Parametric CFD Thermal Performance Analysis of Full, Medium, Half and Short Length Dimple Solar Air Tube

Abstract

In the present decade, research regarding solar thermal air heaters (SAHs) has noticed a continuous progression in thermo-hydraulic performance augmentation approaches. There now exists a wide variety of thermo-hydraulic performance augmentation approaches and researchers have designated various structures. Nevertheless, there seems to be no generalization to any of the approaches employed. The present numerical investigation reports on the thermo-hydraulic characteristics and thermal performance for flow through a varied length (full, medium, half, and short length) dimple solar air heater (SAH) tube. The study highlights recent developments on enhanced tubes to augment heat transfer in SAH. The influence of different length ratio, dimple height ratio (H), and pitch ratio (s) on thermo-hydraulic characteristics have been investigated in the Reynolds number (Re) range from 5000 to 25,000. Air is used as the working fluid. The commercial software ANSYS Fluent is used for simulation. The shear stress transport (SST) model is used as the turbulence model. Thermal energy transport coefficient is increased in the full-length dimple tube (FLDT), compared to the medium-length dimple tube (MLDT), half-length dimple tube (HLDT) and short-length dimple tube (SLDT). Similarly, the pitch ratio (s) has more influence on Nusselt number (Nu) compared to the dimple height ratio (H). The friction factor decreases with an increase in pitch ratio. Nu increases and f decreases with increasing Re for all combinations of H and s. Low s and higher H yields high enhancement of HT and PD. Integration of artificial roughness on the tube increases the values of Nu and f by 5.12 times and 77.23 times for H = 0.07, s = 1.0 at Re value of 5000 and 25,000, respectively, in regard to the plain tube. For all the tested cases, the thermo-hydraulic performances (η) are greater than unity.

CFD Analysis of the Heat Transfer and Fluid Flow Characteristics Using the Rectangular Rib Attached to the Fin Surface in a Solar Air Heater

“…As the heat is transferred from The results show that the SST k-ω model has the lowest MAPEs of 12.96%, 8.18%, and 4.94% for Nu base , Nu side and f s , respectively, among the investigated turbulence model. Thus, the SST k-ω model was employed as a turbulence model for further analysis, which was also used by other researchers [12,[29][30][31].…”

“…h avg = h base A base (T base − T air ) + h side A side (T side − T air ) A tot T avg − T air (11) where the A base and A side are the areas of the fin's base and side surfaces, respectively. The average friction factor, which represents the pressure drop caused by the addition of the rib, was calculated from Equation (12).…”

“…A total of six different shapes were chosen as roughness geometries, and the forward chamfered rectangular rib has the best thermal-hydraulic performance. Alam and Souayeh [12] evaluated the thermo-hydraulic characteristics of a solar air tube with a dimple with various relative heights and pitches of dimple, tube length, and Re. They presented that the presence of artificial roughness on the tube led to an enhancement in Nu by 5.12 times over smooth tube.…”

Heat Transfer Augmentation and Friction Factor Due to the Arrangement of Rectangular Turbulators in a Finned Air Channel of a Solar Air Heater

“…The flow of air in a finned air channel of an SAH is characterized by turbulent and steady-state incompressible flow, and this flow field is governed by the continuity, momentum, and energy equations. Considering the steady-state incompressible turbulence flow, these governing equations can be written as follows [9,35,36]:…”

Efficiency Enhancement in Double-Pass Perforated Glazed Solar Air Heaters with Porous Beds: Taguchi-Artificial Neural Network Optimization and Cost–Benefit Analysis

“…According to [15], the authors applied a techniquie of machine learning regression to estimate thermal efficiency and heat transfer of a helical corrugation with perforated circular disc SAH tubes. Alam and Souayeh [16] conducted a numerical investigation on thermo-hydraulic characteristics, which lead to increasing the heat transfer in SAH.…”