Heat Transfer Enhancement in a Solar Air Heater Channel with Discrete V-Baffles

2014 ◽  
Vol 931-932 ◽  
pp. 1193-1197 ◽  
Author(s):  
Prawat Soodkaew ◽  
Sompol Skullong ◽  
Pongjet Promvonge ◽  
Watanyu Pairok
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Channel Height ◽  
Airflow Rate ◽  
Solar Air Heater ◽  
Transfer Enhancement ◽  
Air Heater ◽  
Smooth Channel

This article presents the study of heat transfer enhancement in a uniform heat-fluxed channel fitted with discrete V-shaped baffles. The experiments are carried out by varying airflow rate for Reynolds number ranging from 4100 to 22,000. The V-baffles with relative height ratio, e/H = 0.15 and the attack angle, α = 45o, are mounted repeatedly on the upper plate only, similar to an absorber plate of solar air heater systems. The effects of four baffle-pitch to channel-height ratios (PR= 0.5, 1.0, 1.5 and 2.0) on heat transfer in terms of Nusselt number and pressure loss in the form of friction factor are experimentally investigated. The experimental results show that the use of the discrete V-baffles leads to a considerable increase in Nusselt number and friction factor in comparison to the smooth channel alone. The V-baffled channel with PR=0.5 provides the highest heat transfer, friction factor and thermal enhancement factor.

scholarly journals Thermal Performance of T-shaped Obstacles in a Solar Air Heater

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1305
Author(s):  
Seung-Yong Ahn ◽  
Kwang-Yong Kim
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Channel Height ◽  
Parameter Study ◽  
Solar Air Heater ◽  
Air Heater ◽  
Performance Factor

This paper proposes T-shaped ribs as obstacles attached to the heat absorber plate in a rectangular solar air heater to promote heat transfer. The thermal and aerodynamic performance of the solar heater was numerically evaluated using three-dimensional Reynolds-averaged Navier–Stokes equations with the shear stress transport turbulence model. A parameter study was performed using the ratios of rib height to channel height, rib width to channel width, and rib width to rib height. The area-averaged Nusselt number and friction factor were selected as the performance parameters of the solar air heater to evaluate the heat transfer and friction loss, respectively. In addition, the performance factor was defined as the ratio of the area-averaged Nusselt number to the friction factor. The maximum area-averaged Nusselt number was found at h/e = 0.83 for a fixed rib area. Compared with triangular ribs, the T-shaped ribs showed up to a 65 % higher area-averaged Nusselt number and up to a 49.7% higher performance factor.

Heat Transfer Enhancement Induced by Cube- and Diamond-Shaped Block Arrays in Two-Pass High-Aspect Ratio Channels With a 180-Degree Turn

2010 ◽  
Author(s):  
Pavin Ganmol ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
Local Heat Transfer ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Smooth Channel ◽  
Sharp Turn ◽  
First Pass

Described in this paper is an experimental investigation of the heat transfer and pressure characteristics in a high aspect ratio, (4.5:1 width-to-height), two-pass channel, with cube-shaped and diamond-shaped block arrays placed in both passes before and after a 180-degree sharp turn. Transient liquid crystal technique was applied to acquire detailed local heat transfer data on both the channel surfaces and the block elements. Reynolds number tested varies between 13000 and 28000. To further explore potential design alternatives for enhancement cooling, the effects of block height, ranging from 1/4, 1/2, 3/4 and full span of the channel height were also evaluated. Present results suggest that a staggered cube-array can enhance heat transfer rate up to 3.5 fold in the first pass and about 1.9 fold in the second pass, relative to the fully-developed smooth channel counterpart. For the corresponding diamond-shaped block array, the enhancement is 3.4 and 1.9 fold respectively. Even though the post-turn turbulence transport in the second pass is generally higher than that in the first pass, the effects of surface-block induced heat transfer enhancement in fact are less prominent in the post-turn region of the second pass. Pressure loss for diamond block arrays is generally higher than that of the corresponding cube-block arrays.

A Comparative Study of Performance of Low Reynolds Number Turbulence Models for Various Heat Transfer Enhancement Simulations

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ankit Tiwari ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Transfer Enhancement ◽  
Low Reynolds

The goal of this study is to evaluate the computational fluid dynamic (CFD) predictions of friction factor and Nusselt number from six different low Reynolds number k–ε (LRKE) models namely Chang–Hsieh–Chen (CHC), Launder–Sharma (LS), Abid, Lam–Bremhorst (LB), Yang–Shih (YS), and Abe–Kondoh–Nagano (AKN) for various heat transfer enhancement applications. Standard and realizable k–ε (RKE) models with enhanced wall treatment (EWT) were also studied. CFD predictions of Nusselt number, Stanton number, and friction factor were compared with experimental data from literature. Various parameters such as effect of type of mesh element and grid resolution were also studied. It is recommended that a model, which predicts reasonably accurate values for both friction factor and Nusselt number, should be chosen over disparate models, which may predict either of these quantities more accurately. This is based on the performance evaluation criterion developed by Webb and Kim (2006, Principles of Enhanced Heat Transfer, 2nd ed., Taylor and Francis Group, pp. 1–72) for heat transfer enhancement. It was found that all LRKE models failed to predict friction factor and Nusselt number accurately (within 30%) for transverse rectangular ribs, whereas standard and RKE with EWT predicted friction factor and Nusselt number within 25%. Conversely, for transverse grooves, AKN, AKN/CHC, and LS (with modified constants) models accurately predicted (within 30%) both friction factor and Nusselt number for rectangular, circular, and trapezoidal grooves, respectively. In these cases, standard and RKE predictions were inaccurate and inconsistent. For longitudinal fins, Standard/RKE model, AKN, LS and Abid LRKE models gave the friction factor and Nusselt number predictions within 25%, with the AKN model being the most accurate.

scholarly journals Experimental analysis of solar air heater using polygonal ribs in absorber plate integrated with phase change material

2021 ◽  
pp. 345-345
Author(s):  
Kumar Varun ◽  
G. Manikandan ◽  
Kanna Rajesh ◽  
Venkata Poluru
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Heat Transfer Enhancement ◽  
Phase Change Material ◽  
Mass Flow ◽  
Solar Air Heater ◽  
Transfer Enhancement ◽  
Absorber Plate ◽  
Air Heater ◽  
Change Material

Heat transfer enhancement in Solar Air Heater (SAH) has been investigated by implementing rough surfaces in the absorber plate. We use paraffin wax is used as Phase Change Material (PCM) integrated with SAH as a Thermal Energy Storage (TES) system. A maximum convective heat transfer is attained during the daytime and retained as latent heat (LH) to discharge heat during OFF radiation. In this investigation, two types of absorber plates were employed such as flat & polygonal-shaped ribs at the test section. Further to investigate the heat transfer enhancement, the research was conducted with and without PCM. The study was carried out at the mass flow rates of 0.062 kg/s, 0.028 kg/s, and 0.01 kg/s to ascertain the enhancement of thermal efficiency and heat discharge duration. The temperatures of absorber plate Tp, ambient Tamb, outlet Tout and PCM along with Solar Intensity I (W/m-2) were taken as the main parameters. The research reveals that the absorber plate with polygonal ribs tested with PCM yields a higher temperature of 77?C with a mass flow rate of 0.062 kg/s during peak radiation. And discharged heat energy from PCM to absorber plate for 3.5 hours with a maximum temperature of 7.1?C.

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.

Use of artificial roughness to enhance heat transfer in solar air heaters – a review

2010 ◽  
Vol 21 (1) ◽  
pp. 35-51 ◽  
Author(s):  
Thakur Sanjay Kumar ◽  
N.S. Thakur ◽  
Anoop Kumar ◽  
Vijay Mittal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Hydraulic Performance ◽  
Solar Air Heater ◽  
Artificial Roughness ◽  
Transfer Enhancement ◽  
Air Heater ◽  
Roughness Elements

Improvement in the thermo hydraulic performance of a solar air heater can be done by enhancing the heat transfer. In general, heat transfer enhancement techniques are divided into two groups: active and passive techniques. Providing an artificial roughness on a heat transferring surface is an effective passive heat transfer technique to enhance the rate of heat transfer to fluid flow. In this paper, reviews of various artificial roughness elements used as passive heat transfer techniques, in order to improve thermo hydraulic performance of a solar air heater, is done. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts. The objective is to provide a detailed review on heat transfer enhancement by using an artificial roughness technique. This paper will be very helpful for the researchers who are researching new artificial roughness for solar air heater ducts to enhance the heat transfer rate and comparing with artificial roughness already studied by various researchers.

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