Thermo-hydraulic Performance Factor Research Articles

Reducing the Cooling Energy Demand by Optimizing the Airflow Distribution in a Ventilated Roof: Numerical Study for an Existing Residential Building and Applicability Map

This work presents a study of a ventilated hollow core slab system (VHCS) that obviates the need to completely replace the slab of an existing residential building. It is assimilated to a heat exchanger to allow its effectiveness to be studied as a function of the area and airflow rate. The balance between the energy consumed by the fan and the heat evacuated by the system is also studied through the use of the thermo-hydraulic performance factor (THPF), for which a series of cases were simulated by CFD following a methodology in which a configuration is achieved by means of the sequential analysis of cases in which both the thermal effectiveness and the THPF are maximized. The configuration chosen in this study was found to benefit from high airflow rates since, although this implies an increase in fan energy consumption, the increase in heat removed is proportionally greater. It has also been found that the design of the airflow distribution through the slab is of high importance as it affects both the heat exchanged with the slab and the pressure losses. An applicability map has been developed as a function of the temperature of the space below and the air temperature at the inlet of the ventilated roof. The heat flux per unit area that the studied envelope is able to evacuate is about 20 W/m2 K.

Optimizing of heat transfer and flow characteristics within a roughened solar air heater duct with compound turbulators

AbstractThermal systems for solar air heating have been widely used in both industrial and residential contexts, and are essential for converting and recovering solar energy. Thermal performance in solar air heaters (SAHs) can be improved through the repetitive application of artificial roughness to the surfaces. This research work includes a numerical evaluation of SAH performance with artificial rough surfaces made up of combined transverse trapezoidal ribs and chamfered grooves. The ANSYS Fluent software version 2023 R1 was used to simulate SAH with varying relative roughness pitch (), relative roughness heights (), and Reynolds number (). The RNG model was chosen to forecast an enhancement in Nusselt number (), friction factor (), and thermohydraulic performance factor (TPF) for the proposed roughness. Out of multiple roughness parameters analyzed, it was determined that the compound turbulator with and , were the most effective. The TPF for this scenario was determined to be 2.12 at . Finally, a numerical based empirical correlations for and in terms of Re, , and were developed.

CFD analysis of artificially roughened solar air heater: a comparative study of C-Shape, reverse C-Shape, and reverse R-Shape roughness element

Solar Air Heater (SAH) serves as a pivotal device for converting solar radiation into heat applications. This study focuses on enhancing the performance of SAH through modifications to the absorber surface by introducing ribs as artificial roughness. A two-dimensional CFD analysis investigates the impact of C-shape, reverse C-shape, and reverse R-shape ribs on thermal and hydraulic performance within the SAH channel. RNG (k-ϵ) turbulence model is employed for numerical simulation and model accuracy is validated against established correlations and literature results. The numerical analysis involves the designing and modelling of the SAH using a constant pitch ratio (P/e) of 14.285 and a height ratio (e/D) of 0.021. The Reynolds number (Re) from 4000 to 18000 was considered for the present study. The result reveals that the present rib geometries significantly enhance heat transfer and fluid mixing, leading to substantial improvements in Nusselt number (Nu) and friction factor (f) by 2.5 to 3.3 times and 2.8 to 5.05 times respectively over smooth duct SAH. The C-shape rib configuration attains the highest Thermohydraulic Performance Factor (THPF) at approximately 2.0078 for a Re of 4000 over reverse C-shape, and reverse R-shape ribs.

Finite element based computational analysis to study the effects of baffle and fin on the performance assessment of solar collector

The present work aims to develop an ideal solar collector layout through a finite element-based parametric study. The thermohydraulic performance factor of the solar collector was investigated with the placement of baffles and fins on the absorber plate. The cross-flow, channel, and twist designs of three alternative baffle/fin configurations were parametrised, and the heat transfer throughout the collector was analysed using COMSOL Multiphysics software. The parametrised design for cross-flow was the angle of solid baffle as 30°, 35° and 40°; whereas, for channel and twist design, the distance between the fins was varied at 50, 100 and 150 mm. The simulated result manifested that channel design had highest convective heat transfer coefficient of 21–27 W m−2 K−1, followed by cross-flow and twist design. Contrarily, twist and cross-flow design had lowest pressure drops of 0.6–1.27 Pa and 0.60–1.06 Pa, respectively, while channel design showed maximum pressure loss (35–467 Pa). The average overall thermal efficiency for cross-flow, channel, and twist design was 76.16 %, 74.26 %, and 70.65 %, respectively. The average thermohydraulic performance factor for cross flow and twist design was 11.25 % and 0.48 % higher, whereas 248.22 % lower for channel design compared to flat plate collector. The performance of the cross-flow 30 design was best out of all the designs in terms of the thermohydraulic performance factor, outlet temperature, pressure drop, and flow homogeneity inside the collector. Cross-flow 30 demonstrated a minimum friction factor of 0.004, comparable to a flat plate collector and had a double heat transfer coefficient.

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.

Numerical Investigation of Reversed Flow Solar Air Heater Roughened With Circular- and Triangular-Shaped Tubes

Abstract The roughness geometry has been introduced to improve the rate of heat transfer in a solar air heater duct. In the current work, circular and triangular shape geometries are used as roughness elements in the rectangular channel to enhance the thermal performance of reversed flow solar air heater (RFSAH). The important parameters selected for the research are Reynolds number (Re = 5000–18,000 (5 values)), pitch ratio (P/e = 4–12 (5 values)), and height ratio (e/D = 0.0392–0.1571 (4 values)). A 2D-computational fluid dynamics (CFD) model was developed using ansys (fluent 2022r1), and simulation was performed using the k−ε (RNG) turbulence model and validated with one set of experimental results for smooth duct and previous research. The findings revealed that the highest value of heat transfer was augmented about 2.18 times and 2.35 times for circular and triangular roughness geometry, respectively, as compared to the smooth channel at a Reynolds number of 12,000. The thermohydraulic performance factor (TPF) is 1.58 and 1.7 at pitch ratios of 6 and 5 for circular and triangular roughness geometry respectively, at Re of 12,000.

Computational analysis of the effect of flow parameters on friction factor and thermal performance of an artificially broken arc rib solar air heater

The use of solar air heaters (SAH), which convert solar energy into heat energy, is one of the most efficient methods currently available for capturing the energy of the sun. However, because SAH have lower thermal efficiency, researchers have been concentrating on developing methods to modify the flow field to artificially boost thermal performance. In this work, a numerical investigation that focuses on a SAH that has been deliberately roughened using broken arc ribs is presented. This numerical analysis aims to determine the impact of incorporating broken arc ribs compared to smooth ones and how various roughness factors affect the friction factor and Nusselt number (Nu). The RNG k-[Formula: see text] turbulence model was used for the simulation. To solve the continuity, momentum, and energy equations, version R19.2 of Ansys FLUENT software was used. The results of the CFD study show that the average Nusselt number increases if there is a greater relative roughness pitch, and it achieves its highest value once relative roughness pitch ([Formula: see text]. The friction factor, on the other side, decreases as the Reynolds number (Re) increases, reaching its lowest value when [Formula: see text] and [Formula: see text]. Maximum value of the thermohydraulic performance factor is observed to be 1.92 when applied to the geometry that corresponds to relative roughness height ([Formula: see text], ([Formula: see text], and [Formula: see text].

Enhancing the performance of a solar air heater by employing the broken V-shaped ribs.

This work aims to enhance the performance of a solar air heater (SAH) by introducing broken V-ribs as roughness elements on the absorber plate. The unit with a conventional flat absorber plate is referred to as the "FSAH," while the unit with a broken V-rib-shaped absorber plate is called the "VSAH." The experiment was performed for three air velocities: 25 m/s, 20 m/s, and 15 m/s and the corresponding air flow rates were 0.037 kg/s, 0.031 kg/s, and 0.023 kg/s, respectively. The results showed that the maximum temperature was experienced on the absorber plate, followed by the glass plate for both SAHs. Overall, the average absorber and glass plate temperatures of the VSAH were 0.6-1.4 °C and 0.4-1.9 °C lower than those of the FSAH. Compared to the FSAH, the experimental results showed that the VSAH experienced useful power and thermal efficiency that were 16.6-19.8% and 15.7-20.4% higher, respectively, while the top surface heat losses were found to decrease by 2.1-8.1%. Due to the disrupted air paths in the VSAH, the observed pressure drop was 113.3-133.3% higher than that of the FSAH. More impotently, the thermo-hydraulic performance factor was always higher 1 and the observed values were 1.48, 1.39, and 1.24 at the va (velocity)values of 15, 20, and 25 m/s, respectively. Therefore, the proposed VSAH had an admirable thermal performance as compared to FSAH. Further, optimization through varying the roughness parameters, namely, relative blockage width (W/w), relative pitch ratio (P/e), number of baffles (n), relative blockage height (e/H), and angle of attack (β) could helped to achieve better performance.

Heat Transfer Enhancement in Laminar Pipe Flow Using Al2O3–Water Nanofluid and Twisted Tape Inserts

Abstract In this study, an attempt has been made to carry out a numerical investigation using water-based Al2O3 nanofluid, flowing through a circular tube under constant inlet temperature and constant heat flux conditions in the laminar flow regime. The water-based Al2O3 nanofluid is used in a circular plain tube first, and then, this process is repeated for the same tube fitted with twisted tape inserts of twist ratio 1.85 at Reynolds numbers ranging from 680 to 2030. For the numerical analysis, ANSYS FLUENT is used to solve three-dimensional conservation equations of mass, momentum, and energy. The simulated results indicate that when twisted tape is used, heat transfer rates increase significantly with the use of nanofluid. In the case of nanofluid with the plain tube, only 10–24% enhancement in heat transfer rate is noted. On the other hand, almost 27–45% increase in heat transfer is observed compared to that with only water when twisted tape is inserted into it. Also, the friction factor increases as the nanoparticle volume fraction increases. However, the effect on the heat transfer rate is more significant than that on the friction factor. The best thermohydraulic performance factor achieved is 2.1 using nanofluids with a 5% volume fraction of the nanoparticles at a high Reynolds number when twisted tape is also inserted.

Experimental analysis of thermal performance of SAH with impinging jet having varying length of perforated jet plate

An experimental setup of an impinging jet solar air heater (IJSAH) was developed to study its thermal and frictional characteristics. Six cases were analysed with the jet holes spanning different lengths across the jet plate. For cases 1 and 2, jet holes spanned 100% and 80% of the length of the jet plate while having jet diameter equal to 3 mm. For cases 3,4, and 5, jet holes were drilled up to 100%, 80%, and 60% of the entire length and the diameter was increased to 6 mm. For case 6, jet holes were drilled up to 100% while keeping jet diameter equal to 9 mm. For each case, variation in Nusselt number, friction factor and temperature rise of the fluid was evaluated for Reynolds number in the range 4913 to 13,103. The efficiency and thermo-hydraulic performance factor with each case were compared. It was concluded that IJSAH with reduced length of drilled section (case 5) developed similar performance to IJSAH having completely perforated jet plate (case 1) while developing significantly lower friction factor. The temperature rise of the fluid and the friction factor developed for case 5 were around 10% and 40% lower than case 1, respectively.

Design, fabrication and investigations of natural convection step serrated fin plate integrated trough array low-cost collector for solar air heating: An application to agricultural crop drying

This paper establishes the design modification procedure for flat plate solar thermal collector and investigates the performance by incorporating a specially designed low-cost Step Serrated Fin Plate Integrated Trough Array (SSFPT) on the sun-facing side of the collector. The idea of integrating trough profile on the step serration is for concentrating heat radiations with a latent heat storing copper pipe at its focal point filled with phase change material, giving tremendous improvements and high thermal and exergy efficiencies. Also, the step serrated fins increase air stagnation and heat acquisition. The performance of the SSFPT collector solar air heater is experimentally investigated and compared with the conventional Flat Plate Collector Solar Air Heater (FPC SAH) of the same collector area by natural convection. The average outlet temperature of SSFPT collector SAH and FPC SAH varies from 44.5 to 74.5 °C and 38.0–48.2 °C and the average stagnation temperature lies between 43.1 and 74.4 °C and 38.5–48.5 °C. The maximum thermal and exergy efficiency of SSFPT SAH is 66.32 % and 23.06 %. This proposed collector achieves a maximum Nusselt number of ∼ 7.11 at Rayleigh number ∼ 441.5 × 103 and a better augmenting effect with a thermo-hydraulic performance factor of 1.4 after 4 h of operational time. The thorough economic analysis yields cost per kWh of the SSFPT collector is 0.10$ which is 0.18$ lesser than conventional FPC SAH.

Solar air heater performance enhancement with differently shaped miniature combined with dimple shaped roughness: CFD and experimental analysis

A numerical study was carried out in a solar air heater (SAH) using different shapes of miniature (V, arc and transverse broken-miniature) combined with dimples on an absorber panel to improve heat transfer. For an experimental and simulation study using ANSYS (Fluent), a dimple with a V-miniature rib was fabricated on a plate (absorber) as a roughness element. By providing the angle of attack (α), relative long way (RLL) length (l/d), relative height (roughness) and relative wire lengths (w/Dh) ranging from 45 to 75°, 15–25, 0.024–0.036 and 0.14–0.21 respectively. The thermohydraulic performance (THP) factor of the proposed roughness was also investigated at Reynolds numbers (Re) ranging from 5000 to 20000. Results of average Nusselt number, turbulent kinetic energy (TKE), fluid flow characteristics and temperature are included to analyse the comparative merits of each dimple with miniature arrangements. The results revealed that among dimples with different miniatures, 90° transverse broken-miniature with dimple shows best thermohydraulic performance at Re below 10,000 while a dimple with V-miniature at an angle of attack (α) 45° shows the highest thermohydraulic performance at Re above 8750. It was found that THP achieved a maximum value of 1.63 at α = 45°, l/d = 20 and w/Dh = 0.18 at Reynolds number 12,500 for the dimple with a V-miniature rib.

ANN model for prediction of thermo-hydraulic performance of a solar air heater with vertical cylindrical ribs

A hybrid computational fluid dynamics-artificial neural network approach is applied to predict the thermo-hydraulic performance factor (THPF) of a solar air heater with vertical cylindrical ribs. 3-D CFD analysis considering effects of rib height, rib diameter, rib pitches are simulated for Re ranging 5000–24000. A total of 504 data sets for different cases are generated using CFD. Based on these data sets, an optimized ANN model is developed to predict the thermo-hydraulic performance. The optimized ANN model has an architecture of 5-25-1 and the mean squared error for this ANN model is 0.000051 for the testing data sets. The maximum THPF value achieved is 1.43 for rib height of 3.5 mm, rib diameter of 3 mm, rib transverse pitch of 20 mm and relative roughness pitch of 10 at Re = 8000. Global sensitivity analysis is also performed based on SHAP (SHapley Additive exPlanations) for the ANN model—Reynolds number is observed to be the most influencing factor with mean absolute SHAP value of 0.031 in predicting THPF along with transverse pitch which has SHAP value very close to Re. Computational CPU time comparison is also performed and approximately 100% reduction is achieved using the optimized ANN model. This research proposed a novel approach that could be successfully implemented in assessing thermal performance of solar-thermal collector systems.

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.

Determination of the heat transfer coefficient by convection, according to shape of the baffles (solar air collector)

This experimental study and mathematical modelling aim to improve the heat transfer by convection in different cases of transversal baffles inside a duct of a solar air collector. The study enabled us to formulate a mathematical equation of the heat transfer coefficient as a function of pressure drop and the mass flow rates. This mathematical model gave results that are close to the actual results in different inclination angles of the baffles (45°, 90°, 135°, and mixed between 135°and 45°). Through these results, it is found that the best heat transfer coefficient by convection was in the mode where = 90° and in the mixed mode. It was also noticed that the pressure drop in the mixed mode was smaller. With respect to the thermo-hydraulic performance factor (THPF), the case =45° was retained as the best case.

Two‐dimensional‐numerical investigation on the influence of first rib distance from the entrance of channel on Nusselt number and pressure drop

AbstractEnhancing the heat transfer coefficient in heat sinks can be achieved by surface modification techniques. Although the addition of ribs increases heat transfer capacity, it also increases pressure drop, lowering the channel's thermohydraulic performance (THP) factor. Rib research began a decade ago, with the majority of studies focusing on new rib designs or factors such as relative roughness pitch, relative roughness height, channel width, and channel height (geometric optimization) to improve THP. The goal of this study is to investigate the influence of the positioning of the first rib from the channel entrance on the Nusselt number, pressure drop, and THP factor with a simple design that could be manufactured easily. Three distinct rib designs are evaluated with rib positioning from the channel entrance, rib thickness, pitch, and Reynolds number as the parameters. It was found that the fluid starts settling up at the ribs as the ribs are moved closer to the channel entry point, thus increasing the pressure drop and reducing the fluid velocity. For the proposed design and dimensions, the Nusselt number increases by 3%–5%, and the pressure drop lowers by 4%–14% when the first rib is placed away from the channel entrance.

Heat Dissipation by Streams of Bifurcated Tubes

There is a need for solutions to provide sufficient cooling from power devices, which produce large amounts of heat. This paper focuses on the influence of design of bifurcated fluid streams to dissipate heat. In this study, a single Y-tubes, a double Y-tubes, and an X-tubes designs are studied numerically under space constraints. For a comprehensive and in-depth performance analysis, both heat dissipation and hydraulic performances are analyzed. The distributions of velocity and temperature in the fluid streams is simulated, also the flow resistances and dissipated heat are calculated. Based on the results obtained, a thermo-hydraulic performance factor is introduced for the designs under study. In addition, the accumulation of undesired substances on the wall surface (fouling) that may influence the heat exchanging capability is studied.

Thermal performance evaluation of a solar air heater with rotating turbulators

A novel concept of rotating circular ribs as artificial roughness has been employed within a two-dimensional rectangular duct to understand their effects on heat transfer and air flow characteristics using CFD. The effects of design parameters such as roughness height, roughness pitch, relative roughness height, relative roughness pitch, and rotational speed of the circular rib are simulated for Reynolds number ranging from 3800 to 18,000 under solar air heater boundary conditions. 54% increase in Nusselt number is observed for rib height of 1.4 mm, pitch of 10 mm, circular rib rotation of 10000 rpm at Re = 3800 as compared with fixed ribs. The maximum thermo-hydraulic performance factor of 1.57 is achieved at Reynolds number of 3800 for the circular ribs—relative roughness height of 0.042 and relative roughness pitch of 25— rotating counter to flow with 10000 rpm. For a given rotational speed of the circular ribs, thermo-hydraulic performance factor decreases at higher flow velocities. Significant increase in Nusselt number with rotating ribs as artificial roughness establishes the potential of this novel approach for solar air heaters.

Performance enhancement of a baffle-type solar heat collector through CFD simulation study

The application of solar energy conversion has been extensively utilized as an alternative energy source to generate heat. This approach would be a step towards sustainable energy development particularly in the manufacturing industry with energy-intensive process. In this paper, thermal enhancement on the key component of a solar energy device – solar heat collector (SHC), has been evaluated by proposing a baffle-type SHC with various geometric configuration in the air passage namely longitudinal baffle and transversal baffle. The performance of SHC is evaluated in term of efficiency, temperature distribution, airflow pattern and pressure drop across the collector outlet through Computational Fluid Dynamic (CFD) investigation. It was observed that maximum collector efficiency was achieved in the Longitudinal-SHC (L-SHC), with a value of 46.2 % followed by Transversal-SHC (T-SHC) and without baffles. Maximum drying temperature at the collector outlet was 332.43 K for L-SHC, showing temperature rise of 0.35 % and 4.21 % from T-SHC and without baffles, respectively. The velocity vector indicated that turbulence flow was created in the T-SHC which consequently improved the heat transfer. Whereas in L-SHC, enhancement was achieved through the prolonged heating time in the passage. Considering the thermo-hydraulic performance factor evaluated, these enhancement features had diminished the effect of pressure drop.

Computational fluid dynamics based numerical study to determine the performance of triangular solar air heater duct having perforated baffles in V-down pattern mounted underneath absorber plate

In the current analysis, the effect of perforated baffles in V-down pattern as artificial roughness on the thermal and hydraulic response of a solar air heater having equilateral triangular passage has been examined. A thorough numerical investigation has been done using ANSYS FLUENT-19.0. Effect of change in roughness parameters, viz., baffle height (e) and open area ratio (β) on thermo-hydraulic performance has been explored. Flow Reynolds number is systematically varied. Study reveals that upon varying the baffle height from 5 mm to 11 mm and open area ratio from 20% to 29%, maximum heat transfer rate is attained at e = 9 mm and β = 20%, respectively. Axial Velocity and Turbulence Kinetic Energy have been plotted for clear view of change in variables. Also, the correlations have been developed for Nusselt number and Friction factor. The thermo-hydraulic performance factor of proposed perforated baffle geometry has been observed to be 2.54 at e = 9 mm and β = 20%. Performance of the SAH with suggested roughness is found to be advantageous than other type of roughness elements studied in recent times.