分离式螺旋热管管外融冰放冷特性分析

在提出分离式螺旋热管蓄冷空调系统的基础上,建立了螺旋热管管外融冰放冷过程的理论模型;分析了蓄冷桶内融冰量及放冷量随时间的变化关系。研究结果表明,在蓄冷桶进口水温一定的情况下,外融冰的循环水流量越大,其融冰放冷过程就越快;在外融冰循环水流量一定的情况下,放冷过程随蓄冷桶进口水温的升高而加快。     

封闭式喷雾冷却系统启动时间

以蒸馏水为冷却工质,对冷凝器内置的封闭式光滑表面喷雾冷却系统进行了启动时间变化规律的实验研究,结果表明喷雾系统不同模块最优启动顺序为冷凝器、泵和加热器。采取6种不同的启动顺序,启动后加热表面的温度不均匀度均小于0.25 ℃。在最优启动顺序下,研究了冷却水流量、泵高度、加热功率和喷雾流量对启动时间的影响。随冷却水流量和喷雾流量增加启动时间缩短,随泵高度增加启动时间略微增大,随加热功率增大启动时间先增大后减小。启动时间影响程度由大到小的因素依次为喷雾流量、冷却水流量、加热功率及泵相对于加热表面的高度。喷雾工质流量由10 mL/min增大到35 mL/min时,封闭式喷雾系统的启动时间缩短了5 000 s。同样操作条件下,封闭式系统的启动时间比开放式系统延长15%~20%。     

Experimental Investigations on Latent Heat Storage Unit using Paraffin Wax as Phase Change Material

Thermal performance of a latent heat storage unit is evaluated experimentally. The latent heat thermal energy storage system analyzed in this work is a shell-and-tube type of heat exchanger using paraffin wax (melting point between 58°C and 60°C) as the phase change material. The temperature distribution in the phase change material is measured with time. The influence of mass flow rate and inlet temperature of the heat transfer fluid on heat fraction is examined for both the melting and solidification processes. The mass flow rate of heat transfer fluid (water) is varied in the range of 0.0167 kg/s to 0.0833 kg/s (1 kg/min to 5 kg/min), and the fluid inlet temperature is varied between 75°C and 85°C. The experimental results indicate that the total melting time of the phase change material increases as the mass flow rate and inlet temperature of heat transfer fluid decrease. The fluid inlet temperature influences the heat fraction considerably as compared to the mass flow rate of heat transfer fluid during the melting process of the phase change material.     

回收湿焓的新风换气节能空调换热部件的两相流模拟

本文着眼于一种回收湿焓的新风换气节能空调,基于Volume of Fluid算法,建立其核心换热部件波纹板换热器板外两相流传热传质的计算模型,并利用该模型模拟分析了壁面热流密度、喷淋水入口温度、喷淋水量、气相进口速度及板间距等因素对板外传热性能的影响。结果表明:热流密度对壁面温度、两相界面温度的影响是线性的;壁面热流密度增大、冷却水喷淋密度减小、气相进口速度提高、板间距减小对传热传质效果具有强化作用。     

Sustainable energy storage – with hot air,or cold air or liquid air

In memory of Sir David John Cameron MacKay FRS FInstP FICE (22 April 1967 – 14 April 2016). David was passionate about sustainable energy. One key element for sustainable energy is energy storage. As a small tribute, this article presents a review from a physics perspective of the thermodynamics of compressed air energy storage. Firstly, I treat adiabatic compressed air energy storage, where the heat of compression of the air is kept in the compressed air. Then I discuss improvements that can be made by combining compressed air energy storage with external heat stores. Next, I address isothermal compressed air energy storage, where the temperature is allowed to equilibrate with the environment. In each case, I consider two scenarios: underground caverns and underwater airbags. Finally, I address the case where the air is compressed and cooled so much that it liquifies. Throughout, I explain that the real point is to store available work, called exergy in the engineering community, rather than energy. Although my treatment is mostly from the ideal point of view of quasistatic processes, I give some pointers to technological implementations of the various methods and to some references on their thermodynamic efficiencies.     

Thermodynamic Evaluation and Sensitivity Analysis of a Novel Compressed Air Energy Storage System Incorporated with a Coal-Fired Power Plant

A novel compressed air energy storage (CAES) system has been developed, which is innovatively integrated with a coal-fired power plant based on its feedwater heating system. In the hybrid design, the compression heat of the CAES system is transferred to the feedwater of the coal power plant, and the compressed air before the expanders is heated by the feedwater taken from the coal power plant. Furthermore, the exhaust air of the expanders is employed to warm partial feedwater of the coal power plant. Via the suggested integration, the thermal energy storage equipment for a regular CAES system can be eliminated and the performance of the CAES system can be improved. Based on a 350 MW supercritical coal power plant, the proposed concept was thermodynamically evaluated, and the results indicate that the round-trip efficiency and exergy efficiency of the new CAES system can reach 64.08% and 70.01%, respectively. Besides, a sensitivity analysis was conducted to examine the effects of ambient temperature, air storage pressure, expander inlet temperature, and coal power load on the performance of the CAES system. The above work proves that the novel design is efficient under various conditions, providing important insights into the development of CAES technology.     

供水温度对CO2空气源热泵系统性能的影响

为探究热泵供水温度对CO2空气源热泵系统性能的影响,保持室外环境温度15.5℃不变,调节热泵供水温度,测试冷却水流量、气冷器出水温度、压缩机排气温度、气冷器CO2进出口温差、压缩机排气压力、压缩机耗功量、系统制热量、气冷器热交换完善度、系统COP的变化情况。结果表明:供水温度由45℃升至85℃,气冷器出水温度、压缩机排气温度、气冷器CO2进出口温差、压缩机排气压力随之增加,冷却水流量随之减小。系统制热量增加了7.3%、气冷器热交换完善度下降了20.0%、系统COP下降了35%、压缩机功耗增加了65.1%。     

无泵吸收制冷系统气泡泵的性能分析

根据两相流流型转换理论,推导出了气泡泵从弹状流向泡状流转变和从弹状流向块状流转变时液体流量、气体流量与管径的关系式;根据空气提升理论、能量平衡、质量平衡推导出了气泡泵的性能关系式。根据上述关系式,具体分析了爱因斯坦制冷循环工况下气泡泵的性能,分析结果表明,在弹状流下限、大的沉浸比时液体循环量较大。     

喷水室典型空气处理过程中空气流速的实验研究

针对纺织厂空调系统的核心-喷水室,研究喷水室内处理空气的冷却减湿和等焓加湿两个典型热湿交换过程。提出Re准数对传热传质有显著作用,而Re数的大小取决于流体速度。通过实验研究当空气流速从3m/s提高到5m/s时对喷水室热湿交换性能的影响,从而确定空气流动速度因素对两个热湿交换效率的影响趋势。根据拟合的数学曲线,总结出当空气的流动速度提高后,热湿交换效率相应提高。从而推动高速喷水室在实际工程中的应用。     

Effect of storage medium on thermal properties of packed beds

The present paper is concerned with studying the effects of storage medium properties on the thermal behaviour of packed beds during charging. A transient one-dimensional two-phase model is used to describe the temperature fields in the air and solid media constituting the bed. The numerical solution of the resulting two-coupled partial differential equations is obtained, and the variation of thermal energy stored with time is computed. Solutions are obtained for a wide range of storage media (the solid phase) properties, namely density, thermal conductivity and specific heat. The results show that increasing either the density or specific heat increases the rate and capacity of energy storage, and decreases the rate of temperature rise throughout the storage medium. On the other hand, increasing the thermal conductivity is found to markedly increase the rate of temperature rise and energy stored inside the bed up to a certain time during charging, beyond which this trend completely reverses. In addition, the thermal storage properties of aluminum, steel and rock-packed beds are computed and compared.     

小型复叠式空气源热泵采暖系统性能影响因素的实验研究

本文探讨了循环水流量﹑热水温度及环境温度等参数对小型复叠式空气源热泵采暖系统性能的影响。实验结果表明:在一定温度范围内,随着制取热水温度的升高,热泵的制热量逐渐降低,热泵的输入功率逐渐增大,系统COP呈下降趋势;当制取的热水温度相同、环境温度较高时,热泵的制热量、热泵平均COP值较高;在一定流量范围内,循环流量越大,热泵的制热能力越高,当制取热水的温度相同时,大循环流量下高温环路的压缩机排气温度越低,运行越稳定。     

热管式相变蓄热换热器储/放能过程中传热特性的实验研究

将热管作为换热元件应用于相变蓄热系统中,研制了一套热管式相变蓄热换热器。采用石蜡作为蓄热材料,对其储、放能过程即内部石蜡的融化与凝固过程进行了实验研究。测定了储、放能过程中不同时刻换热器内石蜡的温度分布; 改变供、取热流体参数,分析了供/取热流体的入口温度与流量对换热器储/放能过程的影响;分析了储、放能过程中能量随时间的变化情况。结果表明,热管在本换热器内极好地发挥了换热元件的作用,换热器运行状况良好,各项功能均能较好地实现。     

Heat Transfer from a Hot Moving Steel Plate by Air-Atomized Spray Impingement

Air-atomized spray cooling of a hot moving AISI 304 steel plate of 6 mm thickness has been investigated experimentally by varying water flow rate and plate velocity at a fixed nozzle-to-plate distance. It is found that the heat transfer coefficient is a non-linear function of surface temperature. The result shows that the cooling rate increases with an increase in the water flow rate. The highest cooling rate has been found for the static plate, whereas for a moving plate, an increasing cooling rate trend has been observed with increasing plate velocity.     

封闭式喷雾冷却系统启动时间

 以蒸馏水为冷却工质,对冷凝器内置的封闭式光滑表面喷雾冷却系统进行了启动时间变化规律的实验研究,结果表明喷雾系统不同模块最优启动顺序为冷凝器、泵和加热器。采取6种不同的启动顺序,启动后加热表面的温度不均匀度均小于0.25 ℃。在最优启动顺序下,研究了冷却水流量、泵高度、加热功率和喷雾流量对启动时间的影响。随冷却水流量和喷雾流量增加启动时间缩短,随泵高度增加启动时间略微增大,随加热功率增大启动时间先增大后减小。启动时间影响程度由大到小的因素依次为喷雾流量、冷却水流量、加热功率及泵相对于加热表面的高度。喷雾工质流量由10 mL/min增大到35 mL/min时,封闭式喷雾系统的启动时间缩短了5 000 s。同样操作条件下,封闭式系统的启动时间比开放式系统延长15%~20%。     

极端高温环境下空气源热泵冷热水机组制冷实验研究

针对现有空气源热泵冷热水机组高温环境运行效果差、效率低、排气温度过高导致停机等问题,设计一套基于准双级压缩循环理论,以R410A为制冷剂的中压补气型空气源热泵冷热水机组。在50℃极端环境温度下,采用中压补气技术,对系统的制冷性能进行实验研究。结果表明:(1)系统出水温度由10℃增至15℃时,制冷量增加77.28%,EER提高59.02%,系统的制冷量、功率和EER均随出水温度的升高而增加;(2)相较不补气模式,系统排气温度由111.9℃降至106.23℃,制冷量由14.14 kW增至16.05 kW,可有效降低排气温度,提升制冷量,能更好提高系统超高温制冷时的稳定性。     

空气热储存、光合作用和土壤垂直水分运动对黄土高原地表能量平衡的影响

地表能量不平衡问题一直是陆面过程研究的一个重要科学难题. 本文利用黄土高原陆面过程试验(LOPEX)资料, 在将垂直感热平流项引入地表能量平衡方程的基础上, 估算了空气热储存和光合作用储存的大小, 并分别用水分守恒关系和两层土壤温度方法计算了浅层土壤水分垂直通量, 考察了空气热储存、光合作用储存和水分垂直运动热量输送对地表能量平衡的影响.结果表明: 黄土高原区自然植被下垫面的空气热储存、光合作用储存和土壤水分垂直运动热量输送平均日变化峰值分别达到1.5, 2.0和7.9 W·m^-2; 在能量平衡方程中引入这三项后, 地表能量闭合度由88.1%提高到89.6%. 空气热储存、光合作用储存和水分垂直运动热量输送对于改善黄土高原地表能量不平衡状况有一定作用, 研究区域的半干旱气候背景和植被状况是导致各热储存量与其他试验区存在差异的根本原因.     

开式单喷嘴喷雾冷却均匀性实验研究

针对高热流密度激光介质高效散热与均匀冷却技术需求,设计并搭建了以去离子水为冷却工质的开式单喷嘴喷雾冷却实验平台,实验研究获得了不同热流密度（16～110 W/cm²）、不同冷却工质流量（200～300 mL/min）以及不同喷雾高度（15～25 mm）下单相喷雾冷却换热系数及其冷却均匀性效果。结果表明：该实验工况下,不同热流密度条件下喷雾高度及工质流量对于单相喷雾冷却换热效率及温度均匀性影响显著;喷雾高度15 mm、工质流量200 mL/min时获得最大对流换热系数为5.93 W/（cm²·K）;喷雾高度15 mm、工质流量250 mL/min时面积20 mm×20 mm的热源表面温度均匀性最佳可优于0.6 ℃。     

Experimental Heat Transfer Coefficients of Waste Heat Recovery Unit in Detergent Manufacturing Process

The waste heat recovery unit is one of the most important units in the chemical process. It recovers waste heat from the exhaust gas of the process resulting in the reduction of heat loss. In the detergent manufacturing process, the particulate air leaving the spray dryer is the exhaust gas containing the large amount of heat. Therefore, a waste heat recovery unit can significantly reduce heat loss. In this work, heat transfer coefficients of a waste heat recovery unit in the detergent manufacturing process were studied. Waste heat from the particulate air is recovered in the shell and coiled tube heat exchanger. The particulate air flows in the shell side, and water flows in the tube side. Four coiled tubes with different coil pitches were investigated. The results show that the tube-side heat transfer coefficient increases as the coil pitch decreases. Loading ratio also has an important effect on heat transfer coefficients. The increase of loading ratio leads to a lower value of the overall heat transfer coefficient. From 100 experiments, empirical correlations for the prediction of tube-side and shell-side heat transfer coefficients were proposed. The results indicate that the predicted heat transfer coefficients agree well with the experimental values.     

A vapour re-compression heat pump using liquidised CaCl2/H2O/NH3 and CaCl2/NaSCN/NH3 systems for thermochemical energy storage

This work was concenned with building and testing a prototype heat pump which incorporated thermochemical energy storage. The heat pump was designed to utilise the cheap ‘Economy 7’ electric tariff. Ammonia was used as the refrigerant and ambient air as a heat source. This heat pump featured two-stage compression and incorporated a liquidised CaCl₂ absorbent. The use of a liquidised absorbent system improved the heat and mass transfer and simplified the construction of the generator/absorber of the heat pump. Both heat pumping and regeneration phases were demonstrated. Experimental tests on liquidised absorbent systems are described together with an analysis of the results.     

Experimental heat transfer study of beef carcasses chilled by mist sprays

Experimental studies were conducted on the chilling of beef carcasses by mist sprays to investigate the effect spray droplet size and Weber number have on the heat transfer and carcass weight loss during spray chilling. Experiments were conducted on 16 beef carcass halves. Half were conventionally chilled by the circulating air in the meat chiller, while the others were chilled by water mist. Tests reveal that spray heat transfer increases with the increase in the spray mass flux. Beef carcasses chilled by mist spray also show a reduction in carcass weight loss with the increase in the spray Weber number.