Testing of coral sand thermal physical parameters and comparative analysis of prediction models

The construction of islands and reefs in the South China Sea is progressing smoothly under the strengthening of China's maritime development. The ground source heat pump technology and energy pile etc., which take shallow reef flat as medium, are essentially a process of energy exchange with reef sand medium, so it is necessary to further grasp the evolution law of thermal conductivity of coral sand. In this paper, coral fine sand of South China Sea reef was examined. Three thermophysical parameters including thermal conductivity, volumetric heat capacity, and thermal diffusivity, were measured, and the influence of dry density and water content on the thermophysical parameters were analyzed. The predicted data by 12 thermophysical parameter models for sand soil were compared with the measured data for analogical analysis. On this basis, an empirical model suitable for predicting the thermal conductivity of coral fine sand was developed. The results show that the thermal conductivity, volumetric heat capacity and thermal diffusivity of coral sand are positively correlated with dry density, and the correlation coefficients of thermal conductivity and volumetric heat capacity with water content are higher than that of dry density, while the correlation coefficient of thermal diffusivity with water content has a "convex" growth relationship, and the correlation coefficient with dry density is much higher than that of water content. The Cote & Konrad model and the Gangadhara Rao model were amended through the linear regression analysis of the measured data. The prediction accuracy of thermal conductivity of coral fine sand by the model was significantly improved. The difference between the predicted and measured values of the volumetric heat capacity of coral sand was significantly reduced by the linear correction of the De Vries model and the Xu model. Based on the binary fitting analysis of the correlation coefficient of Dai model, a prediction model characterizing the thermal diffusivity of coral fine sand was established to provide reference for the design of insulation and temperature control engineering of island reefs as well as the study of thermophysical properties of coral sand.