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Early in history, societies utilize renewable energy sources in response to technical developments and external factors, which resulted in the development of hydropower, wind turbines, and solar PV, as well as their support through policies and agreements. The double ring covered disk resonator solar absorber (DRCDRSA) structures are examined over the spectral range of wavelength 0.2 µm to 2.5 µm (UV-FIR) with the help of finite element method (FEM) in this study. This design achieved effective solar absorption, surpassing 99% over the 0.46 µm band, 95% over 2.05 µm wideband, and 90% over the entire observed spectral range, with an overall average absorbance of 96.38%. In addition, the maximum absorbance is 99.9% with three pick values at the wavelengths of 0.34 µm, 1.35 µm, and 1.51 µm. This research includes a parameter optimization as well as the electric field strength and magnetic field intensity distribution over a three-dimensional solar absorber construction. The structure's angle-polarization study shows it is polarization independent, handles diverse angles, and maintains even absorption up to 60° across all wavelengths. This study explores effective solar heaters for air and water systems, offering promising prospects for maximizing solar energy utilization. [ABSTRACT FROM AUTHOR]

There are many applications, such as fruits, paddy rice drying, and so on, where air heaters are comprehensively used. The provision of ribs in solar energy‐based air heaters has been accredited to be a beneficial approach for escalating its thermal performance. This investigation reveals the performance evaluation of a rectangular sectioned solar air heater duct placed with the curved type of ribs organized in noncontinuous and truncation patterns. Influence of variation of pitch ratio (4.0–12.0), block‐age ratio (0.06–0.1), the ratio of rib height to the radius of rib curvature (0.75–1), and the ratio of rib truncation gap to its height (0–0.75) at different values of Reynolds's numbers (Re) in the range 12,000–37,000 on the performance revealing factors explicitly heat transfer augmentation factor, the ratio of friction factor, as well as overall thermal performance enhancement (OTPE) have been discussed. The experimentation was performed on a similar rectangular air heater as that of numerical simulation with the same boundary conditions. It is figured out from numerical simulation that the provision of a central truncation gap in the arrangement of ribs helped in the development of vortices with minimal pressure loss due to friction. The greatest Nusselt number augmentation ratio between ribbed and plain plates that was attained is of the order of 2.01 for a pitch ratio of 9.0, blockage ratio of 0.08, the ratio of rib height to the radius of rib curvature 0.25 at the highest value of Re. The obtained friction factor ratio between the ribbed plate and the plain plate is of the order of 2.34 for p/y = 9.0 at maximum Re. The highest value of overall thermal performance enhancement (OTPE) is attained as 1.52 at the pitch ratio of 9, at the maximum value of Re. The central truncation gap of the rib pattern promoted the creation of vortices with a decreased pressure loss penalty. The uppermost value of the factor presenting overall thermal performance enhancement in this work is far superior to unity. This suggests that adding curved ribs to the air heater's duct is a helpful way to improve its overall performance. Empirical correlations have been established between the Nusselt number and geometrical parameters, likewise the friction factor and geometrical parameters using the regression study. The values of the Nusselt number, and friction factor that come from experimental work and developed empirical correlations fall between the highest deviation limits of ±9% and ±8%, respectively. This work is certainly helpful in the context of solar air heaters used for applications such as drying paddy rice. [ABSTRACT FROM AUTHOR]

In this paper, a novel tubular solar air heater is introduced. In this air heater, the hot boundary layer is drawn into the absorber tube and can provide thermal energy at moderate temperatures. Several different cases were simulated and a correlation was proposed to predict the collector's effectiveness as a function Rayleigh number and Reynolds number. An equation was derived to find the effectiveness of this collector. Finally, a real case was studied with non-uniform solar flux distribution, as well as radiation heat loss. Good agreement was found between the results and those derived by the proposed analytical method. For different suction values, the first-law and the second-law efficiencies were calculated. Based on the exergy analysis, exergy destruction in absorption is the dominant factor that is unavoidable in low-temperature collectors. It was shown that there is an optimum suction value at which the second-law efficiency is maximized. At the optimum point, temperature rise can reach 54 K, which is hardly possible with a flat plate collector. Based on the exergy analysis, the relation between tube wall temperature and air outlet temperature in their dimensionless forms at the optimum working condition was derived, and it was shown that effectiveness at the optimum working condition is around 0.5. This means that the air temperature rise shall be half of the temperature difference between collector wall and the ambient temperatures. A high outlet temperature besides the low cost of construction and maintenance are the main advantages of this air heater. With such a high temperature rise, this type of collector can increase the use of solar energy in domestic applications. [ABSTRACT FROM AUTHOR]

The mid-chord region of turbine blades typically employs internal cooling channels to enhance heat transfer. However, traditional internal cooling channels are mostly designed in the form of straight channels, and studies based on it may not address the needs of variable cross section channels. Therefore, this study investigates the effect of rib configurations in variable cross section channels on channel performance. First, the cross sectional area of the two-passed channels is modified by altering the inclination angle of the dividers (−3°, 0°, and +3°). The flow pattern and heat transfer features within a two-passed channel with variable cross section under four different rib configurations of NP, NN, PN, and PP are investigated using numerical simulation. N denotes the ribs rotated 45° clockwise relative to the flow direction, while P denotes the ribs rotated 45° counterclockwise. Subsequently, the optimal rib configuration within the variable cross sectional two-passed channels is determined for Reynolds numbers ranging from 10 000 to 50 000. Results show that, at +3°, the PP exhibits the maximum decrease of up to 18.2% in transfer performance factor (TPF), while at −3°, the NN shows the maximum decrease of up to 12.7%. It is evident that the optimal rib configuration for two-passed channels under different divider inclinations is not consistent. At +3°, the NP exhibits the best TPF, while at −3°, the PP demonstrates the optimal TPF. This study provides insights into selecting appropriate rib configurations when the cross sectional area of internal channels within turbine blades varies. Compared to the studies that have focused on traditional straight channels, the research provides guidance for the design of ribbed two-passed channels with varied cross section. [ABSTRACT FROM AUTHOR]

The thermal performance of the flat plate solar collector is very low. The most beneficial and worthwhile method for increasing the thermal performance of a solar‐powered air heater (SPAH) is to include a roughness element in the working zone of heat transfer that is located beneath the shear layer of the absorber surface. In this research work, efforts are made to enhance thermal performance and develop thermal correlations for the estimation of the Nusselt number and friction factor of a roughened SPAH. Experiments are performed for various ranges of flow, Reynolds numbers, and roughness parameters. The experimental technique of liquid crystal thermography is utilized to assess the dispersal of Nusselt number over the roughened surface for all roughness parameters. A maximum thermal performance enhancement index of 2.69 is obtained with the optimum value of the roughness parameter at a relative roughness pitch (RRP) of 9, a relative staggering distance (RSD) of 4, and a relative roughness length (RRL) of 6.15. Second, a mathematical correlation is developed using a regression model to estimate the Nusselt number and friction factor in terms of nondimensional roughness and flow parameters operated as RRP, RSD, RRL, and Re. The degree of discrepancy between the established the relationships and the findings from the experiment reveals incredibly satisfying results. Hence employing twisted V‐ribs as an artificial roughness element no doubt increases the Nusselt number, and thermohydraulic performance enhancement index, but it also exerts less frictional power across the SPAH duct. [ABSTRACT FROM AUTHOR]

The thermohydraulic performance (THP) of a solar air heater (SAH) duct with staggered D‐shaped ribs as roughness geometry is examined in this work using three‐dimensional numerical investigation. The investigation is carried out at roughness parameters of radius of rib to transverse pitch (r/Ptv) ratios of 0.1–0.35 and longitudinal pitch to radius of rib (Plg/r) ratios of 4–10 under varied operating circumstances of Reynolds number (Re) from 10,200 to 20,200. The maximum Nusselt number (Nu) is obtained to be 81.3 at Re of 20,200, r/Ptv as 0.1, and Plg/r as 4. In contrast, the maximum friction factor (f) is obtained to be 0.0169 at Re of 10,200, r/Ptv as 0.35, and Plg/r as 4. In the range of parameters examined, the maximum enhancement in Nusselt number (Nu/Nus) is observed to be 1.35 at an optimal parameter of r/Ptv as 0.1, Plg/r as 4, and Re as 10,200. Correspondingly, the enhancement in the friction factor (f/fs) at this optimum parameter is 1.87. The maximum value of the THP parameter is found to be 1.1 at the same optimum range of parameters. In further analysis, correlations were developed for Nusselt number (Nu) and friction factor (f) in terms of r/Ptv, Plg/r, and Re with a deviation of ±2% and ±1.5%, respectively. [ABSTRACT FROM AUTHOR]

The cost of manufacturing and electricity consumption are key considerations in encouraging the adoption of solar air heaters (SAH) in sunny and low‐income areas. These parameters can have a significant impact on promoting the use of these devices. In this study, solar air heating was designed with the objective of achieving the highest possible efficiency/cost ratio. It is a corrugated channel SAH whose structure is equipped with two barriers perforated with a sufficient number of holes for a good airflow distribution. A new model was developed to evaluate the qualitative parameters that describe the thermos‐energetic behavior of a heating system. These parameters were measured using experimental data obtained under real operating conditions. The thermal model assumes a uniform temperature for the glass, absorber, and insulation of the collector, while the temperature of the circulating air is assumed to vary linearly along the collector. To ensure that these assumptions were valid, the collector was cut into a number of 0.1 m sections in the direction of flow. By comparing the numerical results with the experimental data, the model was validated and then used to calculate the temperature profiles of the different elements of the collector, as well as to estimate the impact of certain operational parameters on its thermal performance. Relative percentage error values, between the numerical and the experimental results, of 1.7517%, 1.0750%, 0.8577%, 2.2371%, and 2.3637% for absorber plate temperature, outlet airflow temperature, useful power, thermal, and effective efficiencies, respectively, are recorded. [ABSTRACT FROM AUTHOR]

In the present experimental study, heat transfer enhancement and friction factor penalty of a solar air heater (SAH) with newly designed artificial roughness attached to the lower side of the absorber plate have been investigated. Multiple open trapezoidal ribs artificial roughness has been designed to take the advantages of secondary flows concerning heat transfer enhancement. Multiple open trapezoidal ribs roughness has been designed considering the following parameters: relative limb length (L/w), angle of attack (α), relative rib height (e/Dh), relative width ratio (W/w), and relative roughness pitch (p/e) having their respective ranges of 0.2–1.0, 0.023–0.054, 6–12, 6, and 60°. The other operating parameter encompassed in the study is the flow Reynolds number, which varied from 2000–16000. The results of the experiment shows that highest augmentation in the Nusselt number (Nu) is observed to be 6.05 times higher with respect to the smooth absorber plate at p/e = 10, L/w = 0.8 and e/Dh = 0.043. In addition, thermohydraulic performance has been evaluated, which is found to be in the range of 3.24–3.79. [ABSTRACT FROM AUTHOR]

Solar air heaters represent a pivotal technology for harvesting renewable solar energy across various applications. This study conducts a comprehensive analysis contrasting the thermal efficiencies between traditional flat absorber plates and innovative pin–fin counterparts, augmented with Multi-Walled Carbon Nanotube (MWCNT) coatings of varying diameters (20–40 nm, 40–60 nm, and 60–100 nm). Rigorous experimental tests were undertaken to gauge energy conversion efficiency, heat transfer characteristics, and overall thermal performance under diverse conditions. Parameters, such as solar intensity, ambient temperature, wind velocity, energy and exergy efficiency, and thermo-hydraulic efficiency, were scrutinized. Findings highlighted the advantages of employing pin–fin absorber plates with MWCNT coatings: the augmented surface area of the pin–fin design facilitated superior convective heat transfer, yielding higher thermo-hydraulic efficiency across varied airflow rates. Smaller MWCNT sizes exhibited superior performance, leveraging increased surface area and heightened thermal conductivity. Additionally, the pin–fin design induced turbulence, bolstering convective heat transfer, while smaller MWCNT coatings reduced drag, leading to elevated ambient wind velocities. Combining pin–fin absorber plates and MWCNT coatings is a promising strategy to amplify solar air heaters' thermal efficiency and energy conversion potential. Notable improvements included a 12% thermo-hydraulic efficiency surge with pin–fin absorbers compared to flat plates, a 16% boost in solar intensity absorption with the 20–40 nm MWCNT coating on pins, and a 24% heat transfer enhancement via the pin–fin configuration based on thermal resistance analysis. [ABSTRACT FROM AUTHOR]

This article presents an in-depth analysis of internally finned tube heat exchangers, which are used in a broad variety of condensers and evaporators for air conditioners, as well as radiators for vehicles and solar air heaters, amongst other places. The growing need for cooling systems that are more efficient and heat exchangers that take up less space has inspired many studies in this area of expertise. This research uses both experimental and computational analysis to compare and contrast the efficacy of various heat transfer enhancement processes in internally finned tube heat exchangers concerning the impacts they each have and the operating parameters they each need. This study aims to investigate how altering the fins' design affects heat transfer and pressure drop under varying operational situations. This paper examines the ranges in which these correlations have been verified, as several correlations have been created to assist in estimating heat transfer and pressure drop characteristics on internally finned tube heat exchangers. This study extensively delves into various analytical approaches such as Log Mean Temperature Difference (LMTD), Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and other methodologies specifically tailored to address the unique goals of the particular problem. To derive a conclusion with practical significance, we categorize these relationships into multiple groups and conduct a comparative analysis. [ABSTRACT FROM AUTHOR]

The application of fins as a solar heat absorber on solar still desalination has gained attention to enhance productivity, efficiency and cut heat losses. Considering the effectiveness of fin configuration, it is still the focus of development by many researchers. To determine the optimum height configuration, this study conducted an experimental analysis of hollow circular fin (HCF) height as variation during the day testing under the Kentingan Sebelas Maret University climates. Moreover, the hollow circular fin is constructed utilizing the SS302 material. The variation used is conventional CS4, which incorporates the supplementary heights of 20 mm, 40 mm, and 60 mm for the hollow circular fins. Overall, the study has identified a consistent decrease in efficiency as the HCF increases, with efficiency gains of 40.96%, 35.39%, and 29.16%. However, different circumstances yield favorable outcomes, exhibiting a notable improvement of 10.30% and 5.57% in enhanced efficiency for 20 mm and 40 HCF, respectively, compared to conventional solar stills against the analysis that can evaluate the energy loss through the partition and solar still wall. A correlation analysis was conducted using both experimental productivity data and analysis prediction data to ensure that this experiment analysis yielded excellent results compared to others. [ABSTRACT FROM AUTHOR]

Motivated by the suboptimal performances observed in existing compressed air energy storage (CAES) systems, this work focuses on the efficiency optimization of CAES through thermal energy storage (TES) integration. The research explores the dependence of CAES performance on power plant layout, charging time, discharging time, available power, and cavern volume. Hence, a range of solutions are examined, encompassing both solid and liquid TES options, alongside the potential utilization of external air heaters. Inefficiencies in solid TES due to significant retention of thermal power within the medium after complete discharge are identified and mitigated through optimization strategies. In addition, solutions to prevent ice formation at the low-pressure expander phase are suggested to avoid icing issues in CAES layouts with liquid TES. Through this comprehensive investigation, the study provides valuable insights into enhancing the efficiency and sustainability of CAES systems. By constructing a volume–power–time conversion table, the research contributes to the advancement of CAES technology, facilitating more efficient energy storage and utilization, thereby addressing critical challenges in the field of energy storage. [ABSTRACT FROM AUTHOR]

Supply disruptions, uncertainty, and unprecedented price rises of fossil fuels due to the recent pandemic and war have highlighted the importance of using renewable sources to meet energy demands. Solar air collectors (SACs) are major types of solar energy systems that can be utilized for space and water heating, drying, and thermal energy storage. Although there is sufficient documentation on the thermal analyses of SACs, no comprehensive reviews of the exergetic performance or qualitative insight on heat conversion are available. The primary objective of this article is to provide a comprehensive review on the optimum conditions at which the thermal performance of diverse types of solar air collectors is optimized. The effect of operating parameters such as temperature rise, flow rate, geometric parameters, solar radiation, and the Reynolds number on the thermal performance of SACs in terms of thermal hydraulic performance, energy, and exergy efficiencies has been reviewed adaptively. Beyond the operating parameters, a deep investigation is outlined to monitor fluid dynamics using analytical and computational fluid dynamics (CFDs) methodologies in the technology of SACs. In the third phase, thermodynamic irreversibility due to optical losses, thermal losses between absorber and environment, heat losses due to insulation, edge losses, and entropy generation are reported and discussed, which serve as the fundamental tools for optimization purposes. [ABSTRACT FROM AUTHOR]

This paper introduces an energy conversion inspired vibration control methodology and presents a representative prototype of tunable bi-stable energy converters. This work is concerned on improving energy conversion and absorption performance of tunable bi-stable clustered energy conversion inspired dynamic vibration absorbers (EC-DVAs). The deterministic parametric analysis of the energy transfer performance of clustered EC-DVAs is conducted. The nonlinear energy capture behaviors including transient energy transfer and snap-through motions are studied. It can be uniformly understood that the excellent energy transfer and conversion efficiency can be achieved by modulating the length ratio from 0.6 to 0.8. It is found that clustered EC-DVAs with four uniform cells and constant length ratio σ = 0.8 can obtain significant energy conversion and targeted energy transfer performance without requiring tedious active regulation when the system is subjected to wide-amplitude impulsive scenarios. Therefore, the proposed tunable bi-stable system composed of clustered EC-DVAs with state-of-the-art adaptive control strategies is a potential alternative for energy reuse and vibration suppression of mechanical components exposed to kaleidoscopic impulses. [ABSTRACT FROM AUTHOR]

A numerical investigation for a solar air heater integrated with a multi-section solar distiller has been conducted with a novel design of solar distiller with interior sections. A mathematical description of the solar distiller is made and solved with a MATLAB code. The air flow in the solar air heater, the water height in the solar distiller, and the number of interior sections have all been studied. To validate the numerical system, an experimental system was built. The theoretical model and the experiment performed appear to be in satisfactory correlation. The best working conditions occur when the system is run with a lower air flow rate, a lower saline water height, and a greater number of interior sections with productivity reaching 1242.6 ml/m2 per day, a gain output ratio (GOR) about 0.622 and air heater efficiency about 35%. In the normal case of output salinity between 0 and 500 ppm, the cost was reduced by 96.7%, and by 96.3% in the case of four interior sections. Water cost reduction is also observable at the same output salinity, with 54.1% at 0 ppm and 62.4% at 200 ppm between number of interior sections = 0 and 4. [ABSTRACT FROM AUTHOR]

In this study, the flow and heat transfer of supercritical hydrogen flowing inside a rocket engine cooling channel with arc ribs and variable heat flux is presented using numerical simulations. The arc ribs are examined in straight and thrust chamber-shaped channels. The results indicate that channel shape and rib geometry play an important role in the heat transfer. The highest performance evaluation criterion η is recorded for a channel with 90° arc ribs of h r / D H = 1/8 in both convex and concave orientations. Compared with a smooth channel, the performance of a channel with 90° convex arc ribs is 13–62% higher (depending on location) for a straight geometry, but it is only 14.7–27.7% higher in a thrust chamber-shaped geometry. The thermal stratification is moderate in the straight channel, but it is intense in the thrust chamber-shaped channel because of the onset of flow separation at the junction of the convergent-divergent section. • Supercritical H 2 heat transfer in straight and thrust chamber-shaped cooling channels with arc ribs are studied. • Under varying heat flux, 90° arc ribs outperform smooth channels by 13%–62% in straight a channel. • In contrast, the 90° arc ribs are considerably less effective in thrust chamber-shaped channels. [ABSTRACT FROM AUTHOR]

Double glazing is one of the effective ways to improve the thermal performance of flat-plate solar air heaters. In this regard, by considering this type of heat exchanger, the free convection flow between two glass covers and the forced convection flow inside the main air channel were analyzed in the present study. The exact implementation of this idea was numerically investigated using COMSOL Multiphysics commercial software. Due to the occurrence of Bénard convective flows in the space between two glasses, the air gap thickness must be optimized so that the positive effect of the presence of the air layer as a suitable thermal insulation is not affected by this phenomenon and does not lead to thermal dissipation. By choosing air gaps of 1 cm to 5 cm and sun radiative heat fluxes of 600, 800, and 1000 W/m2, it was found that the higher rate of heat transfer from the absorber plate into laminar forced convection airflow took place in the air heater with 3 cm air gap. Under the solar irradiation of 1000 W/m2, computations indicated the values of 11.2 K, 9.7 K, and 8.8 K for air temperature increase along the air heaters with the air gap thicknesses of 3 cm, 5 cm, and 1 cm, respectively. Comparisons between the present numerical findings and experimental data reported in the literature revealed an excellent consistency. [ABSTRACT FROM AUTHOR]

Heat transfer systems have been employed in numerous industrial and residential settings to convert and recover heat. One effective approach for enhancing heat transfer rates involves incorporating artificial roughness in the form of regularly spaced ribs on the heated surface. In this particular study, the researchers conducted numerical simulations to analyze the turbulent heat and flow properties within a rectangular duct of a solar air heater (SAH). The duct featured three different types of transverse rib shapes: equilateral‐triangular, trapezoidal, and square sectional ribs. The governing equations have been solved numerically using a finite‐volume technique via ANSYS FLUENT. For solving the transport equations of turbulent kinetic energy and its dissipation rate, the RNG k–ε $\varepsilon $ turbulence model was utilized. At a broad range of Reynolds numbers (6000 ≤ Re ≤ 18,000), relative roughness height (0.021≤e/Dh≤0.043 $0.021\le e/{D}_{h}\le 0.043$), and a fixed relative roughness pitch (P/e=10 $P/e=10$), the Nusselt number (Nu ${Nu}$), friction factor (f $f$), and thermal performance factor (TPF) have been examined. The maximal Nu was obtained for equilateral‐triangular ribs, while the minimum friction factor was seen for square sectional ribs. The highest TPF of 1.591 was achieved with equilateral‐triangular ribs at Re=6000 ${Re}\,=\,6000$ and e/Dh = 0.032. Contours of kinetic energy, turbulent intensity, velocity, and pressure produced significant findings for comprehending the SAH's physical phenomena. [ABSTRACT FROM AUTHOR]

In this paper, six different shape obstacles, namely, Isosceles trapezoid (Type 1), Triangular with curve apex (Type 2), Rectangular with chamfered edges (Type 3), Rectangular with curve edges (Type 4), Triangular with curve corner at bottom (Type 5) and Triangular shape (Type 6) have been tested in inline and staggered fashions in solar air heater (SAH) duct. This work aims to investigate the effect of obstacle shape on heat transfer and friction characteristics. All experiments have been carried out at eight different values of Reynolds number ranging from 2000 to 16000 and fixed value of heat flux of 1000 W/m2. As results, Nusselt number and friction factor characteristics have been presented and discussed. The maximum enhancement in Nusselt number and friction factor are observed in case isosceles trapezoid obstacles (Type 1) and rectangular with curve edges obstacles (Type 4) when mounted in staggered fashion, respectively and their respective average enhancement factor in Nusselt number and friction factor are observed as 2.95 and 4.37. Also, thermo-hydraulic performance parameter (η) of all obstacles in both arrangement have been evaluated and found to be average maximum values 1.88 in case of isosceles trapezoid obstacles (Type 1) in staggered manner. [ABSTRACT FROM AUTHOR]

This study prepares an experimental examination of thermal and hydraulic analysis of an absorber plate integrated with different arrangements of twisted turbulators, including longitudinal, transversal, and oblique orientations. These arrangements are considered for both the integral and the interrupted turbulators over Reynolds number range from 9174 to 55048. Nu ratio and f ratio range from 1.15–2.21 and 1.73–7.79, respectively. The interrupted turbulators with oblique arrangements with the attach angles of 30° and 60° come in the second and third places, respectively, and the maximum criterion value in the latter cases is 1.29 and 1.21. [ABSTRACT FROM AUTHOR]

The performance of a solar air heater roughened with sine wave baffles has been calculated in terms of effective and thermal efficiency. Relative baffle length ($${L_b}/{L_P}), $$ L b / L P) , relative roughness pitch $$ \left({{P_{st}}/e} \right)$$ P s t / e , relative height $$\left({e/H} \right), $$ e / H , angle of attack $$ (\alpha ^\circ)$$ (α ∘) , Reynolds number $$\left({Re} \right)$$ R e , Insolation $$\left(I \right)$$ I and Temperature rise parameter $$\Delta T/I$$ Δ T / I are the operational parameters. The sine wave roughened solar air heater has a higher effective and thermal efficiency than the smooth air heater. The thermal efficiency has boosted to 78%, and the effective efficiency has been improved to 70.8%. A parametric analysis has been carried out to determine the best set of parameters. [ABSTRACT FROM AUTHOR]

The energy requirement of the world will keep on rising, and fossil fuels have been increasingly used in this regard. The use of fossil fuels brings about different sets of problems like climate change, greenhouse gas emissions, etc. So, a desperate need for an alternative source of energy which can be cheap and sustainable is being felt. Renewable forms of energy are environment friendly and can be looked into for our energy needs. Among renewable forms of energy, solar energy is free and extensively obtainable. This paper reviews solar air heater (SAH) that utilizes solar energy to provide medium temperature air output. The main disadvantage of SAH is its low efficiency. So, researchers have used different ways to improve its efficiency. This paper looks into the numerical methods and new techniques implemented by investigators to numerically model a SAH while organizing their results in a tabular form. Subsequently, the study analyses the thermal performance of SAH in terms of thermohydraulic performance parameter (THPP) and organizes their results in tabular form. The maximum THPP achieved among the cases studied was from Jouybari and Lundstrom (Energy 190:116437, 2020) and equalled 5.5. Finally, the current study will provide researchers with a quick view of the turbulence models used by investigators along with information on the number of grids to gauge the computational power required for the study and concludes with few key points on the subjects that can be further explored. [ABSTRACT FROM AUTHOR]

In this paper, an experimental evaluation of a newly developed flat plate double pass solar air heater combined with aluminum cans for drying red pepper was presented. The proposed solar dryer system was designed, modeled, and evaluated. Solar air heater trials were carried out using the absorber's top and bottom plate and aluminum cans for red pepper drying at Bahir Dar, Ethiopia. To test the solar dryer, 100 pieces of red paper were obtained from the Bahir Dar region of Ethiopia for the purpose of experimentation. Microsoft Excel was used to perform statistical analysis of eleven mathematical models. The results show that the mixed-mode solar greenhouse dryer takes less time to dry red pepper than the open solar dryer. In the midday, the solar insolation reached 973 W/m2 and the minimum solar insolation was 220 W/m2 and air is expelled at a rate of 0.0383 kg/s. According to the experimental results, the dryers chamber temperature ranged from 30.9 to 54 °C, while the ambient temperature was between 22.6 and 28.2 °C. The mixed-mode double pass achieves up to 46% and 28% efficiency when used with aluminum can dryers and conventional open sun dryers, respectively. A drying rate of 0.0003395 kg/s was achieved for the open sun dryer system and 0.0000365 kg/s for the mixed mode solar dryer. Using mixed-mode and open-sun solar dryers, the logarithmic model was found to be most effective in explaining the red pepper behavior. Furthermore, a comparison was made between the experimental and predicted moisture ratios through the calculation of the coefficient of determination (R2), the reduced chi-square (X2), and the root mean square error (RMSE). The results show that the logarithmic model achieved the highest value of the correlation coefficient (R2), which was determined to be 0.9978 and 0.9989, while the logarithmic model achieved the lowest value of Chi-square (X2). [ABSTRACT FROM AUTHOR]

The present study has been carried out to improve the overall efficiency of a conventional flat plate solar collector (FPSC) using two different heat storage phase change materials (PCMs). Two grades of paraffin wax—Paraffin‐P116 (PCM‐1) and Paraffin‐5838 (PCM‐2) as PCM are selected for the analysis based on their high heat fusion rate, low thermal conductivity, and suitable phase transition temperature. The present code has been validated with experimental results and it showed a maximum error of 6.43% in predicting the water outlet temperature. Absorber plate temperature, useful heat transfer rate, water outlet temperature and efficiencies are estimated to improve the performance of FPSC with and without PCM for various flow rates (15 lph and 30 lph) with two different weights of PCM (9 kg and 14 kg) for three different locations in India, [Chennai (13.0827° N, 80.2707° E), Bengaluru (12.9716° N, 77.5946° E), and Delhi (28.7041° N, 77.1025° E)]. The maximum increment in the efficiency of FPSC with the use of PCM‐1 is 19.59% and with the use of PCM‐2 is 16.53%. Using 14 kg of PCM‐1 with the conventional FPSC at water inlet flow rate of 15 lph increases the overall thermal efficiency up to 19.59% compared with conventional FPSC. The maximum increase in the percentage of efficiency with PCM‐1 from conventional FPSC for different cases of 15 lph‐09 kg is 16.34%, 15 lph‐14 kg is 19.59%, 30 lph‐09 kg is 14.57% and 30 lph‐14 kg is 18.45%. From the present study, it can be concluded that the overall efficiency of FPSC is increased with the use of 14 kg of PCM‐1 with conventional FPSC at the inlet water flow rate of 15 lph. [ABSTRACT FROM AUTHOR]

In the present study, an experimental test was conducted to investigate the energetic performance of a novel designed solar air heaters (SAHs), with, and without phase change material (PCM). Two identical SAHs were fabricated and tested to compare their performance. The first heater is a jacket‐tube solar air heater (SAH 1), while the second heater is similar to the first but filled with PCM (SAH 2). Experimental results showed that increasing air flow rate increases the daily thermal efficiency. Thermal energy during day hours can be stored in the PCM and used after sunset. SAH 2 gave an additional operating time after sunset for 4 hours at 0.01 kg/s, 2.5 hours at 0.035 kg/s, and 1 hour at 0.06 kg/s. Maximum improvement in the daily thermal efficiency was 15% at SAH 2, more than SAH 1 at 0.01 kg/s air flow rate. Employing PCM, as so as increasing air flow rate can reduce the daily thermal losses. [ABSTRACT FROM AUTHOR]

In this study, the effects of various absorber configurations of a tubular solar air heater are investigated. The models such as direct flow with a standard absorber (DF-SA), swirl flow with a standard absorber (SF-SA), swirl flow with perforated longitudinal fins (SF-PLF), swirl flow with radial fins (SF-RF), swirl flow with perforated radial fins (SF-PRF) are studied. Investigation parameters including Nusselt number, exergy efficiency, PEC, and friction factor are examined with Reynolds numbers ranging from 8488 to 25,464. The findings reveal an enhancement in Nusselt number, PEC, and exergy efficiency corresponding to an increase in Reynolds numbers, while the friction factor decreases. Models employing air-swirl flow entrances demonstrate superior effects in improving the performance compared to direct flow inlets. Notably, the SF-PRF shape records the maximum Nu ratio of (102.5–108%). This model has the maximum values of PEC enhancement ratio of (103.9–106.2%) compared to DF-SA, indicating the enhancement obtained by using swirl flow with perforated ring fins. Analysis of streamlines and distributions of temperature, pressure, and velocity elucidates the effects of perforated radial fins on vortex generation and secondary flow, particularly when incorporating air swirl inlets. [ABSTRACT FROM AUTHOR]

The solar air collector (SAC) with an artificially roughened absorber surface enhances convective heat transfer characteristics compared to a flat surface. In this article, a 2D numerical problem was resolved using ANSYS Fluent 18.2 to enhance the performance of SAC of an indirect type solar dryer by providing right-angle triangle corrugations on the absorber. Seven Reynolds numbers (Re) (ranged from 4000 to 22,000), corrugation height (e) of 10 mm and relative roughness pitch (pitch-to-e ratio, P/e) ranged from 2.75 to 20 were considered as input parameters. The renormalization based k–ϵ turbulence concept was used. The parameters such as velocity, temperature, turbulent kinetic energy, Nusselt number (Nu), Nu ratio, friction factor (f), f ratio and thermo-hydraulic performance parameter (pth) were evaluated for both corrugated and smooth absorbers. The Nu range obtained was from 25.37 to 105.48 in roughened plates and it is 66.47–76.9% enhancement compared to smooth plates. A maximum pth obtained was 1.76 at P/e = 5 and Re = 4000, and hence, P/e = 5 (P = 50 mm) was the best configuration for the SAC. The numerical results obtained were compared with published outcomes in reasonable accordance. [ABSTRACT FROM AUTHOR]

The solar air heater (SAH) equipped with special modified surface geometries is one of the existing technologies capable of converting the solar energy into thermal energy with low associated pressure drop, and it has been used as heat source in a wide range of thermal applications which demand lower operating temperatures (about 30 to 80 °C). In the present research, the use of louvered-winglet longitudinal vortex generators as a passive heat transfer enhancement technique is proposed to numerically investigate the effect of the opened louvers have on the SAH thermo-hydraulic performance for: (i) Reynolds numbers of 5000 and 20,000, (ii) two different types of longitudinal vortex generators (delta winglets and rectangular winglets), (iii) aspect ratios of 2 and 6, (iv) angles of attack of 30° and 45°, (v) ratio between louver area and LVG area of 0.25 and 0.44, (vi) louver flap angles of 10°, 40°, and 60° and, (vii) louver opening direction–pointing to the adiabatic plate or to the absorber plate, both downstream of the main flow. The numerical simulations showed that louvered winglets mounted in common-flow-down configurations are thermo-hydraulically more efficient than the respective non-louvered winglets. Rectangular winglets and higher values of ratio between louver area and winglet area, louver flap angle, and aspect ratio promoted a better thermos-hydraulic performance of the channel. The effect of louver on performance of the SAH channel is more pronounced on rectangular winglet than delta winglet. Moreover, the winglets with louvers toward the adiabatic plate introduce less pressure loss to the SAH than the ones with louvers toward the absorber plate. Maximum thermal enhancement factor of 3.418 was achieved for Re = 20,000. With respect to flow patterns and heat transfer characteristics observed on louvered winglets, a new vortex structure generated by the louver openings is identified, in which is responsible to enhance the hot and cold flow mixing. Finally, the louver presents similar effect on thermo-hydraulic performance of the channel, independently of the Reynolds number. [ABSTRACT FROM AUTHOR]

The efficacy of a latent thermal battery (LTB) system is significantly enhanced through the implementation of a multistage configuration. This study is centered on the utilization of organic phase change material (OPCM) as the storage medium within the LTB, aimed at augmenting the charge and discharge rates of the system. The adoption of a multistage approach effectively mitigates the impact of partial phase transitions within the OPCM, facilitating a higher cumulative charging rate of 2.39°C/min. This arrangement is instrumental in minimizing the instability of heat release from each tank, thereby ensuring a consistent heating process for the working fluid throughout the discharge cycle. Consequently, the multistage LTB demonstrates an elevated power rate, reaching up to 7.64 Watts, with a sustained power duration of 45.5 minutes. Such performance signifies an efficacious heat discharge mechanism, substantially improving the overall functionality of the LTB system. The proposed multistage LTB configuration is particularly advantageous for thermal systems operating at low temperatures, including solar water and air heaters. Additionally, the enhanced charge and discharge rates contribute to an increased effective energy density of the LTB, aligning with the objectives of developing compact and efficient energy storage systems. The findings of this research underscore the potential of multistage LTB systems in maximizing operational efficiency in thermal energy storage, thereby contributing to the advancement of sustainable energy solutions. [ABSTRACT FROM AUTHOR]

• A new finned tube heater used for household frost-free refrigerator is proposed. • The duration of the defrosting cycle is shortened by 12%. • The overall energy consumption is reduced by 0.025 kW·h (10.4%). • FC temperature rise decreases by 2.4 °C. For frost-free refrigerators, the tubular metal sheathed type defrosting heater installed at the downstream of the evaporator is usually stainless steel circular tube defrosting heater (CTDH). During the defrosting process, a large part of the heat leaks into the cabinets of the refrigerator, causing the cabinet temperature to rise. This paper proposes a finned tube defrosting heater (FTDH) by using an aluminum alloy finned square tube as the metal sleeve of the defrosting heater. The external surface area of the defrosting heater is greatly increased due to the existence of the fins, thus strengthening the natural convection between the air and the defrosting heater and shortening the defrosting duration. The defrosting performance (defrosting duration, temperature rise, energy consumption) between FTDH and CTDH are compared experimentally. Results show that the whole defrosting cycle duration is shortened by 12%, while the freezer cabinets (FCs) temperature rise is reduced by 2.1 °C and the maximum FC temperature is reduced by 2.4 °C. In addition, the shorter defrosting operation cycle and the lower FC maximum temperature result in a 10.4% reduction in energy consumption of the whole defrosting cycle. In conclusion, FTDH is promising in refrigerators for reducing the FC temperature rise, shortening the duration and decreasing energy consumption during the defrosting cycle. [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. [ABSTRACT FROM AUTHOR]

The energy efficiency of supplies is crucial for the energy economy. The development of new and more efficient air heaters is a relevant topic for various industrial applications. In the formulation of air heating using a novel and flexible electromechanical system that accomplishes heating air to varying temperatures, this study examines the efficacy of using induction heating as a fundamental component of air heating systems and focuses on the effective heating of moving metal parts by electromagnetic coupling, thereafter transmitting the generated heat to the experimental facilities. The study delved into an exploration of numerous factors within a closed system, encompassing aspects such as area, temperature, and energy. Using a full-bridge ZVS circuit with an inductive coil design, fan speed variations and temperature measurements were systematically carried out to investigate the impact of induction heating on temperature changes within the given experimental setups. The results of an experiment conducted in a half-cubic-meter enclosed environment reveal significant temperature fluctuations with the varying velocities of moving metal elements, presenting a maximal rate of 17.7 degrees Celsius per hour and an efficiency factor of 64.15%. With continued refinement, this innovative technology has the potential to become an energy-efficient alternative to conventional heating techniques for a variety of applications, including industrial operations and residential heating. [ABSTRACT FROM AUTHOR]

In this paper, an air collector with sensible heat storage is numerically solved using the finite difference method. The change in temperatures of the glass, airflow, and absorber plate is assumed to be unidirectional. Meanwhile, heat conduction in the storage material is considered in two dimensions. Six storage materials containing brick, granite, slag, limestone, sandstone, and concrete are simulated unsteadily. Numerical techniques, including an implicit method, an upwind scheme, the Thomas algorithm, and the ADI method, are used to solve a system of differential equations describing the collector. The charging and discharging mechanisms are effectively explained by the two-dimensional temperature distribution of the storage material. Results indicate that the charge and discharge periods are up to 16:00 PM and 24:00 PM, respectively, demonstrating an air temperature difference of 4.5 °C for the granite thickness of 5 cm. Granite and slag are suitable storage materials due to their superior thermal properties. The air channel height has a significant effect on the performance of the collector. The air temperature difference doubles when the channel height is reduced from 5 cm to 2 cm. [ABSTRACT FROM AUTHOR]

The study intends to analyze the thermal performance of a novel solar air heater based on heat pipe vacuum tube solar collector and finned-tube heat exchanger. The solar collector has been introduced with a new header where heat transfer fluid (Therminol-55) gains heat directly in contact with the condenser section of the heat pipe. This eliminates thermal paste application between the condenser and manifold in the existing systems. The system's thermal performance has been experimentally evaluated using two different (four-row and eight-row) finned-tube heat exchangers at four varied air flow rates, viz. 100 kg h–1, 400 kg h–1, 700 kg h–1 and 1000 kg h–1. The system with eight-row heat exchanger performed better than the four-row heat exchanger at each air flow rate. 100 kg h–1 resulted in a maximum rise in temperature of air (55.4 °C) and maximum outlet temperature of air (89.4 °C). Meanwhile, the maximum energy and exergy efficiency of 95.7% and 2.17% were observed at 1000 kg h–1. The maximum effectiveness of the four and eight-row heat exchangers was found as 70.7% and 79.4%, respectively, at 100 kg h–1. The monthly cost saving by utilization of the proposed system is 65.65 $, and the payback period is 12.4 months. The amount of CO2 averted from releasing into the atmosphere is 787.7 kg per month. The results suggest the utility of the proposed solar air heater as an environment-friendly replacement for conventional air heaters for consistent operation in the daytime. The experimental study was performed at the campus of NIT Kurukshetra, India (29.9476°N, 76.8155°E). [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient in solar air heaters suffers from a reduction due to the formation of a laminar sub-layer between the absorber plate and the air in motion. A viable and efficient strategy to augment the heat transfer coefficient involves introducing artificial roughness in the form of ribs. This study employs numerical simulations to examine the turbulent heat and flow characteristics within a rectangular duct of a solar air heater (SAH) featuring trapezoidal ribs as roughness elements. The governing equations were numerically solved using the finite-volume method and ANSYS FLUENT. The transport equations of turbulent kinetic energy and its dissipation rate were addressed by the RNG k-ε turbulence model. The Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) were computed across a broad range of conditions, including Reynolds number (6,000≤Re≤18,000), relative roughness height (0.021≤e/Dnd relative roughness pitch (5≤P/e≤20) under constant heat flux conditions. It was determined that the maximum enhancement ratio of Nu was 2.124 times that of a smooth duct when e/Dh=0.043, P/e=20, and Re=6,000. Additionally, the TPF for the SAH featuring trapezoidal ribs attained a peak value of 1.64. [ABSTRACT FROM AUTHOR]

In this study, the heat transfer augmentation and friction factor of a novel type of solar air heater (SAH), which incorporates longitudinal fins and rectangular turbulators, were investigated numerically with different arrangements of the turbulators. The effects of arrangements of rectangular turbulators placed in a finned air channel on its heat transfer augmentation and friction factor are discussed for Reynolds numbers ranging from 3000 to 15,000 using commercial ANSYS 17.2 software. Four different arrangements are investigated, including Array A, which places turbulators on both the fin's side and base surfaces at the same position; Array B, where turbulators are sequentially placed on the fin's side and base surfaces; Array C, where turbulators are only placed on the side surface; and Array D, where turbulators are placed only on the base surface. Array A showed the highest heat transfer augmentation and friction factor among the investigated arrangements. However, the highest thermo-hydraulic performance (THP), considering both the heat transfer augmentation and friction factor, was obtained in Array B, with a value of 1.36. Consequently, Array B was regarded as the most appropriate and effective arrangement method for the finned air channel of a SAH. [ABSTRACT FROM AUTHOR]

To manage energy-efficient indoor air quality, mechanical ventilation with a heat recovery system provides an effective measure to remove extra moisture and air contaminants, especially in bathrooms. Previous studies reveal that heat recovery technology can reduce energy consumption, and its calculation needs detailed information on the thermal performance of exhaust air. However, there are few studies on the thermal performance of bathroom exhaust air during and after showers. This study proposed a detailed thermal performance prediction model for bathroom exhaust air based on the coupled heat and mass transfer theory. The proposed model was implemented into the AccuRate Home engine to estimate the thermal performance of residential buildings with heat recovery systems. The time variation of the water film temperature and thickness on the bathroom floor can be estimated by the proposed model, which is helpful in determining whether the water has completely evaporated. Simulation results show that changing the airflow rate in the bathroom has little effect on drying the wet floor without additional heating. The additional air heater installed in the bathroom can improve floor water evaporation efficiency by 24.7% under an airflow rate of 507.6 m3/h. It also demonstrates that heat recovery can significantly decrease the building energy demand with the fresh air load increasing and contribute about 0.6 stars improvement for the houses in Hobart (heating-dominated region). It may be reduced by around 3.3 MJ/(m2·year) for the houses in other regions. With this study, guidelines for optimizing the control strategy of the dehumidification process are put forward. [ABSTRACT FROM AUTHOR]