Smooth Solar Air Heater Research Articles

Heat transfer and fluid flow analysis of a solar air heater using conical jet impingement with sine-wave corrugation on absorber plate

In the pursuit of renewable energy solutions, solar air heaters emerge as a promising technology to efficiently harness solar thermal energy for diverse applications such as space heating, agricultural drying and industrial process heating. However, the system’s efficiency is often limited by the low heat transfer capability of air and the formation of laminar sub-layer over the absorber plate. This study addresses the issue by investigating the innovative use of conical jet impingement combined with sine wave corrugations on the absorber plate to enhance heat transfer in solar air heaters. The design parameters include wave amplitude ratio (0.079–0.314), throat jet diameter ratio (0.063–0.141), base jet diameter ratio (0.126–0.251), and Reynolds number (3200–19200) as the operational parameter. The computational fluid dynamics simulations are employed to solve the Reynolds-Averaged Navier-Stokes equations coupled with RNG k-ɛ turbulence model to assess the heat transfer and frictional characteristics, followed by experimental validation. The findings demonstrate a significant improvement in the system’s heat transfer rate with the Nusselt number increase by a factor of 6.71 times compared to a smooth solar air heater, while the friction factor increase by 13.87 times. Furthermore, the highest thermo-hydraulic performance parameter is found to be 2.79 corresponding to Reynolds number of 3200, wave amplitude ratio of 0.079, throat and base jet diameter ratios of 0.126 and 0.220, respectively. The proposed geometry will be helpful for academic researchers and can be adopted by the industries for various applications.

Turbulent flow-thermal-thermodynamic characteristics of a solar air heater with spiral fins

This work proposes a strategy by employing multiple spiral fins (SFs) for enhancing the low heat transfer rate of traditional smooth solar air heaters (SAHs). A numerical study involving the effects of the pitch ratio (P/Dh), quantity (N), and arrangement of SFs on fluid flow, heat transfer, and thermodynamic characteristics of the SAHs was conducted. The research findings indicated that the flow field was homogenized and the thermal boundary layer was weakened by inserting multiple SFs into the smooth SAH. This could increase the heat transfer rate by 30.63–137.51 % and decrease the overall entropy generation by 9.64–57.05 %, causing a 25.01–99.18 % improvement in thermodynamic efficiency. Reducing P/Dh and increasing N could improve the heat transfer rate, increase flow viscous entropy generation, reduce thermal entropy generation, and augment thermodynamic efficiency (ηⅡ). In addition, changing the rotation arrangement of the SFs from the counterclockwise to the counter-swirl improved the thermal-hydraulic performance parameter (THPP). Within the scope of this study, the SAH with P/Dh = 1.5 and N = 5 in a counter-swirl layout achieved the highest THPP of 1.04, and the SAH with P/Dh = 0.6 and N = 5 in an anticlockwise arrangement yielded the lowest entropy generation ratio of 0.43 and the maximum ηⅡ of 18.16 %.

Employment of roughened absorber palate and jet nozzles with different hole shapes for performance boost of solar-air-heaters

In this study, roughened absorber plate and jet nozzle are simultaneously employed to enhance the efficiency of a solar based air heater. The impact of jet nozzle hole shape is comprehensively investigated for the mentioned system which have not been investigated before. Three-dimensional steady-state simulations of incompressible turbulent fluid flow and heat transfer are performed using the Reynolds-Averaged Navier-Stokes (RANS) equations to model the jet solar air heater (JSAH). Five different jet hole shapes (circular, triangular, square, hexagonal, and rectangular) are examined and results are compared with conventional structure. The thermal and hydraulic performance of the JSAH is assessed using a variety of geometric and operating parameters, including jet diameter ratio (dj/Dh), jet hole streamwise pitch (Lj/Dh), and Re number (Re). The results show that the ratio of (Nu/Nus) initially increases and then decreases as the hydraulic diameter of the jet holes increases. Circular jet holes consistently outperform other shapes, while rectangular and triangular jet holes perform poorly. The pressure penalty (f/fs) decreases with increasing (dj/Dh), with circular jet holes exhibiting the lowest value. Increasing the Reynolds number enhances heat transfer and pumping power but leads to a decrease in (Nu/Nus) and negatively affects the THPP of the JSAH compared to a conventional smooth solar air heater. The study also reveals that the THPP initially increases with streamwise pitch (Lj/Dh) but then declines, following the trend of (Nu/Nus). The results demonstrate up to 4.5 times higher Nusselt numbers with a jet solar air heater versus a smooth solar heater. A maximum thermal-hydraulic performance parameter of 1.64 indicates the proposed design's efficacy. This research furnishes critical insights into optimizing solar air heater performance by examining jet nozzle hole shape, streamwise pitch, and Reynolds number. It enables enhancing thermal efficiency and thermo-hydraulic performance.

Effect of jet angle and jet pitch on the Thermo-Hydraulic performance of solar air heater having absorber plate with jet impingement

This numerical investigation focuses on enhancing the heat transfer characteristics and thermo-hydraulic performance of a solar air heater by employing jet impingement over the absorber plate. The study explores the influence of two geometrical parameters, namely jet pitch ratio (P/Dh) and jet angle ratio (α/90), on the heat transfer, frictional losses, and overall performance of the solar air heater with jet impingement (SAHJI) under various flow conditions, represented by Reynolds numbers (Re) ranging from 3500 to 17500. The simulations are conducted using the RNG k-ɛ model with second-order upwind discretization. A comparative analysis is performed between the SAHJI system and a conventional smooth solar air heater (SPSAH) configuration, revealing a significant enhancement in thermal–hydraulic performance with the use of jet impingement. The investigation identifies the maximum thermo-hydraulic performance parameter, reaching a value of 4.12. This peak performance is achieved at specific values of jet pitch ratio (P/Dh) of 1.30 and jet angle ratio (α/90) of 0.094, respectively, at a Reynolds number of 7500. These findings demonstrate the potential of jet impingement as a heat transfer enhancement technique in solar air heaters, contributing to improved overall system efficiency.

Numerical Investigation of Heat Transfer Augmentation of a Curved Solar Air Heater With Inverted T-Shaped Ribs

Abstract Laminar sub-layer formation in a smooth solar air heater (SAH) is one of the reasons for the low heat transfer coefficient. One of the most effective ways to overcome the problem and improve the heat transfer rate inside the SAH is to use artificial roughness in the form of ribs. The present investigation studies the consequence of inverted T-shaped ribs on the absorber plate of a CSAH. The absorber plate is exposed to a constant heat flux of 1000 W/m2 and is made up of aluminum. The investigation is done on the effect of Reynolds number (Re), relative roughness pitch (P/e), and relative roughness height (e/Dh) on entropy generation, fluid flow, and heat transfer characteristics of the system. A 2D fluid domain has been considered for the numerical analysis, and finite volume method is used to solve the equations of continuity, momentum, and energy. The governing equations are solved using the SST k–ω model. Thermo-hydraulic performance parameter (THPP) is also calculated using Nuavg_r and favg_r, which further helped to determine the optimal arrangement of inverted T-shaped ribs on the absorber plate of the SAH. The maximum THPP of 4.7744 is found for P/e = 7.143 at Re = 18,000. Correlation for Nuavg_r and favg_r as a function of Re and P/e is developed. Entropy generation per unit length due to fluid friction and heat transfer has been graphically represented.

Performance Evaluation of Roughened Solar Air Heaters for Stretched Parameters

Artificial roughness applied to a Solar Air Heater (SAH) absorber plate is a popular technique for increasing its total thermal efficiency (ηt−th). In this paper, the influence of geometrical parameters of V-down ribs attached below the corrugated absorbing plate of a SAH on the ηt−th was examined. The impacts of key roughness parameters, including relative pitch p/e (6–12), relative height e/D (0.019–0.043), angles of attack α (30–75°), and Re (1000–20,000), were examined under real weather conditions. The SAH ηt−th roughened by V-down ribs was predicted using an in-house developed conjugate heat-transfer numerical model. The maximum SAH ηt−th was shown to be 78.8% as predicted under the steady-state conditions of Re = 20,000, solar irradiance G = 1000 W/m2, p/e = 8, e/D = 0.043, and α = 60. The result was 15.7% greater efficiency compared to the default smooth surface. Under real weather conditions, the ηt−th of the roughened SAH with single- and double-glass covers were 17.7 and 20.1%, respectively, which were higher than those of the smooth SAH.

Experimental analysis and thermal management of solar air heater roughened with sine wave baffles

In the present study, a thermo-hydraulic performance (THP) of solar air heater (SAH) has been assessed by placing sine wave-shaped baffles on the heat-absorbing surface. The experiments have been performed by varying Reynolds number ([Formula: see text]) ranging from 3000-18,000, relative pitch ([Formula: see text]) ranging from 8 to 14, relative height ([Formula: see text]) ranging from 0.4 to 0.55, relative baffle length [Formula: see text] ranging from 0.054 to 0.081 and angle of attack(α) ranging from 10° to 45° while the duct aspect ratio has been kept fixed at 12. The best set of geometric parameters has been decided based on Nusselt number [Formula: see text] and friction factor [Formula: see text] characteristics of the roughened SAH and compared with the smooth surface SAH, under analogous experimentation conditions. The cost analysis has also been performed and results revels that roughened SAH is more cost-effective than smooth SAH. The correlation for Nusselt number [Formula: see text], friction factor [Formula: see text], and thermo-hydraulic performance parameters (η) have been developed using regression analysis and found an average deviation of ±9.15%, ±7%, and ±9.2% respectively, from experimental results.

Heat transfer and fluid flow analysis of artificially roughened solar air heater

This study aims for computational investigation of roughened solar air heater (SAH) using artificial roughness in the form of double concave ribs. Solar air heater is a type of heat exchanger that utilises the solar radiation to generate heat energy. Smooth solar air heaters are found inefficient due to low convective heat transfer coefficient from absorber plate to air, thus to enhance the heat transfer rate artificial roughness in the form of double concave ribs is employed. Relative roughness height (e/D), relative roughness pitch (P/e) and relative arc radius (r/e) are chosen as geometric variables and analysed at five different values of Reynold’s number (Re) and their effect on heat transfer, friction factor and thermohydraulic performance parameter (THPP) is studied using commercial CFD software Ansys fluent v.15.0. It has been found that the maximum value of THPP is 1.725 for studied range of parameters. Nusselt number increases with increase in Reynold’s number and vice a versa happens for friction factor but in case of relative arc radius (r/e) both Nusselt number and friction factor decreases with increase in r/e.

Exergetic performance evaluation of SAH with inclined ribs used as coarseness in triangular duct

Exergetic efficiency analysis is one of the important tools to determine the thermal performance of Solar Air Heater as it taken useful energy gain and the pumping power in the consideration. In this research, an analytical study is carried out to evaluate the exergetic performance of SAH with inclined rib coarseness attached to the underside of the absorber plate in a triangular duct. The exergetic efficiency were calculated and compared to smooth Solar Air heater. The exergetic efficiency is highest for Reynold number 10000, relative roughness height of 0.043, relative roughness pitch of 12 and angle of attack of 60°. The optimum value of temperature rise parameter is found to be 0.133 Km2/W for all operating and roughness variables. Design plots were also presented in order to help the designers in the design of SAH with inclined ribs for the given range of operating and roughness variables.

Energy and exergy analysis of carbon nanotubes-based solar dryer

Solar dryers play a pivotal role in minimizing drying energy consumption in small farms. Therefore, its development is an urgent need. In this study, a developed solar dryer comprised of a smooth solar air heater, shell and tube storage unit, and drying chamber, has been constructed and tested to dry a Chinese medicinal fungus (Poria Cocos). The dryer has been operated under two airflow rates and then, energy and exergy analysis applied to the system. The results show that: solar air heater averaged thermal and exergy efficiency were 66.2% and 4.6%, 70.2 and 4.4% for 1st and 2nd experiments, respectively. Carbon nanotubes- paraffin wax shell and tube storage unit averaged overall thermal efficiency was 12.2% and 19.6% leading to 8.1% and 11.9% as averaged overall exergy efficiency for 1st and 2nd experiments, respectively. The specific energy consumption (SEC) was 6.545 and 7.917 kWh / kg moisture, also, the dryer's overall thermal efficiency was 36.4 and 30%, for 1st and 2nd experiments, respectively. The final moisture content of Poria Cocos was in the range of 6.6-8% w.b. The system payback period is 1.55 years.

Three-dimensional simulation and experimental validation of solar air heater having sinusoidal rib

ABSTRACT A new geometry of roughness in the sinusoidal form has been investigated computationally using Computational Fluid Dynamics (CFD) software for examining the influence of roughness on heat transfer and fluid friction in solar air heater and results obtained have been compared with experimental results. The simulated results for smooth solar air heater are compared with Dittus-Boelter equation for heat transfer and Blasius equation for fluid friction. The deviation of simulated results are found to be 7.55% and 16.91%, respectively. In order to validate the simulated results experimental test rig was fabricated and experiments were carried out for the same set of parameters used in the simulation. The experimental results indicate that for the roughened absorber plate having a sinusoidal rib, the variation in heat transfer is within 9% from that of simulated results and for fluid friction, deviation is within 4%. The optimal value of thermohydraulic performance (THP) is obtained 2.05 for roughness pitch (P) = 10 mm and Reynolds number (Re) = 4000, where enhancement ratio of Nusselt number (Nur/Nus) and friction factor (ƒr/ƒs) are 2.48 and 1.76, respectively. The experimental value of THP is found to be within 6.77% of the value indicated by CFD analysis. The results are also compared with the triangular and square rib and found that the optimal THP of the proposed rib is 20.06% and 33.31% more.

Numerical investigation on the performance of a solar air heater using jet impingement with absorber plate

Solar air heater is the simplest heating device for utilizing solar thermal energy. Jet impingement technique can be used to amplify the performance of a solar air heater by increasing the heat transfer between fluid and heated surface. Under the present study, an attempt has been made to carry out a numerical investigation on heat transfer behaviour of a solar air heater having absorber plate with impinging jet. 3D-Computational fluid dynamics (CFD) simulation using ANSYS-18.1 has been carried out with RNG k–ɛ turbulence model, and the upwind scheme is applied for the discretization of governing equations. Jet diameter ratio and jet height ratio are the considered system parameters, and their considered ranges are 0.065 to 0.195 and 0 to 0.433, respectively. The performance of solar air heater with jet impingement is investigated under different flow conditions taking Reynolds number ranging from 3500 to 17,500. It has been found that a significant increase in heat transfer for jet impinging solar air heaters is achieved in comparison to smooth solar air heater under similar operating conditions. The maximum heat transfer enhancement of 7.58 with a friction factor penalty of 9.01 times is obtained at jet diameter ratio of 0.0650 and jet height ratio of 0.216 for Reynolds number of 17,500. Maximum thermal-hydraulic performance parameter value of 3.66 is obtained correspond to jet height ratio of 0.216 and jet diameter ratio of 0.065 for Reynolds number of 15,500.

Geometrical Optimization of a Smooth Solar Air Heater Duct

Abstract This study presents the geometrical optimization of a solar air heater. A reasonable working range of geometrical parameters: length 1–3 m, width 0.1–0.5 m, and height 0.005–0.05 m (or aspect ratio 1–20), is investigated as per general applications and installation constraints. The effect of these geometrical parameters on thermal (heat flux and outlet air temperature) and hydraulic (air velocity, mass flowrate, pressure loss and pumping power, and Bejan number) parameters are theoretically studied. Later, a numerical investigation is carried out with an optimum geometry of SAH-duct (length 2.44 mm and width 0.3 m), for aspect ratio 4–18 and Re 3000–15,000. An experimental study is also done to validate numerical results. The heat transfer and frictional loss do not show a significant change in the values for the aspect ratio 8–12.

Heat transfer performance and flow characteristics of solar air heaters with inclined trapezoidal vortex generators

Solar air heaters (SAHs) are widely used devices for solar energy utilization at low temperature. The low convective heat transfer performance limits the energy conversion efficiency. This paper was aimed at investigating the flow characteristics and heat transfer enhancement mechanism, thermal hydraulic performance, and energy conversion efficiency of the SAH fitted with novel inclined trapezoidal vortex generators (ITVGs). The heat transfer performance and flow characteristics of a simplified unit were obtained by numerical simulation. A pair of longitudinal swirls were found close to both sides of each ITVG and the shape of vortex was rectangular in the front view. In the range of this paper, the order of overall thermal hydraulic performance for four different arrangements was listed as: upwind aligned (A1) > mixed staggered (A4) > upwind staggered (A2) > downwind aligned (A3). Furthermore, the A1 arrangement was applied to study the thermal hydraulic performance by altering parameters b/pt, e/H, and pl/H with Reynolds number ranging from 6000 to 18,000. The range of Nu/Nu0, f/f0, EEC, and R3 were 1.24–3.71, 1.39–11.8, 0.26–0.98 and 1.11–1.89, respectively. On this basis, energy and exergy efficiency evaluations were carried out on the practical SAH integrated by sixteen basic units. The energy efficiency and exergy efficiency could be maximally enhanced by 24% and 31% compared with the smooth SAH, respectively.

Experimental Investigation on Thermal Performance in Three-Sided Solar Air Heaters Having an Alignment of Multi-v and Transverse Wire Roughness on the Absorber Plate

Abstract The use of artificial roughness is an efficient and commercial way to appreciate the thermal performance from the collector to the air in solar air heater ducts, for numerous applications such as space-heating, crop-drying, and seasoning of timber industrial purpose. In this paper, the tentative inquiry on thermal enactment using new-fangled of three-sided roughened quadrilateral duct solar air heater having an alignment of multiple-v and transverse wire is performed and compared the outcomes with smooth duct air heater under similar operational circumstances. The modification of an arrangement and operational constraints is inspected within the restrictions, the moral of four-sided duct aspect ratio (W/H) = 8, the Reynolds number occupied from 3000 to 12,000, fraction of pitch to roughness height, P/e in the range of 10–25; ratio of roughness height to hydraulic diameter, e/D in the range of 0.018–0.042; at flow attack angle, α = 60 deg for constant moral of relative roughness width, (W/w) = 6. The augmentation on thermal efficiency in three-sided rugged duct is found to be 23–86% when compared to smooth duct, and the maximum thermal efficiency can occur at P/e = 10 and e/D = 0.042. The enhancement in air temperature flowing under three-sided roughened duct is found to be 49.27% more than that of a smooth duct. The instant innovative form of three-sided roughened solar air warmer would be preferable to those of a smooth solar air heater with respect to heat assignment.

Influence of Rectangular Ribs on Exergetic Performance in a Triangular Duct Solar Air Heater

Abstract Several artificial roughness (ribs) configurations have been used in flat plate solar air heaters (SAH) in recent years to improve their overall performance. In the present work, energy and exergy analyses of rectangular ribs in a triangular duct SAH for varying relative rib heights (e/D = 0.02–0.04), relative rib pitches (P/e = 5–15), and rib aspect ratios (e/w = 0.5–4) are evaluated and compared with smooth SAH. The analysis reveals that the entropy generated due to heat transfer is lower for the ribbed triangular duct compared to the smooth duct. It is also observed that the width of the rib plays a crucial role in minimizing heat losses to the environment. A maximum reduction of 43% and 62% in exergy losses to the environment and exergy losses due to heat transfer to the fluid is achieved, respectively, with a rib aspect ratio (e/w) of 4 compared to the smooth plate. It is found that in contrast to the smooth plate, ribs beneath the absorber plate effectively improves thermal and exergetic efficiency. Maximum enhancement of 36% and 17% is obtained in exergetic efficiency (ηex) and thermal efficiency (ηth), respectively, for e/w = 4, P/e = 10 and e/D = 0.04. Results also show the superiority of the ribbed triangular duct over the ribbed rectangular duct for an application requiring compact SAH with a higher flowrate.

Heat Transfer Enhancement in a Solar Air Heater with Roughened Duct Having Arc-Shaped Elements as Roughness Element on the Absorber Plate

An experimental study has been carried out for the heat transfer and friction characteristics for arc shaped roughness element used in solar air heaters. Duct has an aspect ratio (W/H) of 11, relative roughness pitch (p/e) range of 4–16, relative roughness height (e/D) range of 0.027–0.045, Reynolds number (Re) range of 2200–22,000 and arc angle (α) was kept constant at 60°. The effects of Re, relative roughness pitch (p/e) and relative roughness height (e/D) on heat transfer and friction factor have been discussed. The results obtained for Nusselt number and friction factor has been compared with smooth solar air heater to see the enhancement in heat transfer and friction factor and it is found out that considerable enhancement takes place in case of heat transfer as well as in friction factor. Correlations were also developed for Nusselt number and friction factor. Thermo-hydraulic performance parameter is also calculated for the same.

Heat Transfer and Friction Characteristics of Broken arc ribs roughened solar air heater ducts

A study was conducted to enhance heat transfer of a solar air heater having rectangular duct provided with artificial roughness in the form of broken arc ribs. The duct has an aspect ratio of 12. Five broken arc rib roughened plates having relative roughness pitch of 4, 6, 8, 10 and 12 have been tested for flow Reynolds number between 2, 000 to 16, 000. The arc angle, relative roughness height, relative gap width and relative gap position were fixed as 30°, 0.043, 1.0 units and 0.5 units, respectively. The maximum value of Nusselt number and friction factor was found corresponding to relative roughness pitch of 10. The maximum enhancement in Nusselt number of roughened solar air heater as compared to conventional smooth solar air heater was found to be 159 per cent with a corresponding increase in friction factor enhancement of 132 per cent at relative roughness pitch of 10 and Reynolds number of 12, 000.

Plate Temperature and Heat Transfer Characteristics of Artificially Roughened Solar Air Heater

Higher value of intensity of radiation on absorber plate of solar air heaters and effective heat removal from the plate by the carrier fluid, air, enhances thermal performance of solar air heaters. The paper deals with the experimental results of enhancing the intensity of radiation by means of booster mirrors and that of heat transfer by means of providing artificial roughness on the air flow side of the absorber plate. An enhancement in radiation of about 40% have been found over the normal incident radiation by means of booster mirrors leading to higher rate of heat collection. The thermal performance parameters FR and F’ have been found to increase in the range of 90% to 130% and 92% to 135% respectively in comparison to those of smooth solar air heaters without booster mirrors and in the range of 10% to 15% in comparison to roughened solar air heater without booster mirrors for the same pressure drop due to artificial roughness within the range of the parameters investigated.

Performance evaluation of solar air heater having V-down perforated baffles on the absorber plate

The roughened solar air heater performs thermally better than the conventional smooth solar air heater but is associated with a high pumping power requirement. The effective efficiency based criteria is suitable to design roughened solar air heater duct, as it takes both in accounts the useful heat gain from the system and the pumping power requirement. The thermal and effective efficiency of V down perforated baffled roughened solar air heater is studied analytically and the results obtained are compared with the conventional system. Flow Reynolds number and roughness parameters have combined effect on the heat transfer and fluid flow characteristics. The effective efficiency based criteria to predict the performance suggests using the V down perforated baffled roughened solar air heater in the range of flow Reynolds number 10 000–20 000, which corresponds to the range of solar air heater. It was found that there exists an optimum set of roughness parameters for a given Reynolds number or temperature rise parameter at which effective efficiency is maximum. Designs plots are prepared to predict the optimum set of roughness parameters.