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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] Highlights: • Study on boundary conditions of five kinds of adsorption heat pumps is presented. • Feasibility and economic studies under various working conditions were made. • Suggested ranges of driving and cooling temperatures are given for economic use. - Abstract: The objectives of this paper are to analyze adsorption heat pump (AHP) systems using different working pairs such as silica gel/water, zeolite/water, SAPO-34/water, FAPO-34/water and activated carbon/ammonia, and to carry out their boundary conditions. According to the Clapeyron diagram, adsorption equilibrium equations and energy balance equations, feasibility and economic studies under various working conditions are made. Silica gel/water, SAPO-34/water and FAPO-34/water AHPs can feasibly operate for space heating and domestic hot water. Beyond that, zeolite/water and activated carbon/ammonia AHPs can even feasibly operate for heating network or industrial heating/preheating. However, ranges of economic operation are much stricter than that of feasible operation. Silica gel/water, SAPO-34/water and FAPO-34/water AHPs are not convenient for cold winter except zeolite/water and activated carbon/ammonia AHPs. Activated carbon/ammonia AHP even can economically operate in the cold winter with −15 °C ambient temperature. Floor heating is the most convenient technique for silica gel/water, SAPO-34/water and FAPO-34/water AHPs. Zeolite/water and activated carbon/ammonia AHPs require more than 130 °C and more than 140 °C driving source for economic use, respectively. The sequence according to the value of COPH is as follows: silica gel/water, FAPO-34/water, SAPO-34/water, zeolite/water and activated carbon/ammonia AHPs.
[en] Highlights: • Resorption cycle is proposed for the air conditioners (ACs) of electric vehicles (EVs). • Intermittent working modes of the cycle won’t consume the electricity of on-board batteries. • Resorption working pair of CaCl2-NH4Cl-NH3 has reasonable energy density and high COP. • Energy consumption of resorption AC is reasonable if compared with conventional AC of EVs. - Abstract: Conventional compression type air conditioners (ACs) consume a large part of the electricity of batteries on-board of electric vehicles, and that will make the cruising mileage shorter. Sorption and resorption cycles, which are intermittent, may solve this question by the energy storage phases. Both sorption and resorption cycles are analyzed and compared, and both of them have simpler structure if compared with conventional AC for that only two heat exchangers are required. The equilibrium performance analysis shows that resorption working pairs has higher energy density and coefficient of performance (COP) than that of sorption working pairs when the high temperature salt of resorption cycle is same with the halide of sorption cycle. The experimental Clapeyron curves are studied, and CaCl2-NH4Cl-NH3 has best performance. Compared with MnCl2-CaCl2-NH3 and MnCl2-NH4Cl-NH3, the energy density and COP of CaCl2-NH4Cl-NH3 improves by 160% and 35% at least, respectively. The performance of CaCl2-NH4Cl-NH3 is also compared with that of CaCl2-NH3. They have similar smallest energy density, and CaCl2-NH4Cl-NH3 has higher COP if consider the working conditions in the whole year. The energy required for the electric car with a resorption AC is 0.23–0.265 kWh/km, which is acceptable if compared with the results of conventional AC.
[en] The pressure oscillations during different film boiling modes in He II are studied in this paper. In the sub-cooled film boiling state, a flame-shaped vapour bubble can be seen to be quivering on the planar heater accompanied by a little audible noise, and the pressure oscillation, resulting from both vapour bubble oscillation and liquid column oscillation of bulk He II in a cryostat, is detected. In the noisy film boiling state in saturated He II, a big vapour bubble expands and crushes repeatedly on the planar heater accompanied by a loud acoustic noise, and the pressure oscillation is mainly caused by the crushing and formation of the vapour bubble. There are two possibilities for the occurrence of transition boiling. A theoretical analysis of the pressure oscillation was also carried out, which agreed well with the experimental results. (author)
[en] Highlights: ► We develop one heat pipe type adsorption refrigerator. ► New compound adsorbent of CaCl2/activated carbon–ammonia can work more effectively. ► Combined mass recovery-heat pipe heat recovery can improve adsorption performance. ► Combined mass recovery-heat pipe heat recovery can reduce cycle time. - Abstract: A heat pipe type adsorption refrigerator system is proposed and investigated, which can be powered by solar energy or waste heat of engine. The study assesses the performance of compound adsorbent (CaCl2 and activated carbon)–ammonia adsorption refrigeration cycle with different orifice sets and different mass and heat recovery processes by experimental prototype machine. Specific cooling power (SCP) and coefficient of performance (COP) were calculated with experimental data to analyze the influences of operating condition. The results show that the jaw opening of the hand needle nozzle can influence the adsorption performance obviously and the thermostatic expansion valve (TEV) is effective in the intermediate cycle time in the adsorption refrigeration system. The SCP of the cycle with the mass-heat recovery together (combined recovery process) is superior to that of the conventional cycles with mass recovery or heat recovery independently.
[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] Based upon the fast development of energy efficiency, energy safety and use of renewable and sustainable energy, various energy systems related to residential refrigeration, power generation and storage have been developing. Some of them are in large scale application, while others are still under development. Current status of residential refrigeration, power generation and energy storage technologies have been briefly summarized in this paper. Also, future residential refrigeration, power generation and energy storage technologies are highlighted, and some roadmaps are discussed. -- Highlights: ▸ Current status and future development of residential refrigeration have been briefly summarized and discussed. ▸ Current status and future development of power generation have been briefly summarized and discussed. ▸ Current status and future development of energy storage have been briefly summarized and discussed
[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] Research highlights: → A dynamic mathematical model is built to predict the performance of DCHE system. → Operation time in dehumidification is a crucial parameter to system performance. → Under ARI summer condition, the largest cooling power can reach to 2.6 kW. → Under ARI humid condition, the largest cooling power can reach to 3.4 kW. → System performs better with smaller fin distance and tube diameter. -- Abstract: Desiccant coated heat exchanger (DCHE) system can handle latent and sensible load simultaneously by removing the released adsorption heat in dehumidification process. The system can also be driven by low grade thermal energy such as solar energy. In this paper, a dynamic one-dimensional mathematical model validated by experimental data is established to predict the performance of DCHE system, using conventional silica gel as desiccant material. Cooling performance of DCHE system is calculated under ARI (American Air-conditioning and Refrigeration Institute) summer and humid conditions. Simulated results show that the operation time in dehumidification process is a crucial factor for cooling capacity of DCHE system, which can be enhanced by eliminating the initial period with higher outlet air temperature, the largest cooling power of DCHE system increase from 2.6 kW to 3.5 kW by eliminating first 50 s of operation time under ARI summer condition. The results also prove that the system can provide cooling power to indoor condition with selective operation time when regeneration temperature varies from 50 oC to 80 oC. Besides, the model is adopted to analyze the effects of some structural parameters on system performance under simulated condition. The system performs well in smaller cobber tube external diameter condition, while both transient heat and mass transfer capacity can be enhanced under the condition of smaller distance between the fins.