Nowadays computation methods are so powerful that they predict very close to experiments. performed a comparative study with steam and air for convective heat transfer performance inside a rib-roughened channel. Esmaili, Ranjbar and Porkhail conducted experimental analysis on heat transfer in ribbed microchannels. The work was extended to observe the effect for skewed ribs. Chang, Liou and Lu studied heat transfer enhancement in narrow rectangular channel with two opposite rib-roughened walls. He later extended the work to analyze the influence of turbulence flow structure on the enhancement of heat transfer in those channels. conducted a similar study on rectangular narrow channels with square micro-ribs. conducted study on heat transfer augmentation on rectangular narrow channels with rib turbulators. For this, costly experimental setups are required to evaluate the exact heat transfer and fluid flow mechanism through rib-roughed narrow channels of various shapes, sizes and rib configurations. Heat transfer enhancement in micro/mini-channels with rib-roughened surfaces in the turbulent flow regime creates a high pressure drop. This is because the conventional correlations for predicting the friction factor and convective heat transfer coefficient through smooth narrow channels are not applicable for rib-roughened channels. Although micro-channel or mini-channel heat sink with a rib-roughened surface ensures better heat transfer performances with the expenses of pressure drop, it is difficult to accurately predict the fluid flow and heat transfer mechanisms. These ribs are provided to increase the heat transfer surface area as well as to destabilize the growth of boundary layers. In most cases, the micro-channel and mini-channel heat sinks have their surfaces roughened with ribs (also called turbulence promoters) of various shapes and sizes. where a high heat removal rate is required in the order of 10 2–10 4 W/cm 2. Due to their superior heat transfer performances, they have widespread use in high-performance computer chips, diodes, nuclear fission and fusion reactors, etc. Micro-channel and mini-channel heat sinks are the most lucrative options.
As a result, efficient heat removal techniques have become more challenging issues than ever. With the advancement of technology, the size of a modern machine/device has reduced significantly while their functionality has remained unchanged. Micro-channel and mini-channel heat sinks are the core components of modern heat removal technology. Suggested calibration process is more effective for channel height of 1.2 mm than 3.2 mm. Κ-ε turbulence model is calibrated for rib-roughened narrow rectangular channels using genetic algorithm.Ĭε1 and Cε2 are the most influential parameters on the performance of the model inside rib-roughened narrow channel. Among them, CuO-water nanofluid is predicted to have around 1.32 times higher value of Nu than pure water for the same narrow channel configuration. Al 2O 3-water, CuO-water, and TiO 2-water are studied using the calibrated model to check the potentiality of heat transfer enhancement. Furthermore, three types of nanofluids i.e. The role of the two parameters C ε1 and C ε2 are found to be of primary importance.
Also, up to 15.48% and 18.05% improvements are obtained for p/k = 10 and p/k = 20 respectively when H = 3.2 mm. After calibration, the overall predictive improvements are up to 35.83% and 27.30% for p/k = 10 and p/k = 20 respectively when H = 1.2 mm. Results reveal that the calibrated parameters are not the same for all the narrow channel configurations. These correlations are used to optimize the errors using genetic algorithm. The simulated data are used to develop correlations between the relative errors in predicting the friction factor ( f), Nusselt number ( Nu), and the model parameters using a multivariate nonlinear regression method. These parameters are adjustable empirical constants provided for controlling the accuracy of the turbulence model results when needed.
For this, the four turbulence model parameters, C μ, C ε1, C ε2, and σ k, are calibrated. In this work, an improved version of the κ-ε turbulence model is proposed for better prediction of thermal–hydraulic characteristics of flow inside rib-roughened (pitch-to-rib height ( p/k) ratio = 10 and 20) narrow channels (channel height, H = 1.2 mm and 3.2 mm). Nowadays, applications of turbulent fluid flow in removing high heat flux in rib-roughened narrow channels are drawing much interest.
0 kommentar(er)
