Through the establishment of a mathematical model of underground aquifer which couples water flow with heat transfer,the temperature of pumping well was simulated and analyzed with different aquifer thickness,with temperature variation curve,the design spacing of groundwater heat pump pumping-injection wells was discussed.The simulation results show that,the effect of heat transfixion can be weakened with the increase of aquifer thickness by keeping the spacing of pumping-injection wells;With the same aquifer thickness,the spacing of pumping-injection wells may change within a certain range,but the heat transfixion degree does not change much.With the increase of aquifer thickness,the design spacing of pumping wells decreases.
For solar absorption cooling systems, it is difficult to generate lower chilled water for dehumidifying and cooling, as well as facing intermittency problems. In this work, the novel SACV system for indoor temper-ature and humidity control is proposed, which integrates the SSAR subsystem, the VCR subsystem, and the VMD subsystem. The VMD subsystem and the VCR subsystem solve the dehumidification difficulty and all-weather heating and cooling problems, respectively. This work also proposes a method for deter-mining the collector area that avoids frequent start-ups and shutdowns of the VCR subsystem. Besides, a thermodynamic model of the SACV system is established and validated, and a systematical performance analysis of the SACV system is carried out. For the SACV system, the sensitivity of the parameters to the MCOP is also discussed. Results indicate that the outdoor air temperature, the latent heat load ratio, and the solar radiation intensity are the key parameters for designing the SACV system; further, the evapora-tion temperature and the permeate side pressure are the key parameters for the SACV system optimiza-tion. The SACV system is more suitable for high-humidity environments. Moreover, during the cooling season, the SACV system of a commercial building can realize a power saving rate of 39.82% compared to the conventional VCR system. The proposed SACV system of a commercial building can reduce 19653.59 kg/year carbon emission compared to the conventional VCR system in Nanjing. The carbon reduction rate of the SACV system in the selected cities is rather similar, about 36.78%-39.79%.(c) 2023 Elsevier B.V. All rights reserved.
High photovoltaic (PV) module temperature leads to the degradation of electrical efficiency, and passive PV thermal management systems, such as phase change materials (PCMs) and heat pipes (HPs), have been widely adopted to address this challenge. Due to the low thermal conductivity of PCM and the limited heat exchange capacity in the HP condensation section, this paper proposes a novel configuration for a PV thermal management system utilizing a phase change material/heat pipe coupled module (PV-PCM/HP). The experimental results showed that the performance of the coupled PCM/HP system was superior to that of the single system. A numerical model was developed to simulate and analyze the temperature variation and coupled heat transfer characteristics of the PV-PCM/HP system. The main components of heat transfer gradually change from PCM (PCM-dominated) to HP (HP-dominated), and PCM even plays a negative role during the solidification stage, which means that the coupled thermal management depends on HP only. Four design parameters (the number of HPs, PCM thermal conductivity, PCM phase change temperature, and PCM thickness) of the PV-PCM/HP system are discussed to investigate the effects on the performance of the PV-PCM/HP thermal management system. This shows that the increase in the number of heat pipes and PCM thickness can effectively improve the performance, but they should be determined according to technical and economic analysis. When the PCM thermal conductivity is >2.7 W/(m.K), it has little effect on thermal management performance under the conditions described in this paper. The value of the PCM phase change temperature should be determined according to actual weather conditions, and the purpose is to make the PCM melting period coincide with the period of higher solar radiation and lower phase change temperatures.
空气源热泵"监测外管温变化及运行时间"的化霜判断方法,利用了结霜现象对热泵系统运行参数的时空累积影响效应,需要累积到一定结霜量时才能准确识别,无法实时判断当前换热器的结霜情况.基于此痛点问题,提出一种结霜量预测技术,通过分析结霜过程相关原理,利用神经网络和空气源热泵系统特性,搭建结霜量预测模型,从而对结霜量进行准确识别.试验结果表明,搭建的结霜量预测模型能够实时计算室外换热器的结霜量,且与实际结霜量相比误差在15%以内,对探索更精细更灵敏更智能的化霜判断方式具有参考意义.
In this work, the concept of hot gas direct defrosting（HGDD） of air-source heat pump is proposed at first, which does not need to add a hot gas bypass branch and the refrigerant flow direction during defrosting is the same as that of heating cycle.In the next, the flow rate demand of HGDD was analyzed, the flow rate curve of the electronic expansion valve was improved, and a biconical electronic expansion valve was designed to meet the flow rate demand during heating and hot gas direct defrosting.Finally, the heat loss of R32 refrigerant in the expansion valve under different expansion valve pulses during the hot gas direct defrosting process was simulated using CFD technology, and the results showed that there existed an optimal expansion valve opening to produce the largest defrosting heat at expansion valve outlet.
针对微型无油涡旋制冷压缩机的工作过程,建立了包含径向和轴向间隙的三维流动模型,通过CFD方法进行了数值模拟,分析了压缩机工作腔内部温度、压力的分布情况及流动特性,得到了冷凝温度、泄漏间隙对压缩机容积效率和等熵效率的影响规律.研究结果表明:固定轴向间隙为5µm,径向间隙从 5µm变化到 11µm时,容积效率从86.38%下降到75.11%,等熵效率从 67.78%下降到56.18%.固定间隙均为 7µm,冷凝温度由50℃变化到 55℃的过程中,压缩机的容积效率从 75.35%下降到 73.49%,等熵效率由 59.03%下降到 56.79%.要使压缩机容积效率达到 80%以上,应保证轴向间隙小于 6µm,径向间隙小于9µm,为微型涡旋压缩机的设计提供参考.
氢能技术备受全球关注,被誉为21世纪发展前景最为广阔的二次能源之一.然而,随着氢燃料汽车的广泛使用,车库等密闭空间内发生高压氢气泄漏事故的风险也随之增加.由于这种事故的多样性,尤其是高压氢气泄漏在密闭空间内的扩散特性的复杂性,因而需要进一步研究和探讨这一问题.为解决密闭空间内高压氢气泄漏的安全问题,采用了数值计算和理论分析相结合的方法,分析了不同自然通风条件下空间内氢气的通风情况,总结了氢气在空间内的扩散和分布规律.主要结论如下:在自然通风条件下,通风口的长宽比越接近 1,通风效果越好;将通风口布置在长边的中心位置,效果也更佳;通风口面积增大对氢气扩散影响不大,但在一定范围内增大通风口的面积,会使得高压氢气扩散的初期更加紊乱;提高通风口的高度对提高通风效果作用显著,将通风口高度从 0.5m升高到 2.5m,相同时间、位置处的氢气体积分数能降低 10%左右.研究了高压氢气在受限空间内的扩散特性及参数,研究结果可为氢能技术在受限空间内的安全设计和措施提供参考.
相变材料可有效提高建筑围护的储热能力,为最大限度提高相变砂浆的储能调温能力,选用硬脂酸、月桂酸进行配比设计,采用玻化微珠作为多孔载体,研究了相变复合体系的最佳制备条件.结果表明,随着吸附温度的升高,玻化微珠对硬脂酸-月桂酸复合相变材料的容留率先升高后降低,最佳吸附温度为 55℃.随着吸附时间的增加,玻化微珠对硬脂酸-月桂酸复合相变材料的容留率快速升高后趋于平缓,最佳吸附时间为 60min.相比玻化微珠,硬脂酸-月桂酸/玻化微珠复合体系加热延时约 760s,蓄热时长 300s,冷却延时约 640s,放热时长 680s.选用质量损失率最低的环氧树脂-水泥对复合相变材料进行封装.复合相变材料掺量越多,相变保温砂浆的保温性能越好,可有效控制室内温度的波动变化.
相变储能材料通过吸收大量热量的特性在相态转变过程中储能能力优异,因此成为一类优秀的储能材料.将其应用于混凝土中可获得储能性能卓越的新型混凝土材料,从而实现能量在空间和时间上的合理应用.以石蜡为相变材料,膨胀珍珠岩为定形基底,利用真空吸附法使石蜡包裹在膨胀珍珠岩内,制作成相变骨料.最后使用差式扫描量热分析,扫描电子显微镜分析、红外光谱分析以及热可靠性分析等分析方法,对定相变骨料的结构、储热性能及稳定性进行表征分析.
地埋管具备节能、环保的特点,可用于处理工程内部余热,同时埋管换热会对工程口部的空气产生一定影响.为了分析在岩土不同初始温度的情况下,埋管换热对口部的影响.基于有限元软件,建立了埋管换热模型,岩土初温分别取值 14℃、18℃、22℃,得出了口部内空气的温湿度分布情况.结果发现岩土初温为 14℃、18℃、22℃时,口部内空气的温度场分布存在一定的差异.在埋管换热的过程中,口部横截面内的空气从上至下,温度均出现分层.上层空气温度高于下层的空气温度.而相比较于埋管传入岩土侧的热量,传入空气的热量很小.埋管换热同样影响了空气的相对湿度,空气的相对湿度分布与温度分布相反,研究发现相对湿度的降低有利于口部防潮.
旨在以"双碳目标"为引领,以工程认证和国家级一流专业建设为契机,提炼西南交通大学环专业的专业定位与培养目标,构建工程教育认证背景下人才培养课程体系,对培养符合新时代要求和国际工程教育认证标准的复合型人才具有重要意义.
对低GWP制冷剂R515B在双螺杆单级蒸汽压缩式热泵系统中的性能进行了研究.通过实验对比研究R515B直接替换R134a时系统的性能变化,结果表明:R515B的制热量比R134a降低 27%左右,消耗功率比R134a降低约28%,制热COP比R134a平均提高 1%,排气温度降比R134a低约 15℃.同时建立热泵系统仿真模型,预测R515B在较高冷凝器出水温度下热泵系统的性能,结果表明:R515B具有优良的热力学性能和循环性能,在采用单级蒸汽压缩循环的中高温热泵系统中可实现 88℃以下的高冷凝器出水温度.
采用数值模拟与试验测试相结合的研究方法,对风机盘管内流场优化进行研究.根据风机盘管内流场CFD分析结果,设计符合空气动力学要求的风机出口导流板,并在样机上进行对比实验验证.实验结果显示安装导流板的风机盘管机组在额定流量工况静压提升约 3Pa,机组效率提升 1.62%,制冷量略微下降.
以重庆某办公楼工程为例,针对空调系统冷源方案,结合当地能源政策及空调负荷特点,对常规制冷系统、冰蓄冷空调系统两个方案进行了系统经济技术分析和比较.与常规空调系统相比,冰蓄冷空调系统装机容量小,可节省配电设施费及运行费用,其中年运行费用节约 29.6万元.但由于冰蓄冷系统增加了蓄冰设备,其初投资比常规空调系统增加约 157 万元.因而需要人为制定合理的运行策略,确保经济效益和社会效益.
跨临界CO2 制冷是一种以CO2 作为制冷剂气体冷却过程在临界点以上的新型制冷技术.对近年来CO2 制冷技术的发展进行了概括及分析.针对传统制冷剂与CO2 制冷剂的特点,重点分析了二者在物理性质上的区别,说明了CO2 作为新型制冷剂的可取性;针对提升制冷系数的目标,讨论了两级压缩、膨胀机、回热器的工作原理以及对系统性能的影响.综述了新型双级压缩CO2 制冷循环的研究现状,归纳了CO2 制冷循环进一步改善性能的技术途径.
《建筑环境学》因涉及领域多,覆盖的知识点广而散及理论体系庞大,导致学生学习时不易形成较强的知识系统性,不利于激发学生学习积极性.针对《建筑环境学》课程现状,提出将学科竞赛与建筑环境学课程相融合的教学模式.该教学模式以学科竞赛为牵引,以虚拟化模拟平台为载体,以课程理论教学为能量补给,重建课程目标.从合理分配课程学时、优化专题实训内容、注重多元考核方面进行改革,并结合实际案例开展教学设计和实践.教学效果表明该教学模式发挥了学生的主体作用,调动了学生学习的积极性,有效达成了课程目标,提高了学生综合素养.
飞行器综合热管理是发展高性能飞行器的必要手段,高效的传热装置是综合热管理的重要环节.热管因传热效率高、等温性好、重量轻、尺寸小、维护方便的特点在航空领域展现出巨大的应用前景.概述了热管技术在航空领域的应用需求和面对的特殊条件,依次分析了基于毛细力回液的热管、重力热管、旋转热管、泵驱回路的工作原理和在航空领域的应用场景及适用性,提高抗过载能力和适应飞行姿态变化是热管技术在航空领域应用的主要问题和研究重点.
以夏热冬冷地区某三甲综合医院为例,对比一次回风洁净空调系统和新风热回收梯级处理洁净空调系统的空气处理过程计算,分析系统节能及空调季的运行经济性,确定新风热回收梯级处理热湿变化过程的洁净空调系统,既能满足功能需求,又能实现系统节能.
建设依托网络信息技术的线上教学与常规课堂讲授、辅导的线下教学相融合的高质量本科课程是推进课程改革创新的重要工作,是培养创新创业型、工程应用型人才的根本保证.围绕建环专业的工程热力学课程,基于线上线下模式对课程教学模式改革,通过对开课前、课前、课中和课后环节分别开展线上线下闭环式教学设计,从线上教学资源建设、团队建设、考核评价机制及教学手段与方法改革等方面进行了实践探索,形成持续改进机制,旨在提供课程教学发展新思路.
