Numerical investigation of the thermal protection mechanisms of phase change capsules with orderly stacked layouts applied to pulse power sources in deep wells

Abstract

<p indent="0mm">Currently, the reliance of oil and gas consumption on imported resources in China is indicative of a serious energy supply concern. The mainland of China has been found to contain abundant medium- and low-maturity shale oil resources that represent substantial exploitable reserves of energy supply. The exploitation of medium- and low-maturity shale oil resources, which are comparable to conventional oil and gas resources, can alleviate the problem of energy import dependence. However, low-maturity shale oil resources are mainly enriched in the deep crust, with temperatures reaching 150°C at a 2-km depth. This high-temperature environment might severely limit the operation of electronic equipment. This paper focuses on the thermal protection of pulsed power source equipment in the harsh thermal environment of deep wells. The performance of phase change materials (PCMs) with capsule-like structures having various orderly stacked orientations is numerically investigated. By calculating the inner wall temperature and heat flow, the influence of phase change capsule size and stacked layout on the thermal protection efficiency is analyzed, and the evaluation criteria considering the heat flux density as well as the prediction model for the inner wall temperature are proposed. The results show that the case of phase change microcapsule-glass wool composite structures exhibits improved thermal protection performance, with the inner wall temperature rising rate reduced by 13.8% and 2.35% compared to the case of the glass wool material and microcapsule, respectively. However, the small packed volume of PCMs in the microcapsules restricts further improvement of the thermal insulation. Consequently, PCM capsules of larger size are applied, increasing the PCM proportion and natural formation of closed porous material. Compared to the case of microcapsule-glass wool composite structures, for the case of larger PCM capsules, the temperature at the inner wall is further reduced by 19.3%, and the total heat flow during heating is reduced by <sc>373.7 W/m².</sc> By changing the stacked structure of the capsules, the case of single-layer orientation with large-scale PCM capsules illustrates the best thermal protection performance. The temperature rise rate during the heating period decreases by 1.25% and 5.84% compared to that of the staggered and double stacking structures, respectively, and the total inflow heat flux is also 1.09% and 4.19% lower compared to that of the staggered and double stacking structures, respectively. Based on the results, the prediction model for the inner wall temperature is proposed when applying the single-layer stacked PCM capsules. Note that the average deviation between the prediction model and numerical simulations is &lt; 7%. The maximum temperature difference can be controlled to within ±6°C during 84% of the operating time.