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[en] Highlights: • Solid sorption heat pipe (SSHP) with composite NaBr-NH_3 is proposed for continuous heat transfer. • Both vertical and horizontal SSHPs are investigated. • SSHP features non-isothermal heat transfer performance at sorbent and condenser sections. • The highest radial heat flux in vertical and horizontal SSHPs is 22.1 and 12.4 kW/m"2, respectively. • Both SSHPs have axial heat flux higher than 400 kW/m"2. - Abstract: A novel type solid sorption heat pipe (SSHP) is developed for continuous heat transfer. In contrast to conventional heat pipe (HP), SSHP utilizes the composite sorbent-sorbate as working media to replace the wick structure inside HP. Such a technology is expected to alleviate the heat transfer limits of conventional HP. NaBr is chosen as the sorbent, and the expanded natural graphite treated with sulfuric acid serves as the matrix. A certain molar amount of the sorbate (NH_3) is complexed with the composite sorbent. The desorption, condensation and chemisorption processes of NaBr-NH_3 working pairs are investigated for both vertical and horizontal placed SSHP. The results show that the desorption process of NaBr-NH_3 solid-gas reaction can be carried out while the heating temperature reaches up to 60 °C or above. The highest radial heat flux in both vertical and horizontal placed SSHP is around 22.1 and 12.4 kW/m"2, respectively, while the axial heat flux for both SSHPs is not less than 400 kW/m"2. It can be concluded that the SSHP is characterized by the non-isothermal heat transfer performance and verified to be available for continuous heat transfer. The vertical SSHP has a better overall heat transfer performance than horizontal SSHP under the same condition and NaBr-NH_3 working pairs applied in SSHP is suitable for low-grade thermal energy transfer above 60 °C.
[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] Highlights: • A cross-flow dew point evaporative cooler prototype is investigated. • The performance of a practical evaporative cooling system is tested and analyzed. • A mathematical model is developed for the cross-flow dew point evaporative cooler. • The coupled dehumidification and cooling process is simulated. - Abstract: This paper investigates the cooling potential of a cross-flow dew point evaporative cooler under various conditions. Preliminary study reveals that the dew point evaporative cooler’s performance does not approach its designed capacity when the ambient humidity goes beyond the thermal comfort zone. To address this problem, an air dehumidification process is proposed before the evaporative cooling takes place. It is observed that the cross-flow cooler is able to achieve improved cooling effectiveness when an appropriate inlet air humidity condition is realized. The influence of different dehumidification levels on its cooling capacity and efficiency is subsequently analyzed. Additionally, a mathematical model is developed to predict the cooler performance. Key findings from this study are: (1) The maximum discrepancy between the simulation results and experimental data is within ±3.0%; (2) the overall wet bulb and dew point effectiveness of the cross-flow cooler can reach 1.25 and 0.85 for cooling of the supply air with moderate humidity; (3) the respective wet bulb effectiveness, cooling capacity and COP of the cross-flow system are 0.86, 2.2 kW and 4.6 under humid ambient air condition; and (4) the dehumidification of the supply air enables the cooling capacity and energy efficiency to be improved by 70–135%.
[en] A dual-mode thermochemical sorption energy storage system using working pair of expanded graphite/SrCl2-NH3 was proposed for seasonal solar thermal energy storage. The proposed system has two working modes to produce useful heat with an expected temperature during the discharging phase according to the different ambient temperatures, including the direct heating supply and temperature-lift heating supply. Solar thermal energy is transformed into chemical bonds and stored in summer, and the stored energy is released in the form of chemical reaction heat in winter. The direct heating supply mode is adopted at a relatively high ambient temperature in winter. The effective energy storage density is higher than 700 kJ/kg and the corresponding system COP is 0.41 when the heat output temperature and ambient temperature are 35 °C and 15 °C, respectively. The specific heating power increases with the decrease of heat output temperature for a given ambient temperature. The temperature-lift heating supply mode is adopted to upgrade the heat output temperature at a low ambient temperature below 0 °C in winter. It can produce heat with a temperature above 70 °C although the ambient temperature is as low as −15 °C. It is desirable to further improve the system performance using low mass ratio and high global conversion. Experimental results showed the advanced dual-mode thermochemical sorption energy storage technology is feasible and effective for seasonal solar thermal energy storage. - Graphical abstract: Working temperature range of dual-mode thermochemical sorption energy storage system during the discharging phase in winter. - Highlights: • A dual-mode seasonal solar thermochemical sorption energy storage system is developed. • The sorption working pair is strontium chloride/expanded graphite-ammonia. • Two working modes can be performed according to the different heat requirements in winter. • Energy density and COP of direct heating supply mode are 706 kJ/kg and 0.41 respectively. • Temperature-lift heating supply mode can meet heat demand at low ambient temperature.
[en] Highlights: • A novel self-adaptive sorption system is proposed to reduce nitrogen oxides emission. • Annual required mass of composite sorbents for the novel system ranges from 143 kg to 246 kg. • Annual required volume of composite sorbents is in the range from 358 L to 615 L. • Cost of sorption SCR system by using most composite sorbents is much lower than that of adblue. - Abstract: A novel self-adaptive sorption system is proposed and analyzed, which is considered as an alternative solution to reduce nitrogen oxides emission. Compared with conventional selective catalytic reduction technology, urea solution tank is replaced with sorption reactor for ammonia storage. Composite sorbents are developed with expanded natural graphite treated with sulfuric acid as the matrix. Different sorption working pairs are selected for evaluating working performance of novel system based on testing nitrogen oxides emission of a diesel engine. It is indicated that for operation mode 8, the highest required mass of urea solution per hour could reach 1.9 kg, which is 2.32 times higher than that of composite ammonium chloride. For different composite sorbents, annual required mass ranges from 143 kg to 246 kg and 81 kg to 140 kg in terms of mode 8 and 6 whereas annual required volume is in the range from 358 L to 615 L and 204 L to 350 L, respectively. Cost of novel sorption system by using composite sorbents is generally lower than that of conventional system by using urea solution. It analyzes the feasibility of novel self-adaptive sorption system, which reveals great potential for reducing nitrogen oxides emission.
[en] Highlights: • A promising modular sorption thermal cell is analyzed for combined cold and heat storage. • Permeability of novel composite sorbent is further improved by adding carbon coated nickel. • Sorption rate of novel sorbent is accelerated based on heat and mass transfer enhancement. • Sorption thermal cell of novel composite sorbent has great potentials for scaling applications. - Abstract: Novel composite strontium chloride is developed with expanded natural graphite and carbon coated nickel as the additives. It is indicated that expanded natural graphite and carbon coated nickel are conducive to heat and mass transfer performance, which result in improved sorption characteristic. For composite sorbents with carbon coated nickel, thermal conductivity and permeability range from 0.57 W · m−1 K−1 to 1.93 W m−1 K−1 and from 2.98 × 10−10 m2 to 2.71 × 10−13 m2. Novel composite strontium chloride with carbon coated metal enjoys the faster desorption and sorption reaction rate than that without carbon coated metal. For different evaporation temperatures, sorption quantity of novel composite strontium chloride ranges from 0.28 kg kg−1 to 0.7 kg kg−1. Based on testing results of sorbents with carbon coated nickel, a promising sorption thermal cell is developed and analyzed for combined cold and heat storage, which greatly enhances the versatility and working reliability. Under different working conditions, cold and heat density range from 384 kJ kg−1 to 811 kJ kg−1 and 549 kJ kg−1 to 1648 kJ kg−1. Modular sorption thermal cell could be flexible connected to sorption battery for scaling applications, which reveals great potentials for renewable energy utilization and waste heat recovery.
[en] Highlights: • A small-scale pumpless Organic Rankine Cycle (ORC) system is established. • The maximum power output is 232 W when the hot water inlet temperature is 95 °C. • The highest energy and exergy efficiency are 2.4% and 13.7%. • Pumpless ORC may become one alternative solution to low grade heat utilization. - Abstract: A small-scale pumpless Organic Rankine Cycle (ORC) system driven by the low temperature heat source is established to investigate the overall performance. Hot water temperature from 75 °C to 95 °C is adopted for performance analysis whereas the environmental temperature is about 25 °C. Refrigerant R245fa is selected as working fluid, and scroll expander is employed for power generation. One worth noting fact is that pumpless ORC system shows great potential for low temperature heat recovery. Experimental results indicate that the maximum power output is 232 W, which is obtained at 95 °C hot water inlet temperature. Correspondingly, the average power output is 204 W which is lasted for 6.6 min, revealing the high stability for power generation. For different hot water inlet temperature, the highest energy and exergy efficiency of the system are 2.4% and 13.7%. Besides, performance of novel pumpless ORC system is compared with that of our previous prototype. It shows a remarkable improvement in terms of power output, energy efficiency and exergy efficiency. Power generation process is able to keep constant for 95% of the cycle time. As a result, pumpless ORC may become an alternative solution to low grade heat utilization when compared with conventional small-scale ORC.