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[en] Highlights: • Models of thermoelectric generator arrays in series and parallel under different heat flux were made. • Models of the thermoelectric generator arrays were experimentally verified. • The number of the thermoelectric generators in array for maximum output power was optimized. - Abstract: The study on thermoelectric generator combined with the solar concentrator has increased rapidly in recent years. However, the solar concentrator inevitably causes the uneven distribution of the heat flux, which would significantly impact the performance of the thermoelectric generator array. This work presented the models of thermoelectric generators in series connection and parallel connection. Furthermore, series of experiments were made to verify the rationality of the model. In addition, the discussion based on the model was conducted to optimize the output power. The results indicated that for the thermoelectric generator array with the large heat flux gradient, which may be more effective and efficient to obtain higher output power through giving up lower heat flux part, which also can reduce the number of the thermoelectric generator modules. This work can be as a hint for the optimization of the solar thermoelectric generator
[en] Highlights: • Frosting and heating performance of DX-SAHP under frosting conditions is investigated. • The conditions when DX-SAHP frosts are studied. • The frosting process is observed during 360 min of operating. • The effect of ambient temperature, relative humidity and solar irradiation is analyzed. - Abstract: Direct expansion solar-assisted heat pump system (DX-SAHP) is promising in energy saving applications, but the performance of DX-SAHP under frosting conditions is rarely reported in the published literatures. In this paper, a DX-SAHP system with bare solar collectors for space heating is designed and experimentally investigated in the enthalpy difference lab with a solar simulator. The system is tested under a range of frosting conditions, with the ambient temperatures from 7 °C to −3 °C, the relative humidities of 50%, 70% and 90% and the solar irradiances of 0 W/m"2, 100 W/m"2, 200 W/m"2 and 300 W/m"2. The conditions when the DX-SAHP system frosts are studied. Results show that solar irradiance as low as 100 W/m"2 can totally prevent frosting when the ambient temperature is above −3 °C and the relative humidity is 70%. Besides, the frosting process is observed to be slower than that of fin-and-tube heat exchangers. The evaporator is not seriously frosted and the system performance is not significantly influenced after 360 min of continuous operating. Moreover the effects of ambient parameters, including the ambient temperature and the relative humidity, especially solar irradiation, on the system performance are studied and analyzed. Solar irradiation can effectively prevent or retard frosting, and also improve the heating performance of the DX-SAHP system. The DX-SAHP system is proved to be applicable under frosting conditions.
[en] Highlights: • The PV/T evaporator and air source evaporator connect in parallel and operate simultaneously. • A dynamic model is developed to simulate the behavior of the system. • The thermal and electrical characteristics of the PV/T evaporator are evaluated. • The contribution of the air source evaporator and PV/T evaporator has been discussed. - Abstract: To enable the heat pump water heater maintain efficient operation under diverse circumstances, a novel PV/T-air dual source heat pump water heater (PV/T-AHPWH) has been proposed in this study. In the PV/T-AHPWH system, a PV/T evaporator and an air source evaporator connect in parallel and operate simultaneously to recover energy from both solar energy and environment. A dynamic model is presented to simulate the behavior of the PV/T-AHPWH system. On this basis, the influences of solar irradiation, ambient temperature and packing factor have been discussed, and the contributions of air source evaporator and PV/T evaporator are evaluated. The results reveal that the system can obtain efficient operation with the average COP above 2.0 under the ambient temperature of 10 °C and solar irradiation of 100 W/m2. The PV/T evaporator can compensate for the performance degradation of the air source evaporator caused by the increasing condensing temperature. As the evaporating capacity in PV/T evaporator remains at relatively low level under low irradiation, the air source evaporator can play the main role of recovering heat. Comparing the performance of dual source heat pump system employing PV/T collector with that utilizing normal solar thermal collector, the system utilizing PV/T evaporator is more efficient in energy saving and performance improvement.
[en] Highlights: • A point-focus Fresnel lens photovoltaic/thermal module is proposed and studied. • The electrical model is based on the Shockley diode equation. • The thermal model is based on a two-dimensional steady-state heat transfer model. • An electrical efficiency of 28% and a thermal efficiency of 60% can be obtained. • Influence of independent parameters is investigated by validated models. - Abstract: Characteristics of a high concentration photovoltaic/thermal (HCPV/T) module equipped with point-focus Fresnel lens have been investigated in this paper. Both electrical and thermal models of the module are developed by numerical methods. The electrical model is based on the Shockley diode equation, and the thermal model is grounded on a two-dimensional steady-state heat transfer model. Influences of environmental parameters and coolant water are considered in the models. The inputs of the models consist of irradiance, ambient temperature, wind speed, water temperature and mass flow rate. The outputs mainly include electrical efficiency and thermal efficiency. The simulated results are compared with experimental results and a great agreement is obtained. By the virtue of the validated models, influences of different parameters on module performance are analyzed in detail. The results show that an electrical efficiency of 28% and a thermal efficiency of 60% can be obtained by the HCPV/T module. The electrical efficiency is mainly influenced by solar irradiation rather than cell temperature. The thermal efficiency increases with the increment of irradiance, ambient temperature and water mass flow rate. On the contrary, increasing water temperature and wind speed will lower the thermal efficiency. Also, the HCPV/T module can produce hot water as high as 70 °C without decreasing the electrical efficiency seriously.
[en] The double Wronskian solutions of a non-isospectral Kadomtsev-Petviashvili equation (n-KPE) are derived. One-soliton solution and two-soliton solution are presented, the characteristics of one-soliton and two-soliton scattering are discussed also
[en] In this paper, a new 7 x 7 matrix spectral problem, which is associated with the super AKNS equation is constructed. With the use of the binary nonlinearization method, a new integrable decomposition of the super AKNS equation is presented.
[en] Highlights: • A design approach of PV-coupled solar water heating system (SWHS) is presented. • Two different designs of PV modules are proposed and investigated. • A comparative test rig of PV-coupled SWHS and traditional SWHS is set up. • A flow rate increasing with solar irradiation is recommended. - Abstract: Simple and reliable, PV direct-coupled DC pumps are promising in solar water heating systems (SWHS). However, there is limited experimental data on the performance comparison of PV-coupled SWHS with traditional SWHS. Hence in this study, a comparative test rig is set up to measure and analyze the performance of the PV-coupled SWHS and the traditional system under the same conditions. The experimental results show that on sunny days the PV-coupled SWHS has similar daily thermal efficiency as the traditional SWHS, and slightly higher efficiency after improving the design of the PV module. Under low irradiation, the PV-coupled SWHS gains much more heat than the traditional SWHS, which indicates the potential of the PV-coupled SWHS having much higher efficiency than the traditional SWHS on cloudy days. In order to improve the performance of the PV-coupled SWHS, two different designs of PV module are proposed, and their influence on the pump startup characteristics, the flow rate profile, and the thermal efficiency of the system is investigated. It is found that the modified design of the PV module can reduce the requirement of PV cells and increase the efficiency of the system
[en] A new method for constructing the Wronskian entries is proposed and applied to the differential-difference Kadomtsev-Petviashvilli (DΔKP) equation. The generalized Wronskian solutions to it are obtained, including rational solutions and Matveev solutions.
[en] Highlights: • A design of tri-functional photovoltaic/thermal solar collector is proposed. • The performance of tri-functional PV/T collector is investigated and compared. • The tri-functional PV/T collector is flexible to different working modes and variable seasons. - Abstract: Photovoltaic/thermal (PV/T) solar collectors can provide electric power and thermal energy simultaneously. Either PV/T water collectors or PV/T air collectors can be left unused in some seasons because of the freezing problem of water and seasonal demand of hot air. In this paper, a novel design of tri-functional PV/T solar collector was proposed. The collector can work in PV/water-heating mode or PV/air-heating mode according to the seasonal requirements. Experiments were conducted in different working modes under variable conditions to evaluate the performance of collector. The results show that the daily thermal efficiency achieved 46.0% with the electrical efficiency of 10.2% in PV/air-heating mode. The temperature increase of air reached 20 °C with the flow rate of 0.033 kg/s on a sunny day. The instantaneously thermal efficiency at zero reduced temperature were 37.4% and 44.3% as the air flow rate was 0.026 kg/s and 0.032 kg/s respectively. In PV/water-heating mode, the thermal efficiency of the collector was 56.6% at zero reduced temperature, and the daily thermal efficiency of the system was around 36.0%. Compared with solar collectors presented by other authors, the tri-functional PV/T collector is able to operate efficiently in various conditions