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The present study details the development of a solar dryer with double pass flat plate solar collector having carbon nanodots (CNDs) coated absorber surface. Among the various concentrations of CNDs (0.1, 0.2, 0.5, 1, and 2%), the 0.5% CNDs coated absorber surface recorded the highest absorptance and lowest reflectance with higher spectral selectivity of 0.933. Hence, the 0.5% coating was selected as the optimum concentration and coated over the absorber surface of flat plate solar air collector. SEM image of black painted surface is clear and smooth and CNDs coated absorber surface is having dispersed particle with rough surface. FTIR absorption peak values revealed that the presence of black paint and CNDs in the 0.5% CNDs coated aluminium sheet. The efficiency of collector coated with 0.5% CNDs was calculated at various air flow rate of 0.008, 0.016, 0.018, and 0.021 kg/s and results revealed that the rise in air flow rate from 0.008 to 0.021 kg/s increased the efficiency from 39.22 to 82.99%. The solar dryer connected with the developed collector was tested for the performance and the drying studies revealed that shrimp and false white sardine required 10 h and 11 h drying time during the experimental studies. [ABSTRACT FROM AUTHOR]

The primary objective of this research work is to analyse the effect of double pass on grain refinement during friction stir processing (FSP). The impact of double pass was also assessed on the microstructure, micro-hardness, and tensile strength of the hybrid reinforced aluminum alloy. Field emission scanning microscopy with energy dispersive spectroscopic analysis was used to analyze the grain size distribution as well as the percentage of elements present across the stir zone (SZ) and mode of fracture during the tensile testing. Results show a notable increase in mechanical properties and a huge reduction in grain size when compared to base material (BM). The grain size of SZ in single pass FSP (FSPed-SP) and double pass FSP (FSPed-DP) was reduced to 76.71% and 91.8% in comparison to the BM because repetitive stirring action causes huge dynamic recrystallization. However, peak micro-hardness in FSPed-DP and FSPed-SP was achieved as 30.58% and 22.79% of the BM due to the hall–petch effect. FSPed-DP demonstrated superior ultimate tensile strength and percentage of elongation in contrast to FSPed-SP, which exhibited values of 29.03% and 25% respectively. [ABSTRACT FROM AUTHOR]

This research provides an in-depth analysis of solar radiation's impact on the thermal efficiency of a solar air collector. Using advanced Computational Fluid Dynamics (CFD) simulations in ANSYS Fluent, the study examines temperature distribution and airflow dynamics within the collector across varying levels of solar radiation. The simulations were carefully configured to replicate real-world solar radiation conditions, ranging from 680 W/m² to 1220 W/m², enabling a precise evaluation of the collector's performance under different environmental conditions. Results indicate that at the lowest radiation level (680 W/m²), the collector's outlet air temperature reached a peak of 26 °C, increasing progressively to a maximum of 29°C at 1220 W/m². Temperature patterns varied with radiation intensity, especially at the start of the collector's second pass, where temperatures rose from 30°C at the lowest radiation level to 34°C at the highest. Thermal efficiency calculations for each radiation level reveal that efficiency increases with radiation intensity, peaking at 26.25% at 1220 W/m². These findings highlight the effectiveness of the collector's design in heat absorption and retention, particularly in the second pass, indicating potential opportunities for enhancing solar air collector designs in the future. [ABSTRACT FROM AUTHOR]

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The low performance of solar air heaters (SAHs) has been considered a drawback in commercializing solar thermal systems. The SAH performance is influenced directly by changing the level of the influential parameters. This work experimentally determines the optimum parameters for enhancing a perforated double-pass SAH performance. The interaction of factors related to the performance of circular staggered perforated double pass SAH was discussed based on the design of experiments (DOE) approach. Reynolds number values from 10000 to 30000 and perforation ratios from 3 to 7 were considered model design parameters, while temperature difference, useful heat gain, and thermal efficiency were adopted as responses for the correlating model. Three correlations corresponding to each response with two forms each (actual and coded) were obtained from the DOE analysis. The results revealed that the interaction percentage was 193% for efficiency and 148% for useful heat gain; however, it did not exceed 18% for the temperature difference. The optimum parameters obtained were 30000 for the Reynolds number and 3 for the perforation ratio. At high Reynolds numbers, the thermal efficiency enhancement of perforated SAH was 12.36% higher than the unperforated. The Reynolds number impact on thermal efficiency changed significantly as the perforation ratio varied.

This paper presents a method to predict the double-pass flow stress behavior of hot-rolled niobium (Nb) micro-alloyed steel by combining the constitutive model and back-propagation neural network (BPNN) model (the machine learning (ML) model). The constitutive model is used to predict the first-pass flow stress behavior, and the BPNN model is used to predict the second-pass flow stress behavior. The results show that the ML model can accurately predict the double-pass flow stress behavior at different temperatures and holding time. The second-pass flow stress predicted by the BPNN model is compared with those predicted by the mathematical model in the previous literature. The results show that the BPNN model can more accurately predict the second-pass flow stress than the mathematical model in the previous literature. In addition, the static softening fraction during the interval time is calculated by using the predicted double-pass flow stress curve in this paper. The results show that the precision of the static softening fraction calculated in this paper is not only higher than that of the traditional Avrami kinetic model but also higher than that of the traditional model which couples recovery, precipitation and recrystallization. Therefore, the ML model for predicting the double-pass flow stress behavior has high accuracy and provides a theoretical basis for predicting the double-pass flow stress behavior of other alloys. [ABSTRACT FROM AUTHOR]

In this research study, the development of a theoretical model to estimate the efficiency of a double pass solar air heater (DPSAH) was the main objective. The mathematical model was compared to experimental results and found to be in agreement, both qualitatively and quantitatively. The model used energy balance equations to determine the outlet temperature and could solve the temperature equations of each component of the heater simultaneously. A matrix inversion method was used for this purpose. The study found that increasing the Nusselt number led to an increase in energy efficiency, but also caused a drop in outlet temperature at any solar radiation. The mass flow rate (MFR), with larger flow rates resulting in better efficiencies, had a significant impact on the double pass air heater's efficiency. Thus, increasing of DPSAH’s length increases its thermal performances and reach its maximum values for L=9m. These findings could be beneficial in selecting the most efficient design parameters for DPSAH.

This experimental study explains the phenomena of secondary flow development due to change in rib perforation and the effect on improvement in THPP values due to variation in β and W/w values of a perforated multi-V rib roughness applied in double-pass parallel flow solar air heater (DPPFSAH). The fixed parameters are e/D = 0.043, p/e = 10, α = 60° and W/H = 12, and the range of variable parameters includes β = 0.0–0.31, W/w = 2–10 and Re = 2000–18,000. The optimum values of Nu/Nus, f/fs, THPP and TEIF are observed as 9.66, 12.31, 3.96 and 1.33, respectively, at β = 0.27 and W/w = 6. The maximum improvement in THPP values was 3.96 times and 1.90 times in DPPFSAH with perforation and continuous rib with a smooth plate, respectively. Double-pass SAH outperforms the single-pass SAH. Correlations for Nu and f are also developed for DPPFSAH with ± 14% and ± 7% accuracy. [ABSTRACT FROM AUTHOR]

In this investigation, the effect of replacing the conventional solar absorber with a new solar absorber on the thermal performance of a double-pass solar air heater has been studied experimentally and numerically. Three configurations have been introduced, the first configuration is a double pass solar air heater with a flat plate solar absorber (DPSAHWFP) for the aim of comparison, and the second configuration is a double pass solar air heater with a tubular absorber that includes a set of tubes which are fitted perpendicularly to the direction of airflow (DPSAHWT-1), and the third configuration is double-pass solar air heater with a tubular absorber that involves set of tubes which are fitted in parallel to the direction of airflow (DPSAHWT-2). The experiments have been carried out under indoor conditions at a constant heat flux equal to 1000 W/m2 and different air mass flow rates (0.01– 0.03 kg/s). The results revealed that the air mass flow rate has a substantial impact compared to the rise in air temperature, hence, the thermal performance of solar air heater is directly proportional to increase air mass flow rate. In addition, the experimental and numerical outcomes indicated that for all air flow rates. The (DPSAHWT-2) offers higher thermal performance as compared to other models, where the maximum effective efficiency has been obtained at 0.03 kg/s equal to 80.9 %. Moreover, (DPSAHWT-2) is more efficient than DPSAHWFP and DPSAHWT-1 by 4.2 % and 9.8 % respectively.

With the elimination of solidification defects, friction stir welding becomes the most effective process for joining flat and curved surfaces. Tool geometry (tool pin profile, shoulder diameter) and tool rotation speed mainly contribute to the overall weld quality. The study evaluates the simultaneous effect of tool geometry, rotational speed, base offset and double pass Friction Stir Welding (DP-FSW) on the defect formation and the mechanical properties. Micro-structure and macro-structure have been analysed for weld strength and hardness characterisation, and found, at high tool rotation speed maximum hardness is achieved in the Stir Zone (SZ). A small tunnel present near the middle proved to be more detrimental than the large one at the bottom. Grain refinement in the SZ was 87.2% while augmentation in hardness was 21.3 HV. Maximum tensile strength of approximately 103% with decent bead profile is obtained, using taper cylindrical tool at 710 rpm with 14 mm shoulder diameter. Fractography of the fractured surface revealed a pure ductile failure. It has been discovered that with base offset the strength of the weld is increased. However, reduction of 4.8% was obtained with DP-FSW. Better weld profile gives better strength. With DP-FSW, a significant improvement in bead surface is obtained. [ABSTRACT FROM AUTHOR]

The present work deals with the development of a semi-transparent photovoltaic thermal (PV-T) solar collector (STPVT) through computational fluid dynamics (CFD) modelling using COMSOL Multiphysics. The study was carried out in three stages; firstly, the CFD model was developed for STPVT and validated with experimental data. Secondly, three different configurations of semi-transparent PV-T collector were investigated, i.e., single pass with PV module on top (SPC), double pass with PV module on top followed by glass cover and absorber plate (DPT), and double pass with PV module in between the glass cover and absorber plate (DPS). The absorber plate was incorporated with cross-flow baffles for improved thermal performance due to increased surface area and turbulence. The study found a thermal efficiency of 76.94 % for DPS configuration and a total heat utilisation of 289.63 W at 50 % transparency level, i.e., 2–4 times higher than other configurations. Furthermore, the DPS model was investigated for thermal and electrical performance with different PV module transparency levels (52,42,27,13 %). The DPS with 18 solar cells having 13 % transparency exhibited peak power density (8 %) at 717 W/m2 and 101.89 °C panel temperature, achieving superior thermal efficiency (84 %) and total heat utilisation (315.09 W), surpassing configurations with higher transparency. [Display omitted] • FE model was developed to predict thermal and electrical performance of hybrid solar collector. • Thermal efficiency of DPS was 48.05–75.32 % higher than STPVT, SPC, DPT. • The thermal and electrical efficiency of DPS-18 was found to be 84 % and 8.31 %. • Power density per unit area from DPS-18 was 15.44–43.19 % higher than DPS-10, DPS-12, DPS-15. [ABSTRACT FROM AUTHOR]

In this investigation, the effect of replacing the conventional solar absorber with a new solar absorber on the thermal performance of a double-pass solar air heater has been studied experimentally and numerically. Three configurations have been introduced, the first configuration is a double pass solar air heater with a flat plate solar absorber (DPSAHWFP) for the aim of comparison, and the second configuration is a double pass solar air heater with a tubular absorber that includes a set of tubes which are fitted perpendicularly to the direction of airflow (DPSAHWT-1), and the third configuration is double-pass solar air heater with a tubular absorber that involves set of tubes which are fitted in parallel to the direction of airflow (DPSAHWT-2). The experiments have been carried out under indoor conditions at a constant heat flux equal to 1000 W/m2 and different air mass flow rates (0.01– 0.03 kg/s). The results revealed that the air mass flow rate has a substantial impact compared to the rise in air temperature, hence, the thermal performance of solar air heater is directly proportional to increase air mass flow rate. In addition, the experimental and numerical outcomes indicated that for all air flow rates. The (DPSAHWT-2) offers higher thermal performance as compared to other models, where the maximum effective efficiency has been obtained at 0.03 kg/s equal to 80.9 %. Moreover, (DPSAHWT-2) is more efficient than DPSAHWFP and DPSAHWT-1 by 4.2 % and 9.8 % respectively. [ABSTRACT FROM AUTHOR]

After analyzing the effect of perforation in a single pass solar air heater in part A, an experimental comparative study was performed on a Double Pass Parallel Flow Solar Air Heater (DPPFSAH) roughened with continuous and perforated multi-V rib roughness. In DPPFSAH, for perforated rib roughness, the gain in Nu/Nus, f/fs, and Thermo-hydraulic performance parameter (THPP) for W/w = 6 are 8.33, 9.09, and 2.97, respectively. While for continuous rib for W/w = 6 the values of Nu/Nus, f/fs, and THPP are 5.93, 10.83, and 1.82, respectively, as compared to the smooth plate. The results strongly support the application of perforation in artificial roughness. [ABSTRACT FROM AUTHOR]

Thermo-hydraulic performance of a Double Pass Parallel Flow Solar Air Heater (DPPFSAH) roughened with perforated multi-V ribs has been studied experimentally in a prior study and the effect of variation in open area ratio and change in relative roughness width has been analysed and reported. The current work builds upon the aforementioned earlier study by discussing in detail the methodology and various steps involved in the development of a correlation for variable parameters with Nusselt number and friction factor for DPPFSAH. The outcomes show that perforations in the multi-V ribs lead to a considerable rise in the Nusselt number, a 9.66 times increase in the thermo-hydraulic performance parameter and nearly a four times increase in friction factor compared to multi-V ribs with smoothed walls. Empirical correlations for the Nusselt number and friction factor were obtained for the double pass parallel flow solar air heater with perforated multi-V ribs established with ±14% and ±7%.

The effect of single-pass (SP) and double-pass (DP) friction stir welding (FSW) on metallographic and mechanical properties of joints was investigated in this study. Uniform temperature distribution across the weld cross-section was obtained during double-pass FSW (DP-FSW). SEM and EDS analyses showed an increase in the fraction of second phase particles (SPPs) and the formation of new SPPs by DP-FSW. An increase in hardness values by 13.3% and a severe decrease in joint efficiency by 46.7% were observed by DP-FSW. Fractography examination of fractured surfaces of welded specimens showed a quasi-cleavage and ductile mode of failure in SP and DP joints, respectively. The potentiodynamic polarisation test of base metal and welded specimens indicated the high corrosion resistance of welded specimens. [ABSTRACT FROM AUTHOR]

To investigate the influencing range and optimize values of different operational and system parameters on the double-pass parallel flow solar air heater's (DPPFSAH) thermal, effective, and exergetic efficiencies, an iterative method was used to analyze the governing energy equations using a theoretical model written in MATLAB based on the Nusselt number (Nu) and friction factor (f) correlations developed in the work performed earlier. A comparison between double-pass and single-pass SAHs for mathematical and experimental outcomes was conducted, and the results were found to be fairly consistent. According to the thermo-hydraulic performance indicators, similar to single-pass SAHs, perforated multi-V rib-roughened DPPFSAHs achieve optimum thermal performance for lower Reynolds numbers, which does not change much as the Reynolds number increases above 18,000. This finding can be taken into account when designing any DPPFSAH. [ABSTRACT FROM AUTHOR]

This study focuses on the investigation of enhancing convective heat transfer between the absorber and the air inside a channel. The investigation approaches modeling different absorber through CFD simulation and validating the result with experimental data. Supplying air to both sides of the top and the bottom surfaces of the absorber increase the air mass flow rate and therefore increases the thermal efficiency of the dryer. The studies in a V-grooved absorber attain high hot air velocity; high thermal efficiency resulted from high turbulence created in the duct. For the sample taken with a flow range, 0.01kg/s to 0.06 kg/s, the high output temperature was observed in a lower temperature range and increases as the flow rate increases. At a flow rate 0.01 kg/s, the velocity of hot air passing over the V-grooved absorber attain 0.28 m/s and increased to 1.4 m/s as the mass flow rate increased to 0.06 kg/s. For the rectangular absorber, the velocity of hot air attains 0.15 m/s at a flow rate of 0.01 kg/s and increased to 1.46 m/s as the mass flow rate increases to 0.06 kg/s. The double-sided V-grooved absorber contributes 8 – 12.40% value more efficiency compared to the rectangular plate with the same flow orientation. Further investigation is recommended taking the quantitative analysis obtained in this study and generating qualitative data.

Solar air heater or solar heating system is a very useful solar thermal product used for multiple purposes such as drying, space heating, desalination, and various industrial applications for low temperature. In this communication, a comprehensive study on the energy-exergy analysis of sensible heat storage based on double pass solar air heater with and without the reflector. System is manufactured with locally available materials. Heat storage material (Metco material and aluminium scrap mixture) was used under the bottom layer. Three cases of experiments were planned, namely natural mode (case 1), double pass solar heater (case 2) and double pass solar air heater with reflector (case 3). Case 3 shows the superior thermal performance as compared to case 1 and 2. The outlet temperature varies from 36 to 60oC; 35 to 58.20oC and 38.5o to 73.2oC in Cases 1, 2 and 3, respectively. This was mainly due to the application of the reflector. It provided additional input energy to the solar air heater. [ABSTRACT FROM AUTHOR]

The simplicity of solar flat plate air collector and free availability of solar energy sources attract attention to the optimization of the collector. This study aims to assess the effect of double pass air flow on the performance of flat plate air collectors. The analysis of the performance characteristics of the indirect solar dryer was carried out by CFD simulation with three different smooth, rough and V-grooved surfaces, keeping the lower and lateral collector well insulated and the drying chamber acting as a vertical chimney. The average thermal efficiency of the V-grooved surface, smooth surface, and rough surface is 90%, 78%, and 62% respectively. The total area of the collector is 1.20 × 2.0 = 2.40 m2 with the dimension of drying cabinet width, depth, and height 1200 × 650 × 1000 mm respectively. The pressure drop observed at the entrance to the drying chamber is high in the case of a smooth surface, medium in a rough surface and low in a V-grooved plate which will allow sufficient gas pressure to pass through completely.The air mass flow rate is the most important and effective factor during drying. The humidity of the air, as well as air velocity, is also an important factor in improving the drying rate.

The effect of geometrical parameters of jet impingement on indented protrusion absorber in double-pass solar heat collector (DPSHC) was investigated. For fixed optimum values of protrusion parameters namely arc angle (α p), relative height ratio (e p /D h), and relative pitch ratio (p/D h), four different jet height ratios (H ji /D h) ranging from 0.11 to 0.44 have been used with varying streamwise pitch (X ji /D h) and spanwise pitch ratio (Y ji /D h). At a constant jet diameter ratio (D ji /D h), the Reynolds number (Re) of the airflow fluctuated between 2500 and 22500. It has been found that the H ji /D h plays an important role in the performance of DPSHC and that the maximum value of the Nusselt number (Nu dp) = 544 with friction factor (ff dp) = 0.206 was obtained at X ji /D h =1.32, H ji /D h =0.22, and Y ji /D h =1.32. The investigation reveals that the thermohydraulic performance (η dp) of the DPSHC increases as the Re increases from 2500 to 15000 and after that from 15000 to 22500 it starts to decline. The optimum value of η dp = 3.86 has been found corresponding to Re = 15000, H ji /D h =0.22, X ji /D h =1.32 , and Y ji /D h =1.32. Nu dp and ff dp correlations were developed in terms of jet impingement parameters and the selected range of Re which can be useful for estimating the performance of a DPSHC with the combined technique. The optimum deviation in the Nu dp and ff dp values was ±10%, which correlated well with the experimental results. • Thermal and hydraulic characteristics of DPSHC with jet impingement on protruded plate is presented. • The effect of jet height (Hji) on Nudp was more prominent compared to streamwise pitch (Xji) and spanwise pitch (Yji). • The optimum value of ηdp = 3.87 was obtained at Hji/Dh = 0.22, Xji/Dh = 1.32, and Yji/Dh = 1.32. • Augmentation in Nudp is 4.34 times compared to smooth double pass. • Correlations developed for Nudp and ffdp with a deviation of ±10% for both parameters. [ABSTRACT FROM AUTHOR]

• Energy and exergy analysis of double pass solar air collector with fins and PCM. • A steady state mathematical model is derived to predict collector performance. • A peak efficiency of 73% is observed at conditions of 1000 W/m2 and 0.15 kg/sec. • The solar collector's improvement potential is approximately 980–2209 W. Advanced solar air collectors are widely implemented in research for drying purposes. This research study presents a new steady state energy balance and exergy equations for a novel double pass solar air collector with fins and phase change material (PCM) according to first and second law of thermodynamics. The mathematical equations of energy balance were solved using the matrix inversion method. The predictions were observed at mass flow rates ranging from 0.01 kg/sec to 0.15 kg/sec, and solar radiation ranging between 425 W/m2 and 1000 W/m2. The impacts of solar radiation levels and mass air rates on energy efficiency, exergy efficiency and the improvement potential have been estimated and evaluated. The optimum energy efficiency of proposed collector is 73% at mass air rate of 0.15 kg/sec. The exergy efficiency is nearly 2.5–4.2% at maximum solar radiation level of 1000 W/m2 as well as the lowest and highest improvement potential are 980–2287 W for a solar radiation of 425–1000 W/m2. [ABSTRACT FROM AUTHOR]

An experimental investigation on thermal performance of a solar air heater with and without the usage of spherically encapsulated phase change medium (PCM) is presented in this paper. The PCM, paraffin wax, is filled in spherical balls mounted on the holes of the absorber plate so that heat transfer area is slightly extended. A comparative study of three different configurations of the absorber plate is made. Parameters that influence the collector efficiency are recorded and discussed. The results obtained are compared with a conventional absorber plate without PCM for similar conditions. The mean efficiency obtained for conventional absorber plate without PCM is 31%, for flat absorber plate with PCM is 39%, and for inclined absorber plate with PCM is 43%. The encapsulation efficiency is 40% for flat plate absorber with PCM and 42.2% for inclined plate absorber with PCM and the approximate cost of heating 1 kg of air is INR 0.95/$0.014. [ABSTRACT FROM AUTHOR]

In this study, an assessment based on energy, exergy, economic, and environmental approaches on a double-pass (DP) solar air heater (SAH) having pin finned absorber at different air mass ratios up and down the absorber is investigated experimentally. Four air mass ratios are considered: (i) all the air mass flow passes up the absorber and returns to pass down the absorber (DP), (ii) 2/3 of the airflow passes up the absorber and returns to mix with the remainder of air to pass down the absorber (2/3 DP), (iii) the same as (ii) but 1/3 of the air passes up the absorber (1/3 DP), and (iv) all the air mass passes only down the absorber (single pass, SP). For all mass ratios, the performance of pin finned SAH (P_SAH) is compared with that of flat SAH (F_SAH). The results indicated that the air temperature rise and energy and exergy efficiencies of P_SAH are highly greater than those of F_SAH. The highest average thermal efficiency of F_SAH is 56.7% obtained at DP flow condition, whereas the highest value of P_SAH is 65.21% obtained at 2/3 DP with an increase of 17.6% compared with F_SAH. Also, P_SAH has higher average exergy efficiency of about 34.7% compared to F_SAH. Furthermore, P_SAH achieves energy payback time (EPBT) lower than that of F_SAH, while P_SAH has higher embodied energy. The findings indicated that F_SAH at SP airflow pattern has the maximum energy cost (0.0427 $/kWh), whereas P_SAH at 2/3 DP airflow pattern achieves the minimum energy cost (0.037 $/kWh). Finally, the proposed P_SAH system appears to be more viable from exergoeconomic and enviroeconomic approaches compared to F_SAH. [ABSTRACT FROM AUTHOR]

We described the characterization of an acousto-optic modulation system and the optimization of the set up to improve the efficiency of diffraction in single and double-pass configurations. In the single-pass configuration, the system consists of an acousto-optic modulator, a voltage-controlled oscillator (VCO) and a radio frequency amplifier, in which the diffraction efficiency and the optical power of the diffracted beam were characterized in the function of the applied radiofrequency. Additionally, taking as a reference the need to correct the variation of the diffraction angle that may occur when the system is modulated in frequency in a simple step, its correction is presented by means of the implementation of the configuration in double step. The double-pass configuration consists of a VCO that controls the incoming acoustic signal to the modulator, a modulator which diffracts the incident light and this passes through a retarder sheet to avoid the retroreflection of the beam; Then, using an iris, only order 1 of diffraction of the beam was allowed to pass and a plane mirror was used for working in the infrared which directs the laser in the second pass of it in the modulator. Once the double-pass system had been optimized, the diffraction efficiency curve was obtained. This work is presented as an updated guide for the implementation of an acousto-optic modulation system in a double-pass configuration. [ABSTRACT FROM AUTHOR]

The simplicity of solar flat plate air collector and free availability of solar energy sources attract attention to the optimization of the collector. This study aims to assess the effect of double pass air flow on the performance of flat plate air collectors. The analysis of the performance characteristics of the indirect solar dryer was carried out by CFD simulation with three different smooth, rough and V-grooved surfaces, keeping the lower and lateral collector well insulated and the drying chamber acting as a vertical chimney. The average thermal efficiency of the V-grooved surface, smooth surface, and rough surface is 90%, 78%, and 62% respectively. The total area of the collector is 1.20 x 2.0 = 2.40 m² with the dimension of drying cabinet width, depth, and height 1200 x 650 x 1000 mm respectively. The pressure drop observed at the entrance to the drying chamber is high in the case of a smooth surface, medium in a rough surface and low in a V-grooved plate which will allow sufficient gas pressure to pass through completely. The air mass flow rate is the most important and effective factor during drying. The humidity of the air, as well as air velocity, is also an important factor in improving the drying rate. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) is a method used to obtain nano-structured and ultra-fine-grained materials. There are many methods used for severe plastic deformation of tubular materials. One of these methods is parallel tubular channel angular pressing (PTCAP). In this study, deformation of tubular parts was investigated by using double pass parallel tubular channel angular pressing (DP-PTCAP) method. In the analysis, 5 different channel angles, 4 different cross section expansion rates and 4 different dimensionless lengths were used. The effects of these parameters on the stress, plastic strain and forming force of the tubular parts obtained were analyzed by finite element method. AA6061 material was used in the study. As a result of the analysis, effective strain, forming force and stress in material were decreased with increasing channel angle. It was determined that the plastic strain of the materials obtained with double pass dies was higher than single pass dies. As a result, it can be said that the grain structure of the materials obtained with double pass dies is finer grained than single pass dies. [ABSTRACT FROM AUTHOR]

• New design of the solar air heater (tubular SAH) is experimentally presented. • TSAH achieves maximum air temperature rise of 6.25 °C compared to FSAH at 0.025 kg/s. • Average daily efficiency of TSAH increases by 40.3% compared to the FSAH at 0.025 kg/s. • Efficiency of present TSAH is greater than efficiency of the previous presented SAHs designs. • Pressure drop of the TSAH is greater than FSAH but hasn't an effect on the net results. An experimental study on the performance of double pass Solar Air Heater (SAH) having a new designed absorber is performed. The new SAH absorber is constructed from conductive aluminum tubes adjacent to each other and installed in the same direction of the air flowing inside the SAH. The new SAH performance (called Tubular Solar Air Heater (TSAH)) is studied at various mass flow rates of air inside the SAH. Moreover, it is compared with the performance of Flat plate Solar Air Heater (FSAH) having the same dimensions and materials of the TSAH except the absorber design. Findings indicate that the TSAH has higher outlet air temperature, efficiency and net energy gain and lower top heat loss compared to FSAH. TSAH achieves maximum air temperature rise more than 6 °C compared to FSAH at 0.025 kg/s. TSAH efficiency is greater than FSAH efficiency by about 19.4%, 21%, and 40.3%, at inlet air flow rate of 0.075 kg/s, 0.05 kg/s and 0.025 kg/s, respectively. The outlet air temperature and top thermal energy loss of the TSAH decrease with increasing the air mass flow rate, while its efficiency, energy output, and pressure drop increase. Moreover, TSAH efficiency in case of double air pass is greater than single air pass. Despite the TSAH pressure drop is greater than FSAH pressure drop, but its value is very small to impact the TSAH net thermal energy gain. The designed TSAH performance is found greater than the performance of FSAH and previous designs of published SAHs. [ABSTRACT FROM AUTHOR]

Background: Port wine stain (PWS) is a low flow vascular malformation. The gold standard treatment for PWS in childhood is pulsed dye laser (PDL).There is very little evidence in literature regarding comparison of single pass versus double pass pulsed dye laser in achieving clearance of these capillary malformations. We did a randomized controlled trial to compare outcome of single-pass versus double-pass pulsed dye laser for management of PWS. Methodology: This randomized study trial was performed at Jinnah Burn and Reconstructive Surgery Center/AIMC Lahore, from Jan 2019 to Dec 2019. Sample size of 30 patients was divided into 2 groups (15 patients in each group). Group A was given single pass of pulsed dye laser and patients in group B were subjected to double pass of pulsed dye laser (595nm wavelength, 7mm spot size, pulse width from 2-6ms and radiant exposure of 4-12 J/cm2). Total no of 4 sessions were done with period of 3 weeks between each session and the results were analyzed after 3 months of the last session. Results: The mean of the patient's age was 17±8 years and the mean of time since lesion appeared was 16±8 years. Nineteen participants (63%) were females. Most of the patients (83%) had PWS on face and neck. Double pass PDL was effective in 40% of patients and single pass PDL in 20% (p value <0.05). Conclusion: Double pass is more effective in treating port wine stain as compared to single pass pulsed dye laser. [ABSTRACT FROM AUTHOR]

Double-pass solar air heaters occupy an important place among solar air heating systems, because of minimal heat loss and maximum thermal efficiency with marginal heater size and cost. In the present work, investigations related to the thermal performance predictions have been carried out for double-pass flat and V-corrugated absorber plate solar air heaters under recycle operation. The mathematical models proposed herein are solved using an analytical approach that uses an iterative solution procedure. Furthermore, based on simulation results obtained from the analytical study, the optimum value of the recycle ratio, the mass flow rate, the absorptivity and the emissivity at which the heaters yield the maximum value of the thermal efficiency have been identified and presented using response surface methodology (RSM). The results of RSM revealed that the mathematical models are significant. In addition, results of the present study are validated and compared with previous studies. A reasonable agreement and significant improvement have been achieved.

6061-T6 Aluminum Alloy plates were welded by using Friction Stir Welding (FSW) at different rotation and welding speeds. The effects of two factors on Ultimate Tensile Strength (UTS), which include rotation and welding speed at 2o tool tilt angle, were investigated. Ultimate Tensile strength increases with decrease the welding speeds and increases the rotational speeds. The rotation speeds have a higher effect on ultimate tensile strength when compared with the welding speeds. Friction Stir Processing (FSP, Double pass) led to increasing the ultimate tensile strength and elongation at same welding and rotation speeds. FSP lead to improve fatigue life and reduce residual stress. [ABSTRACT FROM AUTHOR]

The effect of using different absorber plate configurations on the performance of double pass SAH with two inlet ports is presented. Moreover, the effect of using different air flow percentages through the inlet ports is studied for each studied configuration. Four absorber plate configurations are considered; (i) flat plate (ii) pin finned, (iii) corrugated finned, and (iv) corrugated-perforated finned. Moreover, four percentages of the inlet air are considered: (i) 0% of the air flows through the upper inlet port and 100% through the lower inlet port (0%Up), (ii) 33.3% of the air flows through the upper inlet port and the remainder through the lower inlet port (33.3%Up), (iii) 66.7% of the air flows through the upper inlet port and the remainder through the lower inlet port (66.7 Up), and (iv) 100% of air flows through the upper inlet port (100% Up). These percentages are studied at all absorber plate configurations and for the same total inlet mass flow rate of the air. The measurements are carried out during the day using the solar flux and at night using a solar simulator. The results indicate that increasing the upper air percentage decreases the absorber plate temperature and increases the SAH efficiency for all studied configurations. The efficiency of corrugated-perforated pin fin is the greatest and the flat plate absorber plate is the smallest. The maximum efficiency of the SAH is about 70% for flat plate configuration at (100% Up) and about 79% for the pin finned absorber plate at (100% Up). It is about 82% for the corrugated finned configuration at (100% Up) and about 83% for the corrugated-perforated finned absorber plate at (66.7% Up). The solar simulator analysis provides very near values of the efficiencies which assures the results. The cost analysis indicates that the cost of energy gained by the SAH for the flat plate configuration for 0% UP flow has the maximum cost (0.025 $/kW.h) and the corrugated perforated finned absorber plate of 66.7% has the minimum cost (0.021 $/kW.h). [ABSTRACT FROM AUTHOR]

Solar thermal collectors for buildings use a heat transfer fluid passing through heat exchange channels in the absorber. Flat plate absorbers may pass the fluid through a tube bonded to a thermally conducting plate or achieve lower thermal resistance and pressure drop by using a flooded panel or microchannel design. The pressure drop should be low to minimise power input to the circulating pump. A method is presented for choosing the optimum channel hydraulic diameter subject to geometric similarity and pumping power constraints; this is an important preliminary design choice for any solar collector designer. The choice of pumping power is also illustrated in terms of relative energy source costs. Both microchannel and serpentine tube systems have an optimum passage diameter, albeit for different reasons. Double-pass and flooded panel designs are considered as special microchannel cases. To maintain efficiency, the pumping power per unit area must rise as the passage length increases. Beyond the optimum pumping power the rise in operating cost outweighs the increase in collector efficiency. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate mesopic visual acuity and visual quality as measured by objective scatter index (OSI) in pseudophakic eyes with long-term follow-up after implantation of hydrophobic acrylic lenses made from two different lens materials. Setting: This study was carried out in a private clinic. Design: This study was an observational cohort study. Methods: This pilot study included 181 eyes of 136 patients who had undergone cataract surgery with implantation of monofocal hydrophobic acrylic intraocular lenses (IOLs), either Alcon AcrySof (82 eyes) or Abbott Medical Optics' Tecnis (99 eyes). The monocular corrected distance visual acuity (CDVA) of the subjects was recorded under mesopic room illumination and OSI was measured by an optical quality analysis system using double-pass wavefront method. Results: Mean follow-up duration was 60.07±18.82 months. Eyes implanted with Tecnis IOLs had statistically significantly better mesopic CDVA (0.08±0.08) compared to those implanted with AcrySof IOLs (0.11±0.07) (P=0.020). Mesopic CDVA of 20/25 or better was found in 79.8% of eyes in the Tecnis group compared to 62.2% of eyes in AcrySof group. Similarly, OSI was also found to be statistically significantly better for Tecnis IOLs compared to AcrySof IOL group (mean OSI, Tecnis: 1.65±0.92, AcrySof: 2.01±1.36; P=0.033). When glaucomatous eyes were excluded, OSI was still significantly better (P=0.028) in the Tecnis IOL group. Conclusion: The eyes implanted with Tecnis IOLs showed better long-term optical performance in terms of both OSI and mesopic visual acuity in comparison to those with AcrySof IOLs. [ABSTRACT FROM AUTHOR]