微热管阵列式太阳能空气集热-蓄热系统性能试验

Performance experiment on solar air collection-storage system with phase change material based on micro heat pipe arrays

该文采用了以微热管阵列(micro heat pipe arrays,MHPA)为核心元件的真空管型空气集热器与新型相变空气蓄热器,设计搭建了以空气为传热介质的太阳能集热-蓄热系统。集热器采用微热管阵列与真空管结合的新形式,蓄热器以相变温度42℃的月桂酸为蓄热相变材料,测试了系统在不同空气流量下集热过程的集热效率,蓄放热过程中蓄热放热的时间、功率,并在不同空气流量下对蓄热器的蓄热、放热特性进行了研究。研究表明:空气流量240 m^3/h工况下,集热效率最高;蓄热器的蓄热时间和放热时间最短,蓄热功率和放热功率最大,分别是633和486 W;而空气流量60 m^3/h能提供更加稳定的出口温度与放热功率,在供暖与干燥领域更加适用。集热-蓄热过程和放热过程阻力分别小于327和40 Pa,说明放热过程系统阻力损失较小,选用功率较小的风机就可提供空气流动的动力。

Solar energy is a clean, free-pollution renewable energy source. Rational utilization of solar energy provides significant potential in space heating and drying of agricultural crops, and it is an important measure for saving energy. In order to prolong the time of using solar energy, and to maximize the value of use, in this study, a new style solar air collection-storage thermal system is designed, which utilizes micro heat pipe arrays（MHPA） as heat transfer core element. Collection-storage system includes air collector of vacuum glass tube and phase change thermal storage device. The collector adopts a new form of combining MHPA with vacuum glass tubes. Collector includes 20 collecting units, which consists of aluminum fins, MHPA and vacuum glass tube. Aluminum fins are attached by heat-conducting glue. Polystyrene board is used as thermal insulation material of air duct. Thermal storage device uses the lauric acid（a kind of fatty acid） as phase change material（PCM） with phase change temperature 42 ℃. The thermal storage device size is 390 mm × 105 mm × 790 mm, which is filled with 15.5 kg lauric acid with filling fraction of 89%. Circle thermal insulation pipe is applied to connect solar collector and thermal storage device. Axial fan is installed in circle pipe to provide air flowing power from solar collector to thermal storage device. In heat storage process, lauric acid is heated and its temperature is rising. Temperature measuring point between 30 and 60 is selected as experiment temperature scale. The experiment data are recorded by data acquisition ℃instrument Agilent 34970 A. Weather parameters including ambient temperature, solar radiation, wind speed is collected by meteorological station. The measurement of air volume flow rate is performed by air volume cover TS18371. Air volume flow rates of 60, 120, 180, and 240 m3/h are chosen as working conditions which include heat storage process and heat release process. The thermal performance of collection-storage system（heat storage process） is analyzed. The experiment tests the collector efficiency, and thermal charging and discharging time, thermal charging and discharging power of phase change thermal storage device under different air volume flow rate. In a range of tests, air volume flow rate of 60, 120, 180, and 240 m3/h produces collector efficiency of 35.64%, 38.00%, 44.92% and 51.33%, respectively, and 240 m3/h air volume flow rate has the maximum collector efficiency. It is concluded that increasing air volume flow rate can enhance collector efficiency. A high air volume flow rate can strengthen air disturbance and heat convection between air and fins. A large air volume flow rate contributes to short thermal charging and discharging times, and a high thermal charging and discharging power. In the experimental range, 240 m3/h air volume flow rate has a shortest thermal charging and discharging time, which is 161 and 154 min, respectively; and it has the maximum thermal charging power of 633 W and discharging power of 486 W. During heat storage process, thermal charging power is firstly increased and then decreased, which is determined by solar radiation and mean temperature of lauric acid in thermal storage device. In addition, in heat release process, experimental working condition with 60 m3/h air volume flow rate can provide a small fluctuation of outlet temperature and stable thermal discharging power, so it is more suitable in the field of space heating and agricultural products drying domain. Resistance is an important parameter of evaluation system, and it determines the selection and energy consumption of the fan. Pressure drop of collection-storage and heat release process is less than 327 and 40 Pa, respectively. Hence, heat release process has a small resistance loss. And fan with low power can provide impetus to finish air flowing.