共查询到19条相似文献，搜索用时 46 毫秒
1.
相变材料回填地埋管换热器蓄能传热特性 总被引：2，自引：1，他引：1
为了探讨相变回填材料固液相变对地埋管换热器蓄能传热性能的影响,建立了带有相变的垂直U型埋管换热器传热数学模型,并利用显热容法对相变材料的相变问题进行了处理。基于模型的数值求解,分析了夏冬季运行工况下相变材料固液相变对U型埋管换热器蓄能性能及其周围土壤温度热响应特性的影响规律,结果表明：同样条件下,相变材料固液相变会减缓埋管周围土壤温度变化趋势,缩小埋管热影响区域;夏季工况采用较低相变温度、冬季采用较高相变温度的相变材料均可以明显改善其换热效果,同时相变潜热大的相变材料可以明显增加地埋管的蓄能效果。研究结论对于缓解土壤热影响区域、改善地埋管换热器的蓄能传热性能具有重要意义。 相似文献
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土壤蓄热-放热过程中地埋管周围土壤温度特性模拟 总被引：2，自引：1，他引：1
为探索内蒙中部地区地源热泵蓄热-放热过程中地埋管周围土壤温度变化特性,以垂直U型地埋管周围土壤为研究对象,基于有限元分析法建立了二维非稳态传热物理数学模型。在与试验结果进行验证的基础上,对土壤蓄热、放热和蓄热-放热耦合过程进行模拟研究。分析了热作用半径、单位管长换热量和土壤温度随热泵运行时间及运行模式的变化规律;单一条件下的蓄热、放热以及蓄热-放热耦合模式下土壤热平衡问题,探讨了流体入口流速、温度、土壤类型和热泵运行模式等因素对土壤温度场的影响。研究结果表明:热作用半径随蓄热时间的增加而增大且逐渐趋于平缓,热泵运行25和28 d后,热作用半径分别为3.3和3.4 m;流体入口温度对热作用半径及单位管长换热量影响较大但流体流速影响较小,流体入口温度和速度分别为40、60℃和0.6、1.2 m/s时,对应热作用半径分别为3.7、4.5和3.5、3.6 m。合理的间歇运行模式对换热量及埋管周围土壤温度的恢复均有改善;土壤导热系数越大土壤温度恢复时间与效果越佳,土壤导热系数为3.1 W/(m?K)时恢复后温度为9.3℃(土壤初温9.5℃)。此外,蓄热-放热耦合模式下换热量不等对土壤热平衡具有较大影响。试验验证表明,所建模型具有一定的准确性其相对最大误差为5.35%。 相似文献
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为了探讨不同因素对桩基螺旋型地埋管换热性能的影响,建立了桩基螺旋型地埋管换热器的传热数学模型,分析了桩基直径、桩基深度、螺旋管组数、土壤类型对桩基螺旋型地埋管换热量及土壤温度分布的影响,结果表明:增加桩基直径有利于改善桩基的蓄热能力、提高螺旋型埋管的换热性能,但是单位管长换热量会减小,因此,桩基直径不可无限制增加;桩基深度的增加有利于提高桩基螺旋型埋管换热器的换热量,而且对单位长度桩基的换热量影响很小,因此,可以通过增加桩基深度来提高换热量;同样条件下,黏土、砂土、砂岩中砂岩最有利于桩基换热器换热,土壤温度上升速率和幅度最低,而黏土换热效果最差,土壤温度上升速率最快;此外,螺旋管组数越多,换热器换热量越大,但是单位管长换热量会大幅下降。试验验证表明:所建桩基螺旋埋管模型预测出的换热量与土壤温度值与对应试验值吻合较好,其最大相对误差分别在9.7%与9.2%以内。 相似文献
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准确获取管群换热器在复杂土壤中的传热情况,有利于合理设计地源热泵系统。该研究建立了考虑地下水渗流的三维管群分层数值模型,通过引入区域热效率(E)和动态性能损失(Dynamic Performance Loss,DPL)2个指标,评估不同因素对渗流作用下管群在分层岩土中传热的影响。结果表明:当渗流速度为100m/a且渗流层厚度较大时,管群在分层岩土中的传热可以简化为在均质岩土中的传热;通过调整不同导热系数的土壤层的位置和厚度,管群区域热效率的变化可以忽略不计;变等效入口流速和变入口温度的变化对管群区域热效率的影响可以忽略。在渗流速度为100 m/a、连续运行2 000 h、管间距为3 m的叉排管群,下游DPL仅比管间距为6 m的顺排管群高1.27个百分点。因此,当渗流速度为100 m/a且渗流层厚度较大时,建议顺排和叉排的管间距分别为4和3 m。此外,渗流速度越大,管群的区域热效率越大,DPL越低,且趋于稳定的速度越快。研究结果可为合理设计热渗耦合分层土壤中的地埋管管群以及有效缓解土壤热堆积提供参考依据。 相似文献
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针对土壤源热泵系统节能运行的控制需求,该文提出一种面向系统运行控制的地埋管换热器Hammerstein-Wiener(H-W)模型。基于H-W模型结构特性和非线性特征,结合地埋管换热器168 h的实时进出、水温度数据,利用Levenberg-Marquardt寻优算法对H-W模型进行辨识,在此基础上,以48 h的逐时进水温度作为模型输入,模型预测值与相应数据的拟合度为99.44%,验证了H-W模型的预测结果。在连续1 000次的H-W模型辨识与验证测试中,拟合度高于90%的占83%。地埋管换热器H-W模型的辨识速度快、预测结果精度较高,并在持续的在线预测中显示了较强的稳定性,为土壤源热泵系统在线优化控制的实施提供了保障。 相似文献
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模式搜索算法在地埋管换热器热阻确定中的应用 总被引：3，自引：3，他引：0
为了准确确定土壤源热泵系统地埋管换热器的热物性参数和热阻,该文以地埋管换热器线热源模型为基础,结合土壤的热响应试验,提出了一种应用模式搜索算法确定土壤综合导热系数和地埋管换热器热阻的方法。搜索算法实施时,热阻作为一个待定参数,不必考虑换热器的各项物理参数,降低了运算工作量。试验实测结果表明,应用模式搜索算法后该文试验条件下确定的土壤综合导热系数的相对误差为1.42%,热阻的相对误差为1.73%;通过与其他方法比较,模式搜索算法确定的参数的相对误差较小,算法精度较高,可靠性较高;该研究结果为土壤源热泵系统的设计与应用提供参考。 相似文献
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随着能源压力的日益增大,世界各国都十分重视可再生能源的利用与开发,地源热泵技术作为一种清洁、高效的可再生能源,近年得到了较快的发展。该文利用无限长线热源传热计算模型,讨论了介质内过余温度场的分布特性。结果表明：介质内温度响应在孔壁处最大,随离孔壁距离的增加呈指数衰减,随时间的增加而增大;热传播区域随时间的增加而增大,随介质的热扩散系数的增加而增大。针对工程中群埋管换热器情况,利用叠加原理计算群埋管的孔壁温度,定义换热器的热响应半径为其他钻孔引起的过余温度影响系数≤5％时相邻钻孔中心线之间的垂直距离。在大量计算分析基础上,提出了竖直埋管换热器热响应半径计算方法。计算结果表明该文方法具有较好的计算精度,竖直埋管换热器的热响应半径随岩土热扩散系数增大而增大,随持续运行时间增加而增大,随钻孔排数增加而增大,随着钻孔孔径增大而增大;钻孔布置方式不同对钻孔热响应半径的影响较明显,相同布置方式下钻孔直径对其热响应半径的影响较小。针对工程中常见的115和135 mm 2种孔径,绘制了不同岩土介质下钻孔单排、双排和三排以上布置时热响应半径-运行时间的关系曲线。工程算例表明该文方法简单方便,为工程设计提供了便利。 相似文献
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土壤源热泵系统运行特性的快速预测方法 总被引：3，自引：3，他引：0
土壤源热泵系统的逐时运行特性预测对于系统设计和运行策略评估是十分重要的。该文在分析地埋管换热器传热基本原理的基础上,通过与动态负荷作用下"负荷叠加"的G函数法的对比,提出了一种热泵系统运行特性的快速预测方法。在进行年逐时运行特性预测时,通过与采用有限长线热源模型加准三维钻孔热阻模型换热器的某热泵系统算例计算结果的比较,该文预测方法对应的主要性能指标相对误差均低于1%,计算耗时仅为原方法的1/1000。该方法对于土壤源热泵系统的设计和应用具有十分重要的意义。 相似文献
9.
《土壤通报》2017,(6):1338-1346
为了探讨不同因素对竖直U型地埋管周围土壤传热规律影响,在试验验证基础上,基于有限元分析法建立二维非稳态物理数学模型,分析了土壤类型、地埋管管径、热流密度、地埋管管脚间距和热泵运行模式对竖直U型地埋管周围土壤温升率和热作用区域的影响。研究表明:地埋管附近土壤温升率随热泵运行时间的增加呈现先迅速增大后下降最后趋于稳定的变化规律;热作用区域随热泵运行时间的增加而增加;轻土适合作为地源热泵长期运行的蓄热材料;土壤温升率及热作用区域均随地埋管管径和热流密度的增加而增加;热泵间歇运行时,土壤温升率曲线表现为先上升后下降,且随热泵开停比的减小而减小。在本研究计算条件下,地埋管管脚间距宜取120 mm。经试验验证,本研究所建模型吻合度较好,其最大误差为1.4%。 相似文献
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Glenn GM Klamczynski AK Holtman KM Shey J Chiou BS Berrios J Wood D Orts WJ Imam SH 《Journal of agricultural and food chemistry》2007,55(10):3936-3943
A heat expansion process similar to that used for expanded bead polystyrene was used to expand starch-based compositions. Foam beads made by solvent extraction had the appearance of polystyrene beads but did not expand when heated due to an open-cell structure. Nonporous beads, pellets, or particles were made by extrusion or by drying and milling cooked starch slurries. The samples expanded into a low-density foam by heating 190-210 degrees C for more than 20 s at ambient pressures. Formulations containing starch (50-85%), sorbitol (5-15%), glycerol (4-12%), ethylene vinyl alcohol (EVAL, 5-15%), and water (10-20%) were studied. The bulk density was negatively correlated to sorbitol, glycerol, and water content. Increasing the EVAL content increased the bulk density, especially at concentrations higher than 15%. Poly(vinyl alcohol) (PVAL) increased the bulk density more than EVAL. The bulk density was lowest in samples made of wheat and potato starch as compared to corn starch. The expansion temperature for the starch pellets decreased more than 20 degrees C as the moisture content was increased from 10 to 25%. The addition of EVAL in the formulations decreased the equilibrium moisture content of the foam and reduced the water absorption during a 1 h soaking period. 相似文献
13.
感热和潜热的估算在陆气、海气相互作用的研究中具有重要意义;波恩比法是估算感热和潜热的重要方法,它以其低廉、简单和无需知道近地层动力特征的特点而被普遍使用。利用黄土高原陆面过程试验(LOPEX)的观测资料,研究了半干旱区热量在土壤中传递的慢过程对波恩比法估算感热和潜热的影响。结果发现,反映慢过程的传输线法和四边形法比不考虑慢过程的常规法在波恩比法估算感热和潜热的精度方面有一定提高,而反映慢过程的三角形法估算精度低于常规法,究其原因是三角形法计算复杂所致。所以,扣除计算中的不确定因素,考虑慢过程在一定程度上可以提高半干旱区波恩比法的估算精度。 相似文献
14.
Leon Jaccard Pierre Lehmann Marcello Civilini Marco de Bertoldi 《Compost science & utilization》2013,21(3):10-14
? The feasibility of yard waste composting in a closed continuous reactor with heat recovery has been investigated. Results obtained in this research are reported and discussed. In the system, the recovered energy (heat) can be transformed by a heat pump in hot water both for domestic and for residential heating. The organic fertilizer produced can be used in horticulture. 相似文献
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G.P. Sparling 《Soil biology & biochemistry》1981,13(5):373-376
Amending soils with glucose (5 mg g?1) resulted in an immediate increase in microbial activity and within 30 min the rates of heat output and respiration at 22° C were increased by up to 17.8 and 23.4 times, respectively. The increased rate of heat output remained stable for up to 6 h and there was good correlation with the amount of CO2 respired. The soil biomass was calculated by the method of Anderson and Domsch (1978). The rate of heat output of the biomass varied in different soils and ranged from 11.5 to 83.7 Jh?1 g?1 biomass C. In glucose-amended soils, however, the rate of heat output was much more consistent; the soils were in two groups having between 169–265 Jh?1g?1 biomass C or 454–482 J h?1 g?1 biomass C, both the latter two soils were from pasture. The increased rate of heat output from the amended soils was lower than expected from the respiration rate and the heat of oxidation of glucose, suggesting that a proportion of the CO2 respired was from catabolism of substrates other than glucose. Use of 14C-glucose confirmed that between 57–91% of the CO2 was derived from the glucose substrate. 相似文献
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Amorphous soil inorganic materials, specifically allophane. are believed to have a marked effect on soil properties and soil productivity, even in a relatively small amount, due to their large specific surface area, peculiar nature of surface and high chemical reactivity. They seem be present in soils, more or less, but determination of their content is generally semiquantitative or not fully reliable, because allophane includes aluminosilicates in a wide range of chemical composition and of properties, and any satisfactory, quantitative analytical method has not been established. 相似文献
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铁线莲品种耐热性分析及评价指标筛选 总被引：2，自引：0，他引：2
为探讨南方夏季高温对铁线莲生理生化的影响,筛选耐热品种并建立耐热性评价体系,于2015年5-8月,以20个铁线莲品种为试验材料,对其高温半致死温度及高温胁迫下植株热害指数(HII)、相对电导率(REC)、萎蔫程度(WD)等10个生理生化指标性进行测定,并采用主成分、隶属函数、聚类分析和逐步回归等方法对其耐热性进行综合评价。结果表明,20个品种可以分为耐高温、较耐高温、高温较敏感和高温敏感4个类型,其中罗曼蒂克、如古和浪子耐热性较强;高温半致死温度可作为耐热性评价的指标;建立了以HII、REC、叶绿素(CC)和丙二醛(MDA)含量以及超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性等6个指标为变量的铁线莲耐热评价模型。本研究结果为铁线莲品种栽培适应性评价体系的建立和耐热型铁线莲品种选育提供了理论依据。 相似文献
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Heat inactivation characteristics differed for acidic (A), neutral (N), and basic (B) broccoli peroxidase. At 65 degrees C, A was the most heat stable followed by N and B. The activation energies for denaturation were 388, 189, and 269 kJ/mol for A, N, and B, respectively. Reactivation of N occurred rapidly, within 10 min after the heated enzyme was cooled and incubated at room temperature. The extent of reactivation varied from 0 to 50% depending on the isoenzyme and heating conditions (temperature and time). The denaturation temperature allowing the maximum reactivation was 90 degrees C for A and horseradish peroxidase (HRP) and 70 and 80 degrees C for B and N, respectively. In all cases, heat treatment at low temperatures for long times prevented reactivation of the heated enzymes. Calcium (5 mM) increased the thermal stability of N and B but had no effect on reactivation. The presence of 0.05% bovine serum albumin decreased thermal stability but increased the extent of reactivation of A.. 相似文献
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Heat transfer through covering materials of greenhouses 总被引：4，自引：0，他引：4
Conductive, convective and radiative heat transfers are evaluated through single and double walls for a series of materials used as greenhouse covers. Among others, radiative exchanges explicitly take into account the far-infrared partial transmittance of many synthetic materials. The k-values are proposed for cloudless sky, wind speed = 4 m s−1, outside temperature = −10°C. and inside temperature = 20°C. The influence of the wind speed, overcast sky, rain or condensation and thickness of the wall is investigated. 相似文献