Numerical investigation of louver edges effect on the performances of louvered fin compact heat exchanger

The rectangular channel louvered-fin compact heat exchanger (LFCHE) is the most efficient type that has been served in a radiator. However, with this type of heat exchanger, the pressure drop rises by three to four times as the heat transfer increases, which results in decreasing performance. This research is aimed to numerically investigate the louver edges (vertical, inclined, and horizontal) effect on LFCHE performance at different louver angle (θ ) with air inlet velocities ranging from 1 to 30 m/s. A total of twelve models are made and simulated. The result revealed that the horizontal edge decreases the pressure drop up to 24.2% with a 1.01% increase in outlet air temperature over the base model (inclined edge). Thus, louver edge has design which results in higher and lower effect on pressure drop and temperature change, respectively. The research investigated the effects of louver edges using different performance evaluation criteria. At 10 m/s (R e l p  = 972.33) the horizontal edge increases the volume goodness (jf) factor up to 21.49% over the base model. Similarly, the horizontal edged fins resulted in maximum increment of jf-factor by 22% and 25% as compared with inclined edge for louver angles θ of 24 ° (at low R e l p ) and 20 ° (at high R e l p ), respectively. Generally, the horizontally edged LFCHE is proven to have higher performance in cooling the coolant with a minimum air side pressure drop.

Optimization of a novel trapezoidal staggered ribs configuration for enhancement of a solar air heater performance using CFD

A novel transverse trapezoidal staggered ribs configuration as artificial roughness is investigated using CFD to understand the fluid flow and heat transfer behaviors for improving the performance of a solar air heater. In addition, experimental validation of Nusselt numbers for smooth duct against CFD results is established. The staggered ribs arrangement outperforms the continuous ribs and insights obtained from the thermal-fluid flow behaviors are further applied to optimize the staggered arrangements of the rib. Reynolds number Re is varied from 5000 to 24,000, and rib parameters are optimized with a special focus on understanding the effects of discontinuous rib width (w) and gap width (g). Two widely studied shapes of rib, namely, cylindrical and rectangular, are also investigated for the transverse staggered arrangement with the same optimized parameters for the comparison of thermo-hydraulic performances. Trapezoidal ribs having discontinuous rib width of 50 mm and gap width of 10 mm give the maximum thermo-hydraulic performance of 1.57 at Reynolds number of 5000. The optimized staggered trapezoidal ribs outperform the staggered cylindrical and rectangular ribs. However, staggered rectangular ribs give the highest increase in the Nusselt number and these may be preferred for application when pressure drop is not of concern.

Performance analysis of a parabolic trough collector using partial metal foam inside an absorber tube: an experimental study

This paper offers an experimental investigation of the effect of metal foam on the thermal and hydrodynamic performance of a parabolic trough collector (PTC). Metal foams play a crucial role in heat transfer improvement due to their high thermal conductivity. Three different arrangements of metal foams are applied inside the absorber tube of the PTC. The flow regime in the absorber tube is laminar at different Reynolds numbers of 422, 844, 1267, and 1689. Experimental tests are designed with Design-Expert software in which the response surface method is utilized. Experimental results revealed that maximum enhancement in thermal efficiency is related to the periodic array arrangement of the metal foam inside the tube. This arrangement leads to a 14% increase in thermal efficiency. However, in this arrangement, the friction factor increases considerably compared to a plain receiver tube.

Enhancement of thermal efficiency and development of Nusselt number correlation for the solar air heater collector roughened with artificial ribs for thermal applications

The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty.

A review of different twisted tape configurations used in heat exchanger and their impact on thermal performance of the system

Heat transfer in water with the help of solar energy is an effective way to harness renewable energy and reduce reliance on non-renewable sources of energy. The utilization of turbulent promoters is an efficient solution to ameliorate the performance of heat exchangers (HE). The current work summarizes the experimental and numerical behaviour of HE reported in the literature, including the thermal examinations of HT and fluid flow characteristics with various turbulent promoters and tube arrangements. This article reviews multiple studies in which different twisted tape (TT) geometry enhances the HT rate in various HE tubes. The current work also compares the thermal performance (η) of TT configurations in HE tubes using correlations developed by different investigators. Maximum heat transfer and minimum friction factor concerning fluid utilized in the system may also produce the optimal form for twisted tapes.

Applications of extended surfaces for improvement in the performance of solar air heaters-a detailed systematic review

The objective of this research article is to present a comprehensive review of the work carried out to improve the thermal as well exergetic performance of the conventional smooth absorber plate solar air heater (SAH) duct by the use of the various configurations and arrangements of extended surfaces (fins) for the forced convection. In the SAH duct, these extended surfaces are attached along the air-flow path on the top absorber, on the bottom plate, or on the both plate surfaces. It enhances the performance of the conventional SAH by increasing the surface area and makes flow turbulent by their presence. Several experimental, theoretical, and simulation works, which have been performed by the researchers by utilizing the extended surfaces to improve the thermal efficiency based on first law of thermodynamics, exergy, and entropy generation analysis on the basis of the second law of thermodynamics for SAH ducts, have been included in the present article. Subsequently, an effort has been made to calculate the Nusselt number and friction factor by using the correlations reported by the researchers for comparing the performance of different configurations of fin SAHs. This comprehensive review article will be useful for the investigators and researchers who are working in the area of extended surface SAHs.

Experimental testing of solar-based air heater roughed with discrete V-down rib and staggered element

A rough rectangular channel of solar-based air heater (SBAH) is made and tested. The work consists of an effort to perceive the proportion of heat discharge and frictional behavior of air passing over a roughened rectangular channel. The absorber surface of SBAH is roughed with discrete V-down rib and staggered element roughness having different values of relative rib pitch (P/e) that ranged from 6 to 14. Fixed parameters such as relative gap size (g/e), relative staggered element pitch (P'/P), numeral of gaps (N_g), relative staggered element size (r/g), and relative rib height (e/D) are considered 4, 0.4, 3,1, and 0.0433, respectively, all throughout the study. The flow Reynolds number (Re) changes from 4000 to 14,000; consequently the Nusselt number (Nu) and friction factor (f) reach up to 2.16 and 2.73 times, respectively, with respect to plane surface. The optimum rise in terms of thermal-hydraulic performance (THP) is gained analogous to a P/e of 10. The correlation for heat transfer function, R(e⁺), and roughness function, G(e⁺), is given to anticipate the performance of roughness.

Computational analysis on solar air heater with combination of alternate dimple protrusions and intrusions on absorber plate with one rounded corner triangular duct

This study focuses on improving heat transfer by converting one of the corners of the duct to a rounded structure. To study the effect of dimpled shaped protrusions and intrusions on the rounded corner triangular duct with a constant radius of curvature by varying relative streamwise distance (z/e) with a constant transverse distance x'/e = 10,14 and 18. Steady-state, turbulent flow heat transfer under thermal boundary conditions is to be analyzed by varying different Reynolds numbers (5600 to 21000). The duct with dimple-shaped protrusions and intrusions is compared with a simple triangular duct. Optimization of relative horizontal distance (z'/e) by keeping constant protrusion to protrusion distance as z/e = 28 and relative transverse distance as x/e = 10, 14, and 18. It was noted that there was a significant loss in friction and a rise in heat transfer. The relationship between friction factor and Nusselt number was formulated using operating and roughness parameters, using the data collected from the numerical investigation. The friction factor increases significantly with roughness elements, and it is maximum for x'/e = 20 at a low Reynolds number. Nusselt number increases with roughness elements, and it is maximum for x'/e = 14 for all Reynolds numbers and all the models. Enhancement of Nusselt number is due to increase of local heat transfer because of local vortex neat heat transfer zone. The maximum outlet temperature is obtained at a low Reynolds number. The maximum temperature of the heated surface is obtained for Rc = 0.67 h and the minimum for Rc = 0.33 h.

Numerical investigation the hydrodynamic parameters of the flow in a wavy corrugated channel using different turbulence models

In this research, turbulent flow numerical models in a wavy channel were investigated. The studied channel is simulated in two dimensions and symmetrically in the range of Reynolds numbers from Re=10,000 to 80,000. The significant cause of this research is to investigate and determine the appropriate method for estimating the behavior of turbulent flow in a wavy channel. In this research, the behavior of turbulent flow in a wavy channel will be simulated in 7 different ways, which are k-ω SST, k-ϵ RN, k-ϵ Realizable, k-ϵ Standard, k-ω Standard, Reynolds stress and Spalart-Allmaras. The findings of this research show that the impacts of the presence of flow viscosity (friction) and the presence of adverse pressure gradients are factors that strongly affect the velocity profiles in the upstream areas of the corrugated section. Among the studied models, due to better compatibility and guessing of flow and hydrodynamic properties, k-ω SST methods and Reynolds and Spalart-Allmaras stress are introduced as the best methods for such geometries. On the other hand, increasing the accuracy of other turbulence methods is related to the flow physics and geometric structure of each problem. In this research, the hydrodynamic parameters of the flow such as pressure drop, skin friction factor, and dynamic pressure drop coefficient and vortex contours, and pressure are plotted and described.

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 (η_th) of roughened SAH duct.

Effect of fabricated V-rib roughness experimentally investigated in a rectangular channel of solar air heater: a comprehensive review

Solar power is one of the main sources of renewable energy which helps for protecting the environmental and reducing pollution. Technologies and systems for utilizing solar power are the area of research and development for a number of decades. In a solar air heater (SAH), use of fabricated irregularities on its wide face is an effective technique to augment heat discharge for flowing air with a moderate rise in frictional conduct. The necessary conditions for building an effective roughness design are to pick roughness patterns and its geometrical factors such that they may govern the nature of fluid flow with a rise in the heat discharge and lowering pumping losses. Continuous efforts are being carried out by various researchers to optimize the roughness parameters that deliver high heat release rates with low cost of pressure penalty or better thermo-hydraulic performance parameter (THPP). The researchers dominantly studied V-shaped of roughness design because of its better performance characteristics. The main intent of the present paper is to appraise or compile the influence of various V-shaped rib roughness on the thermal behavior of SAH. The outcomes of different V-designed rib roughness in terms of Nusselt number (Nu), and friction factor (f), statistical correlations established related to geometrical parameters and THPP are summarized. A comparative study using different V-designed ribs are also discussed to guide the future research and improvements.