Abstract In order to lighten the tar from coal pyrolysis, the effects of N2, CH4 and H2 atmosphere on the pyrolysis characteristics of Pingshuo bituminous coal were investigated in a small fluidized bed, and Ni-based catalyst was placed downstream of coal pyrolysis to catalyze the upgrading of tar. The results show that both H2 and CH4 atmosphere can improve the conversion of coal pyrolysis and improve the yield of pyrolysis tar. Compared with CH4 atmosphere, the post placed Ni-based catalyst in CH4 atmosphere can increase the tar yield by 10%, increase the gas yield and H2 yield, and transform the pyrolysis tar to the light direction. Through simulated distillation and GC-MS analysis, compared with N2 atmosphere, CH4, H2 atmosphere and CH4 + Ni increased the relative contents of naphtha, phenol oil, naphthalene oil, wash oil and anthracene oil, and the increase showed that CH4 + Ni > H2 > CH4, while the asphalt content decreased. Compared with CH4, the relative contents of aromatic hydrocarbons and aliphatic hydrocarbons increased significantly under CH4 + Ni.

Abstract Taking a demonstration project of a ground source heat pump system under karst geological conditions in Guilin as the research object, based on the measured data under operating conditions in a typical season, and sorted according to the importance of influencing factors, this paper mainly studies the influence of system at very low load rate and unit load rate on the operation effect of ground source heat pump system. The research results show that the ground source heat pump system is in good operating condition when the system load rate is lower than 30.00% and the unit load rate is higher than 80.00% in typical seasons, and the proportion of power consumption of units and pumps meets the energy consumption requirements of transmission and distribution system. During the operation of the heat pump unit in July, the average refrigeration performance coefficient of the unit is 4.48, and the average refrigeration energy efficiency ratio of the system is 3.59; during the operation in January, the average heating performance coefficient of the unit is 4.26, and the average heating energy efficiency ratio of the system is 3.32; the energy saving rate in summer and winter is 30.72% and 35.93%, respectively. The energy-saving effect of the ground source heat pump system is remarkable, and it is worth popularizing and applying in Guilin.

Abstract In view of the complex structural characteristics and special operating environment of the horizontal spiral tube heat exchanger of the shaft sealed nuclear main pump, the numerical simulation method of flow heat coupling is used to analyze the influence of the flow and temperature changes of the fluid on the shell side on the flow field and temperature field of the heat exchanger, explore the influence rules of the inlet parameters on the flow and heat transfer characteristics of the fluid in the heat exchanger, and analyze the enhanced heat transfer performance of the heat exchanger by using the relevant heat transfer criteria. The results show that the horizontal spiral tube fluid generates centrifugal force under the influence of curvature, forming a secondary flow which is different from the straight tube flow heat transfer, and the velocity distribution is concave arc, which will enhance the heat transfer efficiency of the heat exchanger; with the increase of shell side velocity, the degree of fluid disturbance and turbulence increases, while the pressure loss does not change significantly, and the heat transfer performance of the heat exchanger increases; under the given structure and size, the heat transfer performance curve of the heat exchanger shows that the increase of shell side flow and Reynolds number has a significant impact on the enhanced heat transfer of the spiral tube. In practical engineering applications, the heat transfer can be strengthened by appropriately increasing the shell side flow of the heat exchanger.

Abstract The mathematical model of a new flat plate heat pipe PV/T heat pump system is established. The experimental data of the system under various working conditions are obtained through experimental measurement, and the accuracy and reliability of the model are verified. Based on the verified mathematical model, the thermal performance, electrical performance and the performance of the heat pump system are simulated. The results show that under winter conditions, the daily average thermal power, electrical power and COP of the system are 274.5 W, 93.5 W and 2.7 W respectively. Due to the low outdoor ambient temperature in winter, during winter operation, the heat collection system will lose a lot of heat to the surrounding environment through the photovoltaic panel surface, resulting in the heat collection of the system cannot meet the heat demand of the heat pump side, which is intuitively shown as the water temperature of the heat collection tank on the evaporation side shows a downward trend throughout the day. Therefore, the collector module of the system is optimized by adding a collector. After optimization, the daily average thermal power of the system is increased to 654.2 W and the COP is increased to 6.9.

Abstract A new type of regenerative shell-and-tube heat exchanger is designed to solve the problems that the generation load of cogeneration units is limited by the amount of heat supply during the heating period, the peak shaving capacity of units decreases, and the phenomenon of wind and light abandonment in the power system is serious. Considering the advantages of nearly constant temperature and large potential heat release during the heat storage/release process of phase change materials, paraffin is selected as the phase change material, and the phase change area of the heat exchanger is selected as the heat exchange unit. The control variates method is used to simulate the heat storage/release process of the heat exchange unit according to the key factors such as the flow rate of heat transfer fluid, the thermal conductivity of phase change materials and the thickness of phase change layer. The results show that increasing the flow rate of heat transfer fluid can enhance the heat storage capacity of the heat exchange unit and shorten the complete melting time of phase change materials. In order to control the heat at the output end of the heat exchanger during the heat release process, the flow rate of heat transfer fluid should be appropriately selected; using composite materials to improve the thermal conductivity of phase change materials can enhance the heat transfer capacity of the heat exchange unit, and the average heat transfer coefficient of the heat exchange unit is more than 2 times higher than that of pure paraffin at the same heat transfer fluid flow rate; increasing the thickness of phase change layer can prolong the time of maintaining the outlet temperature of heat transfer fluid in the process of heat release.

Abstract In order to study the influence of the corrugated angle and width of enamel heat storage element on the flow and heat transfer performance, a certain enamel heat storage element was numerically simulated by FLUENT software, and the variation curves of internal flow field velocity, temperature distribution, Nusselt number and drag coefficient with Reynolds number were obtained when the corrugated angle and width of the heat storage element were different. The simulation results show that when the ripple inclination increases from 20° to 60°, the resistance coefficient of the heat storage element increases, and the Nusselt number increases, and the increase of the resistance coefficient is greater than that of the Nusselt number; when the ripple width increases from 6 mm to 10 mm, the increase of resistance coefficient is small, and the increase of Nusselt number is large.

Abstract Taking a certain type of combustion chamber as the research object, the numerical simulation is carried out by using RANS (Reynolds averaged Navier-stokes) and LES (large eddy simulation), and the simulation results of the two numerical methods are compared and analyzed. The research results show that the RANS calculation results can reflect the main flow field characteristics in the combustion field, and have certain engineering significance. LES can reproduce specific flow field details such as the weak axial flow region, accurately simulate the location and strength of the shear layer, simulate the dynamic development process of flame, and capture the dynamic characteristics of the combustion flow field. Compared with RANS, LES has more obvious advantages in numerical simulation of the combustion flow field. Through calculation, the precessing vortex core under this working condition is composed of three relatively independent spiral vortex branches, which excites periodic velocity pulsation and pressure pulsation in the combustion chamber. LES captures the dominant frequency with the precession vortex core of 156 Hz.

Abstract The paper presents a numerical study of compact tube-fin heat exchangers with Venetian blades. The influence of the number of Venetian blades on the thermo-hydraulic characteristics of the exchanger is determined. A 3D numerical model was used in the laminar regime and for a Reynolds number variation, based on the hydraulic diameter between 120 and 1,200. By varying the number of Venetian blinds upstream and downstream of the central Venetian blind, it is determined that, for smaller numbers of Reynolds fins with 2 Venetian blades, the highest heat transfer coefficient is obtained. On the other hand, by increasing the air velocity at the model inlet, better heat transfer results are obtained for geometries with a higher number of Venetian blades.

Abstract One of the most important variables to know how efficient a thermal machine is the exergy. In practice, it is one of the least controlled variables. In this research, a thermal exergy study was carried out in a compact pyrotubular steam generator. To achieve this, an energy mass balance and entropy balance were carried out. The energy balance was carried out by direct and indirect methods. The percentages of the exergies of each working substance in the process are specified. The energy yield by the direct method was 0.901 and by the indirect method was 0.882, since each method has its role in the energy analysis. The irreversibilities in the process were 26%. The exergetic efficiency was 0.39, conditioned by a complete combustion in the hearth. It was demonstrated that the steam generator for the real operating conditions is oversized.