土壤水力学特征对水平埋管换热能力的影响分析

以土壤毛管水力特征曲线为基础,通过数值模拟手段,计算分析地下水位线变化对水平换热埋管换热特性、土体热失衡风险和热泵机组技术经济特性的影响规律,并提出“单位热影响面积换热量”这一新的评价指标,讨论土壤水力学特征对水平埋管换热能力的影响规律。研究结果表明：随着地下水位线埋深变浅,埋管水平土壤含水饱和度从12%增加到100%时,在制冷工况下,水平管延米换热量增加了30%,出口水温降低了23%,单位热影响面积换热量提高了47%;制热工况下,水平管延米换热量增加了24%,出口水温升高了25%,单位热影响面积换热量提高了39%。地下水位线埋深和土壤中含水饱和度对水平埋管换热器地下换热效率影响显著。同时,不同水力特征曲线的蓄能土体热失衡风险具有差异性。     

Design of a seasonal thermal energy storage in the ground

Longterm storage of high quantities of thermal energy is one of the key problems for a widespread and successful implementation of solar district heating and for more efficient use of conventional energy sources. Seasonal storage in the ground in the temperature range of up to 90°C seems to be favourable from a technical and economical point of view. Preferably duct systems with vertical heat exchangers can be built in areas without ground water or low flow velocity compared with the geometry of the store and the storage period.

The thermal performance of such systems is influenced by the heat and moisture movement in the area surrounding the heat exchangers. Thermal conductivity and heat capacity are strongly dependent on the water content. This combined heat and moisture transport was simulated on the computer for temperatures up to 90°C. This model calculates the effective heat transfer coefficient and the heat capacity of the soil depending on water content, mineral composition, dry bulk density and shape of soil components. The computer simulation was validated by a number of laboratory and field experiments.

Based on this theoretical work a pilot plant was designed for seasonal storage of industrial waste heat. A heat and power cogeneration unit (174 kW_th) delivers waste heat during summer to the ground storage of about 15 000 m³ with 140 vertical heat exchangers of 30 m depth. About 418 MWh/a will be charged into the ground at a temperature level of 80°C, about 266 MWh/a should be extracted at temperatures between 40°C and 70°C and delivered directly to the space heating system. With this design an economic calculation gave energy prices of 39 US$/MWh which is of the same order as conventional energy prices.     

地源热泵间歇运行下土壤热湿迁移的实验研究

建立地埋管换热土壤热湿迁移过程的实验装置,对地源热泵间歇运行时不同进口流体温度及不同土壤体积含水率下土壤温湿度场的变化特性进行实验研究。实验结果表明∶间歇运行时,入口流体温度的升高会使土壤温度最大值升高,但不利于土壤温度的恢复,土壤体积含水率的增加在一定程度上有利于地下换热和土壤温度的恢复。系统开机后存在土壤温度上升的主上升区,此区温度增幅超过65%,关机后第18小时土壤温度基本恢复至初始温度;系统关停后在温湿度梯度的作用下会出现温度和含水率最大值后移的现象,热源对土壤温度和含水率的作用半径约为280和375 mm;开停比为1∶2时温湿度较1∶1能恢复得更低,合理设置停机时间有利于机组长期有效运行。     

Experimental study of the burning-cave hot water soil heating system in solar greenhouse

In the northern China areas, the traditional heating methods are widely used in solar greenhouse, for example: electric heating, hot air heating, hot water heating, burning-cave heating etc. If copying the assuring building indoor environment of constant heating ways into solar greenhouse, it will further increase building energy consumption, thus improving the efficiency of energy utilization, establishing appropriate growing environment, and realizing the agricultural waste recycling are important ways of consistent with the Chinese conditions, construction of sustainable development, improving the efficiency of the greenhouse production. To solve the problem of traditional heating method for high heating energy consumption, the inharmonious between greenhouse air temperature and soil temperature, uneven soil temperature, the research build the burning cave hot water soil heating system of solar greenhouse experimental platform in accordance with principle of energy cascade utilization. This experiment platform will transfer burning cave internal heat into soil heating system. The soil is evenly heated by system. Through testing the actual operation effect of the burning cave hot water soil heating system of new solar greenhouse, electric heating system, no taking any heating measures system, burning cave hot water soil heating system of solar greenhouse can improve the soil average temperature 5 ∼ 6 °C. This research provides experimental basis for practical applications and promotion.     

Finite difference modeling of heat distribution in multilayer soils with time-spatial hydrothermal properties

In this study, the heat distribution throughout the profile of unsaturated multilayered soil is determined using finite difference method while its thermal diffusivity varies with time and depth. First, the input parameters such as water content, dry density and sand content of the soil profile are provided. These data are coupled with the theoretical approaches to estimate thermal properties of soil such as thermal conductivity and thermal diffusivity of multilayered soil. Second, finite difference method is used to model heat distributions in soil profile taking into account the initial and boundary conditions. A continuity of heat flux between each layer is performed as a condition in the numerical model. A comparison of estimated temperature within time throughout the profile with the thermal probe measurements shows a satisfactory capacity of the numerical model. Finally, different cases of nonhomogeneous and homogeneous soil show that thermal response of homogeneous and nonhomogeneous soils are almost similar at average value of thermal diffusivity where hydrothermal characteristics of each soil layer (such as water content, dry density, and soil texture) are required to calculate this average value.     

场地有机污染土壤原位热修复过程中热质传递机制研究

针对现有原位热修复技术能耗较高且在修复过程中热质传递机制不明的问题,研究了现场试验过程中的土壤温度场变化、修复效果和能耗,采用数值模拟方法对温湿度场的变化进行了验证。结果表明：加热井呈正六边形排布时,修复区域的受热较为均匀,各测温点在修复35 d后,温度均达到200.0℃以上,修复后场地满足第二类用地筛选值;在标准状态下,试验过程中天然气用量总计685 664.0 m³,每修复1.0 m³污染土壤约消耗62.8 m³天然气;加热井热量主要为修复场地侧壁供能,对于位置低于加热井的土壤作用较小,加热井轴向土壤体积含水率分布较为均匀,但加热井底部体积含水率较高,修复区域底部水分不利于修复场地温度的提升,数值模拟和试验数据的吻合度较高,平均相对误差MRE为20%,为场地有机污染土壤原位热修复技术应用提供技术支撑。     

含水率对工程常用土导热系数影响的试验研究

岩土的导热系数对工程施工和工程运行有较大影响,研究不同含水率条件下的导热系数变化规律对岩土的导热理论和工程实践具有重要意义。根据《土工试验规程》制备出粗砂、中砂、细砂、粉砂和粘土等5种工程常用土,试验分析了不同含水率时的导热系数变化规律,并根据试验结果得到5种土导热系数随含水率变化的拟合公式。结果表明,5种土的导热系数均随含水率的增加呈非线性增加。含水率在0~15%时,导热系数由大到小顺序依次为粗砂、中砂、细砂、粉砂和粘土;含水率超出20%时,中砂、细砂、粉砂的导热系数变化趋于平缓并呈轻微下降趋势;含水率大于25%时,粘土导热系数呈下降趋势。     

土壤热湿传递下的直埋电缆载流量数值计算

针对土壤热湿过程对直埋电缆载流量的影响,修正土壤热湿耦合模型,联合MAXWELL方程组,建立电磁一热湿三场耦合模型.利用三场耦合模型和COMSOL Multiphysics软件按正交法计算不同敷设土壤类型、干密度和粒径下的YJV220.6/13×6直埋电缆载流量.通过对比正交计算结果的最大、最小载流量组的磁通密度、发热...     

土壤源热泵地下垂直换热埋管周围非稳态温度场的数值模拟

针对土壤源热泵地下垂直U型换热埋管,建立了周围土壤的非稳态温度场的数学模型,并利用隐式有限差分法进行了数值模拟。通过对制冷和制热工况的模拟,得到土壤温度沿径向的变化规律、埋管出水温度的变化规律及埋管的热作用半径的变化规律。     

太阳辐照下湿份分层土壤中热湿传输的数值模拟

考虑温度对土壤湿分迁移的影响，建立描述存在干饱和层时的土壤热湿传递的数学模型，并就自然环境和恒定太阳辐照下两种情况进行数值模拟，获得不同环境条件下土壤中温度和湿分分布以及水分蒸发的动态特性，分析干饱和土壤层对土壤热湿迁移与水分蒸发以及温度对土壤湿分传输的影响。     

自然环境下湿分分层土壤中热湿迁移规律的研究

建立描述存在干饱和层时的土壤热湿传递的数学模型并进行数值模拟，获得自然环境下土壤中温度、湿分分布以及水分蒸发的动态特性，分析干饱和土壤层对土壤热湿迁移及水分蒸发的影响。数值模拟获得实验支持。     

Performance of a gas engine driven heat pump for hot water supply systems

The present work aimed at evaluating the experimental performance of a gas engine heat pump for hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of ambient air temperature (10.9-25.3 °C), condenser water inlet temperature (33-49 °C) and at two engine speeds (1300 and 1750 rpm). Performance characteristics of the gas engine heat pump were characterized by water outlet temperatures, total heating capacity and primary energy ratio. The reported results revealed that hot water outlet temperature between 35 and 70 °C can be obtained over the considered range of the operating parameters. Also, total heating capacity and gas engine heat recovery decrease by 9.3 and 27.7%, respectively, while gas engine energy consumption increases by 17.5% when the condenser water inlet temperature changes from 33 to 49 °C. Total heating capacity, gas engine heat recovery and gas engine energy consumption at ambient air temperature of 25.3 °C are higher than those at ambient air temperature of 10.9 °C by about 10.9, 6.3 and 1.5% respectively. Moreover, system primary energy ratio decreases by 15.3% when the engine speed changes from 1300 to 1750 rpm.     

On the robustness, effectiveness and reliability of chemical and mechanical heat pumps for low-temperature heat source district heating: A comparative simulation-based analysis and evaluation

Our physical environment is endowed with unlimited amount of natural and artificial sources of energy at various low exergetic levels which leaves them almost impossible to be thermally utilized at such source states. The thermal upgrading of these low exergetic energy sources could render them amenable to various practical thermal usages. This paper provides a comparative study through simulations, of the effectiveness, robustness and reliability of the often two most promising heat upgrading technologies (the chemical and mechanical heat pumps) systems for the sustainable heat upgrading of low-temperature heat sources for district heating. The simulation results reveal that for a low to medium energy demand, low-temperature heat source upgrading using the chemical heat pumps seems more promising than the mechanical heat pumps, while the mechanical heat pump is best suited for high energy demand space heating. In the simulation, use was made of an artificial low-temperature heat source (a nearby pharmaceutical industry waste heat) with source temperature state of between 25 and 35 °C as the feed to the upgrading units. The high energy demand (assumed to be able to serve the space heating energy requirements of a given locality) was estimated to be 923 TJ/annum at a consumer-side temperature level of about 95 °C.

The selected most robust system (the mechanical heat pump-based process) for upgrading the low-temperature heat source at such given high energy demand has been conceptually designed.     

太阳能跨季节储热供热系统试验分析

介绍了一种太阳能-土壤源热泵联合供热系统,对其运行试验数据进行了分析,并对其运行能效比与两种单独由土壤源热泵供热的模式进行了比较。土壤温度的变化不仅与取热速率有关,还与地温的自动恢复能力相关。该试验建筑所在的土壤条件下地温的恢复能力为30～40MJ/d。采用太阳能-土壤源热泵联合系统能效比最高,土壤源热泵单机组双供系统次之,而土壤源热泵单机组单供系统能效比最低。太阳能跨季节储热及土壤源热泵联合供热系统适用于热负荷远大于冷负荷的建筑。     

Heat transfer of horizontal parallel pipe ground heat exchanger and experimental verification

The ground heat exchangers (GHE) consist of pipes buried in the soil and is used for transferring heat between the soil and the heat exchanger pipes of the ground source heat pump (GSHP). Because of the complexity of the boundary conditions, the heat conduction equation has been solved numerically using alternating direction implicit finite difference formulation. A software was developed in MATLAB environment and the effects of solution parameters on the results were investigated. An experimental study was carried out to test the validity of the model. An experimental GSHP system is installed at Y?ld?z Technical University Davupasa Campus on 800 m² surface area with no special surface cover. Temperature data were collected using thermocouples buried in soil horizontally and vertically at various distances from the pipe center and at the inlet and the outlet of the ground heat exchanger. Experimental and numerical simulation results calculated using experimental water inlet temperatures were compared. The maximum difference between the numerical results and the experimental data is 10.03%. The temperature distribution in the soil was calculated and compared with experimental data also. Both horizontal and vertical temperature profiles matched the experimental data well. Simulation results were compared with the other studies.     

A miniature thermoacoustic stirling engine

A miniature thermoacoustic stirling engine was simulated and designed, having overall size of length 0.65 m and height of 0.22 m. The acoustic field generated in this miniature system has been described and analyzed. Some efforts had been paid to coupling and matching, and a miniature thermoacoustic engine and some extra experimental components have been constructed. Analysis and experimental results showed that to obtain better performance of the engine, the diameter of the resonance tube must be chosen appropriately according to the looped tube dimension and the input heating power. It provided an effective way to miniaturize the thermoacoustic stirling heat engine. The experimental results showed that the engine had low onset temperature and high pressure amplitude and ratio. With the filling helium gas of 2 MPa and heating power of 637 W, the maximal peak to peak pressure amplitude and pressure ratio reached 2.2 bar and 1.116, respectively, which was able to drive a refrigerator, a heat pump or a linear electrical generator. The operating frequency of the engine was steady at 282 Hz.     

地源热泵岩土热物性测试简介与分析

地源热泵系统作为利用可再生能源的暖通空调技术,具有节能、环保等优点,在世界范围内被广泛使用。土壤作为地源热泵系统的冷热源,对整个系统有着至关重要的影响。不同建筑负荷特性要求系统对土壤的取放热量不同,二者的不平衡会使土壤的温度发生变化,影响整个系统的运行。对特定建筑地源热泵系统土壤的热物性测试是设计地埋管系统的重要依据。本文对热物性测试的理论依据进行了简单介绍,并对具体事例进行了分析计算,得出岩土体的导热系数等具体热物性参数,为地源热泵系统的精确设计提供了依据。     

孔隙率与含水率对砂质土样导热系数的影响

鉴于研究岩土体导热系数的变化规律及影响因素,对岩土的导热理论和工程实践的现实意义,利用热探针测定了不同孔隙率和含水率条件下的砂质土样导热系数,分析其变化规律,并用1stOpt软件得到孔隙率、含水率与导热系数的拟合公式。计算结果与试验结果表明,导热系数随孔隙率的增加而减小,随含水率的增加而增大,且在一定含水率下,导热系数随孔隙率的增加呈线性减小,孔隙率为0.468~0.511时,导热系数降幅为20.19%;在一定孔隙率下,导热系数随含水率的增加呈非线性增长,含水率0~10%时,导热系数增幅为338.38%,含水率10%~15%时,导热系数的增幅为8.83%。     

土壤蓄冷与释冷过程的模拟研究

综合蓄冷技术与土壤耦合热泵技术的优点，开创性地提出了以土壤作为蓄冷介质的集低温工况、空调工况和制热工况为一体的三工况型土壤蓄冷与土壤耦合热泵集成系统的新设想。并在能量平衡的基础上，建立了埋管管束内层及外层盘管蓄冷、释冷过程的数学模型。通过模拟计算，比较分析了内、外层单根盘管的蓄冷、释冷运行特性，并对单根埋管换热器蓄冷、释冷过程的传递冷量损失及垫层冷量损失进行了初步的分析。     

套管式中深层地埋管换热器传热建模及取热分析

为了研究无干扰换热条件下,中深层地热能的实际取热性能,文章通过数值模拟方法模拟计算了套管式中深层地埋管换热器的名义取热量。模拟结果表明,套管式中深层地埋管换热器的名义取热量随着钻孔深度、大地热流、循环水流量、当地大气年平均温度的增加而增加。套管式中深层地埋管换热器周围土层的地质条件分布也影响着中深层地埋管换热器的名义取热量,具体表现为浅层土层的导热系数越小,中深层地埋管换热器的名义取热量越大;深层土层的导热系数越大,中深层地埋管换热器的名义取热量也越大。通过调整地埋管换热器的相关参数,并选择合适的地埋管埋设地点等优化措施,可使套管式中深层地埋管换热器达到可观的名义取热量。