A Comprehensive Study on Intermittent Operation of Horizontal Deep Borehole Heat Exchangers

Utilizing a deep Borehole Heat Exchanger (BHE) has been recognized as a clean, renewable, low-carbon-emission, and sustainable way for heating of residential buildings and greenhouses. In this study, the long-term performance of horizontal deep BHE in intermittent mode is scrutinized. In this regard, to predict the transient heat transfer process in the deep BHEs, a mathematical model is developed and then verified by using the experimental results. The effect various key parameters including flow rate of circulating fluid, undisturbed ground temperature, inlet fluid temperature, and ground thermal conductivity on the thermal performance of deep BHE in continuous and intermittent mode is studied. According to the results, increasing the flow rate of circulating fluid, undisturbed ground temperature, and ground thermal conductivity is favorable for heat extraction rate. Moreover, the effect of three specific parameters for intermittent operation including periodic time interval, flow rate ratio, and recovery period ratio on the long-term performance of horizontal deep BHE are scrutinized. Based on the results, by decreasing the periodic time interval and increasing the flow rate ratio, the mean heat extraction rate in the period of 30 years is increased and the mean borehole’s wall temperature is decreased. Furthermore, by increasing the recovery period ratio, the heat extraction rate increases significantly while the total extracted energy decreases.

Preparation and Characterization of Super Pure Coal

Industrial washing oil as solvent, super pure coal was extracted and prepared from raw coal using heat extraction technology. The structures of raw coal and super pure coal were characterized by thermogravimetry and Fu Liye infrared spectrum. The results showed that the heat extraction rate of super pure coal was decreased with the increasing of coalification degree. The ash of raw coal which were silicate and alumina can be concentrated by heat extraction technology into coal residue and the mixtures of various structure were mainly composed of aromatic hydrocarbons also can be extracted effectively.

The Impacts of Different CO2 Injection Temperature on Heat Extraction Rate in CO2-EGS Based on CCS Demonstration Project

In this paper we use Majiagou geologic formation in Erdos Carbon Caputure and Storage(CCS) demonstration project aera as artificial geothermal reservoir, and create numerical models of Enhanced Geothermal System(EGS) using CO2 as a heat transfer carrier. In order to analyze the impacts of CO2 injection temperatures on heat extraction rate and the sustainability of CO2-EGS, five cases with different CO2 injection temperature are designed. Simulation results show that the range of the average heat extraction rate of case 1～5 is 6.56～8.47MW in the whole CO2-EGS operation period. The heat extraction rates vary over time, And it is 6.37～7.9MW in CO2 and water displacement stage and 6.64～8.68MW after aqueous phase dispear respectively. Injection temperature of CO2 significantly impacts the heat extraction rate of EGS .

Microstructural Variations in Melt-Spun Rapidly Solidified Ribbons

Rapid solidification produces a wide variety of sub-micron scale microstructure. Generally, the microstructure depends on the imposed melt undercooling and heat extraction rate. The microstructure can vary strongly not only due to processing parameters changes but also during the process itself, as a result of recalescence. Hence, careful examination of different locations in rapidly solidified products should be performed. Additionally, post-solidification solid-state reactions can alter the microstructure.The objective of the present work is to demonstrate the strong microstructural changes in different regions of melt-spun ribbon for three different alloys. The locations of the analyzed structures were near the wheel side (W) and near the center (C) of the ribbons. The TEM specimens were prepared by selective electropolishing or ion milling.