High Pump Power Research Articles

Study on heat dissipation performance of a lattice porous structures under jet impingement cooling

For improving the heat dissipation of heat sink, a porous lattice structure under jet impingement was developed and its flow and heat transfer properties were investigated via simulation and experiments. The effects of its height (4–12 mm), porosity (0.52–0.92) and jet velocity (1–4 m s-1) on the flow and heat transfer characteristics were investigated. Results show that for a given inlet velocity, as the decrease of porosity, the heat transfer is increased, as well as the pressure drop or pump power. For a low pump power case, higher porosity such as 0.82 will be helpful for heat transfer, but lower porosity will be helpful for a high pump power instance. As the increase of height of lattice structure, the Nusselt number increased and subsequently decreased, with an optimal height of 6 mm. The lattice porous structure offers better heat transfer performance with comparison to conventional fin and foam fin heat sinks. At CfRe3 equal to 8.45 × 1012, the Nusselt number of the lattice porous structure is approximately 35% more than the other two structure. Also, Experiments were carried out in this study and experimental results agreed well with the simulated ones.

Investigation of energy dissipation mechanism and the influence of vortical structures in a high-power double-suction centrifugal pump

The extensive applications of double-suction centrifugal pumps consume a considerable amount of energy. It is urgent to reveal the detailed energy dissipation generation and find the critical factor for pump performance enhancement. In this investigation, the internal flow field of a double-suction centrifugal pump was obtained by solving the Reynolds averaged Navier–Stokes equations. The entropy production method was utilized to calculate and visualize irreversible energy dissipation. The Omega vortex method was utilized to identify vortical structures and determine the temporal and spatial relationship between entropy production and vortices. The results indicate that the entropy production in the main flow regions was critical in hydraulic loss, accounting for 54%–71% of the loss, and turbulent dissipation in the main flow regions of the impeller and volute casing dominated the variation of pump efficiency. The near-wall entropy production in the impeller positively correlated with the flow rate, but the impact was insignificant in volute casing. Although the suction chamber contributed minimally to the hydraulic loss, the backflows at the impeller inlet were relieved near the ribs, and the dissipation at the impeller inlet was reduced when the blade leading edges passed the ribs. By adopting Omega vortex identification, wake vortices, separation vortices, and their interactions were determined to correlate strongly with hydraulic loss in volute channels and near cutwaters. Furthermore, these vortices were influenced by the back flows from the impeller sidewall gaps. Additionally, this study can also provide the foundational principles for the optimal design of this type of pump.

Numerical study on shell and tube heat exchangers with different baffles configurations

PurposeThe purpose of this paper is to give a comparison between different type of baffles for a better application. Computational analysis of heat transfer and fluid flow through plain, flower and perforated baffles for heat exchanger.Design/methodology/approachNumerical simulations for heat exchangers with plain, flower and perforated baffles are carried out with finite volume method. The thermal-hydraulic performance for the three types is presented in the same conditions.FindingsThe perforated baffles generate low shell pressure with high Nusselt number; transverse baffles give the best heat transfer with high pumping power. The overall performance coefficient of these three types of heat exchangers shows that the perforated baffles have a highest and the transverse baffles have the lowest. Analysis of the results show that perforated transverse baffles produce pressure drop lower by 6.68% than transverse baffles and 2.64% lower than flower baffles. The pumping power for perforated transverse baffles lower by 13.3% to the transverse baffles and 4.72% lower than that of flower baffles. The Nusselt number for perforated baffles higher by 4.16% to the flower baffles and 2.77% with transverse baffles. The overall performance factor in the heat exchanger with perforated baffles higher by 5.55% to that with transverse baffles and 3.46% with flower baffles. Recirculation areas are reduced in shell with perforated baffles and velocity distribution becomes more uniform.Originality/valueUsing of perforated baffles in heat exchanger give the best overall performance factor.

HEAT PUMPS AS A TREND OF LOW-CARBON ENERGY DEVELOPMENT

An overview of the energy and economic problems of using heat pumps is given. The stages of the development of the world and European energy industry with their inherent economic and financial crises and their influence on the application volume of heat pumps are shown. The main regulatory and technical legislation of European countries in the scope of heat pumps and related sectors of the economy is presented. The main factors of the use of heat pump equipment are considered, the challenges and possible development trends are analyzed. Energy management and economic measures that contributed to the growth of heat pump implementations during the global energy crisis of 2021–2022 are assessed. The current state of heat pump use in the world, in Europe, in particular in Germany and Poland, is given. The reasons and organizational measures that led to the active growth of heat pumps in some European countries are indicated. The recent Polish experience in the favorable policy of active support of heat pump technologies and electrification of heat supply is evaluated in detail. An example of economic indicators for a typical building of the European energy efficiency standard with various options for heat supply, including heat pump technologies, as well as individual photovoltaics, is given. The use of high-power heat pumps (more than 100 kW) in centralized heat supply systems and various industries in Europe is analyzed. The prospects for the development of heat pumps from the point of view of the electrification of heat supply, the achievement of low-carbon energy and the prevention of harmful climate changes are outlined. It is recommended to use the positive experience of Poland in the policy of supporting heat pumps in the reconstruction of residential buildings destroyed by the war in Ukraine. Bibl. 37, Fig. 9, Tab. 5.

Research on the Thermal Effect of Micro-Channel Cooled Thin-Slab Tm:YAP Lasers

Using the finite element method and the heat conduction equation, the temperature, stress, and end-face deformation in Tm:YAP crystal under high pump power were analyzed. Combined with gradient doping technology, an effective way to improve the internal heat distribution of the crystal was studied. The results showed that when the total pump power was 200 W, under the same cooling conditions, the maximum temperature difference inside Tm:YAP decreased from 58 K to 25 K after gradient doping. The thermal stress and end-face thermal deformation were also significantly improved. In addition, a reasonable micro-channel structure also effectively removed the heat generated inside the crystal.

Nonlinear phase shifts induced by pumping spin waves in magnonic crystals

A nonlinear phase shift of low-power spin waves (SWs) induced by a high-power pumping SW excited both inside and outside the magnonic band-gaps of a magnonic crystal has been studied. The magnonic crystal with spatially periodic thickness is fabricated from an yttrium iron garnet film by chemical etching. The results show that the phase shift of the low-power SWs can be effectively controlled by variation of power level of the pumping SW. This induced nonlinear phase shift is weakened if the pump frequency lies in the magnonic bandgap. The data obtained are well explained by contradirectional coupling of the high-power forward and reflected spin waves. A theoretical model for this effect is presented. Our findings are important for the further progress in SW computing.

Effect of roughness characteristics of hydraulic fractures on the proppant transport using supercritical CO2

The morphology of rough fractures significantly affects proppant transport in hydraulic fractures. The fracture roughness is even more critical in proppant transport using supercritical CO2 since supercritical CO2 produces rougher fractures than other conventional fracturing fluids. In this study, we used roughness characteristics of the fractures generated by using supercritical CO2 and real rock samples determined by direct measurement together with coupled CFD (Computational Fluid Dynamics)-DEM (Discrete Element Method) to investigate the effects of different roughness characterization parameters on the efficiency of proppant transport using supercritical CO2. Laboratory experimental data of proppant transport in supercritical CO2 within the fracture were used to verify the reliability of the model. The results show that as the ratio of proppant diameter to average width of rough fracture increases, the proppant is more likely to bridge or even form sand blockage when transported in rough fractures, while better transport can be obtained when the ratio is less than 0.4. The main form of proppant particle transport within the rough fractures are the scouring and throwing of particles as the slurry flows through the bridging locations. In addition, the variation of root mean square (RMS) of asperity height values and fractal dimensions can have dissimilar effects on the proppant transport in rough fractures. The distance of proppant transport within the fracture decreases with the increasing fractal dimension, but increasing the RMS of asperity height value will yield proppant transport to longer distance. The proppant is transported farther in rough fractures than in planar fractures, but also, the required pumping pressure is higher in rough fractures, and the pumping pressure is positively related to the fracture roughness. Since using supercritical CO2 for fracturing produces rougher fractures than that of water-based fracturing fluids, higher pump power is required for efficient proppant transport using supercritical CO2, otherwise sand plug may occur. The results of this study lead to a better insight into the proppant transport behavior using supercritical CO2 in rough rock fractures and, therefore, would be useful for the improved field design of waterless fracturing operations conducted by using supercritical CO2.

Compensation of Phase Noise Induced by Higher–Order Codirectional Raman Amplifiers

Codirectional Raman amplification with higher–order pumping is a promising solution for improving performance of commercial unrepeatered submarine links and thus to allow for an upgrade to advanced modulation formats offering larger capacity. However, power fluctuations of the involved high–power pump induce phase shifts in phase modulated signals via the nonlinear Kerr effect that destroy the theoretically possible performance improvement. A technique for reducing the impact of this effect on system performance by jointly processing signals of neighboring channels and evaluating the phase of both channels at a time for symbol detection is presented and evaluated.

Development and characterization of a quaternary nitrate based molten salt heat transfer fluid for concentrated solar power plant

Over the past few years, there has been growing interest in using inorganic quaternary nitrate-based molten salt mixtures as a highly effective heat transfer fluid (HTF) for concentrated power plants, primarily because they can achieve low melting temperatures. However, the high viscosity of these salt mixtures is still a significant challenge that hinders their widespread adoption. The high viscosity leads to high pumping power requirements, which increases operational costs, and reduces the efficiency of the Rankine cycle. To address this challenge, this study developed and characterized a novel quaternary molten salt, focusing on the effect of LiNO3 additions on the salt's viscosity, thermal conductivity, melting point temperature, heat capacity, and thermal stability. The quaternary mixture comprised KNO3, LiNO3, Ca(NO3)2, and NaNO2, with varying percentages of each salt. The study utilized various standard techniques to examine the characteristics of the developed mixture. Results showed that increasing LiNO3 content led to a decrease in melting temperature, higher heat capacity, improved thermal stability, conductivity, and reduced viscosity at solidification temperature. The lowest endothermic peak for the new mixture emerged at 73.5 °C, which is significantly lower than that of commercial Hitec and Hitec XL, indicating better potential for use as a heat transfer fluid for concentrated solar thermal power plant applications. Furthermore, the thermal stability results showed high stability up to 590 °C for all the samples examined. Overall, the new quaternary molten salt shows promise as a potential replacement for current organic synthetic oil, offering a more efficient solution.

Tunable ultra-narrow linewidth diode laser for multiple metastable rare gas pumping.

We present what we believe to be a novel external cavity feedback structure based on a double-layer laser diode array with volume Bragg grating (VBG). Diode laser collimation and external cavity feedback result in a high-power and ultra-narrow linewidth diode laser pumping source with a central wavelength of 811.292 nm, spectral linewidth of 0.052 nm, and output power exceeding 100 W, with external cavity feedback and electro-optical conversion efficiencies exceeding 90% and 46%, respectively. The temperature of VBG is controlled to tune the central wavelength from 811.292 nm to 811.613 nm, covering the Kr* and Ar* absorption spectra. We believe this is the first report of an ultra-narrow linewidth diode laser that can pump two metastable rare gases.

Dynamic behaviors of special noise-like pulses and rogue waves in an L-band ultrafast fiber laser

We demonstrate a composite regime of the special noise-like pulses (NLPs) and rogue waves (RWs) in an L-band dispersion-managed fiber laser. Apart from stable ultrashort pulses, the fiber laser can easily generate unique NLPs with clear peak on broad spectrum at high pump power and proper polarization state. In this regime, these tiny pulses with irregular intervals experience random fluctuations, making the dynamic evolutions of these pulse envelopes look like the endless undulating mountains along the hundreds of intra-cavity roundtrips. In addition, the real-time observation based on the time-stretch technique shows that there are the unique lacking pieces and changeable pulse durations in this NLPs regime. Besides, the chaotic pulse packets with intensity fluctuations are observed at the proper condition, showing the typical statistical distribution with L shape, which can be called as the typical RWs. It is believed that these results will facilitate the further understanding of the nonlinear characteristics of the NLPs and RWs in ultrafast fiber lasers.

Passively mode-locked Yb-doped fiber laser based on CNT-film sandwiched between the multimode fiber connectors

We propose and demonstrate a saturable absorber (SA) of composite mode-locked mechanisms based on the Carbon nanotube (CNT) film sandwiched between the multimode fiber (MMF) connectors (CNT-MMF) for achieving passively mode-locked fiber laser. Compared with that CNT-film sandwiched between the single-mode fiber (SMF) connectors (CNT-SMF), the modulation depth is increased 1.48% and the saturation intensity decreases, which is the main reason that the fiber laser based on CNT-MMF-SA can achieve full mode-locked and work for a long time at higher pump power. However, the fiber laser based on the CNT-SMF-SA can only occur the Q-switched mode-locked state and the CNT-film is easily burned out. Further, the structure of the CNT-MMF provides an effective way for obtaining high damage threshold and improving the performance of the fiber laser based on various nanomaterial films. Our work dramatically broadens the design possibilities in terms of technology and provides convenient architectures for the nanomaterial-based mode-locked fiber laser.

Optical bistability and four-wave mixing response of a quantum dot coupled to an optomechanical photonic crystal nanocavity

We theoretically explore the nonlinear optical response including optical bistability and four-wave mixing (FWM) process in a hybrid cavity quantum electrodynamic (C-QED) system. The hybrid C-QED system consists of a quantum dot (QD) which is coherently driven by two-tone laser fields and embedded in an optomechanical photonic crystal (PhC) nanocavity. Our theoretical analysis demonstrates optical bistability, where the steady-state photon number follows a constant rise in the gain of the switch by controlling a strong pump field driving the QD. A strong coupling between quantised fields and matter (e.g. in optical cavities) is a successful approach for conventionally modifying the dressed state and by altering the field parameters, the modulation of QD dressed state is accomplished. In addition, we list the influence of off-resonant detuning, exciton-nanocavity coupling strength and Rabi coupling strength in our proposed system which generates a controllable four-wave mixing (FWM) signal in the output probe field of the system. The intensity of the FWM is significantly changed when strong coupling and high pump power are present simultaneously and results in the formation of an optomechanically induced transparency (OMIT) window and slow light. The investigation of the proposed system have potential application towards on-chip QD-based nanophotonic devices.

Optical frequency transfer with below 10−21 uncertainty using a DFB–laser-based fiber Brillouin amplifier

Exploiting the outstanding performance of optical atomic clocks for improved timekeeping, relativistic geodesy, and fundamental physics beyond the standard model demands comparing distant state-of-the-art optical clocks. Interferometric optical fiber links have been demonstrated as an eminent method for such frequency comparisons over distances up to thousands of kilometers. However, for such distances, the optical fiber attenuation mandates signal amplification. Fiber Brillouin amplification (FBA) has been proven as an efficient amplification technique for coherent frequency transfer. Demonstrated FBA schemes have been designed based on costly narrow-linewidth pump lasers and analog pump-to-signal phase locking schemes. Furthermore, the high pump power requirement of these FBAs hinders the integration of FBA-based frequency dissemination on fiber connections for shared telecommunication signals in the C-band. In this paper, we propose and experimentally demonstrate a novel FBA module (FBAM) employing cost-effective distributed feedback (DFB) pump lasers assisted by a digital phase locking scheme based on a field programmable gated array. The new FBAM is compact, cost-effective, and directly applicable to different bands, which opens up new opportunities to establish a frequency metrology infrastructure within existing telecommunication fiber networks. Additionally, the small-footprint of the DFB-FBAM allows for frequent amplification stages with lower pump power to reach continental scale optical metrology links with an optimized signal-to-noise ratio. We characterized the DFB-FBAM’s frequency transfer uncertainty using a two-way layout over an in-lab 100 km long optical fiber link and reach a fractional frequency instability of 9.3 × 10−22 at a 10 ks integration time. The DFB-FBAM characterizations show uncertainty contributions of (−2.1 ± 3.3) × 10−22 and below for averaging times >100 ks. For the first time, we assess the temporal Brillouin frequency shift variations in an underground fiber link and implement a scheme to track these changes in a remote FBAM.

Laser cooling by over 7 K in Yb-doped ZBLAN fibers with high-power pumping at atmospheric pressure.

Anti-Stokes fluorescence (ASF) cooling has been demonstrated to be a viable method for balancing the waste heat produced in gain materials. In addition, radiation-balanced fiber lasers and amplifiers at atmospheric pressure have recently been developed. Here, we evaluate the cooling characteristics in a long section of a Yb-doped ZBLAN fiber with high pump power. The fiber has a 200-µm-diameter core and is doped with 3 wt. % Yb3+. As indicated by a thermal camera, cooling by over 7 K below ambient temperature was achieved by core pumping at 1030 nm. The temperature drop distribution at multiple measurement points in the fiber was evaluated with a maximum pump power of tens of watts. The results demonstrate the excellent ASF cooling performance of Yb-doped ZBLAN fibers. This study has great significance for the development of high-power radiation-balanced fiber lasers.

Engineered zero-dispersion microcombs using CMOS-ready photonics

Normal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS foundry-produced microresonators is an important step toward scalable production. However, the chromatic dispersion of CMOS devices is large and impairs the generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a coupled-ring resonator configuration. Operating in the turnkey self-injection locking mode, the resonator is integrated in a hybrid manner with a semiconductor laser pump to produce high-power efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons), and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency, and temporal waveform. This integrated hybrid system could be used in coherent communications or for ultrastable microwave signal generation by two-point optical frequency division.

Heat exchange mechanism analysis and structural parameter optimization for series-combined microchannel heat sinks

This study presents a heat exchange mechanism analysis and an optimization of structural parameters of a built-in series combined microchannel heat dissipation platform, aiming to address the problems of low heat exchange and high pumping power caused by the mismatch in the selection of the structural parameters of the microchannel heat sink (MHS). A numerical calculation model was built in Fluent, and the temperature difference, pressure difference, and their ratio between the inlet and outlet of the MHS were used as the evaluation indicators. Using an orthogonal test, the influence of multiple parameters on the heat exchange effect was investigated. It is found that the shape of the microchannel is the main factor affecting the heat exchange phenomena, and the optimal combination of parameters such as the height, width, and length of the rectangular microchannel is obtained by a genetic algorithm. Physical transformation and heat exchange experiments were carried out. It was highlighted that the comprehensive performance of the optimized cooling system has been improved to varying degrees under different inlet flow conditions. At an inlet flow rate of 2.0 m3 h−1, the pressure difference and pumping power consumption are reduced by 24.9%, and the maximum temperature difference and heat dissipation power are increased by 21.0%. An experimental study on the heat exchange effect of MHSs with different numbers of serial pieces was carried out. With a number of MHSs of 15, the heat exchange is found to be sufficient, and the maximum heat exchange estimated was 9289.52 W.

Kerr soliton frequency comb generation by tuning the coupling coefficient in coupled nonlinear microcavities.

Kerr soliton frequency comb generation in nonlinear microcavities with compact configurations are promising on-chip sources. Current Kerr comb generation by using a single microcavity with a tunable CW pump laser or high-power femtosecond pulse pump are difficult to be integrated on chip. In this paper, we propose an on-chip soliton comb generation scheme by tuning the coupling coefficient of two coupled microcavities instead of tuning the wavelength of the cw pump laser or using a pulsed pump laser in a single microcavity. The two microcavities are assumed to be identical. We showed by numerical simulation that Kerr comb generation is possible in both the blue and red detuned regions of the main microcavity in the coupled cavity system. We further found that the range and boundary of the soliton generation region of the couple microcavities depend on the coupling coefficient between the coupled cavities. To ensure that the modes being coupled have identical optical paths, we designed a Sagnac loop structure which couples the clockwise and counterclockwise modes in a single microcavity and demonstrated Kerr comb generation in both the blue and red detuned regions by tuning the coupling coefficient. The proposed Kerr comb generation scheme can be utilized for chip-scale integrated soliton comb sources, which will contribute to the development of on-chip applications.

Dynamic process of dissipative soliton build-up in mode-locked fiber laser

We experimentally studied the dynamic process of dissipative soliton build-up by dispersive Fourier transform in net normal dispersion cavity. The oscillation of spectral bandwidth and pulse energy before the stabilization of dissipative soliton was observed, the build-up and termination of the double dissipative solitons accompanied with soliton explosion and energy interaction were observed with higher pump power. Simulation of dissipative soliton build-up process was demonstrated through the extended nonlinear Schrödinger equation, negative feedback mechanism was summarized as the reason of the pulse oscillation during the build-up process.

Temperature dependence of LiTaO3 refractive index: Correction of Sellmeier equation

We report a new and more precise Sellmeier equation derived using the quasi-phase-matching curves obtained from the study of the optical parametric generation (OPG) in 1D periodically poled LiTaO3 (1D-PPLT) of different periods at low and high pump power.