例为1:2且戊二醛(GA)添加量为15%时的复合气凝胶(C1L2-A15)的压缩强度高达3.03 MPa,较纯羧甲基纤维素钠(CMC)气凝胶增长了7倍左右;热导率低至0.022 W/(m·k),保温效果较好;多孔的三维网络更加致密,改善了复合气凝胶的形貌结构;复合气凝胶的残炭量高达37%,一定程度上提高了热稳定性。

吸收-压缩热泵回收高水分杂醇烟气余热研究

为了处理煤化工过程中产生的有害副产杂醇并回收热能,本文设计了一台以杂醇为燃料的热水锅炉,并在锅炉尾部加装了一种新型吸收-压缩复合热泵来回收烟气余热,通过Aspen Plus软件对热泵回收烟气余热流程进行模拟。结果表明杂醇烟气蕴含丰富潜热,采用该新型热泵能实现余热有效回收,额定工况下能使锅炉热效率提高11.01%。进一步研究了压缩机压比、回水温度和锅炉负荷对热泵性能的影响,并提出分别基于节能和碳减排效果的热泵性能系数COP_(a)和COP_(e)来全面分析热泵的运行性能。结果发现在压比为9.6时热泵COP_(a)和COP_(e)最高,且在压比小于9.6时,热泵性能会受回水温度升高的影响较大。随着锅炉负荷的增大,热泵系统的COP_(a)和COP_(e)先增大后减小。本文研究可为高水分烟气余热的深度回收和新型复合热泵的应用提供一些理论依据。

氟化钇对粉煤灰基堇青石陶瓷合成及性能的影响

本文以粉煤灰、滑石、氧化铝和氧化镁为原料,加入质量分数为0%、0.5%和1.0%的氟化钇,通过高温烧结制备了粉煤灰基堇青石陶瓷样品,研究了氟化钇掺量对样品的物相组成、显微结构及主要性能的影响。结果表明,氟化钇的引入可降低堇青石的生成温度,提高堇青石的物相转化率,显著改善材料的力学性能,同时对热学性能亦有一定积极影响。当氟化钇添加量为0.5%时,样品的综合性能最优。当烧结温度为1300℃时,XRD未见明显杂质峰,样品的体积密度为2.15 g/cm^(3),开孔孔隙率为7.49%,吸水率为3.49%,压缩强度为252.27 MPa,经5次热震试验后压缩强度仍然高至204.65 MPa,比热容为0.770~0.931 J/(g·℃)(25~150℃),热膨胀系数为2.54×10^(-6)℃^(-1)(100~800℃)。与不含添加剂的样品相比,添加0.5%氟化钇样品的体积密度增加了5.2%,开孔孔隙率降低了58.6%,吸水率降低了60.6%,而压缩强度增加了4.6倍,比热容增强而热膨胀系数降低。在粉煤灰基堇青石陶瓷的烧结过程中,氟化钇的引入可使其在较低的温度下形成液相,提高元素迁移率,促进晶粒发育完全且具有细化晶粒的明显效果。氟化钇作为一种有效的烧结助剂,微量的添加即可显著改善粉煤灰基堇青石陶瓷的综合性能。本工作拓宽了高效烧结助剂选择范围,可为高质量陶瓷材料的高温烧结提供一定参考。

磷石膏热处理制备免烧建材

这是一篇陶瓷及复合材料领域的论文。磷石膏排放量大,利用率低,资源化利用迫在眉睫。该研究以磷石膏为原料,经过激发预处理的磷石膏在不同温度下热处理,研究热处理温度对磷石膏的物相和微观结构,以及将其制备成免烧建材样品后的抗压强度、物相、微观结构的影响规律。结果表明,随着热处理温度的升高,二水石膏晶体结晶度增加,晶型发生转变,经过80℃热处理后的二水石膏晶粒致密,并且部分转变为半水石膏,由半水石膏水化重结晶生成的二水石膏对空隙进行填充,形成了结构致密,晶体相互粘合的内部微观结构,大大提高了免烧建材的抗压强度。免烧样品(磷石膏与水泥质量比为4∶1)养护7 d和28 d抗压强度达到36.45 MPa和38.12 MPa,并且浸水24 h的样品仍能保持21.03 MPa的抗压强度。

搅拌站废浆对水泥水化硬化的影响机理

为减少搅拌站废浆对环境影响和促进废浆回收利用,本文利用搅拌站废浆替代部分拌合水,通过凝结时间、抗压强度、电阻率、水化热、孔结构测试和水化产物分析,研究废浆对水泥水化硬化的影响。结果表明,掺入废浆后,试样的凝结时间缩短,抗压强度提高,DSC曲线中第二放热峰出现时间提前,3 d电阻率增大,水化产物生成量增多,孔隙率降低。废浆掺量越高,促凝效果越好,水化产物Ca(OH)_(2)生成量越高。当废浆掺量为100%(质量分数)、放置时间为12 h时,试样的初凝时间和终凝时间较空白组分别缩短了69和87 min, 28 d龄期时Ca(OH)2生成量增多,对试样强度提升效果最佳,较空白组3 d强度提升了36.2%,7 d强度提升了32.7%,28 d强度提升了8.1%。