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[en] A mini-type solar-powered absorption cooling system with a cooling capacity of 8 kW was designed. Lithium bromide-water was used as the working pairs of the chiller. Solar collectors with an area of 96 m2 were installed. A water storage tank with a volume of 3 m3 was used to store the hot water from the solar collectors. The experimental results showed that the average values of PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) of the test room were 0.22 and 5.89, respectively. Taking the average value of PMV and PPD into consideration, the solar cooling system could meet the indoor thermal comfort demand with the comfort level of A. The power consumption was reduced by 43.5% after introducing the stepped utilization of energy into the air handling unit. Meanwhile, a theoretical model was established based on Matlab to predict the variations of the system performance with ambient parameters. It is shown that the solar radiation intensity has a greater impact on the performance of the solar powered absorption cooling system compared with the ambient temperature. It is also shown that the indoor air temperature goes down with the increase of the solar radiation intensity as well as the decrease of the ambient temperature. -- Highlights: • The energy step utilization improved the performance of a solar cooling system. • Thermal environment of Class A was achieved by using radiant cooling. • Solar radiation intensity has prominent impact on the solar cooling system
[en] Highlights: • Performance of desiccant coated heat exchanger AC system is predicted. • Effects of main operation parameters and climatic conditions are discussed. • Regeneration temperature of 30 °C is recommended under simulation condition. • Higher ambient humidity ratio results in increased humidity ratio of supply air. • Temperature of ambient air has neglectable effect on supply air. - Abstract: Conventional air source heat pump system faces several challenges when adopted in winter season. Solid desiccant air conditioning system can provide humidification and heating power simultaneously and can be driven by low grade thermal energy; it provides a good alternative for air source heat pump systems. However, conventional solid desiccant air conditioning system adopts desiccant wheel with high cost as core component, which hinders the development of such system. Recently, desiccant coated heat exchanger (DCHE) with low initial cost and high efficiency was developed and this paper aims to investigate performance of DCHE air conditioning system adopted in Shanghai winter season. Performance of the system is predicted by a developed mathematical model where supply air states, mass of humidification and coefficient of performance (COP) are adopted as performance indices to evaluate the feasibility and energy utilization ratio of the system. Effects of regeneration water temperature on system performance are analyzed. It is found that under the simulation condition, relatively low regeneration temperature (such as 20 °C) cannot meet the designed standard and relatively high regeneration temperature (such as 40 °C) provides too much extra heating power, thus moderate regeneration temperature around 30 °C is recommended. Meanwhile, switch time is a crucial operation parameter for the system to obtain satisfied supply air, switch time from 40 s to 80 s and from 70 s to 240 s are recommended for transient and average supply air states, respectively. Both mass of humidification and COP increase with increasing regeneration temperature under simulation condition. Also, influences of ambient air temperature and humidity ratio on system performance are discussed to study the feasibility of such system regarding different climatic conditions. Results show that higher humidity ratio of ambient air results in increased humidity ratio of supply air, temperature of ambient air has neglectable effect on supply air. In conclusion, DCHE air conditioning system can be adopted for winter operation with moderate selection of regeneration temperature as well as switch time.
[en] Highlights: • A novel composite adsorbent for air-to-water system is proposed. • The water uptake performance of ACF-CaCl_2 is three times more than silica gel-CaCl_2. • SEM, ICP and ASAP2020 are adopted to analyze the micro characteristics of compounds. - Abstract: A novel composite adsorbent of host matrix of CaCl_2 was developed to increase mass transfer area and enhance adsorption performance for air-to-water system under hot and humid conditions. The host matrix is activated carbon fiber felts (ACF FELT) fabricated by viscose-based fibers. Scanning electron microscope (SEM) and Micromeritics ASAP2020 were adopted to observe the micro characteristics of matrix. Inductive coupled plasma emission spectrometer (ICP) was used to test the quality of impregnation and water crystallization carried by calcium chloride in synthesis. The preparation processes, pore structures, quantities of crystallization water of calcium chloride and impregnated salt, as well as the non-equilibrium adsorption performances were studied, and the results were compared with the composite adsorbents with SC matrix. Research shows that ACF is more suitable as the matrix of composite adsorbents, and ACF30 has the best sorption performance of water uptake 1.7 g/g, which is three times more than silica gel-CaCl_2. Furthermore, ACF compound can be retested without rupture or carryover. Coefficient of adsorption rate of water uptake was obtained using Linear Driving Force model.
[en] A 1 kWh lab-scale sorption prototype using LiCl-water was theoretically and experimentally investigated for sorption thermal energy storage. A type of consolidated composite matrix is developed for the system by using AC (activated carbon), LiCl, expanded natural graphite treated with sulphuric acid (ENG-TSA) to increase heat transfer and SS (silica solution) to enhance mechanical strength. Thermal conductivity and permeability were measured first. A two-dimensional model considering the combined heat and mass transfer was developed to predict the sorption kinetics of the reactor. Under the operation condition of a charging temperature of 85 °C and a discharging temperature of 40 °C, the experimentally recovered heat is 2517 kJ, resulting a heat storage efficiency of 93%. The heat storage density is 874 kJ/kg consolidated sorbent or 2622 kJ/kg LiCl. The experimental results of the prototype were compared with the simulated results. The established two-dimensional model proves to be effective since the general evolution trends of experimental and simulated outlet fluid temperatures are in good agreement. An average gap of about 0.4 °C between the experimental and simulated outlet temperature may be caused by the heat loss and the constant pressure assumption. - Highlights: • A 1 kWh lab-scale sorption prototype using LiCl-water was set up for sorption thermal energy storage. • A two-dimensional model considering the combined heat and mass transfer was developed. • The experimental results were compared with the simulated results. • The heat storage density is 874 kJ/kg consolidated sorbent or 2622 kJ/kg LiCl.
[en] Carbon nanotube (CNT) is considered as a kind of potential adsorbent because of its large surface area, uniform micropores and unique physicochemical properties. The adsorption performance of ammonia on the packed multi-walled carbon nanotubes (MWCNTs) were studied in this paper. Firstly, the packed MWCNTs were characterized by the scanning electron microscope (SEM) and transmission electron microscopy (TEM). Secondly, the effect of working pressure and adsorbent temperature on the adsorption capacity of ammonia by the packed MWCNTs was investigated. Thirdly, Langmuir and Freundlich models were used to analyze the equilibrium adsorption data and the adsorption kinetics was also discussed using a classical gas diffusion model. The Freundlich isotherm model could elucidate well the adsorption of ammonia on the MWCNTs when compared to the Langmuir equation. The research results showed that the equilibrium adsorption amount of ammonia by the MWCNTs varied between 22.69 and 90.05 mg/g_C_N_T at the adsorbent temperature of 25–35 °C and working pressure of 0.368–0.744 MPa. It seems that the pure MWCNT is not appropriate to act as the adsorbent for the solid–gas adsorption refrigeration due to its low adsorption capacity. However, our research indicates that the MWCNTs can be used as additive to some other chemical adsorbents to improve their heat transfer characteristics. - Highlights: • Adsorption performance of ammonia on packed MWCNTs was studied. • Effects of working pressure and temperature on the adsorption capacity were investigated. • Adsorption equilibrium data and kinetics of ammonia on MWCNTs were analyzed. • Equilibrium adsorption amount of ammonia varied 22.69–90.05 mg/g_C_N_T at different temperatures and pressures
[en] Energy conversion technologies, especially for power generation and refrigeration technologies driven by the low temperature heat, are gathering the momentum recently. This paper presents a novel resorption system for electricity and refrigeration cogeneraion. Compared with adsorption refrigeration system, resorption refrigeration is characterized as safety and simple structure since there is no ammonia liquid in the system. The cogeneration system is mainly composed of three HTS (high temperature salt) unit beds; three LTS (low temperature salts) unit beds, one expander, three ammonia valves, two oil valves, four water valves and connection pipes. Chemical working pair of MnCl_2–CaCl_2–NH_3 is selected. Since scroll expander is suitable for small type power generation system, it is chosen for expansion process. 4.8 kg MnCl_2 and 3.9 kg CaCl_2 impregnated in expanded natural graphite treated with sulfuric acid (ENG-TSA) are filled in the cogeneration system. Experimental results show that maximum cooling power 2.98 kW is able to be obtained while maximum shaft power is about 253 W with 82.3 W average value. The cogeneration system can be utilized for the heat source temperature lower than 170 °C. Total energy efficiency increases from 0.293 to 0.417 then decreases to 0.407 while exergy efficiency increases from 0.12 to 0.16. - Highlights: • A resorption system for power and refrigeration cogeneration is established and investigated. • ENG-TSA as the additive improves the heat and mass performance of composite adsorbent. • The highest shaft power and refrigeration power are 253 W and 2.98 kW, respectively. • Total energy efficiency of the system increases from 0.293 to 0.417 then decreases to 0.407.
[en] A composite material was developed as sorbent for sorption thermal energy storage (TES) which was used to recycle the low-temperature heat in industry and life fields in this study. The composite sorbent was formed by strontium bromide (SrBr_2) and the additive of expanded natural graphite treated with sulfuric acid (ENG-TSA). Sorption characteristics, kinetic sorption performance, thermal conductivity and permeability of 15 samples were studied. The material test results indicated the following: (1) the composite SrBr_2 is of high energy density and good mass transfer performance; (2) it can be regenerated below 100 °C; (3) the additive of ENG-TSA greatly improves the heat transfer performance, while no degradation is observed on sorption water uptake; (4) the optimal composite sorbent is of 743 kg/m"3 and with 10 wt% ENG-TSA. An lab-scale sorption TES system with 1 kWh design capacity was established and investigated. Under the conditions in winter seasons: charging temperature T_c_h_a is 80 °C, discharging temperature T_d_i_s is 35 °C, condensing temperature T_c is 15 °C, evaporating temperature T_e is 15 °C, the heat storage capacity can reach 1.02 kWh. The heat storage density obtained is 242 Wh/kg composite sorbent and the heat discharging power is 67.4 kW/m"3 composite sorbent. - Highlights: • A new type of consolidated composite SrBr_2 sorbent was developed. • We tested the thermal properties and sorption performance of samples. • The optimal composite sorbent was chosen for thermal energy storage. • A 1 kWh sorption thermal energy prototype was investigated.
[en] Highlights: • A Bi_2Te_3 TEC with silica aerogel encapsulation is proposed. • A three dimensional model for the TEC is developed. • This model first considers the effect of air gap and aerogel. • Different thicknesses of aerogel encapsulation for TEC are discussed. - Abstract: A Bi_2Te_3 TEC with silica aerogel encapsulation is developed. Silica aerogel with different thicknesses is filled in the void spaces around the TE legs and started from cold-side ceramic plate. A three dimensional mathematical model for the TEC is developed. This model considers the effect air gap and silica aerogel. (Bi_0_._2Sb_0_._8)_2Te_3 and Bi_2(Te_0_._9_7Sb_0_._0_3)_3, which have temperature-dependent TE properties, are selected to be p-type and n-type TE materials. Also, an experimental test bench is built to validate the three dimensional model. The performances of non-silica aerogel encapsulated TEC with and without consideration of air gap are investigated. Meanwhile, the effects of different thicknesses of silica aerogel encapsulation under different T_as and V_as are analysed. The results show that the cold side ceramic and interconnector, and cold part of TE legs can be insulated effectively while the hot part of TE legs can be effectively dissipated using part silica encapsulation when T_h ⩾ T_a ⩾ T_c. The maximum Q_c at L_a_e_r = 0.8 mm is nearly increased by 7% as compared with that at L_a_e_r = 0 mm when T_a = (T_c + T_h)/2. Moreover, apart from the cold side interconnector, L_a_e_r should be about 2%, 15% and 25% of the L_l_e_g corresponding to the maximum Q_c condition when T_a = T_c, T_a = (T_h + T_c)/2 and T_a = T_h, respectively. The value of L_a_e_r can be (T_a−T_c)/(T_h−T_c)L_l_e_g corresponding to the optimum COP condition
[en] Highlights: • A novel resorption thermal energy storage system is established. • Working pair of MnCl_2−CaCl_2−NH_3 is chosen for heat and refrigeration cogeneration. • The largest energy storage density reaches 1706 kJ/kg. • The maximum average cooling power is 1.07 kW during discharging phase. • The largest energy and exergy efficiency are 0.87 and 0.35 respectively. - Abstract: Sorption thermal energy storage (STES) is perceived as one prospective way of thermal energy storage (TES) owing to the advantages of high energy density, negligible heat loss, flexible working modes and long-term storage capability. Based on STES, this paper exhibits an innovative resorption thermal energy storage (RTES) system, and the experimental prototype is established for heat and refrigeration cogeneration. Working pair of MnCl_2−CaCl_2−NH_3 is chosen, 4.8 kg MnCl_2 and 3.9 kg CaCl_2 impregnated in expanded natural graphite treated with sulfuric acid are filled in two sorption beds respectively. Experimental results indicate that the largest energy storage density reaches 1706 kJ/kg when charging and discharging temperature are 160 °C and 30 °C, respectively. The maximum average cooling power achieves 1.07 kW during discharging phase and corresponding SCP is 27.33 W/kg within the overall cycle period. When charging temperature increases from 135 °C to 160 °C, the energy efficiency of the resorption system for heat and refrigeration cogeneration augments steadily from 0.72 to 0.87 while the exergy efficiency rises slowly from 0.29 to 0.35.
[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.