多场耦合条件下的莫高窟洞窟热湿环境调控理论与技术研究

In order to avoid the phenomenon of the murals in Dunhuang Mogao Grottoes falling off, a relatively stable thermal, humidity and soluble salt environment should be required. The phenomenon is caused by repeated dissolution and crystallization of the soluble salt by humidity effect in the support layer and plaster layer of the murals. The existing research on the mural protection technology is only in two main respective aspects: blocking water and desalinating water. But the migration of water and salt in Mogao Grottoes would be affected by multi-fields coupling interaction, just like thermal, humidity and pressure from indoor and outdoor, thermal, humidity, pressure, and soluble salt concentration in the wall body, etc. Firstly, based on previous data and research result in this project, mechanical air supply pressure dehumidification system for the grottoes will be installed. Next, the layout of thermal, humidity and salt environment from the pigment layer and the support layer in the grottoes murals will be simulated and measured in the project. And then, the suitable theory of controlling thermal and humidity environment and the strategy of adjusting and controlling atmospheric pressure in the grottoes will be proposed. All of these steps will solute the efflorescence problem radically and protect the murals. This research will promote the protection technology of Mogao Grottoes murals. The suitable controlling technology of thermal and humidity in grottoes will have important scientific function and can be used in real projects.

为了避免敦煌莫高窟壁画支撑体和地仗层中的可溶盐受湿度影响反复溶解、结晶，致使壁画脱落，需要为洞窟壁画提供相对稳定的热、湿、可溶盐环境。已有的莫高窟壁画保护研究主要从阻水、脱盐两方面开展工作。但是，莫高窟实际壁体内水、盐运移受洞窟内外空气温湿度、压力、壁体内温湿度、压力及可溶盐浓度等多场耦合相互作用影响。本项目基于敦煌研究院前期数据和成果，在实验窟内安装机械加压除湿送风系统，对洞窟内、壁画颜料层及壁画支撑体内热、湿、可溶盐环境分布进行模拟和实测分析，提出在极端天气条件下洞窟内部适宜的热湿环境控制理论和气压调控策略，从根本上解决壁画酥碱问题，保护壁画。本研究将会促进莫高窟壁画保护科技水平的进步，对于洞窟适宜的热湿环境控制技术，具有十分重要的科学意义和工程应用价值。

近年来甘肃敦煌莫高窟窟区较为频繁的出现短期急降雨气候，改变了持续干燥的沙漠气候，窟区短期急降雨造成水汽侵入洞窟内，引起洞窟内热湿环境的扰动，会导致壁画地仗层内水盐迁移和激活盐害。为了创造稳定的壁画赋存微环境,本项目尝试研究主动式和被动式结合的预防性保护措施，即利用机械送风加压防水汽渗透系统，抵御潮湿大气向洞窟渗透，结合窟区景观调节技术，为洞窟创造较为稳定的湿环境。取得了如下主要成果：①摸查了莫高窟窟区及大、中、小型洞窟微气候现状，总结了窟区地形、景观对微气候影响规律，及洞窟形制与微气候关系规律。②建立莫高窟内外空气交换理论模型。基于对莫高窟建筑形制的调研及窟内微气候模拟分析，结合建筑内外空气交换理论研究，提出了基于窟内外空气交换的建筑模型，并提出了窟内外空气交换理论模型。③依据窟内外空气交换模型及洞窟气密性，确定洞窟机械通风系统送风量的计算方法。通过现场试验及测试数据显示，该系统有效的抵御了窟外潮湿空气渗入，并对窟内微气候的扰动不及人员走动的影响，最大程度减少对窟内稳定的微环境的影响。④测试了地仗层的热物性参数，理论研究揭示了地仗层的传热传湿机理，并通过数值计算定量分析传热传湿过程，为机械送风系统对地仗内热湿传递及病害形成研究提供了理论基础。本项目对于改善莫高窟洞窟内热湿环境，更好地保护莫高窟壁画，具有重要的理论意义和应用价值。同时也为极端环境下洞窟热湿环境调节策略及干旱环境下的土遗址保护提供科学指导。