•The magnetic field effects on the EIT in the room temperature for the multilevel V-type model using both the 87Rb D1 and D2 line have been studied.•Multiple EIT windows at a moderate magnetic field ...are observed.•When pump laser is tuned to the 87Rb-D2 transition and 87Rb-D1 transition is used as a probe field, the separation between the two splitted EIT peaks gradually increases with the increase in magnetic field.•The effect of pump field power on the splitted EIT peaks at a particular magnetic field has been investigated.•This study of generating multiple EIT windows in a magnetic field may be useful in multi-channel quantum information processing, in optical magnetometry and in precession spectroscopy.
We have studied the effect of an external magnetic field on the electromagnetically induced transparency in a multi-level V-type system of 87Rb using D1 and D2 lines. We apply the magnetic field at room temperature parallel to the direction of co-propagating pump and probe laser beams. Five independent EIT peaks are observed at a moderate magnetic field of 72.5 G, when 87Rb-D1 line is addressed by the pump laser and the probe laser is scanned across the 87Rb-D2 transitions. When the pump laser is tuned to the 87Rb-D2 transition, we could resolve two EIT peaks at the similar magnetic field. The effects of magnetic field and pump field power on the Zeeman split EIT peaks are also investigated. A theoretical model is developed considering the multiple Zeeman sublevel to reproduce the observed spectra.
Many efforts have focused on ratiometric upconversion temperature sensing, but little attention has been paid to its measurement accuracy. Herein, the effect of excitation energy on temperature ...sensing is investigated comprehensively by using the hexagonal NaGdF4:Yb3+/Er3+ upconversion nanocrystals. It is demonstrated that the non-thermally coupled thermometer can reliably measure the temperature only when it operates in the suitable temperature range or under constant excitation conditions. By contrast, the classic thermal-coupled one does not suffer from these problems. Our research provides new insight into non-thermally coupled upconversion thermometers.
•1. The influence of excitation energy on ratiometric temperature sensing is investigated.•A physical explanation for the non-thermally coupled temperature sensing is given.•3. The non-thermally coupled thermometer can detect temperature accurately only when it works in a suitable condition.
•Optical cavity solitons (CSs), whose pulse property is unique, have shown great potentials in optical soliton communication systems. Here, we theoretically investigated the launch conditions and ...parameter variation tolerances of cavity soliton in nonlinear fiber resonant cavity.•The effect of pump pulse laser peak power, continuous wave (CW) pump laser power, pump pulse width, pump detuning, dispersion condition, fiber nonlinear coefficient and fiber length on the CS pulse performance is detailedly investigated and deeply analysed.•The synergistic effect of CW pump laser power and pump pulse peak power, and the synergistic effect of dispersion condition, fiber nonlinear coefficient and fiber length on the generation and property of CS pulse are respectively discussed and summarized.•The launch conditions and parameter variation tolerances of cavity soliton in nonlinear fiber resonant cavity have been successfully generalized. These results can provide important instruction to the experimental generation and optimization of CS pulse.
All optical soliton communication is a new generation of ultra-long distance and ultra-high speed optical fiber communication technology. Optical cavity solitons (CSs), whose pulse property is unique, have shown great potentials in optical soliton communication systems. Here, a theoretical model of nonlinear fiber resonator for CS generation is proposed. The effect of pump laser and resonant cavity parameters on the CS pulse performance is detailedly investigated and deeply analysed. Furthermore, the synergistic effect of continuous wave (CW) pump laser power and pump pulse peak power, and the synergistic effect of dispersion condition, fiber nonlinear coefficient and fiber length on the generation and property of CS pulse are respectively discussed and summarized. Finally, the launch conditions and parameter variation tolerances of cavity soliton in nonlinear fiber resonant cavity have been successfully generalized. These results can provide important instruction to the experimental generation and optimization of CS pulse.
Er3+/Yb3+ co-doped ferroelectric ceramic BaBi2-0.04-yNb2Er0.04YbyO9 (y = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, and 0.12) are prepared by solid-state method and investigated for their structural and ...upconversion luminescence properties. High-resolution X-ray pattern investigation confirmed the ceramic's orthorhombic structure. Microstructure of sintered ceramic surface resembles plate-like structures and consists of non-uniform grains that are randomly oriented. Upconversion luminescence (UCL) spectra revealed two prominent green emission bands near 535 and 557 nm and a notable red band at 672 nm, corresponding to a 980 nm excitation wavelength. Decay time measurements support the effective energy transfer from Yb3+ to Er3+ ions. The average lifetime increases with increasing Er3+/Yb3+ doping concentration up to the optimal concentration (y = 0.10). Pump power dependence demonstrates that two photons are required to generate green and red UC illumination. The absolute sensitivity, Sa (0.69% K−1 and 0.58% K−1) and relative sensitivity, Sr (1.1% K−1 and 1.01% K−1) have been recorded for the first time on Er3+/Yb3+ co-doped BaBi2-0.04-yNb2Er0.04YbyO9 ceramic at y = 0.06 and 0.10, respectively, suggesting it is a viable non-contact sensor ceramic whose sensitivity can be tuned by varying dopant concentrations.
•Contactless temperature sensitivity of Er/Yb co-doped BaBi2-0.04-yNb2Er0.04YbyO9 ceramic has been reported for the first time.•The thermometric performance is observed in a wide temperature range (303 K–573 K).•Efficient tunable sensitivity is achieved with varying Yb3+ concentrations, y = 0.06 and 0.10 (Sa = 0.69% K−1 and 0.58% K-1).•The energy transfer efficiency from Yb3+ to Er3+ ions increases by 32%, supported by time resolved measurements.
•Performance optimisation of PVT system with copper oxide nanofluid application as a coolant.•Investigation on the influence of nanofluid volume concentration and flow rate on the performance of PVT ...system.•Novel study determining the impact of nanofluid concentration and flow rate on pump power usage system.•Identification optimum performance of PVT system with nanofluid concentration and flow rate selection.
Nanofluids application has now become a conventional cooling medium in PVT technology. However, there is little knowledge in the current literature about the PVT operational conditions for optimum performance. This paper aims to investigate the PVT optimum operating conditions with CuO nanofluid application. TRNSYS simulation platform is used in this investigation by developing a numerical equation-based model. The input parameters investigated are nanofluid volume concentration from 0.10 % to 0.50 % and fluid flow at 60 kg/h, 80 kg/h and 120 kg/h. The influence of these inputs was observed on the system’s PV cell temperature, electrical efficiency, thermal efficiency, net electrical output and pump power consumption. The results showed that at 60 kg/h flow, the increment in nanofluid concentration from 0.10 % to 0.50 % caused an increase in electrical efficiency by 1.11 % with a 3.30 % increase in thermal efficiency. Similarly, at 0.10 % volume concentration, when mass flow was raised from 60 to 80 kg/h, the improvements in electrical efficiency were 1.46 % and for 80–120 kg/h the electrical efficiency of the system dropped by 0.08 % due to higher pump power consumption. Overall, the electrical efficiency improved by 1.36 % for 60–120 kg/h mass flow. The thermal efficiency improvements were 4.15 %, 1.07 % and 5.27 %, at the same corresponding flow rates. Net electrical output analysis of the system showed that an increase in volume concentration and fluid flow rate changes the density of nanofluid which in turn increases the pump power consumption. The analysis also identified that the optimal operating conditions for the system are 0.10 % CuO concentration and 80 kg/h mass flow.
•Distributed parameter models of counter and cross flow PFHE are constructed.•Effect of longitudinal heat conduction on heat transfer performance of counter flow PFHE is investigated.•Effect of ...configuration and operation parameters on heat transfer amount and pump power of cross flow PFEH is studied.•Improved structures of cross flow PFHE are proposed.
The distributed parameter models of counter flow and cross flow plate fin heat exchanger (PFHE) are constructed to investigate their thermodynamic characteristics. In practical application, the cold end of PFHE may be directly connected to the cold equipment. Therefore, the effect of longitudinal heat conduction (LHC) under different thermal boundary conditions set on two ends of the separating plates (SPs) is investigated based on the model of counter flow PFHE. It is found that LHC effect transmits the effect of boundary condition on two ends of the SPs into the inner domain of PFHE. The LHC effect on the heat transfer performance of PFHE is positive when setting appropriate boundary condition on two ends of the SPs. When considering LHC, compared with the adiabatic boundary conditions on two ends of the SPs, the effectiveness of constant wall temperature boundary conditions increases by 31.7 ∼ 35.8 %, and the effectiveness of constant heat flux boundary conditions increases by 22.8 %. The model of cross flow PFHE is used to investigate the effect of configuration and operation parameters on the heat transfer amount and the pump power. The cross flow PFHE is optimized to arrive at the maximization of heat transfer amount per unit pump power (HTPUP). In the three-stream cross flow PFHE studied, the heat transfer amount almost doesn’t change when the xz projected area is maintained and one projected length (z side length) is changing. The pump power is the lowest and the HTPUP is the largest when z side length of PFHE (z side is the flow direction of the fluid with large mass flowrate) is 0.15 ∼ 0.2 m.
To improve the stability and efficiency of electric motors, an advanced cooling method that can replace the existing water-cooling method is required. Even though various studies utilized a liquid ...refrigerant in the cooling system, none of studies explicitly presented the cooling performance enhancement of motor by the superior heat transfer of flow boiling. In this study, a flow boiling cooling method using R134a is applied with a conventional water-cooled motor design, and its cooling performance is compared to that of a water-cooled motor. A transient three-dimensional lumped parameter thermal model based on cylindrical coordinates is developed. This model can calculate the heat loss of an electric motor, and determine the heat transfer and temperature change inside a motor under a given driving condition. The results indicate that the flow boiling cooling method maintains the winding at a temperature lower than the conventional water-cooling method. The power consumption of the pump required for motor cooling is reduced reliably by applying flow boiling cooling. However, it is necessary to use the appropriate refrigerant flow rate by considering the heat lost from the motor. If not, the two-phase heat transfer stops owing to complete vaporization of the refrigerant inside the motor. To realize efficient flow boiling cooling, the minimum required volume flow rate of R134a considering the motor driving condition is suggested in this study.
•An advanced motor cooling method using flow boiling with two-phase refrigerant is proposed.•The cooling performance of flow boiling is compared analytically to that of conventional water cooling.•A transient 3-d lumped parameter thermal model of an electric motor based on cylindrical coordinates is developed and validated.•By introducing flow boiling cooling, motor cooling performance and vehicle efficiency are improved.
•Energy consumption of pumping process was considered in analysis of a PVT system.•CNT-nanofluid resulted in improvement of electrical and thermal efficiency compared to pure water.•Experimental pump ...power demonstrated a reduction of o.9% of electrical efficiency.•Increase of nanofluid thermal conductivity developed the allowable pump power.•Non-continuous working of pumping system reduced the energy consumption up to 50%.
In this study, a numerical simulation has been accomplished to investigate the performance of a photovoltaic thermal system (PVT) with respect to the energy consumption of fluid circulating. Three dimensional numerical models of the PVT system were conducted in ANSYS Fluent software using water-CNT nanofluid as working fluid. Three configurations of heat collectors were modeled to select the more efficient design for collecting the heat of the PV module. By applying the duct channel heat collector, the effects of CNT concentration and nanofluid flow rate on the electrical and thermal efficiency of PVT system were studied. With flow rate of 50 L/h of 0.1 v/v% CNT-nanofluid, the electrical efficiency of PVT system increased 11% in comparison to PV system at ambient temperature of 40 °C. According to the inconsistency of thermophysical properties of nanofluid, a sensitivity analysis was conducted to indicate the impact intensity of nanofluid thermal conductivity. It indicated that the application of a 15 W pump in PVT system decreased the electrical efficiency from around 13.9% to 12.9%. A coefficient of cooling efficiency (CCE) is introduced to compare the extra gain electrical energy with the energy consumption of the pumping system. By increasing the thermal conductivity of nanofluid, the CCE increased from 0.985 for 25 W pump to 1.015 for 20 W pump. Two practical methods were suggested and investigated with transient simulation to decrease the energy consumption of the pumping process up to 50%.
