基于微热管阵列的平板太阳能热水器的性能试验

Performance experiments for flat plate solar water heater based on micro heat pipe array

为了检验一种新型平板太阳能热水器的性能,该文对其核心部件—基于微热管阵列的集热器及其组成的热水器进行了热性能试验。集热器热性能测试结果表明,微热管阵列平板太阳能集热器瞬时效率的斜率为4.7,截距为0.80,分别优于国家标准要求值11.0%和22.3%。在满足测试要求的天气情况下,对微热管阵列平板太阳能热水器进行的多次热性能测试结果表明,热水器的日有效得热量均高于国家标准要求值,日平均集热效率均高于60%。同时,该热水器具有承压能力强、无炸裂、轻巧、成本低、无需焊接、抗冻性能好、易于建筑一体化等优势。基于微热管阵列的平板太阳能热水器由于性能优异,并能克服现有太阳能热水器的缺点,具有广阔的应用前景。

A novel flat plate solar water heater based on the micro heat pipe array （MHPA） was invented, and the experiments were carried out on the MHPA heat collector and water heater to test their thermal performance. Owing to its distinctive structure, the MHPA has good heat transfer ability, high reliability, high compressive strength and low cost. The structure and character of the novel collector with MHPA as the high-efficiency heat transfer element are as follows. First, the contact surface between the absorber and the MHPA is so large that the heat resistance is smaller than the traditional one, thus its thermal transfer capability is greatly improved. Second, the condenser section of the MHPA is connected closely to the heat exchanger with dry type. The heat pipes do not contact with water, which precludes scaling and leakage in the collector. Third, the MHPA uses low freezing points of the refrigerants, which makes the collector more suitable for extremely cold areas. Fourth, the MHPA is made of aluminum instead of copper, which could reduce the fabrication cost significantly. Fifth, the unique heat exchanger could exclude water easily, which could prevent the frozen cracking of the collector in winter. Consequently, compared with other conventional evacuated glass tube solar water heaters, the novel flat plate solar water heater offers the additional benefits of high compressive strength, light weight, high reliability and durability, easy integration into buildings, and resistance to freezing during the winter months. Compared with traditional sheet-and-tube structure flat plate solar water heaters, this novel solar water heater also demonstrates many advantages： lower cost, absence of welding, resistance to freezing. The experiments focused on the novel collector＇s instantaneous efficiency. The test results for the collector＇s instantaneous efficiency show that the slope and intercept of the instantaneous efficiency curve are 4.7 and 0.80 respectively, which are 11.0% and 22.3% superior to the technical data of the Chinese national standard. The high maximum instantaneous efficiency can be attributed to high transmittance of the glass cover and good absorption of the absorber, as well as great performance of micro heat pipe array. Due to the excellent isothermal characteristic of the MHPA, the absorber have uniform temperature field so that the heat loss by natural convection in the collector is reduced, thus the novel fiat plate solar collector have relatively low heat loss factor. The low emissivity of absorber film also reduces the radioactive heat transfer between the absorber and glass cover. Finally, a detailed experimental study focusing on the thermal performance for the novel fiat plate solar water heater based on the MHPA is conducted during daytime over several days. The test results show that the effective heat gain per contour aperture area for the novel flat plate solar water heater are higher than that of the Chinese national standard, and all of the average daily thermal efficiency are higher than 60%. Therefore, the fiat plate solar water heater based on the MHPA has the broad application prospect because of its excellent performance.