Increasing Pump Power Research Articles

Numerical analysis of micro-channel heat sink using ethylene glycol based nanofluid in case of electronics cooling

As size of Integrated circuit is goes on decreasing and number of elements per chip increases, the heat dissipation per unit area of IC increases. Therefore, nanofluid forced convection cooling using an micro-channel heat sink is introduced as new research topic for efficient cooling of IC devices. In this manuscript, ethylene glycol base nanofluid has been studied by using five different oxide nanoparticles including Al2O3, TiO2, CuO, SiO2 and ZnO and varying their concentration from 0 to 10% volume fraction. Single phase model has been considered in simulation analysis using ANSYS Fluent 13.0 software and the results obtained from simulation have been validated with previous experimental and simulation work. Furthermore, several aspects of parameters such as local thermal resistance, pumping power and local heat transfer coefficient are presented in below manuscript. From the result it is analysed that ethylene glycol base nanofluid increases the heat transfer parameters very effectively. Further, as concentration of nanoparticle sis increases the convective heat transfer coefficient and pumping power increases. Also, CuO-EG nanofluid cooled electronics devices more efficiently compared to other nanofluid which are considered in this study.

Influence of annealing time on random lasing from ZnO nanorods

Highly stabile single mode and multi-mode random lasing emissions were observed from ZnO nanorods array prepared on glass substrates using chemical deposition technique. By varying the post-growth-annealing time, nanorod diameters between 54 and 78 nm with population densities between 75 and 95 nanorods/µm2 were obtained. Depending on the population density and diameter of the nanorods, single, double and triple random lasing emissions were observed with lowest threshold of 209 mJ/cm2. Furthermore, the lasing threshold showed an obvious dependency on the nanorods density. The lasing emission maintained its wavelength with increasing pump power, indicating high stability of the lasing mode(s).

Optimization of the finned double-pipe heat exchanger using nanofluids as working fluids

The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost. Increasing fin dimensions increases the annulus hydraulic diameters. Even though the total volume of the heat exchanger remains unchanged between the finned and bare designs, the heat duty increases with increased heat transfer area for the finned design. The fins should be designed, and the dimensions should be calculated with special attention for different flow rates and heat exchanger dimensions. In this study, number, geometry and dimensions of the fins are determined using the algorithms available in the literature. The operational condition optimization is carried out accompanied with the cost analysis. In addition, the effects of the types of working fluids and fouled and clean cases are investigated for the total heat transfer enhancement in parallel with performance, lifetime and cost issues. A detailed analysis is presented for finned and unfinned double-pipe heat exchanger models for pure engine oil and its nanofluid mixtures with Ti, TiO2, Cu, CuO, Al and Al2O3 nanoparticles, multi-wall carbon nanotubes and graphene nanosheet having a constant particle concentration in the liquid phase. The nanofluid is flowing in annulus side, whereas the seawater is flowing in the tube side. It is observed that both the pressure drop and the pumping power increase with the increasing fin number and decrease with the cleanliness factor, whereas the total tube number decreases with increasing fin number. It is found that different types of nanofluids affect the cost and optimum annulus side velocity significantly. The results are summarized in several figures that consider the increasing Reynolds number with the cleanliness factor, the heat transfer coefficient and the pressure drop, the friction factor with changing mass flow rate and the cost values with corresponding annulus side velocities. Finally, the overall characteristics of the trend lines are provided in the figures.

Passively Q-Switched Erbium-Doped Fiber Laser with TiSe<sub>2</sub> as Saturable Absorber

The TiSe2 nanosheets were prepared by means of ultrasound-assisted liquid phase exfoliation (LPE) and the nonlinear saturable absorption properties were experimentally investigated. The modulation depth, saturation intensity and nonsaturable absorbance of the prepared 1T-TiSe2 SA were 15.7%, 1.28 MW/cm2 and 8.2%, respectively. Taking advantage of the saturable absorption properties of TiSe2-based SA, a passively Q-switched erbium-doped fiber (EDF) laser was systematically demonstrated. The pulse repetition rates varied from 24.50 kHz up to 73.79 kHz with the increasing pump power. The obtained shortest pulse width was 1.31 μs with pulse energy of 79.28 nJ. The system presented merits of low-cost SA preparation, system compactness, superb stability and high competition.

High-power 1.6 μm noise-like square pulse generation in an all-fiber mode-locked laser

We demonstrate generation of high-power and large-energy noise-like square pulses at 1612 nm in an all-fiber dumbbell-shaped mode-locked Er: Yb co-doped double-clad fiber (EYDF) laser. The custom couplers with high power handling keep the laser function well. Large-mode-area EYDF with high power handling and enough high pump power make it possible to obtain high output power in the oscillator. Compared with figure-eight structure, strictly all-fiber dumbbell-shaped structure without isolator and optimizing splicing loss could reduce intra-cavity loss and improve optical to optical efficiency, which could reduce heat accumulation and enhance the power carrying capacity of EYDF. In order to study the influence of in-band absorption on output wavelength, EYDF1 and EYDF2 with different in-band absorption coefficients are accessed to intracavity, respectively. It is directly demonstrated that regulation of in-band absorption is an effective way to control the output wavelength. Strong in-band absorption could restrain the emission of C-band and make the wavelength range above 1.6 μm obtain enough gain. Linear insertion loss is another important factor to affect the emission wavelength in EYDF fiber laser. At pump power of 8 W, maximum average output power with emission wavelength above 1.6 μm can reach 1.16 W, corresponding to a single pulse energy of 1.26 μJ. SNR of output pulse is 70 dB which indicates the high stability of mode-locking. In order to verify and evaluate influence of insertion loss on the output characteristics of mode-locked laser, a variable attenuator is inserted in experimental setup, allowing us adjust the linear loss of the cavity. By increasing pump power and adjusting PCs, mode-locked pulses could be obtained on the condition of large additional insertion loss. Even though ~ 10 dB additional insertion loss is introduced, the oscillation still could function at 1612 nm and keep stable mode-locked state. This result demonstrates our oscillation could bear strong additional loss and own strong robustness. If excessively large additional insertion loss is added, 1566 nm becomes the central emission wavelength and wavelength component at 1612 nm almost disappears. Our investigation supplies a direct guideline to design high-power fiber laser with emission wavelength above 1.6 μm.

Spatiotemporal evolution and spectral character of second harmonic generation in optical microresonator

With the consideration of the second and the third order nonlinear effect, the Lugiato-Lefeve equation which describes the field evolution of the fundamental frequency wave and the second harmonic wave is introduced. Based on the Lugiato-Lefeve equation, the generation of the second harmonic wave in the SiN microresonator is analyzed, and the effect of the each parameter on the dual field is studied. Simulation results indicate that the stable field of the fundamental frequency wave is of flat top pulse, and the field of the second harmonic wave is of sinusoidal distribution. When the detuning parameter increases, the power of the dual wave inside the microresonator oscillates, and the stable power weakens, the stable light field is periodically varied. Moreover, the chaos emerges as detuning parameter becomes large. The stable field can be generated in the microresonator with the weak pump power. However, because of the high pump power, the dispersion and nonlinear effect are enhanced, resulting in the periodic light field. Furthermore, the oscillation of the dual power curve is aggravated, as the pump power increases. In addition, the turning patterns can be observed by choosing the special dimension of microresonator. Theoretical analysis results are significant for studying the generation of the second harmonic wave in the microresonator.

Off-axis pumped Hermite-Gaussian mode solid-state laser

To study the modes’ pattern and the modes’ competition behavior of an off-axis pumped solid-state laser, a small signal approximation method is derived, which simplifies the multiple-mode differential equations into liner algebraic equations. When the pump beam radius is small, the higher-order Hermite-Gaussian modes emerge successively with the off-axis displacement increasing, while the pattern evolution shows some complexity when the pump radius is larger. The percentage of the modes with a small pump power near the threshold, calculated with the small signal method, is close to that calculated at a higher pump power by directly solving the rate equations numerically. This indicates that we can estimate the modes’ pattern of an actual high power laser by using the small signal method. For a multiple Hermite-Gaussian modes off-axis pumped solid state laser, as the pump power increases, the photon number of the mode increases linearly as its net gain becomes positive, while that of the second mode with a smaller net gain does not increase immediately as it becomes positive successively. Larger pump power is required until the photon number begins to increase. The increasing slope of first mode decreases as the second mode begins to grow. The dynamics of the modes’ competition presents cross spiking and cross relaxation process before they become stable. Moreover, the outputs of the modes HG<sub>00</sub>-HG<sub>50</sub> are experimentally demonstrated, and the spot evolution with the off-axis displacement agrees very well with the calculated result.

Development of Optimization Sensitivity Equation by Multiple Linear Regression and Correlation Analysis

Gas pipeline pressure-flow problem are affected by varieties of factors notably frictional pressure drop and other pressure drops components. These problems inevitably result in the reduction of the operating efficiency of gas pipelines by virtue of reduction in the line throughput and increased pressure drop along the line. It has been established that increased pressure drop will ultimately lead to increased pump power as well as higher cost of design, construction and operations of gas pipelines. These prevailing factors prompts the need to ascertain the stability and reliability of the optimal flow results. The develop sensitivity model prediction was hinged around ∆L/L (%) being zero. It invariably confirmed that the results of optimal flow capacity are more sensitive to changes in upstream and downstream pressures. It was least sensitive to pressure gradients. The governing conditions being that changes in pipe diameter, ∆D/D (%) and flow capacity, ∆Q/Q (%) were in the order of 5%.

Development of Optimization Sensitivity Equation by Multiple Linear Regression and Correlation Analysis

Gas pipeline pressure-flow problem are affected by varieties of factors notably frictional pressure drop and other pressure drops components. These problems inevitably result in the reduction of the operating efficiency of gas pipelines by virtue of reduction in the line throughput and increased pressure drop along the line. It has been established that increased pressure drop will ultimately lead to increased pump power as well as higher cost of design, construction and operations of gas pipelines. These prevailing factors prompts the need to ascertain the stability and reliability of the optimal flow results. The develop sensitivity model prediction was hinged around ?L/L (%) being zero. It invariably confirmed that the results of optimal flow capacity are more sensitive to changes in upstream and downstream pressures. It was least sensitive to pressure gradients. The governing conditions being that changes in pipe diameter, ?D/D (%) and flow capacity, ?Q/Q (%) were in the order of 5%.

Jet Impingement Heat Transfer Enhancement by U-Shaped Crossflow Diverters

AbstractArray-jet impingement is typically used in gas turbine blade near-wall cooling, where high rates of heat dissipation is required. The accumulated crossflow mass flux results in significant reduction in jet effectiveness in the downstream rows, leading to reduced cooling performance. In this paper, a jet impingement system equipped with U-shaped ribs (hereafter referred as “diverter”) was used for diverting the crossflow away from the jets emanating from the nozzle plate. To this end, a baseline configuration of array-jet impingement onto smooth target surface is considered, where the normalized jet-to-jet spacing (x/dj = y/dj) was 6 and the normalized jet-to-target spacing (z/dj) was 2. Crossflow diverters with thickness t of 1.5875 mm and height h of 2dj (= z) were installed at a distance of 2dj from the respective jet centers. Detailed heat transfer coefficients have been calculated through transient liquid crystal experiments carried out over Reynolds numbers ranging from 3500 to 12,000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection, thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. This benefit in heat transfer came at a cost of increased pumping power to maintain similar flow rate in the system. At a given pumping power, crossflow diverters yielded an enhancement of 9–15% in heat transfer compared with the baseline case.

Peak-power-clamping in an all-polarization-maintaining Q-switched mode-locking fiber laser.

We report the peak-power-clamping (PPC) effect in a polarization-maintaining (PM) Q-switched mode locking fiber laser. The laser cavity with a compact and stable all-PM fiber configuration can clearly demonstrate three different output states including normal Q-switching, PPC Q-switching, and PPC Q-switched mode-locking (QML) with the increasing pump power. To the best of our knowledge, it is the first time that PPC effect is successfully obtained and analyzed from the Q-switching to QML. This research extends the theory of PPC in pulsed lasers and reveals the potential to achieve ultra-high pulse energy.

Experimental exploration of mode-locking evolution mechanism in dual-ring fiber laser

We explored experimentally the mode-locking (ML) evolution mechanism of a dual-ring fiber laser. Increase of the total pump power up to 860 mW allowed the observation of the state changes from single-ring ML, dual-ring ML, to dual-ring self-starting ML. Moreover, a group of wave plates and a fixed polarization beam splitter were applied in each subring as precise attenuators. Rotation of each wave plate for an entire turn allowed the investigation of the ML evolution of the two subrings based on the intracavity power variation in each subring. The variation periodicity of the output power was analyzed for each subring and was found to be consistent with the theoretical results. Furthermore, the ML detachment threshold in each subring was estimated to explain the ML evolution. Our study provides a deeper understanding of the ML evolution in dual-ring fiber lasers and can aid their future optimal design for dual comb applications.

All-Fiber Mode-Locked Laser Based on Mamyshev Mechanism With High-Energy Pulse Generation at 1550 nm

An all-fiber mode-locked laser based on Mamyshev mechanism operating at 1550 nm is demonstrated. Self-phase modulation and offset spectral filtering provide high peak-power pulse selection in the laser cavity and induce mode locking. With selected operating parameters, the all-fiber mode-locked laser easily achieves mode locking without external seed pulses or auxiliary starting arms, making the laser convenient to operate. Pulses with maximum energy ∼18 nJ and width 230 fs are obtained. Pulse width is almost unchanged with increasing pump power, while pulse energy increases linearly. Starting of the mode-locked laser based on Mamyshev mechanism and output spectra with different pump powers are experimentally investigated.

Raman competition from ultra-broadband modulation instability gain in the As2Se3 glass photonic crystal fiber filled with argon gas

Based on the As2Se3 glass photonic crystal fiber (PCF) filled with Argon gas, pressure- and power-dependent modulation instability(MI) gain properties are studied. Two narrow MI gain bandwidths in the Stokes or anti-Stokes region expand gradually with the increasing light power, and merge into an ultra-broadband gain profile eventually by increasing the pump power from 1 W to 9000 W at a fixed gas pressure. Further increasing pump power will result in the reduction of the gain bandwidth and the formation of a constant narrow-band gain peak, which is a novel phenomenon and observed in our work for the first time. When the argon gas pressure is changed from 1 P0 to 400 P0, a similar gain characteristic is also found. However, their maximum gain bandwidths are reduced from 5065 nm to 3833 nm with the increase of the gas pressure, and their pump power required to generate the narrow-band gain spectrum are reduced from 8450 W to 3060 W. These results indicate that the formation of the ultra-broadband MI gain mainly depends on some nonlinear effects rather than stimulated Raman scattering (SRS) effect, while the single gain peak with a narrow bandwidth mainly results from the SRS effect. And they also show that, it is feasible to control the MI gain characteristic in the mid-infrared region by changing the Argon gas pressure in the As2Se3 PCF, and this scheme can also be used in optical communication and spectral shaping in the future.

Q‐switching pulses generation with samarium oxide film saturable absorber

AbstractQ‐switching pulses generation in an erbium‐doped fiber laser (EDFL) was demonstrated by using a samarium oxide (Sm2O3) film as a saturable absorber (SA) for the first time. The passively Q‐switched EDFL operated stably at 1567 nm with tunable repetition rates, ranging from 47 to 66 kHz with the increase in pump power from 51.0 to 88.1 mW. At 88.1 mW pump power, the maximum pulse energy and the minimum pulse width were obtained at 26 nJ and 5.6 μs, respectively. These results demonstrated that the proposed Sm2O3 SA is viable for the construction of a flexible and reliably stable Q‐switched pulsed fiber laser in the 1.5 μm region.

Heat transfer enhancement in a counter-flow sinusoidal parallel-plate heat exchanger partially filled with porous media using metal foam in the channels’ divergent sections

This is a numerical study of heat transfer and flow in a counter-flow sinusoidal parallel-plate heat exchanger using metal foam in the channels’ divergent sections. The cold water fluid with Reynolds number of 100 and hot oil fluid with Reynolds number of 2 enter the downer and upper channels of the heat exchanger, respectively. The sinusoidal heat exchanger is investigated with two-wave amplitudes (0.3 and 0.6 cm), two wavelengths (6 and 12 cm) inserting the porous media with three particle diameters (0.1, 0.05 and 0.01 mm) and three thicknesses (A/3, 2A/3, and A). Darcy–Brinkman–Forchheimer and local thermal non-equilibrium models are used. To evaluate the increased heat transfer versus the increased pumping power, a dimensionless number called performance evaluation criteria (PEC) has been defined in the current study. The obtained results showed that the heat transfer rate, effectiveness and overall heat transfer coefficient of the heat exchanger are increased up to 19.2%, and the PEC number is enhanced to 1.171 in the optimum case with wave amplitude, wavelength, metal foam particle diameter and thickness equal to 0.6 cm, 6 cm, 0.01 mm and 2A/3, respectively. Moreover, since the metal foam is embedded in the wake region of the heat exchanger or channels’ divergent sections, its effect on pumping power is subtle, which is an advantage of using the porous medium at these regions.

Linear‐cavity mode‐locked fibre laser with cylindrical vector beam generation

A cylindrical vector beam (CVB)-pulsed fibre laser with compact linear-cavity configuration has been demonstrated, using a two-mode fibre (TMF) Bragg grating (TM-FBG) for mode discrimination and a semiconductor saturable absorber mirror (SESAM) for passive mode-locking. As a result, mode-locked CVB pulses with fundamental repetition rate of 10.295 MHz have been obtained. Besides, with increased pump power harmonic, mode-locked CVB pulses have been achieved, for the first time.

Enhanced nonlinear optical properties of solution dispersed carbon dots decorated graphene oxide with varying viscosity

Nonlinear optical response of solution dispersed Carbon Dots decorated Graphene Oxide (CDs-GO) with viscosity has been investigated. Spatial self-phase modulation and Z-scan technique were utilized to study the nonlinearity of the composite which was synthesized by microwave assisted route. The strong self-diffraction effect was observed on excitation with 403,450 and 532 nm wavelengths from a DPSS laser. The estimated value of χ(3) is 3.2 × 10−4 esu in water obtained using SSPM technique. The nonlinearity of the sample is due to the reorientation of the graphene oxide sheet with the strong electromagnetic field of lasers and two photon absorption. Enhanced nonlinearity observed with increase in input pump power and viscosity of the solvents endows them new potentials in nonlinear optical applications.

Optimum thermo-hydraulic performance of solar air heater provided with cubical roughness on the absorber surface

ABSTRACTHeat transfer augmentation in solar air heaters (SAHs) can be achieved economically and conveniently using artificial roughness elements on the absorber surface. Cubical roughness elements used in this investigation produces better heat transfer characteristics. However, this enhancement is particularly accompanied by increased pumping power due to increased friction. This study presents the results of the experiments carried out to determine the optimum design and operating conditions which gives a better thermohydraulic performance. Efficiency index () is often used as thermohydraulic performance parameter which is evaluated using correlation = (()/()). Experiments are conducted within the limits of Reynolds number () from 3000 to 8000, relative roughness pitch () of 10 to 20 and relative roughness gap () of 4 to 8. Relative roughness height () of 0.06 and aspect ratio () of 5 is maintained constants. Substantial enhancement in the Nusselt number (59.1–72.7%) accompanied by a large increase in the friction factor (138.7–179.4%) over SAH with smooth absorber plate is achieved. Optimum thermohydraulic performance is obtained for lower values of the Reynolds number, relative roughness pitch () value 20 and relative roughness gap () of 8.

Self-organized structures of bound states in a 2 μm dispersion-managed mode-locked fiber laser

We report on the experimental generation of various self-organized structures of bound states in a near zero-dispersion mode-locked fiber laser. When the pump power is fixed at 492 mW, appropriately adjusting polarization controllers, the switching of the cavity feedback results in the evolution from the single pulse to the dispersion-managed soliton (i.e., stretched-pulse) pair. With the increase of pump power, bound states composed of more than two pulses can also be observed. Our results of the self-organized structures might enlarge the data-carrying capacity of current fiber-optical communication systems and benefit the investigation of nonlinear dynamics of bound states in fiber lasers at 2 μm.