scholarly journals A CFD Analysis on the Influence of Upstream Surface Geometry Modifications of Clerestory Shaped Rib on Heat Transfer Characteristics of Solar Air Heater

2021 ◽  
Vol 18 (3) ◽  
pp. 8907-8926
Author(s):  
Dr. Dolfred Vijay Fernandes ◽  
Manjunath M.S.
Keyword(s):  
Heat Transfer ◽  
Enhancement Factor ◽  
Recirculation Zone ◽  
Lower Surface ◽  
Vertical Surface ◽  
Solar Air Heater ◽  
Dimensional Approach ◽  
Surface Geometry ◽  
Thermal Enhancement ◽  
Thermal Enhancement Factor

Two-dimensional numerical analysis is conducted to determine the influence of upstream surface modifications of a novel clerestory shaped rib turbulator on thermal performance augmentation. The upstream surface of the rib is divided into two parts where the upper rib surface is always normal to the incoming flow and the lower rib surface, which is inclined to the flow. The elevation of the vertical surface is varied using non-dimensional approach length (h/e=0, 0.25, 0.5 and 0.75), and the inclination of the lower surface is varied using the rib angle (θ=15°, 45° and 90°). The relative roughness height and pitch of rib is fixed as 0.0421 and 12.5, respectively. RNG k-ϵ turbulence model is used in the analysis, and Reynolds number is varied from 8000-20000. The results reveal that the combined effect of flow impingement and the suppression of formation of recirculation zone leads to increased heat transfer. Lower values of non-dimensional approach length and rib angle provides a higher thermal enhancement factor. The highest increase in Nusselt number is found to be about 1.82 times that of the smooth duct at Re=8000 for h/e=0.25 and rib angle of 15°. The maximum thermal enhancement factor is found to have a range of 1.6-1.45 for an approach length of 0.25 and a rib angle of 15°.

CFD analysis for thermal performance augmentation of solar air heater using deflector ribs

2020 ◽  
Vol 14 (3) ◽  
pp. 7282-7295
Author(s):  
R. Venkatesh ◽  
Nitesh Kumar ◽  
N. Madhwesh ◽  
Manjunath M.S.
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Enhancement Factor ◽  
Air Gap ◽  
Solar Air Heater ◽  
Number Range ◽  
Reynolds Number Range ◽  
Thermal Enhancement ◽  
Gap Height ◽  
Thermal Enhancement Factor

This paper presents the effect of deflector ribs on the thermal performance of flat plate solar air heater using Computational Fluid Dynamics (CFD) methodology. The analysis is carried out using two-dimensional computational domain for the Reynolds number range of 6000-18000. RNG k-є turbulence model is used to capture the turbulence characteristics of the flow. The deflector rib has a cross-section of isosceles triangle and is placed transversely with respect to the flow. The distance between consecutive ribs is varied as 40mm, 80mm, 160mm and 320mm while the air gap height is varied as 2mm, 3mm, 5mm and 10mm. The numerical model is validated against the well-known correlation of Dittus-Boelter for smooth duct. The simulation results reveal that the presence of deflector ribs provide augmented heat transfer through flow acceleration and enhanced turbulence levels. With reference to smooth duct, the maximum achieved heat transfer improvement is about 1.39 times for the inter-rib distance of 40mm and an air gap height of 3mm while the maximum fiction factor achieved was about 3.82 times for pitch value of 40mm and air gap height of 3mm. The highest thermal enhancement factor is achieved for the pitch value of 320mm and an air gap height of 3mm at Re=6000. The air gap height value of 10mm exhibits thermal enhancement factor values lesser than 1.0 and hence is not recommended for use as heat transfer enhancement device for the entire Reynolds number range used in the analysis. The pitch value of 320 mm exhibits thermal enhancement factor greater than 1.0 for almost all the Reynolds number range used in the analysis and varies between 0.93 and 1.07.

Thermal performance enhancement of flat plate solar air heater using transverse U-shaped turbulator - A numerical study

2019 ◽  
Vol 13 (3) ◽  
pp. 5562-5587 ◽  
Author(s):  
M. S. Manjunath ◽  
R. Venkatesh ◽  
N. Madhwesh
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Enhancement Factor ◽  
Performance Enhancement ◽  
Numerical Study ◽  
Solar Air Heater ◽  
Air Heater ◽  
Relative Pitch ◽  
Thermal Enhancement ◽  
Thermal Enhancement Factor

The aim of this study is to determine the effect of U-shaped rib turbulator on the flow and heat transfer characteristics of flat plate solar air heater using two dimensional CFD analysis. The analysis is carried out using the CFD software tool ANSYS Fluent for the flow Reynolds number ranging from 9000 to 21,000.The relative pitch(P/e) of the U-shaped rib is varied as 5, 10, 25 and 40 for a fixed relative rib height of 0.0421. It is shown that the U-shaped rib augments the Nusselt number by about 1.76 times while the friction factor increased by about 1.95 times with reference to smooth duct for a relative pitch of 10 and 5 respectively. The maximum thermal enhancement factor is obtained as 1.5 for the configuration of P/e=25. A comparative analysis of U-shaped rib with circular rib reveals that the U-shaped rib turbulator is found to be more effective in providing heat transfer enhancement and has about 15% higher thermal enhancement factor as compared to circular turbulator.

scholarly journals Experimental investigation of the effect of wave turbulators on heat transfer in pipes

2021 ◽  
pp. 183-183
Author(s):  
Sendogan Karagoz ◽  
Semih Erzincanli ◽  
Orhan Yildirim ◽  
Ilker Firat ◽  
Mehmet Kaya ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Enhancement Factor ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Thermal Enhancement ◽  
Enhancement Factors ◽  
Thermal Enhancement Factor

This experimental study deals with the heat transfer and friction effects of sinusoidal part turbulators for single-phase flows occurring in a circular shaped pipe. Turbulators with three different radius values are placed in the pipe to make the flow turbulent. In this way, changes in Nusselt number and friction coefficient are examined. As a result of the experiments made with Reynolds numbers in the range of 6614-20710, the increase rates of the Nusselt numbers of turbulators with 20 mm, 110 mm and 220 mm radius compared to the empty pipe were obtained as 153.49%, 85.36%, and 52.09%, respectively. As a result of the decrease in the radius, there was an increase in the Nusselt number and the friction factor. Parallel to the Nusselt number, the highest friction factor was obtained in the smallest radius turbulator. It was found that the thermal enhancement factors of 110 mm and 220 mm radius turbulators increased by 179.54% and 132.95%, respectively, compared to the 20 mm radius turbulator. Similarly, it was determined that the thermal enhancement factor of the 110 mm radius turbulator increased by 20% compared to the 220 mm radius turbulator.

scholarly journals Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1482
Author(s):  
Yuting Jia ◽  
Jianwei Huang ◽  
Jingtao Wang ◽  
Hongwei Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Enhancement Factor ◽  
Height Ratio ◽  
Flow And Heat Transfer ◽  
Thermal Enhancement ◽  
Pin Fins ◽  
Micro Pin Fins ◽  
Thermal Enhancement Factor

A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger.

Influence of stepped cylindrical turbulence generators on the thermal enhancement factor of a flat plate solar air heater

Solar Energy ◽  
2020 ◽  
Vol 198 ◽  
pp. 295-310 ◽  
Author(s):  
A. Leander Antony ◽  
Shreyas P. Shetty ◽  
N. Madhwesh ◽  
N. Yagnesh Sharma ◽  
K. Vasudeva Karanth
Keyword(s):  
Flat Plate ◽  
Enhancement Factor ◽  
Solar Air Heater ◽  
Air Heater ◽  
Thermal Enhancement ◽  
Thermal Enhancement Factor

Numerical Investigation of Flow Friction and Heat Transfer in a Channel with Various Shaped Ribs Mounted on Two Opposite Ribbed Walls

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Khwanchit Wongcharee ◽  
Wayo Changcharoen ◽  
Smith Eiamsa-ard
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulence Model ◽  
Enhancement Factor ◽  
Temperature Fields ◽  
Flow Friction ◽  
High Heat Transfer ◽  
Thermal Enhancement ◽  
The One ◽  
Thermal Enhancement Factor

Heat transfer and fluid flow characteristics through a channel with two - dimensional transverse ribs are numerically investigated. The effects of different shaped ribs (rectangular rib, triangular rib, cylindrical rib, concave-concave rib, convex-concave rib, long convex-short concave rib and long concave-short concave rib) are examined. The investigation is performed for the ribs mounted on top and bottom walls with rib pitch to height ratio (P/e) of 6.67, in Reynolds number between 3000 and 7000, under constant wall temperature condition. For the present case, the data predicted by SST k-omega turbulence model show better agreement with the experimental data, than those predicted by RNG k-epsilon turbulence model. The mean heat transfer, flow friction, temperature fields and the local heat transfer coefficients as well as the flow structure behaviors are reported. For the ribs considered, the channel with triangular-ribs yields the highest Nusselt number, the one with concave-concave rib provides the highest friction and the one with cylindrical rib show the best thermal enhancement. At the similar condition, the triangular rib gives higher Nusselt number than that provided by the cylindrical one by around 29.3 percent, while the cylindrical rib offers the highest thermal enhancement factor of 1.4 which is higher than that of the cylindrical one by around 1.33 percent while the cylindrical rib offers the highest thermal enhancement factor of 1.33 which is higher than that of the triangular one by around 9.6 percent. In addition, in spite of their high heat transfer, the concave-concave rib and long concave-concave rib yield low thermal performance factors, due to the prominent effect of high friction factor.

scholarly journals Heat Transfer Performance of a Novel Multi-Baffle-Type Heat Sink

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 979
Author(s):  
Xin Cao ◽  
Huan-ling Liu ◽  
Xiao-dong Shao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Enhancement Factor ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Thermal Enhancement ◽  
Thermal Enhancement Factor

A new type of multi-baffle-type heat sink is proposed in this paper. The heat-transfer coefficient and pressure drop penalty of the employed six heat sink models are numerically investigated under five different inlet velocities. It is shown that Model 6 (M6) has excellent heat transfer performance as its heat-transfer coefficient reaches a value of 1758.59 W/m2K with a pressure drop of 2.96 × 104 Pa, and the temperature difference between the maximum and the minimum temperature of the heating surface is 51.7 K. The results showed that the coolant for M6 is distributed evenly to each channel at the maximal degree. The phenomena of the maldistribution of temperature is effectively improved. Moreover, the thermal resistance and thermal enhancement factor for the six models is also examined. M6 possesses the lowest total thermal resistance and largest thermal enhancement factor compared to the other five models. Furthermore, an experimental platform is set up to verify the simulation results obtained for M6. The simulated heat-transfer coefficient and pressure drop values agree well with the experimental results.

scholarly journals Numerical Investigation of Microchannel Heat Sink with Trefoil Shape Ribs

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6764
Author(s):  
Sadiq Ali ◽  
Faraz Ahmad ◽  
Kareem Akhtar ◽  
Numan Habib ◽  
Muhammad Aamir ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Enhancement Factor ◽  
Microchannel Heat Sink ◽  
Smooth Channel ◽  
Thermal Enhancement ◽  
Fluent Software ◽  
Overall Performance ◽  
Thermal Enhancement Factor

The present study investigates the thermo-hydraulic characteristics of a microchannel sink with novel trefoil Shaped ribs. The motivation for this form of rib shape is taken from the design of lung alveoli that exchange oxygen and carbon dioxide. This study has been conducted numerically by using a code from the commercially available Fluent software. The trefoil shaped ribs were mounted on the centerline of different walls of the microchannel in three different configurations. These consisted of base wall trefoil ribs (MC-BWTR), sidewall trefoil ribs (MC-SWTR), all wall trefoil ribs (MC-AWTR) and smooth channel (MC-SC) having no ribs on its wall. The streamline distance between the ribs was kept constant at 0.4 mm, and the results were compared by using pressure drop (Δp), Nusselt number (Nu), thermal resistance (Rth) and thermal enhancement factor (η). The results indicated that the addition of trefoil ribs to any wall improved heat transfer characteristics at the expense of an increase in the friction factor. The trends of the pressure drop and heat transfer coefficient were the same, which indicated higher values for MC-AWTR followed by MC-SWTR and a lower value for MC-BWTR. In order to compare the thermal and hydraulic performance of all the configurations simultaneously, the overall performance was quantified in terms of the thermal enhancement factor, which was higher than one in each case, except for MC-AWTR, in 100 < Re < 200 regimes. The thermal enhancement factor in the ribbed channel was the highest for MC-SWTR followed by MC-BWTR, and it was the lowest for MC-AWTR. Moreover, the thermal enhancement factor increases with the Reynolds number (Re) for each case. This confirms that the increment in the Nusselt number with velocity is more significant than the pressure drop. The highest thermal enhancement factor of 1.6 was attained for MC-SWTR at Re = 1000, and the lowest value of 0.87 was achieved for MC-AWTR at Re = 100.

scholarly journals Thermohydraulic Performance Improvement in Heat Exchanger Square Duct Inserted with 45° Inclined Square Ring

2020 ◽  
Vol 2020 ◽  
pp. 1-22
Author(s):  
Amnart Boonloi ◽  
Withada Jedsadaratanachai
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Enhancement Factor ◽  
Flow Behavior ◽  
Square Duct ◽  
Thermal Enhancement ◽  
Performance Development ◽  
Thermal Enhancement Factor

Thermal performance development, heat transfer structure, and flow behavior in the heat exchanger square duct equipped with a 45° inclined square ring are investigated numerically. The effects of flow blockage ratios and spacing ratios for the inclined square ring on fluid flow and heat transfer are considered. The Reynolds number (Re = 100–2000, laminar regime) based on the hydraulic diameter of the square duct is selected for the present work. The numerical domain of the square duct inserted with the 45° inclined square ring is solved with the finite volume method. The SIMPLE algorithm is picked for the numerical investigation. The heat transfer characteristics and flow topologies in the square duct inserted with the inclined square ring are plotted in the numerical report. The heat transfer rate, pressure loss, and efficiency for the square duct placed with the inclined square ring are presented in forms of Nusselt number, friction factor, and thermal enhancement factor, respectively. As the numerical results, it is detected that the heat transfer rate of the heat exchanger square duct inserted with the inclined square ring is around 1.00–10.05 times over the smooth duct with no inclined square ring. Additionally, the maximum thermal enhancement factor for the heat exchanger square duct inserted with the inclined square ring is around 2.84.

Heat Transfer Analysis of a Finned Solar Air Heater

1988 ◽  
Vol 110 (2) ◽  
pp. 145-155 ◽  
Author(s):  
F. Issacci ◽  
Y. Zvirin ◽  
G. Grossman
Keyword(s):  
Heat Transfer ◽  
Theoretical Method ◽  
Lower Surface ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Solar Air Heater ◽  
Governing Equations ◽  
Reversed Flow ◽  
Air Heater ◽  
Transfer Processes

A theoretical method is presented for the investigation of a reflective fin solar air heater. The heat transfer processes include radiation in both the solar and IR spectra, mixed convection (forced and natural) in the air and conduction in the fins. The governing equations have been solved numerically to obtain the velocity and temperature fields in the developing and developed flow regions. The efficiency of the finned structure is then calculated, and the results of a parametric study are shown. It has been found that natural convection effects are significant and strong buoyancy leads to separation and reversed flow. The efficiency increases with lower surface emissivity and lower thermal conductivity of the fins.

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