The Study on Measuring Method of Heat Exchange Pipe Deformation and Displacement Based on Thermal Strain

Abstract

Thermal deformation of heat exchange pipe is the significant source of structural variation in ground heat exchange system, which could weaken the capability and reduce the reliability of heat transfer system after long-time operation. The experimental study of thermal deformation of heat exchange pipe should be carried out to explore its thermal behavior. The strain measuring method was applied to the study on thermal deformation and displacement, which was deduced from the measured strain in heat exchange pipe. The verifying experiment was carried out to analyse its feasibility in preliminary simulation environment. The result showed that strain measuring method is applicable and could be conducive to the deformation monitoring of heat exchange pipe in practical projects. IntroductionWith the rapid development and application of ground source heat pump and large temperature difference energy storage technology, the gradual performance degradation and even failure of ground heat exchange system were emerging, and also its reliability and durability have been paid more and more attention. Since the 1990s, many countries in Europe and America have carried out some preliminary study on these problems. In Sweden, Anna Gabrielsson [1] had monitored the UTES for three years, large vertical settlements appeared in the underground structure after two freeze/thaw cycles, which caused the unexpected buckling of pipe and resulted in a reduced flow in pipe. In the U.S.A., Marita Allan [2] developed the study of thermal stresses, deformations and thermal fractures of backfill material, which would influence the heat transfer. In Canada, Lenarduzzi Frank [3] announced the problem of vertical ground pipes squeeze in a GSHP project during the first heating season, at the same time, a series of model experiments were conducted to search for the cause of pipe squeeze. In Britain, Bourne [4] studied the temperature stress of heat exchanger piles and found that great temperature stress accumulation can lead to heat exchange structural failure.However,heat exchange pipe, as the most sensitive part to temperature, its deformation by temperature changes should be an important factor for the failure of ground heat exchange structure. Therefore, it is necessary to study the characteristics of pipe's thermal deformation firstly. The technology of strain measurement provides an effective means to develop this study