Solar Air Heater Duct Research Articles

Effect of various configurations of permeable ribs on thermal performance of solar air heater as source of clean energy

Solar air heater (SAH) ducts have poor thermal efficiency, which can be improved by introducing ribs. This study is focused on the numerical investigation of heat transfer and pressure drop of a permissible ribbed SAH duct. The flow domains for three different permissible rib geometries, i.e. horizontal slit, 30° inclined slit and 30° inclined split slit, were analysed. Different turbulence models based on two equations were compared with the experimental results for the solid rib model. The realisable, k-ε turbulence model obtained the less error of enhancement heat transfer when compared with the experimental work for solid rib. An increase in heat transfer was noted for permissible rib geometry due to secondary vortices. An increase of 12.4%, 7.4% and 1.6% was observed in average heat transfer for horizontal, 30° inclined slit and 30° inclined split slit configurations for the Reynolds number value of 12800, respectively. Inclined split slit gave the maximum friction factor when compared to other permissible rib cases. An improvement of 14%, 8.6% and 3.3% was observed in thermal performance for 30° inclined split, 30° inclined and horizontal slit at the Reynolds number value of 12800.

Exergy-Based Thermo-Hydraulic Performance of Roughened Absorber in Solar Air Heater Duct

This paper presents the thermo-hydraulic performance of small conical ribs on the absorber plate of a solar energy air heater (SAH) using exergy analysis. Application of conical protrusion ribs on the absorber is an attractive solution for enhancing the thermal performance of a SAH. However, these ribs are also responsible for high friction losses and increased fan power consumption caused by the turbulent air flow. To optimize the rib design, it is vital to consider both thermal and hydraulic performance at the same time. The SAH was assessed using an analytic method which predicts the exergy efficiency under operating parameters (e.g., Reynolds number, solar insolation and temperature increase parameter). The following geometric quantities of ribs were evaluated for optimum exergy efficiency: the relative rib height (e/D), which was in the range between 0.200 and 0.044, and the relative rib pitch (p/e), which was in the range between 6 and 12. The combination of a relative rib height of 0.044 and relative rib pitch of 10 exhibits the highest exergy efficiency of 0.0202. The optimization of the rib geometric quantities parameters was performed by considering the temperature increase parameter, aiming to achieve maximum exergy efficiency. The combination of rib parameters e/D = 0.044 and p/e = 10 are noted to yield best performance when operating at a temperature increase parameter above 0.0141 K∙m2/W.

A critical review on different roughness geometries and their effect on heat transfer and friction factor.

Solar air heater (SAH) is simple and the greatest effective approach to utilize and convert solar energy into thermal energy for heating utilizations. The employment of artificial roughness under side of the observer surface is the key technique for augmenting heat transfer with minimal friction factor penalty. Current paper summarized different kinds of artificial roughness used in SAH, which augments its performance. In this review article, 96 research papers are cited, which provide detailed information about the effect of different geometrical parameters on heat transfer and friction factor. This paper also brings the information about the optimum roughness parameters and heat transfer and friction factor correlation developed by different investigators in tabular form. Optimum roughness parameters and empirical correlations are used for comparative analysis of heat transfer, friction factor, and thermo-hydraulic performance parameter (THPP) of different roughness geometries. The best performing roughness geometry is reported on the basis of comparative analysis. Mathematical model is developed for predicting the thermal efficiency (ηth) of roughened SAH duct.

CFD based heat transfer correlation for ribbed solar air heater

To assess the influence of artificial roughness on heat transfer in solar air heater ducting, a variety of alternative approaches have been used to investigate the problem. In this article, an absorber plate of SAH attached with rib roughness is numerically analysed. Adding ribs to a solar air heater duct's surface is an excellent means of increasing the performance of the system. In this article a numerical analysis is carried out to investigate the turbulent air-flow for various rib arrangements. This study aims to find effect of pitch of rib roughness element on the heat transfer property of solar air heater. The studied parameters are rib height and pitch for moderate range of Reynolds number. Highest enhancement in Nusselt number was determined. A new heat transfer correlation is developed in this article for the rib roughened solar air heater. A linear stepwise regression algorithm is used to reduce the resulting data to correlation. The developed correlation accurately predicts all Nusselt number data to within ± 6% relative absolute deviation.

Selection of optimal parameters using PSI approach of a dimpled-V pattern roughened solar heat collector

The present article examines the selection of parameters of dimpled rib with combined V-type rough surface solar air heater (SAH) duct that shows maximum performance. One side of article carried experimental study of dimpled rib with combined V-type rough surface for heat transfer enhancement of SAH duct, whereas, on other side Preference selection index (PSI) technique has been employed on different enactment criterions to attain the preeminent set of elements which are be responsible for the premier thermal performance of SAH. The finest set of dimpled rib with combined V-type rib parameters attained by offered technique is, rib width ratio of 5.0, print diameter of 1.0, relative pitch of 9.0, flow attack angle of 55° and Reynolds number (Re) of 17,000.

CFD analysis of heat transfer performance of ribbed solar air heater

Adding ribs to a solar air heater duct's surface is an excellent means of increasing the efficiency of the system. In this article, a SAH with circular and semi-circular rib roughness is numerically analysed. This study is carried out in ANSYS Fluent v16 using the RNG k-ε turbulence model. For momentum and energy equations, the second-order upwind scheme is selected. The SIMPLE algorithm is used to couple velocity–pressure. To accurately predict different parameters, a low convergence criterion is chosen for all residuals. Present investigation is done for different e/D values and Re ranging from 3800 to 18,000 in the turbulent flow region. The result showed that the semi-circular rib gives the highest TEF. The TEF has been found to have a maximum value of 1.76 at Reynolds number 15,000.

CFD analysis of fluid flow and heat transfer in solar air heater having sinusoidal roughness

CFD analysis of fluid flow and heat transfer in solar air heater (SAH) having sinusoidal (sine square function) rib roughness provided underneath the absorber plate facing towards the fluid flow inside the SAH duct has been carried out in the range of parameters, i.e., roughness pitch (P) 10 mm-18 mm, roughness height (e) 0.7 mm-1.2 mm and Reynolds number (Re) 4,000-15,000. In order to find the optimal thermohydraulic performance (THP), a parameter indicating the maximum heat transfer at the cost of minimum pumping power is required. The fine and uniform mesh has been used to resolve the viscous sublayer. Vortex (circulation) formed near the wall creates local turbulence and acts as a heat exchanger between the hot absorber surface and the main flow. The optimal value of THP (ɳ) has been found to be 2.03 which has been compared with other roughness models (triangular and rectangular) and found to be the maximum among the three models.

IMPACT OF CHANGING ABSORBER SHAPE ON AN AIR FLOW BEHAVIOR IN A THERMO-SOLAR CONVERTER

In this paper, a two-dimensional numerical study of heat exchange by forced convection of an incompressible laminar flow in a solar air heater duct (SAH), which is equipped with a shoulder attached to the absorber, was performed. The impact of three locations of this shoulder and their three heights on friction losses, as well as the drag coefficient, the variations of velocity, and temperature at the exit section of the SAH, were analyzed for a volume flow rate in the range [20-80 m3/h.]. The results obtained numerically prove that the insertion of a shoulder on the absorber improves the heat transfer and the dynamics of the flow very significantly. An average temperature difference (inlet-outlet) of the collector of 23.51 °C at 29.94 °C and 50.64 °C at 67.53 °C is acquired respectively for the high and the low flow rates. This paper also showed that the height of the shoulder used can ensure an acceleration of the flow with an axial variation of the order of 1.25 up to 2.5 times (> twice) compared with the simple case.

Thermal performance analysis of apex-up discrete arc ribs solar air heater-an experimental study

The most efficient way to enhance the heat transfer performance of the Solar Air Heater (Sol-AHs) duct is by providing an artificial roughened plate. The present study compared the Thermo-hydraulic performance of a novel apex-up discrete arc rib absorber plate Solar Air Heaters (Sol-AHs) with existing best downstream flow ribs geometries. Furthermore, the parameters air flow angle of attack (α) of 30°, 45° and 60° and Reynolds number of 3000–14000 are examined by considering relative gap width (g/e) as 4, rib height to hydraulic diameter (e/Dh) as 0.045, a ratio of rib pitch to rib element diameter as 10, number of gaps as three. The results show that the new apex-up discrete arc rib absorber plates have superior thermal performance than the existing best apex-down ribs geometries. Maximum augmentation in Nu achieves an α of 30° that is 2.92 times the smooth plate. Thermo-hydraulic performance (THPP) is observed to be optimum at Re of 10000 and α of 30°. Correlation for heat transfer and roughness function obtained for varying air flow angle of attack.

Thermal–hydraulic analysis of a solar air heater fitted with a wire-roughened absorber plate

This study is to evaluate heat transmission and friction in a rectangular solar air heater with a V-shaped wire rib roughness on the absorber plate that operates in fully formed turbulent flow. Additionally, studies are performed to generate prediction equations for the average friction factor, Stanton number, and efficiency index. The Reynolds number [Formula: see text]–[Formula: see text], angle of attack [Formula: see text]20[Formula: see text]–90[Formula: see text]), relative roughness pitch [Formula: see text]–[Formula: see text], relative roughness height [Formula: see text]–[Formula: see text], and the aspect ratio [Formula: see text]–[Formula: see text] was varied. The efficiency index [Formula: see text] is commonly employed as a thermo-hydraulic performance metric. It is computed as [Formula: see text]. The wire roughness and airflow parameters [Formula: see text] are optimized to maximize heat transfer while retaining minimal friction losses. On the basis of resemblance criteria, average Stanton numbers, average Nusselt numbers, and even average friction factors are derived. The results are compared to those obtained with a smooth absorber duct under similar airflow circumstances in order to assess the increase in heat transfer coefficient and friction factor. The [Formula: see text], and [Formula: see text] have a significant influence on thermo–hydraulic performance, according to these studies. With [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], the optimal configuration geometry for wire roughness and solar air heater duct is identified.

A Review on Heat Transfer Enhancement of Solar Air Heater Using Various Artificial Roughed Geometries

Solar air heater acts as one of the important components in utilization of solar energy. The air heater absorbs the irradiance and converts it into heat energy at the absorbing surface. The thermal energy is further use in heating flowing air through the duct. Solar air heaters are cost effective as well as simple in design. Solar air heater can be used in space heating, timber seasoning and agricultural drying. In spite of all these advantages the solar air heater has certain challenges such as the air has low heat transfer coefficient. The heat transfer rate from the heated absorber surface to the air is low. Hence in order to enhance the heat transfer coefficient the surface area either increases or the flow made to be turbulent. In order to do so the artificial roughened element must be incorporated on the heated surface. The use of artificial roughness is considered as an effective technique to enhance the heat transfer rate of fluid flowing through the duct of solar air heater. The heat transfer and friction characteristics of number of roughness geometries incorporated solar air heater have been investigated. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heater in order to improve thermal and thermo hydraulic performance of solar air heater ducts.

Experimental Investigation of Local Heat Transfer Measurement Having Inclined Discrete Ribs of Solar Air Heater Duct Using LCT Technique

Abstract The steady-state experiment using liquid crystal thermography has been conducted for the analysis of Nusselt number distribution over the absorber surface of solar air heater (SAH) duct having a gap with the staggered arrangement in inclined rib geometry to recuperate its thermal performance. The heat transfer experiment is performed with uniform heat flux and thermo-chromic liquid crystal (TLC) is utilized to show the temperature distribution profile over the ribbed surfaces of the rectangular duct of aspect ratio of 5. The colored pattern image of TLCs was acquired using a 3CCD (charged couple device) camera and exported to a Tagged Image File Format (TIFF) file format using frame grabbing SOFTWARE SAPERALT which was further processed to get hue, saturation, intensity (HSI) values. The flow parameters considered in this present investigation are Re, d/W, and g/e varied from 4000 − 12,500, 0.15 − 0.45, and 1 − 4, respectively. Experiments has been performed with fixed P/e, r/e, p′/P, α, and e/Dh of 10, 2, 0.6, 60 deg, and 0.0303, respectively. The influence of relative gap position and relative gap width on flow pattern has been analyzed. The maximum augmentation in Nu and f over the smooth duct was obtained as 4.01 and 4.28 times, respectively, at the optimum value of d/W = 0.35 and g/e = 2 under similar flow conditions. The maximum value of THPP obtained at d/W and g/e of 0.35 and 2, respectively, and Reynolds number of 12,445.

Enhanced Solar Air Heaters For Crop Drying

Solar air heaters are placed on farms to provide heat for the drying of grain and crop harvesting and harvesting. The results of the thermal study showed that solar air heaters are capable of providing a sufficient increase in air temperature under the majority of crop drying circumstances studied. The restricted thermal capacity of air, as well as the low heat transfer coefficient between the absorber plate and the air flow via the ducting system, both contribute to the overall thermal efficiency of solar air heaters. Solar air heaters must be more efficient in order to be more affordable. This may be accomplished by increasing the heat transfer coefficient between the absorber plate and the air flow passing through the duct. More heat transfer coefficients can be increased by using either active or passive approaches. In most situations, it may be cost-effective to use solar air heaters and incorporate artificial roughness on the absorber plate. The rate of heat transmission from the solar air heater’s duct to the fluid flow may be increased by creating artificial roughness on the surface of the duct. The study focused on several roughness element geometries for solar air heater ducts, and the results indicated that there is a link between the two. This paper attempts to find ways to artificially increase the heat transfer capacity of solar air heaters’ ducts by using element geometries which have been utilised in solar air heaters’ heat transfer devices.

Enhanced Solar Air Heaters for Crop Drying

Solar air heaters are placed on farms to provide heat for the drying of grain and crop harvesting and harvesting. The results of the thermal study showed that solar air heaters are capable of providing a sufficient increase in air temperature under the majority of crop drying circumstances studied. The restricted thermal capacity of air, as well as the low heat transfer coefficient between the absorber plate and the air flow via the ducting system, both contribute to the overall thermal efficiency of solar air heaters. Solar air heaters must be more efficient in order to be more affordable. This may be accomplished by increasing the heat transfer coefficient between the absorber plate and the air flow passing through the duct. More heat transfer coefficients can be increased by using either active or passive approaches. In most situations, it may be cost-effective to use solar air heaters and incorporate artificial roughness on the absorber plate. The rate of heat transmission from the solar air heater's duct to the fluid flow may be increased by creating artificial roughness on the surface of the duct. The study focused on several roughness element geometries for solar air heater ducts, and the results indicated that there is a link between the two. This paper attempts to find ways to artificially increase the heat transfer capacity of solar air heaters' ducts by using element geometries which have been utilised in solar air heaters' heat transfer devices.

Comprehensive thermo-fluid analysis of staggered rib arc roughness in single pass solar air heater duct

ABSTRACT The present study is carried out to determine the effect of symmetric arc roughness with staggered elements used in solar air heater ducts. The study of arc roughness with staggered elements available in the literature lacks the study of a number of gaps, gap width, staggered pitch, and staggered length in Nusselt number and friction factor evaluation. The studied parameters are number of gaps (Ng ) as 2–5, relative gap width (g/e) as 0.5–2.0, relative staggered pitch (p’/p) as 0.2–0.8, relative staggered length (r/e) as 1.5–4.5, relative roughness height (e/Dh ) as 0.045, arc angle (α) as 30° and relative roughness pitch (p/e) as 10 for Reynolds number (Re) range 3000–14000. Thirteen roughened plates have been evaluated. The highest enhancement in Nusselt number and friction factor recorded is 3.23 and 4.01 times smooth duct, and highest thermohydraulic performance (THP) reported is 2.34. The performance of investigated roughness is compared with the existing best arc roughness geometry.

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.

Experimental study on thermo-hydraulic performance of a solar air heater with rectangular perforated duct inserts

This paper examines the results of experiments conducted on a glazed solar air heater duct which is modified with an additional rectangular duct insert having perforation on its top surface. This modified rectangular duct of varying height is designed to split the incoming air into the absorber. This is presumed to create a pressure difference above and below the perforated surface that will enhance the convective heat transfer due to the cross-flow effect. It is observed from the experiments that the drop in pressure along the absorber passage decreases with an increase in the height, increase in hole diameter, and the number of rows of the hole. It is established from the experiments that thermal efficiency is found to be maximum for the height ratio (h/H) of 0.66 when compared to height ratios of 0.50 and 0.83, perforated duct inserts. Further, by varying the hole diameter ratio and the number of rows, it is noted that two rows of holes with hole diameter ratio of 0.096 configuration gives the maximum thermal efficiency of 84.8% and thermo-hydraulic efficiency of 81.06%.

Factors influencing the performance of solar air heater (SAH) having artificial coarseness: a review

A review of studies focused on promoting the rate of heat transfer with the help of an optimum rise in friction factor, by offering a simulated irregularity to the interior surface of the absorber plate of SAH, is expressed. In this article an effort has been made to explore different coarseness configurations as used by number of researchers to boost the SAH heat transfer rate. Furthermore, different correlations developed by researchers for Nusselt number and friction factor are also presented. On the basis of these correlations, thermohydraulic performance variable was calculated and attributed for various coarseness configurations. Friction factor and Colburn factor of various coarseness configurations have also been compared and presented. This review focused on use of different coarseness configurations with different coarseness parameter and flow parameter is deeply discussed from which future researchers can easily identify that which coarseness is to be used for designing SAH duct for the better augmentation of heat transfer and friction factor. It also helps the researchers to determine the optimum value of coarseness parameter so that the SAH works efficiently and effectively.

Multi objective optimization of cylindrical shape roughness parameters in a solar air heater

Roughening the absorber plate of a solar air heater is a convenient technique to increase the rate of heat transfer. This study aimed to investigate the effect of discrete cylindrical shape roughness elements on the heat transfer and flow characteristics of a square duct solar air heater using Computational Fluid Dynamics (CFD) simulations. A multi objective optimization algorithm was applied to find the optimum values of four roughness parameters including the roughness diameter (d), height (e), longitudinal pitch (L), and transverse pitch (S). The objectives of the optimization were maximizing the Nusselt number (Nu) and minimizing the friction factor (f). The optimization procedure includes designing of experiments, generating response surfaces, and determining optimum roughness parameters. The optimal space filling design (OSFD) of experiment method was employed to investigate the effect of roughness parameters on the Nusselt number and friction factor with a minimum number of numerical experiments. Once the designed numerical experiments were performed, the Kriging response surface method was used to express the relationships between the Nusselt number and friction factor with the roughness parameters. Then, the non-dominated sorting genetic algorithm II (NSGA II) was applied to determine the optimum roughness parameters. The optimum values of roughness diameter, height, longitudinal pitch, and transverse pitch relative to the channel height (H) were found to be d/H = 0.055, e/H = 0.053, L/H = 0.192, and S/H = 0.158, respectively which yielded a thermo hydraulic performance parameter of 1.20.

3D simulation and parametric optimization of a solar air heater with a novel staggered cuboid baffles

Thermal performance enhancement of solar air heaters is critical for efficient utilization of energy. In the present work, a numerical study and parametric optimization of turbulent convective heat transfer in a solar air heater duct with novel staggered cuboid baffles placed on the absorber plate are investigated. The heat transfer and pressure loss characteristics are analyzed, and an optimization procedure based on the Taguchi experimental design method is used to obtain the baffle's optimum geometry and arrangement. The numerical results reveal that the proposed optimum design performs better than the existing ones. It is also indicated that the relative baffle height (c/H) and relative baffle pitch (s/H) are the most influential parameters on the efficiency and thermo-hydraulic performance factor. Also, the thermo-hydraulic performance factor of the optimum baffled solar air heater is 3.43, 2.80 and 2.38 at Reynolds numbers 5080, 7620 and 10160, respectively. Depending on the Reynolds number, the thermo-hydraulic performance factor of the proposed baffled is up to 17.5% better compared with the performance of the best design reported in the literature.