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Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Science Technology & Engineering is the property of Chinese Society of Technology Economics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wet grain drying is a significant processing step in grain production. Grain in-bin drying is one of the most widely-used and effective drying ways to integrate with drying and storage in grain drying areas. Therefore, this study aims to clarify the performance and energy consumption of liquid desiccant dehumidification grain in-bin drying using a layered model. A system of grain in-bin drying was also designed using liquid desiccant dehumidification driven by a heat pump. New technology was finally developed to achieve safe, efficient, and energy-saving grain drying and storage process for grain in-bin drying. The mathematical models were established to verify, including heat pump, dehumidifier/regenerator, and grain in-bin drying. A specific process was simulated, where the top layer of rice with a grain pile height of 3 m and initial moisture content of 0.2 (wet basis) was dried to reach the safe moisture content of 0.135 (wet basis) by the air flow rate of 120 m³/(h·t) under different outdoor weather parameters with the air temperature of 20-32 ℃ and relative humidity of 55%-80%. Some parameters were determined, including the drying time, the unit and total energy consumption, the dry matter loss (DML), and the whiteness of the top rice after drying. After that, a comparison was made on the performance of the system with various drying. The results showed that the range of drying completion time was 194-358 h. Taking the grain temperature of 20 ℃ and 25 ℃ as examples, the drying completion time was within 21 and 14 d of the safe drying period, respectively. Both met the requirements of a safe drying period, indicating the feasibility of drying time specification. Moreover, the DML top layer of rice after drying was 0.33%-0.52%, where most of the weather parameters met the specification requirement of DML < 0.5%. The initial whiteness value of the top layer of rice was 51.5, while the whiteness value after drying was 51.331-51.452 acceptable in the market (>45), indicating that the overall whiteness value decreased slightly after drying. The suitability of the heat balance model and thin-layer drying equation were verified, where the air entered the grain bin in a state close to the outdoor air temperature and low humidity after dehumidification and heat exchange. Furthermore, the unit energy consumption range was 2.09-3.25 kW·h/ (1% moisture·t), and the total energy consumption was 6 930-9 530 kW·h. It was more conducive to reduce the unit and total energy consumption of the system for high drying efficiency when the outdoor air temperature was higher than before. Nevertheless, the high temperature may lead to more DML of the top layer of rice, even to lower quality. It was found that each thin layer of rice met the dual specification requirements of DML (<0.5%), and the unit energy consumption of the system (<2.5 kW·h/(1%·t)) at the air temperature of 30 ℃. The drying rate and energy consumption under the summer parameters were better than those under the autumn, whereas, the DML and color of rice were inferior to the autumn parameters. The improved system presented a fast speed, less energy consumption, and better rice-related quality, compared with heat-pump drying. Consequently, the system performed well in terms of drying time, energy consumption, and rice-related quality indicators under specific weather conditions, indicating the appropriate and accurate model. The finding can provide a preferred choice for safe, efficient, and energy-saving grain in-bin drying. [ABSTRACT FROM AUTHOR]

The liquid dehumidification and heat pump hybrid (LDHP) system, the temperature-humidity independent control (THIC) system and traditional heat pump (HP) system have been being studied by researchers. In the LDHP system, the supply air was cooled by heat pump firstly and then was sent to the dehumidifier for dehumidification, finally the air after dehumidification was sent to the indoor environment. The heat and mass transfer in dehumidifier and regenerator would release/absorb moisture latent heat; therefore, heat absorption/extraction through a heat pump could be used to achieve isothermal dehumidification/regeneration in an ideal process. In the THIC system, the liquid dehumidification system was adopted to handle the fresh air and part of the return air, which was utilized to deal with the entire latent heat load indoors. Meanwhile, the rest of return air was cooled by the heat pump so as to remove indoor sensible heat load. In the ideal HP system, the outdoor air was preheated by indoor exhaust air in the total heat exchanger, and then mixed with return air, Then the mixed supply air was cooled and condensate by the heat pump. Under ideal conditions, the process from reheating the air under dew point to reach the air supply state was able to absorb heat from outdoor by the ideal heat engine in which the air under dew point was heated and output work yielded at the same time. In this paper, models of ideal reversible process were constructed to analyze the theoretical maximum of the coefficient of performance (COP) for the above-mentioned system under different conditions. Meanwhile, the influences of different supply air temperature, enthalpy humidity ratio, indoor and outdoor environmental air conditions on the COP of those system were also discussed. Results indicated that increasing the supply air temperature difference or reducing the enthalpy humidity ratio would decrease the COP of three mentioned systems in ideal condition, and simultaneously the COP was more significantly affected by the supply air temperature difference. When the enthalpy humidity ratio was 5 000, the supply air temperature difference increased from 2 to 10 ℃, COP of LDHP system and HP system fell by 26% and 18% respectively, which was far below the 63% of THIC system. When the enthalpy humidity ratio ranging from 4 000 to 20 000, the COP of LDHP, THIC and HP system increased by 28%, 99% and 33%, respectively. At the same time, the influences of indoor and outdoor environmental air parameters on the COP of those systems were also involved. The COP of the three systems all increased with increasing the indoor air design temperature or relative humidity, which had nearly doubled in the whole simulation range. Meanwhile, during the process of the outdoor environmental air temperature and relative humidity varying from 28 ℃, 60% to 38 ℃, 85% , the COP of LDHP system, HP system, THIC system decreased by 78.3%, 59.7% and 52.1% respectively, and the COP was more obviously affected by the air temperature. Furthermore, the COP of the LDHP system was the largest, followed by the HP system, and the THIC system was the lowest under the simulation conditions. The research results in this paper provided a theoretical guidance for the selection and optimization of the three air-conditioning methods. [ABSTRACT FROM AUTHOR]

Liquid desiccant cooling system, as a good alternative to traditional electric refrigeration air conditioner, is environmentally friendly and can be driven by low-grade energy while it can improve indoor air quality and has high energy storage capacity. The regeneration technique, a key technique in the liquid desiccant cooling system, must be developed before it is widely applied in variety of buildings. The present methods of solution regeneration have electrodialysis, membrane energy exchanger, ultrasonic atomization regeneration, packing tower, and so on. The first three have complicated structures and high costs for their application on a large scale. The packing tower regenerator because of its simple structure and being driven possibly by low-grade energy has attracted many attentions across the world. In packing tower regenerators, the internally-heated liquid desiccant regenerator is a kind of high-efficient solution regeneration device. To improve the reliability and economy of internally-heated regeneration technique, the mathematical models of pre-heated and internally-heated regeneration are established based on the energy and mass conservation between solution and air as well as the energy conservation between heated water and solution in this paper, which include parallel flow, counter flow and cross flow with 2 kinds of different flow directions of heated water respectively, and their theoretical performances are numerically simulated and compared with each other. As for the regeneration performances affected by the ways of heating solution and flow directions of heated water, the simulation results show that regeneration performances of internally-heated type are about 2-4 times that of pre-heated type in most conditions, which means the internally-heated regenerator has a better performance. And the regeneration performances are greatly influenced by the flow-rate ratios of solution to air and heated water to air. With the decrease in flow-rate ratio of solution to air and the increase in flow-rate ratio of heated water to air, the regeneration performances of the internally-heated regenerator are increasingly better than that of the pre-heated regenerator. At the maximum point of the internally-heated (flow-rate ratio of solution to air is 0.1 and flow-rate ratio of heated water to air is 0.95, flow-rate ratio of air is 1 kg/s), the rate of evaporation is calculated to be 20 times that of the pre-heated at its maximum point (flow-rate ratio of solution to air is 0.4, flow-rate ratio of heated water to air is 0.65). The flow direction of heated water in internally-heated regenerator is divided into 2 conditions: Heated-water is parallel to solution (DirectionⅠ) or counter to solution (DirectionⅡ). It is also found the regeneration performances, when the heated water flows counter to solution, are superior to heated water paralleling to solution and are increased by 5% at most. As for the effects of the numbers of heat transfer units (NTU1 and NTU2), the regeneration performances in general increase with the increase in NTU1 and NTU2, and a fitted curve combining NTU1 with NTU2 occurs that presents the rapidest increase in regeneration performance with the increasing of NTU1 and NTU2. Besides, it is also exposed that parallel type shows the largest concentration difference of solution and the cross type is about 97% of that, while the counter type only reaches about 87% as much as parallel type in the worst condition. The results in this paper can offer theoretical supports for the optimal design of internally-heated regenerator. [ABSTRACT FROM AUTHOR]

Solar liquid desiccant air-conditioning system has attracted many attentions owing to the advantages of utilizing low grade thermal energy such as solar energy, in which the solar collector and regenerator can be designed respectively. In addition, solar collector and solution regenerator can be combined together to construct solar collector/regenerators (C/Rs) that have better performance of regeneration. Solar C/Rs are the key component of system, because the cooling capacity of system is determined mainly by the regeneration efficiency. Moreover, in order to reduce top heat losses and eliminate contamination of the solution by dust, the C/Rs can be covered with the glazing plate. An experimental study on the effect of glazing plate height of solar C/Rs indicated that the optimum glazing plate height is 0.07 m, and the performance of the optimally glazed C/R is better than an unglazed C/R for hot humid climates. Analysis based on experimental data and numerical simulation was presented, and the results show a higher inlet solution temperature can increase the performance of regeneration. So the method of preheating the inlet solution was adopted to increase the efficiency of solar C/R, and solution heat recovery device was used to preheat the inlet solution by recovering the heat from the outlet solution. However, there have not been sufficient studies on the effect of various parameters on C/R performance with solution heat recovery. In this paper, the solution heat recovery device, by recovering heat from the outlet solution to preheat the inlet solution, was adopted to increase the efficiency of solar C/R. The numerical simulation method was adopted for analyzing the effects of the glazing plate height, solution parameters, air parameters, solar radiation intensity and other factors on the regeneration efficiency of solar C/R with solution heat recovery. Several physical assumptions were made, followed by modeling of counter-flow regeneration. And the previous experimental data were used for the comparison with the numerical results to validate numerical model. In the simulation conditions, the results show: Using a heat recovery device can improve the regeneration efficiency by 93.6% equivalent to adding 0.8 m length of C/R; the higher efficiency of heat recovery device causes the higher regeneration performance; the flow rates have an optimum value, which yields a maximum rate of water evaporation and regeneration efficiency. The optimum values of flow rates of solution (or air) increased with the increase in air flow rate (or solution flow rate), and the optimum ranges of flow rates of solution and air are 8-15 and 100-150 kg/h, respectively. The optimum range of glazing plate height is 0.08-0.1 m when flow rates are in the optimum ranges; higher inlet temperature of solution or air both can increase regeneration efficiency, but the method of heating solution is much more effective than heating air; the decrease of inlet concentration of solution or relative humidity of air both can be in favor of solution regeneration; the higher solar radiation intensity yields better performance of regeneration for the solar CR with heat recovery. All these results can provide guidance for the design and performance analysis of the solar CR. [ABSTRACT FROM AUTHOR]

At present, the most widely used air conditioner is vapor compression cooling systems driven by electrical power.The dehumidification method of vapor compression cooling systems is often to cool the air below its dew point, and so the approach consumes much electrical energy, particularly when the air should be reheated after the dehumidification process.Besides the traditional dehumidification method(cooling the air below its dew point), the air may also be dehumidified by liquid desiccant and the liquid may be regenerated by solar energy.As a result, solar energy driven liquid desiccant cooling systems have emerged as a potential alternative to conventional vapor compression systems for cooling and air conditioning.Two important parts of the solar liquid desiccant air conditioning system are the regenerator in which the weak solution is concentrated, and the solar collector in which solar radiation is transformed into heat energy.The 2 components may achieve their own functions respectively.The weak desiccant solution flows into the solar collector and absorbs the solar thermal energy, leading to the increase in its temperature, and then the heated weak desiccant solution flows into the regenerator and contacts with the passing air stream.In the regenerator, moisture is evaporated from the hot weak solution and then removed by the passing air, and as a result the weak solution is concentrated.On the other hand, solar collector/regenerators(C/Rs) are designed to achieve the dual functions of solar collector and solution regenerator for high regeneration efficiency.In order to increase the efficiency of solar solution C/R, a method of solar air pretreatment solution grading C/R is put forward in this paper.The solar air pretreatment solution grading C/R is chiefly made up of the first grade solar C/R, the second grade solar C/R and the packed bed dehumidifier.The first grade solar C/R adopts directly surrounding air for regenerating solution with low concentration that is used to dehumidify the regeneration air for regenerating solution with high concentration in the second grade solar C/R.Such design aims to increase regeneration efficiency of strong solution in the second grade solar C/R.A mathematical model on solar air pretreatment solution grading C/R is built by defining quality factor of evaporation rate of water vapor that is used to show difference of regeneration performance of different concentration solutions under other same parameters.In that model, effective solution proportion and effective storage capacity are defined to describe the performance of solar air pretreatment solution grading C/R.The simulation results show when the efficiency of heat exchange used for solution pre dehumidification is equal to 0.69, the effective storage capacity reaches the maximum.Moreover, the effective storage capacity increases with the increasing of the product of specific surface area and tower length.There are critical values for relative humidity of surrounding air and solar radiation intensity that are used for judging if the new solution regeneration method is superior to direct solar solution C/R.Simulation results show the critical values for relative humidity and solar radiation intensity are 60% and 780 W/m2 respectively under given simulation conditions in the paper.When the relative humidity of surrounding air is greater and the solar radiation intensity is weaker than its own critical value, solar air pretreatment solution grading C/R has greater superiority compared with traditional solar C/R.Finally, it is concluded that the proposed solar air pretreatment solution grading C/R performs satisfactorily for regenerating the solution with high concentration under the climates of high humidity and low solar radiation in southern China. [ABSTRACT FROM AUTHOR]