Direct Pumping Research Articles

Methodology for validating autonomous and direct photovoltaic pumping in drip irrigation

Methodology for validating autonomous and direct photovoltaic pumping in drip irrigation

Research on gas-liquid interface parameters related to thermal performance of frost-free evaporator of air source heat pump

Direct spray frost-free air source heat pumps (FFASHPs) base on liquid desiccant solutions are a more promising renewable energy technology for developing net-zero emission buildings. In order to improve the thermal performance of the frost-free evaporator, a numerical mode was established based on the penetration theory and the two-film theory to reveal the interfacial heat and mass transfer mechanism of LiCl solution falling film absorption on the air side of the frost-free evaporator. The distribution characteristics of temperature, water vapor concentration, effective diffusion coefficient, morphology, velocity and pressure at the interface under different air Reynolds numbers and temperatures were analyzed. The results show that the distribution uniformity of interface parameters has a greater effect on heat transfer performance than its average value. The critical Reynolds number is 391.0 under the present study, and the distribution uniformity of interface parameters and the intensity of interface fluctuation are improved, and the thermal performance reaches the peak. The COP of FFASHP system can be improved effectively when the frost-free evaporator is operated under the critical condition matching its parameters. The purpose of the study is to provide theoretical support for the performance improvement and efficient operation of frost-free evaporators.

Orthogonal polarization dual-wavelength Nd: GdVO4 laser at 1341 nm and 1344 nm with 880 nm LD direct pumping

Orthogonal polarization dual-wavelength Nd: GdVO4 laser at 1341 nm and 1344 nm with 880 nm LD direct pumping

Experimental study on the operating characteristics of multiple collector direct expansion solar-assisted heat pump

Solar thermal application is one of the most important ways to replace fossil energy. The discontinuous heating character and low heating efficiency are two key factors that limit the large-scale promotion of solar thermal application. Large-scale direct expansion solar heat pump systems (DX-SAHP) can provide high efficiency and low-cost continuous heating. However, the characteristics of multiple collector arrays and the system's performance still need more research and exploration. In this paper, a DX-SAHP system with multiple solar collectors was constructed and the work process of the system under different operation conditions was expressed. An experimental platform with two DX-SAHP system was built and studied, and each system contained a 10HP compressor, 16 set solar collectors and one fin evaporator in parallel. The results show that the coefficient of performance (COP) of the system running with solar collectors was nearly 30 % higher than that with the fin evaporator under constant frequency mode, and nearly 45 % under variable frequency mode, indicating that such a system has better performance under variable frequency operation mode. The refrigerant in the collector/evaporators were distributed uniformly in equal-path connection mode, which was beneficial in promoting the system's performance. The heating performance of the system under sunny and cloudy weather conditions was analyzed and discussed, respectively. The test results indicated that the COP of the system on sunny or cloudy days was higher than 4.0, and the maximum hourly COP can reach 11.3 and the maximum hourly heating capacity was 27 kW.

Experimental study on electricity generation performance of T‐type direct‐expansion solar PVT heat pump system

AbstractFocusing on the electricity generation performance of a direct expansion solar PVT heat pump system, a novel T‐type optimized collector/evaporator was designed. The experiment used refrigerant R410a as the working medium and was conducted under the average winter ambient temperature of 16°C in Fuzhou. Through experimental comparison, the differences in panel temperature, electricity generation, and efficiency under different radiation intensities were tested against traditional PV panels and honeycomb PVT panels. The experimental results showed that the T‐type PVT system exhibited significant advantages under various weather conditions. The back panel temperature was reduced by 12.74, 8.52, and 13.06°C compared to traditional PV panels and honeycomb PVT panels, respectively, and it maintained a stable increase in electricity generation. The maximum instantaneous electricity output increased by 56.6% relatively, and the total electricity generation increased by 9.3% to 14.5% compared to traditional PV panels. The photoelectric efficiency reached 21.54% and 22.6%, surpassing traditional PV panels and honeycomb PVT panels, with measured values relatively increased by 1.7%, 2.38%, and 2.76%, respectively. Economic evaluation indicated that the T‐type PVT system could save on self‐generated electricity costs, achieving savings of up to 386.50 and 210.81 yuan/year compared to traditional PV panels and honeycomb PVT panels. The T‐type PVT system demonstrated clear advantages in self‐generated electricity costs, significantly reducing costs for application scenarios and providing strong support for the practical application of renewable energy technologies.

MODELING OF SYSTEMS WITH THE PHOTOVOLTAIC POWER SOURCE AND WATER PUMPS

The article is devoted to the calculation of systems consisting of a solar photovoltaic power source and water pumps. It is noted that such systems can be used both in households or industry, and in agriculture, in particular for irrigation. Several variants of water pumps are shown. An analysis of the operational modes where the photovoltaic power source is connected to the pump has been carried out. The selection of equipment was carried out and the expediency of using a system with an electric energy booster was indicated. A booster for providing current during start-up modes can be a capacitor, a battery of capacitors or an ionistor. Emphasis is placed on the fact that for doing of such systems it is necessary to apply modeling with the use of electrical models. It is shown that for developing of electric models of solenoid-based pumps and pumps based on rotating direct current motors, it is necessary to use the methods of electromechanical analogies. Electrical models of a photovoltaic power source and, based on analogies, a solenoid-based pump and a direct current motor-based pump with permanent magnet excitation and parallel excitation were developed. When developing electrical models, controlled sources of voltage and current were used with mutual influence of the electrical and mechanical parts of the pumps. The need to use direct current motors with parallel excitation is indicated, as they are more stable to emergency modes. It is also stated that in general, the mechanical load of the rotating part of motors is non-linear and depends on the number of revolutions of the shaft. A nonlinear resistance that models a nonlinear mechanical load is shown, and it is noted that the higher-order nonlinearity is insignificant. Conclusions are drawn and further development in the direction of the use of digital technologies is outlined.

Chirped periodically poled lithium-niobate-on-insulator micro-waveguides for broadband second-harmonic generation.

Periodically poled lithium niobate (LN) waveguides based on quasi-phase matching schemes, benefiting from their high nonlinear coefficient (d33) and strong optical confinement, are widely employed for implementing efficient second-harmonic generation (SHG). Here, we report broadband SHG in z-cut chirped periodically poled lithium-niobate-on-insulator (CPPLNOI) ridge micro-waveguides. Nearly 90-nm-wide SHG at the telecom band is achieved, along with an averaged normalized efficiency of 7.5%/(W·cm2). We also demonstrate simultaneous generation of second as well as cascaded third and fourth harmonics under direct pumping of femtosecond pulses. This work would benefit applications for frequency conversion of a wideband coherent light source.

Optimal high-pressure correlation for transcritical CO2 cycle in direct expansion solar assisted heat pumps

Heat demand may be met sustainably by a solar-assisted heat pump that CO2 as a refrigerant. This is made possible by the employment of an ecologically benign refrigerant and a renewable energy source that enhances system performance. At the ideal high pressure, the CO2 heat pump running in a transcritical cycle will function at its highest coefficient of performance (COP). In that way, this study aims to present correlations for calculating the optimum high pressure in a CO2 direct expansion solar assisted heat pump (DX-SAHP). In this study a mathematical model for compressor, solar evaporator and gas cooler was developed and validated experimentally. The mean difference between the mathematical model and experimental results are −3.9%. Two new equations are proposed to calculate the optimum high pressure in a CO2 DX-SAHP. The first one considered environment temperature, water outlet temperature and evaporating temperature, which are easy to measure. These facilities the use of correlation to control the heat pump. The second one considered environment temperature, water outlet temperature and solar radiation, which are more suitable for designing CO2 DX-SAHP. A data base with 100 optimum points was used to curve fitting. Another data base with 50 optimum points was used to compare the results obtained from curve fitting and correlations for the optimum high pressure available in the literature. The proposed correlations shown a maximum error lower than 10.2% despite of the correlations available in the literature from which the errors are about 30%.

First Achievement of Yellow Laser Operation in Dy3+-Doped Borate Crystals.

Continuous-wave (CW) yellow lasers have been demonstrated successfully by using a GaN laser-diode (LD) pumping in borate crystals for the first time. The Dy3+:GdMgB5O10 (Dy:GMB) crystal with dimensions up to 33 × 19 × 15 mm3 is grown by the top-seeded solution growth method, and the polarized spectroscopic properties are investigated systematically at room temperature. The line strengths, Judd-Ofelt (J-O) intensity, spontaneous transition rates, fluorescence branching ratios, and radiative lifetimes are calculated in detail by the Judd-Ofelt theory. Under direct pumping of 452 nm LD, a compact continuous-wave yellow laser with a maximum output power of 628 mW and laser wavelength of 581 nm is generated based on a Y-cut Dy:GMB crystal. To our knowledge, it is not only the highest output power for yellow laser obtained in Dy3+-doped crystals but also the first yellow laser operation achieved by borate crystals under direct LD pumping. The results reveal that the Dy:GMB crystal is an optical material with important application prospects in yellow laser.

Nuclear-excited source of coherent and incoherent radiation with direct nuclear pumping

Uranium fission fragments, as well as the products of 3He(n,p)3H and 10B(n,α)7Li nuclear reactions were utilized in the nuclear reactor for gas ionization and excitation. However, the 6Li(n,α)3H nuclear reaction was less examined. The use of lithium-6 as a surface source of excitation of the gas medium, due to the long path length of tritium nuclei in the gas, allows to excite large volumes of gas as opposed to using 235U or 10B.While investigating the luminescence of noble gases in the core of the IVG.1M research reactor, we noted an appearance of alkali metal lines and a sharp increase in the intensity of these lines at temperatures above 570 K. It was determined that the population of levels of lithium atoms has practically no effect on the population of the 2p-levels of atoms of noble gases. The selectivity of p- and s-levels deactivation by lithium atoms implies the possibility of creating inversion of population at 2p-1s transitions of noble gas atoms. Successful experiments to study the luminescence of gases upon excitation by 6Li(n,α)3H nuclear reaction products allow us to proceed to experiments to achieve the laser action threshold and study the lasing characteristics of gas mixtures at the IGR pulsed nuclear reactor with thermal neutron flux density up to 7∙1016 n/cm2s. For this purpose, an experimental device designs were proposed to perform experiments on the IGR reactor. A step-by-step procedure of fabrication of a nuclear-excited source for excitation of gas mixtures is provided. The results of reactor experiments aimed at determining the spectral and temporal characteristics of optical radiation during excitation of gas mixtures by 6Li(n,α)3H nuclear reaction products are presented.

Energy analysis of a direct expansion heat pump assisted by a thermal photovoltaic panel for hot water production in several regions of Brazil

This study focused on evaluating the energy performance and economic viability of a direct expansion photovoltaic-Thermal Heat Pump (PV-T/HP) system for residential heating applications in various regions of Brazil. A detailed mathematical model was implemented to compare the PV-T/HP system with other solar heating technologies, as photovoltaic with solar evacuated tubes collector (PV+TSC) and photovoltaic with electrical heat water (PV+EHW), analyzing key metrics such as electrical efficiency, thermal efficiency, and levelized cost of heat (LCOH). The study revealed variations ranging from 7.5 to 2.5 in the Coefficient of Performance (COP) of the heat pump under different solar irradiation and ambient temperature conditions, emphasizing the necessity for future optimization to enhance the system performance. Results indicated that cities with the lower ambient temperature such as Belo Horizonte and Porto Alegre exhibited favorable conditions for the PV-T/HP system, leading to increased energy generation and positive net electricity production. The study highlighted the need for tailored strategies to control system operations, limit compressor consumption, and improve overall efficiency. These findings contribute to the understanding of PV-T/HP systems in residential heating applications, showcasing their potential for sustainable energy solutions in Brazil.

Recent advancements in solar collector-evaporator for direct expansion solar heat pump

The direct expansion solar heat pump (DX-SHP) is a competent and sustainable option for domestic heating and drying applications. The solar collector-evaporator is a vital component of DX-SHP, which operates on solar energy and low-temperature ambient energy. The heat collection capacity, coefficient of performance, and evaporation temperature are used to quantify its performance. In this context, a systematic literature review on recent advancements in the collector-evaporator of DX-SHP is presented. This paper highlights and discusses the various configurations of solar collector-evaporators, theoretical and experimental investigations, and the selection method of eco-friendly refrigerants. The impact of different performance factors, such as ambient conditions, structural parameters, and types of refrigerants, on solar collector-evaporators is also reviewed. The optimal range for solar radiation, wind speed, and temperature is found to be 350 W/m2-700 W/m2, 0.5 m/s -2.5m/s, and 5°C to 35°C. The DX-SHP system produces hot water from 15°C to 60°C, with an average COP of 1.5 to 4.5. The finned solar collector-evaporator with R290 refrigerant performs optimally in various climatic conditions. Integrating solar collector-evaporators with innovative technologies such as microchannel, heat pipe, thermoelectric generators, photovoltaic thermal collectors with compound parabolic and Fresnel lenses can improve the system's performance. In this review, researchers can find scope for performance enhancement of the collector-evaporator used in DX-SHP.

Studies on hybrid solar collector with water driven solar tracking unit

ABSTRACT The current solar concentrating collectors can be driven by water gravity without using a torque motor. It saves the electricity required to drive the large solar concentrating collectors. The objective of this study is to simulate and experimentally evaluate a novel hybrid system that combines photovoltaic and thermal technology with a hydro-powered solar tracking unit. The device consists of a hybrid solar collector, which is a multi-reflector compound parabolic collector (MRCPC), an evacuated tube receiver, photovoltaic (PV) panels, and a tracking system. The tracking mechanism attaches the tracking weights to both sides of a chain and sprocket. This hybrid collector rotates around its axis by adjusting the weight of the water in each of the monitoring weights. The system integrates a 12-volt direct current pump (operated by photovoltaic power) for tracking, with flow rate control. A mathematical model is developed and applied to determine the ideal tilt angle for a solar concentrating collector. The model was then used to compare the actual tilt angle and minimize errors in tracking. An experimental investigation used a flow rate of 0.8 LPM. The study achieved a mean tracking error of 2.05º, a maximum thermal efficiency of 43.65%, a maximum solar PV efficiency of 11.30%, and a maximum overall efficiency of 29.81%. An analytical method was developed to simulate the collector’s outlet temperature.

The advantage of running a direct expansion CO2 heat pump with solar-and-air simultaneous heat sources: experimental and numerical investigation

Dual-source solar-air heat pumps represent a promising solution for overcoming the limitations associated with single-source utilization, thereby enhancing heat pump performance. However, running the heat pump by alternatively employing the more advantageous source requires the integration of a controller capable of continuously monitoring and predicting the heat pump's performance in response to dynamic environmental and operational variables. Even so, a selective alternate operation does not allow to get the maximum possible performance from the use of the two heat sources. A different approach to address this challenge is the simultaneous utilization of the two sources, by properly combining two evaporators in the CO2 circuit. This paper presents an experimental investigation of a dual-source heat pump using CO2 as refrigerant, which can operate in three different evaporation modes: air-mode (using a finned-coil evaporator), solar-mode (using a photovoltaic-thermal PV-T evaporator), and simultaneous-mode (using both the evaporators simultaneously). The novel solution presented here does not require to split the refrigerant flow rate between the two evaporators and at the same time it solves the problem of possible maldistribution at the inlet of the evaporators. Experimental data indicate that the heat pump operating in simultaneous-mode allows to increase the evaporation pressure and the coefficient of performance compared to operation in air-mode or solar-mode. The measurements have been employed for validating a model of the system, capable of predicting steady-state and dynamic performance under various environmental and operational conditions. Simulation results show that the simultaneous-mode operation can be outperformed by the solar-mode only at high irradiance and low air temperature, when the evaporation temperature gets higher than the air temperature. Finally, the impact of the number of PV-T collectors and solar irradiance on the heat pump performance has been simulated and discussed. On this regard, the simultaneous use of the two heat sources adds more flexibility to the system and its design, because even the availability of a small solar area can contribute enhancing the performance over the mere air source heat pump.

Modeling, simulation and efficiency assessment of a direct coupled water pumping PV system in semi-arid coastal areas

Photovoltaics (PV) energy is a solution for the electrification of developing countries, especially for remote rural zones. The use of solar energy in water pumping is the most adopted solution for rural and desert regions. The modeling, simulation and analysis of the PV system of water pumping is a vital step before assembling this system on any place, which allows a better understanding of its behavior in real weather conditions on that place. In this paper, we investigate the performance of a water pumping photovoltaic system consisting of a PV generator coupled with a DC-motor which drives a centrifugal pump that draws water from a well and delivers it to a reservoir. The characteristics of the components of this system allow researchers, manufacturers, and social communities to understand better the functioning of these components. Our simulation results were meticulously cross-verified against the module manufacturer’s data sheet, revealing a maximum relative percentage error of 1.12 %. This attests to the coherence between the manufacturer’s stipulations and our simulated values. Furthermore, we ascertain commendable efficiency in the motor-pump system, particularly noteworthy for elevated irradiation levels, while maintaining acceptable performance even under minimal irradiation conditions.

The effects of solar insolation and cloud opacity on the optimum array size for a direct-coupled solar pumping system

The widespread adoption of solar photovoltaic pumping technology requires pertinent information on the sizing and design of these systems. This research investigated how the ratio of photovoltaic array peak power to motor power consumption, solar insolation and cloud opacity affects the water yield of a direct-coupled solar PV pumping system. The specific aim was to estimate the optimum photovoltaic power to motor power consumption (OPVM) ratio for a 3 W DC pump under Jamaican weather conditions. The PVM ratio is the ratio of peak array power to nominal motor power consumption. Four experimental direct coupled solar pumping systems were set up and the water yield for each measured daily for thirty days. Each system was identical in every respect except each having a different solar array peak power. The findings show that there is a strong correlation (Pearson coefficient of −0.903) between solar insolation and the optimum photovoltaic power to motor power consumption ratio. Additionally, there was found to be a strong correlation between average cloud opacity and optimum photovoltaic power to motor power consumption ratio (Pearson coefficient of 0.899). Both correlations were shown to be statistically significant, with both yielding p-values <0.001. The findings of the correlation analysis indicate that a relatively large PVM ratio would be economical when used on a site that regularly receives relatively low insolation and heavy cloud cover. Finally, the daily optimum photovoltaic power to motor power consumption ratio ranged from approximately 2.3 to 5.0. Generally, it was observed that the OPVM ratio shifted below 2.4 on clear sunny days and above 4.0 on very cloudy days. While these conclusions may not exactly extrapolate to scales of practical application, performance metrics of larger systems are expected to bear some similarity. Being guided by these results, additional studies at these larger scales are recommended.

Performance comparison of a direct heat pump using R1234yf and indirect heat pumps using R1234yf and R290 designed for cabin heating of electric vehicles

When using R290 as an alternative to R1234yf for heat pump (HP) cabin heating systems, indirect system (IDS) should be employed to address safety issues owing to its high flammability. However, studies comparing the performance of a direct system (DS) using R1234yf and an IDS using R290 are limited. In this study, the performance characteristics of DS-HPR1234yf, IDS-HPR1234yf, and IDS-HPR290 were compared to verify the feasibility of applying R290 to cabin heating systems in electric vehicles. Compared with DS-HPR1234yf, the heating capacity (QHP) and compressor work (WHP) of IDS-HPR1234yf decreased by 2.8% and increased by 4.5% on average, respectively, owing to the system configuration effects. QHP and WHP of IDS-HPR290 increased by 42.1% and 51.0%, respectively, over those of DS-HPR1234yf owing to the refrigerant and system configuration effects. Thus, at −20 °C, COPHP (HP's coefficient of performance) of IDS-HPR290 was 1.8, which was 4.9% higher than that of DS-HPR1234yf, owing to the high decrease rate of WHP. Additionally, considering the use of HP and positive temperature coefficient (PTC) heaters, COPHP + PTC of IDS-HPR290 was 6.7–22.1% higher than that of DS-HPR1234yf owing to its superior QHP, and the driving range (DR) of IDS-HPR290 was 7.2–20% higher than that of DRPTC.

High-power 2.3 µm Tm:YLF laser with intracavity upconversion pumping by a Nd:ASL laser at 1051 nm.

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 µm. This leads to a record-high output power at 2.3 µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81 W at 2.3 µm for 32 W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.

Numerical analysis of cascade lasing in Ho:ZBLAN fiber lasers with efficient output at ∼750 nm

Recent advances in blue-emitting laser diodes (LDs) have enabled visible laser operation in rare-earth-doped fluoride fibers. Therefore, investigation of the power scaling of visible fiber lasers enabled by direct blue diode pumping is significant. In this study, we numerically investigated the performance of a continuous-wave (CW) Ho:ZBLAN fiber laser operating at approximately 750 nm for the 5F4,5S2→5I7 transition using a cascade lasing process. Direct diode pumping at 450 nm is used in conjunction with double-clad fiber geometry. Simultaneous lasing for the mid-IR 5I7→5I8 transition effectively depopulated the 5I7 level and significantly enhanced efficiency and power scalability. A slope efficiency of 49% was associated with the calculated CW output power of 14.2 W at a launched pump power of 30 W. This study demonstrates the significance of depopulating the lower laser level in the development of an efficient Ho:ZBLAN 750 nm fiber laser and offers an alternative approach for developing high-power visible laser sources.

Performance prediction of a centrifugal pump working in direct and reverse mode using Computational Fluid Dynamics

The operation of centrifugal pumps as centripetal turbines can be useful to produce cheap energy in rural zones or developing nations. However, the optimum coupling between the flow and the geometry of the machine cannot be kept in reverse working conditions, and hence the flow instabilities are expected to be much higher. This paper presents a numerical investigation on the unsteady flow in a commercial centrifugal pump operating in direct (pump) and reverse (turbine) mode. Numerical simulations were conducted for several flow rates to investigate the properties of the global flow within the machine. The numerical model was additionally used to estimate the radial load on the impeller, as a function of flow rate, for both modes of operation.