Maximum Thermohydraulic Performance Research Articles

Thermo-hydraulic performance of solar air heater with built-in one-eighth sphere vortex generators

The primary objective of optimizing solar air heaters is to enhance their thermal efficiency, and the incorporation of perturbing elements into the absorber plate has proven to be an effective approach. The present study employed an electric heating plate to simulate solar heating and proposed a novel one-eighth sphere vortex generator to create strong longitudinal vortices and weak transverse vortices, thereby achieving enhanced overall performance. The experimental investigation focused on examining the impact of parameters, including deflection angle (α), relative transverse pitch (S/H), relative longitudinal pitch (L/H), relative height (e/H), and Reynolds number (Re), on both heat transfer and flow characteristics. The results show that new vortex generator performs best at deflection angles of 180°. The maximum thermo-hydraulic performance parameter of 2.03 was observed in this study. Additionally, it was found that the maximum Nusselt number (Nu) and friction factor (f) were 2.45 and 1.96 times higher than those obtained for a smooth duct, respectively. New correlations of Nusselt number (Nu) and friction factor (f) were developed to predict the heat transfer and flow resistance characteristics of solar air heater with built-in one-eighth sphere vortex generators. This study proposes a new idea to enhance the performance of solar air heaters.

Thermohydraulic performance parameter based experimental investigation of frustum shaped roughened solar air heater

An outdoor experimental investigation was conducted to explore the thermohydraulic characteristic (Nusselt no. and friction factor) of artificial roughened solar air heater (ARSAH) having frustrum shaped roughened element on absorber plate. Data were recorded and further processed to generate Nusselt number and friction factor correlation to predict the effect of flow and roughness parameter on performance of ARSAH. The investigation was conducted by varying Reynolds number in range of 2500–12,500. Dimensionless parameter for Frustrum shaped roughness was relative frustum height (e/Dh) from 0.013 to 0.054, relative frustum pitch (p/e) from 8 to 14, Relative frustum height to base diameter (e/d1) from 0.37 to 0.75, relative frustum diametral ratio (d1/d2) from 1 to 3. Maximum performance for ARSAH was obtained corresponding to the optimum value of flow and geometric parameter. The geometric orientation of the proposed roughness geometry produced tremendous rise in Nu with an acceptable rise in friction (f). Maximum enhancement in Nu for varying p/e, e/Dh, e/d1, and d1/d2 was, 4.58, 5.21, 6.62 and 6.09 times and that of friction was 5.59, 4.69, 4.92 and 4.66 times respectively over conventional SAH. Maximum Thermohydraulic performance was 3.7, 3.6, 3.9 and 3.8 at p/e = 12, e/Dh = 0.054, e/d1 = 0.75 and d1/d2 = 3.

Thermo-hydraulic performance investigation of double pass solar air heater integrated with PCM-based thermal energy storage

The solar air heater (SAH) is one of the ways to utilize solar energy for the purpose of drying, greenhouse heating and air conditioning. However, the SAHs are unable to deliver reliable thermo-hydraulic performance as a result of the intermittent nature of solar energy and the low convective heat transfer coefficient. Thus, in the present study, a three-dimensional numerical investigation is performed to study the thermo-hydraulic performance of the double pass solar air heater (DPSAH) having semi-cylindrical PCM tubes and perforated baffles as roughness geometry. The parameters selected for this study include baffle height ratio (eb/H) from 0.4 and 0.8, tube radius ratio (rt/H) from 0.2 and 0.5, and Reynolds numbers (Re) from 3000 and 13,000. Experimental validation has been conducted to verify the numerical results, and it has been found to be well-validated with mean absolute errors of 6.5 % and 1.2 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number (Nur) is found to be 200.08 at Re of 13,000, while the maximum friction factor (fr) is measured to be 0.6290 at Re of 3000, which corresponds to eb/H of 0.8 and rt/H of 0.3. The maximum heat transfer enhancement (Nur/Nus) in comparison to the smooth duct is found to be 5.08 times with a maximum friction factor increment (fr/fs) of 65.80 times, which corresponds to eb/H of 0.8, Re of 13,000 and rt/H of 0.3. The maximum thermo-hydraulic performance parameter (THPP) is observed to be 1.83 at Re of 13,000, rt/H of 0.2 and eb/H of 0.4. This study contributes to the design and optimisation of SAHs by incorporating thermal energy storage and roughness geometries.

Thermo-hydraulic performance enhancement of a solar air heater using rotating cylindrical turbulators

A novel concept of rotating cylindrical ribs as artificial roughness in a solar air heater to enhance its thermo-hydraulic performance factor has been investigated using 3D computational fluid dynamics. The rotational speed is varied from 2000 RPM to 10,000 RPM on the static ribs optimised for height (e), diameter (d), longitudinal pitch (P), and transverse pitch (S) at Reynolds number (Re) ranging from 5000 to 24000. The optimised static ribs configuration having e = 3.5 mm, d = 3 mm, S = 20 mm, and P/e = 10 is experimentally validated to establish the accuracy of rotating ribs performance computed using computational fluid dynamics. The maximum thermo-hydraulic performance factor of 1.89 is achieved—32 % higher than the best performance for static ribs—using rotational ribs for the rotational speed of 10,000 RPM at Re = 5000. A comparison between parallel and perpendicular orientations of rotating ribs with respect to the absorber plate establishes that perpendicular ribs configuration is highly desirable to reduce the pressure drop penalty, in turn, enhancing the thermo-hydraulic performance. The performances of the proposed perpendicularly oriented rotating cylindrical ribs are also compared with the performances reported in the literature for static ribs of different shapes having the same orientation with respect to absorber plate and it is observed that rotational ribs outperforms all the other static ribs.

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.

Optimization of a novel trapezoidal staggered ribs configuration for enhancement of a solar air heater performance using CFD

A novel transverse trapezoidal staggered ribs configuration as artificial roughness is investigated using CFD to understand the fluid flow and heat transfer behaviors for improving the performance of a solar air heater. In addition, experimental validation of Nusselt numbers for smooth duct against CFD results is established. The staggered ribs arrangement outperforms the continuous ribs and insights obtained from the thermal-fluid flow behaviors are further applied to optimize the staggered arrangements of the rib. Reynolds number Re is varied from 5000 to 24,000, and rib parameters are optimized with a special focus on understanding the effects of discontinuous rib width (w) and gap width (g). Two widely studied shapes of rib, namely, cylindrical and rectangular, are also investigated for the transverse staggered arrangement with the same optimized parameters for the comparison of thermo-hydraulic performances. Trapezoidal ribs having discontinuous rib width of 50 mm and gap width of 10 mm give the maximum thermo-hydraulic performance of 1.57 at Reynolds number of 5000. The optimized staggered trapezoidal ribs outperform the staggered cylindrical and rectangular ribs. However, staggered rectangular ribs give the highest increase in the Nusselt number and these may be preferred for application when pressure drop is not of concern.

Thermo-hydraulic performance of solar air heater having discrete D-shaped ribs as artificial roughness.

In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R2. The numerical investigation is carried out at rib radius to transverse pitch ratio (r/Pt) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (Pl /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of Pl/r, while the ratio r/Pt is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/Pt of 0.25 and Pl/r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/Pt as 0.10-0.35 and Pl/r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.

Enhancing energy harvesting performance of a flat plate solar collector through integrated carbon-based and metal-based nanofluids

Flat Plate Solar Collectors (FPSCs) have been widely employed in the production of renewable energy for a significant period. To enhance their thermal performance, the utilization of nanofluids as heat transfer fluids has emerged as a popular approach. However, many research works were only carried out with conventional metal-based nanofluids. This numerical study investigates the effects of incorporating two carbon nanotubes, namely single-walled carbon nanotube (SWCNT)/water and multi-walled carbon nanotube (MWCNT)/water, on the fluidic and thermal performance of FPSC. The Nusselt (Nu) and Stanton (St) numbers, as well as the frictional characteristics, are measured and compared to those of metal-based nanofluid of alumina (Al2O3)/water at volume concentrations up to 1%. It is found that Nu increases with a higher Reynolds number (Re) while deteriorating at a higher volume concentration. The lowest Nu was recorded for SWCNT/water in the current investigation. The Stanton number increases with a higher volume concentration and decreases with an increase of Re. Notably, the maximum value of 0.001801 is obtained for the SWCNT nanofluid. The outlet temperature decreases maximum for SWCNT/water with the increase of Re and volume concentration while the friction factor decreases with increasing Re and is independent of the type of nanofluids. Maximum thermo-hydraulic performance parameter of 1.48, 1.32 and 1.29 is achieved for SWCNT, Al2O3 and MWCNT, respectively.

Enhancement of thermal efficiency and development of Nusselt number correlation for the solar air heater collector roughened with artificial ribs for thermal applications.

The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty.

Thermal performance of solar air heater having discrete symmetrical arc rib with staggered rib roughness

This paper investigates physics of forced flow underneath the absorber plate in solar air heater (SAH) integrated with new arc geometry namely discrete symmetrical arc rib with staggered rib roughness. This article signifies the impact of roughness pitch relative to rib height (p/e) on the thermal performance of rectangular roughened SAH duct having discrete symmetrical arc rib with staggered rib (present study). Novel arc rib geometry (present study) is achieved by providing an additional gap in a significantly long continuous arc segment of existing best arc rib geometry to break the boundary layer reformation along it. Range of parameters considered for experimental run for new geometry were Reynolds number (Re) as 3000–15,000, roughness pitch relative to rib height (p/e) of 6–14, flow attack angle (α) of 30°, staggered rib pitch relative to roughness pitch (p′/p) of 0.4, number of symmetrical gap over full arc (Ng) as 6, number of additional gap in symmetrical arc elements (ng) as 5, gap width relative to rib height (g/e) as 3, rib height relative to hydraulic diameter (e/Dh) as 0.043, relative gap position (d/w) and additional gap width relative to rib height (g′/e) as 0.65 and 1 respectively. Five different roughened test plate with the variation of p/e as 6, 8, 10, 12, and 14 were tested. Optimum augmentation is perceived in Nu at p/e as 10 and for f at p/e as 8. Maximum thermo-hydraulic performance parameter (THPP) is achieved at p/e as 10 that corresponds to Re as 6000. Correlation, mathematical model, performance prediction and economic evaluation have also been done under different operation conditions.

Thermohydraulic performance augmentation in a solar air heater using a perforated circular segment vortex generator

Hybrid turbulators have been introduced as a feasible solution to improve heat transfer in fluid channels. In this study, a perforated circular segment was used as a vortex generator to enhance the heat transfer rate in an air collector duct. The effects of key parameters, including Reynolds numbers ranging from 6000 to 18,000 (four values), angles of attack from 30 to 90° (five values), and inline and staggered segment arrangements, on heat transfer, pressure loss, and thermohydraulic performance were investigated. A 3D numerical simulation using the RNG k-ε turbulence model with experimental verification was performed in this study. The results showed that the maximum thermohydraulic performance parameter was 1.3, and an attack angle of 30° provided the best performance. Strong turbulence occurred with an angle of attack of 60°, which caused a large pressure loss in comparison with the heat transfer enhancement. The maximum turbulence kinetic energy shifted from the root to the peak of a segment when the angle of attack increased. The Nusselt number and friction factor of the staggered configuration were 1.72 times and 1.88 times the corresponding values of the inline arrangement.

Designing of low cost solar air heater equipped with roughness of streamlined cross-section

In the current investigation an attempt is made to design a low cost solar air heater (SAH) using numerical simulation and exergy analysis approach. The thermo-hydraulic behaviour of SAH duct (aspect ratio = 10) with rib roughness of rectangular and symmetric half NACA 0020 (reverse orientation) cross-sections on one of its broad walls are analysed numerically. This novel design of the symmetric half NACA 0020 has been tailored to maximise heat transmission by capitalising on the benefits offered by secondary flows. For Reynolds numbers (Re) ranges from 6000 to 18000, fixed relative roughness pitch (P/e = 13), and relative roughness height (e/D = 0.06), the Nusselt number (Nu) and friction factor (f) are calculated. Ribs with NACA 0020 cross-section have higher heat transfer and lower flow friction. With NACA 0020 rib roughness, the maximum thermo-hydraulic performance parameter (THPP) is observed at Re = 6000. Contours of temperature, pressure, turbulence kinetic energy and velocity streamlines provides essential information for explanation of phenomenon in the SAH. Experimental results are used to validate the numerical outcomes. Exergy analysis is also carried out for the comparison of performance of SAH roughened with bluff (rectangular) and streamlined (reverse NACA 0020) roughness elements.

Thermohydraulic optimization of artificial roughness in photovoltaic-thermal (PVT) system using genetic algorithm

The photovoltaic-thermal system is a solution for using solar energy to produce both electric and thermal power. In the present study, artificial curved roughness is used in the collector flow channel to investigate its effect on the performance of the system. The effect of artificial roughness characteristics, working fluid type and Reynolds number on thermohydraulic performance is investigated by numerical simulation and optimization of the system. The results show that the addition of artificial roughness in laminar and turbulent flow deteriorates and enhances the thermohydraulic performance of the system, respectively; so that the maximum performance improvement is achieved at the beginning of the considered range of the turbulent flow. The maximum thermohydraulic performance is related to geometry with a roughness angle of 30°, a relative height of 0.04, and a relative pitch of 16. In addition, changing the working fluid from water to nanofluid, as well as increasing the flow rate, increases the system overall efficiency. For instance, using water-based Ag–MgO and CNT nanofluids in the Reynolds number of 10, the system overall efficiency is %64.74, %67.73, and %74.69, respectively. The results of multi-objective optimization based on genetic algorithm show that the best thermohydraulic performance, electrical and thermal efficiency are 1.203, %9.68, and %75.79, respectively, which are obtained in Reynolds number of 3537 for water-based CNT nanofluid. Also, the optimum Reynolds numbers using water and water-based Ag–MgO nanofluid are 4046 and 3936, respectively.

Solar air heater with rotating circular ribs: Hybrid CFD-ANN approach for prediction of thermo-hydraulic performance

A hybrid computational fluid dynamics-artificial neural network approach is implemented to predict the thermo-hydraulic performance factor of a solar air heater with rotating circular ribs. Effects of rib height, rib pitch, and rib rotating speed are investigated for Reynolds numbers ranging from 3800 to 18000. A total of 432 different cases are simulated using CFD. Based on these data sets, an optimized ANN model is developed to predict thermo-hydraulic performance. The optimized ANN model has an architecture of 4-17-17-1 and it has a mean squared error of 3.89 × 10−6 for the testing data sets. The maximum thermo-hydraulic performance achieved is 1.57 for rib height of 1.4 mm, rib pitch of 25 mm, rib rotating speed of 10000 rpm at Reynolds number = 3800. The generalization capacity of the optimized ANN model is tested using experimental results and it is found that ANN predictions are in agreement with CFD simulation results. A comparison of computational time is also performed and approximately 100% reduction in computational time is achieved using the optimized artificial neural network model. This research establishes that ANN can be an excellent design tool for assessing the performance of novel solar air heaters.

Sustainability and Cost Effectiveness Analysis of Staggered Jet Impingement on Solar Thermal Collector

The sustainability index, waste energy ratio and improvement potential of a staggered air jet impingement on the staggered spherical protrusions of a roughened absorber plate were derived for the present study to evaluate exergy losses and irreversibility in the system. The experimental analysis was carried out for selected parameters: relative streamwise pitch, relative spanwise pitch and relative jet diameter to hydraulic diameter ratio. The flow Reynolds number ranged from 4000–18,000. The augmentation in Nusselt number and friction factor compared to a smooth surface was 4.9 and 12.4 times, respectively. The statistical correlation developed determined the maximum thermohydraulic performance parameter and exergetic efficiency be 3.02 and 3.87%, respectively. The magnitude of the sustainability index, waste energy ratio and improvement potential was found to be 1.0347, 0.962 and 10.84, respectively, for the entire range of tested parameters. A cost analysis was also performed to evaluate the cost-effectiveness of the solar thermal system with and without turbulent promoters.

Heat Transfer Augmentation of a Solar Air Heater Using a Twisted V-Shaped Staggered Rib Over the Absorber Plate

Abstract An effort is made to study the performance of a solar air heater having the absorber surface roughened by providing staggered, twisted, and V-shaped ribs roughness. The liquid crystal thermography technique is applied to get the Nu distribution over the surface. Experimentation is done for Reynolds number ranges from 3000 to 21,000, relative roughness to pitch ratio (P/e) from 7–11 and relative staggered distance (d/e) of 2–6, for the fixed angle of attack (α), relative twist length (y/e), and relative roughness length (S/e). It is found that the maximum Nusselt number and friction factor augmentation are 3.43 and 2.57 times than that of the smooth duct. The maximum thermo-hydraulic performance (THP) value obtained is 2.69 for the P/e of 9 and d/e of 4. It can be inferred that staggered twisted V-shaped rib roughness helps to get the enhanced Nu with minimum friction penalty.

Analytical investigation on thermo hydraulic performance augmentation of triangular duct solar air heater integrated with wavy fins

ABSTRACT Present work deals with performance improvement of triangular duct solar air heater by integration of wavy fin on absorber plate. An analytical model has been developed for the investigation of design parameters such as fin pitch ratio with ranges 0.05–0.2 and fin amplitude ratio with ranges 0.025–0.125. MATLAB code is generated to solve the energy balance equations by iterative procedure. The influence of design parameters on effective thermal and thermal efficiency is presented and its influences are discussed. Increasing the fin pitch ratio decreases the thermal and thermo hydraulic efficiency drastically. The positive effect of fin amplitude ratio is observed; increasing of fin amplitude ratio improves the thermal efficiency and effective efficiency up to the critical Reynolds number. The peak thermal efficiency of 85% is observed and thermo hydraulic efficiency of 80.16% is found at fin pitch ratio of 0.05 and fin amplitude ratio of 0.125. The maximum thermo hydraulic performance enhancement is 15.7% as it compared simple conventional solar triangular duct air extractors. The design plots are developed to select the performance parameters to attain required temperature rise values.

Influence of twisted tape length on the thermal performance of a heat exchanger tube

The application of twisted tape inserts in heat exchangers allows higher heat transfer rates with a simultaneous loss of energy due to turbulence and friction. In a conventional approach, the twisted tape is placed in the entire length of the heat exchanger. The present study explores the effect of the length of the twisted tape insert at a different twist ratio (TR) for 4700 < Re < 22,800. The insert length ratio (LR) ranges from 0.25 to 1 and the TR ranges from 1.5 to 6. The maximum Nusselt number corresponds to the LR of 0.75 at a TR of 1.5. The maximum thermo-hydraulic performance is found to be 3.2 for the LR of 0.75 at a TR of 1.5.

Analysis and Implementation of Thermal Heat Exchanger Tube Performance with Helically Pierced Twisted Tape Inserts Using ANFIS Model

The present work used ANFIS, an adaptive neuro-fuzzy inference system modeling to analyze the effect of the variable parameters of helically pierced twisted tape inserts on the Nusselt number, friction factor, and thermo-hydraulic heat exchanger tube performance. The experimental data utilized for ANFIS modeling considered a diameter ratio ranging from 0.57 to 0.80, a relative pitch ratio ranging from 0.046 to 0.107, a perforation index ranging from 5% to 20% as variable twisted tape parameters and flow parameters. The Reynolds number varies from 4000 to 30000. The analysis showed that the maximum thermo-hydraulic performance was obtained at a diameter ratio of 0.65, a relative pitch ratio of 0.085, and a perforation index equal to 10%. The result predicts that the ANFIS model and experimental results are in good agreement as they have only ±0.53% deviations.

Thermo-hydraulic and exergetic performance of a cost-effective solar air heater: CFD and experimental study

An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of secondary flow strengthening the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6–1 to obtain the optimum baffle pitch for 6000 <Re < 14000. The impact of gaps at leading, trailing, and both leading and trailing apices are studied as three different configurations with the optimum Rp. A maximum thermo-hydraulic performance of 2.69 is obtained for the gap at the trailing apex. The proposed design has a higher collector efficiency, 55–70%, compared to the ribbed rectangular SAH design exhibiting 30–55%. With lower exergy losses, the present SAH design has higher exergetic efficiency (1.5%–2.2%)than ribbed rectangular SAH (0.9%–1.7%) for the range of Re studied. Further, at low Re, the present SAH design has a higher coefficient of performance, indicating that it is cost-effective than ribbed rectangular SAH designs.