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Algerian Mzab traditional houses, using passive techniques since the eleventh century (from 1012 to 1882), have seen recent modifications. Analysis of 612 questionnaires and interviews with Mzab residents reveals 81.2% of these houses have been modified. Modifications include adding floors, thinning walls, and replacing lime with cement, driven by the need for space, ventilation, and modernisation. However, such modifications often increase energy consumption, with residents requiring more heating in winter and air conditioning in summer. This reliance on fossil fuels exacerbates regional climate insecurity. Planting roof terraces and using high-insulation building materials can reduce energy consumption in modified Mzab houses. [ABSTRACT FROM AUTHOR]

Nowadays, renewable energy sources (RESs) are widely used as distributed generation sources, leading to issues such as unintentional islanding, protection concerns, and reverse power flow. Unintentional islanding is dangerous because it can endanger utility workers, damage DG units, and jeopardize grid stability. To overcome these issues, Researchers are developing islanding detection schemes. This article proposes a novel passive technique for islanding detection of multi-bust test systems, based on the differential impedance of a series inductor. The differential impedance changes during islanding and non-islanding events. However, in grid-connected mode, the voltage and frequency of the microgrid are handled by the utility grid. Therefore, no significant changes in differential impedance occur. The voltage and frequency of the microgrid are not handled by the power grid while in islanded mode. Therefore, the differential impedance varies significantly. The islanding is detected if the value of differential impedance is greater than the predefined threshold. This scheme detects islanding in 24 ms at zero mismatch power, has no impact on power quality, and is computationally simple. The proposed approach easily discriminates between islanding and non-islanding events. The distribution test system is simulated in MATLAB/Simulink environment. Additionally, the novel passive technique has been validated on an OPAL-RT real-time platform. [ABSTRACT FROM AUTHOR]

The utilization of hybrid nanofluids has gained essential consideration in thermal engineering. Changes in the thermal characteristics of the base fluid are responsible for the improved thermal conductivity brought about by hybrid nanoparticles and their shapes. For this goal, in this paper, the two-phase 60%:40% SiO2-MWCNT/water hybrid nanofluid flow at the Reynolds number range of 3000–10,000 in a square duct is investigated concerning first- and second-law analysis. The turbulent flow regime is modeled using the RNG k–ε turbulence approximation. The hybrid nanofluid is modeled via a mixed model. The parameters used in this study are three different nanoparticle shapes (cylindrical, spherical, and platelet) and nanoparticle volume fractions (0.2%, 0.6%, and 1.0%). The distributions of the Nusselt number, friction factor, entropy generation, exergy destruction, exergy efficiency, temperature, and velocity contours are investigated in detail for the above parameters. It is found that the most significant increases in PEC are seen in hybrid nanofluids with the PC and PP shapes, at 2.27 and 3.24%, respectively. It has been shown that the exergy destruction of hybrid nanofluids with the second nanoparticle forms C and P is 43.90% and 58.74% more than that of a S one when PS-, PC-, and PP-shaped nanoparticles are utilized. The hybrid nanofluid with the PS shape has the highest exergy efficiency, whereas the SP-shaped nanofluid has the lowest. [ABSTRACT FROM AUTHOR]

A self-induced Q-switched erbium-doped fiber laser operating at 1563 nm was achieved by integrating a passive modulator based on tantalum aluminum carbide (Ta2AlC) MAX phase film embedded into polyynyl alcohol. The modulator, serving as a saturable absorber (SA), established a modulation depth of 9% and a saturation intensity of 0.3 MW cm−2. Upon integration of the film SA, a stable Q-switched fiber laser was obtained, generating pulses with a minimum width of 7.6 µ s at a repetition rate of 45.1 kHz, within a pump power range of 24.9–59.7 mW. The corresponding maximum average output power, maximum pulse energy, and highest peak power were determined at 1.6 mW, 36.2 nJ, and 4.7 mW, respectively. The RF fundamental spectrum exhibited a good signal-to-noise ratio of 61 dB, indicating excellent pulse signal quality. This demonstration of Ta2AlC MAX phase film Q-switched laser may open promising possibilities for scientific applications such as material processing. [ABSTRACT FROM AUTHOR]

Failure of islanding detection techniques leads to improper operation of DGs, risk for working personnel, loss of control over voltage and frequency, uncoordinated protection, poor power quality, etc. Therefore, the islanding event (IE) should be identified, and its detection algorithm should be incorporated according to the standard guidelines. Through this paper, a communication-assisted passive islanding detection technique (IDT) is proposed based on an index, which is the ratio of multiplications of superimposed negative sequence voltages and currents of DG and grid sides. Proposed ID is implemented in the modified IEEE-13 bus system through the micro phasor measurement unit. The calculated index is compared with a set threshold to discriminate between the IEs and non-islanding events (NIEs). The calculation of threshold is not very complex as compared to other schemes. The efficacy of the proposed IDT is tested under various system conditions, such as zero power mismatch (ZPM), wide range of active power mismatch, and reactive power mismatch. DG disconnection and unbalanced load test cases are also performed under ZPM condition. Similarly, different NIEs like capacitor switching, load switching, nonlinear load and different fault cases are verified through the proposed IDT. Real-time implementation of proposed IDT is conducted using opal-RT. [ABSTRACT FROM AUTHOR]

An ultrashort pulse erbium-doped fiber laser (EDFL) in anomalous group delay dispersion (GDD) has been proven to produce a soliton wave production at 1596 nm. The mode-locking operation was generated by employing a vanadium pentoxide-polyethylene glycol (V2O5)-(PEG) film as absorber for all-fiber ring setup. Under anomalous dispersion, the soliton mode-locked laser produced a peak wavelength with 2.7 nm spectral bandwidth and Kelly sidebands. Under this condition, we obtained pulse energy of 210 nJ and pulse width of 1.40 ps. The maximum peak electrical power of 150 kW was calculated at the maximum pump power. These findings shows that the V2O5-PEG film can be a good saturable absorber (SA) device in generating stable mode-locking fiber laser at the 1.55-area. [ABSTRACT FROM AUTHOR]

A novel design of “X–V rib” turbulators is proposed to improve fluid blending and to perturb thermal boundary layer (TBL) in a heat exchanger (HX) duct. Better fluid blending and more highly disturbed TBL are the two important factors for the improvement of HX performance. Effects of X–V rib geometrical parameters including rib height ratios (b/H = 0.05–0.20), rib arrangements (V-tip pointing upstream called “V-Upstream (VU)” and V-tip pointing downstream called “V-Downstream (VD)”) and rib types (I, II and III) on air stream and thermal mechanisms are numerically investigated in a 3D model. The numerical model is solved with the finite volume method (a commercial code) and a commercial program. Laminar air flow (inlet conditions with Re = 100–2000) is a selected range of the present investigation. Firstly, the created numerical model for the ribbed duct is validated with two significant topics: 1. Plain duct validation and 2. Optimum grid elements (grid independence). The validated results show that the ribbed-duct model has great reliability to simulate air stream and thermal characteristics. According to the numerical results, the disturbed TBL is obviously found in all rib types. Moreover, it is observed that the core flow disturbance occurs and improves fluid blending. The outcomes from the present investigation point out that the knowledge about flow structure and thermal mechanism are important guidelines for the development of vortex turbulators and HX improvement. For the thermal assessments, it is found that the best Nusselt number ratio (Nu/Nu0) is 11.80 for the type III X–V rib with b/H = 0.20 in the VD-direction. Additionally, the maximum thermal enhancement factor within our investigated range is 3.48 at Re = 2000, b/H = 0.20, type II X–V rib in the VU-direction.

Thermal performance enhancement in a square channel heat exchanger (HX) using a passive technique is presented. Vortex turbulator insertion in a square channel HX as a passive technique is selected for thermal improvement. The vortex turbulator of interest is discrete X-V baffles (XVB). The discrete XVBs are inserted in the square channel with the main aim of generating vortex flow. The vortex flow generated can support the enhanced convective heat transfer coefficient and also enhance HX performance. Effects of baffle configuration (type A and B), baffle size (w/H=0.05, 0.10, 0.15 and 0.20), baffle distance (e/H=1, 1.5 and 2) and flow direction (±x air flow paths) on fluid flow and thermal topologies are numerically investigated by using a commercial code. As shown by the numerical results, the predicted flow configuration with the discrete XVB insertions, which include impinging and vortex streams, is found through the HX channel. The perturbing thermal boundary layer and greater air blending are also found through the HX channel inserted with the discrete XVB. These mechanisms promote and augment the convection heat transfer coefficient, heat transfer rate and rise thermal potentiality. The maximum Nusselt number of the channel with the baffles inserted is 11.01 times upper than that of the smooth channel, while the greatest thermal performance factor (TPF) is observed to be around 3.45. [ABSTRACT FROM AUTHOR]

Malfunctioning of islanding detection algorithms leads to system instability, failure of reclosing, and damage to load-side equipment. It also threatens security personnel. Therefore, islanding detection is an essential task for the proper functioning of the distribution system. In this paper, an islanding detection technique is presented for a grid-connected distributed power generation system. The proposed islanding detection technique is based on the change in superimposed positive sequence apparent power (CSPSAP). The CSPSAP-based islanding detection technique discriminates islanding and non-islanding events. The accessibility of positive sequence components makes the technique suitable for islanding detection for a wide range of active and reactive power mismatches. It works effectively in zero power mismatch conditions. The effectiveness of the proposed technique is verified for islanding events in cases of distributed generation disconnection with the inclusion of noise, various irradiances, and unbalanced load. Even the proposed technique proves its efficacy under various non-islanding events such as capacitor switching, different fault cases, and load switching. The impact of the proposed technique is also validated in cases of islanding and non-islanding under weak grid systems. The proposed islanding detection technique is fast due to the utilization of local measured parameters at the point of common coupling and does not have power quality degradation issues. Effects of the false detection zone and non-detection zone are also discussed with regard to the proposed technique. The proposed technique is also validated on the real-time platform of the OPAL-RT. MATLAB 2018a software is considered to model and simulate a microgrid. [ABSTRACT FROM AUTHOR]

Peltier refrigerators are an environmentally friendly cooling method, as they require no refrigerants and have no moving parts. However, effective cooling requires optimal-strong heat rejection from the hot side of the Peltier module. This research proposes and tests a self-capillary ultra-thin (0.1 mm) water-attracting coated PVC membrane (SCCP) as an innovative effective heat rejection mechanism. The SCCP cools the hot side of the Peltier module to temperatures even lower than ambient air, without external power. The cooling effect is achieved through the evaporation of a thin water film on the hot surface, driven by capillary action, which releases latent heat. This process can occur under natural or forced convection, both of which are investigated under various voltage and temperature conditions. The SCCP method was compared to traditional heatsinks and showed superior performance, with the hot side temperature being not only cooler than that in heatsink mode but also cooler than the ambient temperature in most cases. Additionally, the SCCP method demonstrated reduced sensitivity to ambient temperature changes, with only a 2–3° increase in the hot side temperature when the ambient temperature was raised by 10°. The findings suggest that SCCP is a promising technique, with further results discussed. [Display omitted] • An innovative heat rejection idea is proposed for hot side of Peltier cooler. • The idea is the application of an ultra-thin self-capillary coated PVC sheet. • This sheet absorbs the water automatically and makes a thin wet surface. • The surface evaporation releases huge latent-heat-based cooling effect. • The method was found so promising and more powerful than common heatsink. [ABSTRACT FROM AUTHOR]

The current experimental study focuses on designing novel shapes of transverse turbulators to improve the performance of solar air heaters. Fourteen designs are derived from the original case having length × width × thickness of 30 mm × 15 mm × 0.8 mm. These turbulators are tested in a rectangular channel, and the thermal and hydraulic transport performances of the fitted channel are compared with those obtained for the vacant channel. Although the novel geometries may provide a weaker thermal characteristic through the channel, the penalty in the hydraulic characteristic is decreased significantly compared to the original shape, leading to better overall hydrothermal performances. It is found that the novel designs of transverse turbulators own lower values of heat transfer coefficient, that is ranging from 12.1% to 45.2%, whereas the pressure drop decreases within the range of 48%–91% at the studied Reynolds numbers (Re = 1643, 3286, and 4929). The results show that the Nusselt number ratio (Nufitted/Nuclear) gets reducing trend with increasing Re, while the friction factor ratio (ffitted/fclear) gets increasing trend. An appropriate tradeoff between thermal and hydraulic characteristics is established by using a specific design which presents minimum values of pressure drop and maximum values of the performance index. The highest index of 1.69 is recorded for this turbulator design at Re = 1643. [ABSTRACT FROM AUTHOR]

The combined effect of water-based GO and Al2O3 nanofluids and Propeller Turbulator (PT) insert on enhancement in thermal performance of counter-flow double tube heat exchanger is investigated experimentally. Experiments were carried out with a hot water flowrate of Re = 2500 in the inner tube fitted with a propeller insert (NP: 6, 8, 10) and variable flow rates (500 ≤ Re ≤ 5000) of water-based GO and Al2O3 nanofluid (vol.%: 0.05, 0.1, 0.15) flowing in the annulus. Experimental results show that, Nusselt number increased by 29.43% and TPF by 1.32 times for tube fitted with 10 propellers and 0.15 vol.% of Al2O3 nanofluid. In the conducted combinations, the extreme increase was noted for the higher number of propellers and higher vol.% of Al2O3 nanofluid combination, with a slight increase in friction factor. Nusselt number and friction factor correlations were developed and predicted well within −14% to +10% and −10% to +5%, respectively. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) technology adoption in recent years has experienced significant growth due to its inherent advantages over alternative technologies. Nevertheless, there is a concern regarding performance deterioration due to high operating temperatures. Various thermal management methods have been studied to address this issue, each having its own advantages and disadvantages. Hence, a comprehensive review aimed at developing effective passive cooling techniques was undertaken and two techniques were finalized for outdoor testing viz. natural circulation loop based cooling (PV-NCL) and evaporative cooling (PV-EVP). Though the former version could drop module temperature by 7.4 °C–13.9 °C (Power output increment in the range of 3.5 %–6.7 %), this improvement was not sustained throughout the day due to factors such as flow resistance within the loop and a lack of convective cooling in the vicinity of the cooler. Subsequent experiments confirmed that loop resistance played a dominant role in this phenomenon. Additionally, concerns about water circulation in PV-NCL were resolved through a comparison with water duct-integrated PV. On the other hand, the innovative gravity-assisted water flow for evaporation method (PV-EVP) yielded more promising results, with a power output enhancement ranging from 3.7 % to 11.5 %. However, considering the in-field operational issues, PV-NCL with a modified design will likely be the best technique. [Display omitted] • Efficient passive cooling techniques for photovoltaic modules. • A novel application of natural circulation loop in PV thermal management. • Dominance of natural circulation flow over still water cooling. • Evaporative method of cooling with negligible water consumption. [ABSTRACT FROM AUTHOR]

Swirl device is seen as a path to enhance the efficiency of a thermal switch. Swirl device with fabricated form of porosity and v-cuts twisted tape (tt) inner pipe insert helps to augment performance by improving the heat transfer (U) coefficient. This work is related to the thermal performance factor (TPF), friction factor (ff) and Nusselt (NNu) number in the inner tube inserted with a innovative design of Alternate Perforated V-Notch (APVN) tape having twisted ratio 6.25 incorporating porosity amount of Rp = 1.087% and width (w/W) ratio = 0.333, were investigated features to improve heat transfer rate. Enhancement in turbulent generation of the primary flow into the secondary flow with this design. Experiment test was performed on a pipe in pipe tubes of (d) internal diameter of 0.013 m with test section length of 0.9 m. Temperature of the warm water had kept constant at 60 °C within the Reynolds number range of 2246–16,224. The heat exchanger with empty tube (without tt) and the input of normal twisted tape (tt) has been checked. In addition to the investigated range, NNu, ff and TPF in the tube with APVN twisted tape insertion were observed (Rp - ratio) 1.833–2.276, 2.155–4.549 and 1.84–1.778 times more than the values of empty tube. The presented work is very useful in the field of energy conservation through maximum transfer of heat in the industrial process.

In a Supersonic combustion ramjet (Scramjet) engine, combustion occurs at supersonic velocity as incoming air remains supersonic. Scramjet engines have complex flow phenomena taking place inside the combustor. In a scramjet combustor, mixing and combustion should take place within few milliseconds. In the present study, two additional trailing struts with no fuel injection are placed a short distance downstream of the fuel injection strut. Effect on combustion performance using these strut-based flame stabilizer configurations are assessed. Reynolds averaged Navier-Stokes equations are solved with turbulence model and species transport equations. Validated results of the single strut are compared with the different strut configurations. It is found that the placement of trailing struts have a vital role. High-pressure zones, shock reflections, recirculation region, and expansion fan in between combustion region and the trailing struts enhance the combustion efficiency. Strut configuration introducing high-pressure regions outperformed other strut configurations due to the formation of a strong recirculation region in the core combustion region. Combustion efficiency is found to have a maximum improvement of 67.14% compared with single strut-based flame stabilizer. Total pressure loss also increased due to the introduction of additional struts. • Combustion performance is enhanced by introducing additional struts. • Combustion performance is affected by the location of these additional struts. • High-pressure regions, recirculation zones, oblique shock, and expansion fan enhance combustion efficiency. • Additional struts enhance combustion efficiency with minimal rise in pressure loss. [ABSTRACT FROM AUTHOR]

Drying of agricultural products is an energy demanding process. Solar energy as an alternative source is becoming more popular, especially in developing nations, due to high costs, unavailability of fossil fuels, and environmental hazards. The utilization of clean and green energy resources in the sector of drying agricultural products has increased in response to the rising environmental concerns. A solar dryer combined with a thermal energy storage system is reasonably efficient for continuous and consistent drying of agricultural produce in the temperature range of 40 - 75°C, which is required for drying most agricultural items. Traditional drying systems require fossil fuels; therefore, these dryers have become a natural alternative to replace it. For the last several decades, a large number of researchers have studied the use of a solar dryer to dry crops and food products. This review study focuses on the significant contributions made in the field of solar drying systems thus far, as well as the most current breakthroughs in drying technology. Solar dryers that provide drying during the hours when the sun is not shining have been specifically noted. Some different methods have also been considered, such as the use of phase change materials (PCMs) and desiccant materials to increase the dryer's performance and efficiency. [ABSTRACT FROM AUTHOR]

• Islanding detection in microgrid system. • Results analysis for nonlinear load switching, capacitor switching, single pole tripping. • Result analysis for symmetrical fault. • Tripping of other DG excepted targeted DG. • Voltage ride through problem. In this study, a communication assisted passive islanding detection technique is proposed for microgrid having converter based distributed generation (DG) resources. In the proposed approach, the matrix pencil method is applied to reconstruct the voltage signal then both the raw signal and reconstructed signals are used to estimate phasor magnitudes using Discrete Fourier Transform (DFT). Full cycle DFT is unable to eliminate the decaying DC component completely in one cycle from the actual input signal, whereas the reconstructed signal is a filtered signal. Hence, subsequent to the application of DFT, the difference between actual and reconstructed signal becomes negligible during steady state condition but exists only if an event occurs in the microgrid. Utilizing the well-known fact presence of DC component in initial stage at the time of transient event, the magnitude difference of raw and reconstructed signals is computed at a given end. Accordingly, an index for each phase is calculated considering difference from both sides; point of common coupling (PCC) and DG. The target DG gets detected as being islanded from the main grid, if the indices of all the three phases remains positive i.e., greater than zero. The results obtained for tested conditions indicate that all the three indices of phases retain simultaneously positive sign only for islanding event. On other hand, non-islanding cases involve at least one or more phases indices being of negative sign. The proposed approach is tested on signals generated from simulation model. Also, the obtained results for signals from real-time test bed executed using Opal-RT, proves the superiority, robustness, and reliability of the proposed islanding detection algorithm. [ABSTRACT FROM AUTHOR]

We achieved a self-induced Q-switched erbium-doped fiber laser (EDFL) operating at 1559.4 nm through the integration of a Titanium Aluminum Nitride, Ti 4 AlN 3 MAX phase film as a saturable absorber (SA). The MAX phase was embedded into a polyvinyl alcohol (PVA) matrix, ensuring contamination-free compatibility. The SA film demonstrated a modulation depth of 17% and saturation intensity of 0.5 MW/cm². Integration of the film enabled stable Q-switching, producing pulses with 5.75 µs width at 59.2 kHz repetition rate and 29.9 – 64.7 mW pump power. Parameters included a maximum average output power of 2.34 mW, maximum pulse energy of 39.5 nJ, and highest peak power of 6.87 mW. The RF spectrum exhibited a 63 dB signal-to-noise ratio, indicating high pulse signal quality. This demonstration of Ti 4 AlN 3 MAX phase film Q-switched fiber laser holds promise for applications including biomedicine. [ABSTRACT FROM AUTHOR]

In this research, a numerical macroscopic approach has been employed to analyze nanofluid entropy generation and turbulent flow through a circular heat exchanger with an innovative swirl flow device. A homogenous model was considered for nanofluid. Minimizing entropy generation can be considered as a very important goal for designing a heat exchanger, so we focus on this factor in the present attempt. Simulations were presented to show the influences of the geometric parameter (revolution angle) and inlet velocity on hydrothermal and second-law treatment. Related correlations for thermal and frictional entropy parameters as well as Bejan number have been presented. Outputs reveal that augmenting revolution angle increases the frictional entropy generation. Increasing secondary flows leads to a reduction in thermal entropy generation due to a decrement in thermal boundary layer thickness. By improving convective flow, Bejan number reduces. [ABSTRACT FROM AUTHOR]

Exploring new saturable absorber (SA) materials is important for the advancement fibre laser technology especially in the improving the performance of Q-switched and mode-locked fiber lasers, which have tremendous applications in areas such as material processing, telecommunications, biomedical imaging, and scientific research. Here, we prepared a layer of Neodymium Oxide (Nd 2 O 3) film as a nonlinear optical device to obtain the Q-switched and mode-locked pulses in the Erbium-doped fiber laser (EDFL) cavity. The developed Nd 2 O 3 film recorded excellent optical properties with the saturable absorption of 2.8%, saturation intensity of 0.8 MW /cm2 and non-saturable loss of 59.0%. By integrating the Nd 2 O 3 film into a simple ring EDFL's cavity, a stable and robust Q-switched laser operating at 1558 nm was realized as the pump power is set between 45 and 92 mW. The average output power improved from 4.70 to 9.57 mW as the strength of the pumping was raised from 45 to 92 mW. The repetition rate and pulse width are tunable from 71 to 89 kHz and 3.48–2.56 µs, respectively as the pump power is escalated within the same range. The fundamental frequency of electrical signal exhibits signal-to-noise ratio (SNR) of 62 dB and this signifies the excellent stability of the Q-switching operation. In an extended EDFL cavity, the Nd 2 O 3 SA can produce a mode-locked soliton pulse operating at 1559.29 nm. The laser run at repetition rate of 1.89 MHz and pulse duration of 3.73 ps while recorded the highest peak power of 1.7 kW at pump power of 97.62 mW. [ABSTRACT FROM AUTHOR]

The present study aims to assess the thermohydraulic characteristics of smooth tri-lobed spiral tube (STST) and twisted tri-lobed spiral tube (TTST) numerically. Water with constant thermophysical properties is considered as the working fluid. The Reynolds number, based on the inlet conditions, varies from 500 to 2500 and a constant temperature of 323.15 K is regarded as the boundary condition of the tube wall. Temperature and flow field inside the tube are simulated utilizing a three-dimensional, stationary finite volume method (FVM) and a computational grid consisting of polyhedral elements. The influence of cross-section rotation for the STST and the effects of twist number, pitch ratio, and different cross-sections for the TTST are evaluated on the thermohydraulic parameters of the heat exchanger. According to the results, the optimized geometric configuration for STST in order to have the best performance occurs when the cross-section of the tube inlet has a rotation angle of −30°, resulting in 11.14% increase in the performance evaluation criteria (PEC) parameter. According to the findings for TTST, the Nusselt number (Nu) and friction factor (f) increase continuously by increasing the number of tube twists. Furthermore, from the PEC point of view, the TTST with a low pitch ratio close to 1 exhibits the best findings. Comparing the optimized results of STST and TTST indicates that the highest value of PEC (1.25) is achieved for TTST with a pitch ratio of 1.25 and a twist of 13 turns, which occurs at the Reynolds number of 1000. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • TT and twisted-tape are used to intensify heat transfer in an agitated heat exchanger. • Water is working fluid, and Reynolds number is between 4250 and 12750. • The TT yields higher Nu and f than the ST up to around 58% and 33%. • Maximum value of 2.28 is recorded for the considered performance index. Abstract In the current study, the thermal and hydraulic characteristics are experimentally investigated in an agitated heat exchanger which has an inner U-tube as the main flow path. This type of heat exchanger has been investigated for the straight flow path by few researchers, but not for the twisted configuration, particularly fitted with the twisted-tapes. Hence, the U-tube drowned in shell side liquid has two straight and twisted configurations filled with the twisted-tapes. In order to investigate the effects of the twist ratio, two different twisted-tapes are employed in turbulent flow with Reynolds number ranging from 4250 to12750 by using water as working fluid. The results of straight-tube and twisted-tube alone are considered for comparisons. It is found that the heat transfer coefficient and pressure drop of the straight-tube and twisted-tube fitted with twisted-tapes are higher than those of the straight-tube and twisted-tube alone, and evidently, both the parameters increase with the decrease in the twist ratio. Further, the twisted-tube yields higher Nusselt number and friction factor than the straight-tube up to around 58% and 33%, respectively, while the Nusselt number and friction factor of the twisted-tube fitted with the twisted-tapes are, respectively, 33–168% and 46–82% higher than those of the straight-tube. Over the range studied, the maximum performance index of 2.28 is recorded with the use of the twisted-tape with lower twist ratio in the twisted-tube for the minimum Reynolds number where the Nusselt number and friction factor increase up to 168% and 61% of those in the straight-tube. [ABSTRACT FROM AUTHOR]

A passive compressive device (PCD), which works at millimeter waves, is proposed in this paper. In a passive manner, the device allows to compress the signals from multiple separate channels into a single or a reduced number of channels. This permits a simplification of the transmitter or receiver chains for radar imaging applications. The PCD is a 3-D cavity that ensures each channel to be decorrelated with each other. If the transfer functions are known, the compressed signals are decompressed in postprocessing. This paper proposes a suitable method to estimate simultaneously the transfer functions of the PCD. This is validated by measurements in a multiple-input-multiple-output (MIMO) configuration to produce a complex synthetic aperture radar image. Measurements revealed that the point spread function generated by the MIMO configuration with the use of the PCD leads to almost similar results, in terms of spatial resolution and sidelobe level ratio, as those of a single-input-multiple-output configuration (uniform amplitude), with a fewer receiving elements. [ABSTRACT FROM AUTHOR]

A $4 \times 1$ passive compressive device (PCD), which works at millimeter wave, is proposed in this study. In a passive manner, the device allows to compress the signals from four separated channels into a single channel. The PCD is a three-dimensional cavity that ensures each channel to be decorrelated with each others. Associated with a Luneburg lens, this allows to generate four distinct beams that are focused in different sectors. This is a multibeam real aperture radar configuration that allows to detect targets in real time. The configuration is validated by measurements. [ABSTRACT FROM AUTHOR]

This study experimentally examines the hydrothermal performance of horizontal Double Pipe Heat Exchangers (DPHEs) with and without continuous Helical Tape Insert (HTI) conducted on the outer surface of the internal pipe. Ten DPHEs of counter-flow configurations were constructed; nine of them were with HTI fabricated with different ratios of HTI height to the clearance between the two pipes ( δ ), and different ratios of HTI pitch to HTI diameter ( λ ). The experiments were performed with pure water in both sides with 2050 ≤ R e a n ≤ 15925 , and R e t ≈ 26700 . Compared with plain annulus-case, the results showed that using the HTI increases both annulus average Nusselt number ( N u ¯ a n ) and Fanning friction factor ( f a n ), with average increases of 69.4–164.4% and 48.6–113.1%, respectively, when δ increases from 0.275 to 1, and with average increases of 78.1–183.2% and 67.6–99.2%, respectively, when λ decreases from 1 to 0.333. The hydrothermal performance index ( HTPI ) was determined to compare the performance of DPHEs with HTI to that of plain annulus case. The results demonstrated that HTI of δ = 0.667 provides the highest HTPI , while HTPI increases with decreasing λ. Finally, correlations for N u ¯ a n , f a n , and HTPI for DPHEs with HTI in the annulus as a function of the investigated parameters were proposed. [ABSTRACT FROM AUTHOR]

This paper theoretically analyses the thermal performance of extended surface of absorber tubing in a flat plate solar collector by using a passive technique to reduce the thermal barrier in a conventional flat plate solar collector. This technique changes the geometry of the flow path of the fluid. The objective is to increase the convective heat transfer coefficient with minimum pressure drop while enhancing the effective heat transfer area between the absorber fluid and the surface it is in contact with. The two types of velocity enhancers used and compared in the work are rod and tube. The velocity enhancers are kept frictionally engaged within the inner side of the absorber tube wall, with the tubes and rod being parallel to fluid flow path. It was found that, while increasing pumping power minimally, the rod velocity enhancer provides greater heat transfer rate than the tube velocity enhancer configuration. Compared to the plain tube, the increase in efficiency of the rod and tube velocity enhancers are 15% and 10%, respectively. [ABSTRACT FROM AUTHOR]

This work experimentally investigates the characteristics of convective heat transfer and pressure drop of water flow in the annulus-side of horizontal double pipe heat exchangers. Twelve heat exchangers of counter-flow configurations are constructed with/without Single Segmental Perforated Baffles (SSPBs), which are fabricated with different holes spacing, void, cut, pitch ratios and inclination angle. The experiments are performed for annulus-side Reynolds number from 1380 to 5700, and for Prandtl number from 5.82 to 7.86. The results revealed that increasing SSPBs holes spacing and void ratios and inclination angle and decreasing SSPBs cut and pitch ratios increase the annulus average Nusselt number ( N u ¯ a n ) as well as friction factor ( f a n ). The thermal performance index ( TPI ) is calculated to compare the thermal performance of perforated baffled double pipe heat exchangers with un-baffled one. It is observed that increasing SSPBs holes spacing ratio and inclination angle, and decreasing SSPBs void ratio, cut ratio and pitch ratio enhances the thermal performance index. Finally, correlations for N u ¯ a n in addition to f a n for concentric tube heat exchangers with SSPBs as a function of the investigated parameters are obtained. [ABSTRACT FROM AUTHOR]

Image forgery and image forgery detection are emerging as well as hot research topics among researchers. In today's digital scenario, images are playing a major role in our day to day life and its manipulation is increasing exponentially. This manipulation is known as Image forging. In this review paper, we will study image forging, its types and detection process. [ABSTRACT FROM AUTHOR]

Nowadays, Dynamic Adaptive Streaming over HTTP (DASH) has become very popular in streaming multimedia contents. In DASH, a client estimates current network bandwidth and then determines an appropriate video quality with bitrate matching the estimated bandwidth. Thus, estimating accurately the available bandwidth is a significant premise in the quality of video streaming, especially when network traffic fluctuates substantially. To cope with this challenge, researchers have presented various filters to estimate network bandwidth adaptively. However, experiment results show that current schemes either adapt slowly to network changes or adapt fast but are very sensitive to delay jitter and produce sharply changed estimation. This paper presents a novel bandwidth estimation scheme based on Moving Average Convergence Divergence (MACD). We applied an MACD indicator and its two thresholds to classifying network states into stable state and agile state, based on the network state different filters are applied to estimate network bandwidth. In the paper, we studied the performance of various MACD indicators and the threshold values on bandwidth estimation. Then we used a DASH proxy-based environment to compare the performance of the presented scheme with current well-known schemes. The simulation results illustrate that the MACD-based bandwidth estimation scheme performs superior to existing schemes both in the speed of adaptively to network changes and in stability in bandwidth estimation. [ABSTRACT FROM AUTHOR]