地质科技通报 (May 2024)
Experimental study of recirculating heat transfer in geothermal wells with nanofluids
Abstract
Objective Enhancing the heat transfer performance of heat transfer media is an effective means of efficiently exploiting geothermal resources. Numerous studies have shown that the addition of nanoscale metals or metal oxides to fluids can effectively improve the heat transfer capacity of the fluid. The physical parameters that can impact the heat transfer performance of nanofluids are type, mass fraction, size of the nanoparticle, dispersant mass fraction. Additionally, the flow rate can have an important effect on the heat transfer performance of nanofluids. Methods In this study, spherical nano-CuO and spherical nano-Al2O3 were used as nanomaterials for configuring nanofluids. The particle size of nanomaterials ranges from 20 nm to 50 nm. Sodium dodecylbenzene sulfonate was selected as the dispersant for configuring the nanofluids. Basic heat transfer experiments are performed on nanofluids by utilizing a self-constructed basic heat transfer experimental setup. The physical parameters of the nanofluids were also optimized. In addition, a self-designed experimental setup for recirculating heat exchange was established. This experimental system uses geothermal water from hydrothermal geothermal wells as the heat source. The experimental system was also utilized for field testing in a hydrothermal-type geothermal well in Yingshan County, Hubei Province. The preferred nanofluid and deionized water from the basic heat transfer experiments were subjected to on-site circulating heat transfer experiments. Comparison of the circulating heat transfer performance of nanofluids and water under actual heat source conditions in the field. The effect of the flow rate on the heat transfer performance of nanofluids and water under real heat source boundary conditions in the field is also discussed. Results The results show that (1) the heat transfer performance of CuO nanofluids is better than that of Al2O3 nanofluids. (2) There is a negative correlation between the heat transfer performance of nanofluids and the nanoparticle mass fraction. (3) The nanofluid warming efficiency was highest at a 1% mass fraction of CuO nanoparticles. The nanofluid temperature increased from 25 ℃ to 79.2 ℃ in 150 s. The nanofluid temperature increased by 4.1 ℃ more than that of deionized water in the same amount of time. Moreover, the wettability of the nanofluid-heat source interface decreases with increasing nanoparticle mass fraction. The heat transfer performance of nanofluids increases and then decreases with increasing particle size. The best heat transfer performance of the nanofluid was achieved when the nanoparticle size was 40 nm. (4) The heat transfer performance of nanofluids is negatively correlated with the dispersant mass fraction. The best heat transfer performance of the nanofluid was achieved when the dispersant mass fraction was 1%. (5) The heat transfer performance of the nanofluid is negatively correlated with the flow rate when the fluid is in laminar flow. The motion of nanoparticles is progressively more intense when the fluid is in a turbulent state. This phenomenon can effectively enhance the heat transfer performance of nanofluids. Conclusion The research results can provide a basis for the application of nanofluids in geothermal heat transfer to improve the heat transfer efficiency of geothermal systems. It also provides theoretical references for the selection of nanofluid parameters as well as fluid flow rate parameters applied to geothermal heat transfer.
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