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[en] In this study, a small scale hybrid solar heating, chilling and power generation system, including parabolic trough solar collector with cavity receiver, a helical screw expander and silica gel-water adsorption chiller, etc., was proposed and extensively investigated. The system has the merits of effecting the power generation cycle at lower temperature level with solar energy more efficiently and can provide both thermal energy and power for remote off-grid regions. A case study was carried out to evaluate an annual energy and exergy efficiency of the system under the climate of northwestern region of China. It is found that both the main energy and exergy loss take place at the parabolic trough collector, amount to 36.2% and 70.4%, respectively. Also found is that the studied system can have a higher solar energy conversion efficiency than the conventional solar thermal power generation system alone. The energy efficiency can be increased to 58.0% from 10.2%, and the exergy efficiency can be increased to 15.2% from 12.5%. Moreover, the economical analysis in terms of cost and payback period (PP) has been carried out. The study reveals that the proposed system the PP of the proposed system is about 18 years under present energy price conditions. The sensitivity analysis shows that if the interest rate decreases to 3% or energy price increase by 50%, PP will be less than 10 years. (author)
[en] A constant temperature and humidity air-conditioning system driven by ground source heat pumps was designed and constructed in an archives building in Shanghai, China. The system consists of two water-to-water heat pumps and 280 boreholes with 80 m in depth. In order to keep the temperature and humidity constant, the operation mode that one heat pump ran in heating mode and the other one ran in cooling mode was deployed. According to the experimental results under typical winter weather condition of Shanghai, the average COP of the heat pump in heating mode was 5.2. The average temperature and relative humidity of the archives house were 22.8 deg. C and 52.5%, respectively. It was found that the operation mode we deployed could reduce the heat absorbed from the soil by 20%. Theoretical analysis showed that it was helpful for the earth energy conservation with one heat pump operated in cooling mode in winter. It was also shown that the decrease range of temperature of the soil in the middle of two boreholes would reduce with the increase of the distance between two boreholes. The distance between two boreholes is suggested to be 4-5 m in Shanghai.
[en] A two-stage solar powered liquid-desiccant dehumidification system, for which two kinds of desiccant solution (lithium chloride and calcium bromide) are fed to the two dehumidification stages separately, has been studied. In the studied system air moisture (latent) load is separately removed by a pre-dehumidifier using cheap calcium chloride (CaCl2) and a main dehumidifier using stable lithium bromide (LiBr). Side-effect of mixing heat rejected during dehumidification process is considerably alleviated by an indirect evaporative cooling unit added between the two dehumidification stages. The feasibility of high-desiccant concentration difference achieved by reusing desiccant solution to dehumidify air and regenerating desiccant repeatedly is analyzed. By increasing desiccant concentration difference, desiccant storage capacity is effectively explored. It is found that the pre-dehumidification effect of CaCl2 solution is significant in high ambient humidity condition. Also seen is that the desiccant investment can be decreased by 53%, though the cost of equipments is somewhat increased, and the Tcop and COP of the proposed system can reach 0.97 and 2.13, respectively
[en] In the waste heat recovery process, heat source temperature control and thermal management are always required to ensure safety and high efficiency of the waste heat recovery system. To this aim, the conventional method is to establish a series of independent heat transfer units and adopt a complex control strategy, which makes the system very complex and only applicable for a specific object. The concept of 'integrated thermal management controller' (ITMC) is presented in this work to provide a novel method to solve the above problems. A two-dimensional heat and mass transfer model is developed to analyze and predict the operation performance of the ITMC. The numerical analysis indicates good heat source temperature control and thermal management performance of the ITMC. In addition, an experimental prototype is established, and test data are presented, which agree well with the numerical results and verify the correctness of the model
[en] An ammonia-water absorption cycle is suggested to transport heat over long distance, in which thermal energy is transferred into chemical energy in the heat source site by the change of solution concentration. So there is no heat insulation requirement for the transportation pipelines. In the user site the chemical energy could be released with heating or cooling. An experimental prototype has been built to investigate the system performance. The experiments include two parts: heating is obtained from absorber (user site) in transition season by ammonia-water absorption heat pump cycle, in which a hot water outlet temperature at about 64 deg. C can be reached and the system COP is 0.47 (absorption temperature at 66 deg. C). Cooling is obtained from evaporator (user site) in summer by ammonia-water absorption refrigeration cycle, in which a chilled medium outlet temperature at about 8 deg. C can be reached and the system COP is 0.43 (evaporation temperature at 4.6 deg. C). The investigation of the transportation parameters also shows that the pump electric consumption can be reduced greatly in comparison with the conventional heat transportation method. The ammonia-water absorption cycle is a potential and efficient way of heat transportation over long distance.
[en] A novel constant volume test unit was built to study the adsorption performance of a new type composite adsorbent. This test unit can measure the adsorption isosteres of the working pairs. The adsorption isosteres are the curves of the adsorption pressure variation with the adsorption temperatures at constant adsorption quantities. Compared to the former test results of isothermals and isobars, the isosteres are better for the calculation of the adsorption heat, desorption heat and the selection the adsorption working pairs. Three experimental results were obtained: the first result was that the expanded graphite powders were superior to the expandable graphite powders to facilitate the transportation of working fluid in the composite adsorbent. The second one was that the composite adsorbent treated by solution is more homogeneous than the simple mixed composite adsorbent and the treated composite adsorbent has a better mass transfer performance. The last one was that the adsorption isosteres was the same one not only in the heating process but also in the cooling process and this performance was not relevant to the homogeneity of the composite adsorbent
[en] Conventional waste heat recovery systems have problems of complex distributed configuration, difficult assembling, and bad versatility. Especially, the control strategy, necessary for safety reasons and high energy efficiency, is complex due to the heat source temperature control and thermal management. The concept of 'Thermal Management Controller' (TMC) is presented in this work to provide an alternative to solve these problems. An engineering model, based upon lumped-heat capacity and a moving vapor-NCG front, is created to predict the TMC transient behavior. In addition, experimental results are presented and show an excellent agreement with the numerical results, which validates the model. Computation results are used to predict the transient behavior of a TMC, and assess the relative influence of various parameters. In particular, the hot water flow rate has a greater effect on the system response speed than other operational variables. However, the input heat shows great influence on the system start-up speed. Furthermore, some design parameters, such as the working fluid, gas reservoir volume, NCG filled inventory, and heat transfer area density, have a considerable effect on the system transient behavior
[en] In this study, a small scale hybrid solar heating, chilling and power generation system, including parabolic trough solar collector with cavity receiver, a helical screw expander and silica gel-water adsorption chiller, etc., was proposed and extensively investigated. The system has the merits of effecting the power generation cycle at lower temperature level with solar energy more efficiently and can provide both thermal energy and power for remote off-grid regions. A case study was carried out to evaluate an annual energy and exergy efficiency of the system under the climate of northwestern region of China. It is found that both the main energy and exergy loss take place at the parabolic trough collector, amount to 36.2% and 70.4%, respectively. Also found is that the studied system can have a higher solar energy conversion efficiency than the conventional solar thermal power generation system alone. The energy efficiency can be increased to 58.0% from 10.2%, and the exergy efficiency can be increased to 15.2% from 12.5%. Moreover, the economical analysis in terms of cost and payback period (PP) has been carried out. The study reveals that the proposed system the PP of the proposed system is about 18 years under present energy price conditions. The sensitivity analysis shows that if the interest rate decreases to 3% or energy price increase by 50%, PP will be less than 10 years.
[en] An innovative multifunction heat pipe type sorption refrigeration system is designed, in which a two-stage sorption thermodynamic cycle based on two heat recovery processes was employed to reduce the driving heat source temperature, and the composite sorbent of CaCl2 and activated carbon was used to improve the mass and heat transfer performances. For this test unit, the heating, cooling and heat recovery processes between two reactive beds are performed by multifunction heat pipes. The aim of this paper is to investigate the cycled characteristics of two-stage sorption refrigeration system with heat recovery processes. The two sub-cycles of a two-stage cycle have different sorption platforms though the adsorption and desorption temperatures are equivalent. The experimental results showed that the pressure evolutions of two beds are nearly equivalent during the first stage, and desorption pressure during the second stage is large higher than that in the first stage while the desorption temperatures are same during the two operation stages. In comparison with conventional two-stage cycle, the two-stage cycle with heat recovery processes can reduce the heating load for desorber and cooling load for adsorber, the coefficient of performance (COP) has been improved more than 23% when both cycles have the same regeneration temperature of 103 deg. C and the cooling water temperature of 30 deg. C. The advanced two-stage cycle provides an effective method for application of sorption refrigeration technology under the condition of low-grade temperature heat source or utilization of renewable energy
[en] The performance analyses of a sorption refrigeration system with different mass recovery processes are presented, in which compound adsorbent of CaCl2 and activated carbon is used to improve the mass and heat transfer performances of sorption bed. The heating, cooling and heat recovery processes between two sorption beds were performed by multifunction heat pipes without additional power consumption. The experimental Clapeyron diagrams showed that the cycles with mass recovery (MR), with heat and mass recoveries (HMR), and with mass and heat recoveries (MHR), have better thermodynamic performances when compared with the sorption cycle without mass recovery (MR0). The implementary order of mass recovery and heat recovery has strong influence on the efficacy of mass recovery while it has little influence on the efficacy of heat recovery. In sorption cycles with HMR and with MHR, the hot beds can be pre-cooled and cold beds can be pre-heated effectively during the switching process, and heat consumption from external heat source during desorption phase is thereby reduced. Mass recovery can enlarge cycled refrigerant mass due to the transfer of refrigerant gas between two sorption beds during mass recovery process. In comparison with sorption cycle with MR0, sorption cycles with MR, with HMR, and with MHR can generally improve the coefficient of performance (COP) and specific cooling power (SCP) by more than 20% and 16%, respectively. Especially, sorption cycle with MHR has the highest performance among different mass recovery processes due to the fact that MHR has the advantages of MR and HMR, and it can improve the COP by 46.7% when compared with the cycle with MR0