Experimental Investigation of Heat Transfer and Friction Characteristics of Arc-Shaped Roughness Elements Having Central Gaps on the Absorber Plate of Solar Air Heater

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Navneet Kumar Pandey ◽  
Vijay Kumar Bajpai
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Friction Factor ◽  
Angle Of Attack ◽  
Solar Air Heater ◽  
Maximum Enhancement ◽  
Friction Characteristics ◽  
Air Heater ◽  
Circular Arcs

Thermal performance of solar air heater does not take into account the energy loss due to friction for propelling air through the duct. In this work, an experimental investigation has been carried out to study the effect of heat transfer and friction characteristics of turbulent flow of air passing through rectangular duct which is roughened by circular arcs having gaps of 2 mm in between arranged in angular fashion, and the roughened wall is uniformly heated. The thermal and friction characteristics are governed by duct aspect ratio (W/H), hydraulic diameter (D), and relative roughness pitch (P/e), angle of attack of angular arc (α), and Reynolds number (Re). Experiments encompassed the Reynolds number ranges from 3600 to 15,100, P/e ranges from 6 to 20, and angle of attack of angular arc of flow over the protrusions ranges from 15 deg to 75 deg. The results have also been compared to W-shaped roughness inclined at 45 deg. The maximum enhancement in heat transfer and friction factor is 3.15 and 3.93 times as compared with smooth duct. Arc with gaps have also been observed to be better than their W-shaped counterparts. These experimental results have been used to study their influence on Nusselt number and friction factor, and empirical relations have been derived using regression analysis.

Experimental Investigation of Thermohydraulic Performance of the Solar Air Heater Having Arc-Shaped Ribs With Multiple Gaps

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Sheetal Kumar Jain ◽  
Ghanshyam Das Agrawal ◽  
Rohit Misra
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Nusselt Number ◽  
Friction Factor ◽  
Solar Air Heater ◽  
Artificial Roughness ◽  
Absorber Plate ◽  
Maximum Enhancement ◽  
Air Heater ◽  
Absorber Surface

Abstract In the present research, the thermohydraulic performance of a solar air heater having artificial roughness in the form of arc-shaped ribs with multiple gaps has been investigated experimentally and compared with that of a solar air heater having smooth absorber plate. The performance has been investigated in terms of enhancement in the Nusselt number and friction factor. Results of the present work have also been compared with previously published work. Reynolds number and arc angle (α) were varied from 3000 to 18,000 and 30 deg to 75 deg, respectively. Present roughness results in a higher rate of heat transfer from the absorber surface to air, but it also imposes a penalty in terms of the increased friction factor. Maximum enhancement in Nusselt number, friction factor, and thermohydraulic performance parameter for the roughened absorber surface is found to be 3.74, 2.69, and 2.75 times that of the smooth plate, respectively. Correlations of heat transfer and friction factor for proposed roughness have also been developed.

Heat Transfer and Friction Factor Correlations for Solar Air Heater With Gap in V-Rib With Symmetrical Gap and Staggered Ribs

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Sumer Singh Patel ◽  
Atul Lanjewar
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Smooth Surface ◽  
Heat Transfer Analysis ◽  
Operating Parameters ◽  
Solar Air Heater ◽  
Gap Size ◽  
Maximum Enhancement ◽  
Air Heater ◽  
Relative Roughness

Abstract The present experimental study is concerned with heat transfer analysis of air flowing in solar air heater duct with a gap in V-rib with symmetrical gap and staggered ribs geometry. The investigated parameters are Reynolds number (Re) of 4000–14,000, relative roughness pitch (p/e) of 12, relative roughness height (e/Dh) of 0.043, angle of attack (α) of 60 deg, relative staggered rib pitch (p′/p) of 0.65, relative gap size (g/e) of 4, relative staggered rib size (r/e) of 4, relative gap position of additional gap in each symmetrical rib elements (d/w) of 0.65, relative gap size of additional gap in each symmetrical rib elements (g′/e) of 1, number of main gaps (Ng) of 1, 2, 3, 4, and number of additional gap (ng) varying from 1 to 5. Fourteen roughened absorber plates were tested. The maximum enhancement in Nusselt number (Nu) and friction factor (f) was 2.34 and 2.79 times that of smooth surface corresponding to the number of main gaps (Ng) of 4 with the number of additional gaps (ng) of 4. The performance of the gap in V-rib with symmetrical gap and staggered rib geometry has been compared with the existing latest V-rib geometry and smooth surface. The proposed gap in V-rib with symmetrical gap and staggered ribs geometry has a better performance than the existing latest V-rib geometry. The following correlations have been developed for heat transfer and friction factor in terms of roughness and operating parameters. Heat transfer:Nur=0.0073(Re)0.9788(Ng)0.2790(ng)0.0184exp[−0.1678(ln(Ng))2]exp[−0.0129(ln(ng))2] Friction factor:fr=0.0477(Re)−0.0678(Ng)0.5919(ng)−0.0562exp[−0.4922(ln(Ng))2]exp[−0.0487(ln(ng))2]

scholarly journals CFD Analysis on the Heat Transfer and Fluid Flow of Solar Air Heater having Transverse Triangular Block at the Bottom of Air Duct

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1099
Author(s):  
Hwi-Ung Choi ◽  
Kwang-Hwan Choi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Design Parameters ◽  
Solar Air Heater ◽  
Air Heater ◽  
Geometric Conditions ◽  
Computational Fluid Dynamics Analysis ◽  
Triangular Block

In this study, a two-dimensional CFD (computational fluid dynamics) analysis was performed to investigate the heat-transfer and fluid-friction characteristics in a solar air heater having a transverse triangular block at the bottom of the air duct. The Reynolds number, block height (e), pitch (P), and length (l) were chosen as design parameters. The results are validated by comparing the Nusselt number predicted by simulation with available experimental results. Renormalization-group (RNG) k - ε model with enhanced wall-treatment was selected as the most appropriate turbulence model. From the results, it was found that the presence of a transverse triangular block produces a higher Nusselt number than that of smooth air duct. The enhancement in Nusselt number varied from 1.19 to 3.37, according to the geometric conditions investigated. However, the use of transverse triangular block also results in significantly higher friction losses. The thermohydraulic performance (THPP) was also estimated and has a maximum value of 1.001 for height (e) of 20 mm, length (l) of 120 mm, and pitch (P) of 150 mm, at Reynolds number of 8000. Furthermore, in the present study, correlations of the Nusselt number and friction factor were developed as a function of geometrical conditions of the transverse triangular block and Reynolds number, which can be used to predict the value of Nusselt number and friction factor with the absolute percentage deviations of 3.29% and 7.92%, respectively.

Heat Transfer Augmentation Using an Innovative Helicoidal Finned Absorber Plate in a Solar Air Heater—A Numerical Study

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Shantanu Purohit ◽  
N. Madhwesh ◽  
K. Vasudeva Karanth ◽  
N. Yagnesh Sharma
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Diameter Ratio ◽  
Wire Diameter ◽  
Solar Air Heater ◽  
Absorber Plate ◽  
Air Heater ◽  
Pitch Ratio

This study presents an innovative idea to augment heat transfer to an air heater using helicoidal finned arrangement. A parametric analysis of the helicoidal shaped fin geometry is considered with helicoidal pitch ratio of 0.1666–0.3, fin diameter ratio of 1.75–2. For the placement of the fin beneath the absorber plate, longitudinal pitch ratio ranging from 0.0416 to 0.1666 are used. The flow Reynolds number used for the study ranges from 4800 to 25,000. The effects of helicoidal pitch ratio, wire diameter ratio and longitudinal pitch ratio on Nusselt number and friction factor have been discussed. It is seen from the analysis that there is a significant improvement in Nusselt number for the case of helicoidal fin of wire diameter ratio of 1 when compared to base model as well as straight fin model for the operating range of Reynolds number. It is also observed from the analysis that for the helicoidal fin configuration of helicoidal pitch ratio of 0.2333, friction factor appears to be moderate. Flow and roughness parameters for roughened solar air heater have been optimized using thermal-hydraulic enhancement factor (THEF). The study reveals that by the use of helicoidal fins, maximum enhancement in the Nusselt number is found to be 2.21 times when compared to the base model for longitudinal pitch ratio of 0.0416, helicoidal pitch ratio of 0.166 for a fixed wire diameter. The improvement obtained in performance corresponding to increased Nusselt number establishes the efficacy the helicoidal fin design for the absorber plate.

scholarly journals Computational fluid dynamics analysis of a V-rib with gap roughened solar air heater

2018 ◽  
Vol 22 (2) ◽  
pp. 963-972 ◽  
Author(s):  
Jitesh Rana ◽  
Anshuman Silori ◽  
Rajesh Maithani ◽  
Sunil Chamoli
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Angle Of Attack ◽  
Solar Air Heater ◽  
Computational Domain ◽  
Cfd Analysis ◽  
Air Heater ◽  
Relative Roughness ◽  
Computational Fluid Dynamics Analysis

A CFD analysis of a solar air heater has been carried out using V-shaped ribs as artificial roughness on the absorber plate. The relative roughness pitch, P/e = 6-12, Reynolds number of 3800-18000, relative roughness height, e/D = = 0.042, and angle of attack, ? = 30?-75?, have been selected as design variables of V-shaped rib for analysis. The ANSYS FLUENT 15.0 with renormalization group k-? turbulence model is selected for the analysis of computational domain of solar air heater. The enhancement of Nusselt number and friction factor with Reynolds number for different values of a relative roughness pitch are presented and discussed by CFD analysis. The effect of angle of attack and Reynolds number on enhancement of Nusselt number and friction factor is also presented. The optimum value of rib configuration based on constant pumping power requirement has been derived using thermohydraulic performance parameter and has been found maximum at angle of attack of 60? and P/e = 10.

Heat transfer measurement in a rectangular channel of solar air heater with Winglet type ribs using liquid crystal thermography

2021 ◽  
pp. 1-9
Author(s):  
Amit Kumar ◽  
Apurba Layek
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Crystal ◽  
Rectangular Channel ◽  
Angle Of Attack ◽  
Solar Air Heater ◽  
Air Heater ◽  
Liquid Crystal Thermography ◽  
Relative Roughness ◽  
Absorber Surface

Abstract This paper deals with the study of heat transfer in solar air heater consisting of Winglet shaped roughness on the absorber plate using liquid crystal thermography technique. The winglet type roughness element was placed on the absorber surface of a rectangular channel solar air heater having an aspect ratio of 4. The absorber surface was heated uniformly by a constant heat flux of 800 W/m2. The non-dimensional roughness parameter considered as relative roughness pitch i.e., P/e, and its values range between 5-12 with Reynolds number (Re) range between 6500 - 22000. The value of angle of attack i.e., alpha and relative roughness width i.e. (W/w) were kept constant, and the relative roughness pitch was varied to measure the heat transfer coefficient. The enhancement in heat transfer has been compared and it is observed that at P/e of 8 for the angle of attack (α) of 60 degrees resulting it's optimum value. The enhancement of heat transfer with the increase in Reynolds number is also noted.

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