Transactions of the Chinese Society of Agricultural Engineering, the 1st in Agricultural Engineering, is supervised by China Association for Science and Technology, and sponsored by Chinese Society of Agricultural Engineering. It aims to introduce the latest scientific achievements and developing trends of Agricultural Engineering and provides the academic developments abroad and domestic of the discipline. The scope covers agricultural water-soil engineering, agricultural information and electrical technology, agricultural products processing engineering.
The journal is included in EI, JST, Pж(AJ), CA and CSCD.
Editor-in-Chief Zhu Ming
Deputy Editor-in-Chief Wei Xiuju Zhang Ruihong Xi Weimin Wang Liu Wang Yingkuan Li Pingping Ying Yibin Tong Jin Yun Wenju Zhao Chunjiang Kang Shaozhong
The exergy is defined as the maximum useful work possibly during a thermal dynamic process that brings the system into equilibrium. Analysis of exergy utilization provides a fair and effective method for evaluating the energy efficiency. Since drying is a comprehensive process involving complicated interaction among different materials, exergy analysis is especially helpful in rating the efficiencies of different drying strategies. However, the mechanism behind the exergy transfer and conversion during drying has not yet been fully investigated and understood. At present, the lack of theoretical analysis is hindering the implementation and progress of the sophisticated applications. The theoretical difficulties include the quantitative understanding and expression of the coupling effect in different exergies. In this article, we analyzed the exergy transfer and conversion between grain and drying medium. In a drying process, the ultimate goal is to reduce the water content in the grain until it is in the dryness that is the same as the environment where the grain is stored. Therefore, we defined exergy as zero when the system was in equilibrium with the ambient environment. Based on the comprehensive coupling of the potential energy difference, temperature gradient, and pressure gradient, the theoretical models of thermal exergy, flow exergy, diffusion exergy, and exergy efficiency were given. We also studied the relationships and restrictions of different exergies based on the enthalpy-water diagram. Our results revealed that drying was the result of the simultaneous action of thermal exergy, diffusion exergy and flow exergy. The conversion and transfer of thermal exergy could be directly characterized by water vaporization, which was driven by the temperature gradient in the system. Most of the thermal exergy was directly converted to the latent heat of evaporation. Regardless of the number and type of the heat sources, the thermal exergy transfer was always directly related to the temperature gradient of the drying system. Diffusion exergy originates from the excess water in grain. The vapor pressure difference between the wet grain and the drying medium will naturally drive the water transfer, making the wet grain to dry medium. The temperature gradient and pressure gradient both had important effects on the diffusion process. When the temperature gradient was opposite to the vapor pressure gradient, the exergy efficiency was enhanced; otherwise, the exergy efficiency was weakened. The flow exergy maintained the potential difference necessary for the transfer of heat exergy and diffusion exergy. Without flow exergy, the transfer of heat and wet exergy could not be effectively carried out. In a naturally ventilated drying system, the exergy difference between the wet grain and drying medium was the driving force behind the drying process. Drying could be summarized as the process of exergy transfer and conversion, converting physical conditions of wet grain into to conditions of the drying medium. Different from isolated systems, the thermal equilibrium of a drying process was determined by the ambient environment which was always static regardless of the size of energy and mass transfer. The drying process still followed the second law of thermodynamics. However, the entropy increase of the ambient environment was negligible. The thermal exergy, diffusion exergy and flow exergy could all be expressed in state functions. We provided the time-dependent state functions of exergy and exergy efficiency to reveal the change of exergy flow density and efficiency according to the environmental conditions and the conditions of the grain. These theoretical models could be applied to making fair and reasonable evaluation on the energy utilization in practical applications. Based on the theoretical analysis of exergy and its efficiency, the largest exergy loss process could be predicted and prevented. These models provided a scientific basis for evaluating the energy utilization in a drying system, and could be used to optimize the drying process.
Plastic film is widely used in Xinjiang area, and it is hard to separate and collect the residual film of plough layer because of serious fragmentation. To solve the problem of residual film recovery in plough layer, we designed and developed a chain-sieve type plastic residual film recovery machine. The machine consists of excavating shovel, barrier clearing mechanism, transmission mechanism, eccentric wheel, link mechanism, chain-tooth mechanism, film separating roller, vibration mechanism, and frame and film box. The power of each part is provided by the transmission mechanism. The soil film mixture is excavated into the chain tooth mechanism by excavating shovel, and then the chain-tooth mechanism is used for the first separation and sieving of the soil film mixture. After that, the sieved soil film mixture is transported to the vibration mechanism. The tail part of the chain-tooth mechanism is equipped with a film seperating roller, which scrapes the film wound on the mechanism. Finally, the residual film is sent to the film box by vibration mechanism. Vibration mechanism consists of vibration sieve and link mechanism, and the vibration and swing of vibration sieve is controlled by the link mechanism. The soil film mixture is separated by the vibration sieve and then is conveyed to the film box. The size and parameters of the machine was determined by analysis and calculation. The key working parts of the machine were simulated and analyzed in ADAMS, and relevant motion parameters were obtained. The separation of the soil film mixture by the vibration mechanism requires that the speed range of the eccentric wheel was 25.79 rad/s ≤
ω ≤ 31.40 rad/s. According to the theoretical calculation and test, the speed of the eccentric wheel was determined to be 255 r/min. The central composite design method of Box-BenhnKen was used to analyze the effect of working parameters on the residual film rate of recovery. The three factors, three levels and one regression orthogonal test design was adapted, and the moving speed, depth into soil and speed of driving wheel of conveyor chain were selected as the influence factors. In April 2017, a field test was carried out in the Sixth Regiment of the First Agricultural Division of Xinjiang Production and Construction Corps. The test area was divided into 17 test plots (each plot is 25 m × 4 m), and the residual film rate of recovery of plough layer at each test plot was calculated. The test results showed that the average residual film rate of recovery (
ε) of plough layer was 83. 34%. Response surface methodology was used to analyze the effects of various factors on the rate of recovery, and the regression model optimization results were that the moving speed was 1.317 m/s; depth into soil was 117.066 mm; the speed of driving wheel of conveyor chain was 65.106 r/min. When the amplitude of the vibration mechanism was 79.1 mm and the speed of driving wheel of conveyor chain was 255 r/min, the residual film rate of recovery of field test was 85.07%, and the parameters optimization results met the requirements. Moreover, the machine met the performance requirements of plough layer residual film recovery. The method of combining chain-tooth mechanism with vibration mechanism provided a new idea for the residual film recovery of plough layer.
With the development of the global economy and the improvement of people’s living standards, the demand for traditional energy is increasing, which has led to serious energy shortage and increasingly serious environmental pollution. More and more attention has been paid to thermoelectric power generation technology which takes the industrial and automobile waste heat as a heat source. In order to plant out-of-season plants and southern plants, the northern greenhouses generally use a heating pipeline for heating. Cathodic protection, as the main protective measure for buried pipelines, plays an important role in pipeline protection. In order to alleviate the corrosion rate of heating pipelines, the method of joint use of external anti-corrosion insulation layer and cathodic protection is generally adopted during the deployment of metal pipelines. This is also the most economical and reasonable anti-corrosion measure. Cathodic protection protects the metal from being corroded by the environmental media (such as soil), protect pipelines or equipment by corrosion with the auxiliary anode or sacrificial anode materials, thereby achieving the purpose of prolonging the service life of the protected pipeline and improving its safety and economy. However, the cost for conventional external-current cathodic protection methods is high with a large footprint, and the protection life of the sacrificial anode method is too short. Therefore, in order to provide reliable external-current cathodic protection for greenhouse heating pipelines, this article used the waste heat from the surface of the underground heating pipelines, through direct conversion of thermal energy into electrical energy by a thermoelectric power plant, to provide the cathodic protection of the external current mode for the buried heating pipeline. The technology has the advantages of green, environmental protection, simple structure, safety, and reliability. This article focused on the research of thermoelectric power generation systems, introduced the basic theory of thermoelectric power generation, and derived the relationship of characteristic parameters of the thermoelectric cell. Based on the output characteristics of the thermoelectric cell, this article designed a self-powered system based on the BQ25504 chip. The system collected the thermoelectric energy and continuously supplied it in the maximum power point tracking mode during operation. The thermoelectric conversion energy was collected by the BQ25504 chip produced by TI and then supplied by the step-down regulator chip LM317 to cathodically protect the buried heating pipeline. The design used the temperature of the pipeline as a heat source, and it had the advantages of almost no land occupation, long-term use, flexible protection, and energy saving. Through field tests, the temperature difference between the cold and the hot ends of the device was found to be 33.2 °C, which proved that the greenhouse heating pipeline was a heat source worthy of utilization. Finally, through the natural corrosion test, it was found that when the horizontal distance of the anode bed was 1.69 m and the protection potential provided by the device was −1 100 mV, the degree of protection to the pipeline could reach 92.79%. This study provides a more feasible solution for the protection of greenhouse heating pipelines, and at the same time, the short-distance pipeline protection technology of the external current mode was also explored.
The thermal insulation performance of granary envelope has important impacts on the safety of grain storage and granary energy consumption. The roof of a granary is usually very large. Since roof is the position that receives the strongest solar radiation in the granary, the external heat is mainly transferred into granaries through roofs. Therefore, granary roof is the key part in the design of thermal insulation in the building envelope of granaries. Double-skin ventilated roof, high reflectivity coatings for roof, and thermal insulation material are three popular techniques of granary roofs for storage safety and more energy saving. According to different solar radiation levels and different climatic characteristics, the optimum thermal insulation thicknesses of roofs are different in different areas of China. In this paper, the transient heat transfer model of multi-layer roof was presented and validated for calculating the energy consumption of ordinary roofs in low-temperature granaries. By considering the influence of natural ventilation, a heat transfer model of double-skin ventilated roof was proposed and validated for determining the energy consumption of double-skin ventilated roofs. In this pater, the
P1–
P2 economic models were used to study the optimum thermal insulation thicknesses of the ordinary multi-layer roof and the double-skin ventilated roof of the low-temperature granaries in Changsha. The effect of different solar radiation reflectivities of exterior surface was considered in determining the optimum thermal insulation thickness of the low-temperature granary roof in Changsha. The optimum thermal insulation thicknesses of two thermal insulation materials including EPS and XPS were calculated for ordinary roof and double-skin ventilated roof of the low-temperature granary in Changsha by using
P1–
P2 economic model respectively. Then, on the basis of life cycle cost analysis, the life-cycle total (LCT) costs, life cycle saving (LCSs), and payback periods were calculated. The results of this research show that the solar radiation reflectivity of the exterior surface has a significant impact on the economy and the optimum thermal insulation thickness of the low-temperature granary roof in Changsha. The double-skin ventilated roof can reduce the optimum thermal insulation thickness of low-temperature granary roofs. Double-skin ventilated roofs and high reflectivity coatings for roof should be adopted in the low-temperature granary roof in Changsha for more energy conservation and less environmental pollution. The optimum thermal insulation thicknesses of XPS and EPS range from 0.106 to 0.183 m for ordinary roofs of low-temperature granaries. The maximum LCSs range from 417 to 633.38 RMB CNY/m
2. The payback period ranges from 2.39 to 2.96 a. EPS has a thicker optimum thermal insulation layer than XPS. Besides, EPS also has a shorter payback period of optimum thermal insulation thickness of roof than XPS. The optimum thermal insulation thickness of the roof falls with the rise in solar radiation reflectivity of the exterior surface of the roof. The double-skin ventilated roof can shorten the payback period of the optimum thermal insulation thickness of the low-temperature granary roof. In addition, this determination method of optimum thermal insulation thickness of roofs is of vital importance to guiding design process of thermal insulation thickness of low-temperature granary roofs.
In the background that the country pushes forward the new type of urbanization, spatial planning, and urban agglomeration planning, it is of great significance to scientifically cognize the driving-force mechanism of urban land expansion for the urban agglomeration, which is important for the sustainable development of land use and planning for urban agglomeration. With Wuhan metropolitan area as taken an example, the paper uses the land use data, socio-economic factors, neighborhood factors, and natural factors in 1995, 2000, 2005, 2010, and 2015 to construct the Logistic–GTWR (Logistic geographically and temporally weighted regression) model, which couples the spatial heterogeneity and temporal non-stationarity. The model is used to explore the driving forces and its spatio-temporal differentiation pattern of urban land expansion in Wuhan metropolitan area. The results highlight the following points: 1) The Logistic–GTWR model that couples spatial heterogeneity and temporal non-stationarity has a better performance than the global logistic regression model and the Logistic–GWR (Logistic–Geographically Weighted Regression) model which only considers the spatial heterogeneity. Consequently, the applicability of Logistic–GTWR model in driving force analysis of urban land expansion is verified. 2) There are significant disparities in the spatio-temporal patterns for various driving forces of urban expansion in Wuhan metropolitan area. For example, the high-value areas of population shrank, spread, and then stabilized around Wuhan. At last, a circular distribution pattern was formed around the central part of Wuhan metropolitan area as time went by. The high-value areas of GDP per acre firstly shifted to the west, then gradually balanced, and finally concentrated around Wuhan, Macheng, and Chongyang. The effect of polarization played a dominant role in the process of urbanization in Wuhan, and its influence range was constantly expanding with apparent rent-seeking effects. 3) Population and economy were the core driving forces of urban expansion in Wuhan metropolitan area in 20 years and the influences of the two factors were increasing year by year. The influence of distances to national roads, highways, and provincial roads slightly grew. 4) The central and eastern cities were mostly those where population and economy were the core driving forces. The influence of DEM was gradually prominent in the development of Wuhan on account of rapid development and decreasing land resources. The cities in the west were mainly restricted by DEM and driven by traffic, where the differences between the east and the west were obvious. However, the intensities of the population and economy in western cities gradually increased since 1995. The effects of population and economy on western cities were on an uptrend since 1995. Similarly, the intensity of population was gradually increasing in Xianning and Huanggang. In Wuhan, Xiaogan, Xiantao, Tianmen, and Qianjiang, economic factors had an increasing trend year by year. This research provides a model that couples spatial heterogeneity and temporal non-stationarity, depicting more detailed spatio-temporal differentiation characteristics of driving factors, which is beneficial to the meticulous management of land resources.
