热管真空管太阳能集热器及集热系统在自然条件下的热性能动态测试与预测模型研究

At present, the steady-state test method is predominantly used by domestic and abroad test standards for determining the thermal performance of solar collectors. The steady-state test method usually requires strict test conditions that are difficult to meet, accompanying with a long test period. And the thermal collecting efficiency curve obtained by the steady-state test performs poorly in the thermal performance predictions of solar collectors and solar collecting systems under natural conditions with variable solar irradiance and ambient temperature. Although there is some breakthrough work on the thermal performance dynamic test methods of solar collectors in the existing investigations, the accuracy levels of thermal performance predictions by the methods are not high. Because they did not combine the considerations of dynamic thermal performance predictions of solar collectors and systems. The heat pipe evacuated tube solar collector, which possesses particular thermal capacitance, is taken as the present study object. In this project, characterization models of dynamic thermal performances of the heat pipe evacuated tube solar collectors and collecting systems are studied combining with theoretical and experimental methods, starting from the collector transient thermal balance equations of one-node and multi-node lumped capacitance parameters. The main content contains: the investigation of dynamic thermal performance test and prediction models under natural conditions applied to heat pipe evacuated tube solar collectors; experimental validation and amendment of the test and prediction models; extending the developed solar collector models to the thermal performance tests and predictions of solar collecting systems under natural conditions. The project is aimed at revealing the inner correlation between the dynamic thermal performances of the solar collectors as well as the solar collecting systems under natural conditions and the characteristic parameters. It will provide convenient test method and accurate prediction model references for real engineering application.

当前国内外的太阳能集热器热性能测试标准以稳态测试方法为主，其测试条件严格、周期较长，且得到的集热效率曲线在用于太阳辐照和室外温度变化的自然条件下集热器及集热系统热性能预测时准确度欠佳。既有研究在集热器热性能动态测试方法方面虽有一定的突破，但通常未结合集热器及系统动态热性能预测考虑，预测准确度不高。本项目针对热容较为特殊的热管式真空管太阳能集热器，从“单点”和“多点”集总热容参数瞬态热平衡方程出发，结合理论与实验，研究该型集热器及集热系统的动态热性能表征模型。主要内容有：适用于热管式真空管型太阳能集热器在自然条件下的热性能动态测试模型及预测模型理论研究；测试与预测模型实验验证与修正；将相关集热器模型推广至太阳能集热系统自然条件下的热性能测试与预测中。项目旨在揭示相关集热器及集热系统在自然条件下的动态热性能与特征参数之间的内在关联，为其在实际应用中提供便捷的测试方法和准确的预测模型参考。

太阳能作为清洁可再生能源之一，对其充分有效地利用，能够减少化石能源消耗，起到节能减排和降低环境污染的效果。然而，太阳能在本质上是一种时间上不连续、空间上密度低的不稳定性能源，太阳能热利用技术的发展受到其不稳定特性的制约。为了更好地理解太阳能热系统的不稳定性，需要对太阳能集热器及集热系统在自然变化条件下的动态热性能进行较为准确的物理数学描述，从而设计出更好的太阳能热系统和革新相关技术。对太阳能集热器及集热系统在自然条件下动态热性能的准确表征，可为太阳能热利用技术的发展夯实理论基础。鉴于此，本项目探究了太阳能集热器及集热系统的动态热性能表征模型，主要研究包括：适用于热管式真空管型太阳能集热器在自然条件下的热性能动态测试模型及预测模型理论研究；测试与预测模型实验验证与修正；将相关集热器模型推广至太阳能集热系统自然条件下的热性能测试与预测中。项目研究解析推导了改进的集热器热性能动态表征模型，扩宽了模型适用条件，使得其适用于自然变化气象条件下的多种工况，如集热器进口温度变化速率较大、较宽变化范围的散射辐射比率及不同入射角修正等情形；结合相关理论分析和实验验证，诠释了改进的表征模型与热惯性修正模型（TICM）之间的关联特征，定义了集热器动态响应时间常数，给出动态时间常数与静态时间常数之间的关联式。在此基础上，将集热器动态热性能表征模型推广到太阳能集热系统的动态热性能表征，类比定义相关关联特征参数进行模型描述及论证。该研究揭示了太阳能集热器及集热系统的动态热性能与相关特征参数之间的内在关联，为太阳能系统在实际应用中提供便捷的测试方法和较为准确的预测模型参考，为太阳能热系统的匹配设计、系统控制模式和控制策略开发等热利用技术提供了一定等理论基础和技术支撑。