Fluid flow and heat transfer analysis for heat transfer enhancement in three sided artificially roughened solar air heater

Solar Energy ◽  
2014 ◽  
Vol 105 ◽  
pp. 27-35 ◽  
Author(s):  
B.N. Prasad ◽  
Arun K. Behura ◽  
L. Prasad
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n

Gas turbine blade tips encounter large heat load as they are exposed to the high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip life time. This paper presents numerical predictions of turbulent fluid flow and heat transfer through two-pass channels with and without guide vanes placed in the turn regions using RANS turbulence modeling. The effects of adding guide vanes on the tip-wall heat transfer enhancement and the channel pressure loss were analyzed. The guide vanes have a height identical to that of the channel. The inlet Reynolds numbers are ranging from 100,000 to 600,000. The detailed three-dimensional fluid flow and heat transfer over the tip-walls are presented. The overall performances of several two-pass channels are also evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide vanes are 10∼60% higher than that of a channel without guide vanes, while the pressure loss might be reduced when the guide vanes are properly designed and located, otherwise the pressure loss is expected to be increased severely. It is suggested that the usage of proper guide vanes is a suitable way to augment the blade tip heat transfer and improve the flow structure, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip-wall directly.


2021 ◽  
pp. 345-345
Author(s):  
Kumar Varun ◽  
G. Manikandan ◽  
Kanna Rajesh ◽  
Venkata Poluru

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.


2010 ◽  
Vol 21 (1) ◽  
pp. 35-51 ◽  
Author(s):  
Thakur Sanjay Kumar ◽  
N.S. Thakur ◽  
Anoop Kumar ◽  
Vijay Mittal

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.


Author(s):  
Shian Li ◽  
Gongnan Xie ◽  
Bengt Sunden

Purpose – The employment of continuous ribs in a passage involves a noticeable pressure drop penalty, while other studies have shown that truncated ribs may provide a potential to reduce the pressure drop while keeping a significant heat transfer enhancement. The purpose of this paper is to perform computer-aided simulations of turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls. Design/methodology/approach – Computational fluid dynamics technique is used to study the fluid flow and heat transfer characteristics in a three-dimensional rectangular passage with continuous and truncated V-shaped ribs. Findings – The inlet Reynolds number, based on the hydraulic diameter, is ranged from 12,000 to 60,000 and a low-Re k-e model is selected for the turbulent computations. The local flow structure and heat transfer in the internal cooling passages are presented and the thermal performances of the ribbed passages are compared. It is found that the passage with truncated V-shaped ribs on opposite walls provides nearly equivalent heat transfer enhancement with a lower (about 17 percent at high Reynolds number of 60,000) pressure loss compared to a passage with continuous V-shaped ribs or continuous transversal ribs. Research limitations/implications – The fluid is incompressible with constant thermophysical properties and the flow is steady. The passage is stationary. Practical implications – New and additional data will be helpful in the design of ribbed passages to achieve a good thermal performance. Originality/value – The results imply that truncated V-shaped ribs are very effective in improving the thermal performance and thus are suggested to be applied in gas turbine blade internal cooling, especially at high velocity or Reynolds number.


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