Natural convection effect on heat transfer in saturated soils under the influence of confined and unconfined subsurface flow
Natural convection effect on heat transfer in saturated soils under the influence of confined and unconfined subsurface flow
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DOI：
10.1016/j.applthermaleng.2023.121805
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发表时间：
2023-10
影响因子：
6.4
通讯作者：
Fereydoun Najafian Jazi;Omid Ghasemi-Fare;T. Rockaway
中科院分区：
文献类型：
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作者：
Fereydoun Najafian Jazi;Omid Ghasemi-Fare;T. Rockaway
近年来，已有研究证明，在饱和土壤中，即使存在地下水流动，自然对流也会显著影响地热系统附近的换热。然而，这一现象只在有密闭地下水流动的情况下进行了研究。因此，本研究建立了一个完全耦合的热液模型，以定量确定无侧限地下水存在时自然对流对换热的影响，并比较两种不同情况下土壤的水热响应。结果表明，自然对流的影响取决于土壤渗透性、地下水流速和加热器温度的耦合作用。结果表明，在地下水流速小于10 ~ 7 m/s的情况下，当瑞利数大于50时，自然对流的作用不可忽略，而对于其他地下水流速，只有当浮力比大于20时，自然对流的作用才会起作用。研究还表明，在探索的场景中，选择承压地下水流量而不是无承压地下水流量会导致47%至173%的误差。当加热器与地表的相对距离在0 ~ 15 m和30 m之间变化时，忽略自然对流导致的土壤温度误差分别高达43%、48%和60%。
Recently, it has been proven that natural convection significantly impacts heat transfer close to geothermal systems in saturated soils even in the presence of groundwater flow. However, this phenomenon has only been investigated in the presence of confined groundwater flow. Therefore, in this study, a fully coupled hydrothermal model was developed to quantitatively determine the natural convection influence on heat transfer in the presence of an unconfined groundwater flow and to compare the hydro-thermal response of soil under these two different scenarios. Results showed that natural convection influence depends on the coupled effects of soil permeability, groundwater velocity, and heater temperature. According to the results, in the case of a groundwater flow velocity less than 10− 7 m/s, natural convection role is non-negligible when Rayleigh number is greater than 50, while for other groundwater velocities, that matters only when Buoyancy ratio is greater than 20. It was also shown that choosing a confined groundwater flow over an unconfined one led to an error of 47% to 173% in the explored scenarios. Furthermore, it was revealed that when the relative distance of the heater from the surface alters from 0 to 15 and 30 m, the error in the soil temperature due to neglecting natural convection can be as high as 43%, 48%, and 60%, respectively.