Abstract Contact thermal resistance is an important indicator of the efficiency of heat transfer between contact interfaces. The contact thermal resistance between the interfaces of superalloy GH4169 in high temperature was investigated by using ANSYS. The real surface morphology of superalloy was obtained with optical microscope, and its surface model was reconstructed in ANSYS. Based on the theory of structural mechanics, the elastoplastic deformation of the micro structure of the contact interface is simulated, and analyzed and obtained the contact thermal resistance between contact interfaces. The effect of interface temperature on the radiative heat transfer between the contact interfaces was studied. At the same time, the impact of radiation heat transfer between contact interfaces in high temperature is considered. Finally, it was tested by using an experimental test device. The result show that the maximum deviation between the contact thermal resistance and the contact thermal resistance was 12.60%, and the contact thermal resistance between superalloy interfaces decreases with the increase of interface temperature and contact pressure; the contact interface temperature difference increases first and then decreases with the increase of interface temperature.

Abstract The study of the performance of high-efficiency heat pump systems has been a hot issue of general interest in the field of heat pump air conditioning. For the designed and developed two-stage casing tandem heat exchanger of heat pump system, the 3D finite volume method and the realizable k-ε  model are used to numerically analyze the influence law of inlet fluid temperature and flow velocity on the overall heat transfer coefficient as well as the Nussle number of inner and outer tubes. The results show that decreasing the inlet water temperature or increasing the inlet refrigerant temperature can improve the overall heat transfer performance; Nu in  increases with the increase of water and refrigerant flow rates, while Nu out  increases with the increase of water flow rate but decreases with the increase of refrigerant flow rate; Nu in  and Nu out  both increase with the decrease of water temperature or refrigerant temperature increases.

Abstract Phase change energy storage materials are widely used in the fields of battery thermal management and solar power generation due to their characteristics of storing and releasing energy periodically. However, their further applications are limited by their low thermal conductivity. The addition of high thermal conductivity foams provides an effective method to address this shortcoming. A three-periodic minimal surface (TPMS) was used to generate an aluminum foam skeleton, and the variation of phase change heat storage of the aluminum/paraffin composite phase change material was numerically simulated based on the pore scale. The results showed that the addition of aluminum skeleton enhanced the heat storage and shortened the melting time, and the melting time of the composite phase change material was shortened by 68%, 75% and 80% when compared with pure paraffin wax at the porosity of 0.90, 0.85 and 0.80, respectively, and the temperature field was more uniform during the heat storage process, The thermal non-equilibrium effect between the aluminum skeleton and the paraffin wax is verified, and the lower the porosity of the aluminum/paraffin composite phase change material, the more obvious this effect is.

Abstract In order to study the temperature change trend of the surrounding geotechnical soil during the operation and thermal recovery of the medium-deep geothermal buried pipe and the influence of the geotechnical soil on the operational stability of the vertical buried pipe after thermal recovery. Based on the data of geological stratum in Guanzhong area and the actual engineering application of medium-deep geothermal buried pipe heating system in Xi ’an New Area, the influence law of medium-deep geothermal buried pipe heat exchanger on surrounding geotechnical soil i s simulated and analyzed by FLUENT software. The results show that: after four months of heating operation, in the upper layer of the geotechnical soil, the reverse heat exchange zone appears due to the higher fluid temperature; in the lower layer of the geotechnical soil, the temperature decreases more with the increase of depth and shows a linear increase in the depth direction; without considering the groundwater seepage, after eight months of thermal recovery of the geotechnical soil after heating, the maximum temperature difference after recovery is 3.02 ℃, and the average temperature difference after recovery is 1.30 ℃ The maximum temperature difference after recovery was 3.02 ℃ and the average temperature difference after recovery was 1.30 ℃. The geotechnical thermal recovery temperature difference has no significant effect on the long-term operation of the buried pipe, and it can be operated continuously and stably for a long time. Practice shows that due to the influence of various factors such as stratigraphic structure, stratigraphic pressure, radioactive decay and stratigraphic thermal conductivity, the actual stratigraphic temperature below 2000m recovers rapidly without significant temperature decay, fully reflecting the characteristics of the Earth’s constant temperature body.

Abstract Boiler combustion system is a typical dynamic system with many variables, strong coupling, large-lag, and multiple input/output. It is very difficult to build a combustion system model that conforms to the actual working conditions. This paper presents a new modeling method of boiler combustion system based on bidirectional threshold cycle unit (Bi-GRU), and establishes the training model of combustion system under variable load (low, medium and high load) conditions. At the same time, gradient lifting decision tree (GBDT) is used to reduce the dimension of input characteristic matrix. GBDT model can evaluate the weight of input features under different loads and outputs, and can identify the feature with the largest weight proportion on the basis of retaining the original physical meaning of the feature. The feature selection model based on GBDT can not only reduce the original input dimension, but also provide theoretical guidance for the subsequent combustion control strategy. The calculation results of actual operation data show that the new combustion system model established by Bi-GRU and GBDT can accurately reflect the dynamic changes of main steam flow, main steam pressure and NOx emission under different loads. Compared with the traditional recurrent neural network (RNN) model, the accuracy and performance of the new model in this paper are significantly improved, and the structure is simple and the amount of calculation is small.

Abstract In view of the large energy consumption of the regeneration process in the chemical absorption decarburization process, on the basis of the enrichment classification flow process, the nanoscale ceramic film is used as a new heat exchanger between the enriched liquid and the regeneration gas. The porous ceramic film is capable of coupling thermal-mass transfer to effectively recover part of the water vapor and the heat carried in the regeneration gas, so as to reduce the regenerative energy consumption of the system. The effects of parameters such as regeneration temperature, flow rate, molar fraction of water vapor, and MEA enrichment temperature, flow rate, and MEA concentration of shunt on the hydrothermal recovery effect of ceramic membranes of different pore sizes and lengths were studied by using the heat recovery flux and water recovery rate as the indicators. The results show that the hydrothermal recovery performance of the ceramic membrane increases with the increase of MEA enrichment flow, but decreases significantly with the increase of the enrichment temperature. At the same time, with the increase of regenerative gas velocity and the molar fraction of water vapor in the regenerative gas, the heat recovery flux will increase. The heat recovery performance of the 10 nm ceramic membrane is better than that of the 20 nm ceramic membrane.

Abstract Roasted and ground coffee residue was investigated as an adsorbent lignocellulosic material capable of removing methyl orange dye from aqueous solutions by means of batch adsorption experiments. The effects of experimental parameters on the adsorption behavior, such as initial dye concentration, adsorbent dosage, initial pH and temperature were studied. A better adsorption of the dye was observed at acid pH, low temperature and with an adsorbent dosage of 6 g/L. A Pseudo-second order kinetics was found according to the Lagergren kinetic model. A maximum adsorption capacity of 1.3 mg methyl orange per gram of adsorbent was calculated by fitting the Langmuir model. The adsorption of methyl orange on the adsorbent analyzed was found to be exothermic in nature. The roasted and ground coffee residue was found to be viable for the primary treatment of wastewater contaminated with azoic-type compounds.

Abstract The modification experiment of Inner Mongolia Baiyinhua lignite by hot air at 200 ℃ for 1 h was carried out. The structural changes of Baiyinhua lignite before and after thermal modification were analyzed by infrared spectrum. The results show that the moisture and oxygen content in lignite are greatly reduced by thermal modification, and the carbon content and calorific value are also increased to varying degrees. In the process of thermal modification, various oxygen-containing functional groups in lignite are reduced in different degrees due to thermal decomposition. Thermal modification also causes substitution reaction of aromatic hydrocarbons in lignite, CH2 in aliphatic hydrocarbon structure breaks, but hydroxyl group in lignite does not change significantly before and after thermal modification.

Abstract The wet saturated flue gas discharged by coal-fired utility boilers leads to a large amount of low-temperature waste heat loss. Inorganic ceramic membrane is acid-base resistant and has strong chemical stability. It is an ideal material for recovering low-temperature waste heat from flue gas. The experiment of waste heat recovery of flue gas was carried out with inorganic ceramic membrane as the core, and the characteristic parameters of low-temperature flue gas at the tail of the boiler were analyzed; taking 316 L stainless steel as the comparative object, the strengthening effect of inorganic ceramic film on improving heat recovery power and composite heat transfer coefficient was discussed. The results show that the waste heat recovery of flue gas is mainly the evaporation latent heat recovery of water, accounting for about 90%; circulating water is used as cooling medium, and the waste heat recovery capacity of flue gas is stronger; compared with circulating water, when air is used as the cooling medium, the effect of inorganic ceramic membrane flue gas waste heat recovery is more significant, and the enhancement coefficient is as high as 9; increasing the flue gas flow is helpful to improve the heat recovery power and composite heat transfer coefficient; at the same time, inorganic ceramic membrane can also recover condensate with high water quality. The results of this paper can provide a reference for the application of inorganic ceramic membrane in flue gas waste heat recovery.

Abstract With increasing environmental concerns, much effort has been spent in research regarding development of sustainable processes for production of fuels and chemical products. In this context, hydrothermal liquefaction (HTL) has gained increasing attention, as a possible route for the chemical transformation of organic raw-materials, some sort of biomass, for example, into liquid oils at temperatures usually below 400 °C, under moderate to high pressures (5–25 MPa), usually in the presence of a suitable catalyst. In the present work the thermogravimetric (TG) behavior under inert atmosphere of pure green coconut fiber and mixtures thereof with a spinel phase (Fe2CoO4), acting as catalyst has been studied. Spinel samples have been produced at 1,000 °C and different calcination times (3 h, 6 h and 9 h). Both raw and synthesized materials were characterized through different techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and Infrared Absorption Spectroscopy (FTIR). According to the TG data, the catalyst produced during a calcination time of 9 h showed a superior behavior regarding the lignin full thermal decomposition, which developed without fixed carbon formation. The results further suggest that the mixing process has a significant effect over the measured degradation kinetics, as it has a direct influence over the contact between catalyst and fibers. The kinetic modelling applied to the dynamic TG signal allowed a quantitative representation of the experimental data. The global process activation energy and order have proven to be respectively, 85.291 kJ/mol and 0.1227.