Rectangular Solar Air Heater Duct Research Articles

Effect of artificial coarseness on the performance of rectangular solar air heater duct: a comparative study

Effect of artificial coarseness on the performance of rectangular solar air heater duct: a comparative study

Experimental Assessment of Thermohydraulic Performance of a Rectangular Solar Air Heater Duct Using Twisted V-Shaped Staggered Ribs

AbstractThe present experimental effort aims to determine the thermohydraulic performance of a rectangular solar air heater duct with V-shaped ribs staggered over the absorber plate. The performance test is conducted with variable roughness constraints, including relative roughness pitch (P/e) values between 7 and 11, relative staggered distance (d/e) values between 2 and 6, and relative arm length of twisted V-rib (S/e) values between 4.39 and 10.26, and flow Reynolds number values between 3000 and 21,000. The method of liquid crystal thermography is used to observe the dispersion of the Nusselt number over the roughened absorber surface. The maximum Nusselt number and friction factor enhancement ratio for roughened surfaces is determined to be 3.43 and 2.57 times that of a smooth plate, respectively. The parameters of rib configurations are adjusted based on the achieving greatest thermohydraulic performance (THP) index, which corresponds to P/e of 9, d/e of 4, and S/e of 6.15, yielding an optimum thermohydraulic performance measure of 2.69.

A detailed review on research, technology, configurations and application of wire ribs as artificial roughness in rectangular solar air heater duct

Use of artificial roughness in the duct of solar air heater (SAH) has been an interesting area of research during the last few decades. In present review article a holistic view about application of circular shape wire ribs as roughness element and its different geometry on the absorber plate of SAH duct for performance enhancement has been done. This article, reported in details numerous experimental as well as analytical studies for rib roughened SAHs which have been carried out by different researchers positively. Correlations for heat transfer and friction factor, developed by various investigators for different artificially roughened solar air heaters (SAHs) geometry have been reported in chronological order and in well tabulated form. The roughness and operating parameters into which investigators have obtained their maximum performances of SAHs have also been presented separately in the table. Effects of various rib roughness parameters on heat transfer and fluid flow process are also discussed in details.

Thermal enhancement study of a transverse inverted-T shaped ribbed solar air heater

In the present study, the heat transfers and flow fields analysis in solar air heater duct having of transverse inverted-T shaped ribs is performed. The significant outcomes are presented in terms of Nusselt number, friction factor, thermal enhancement factor, and visualization of different fluid properties for the solar air heater (SAH). The computational exercise is done by considering various non-dimensional parameters like Reynolds number (Re), relative roughness pitch (P/e), and relative roughness height (e/Dh) for the test to enhance the rate of heat transfer through the rectangular SAH duct. The relative roughness pitch and Reynolds number are varied from 7.14 to 17.86 and 3800 to 18,000 respectively, considering a fixed value of relative roughness height of 0.042. A two-dimensional computational domain is selected for the study where an absorber plate made up of aluminum is subjected to a constant and uniform heat flux of 1000 W/m2. Among the various turbulence models, the RNG k-ɛ model with enhanced wall treatment is accepted as the most appropriate model to simulate the governing eqs. A Thermal enhancement factor of 1.87 is obtained as a result of enhancement in heat transfer for the SAH with an inverted T-shaped rib roughened absorber plate. The correlations are obtained for the Nusselt number and friction factor as a function of Reynolds number and relative roughness pitch by carrying out a non-linear regression analysis.

A Review on the Influence of Provision of Artificial Roughness on Thermal Performance of a Rectangular Solar Air Heater Duct

A Review on the Influence of Provision of Artificial Roughness on Thermal Performance of a Rectangular Solar Air Heater Duct

Heat transfer and friction in rectangular solar air heater duct having spherical and inclined rib protrusions as roughness on absorber plate

ABSTRACTIn this work, an experimental investigation on heat and fluid flow characteristics of artificially roughened solar air heater duct has been carried out. The roughness and operating parameters covered a range of Reynolds number (Re) from 2000 to 20000, relative roughness pitch (P/e) from 15 to 30, relative rib length (r/g) from 0.4 to 1.0, and relative rib pitch (Pr/P) from 0.2 to 0.8. Other parameters, i.e., relative roughness height (e/D), angle of attack (α), and relative roughness gap are kept constant. Results show that the considerable enhancement in Nusselt number and Thermo-hydraulic performance has been obtained with an increase in friction factor using roughened surface.

Numerical study on thermal hydraulic performance improvement in solar air heater duct with semi ellipse shaped obstacles

This paper presents numerical study on heat transfer and friction characteristics in rectangular solar air heater duct with semi elliptical shape obstacles. 3-D simulations have been conducted using Renormalization-group k-ε turbulence model. Obstacles are placed on the absorber plate in V-down shape at different angle of attack (α), ranging from 30° to 90°. Two different arrangements of obstacles namely; inline and staggered arrangements have been investigated. Four different values of Reynolds number, ranging from 6000 to 18,000 have been considered to determine the values of Nusselt number and friction factor. Angle of attack (α) and obstacles arrangement significantly affect the Nusselt number and friction factor. In staggered arrangement, maximum enhancement in Nusselt number and friction factor have been observed 2.05 and 6.93, respectively, at an angle of attack (α) of 75° and corresponding enhancement in case of inline arrangement are found as 1.73 and 6.12, respectively. The maximum enhancement in Nusselt number at 75° angle of attack is due to combined effect of high turbulence and lateral movement of air flow. Thermohydraulic performance has also been determined which shows staggered arrangement are more superior than inline arrangement for all values of angle of attack (α) investigated in present study.

Experimental investigation of thermo hydraulic performance due to angle of attack in solar air heater duct equipped with V-shaped perforated blockages

An experimental investigation has been performed to study the effect on thermo hydraulic performance parameter of V–shaped perforated blockages attached on one broad heated wall of a rectangular solar air heater duct. The rectangular duct was equipped with V–shaped perforated blockages having aspect ratio of 12. The geometrical parameters of blockage were taken as relative blockages height value of 0.8, relative pitch ratio value of 8, open area ratio value of 20%. An angle of attack was varied from 30° to 75°. The experiment encompassed with Reynolds number from 2,000 to 20,000. Experimental data has been collected to calculate Nusselt number, friction factor and thermo–hydraulic performance parameter. It was observed that there was a significant effect on Nusselt number, friction factor and thermo hydraulic performance parameter due to angle of attack.

Effect of circularity of perforation holes in V-shaped blockages on heat transfer and friction characteristics of rectangular solar air heater duct

The effect of non-circular perforation holes in term of circularity of V-shaped blockages attached to one heated wall of a rectangular duct of solar air heater. Five different hole shapes ranging from circular to square to rectangular in the circularity range of 1–0.6 have been used with varying relative pitch of 4–12, relative blockage height of 0.4–1.0, open area ratio of 5–25% and angle of attack of 30–75° and Reynolds number of flow was varied between 2000 and 20,000. It has been found that there exists an optimum non-circular shape of perforation holes that yields maximum value of Nusselt number; a perfectly circular hole performs substantially inferior as compared to a non-circular hole of considerable non-circularity (ψ=0.69). An improvement of Nusselt number value in the ratio of 1.13 has been found when circular perforation holes are replaced by rectangular holes of circularity of 0.69. Correlations of Nusselt number as well of friction factor are established in term of Reynolds number and geometrical parameters of blockages which can be used to predict the values of Nusselt number and friction factor with considerably good accuracy.

Fluid flow and heat transfer analysis for heat transfer enhancement in three sided artificially roughened solar air heater

Analytical results are available in plenty for heat transfer and friction factor for artificially roughened solar air heaters. Provision of artificial roughness of various geometries and orientations on the absorber plate in solar air heaters have remained limited to only one side (top side) of the solar air heater duct which results in higher values of heat transfer and associated pressure drop. The present paper deals with the analysis with respect to fluid flow and heat transfer in a novel solar air heater having artificial roughness on three sides (the two side walls and the top side) of the rectangular solar air heater duct, with three sides glass covers. Equations for friction factor and heat transfer parameter have been developed. The analytical values of friction factor and heat transfer parameter have been found to be 2–40% more and 20–75% more than those of the respective values of (Prasad and Saini, 1988) for the same range of the values of operating parameters p/e, e/D and Re and fixed values of W and B. The present novel type of solar air heater would be superior to those of only one side artificially roughened solar air heaters with respect to heat transfer.

Experimental Investigation of Thermohydraulic Performance of a Rectangular Solar Air Heater Duct Equipped with V-Shaped Perforated Blocks

This paper presents the thermohydraulic performance of rectangular solar air heater duct equipped with V-shaped rectangular perforated blocks attached to the heated surface. The V-shaped perforated blocks are tested for downstream (V-down) to the air flow at Reynolds number from 2000 to 20000. The perforated blocks have relative pitch ratio ( P/e) from 4 to 12, relative blockage height ratio ( e/H) from 0.4 to 1.0, and open area ration from 5% to 25% at a fixed value of angle of attack of 60∘ in a rectangular duct having duct aspect ratio ( W/H) of 12. Thermohydraulic performance is compared at different geometrical parameters of V-shaped perforated blocks for equal pumping power which shows that maximum performance is observed at a relative pitch of 8, relative rib height of 0.8, and open area ration of 20%. It is also observed that the performance of V-shaped perforated blocks was better than transverse-perforated blocks.

Heat transfer coefficient and thermal losses of solar collector and Nusselt number correlation for rectangular solar air heater duct with longitudinal fins hold under the absorber plate

An experimental investigation has been carried out for a series of system and operating parameters in order to analyze the effect of mass flow rate on heat transfer and Nusselt number characteristics in solar air heater. Experiments are performed at different air mass flow rates; varying from 0.012 to 0.016 kg/s, about hot summer days of Mai 2012. Hourly values of global solar radiation and some meteorological data (temperature, wind speed, relative humidities, etc.) for measuring days are obtained from the Biskra city of Algeria. The experiments encompassed the flow Reynolds number in the range 965.48–1301.4. Longitudinal fins were used inferior the absorber plate for an increase the heat exchange and render the flow fluid in the channel uniform. The effects of mass flow rate of air on the outlet temperature, Nusselt Number, Reynolds Number, Prandtl Number, the heat transfer in the thickness and length of the solar air collector were studied. For this effect was have created a new correlation correspondent of solar air collector with using fins it was written Nu = κ0Re1.36Pr−0.68exp(0.342m)h[−0.018Pr].

Heat Transfer and Friction Factor Correlations for Rectangular Solar Air Heater Duct Having 60° Inclined Continuous Discrete Rib Arrangement

The heat transfer coefficient between the absorber plate and air can be considerably increased by using artificial roughness on the underside of the absorber plate of the solar air heater. An experimental study has been carried out for enhancement of heat transfer coefficient of a solar air heater having roughened air duct provided with artificial roughness in the form 60° inclined discrete rib. Increment in friction factor by provided with such artificial roughness element has also been studied. The effect of system parameters such as relative roughness height (e/D), relative roughness pitch (P/e) and relative gap position (d/W) have been studied on Nusselt number (Nu) and friction factor (f) with relative gap width (g/e) 1 and Reynolds number (Re) varied from 4105 to 20526. Considerably enhancement in heat transfer coefficient has been achieved with such roughness element. Using experimental data correlations for Nusselt number and friction factor have also been developed for such solar air heaters, which gives a good agreement between predicted values and experimental values of Nusselt number and friction factor. Research Article British Journal of Applied Science & Technology, 1(3):67-93, 2011 68

Heat transfer and friction characteristics of rectangular solar air heater duct using rib-grooved artificial roughness

Experimental investigation on the heat transfer and friction characteristics of rib-grooved artificial roughness on one broad heated wall of a large aspect ratio duct shows that Nusselt number can be further enhanced beyond that of ribbed duct while keeping the friction factor enhancement low. The experimental investigation encompassed the Reynolds number range from 3000 to 21,000; relative roughness height 0.0181–0.0363; relative roughness pitch 4.5–10.0, and groove position to pitch ratio 0.3–0.7. The effect of important parameters on the heat transfer coefficient and friction factor has been discussed and the results are compared with the results of ribbed and smooth duct under similar flow conditions. The present investigation clearly demonstrates that the heat transfer coefficient for rib-grooved arrangement is higher than that for the transverse ribs, whereas the friction factor is slightly higher for rib-grooved arrangement as compared to that of rectangular transverse ribs of similar rib height and rib spacing. The conditions for best performance have been determined. Correlations for Nusselt number and friction factor have been developed that predict the values within reasonable limits.

Heat transfer coefficient and friction factor correlations for rectangular solar air heater duct having transverse wedge shaped rib roughness on the absorber plate

As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17 φ −1.0264< p/ e<12.12; and rib wedge angle ( φ) of 8, 10, 12 and 15°. The effect of parameters on the heat transfer coefficient and friction factor are compared with the result of smooth duct under similar flow conditions. Statistical correlations for the Nusselt number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the flow Reynolds number.

Heat transfer and friction factor correlations for rectangular solar air heater duct packed with wire mesh screen matrices

Experimental investigations into heat transfer and fluid flow characteristics of a solar air heater having its duct packed with wire mesh screen matrices were carried out. The investigations covered a wide range of geometrical parameters of wire mesh screen matrix (wire diameter, pitch and number of layers). Generalized correlations have been developed for heat transfer coefficient and friction factor for air flowing through the bed of wire mesh screen matrix packed in the solar air heater duct in a cross flow arrangement. Correlations developed for Colburn J-factor and and friction factor indicate that heat transfer coefficient and friction factor are strong functions of geometrical parameters of matrices. These correlations have been found to predict the experimental data with reasonable accuracy.