Search

• Thermal behavior of rectangular fins located within a square cavity were analyzed. • Inverse CFD method and experimental data were adopted for heat transfer prediction. • Suitable turbulence model based on the RMSE of the flow model were selected. • Effect of fin geometry on the flow and heat transfer within a cavity was evaluated. • Effect of PCM heat sink on the flow and heat transfer within a cavity was studied. This study examines the fluid flow and heat transfer characteristics of rectangular fins positioned within a square cavity through the use of the inverse three-dimensional computational fluid dynamics (CFD) method, experimental analysis, and the constant heat transfer rate assumption. This paper proposes a heat sink that uses a phase change material (PCM) made of paraffin within a small cavity. The inverse CFD method, combined with the least squares method, root mean square error, and excessive experimental data, is adopted to predict the unknown heat transfer rate Q and absorption heat Q ab. One of the objectives of this study is to investigate the effect of the PCM heat sink on fluid flow and heat transfer characteristics within a cavity. A sequence of tests on various flow models indicates that employing the RNG k-ε turbulence model with the standard wall function is the most suitable choice for all scenarios in the three-fin model. Conversely, the zero-equation model proved to be a more adequate fit for the PCM heat sink. Another objective of this study is to study the effect of the height of the PCM heat sink on Q and Q ab. The incorporation of a PCM heat sink results in a further improvement in the efficiency of heat dissipation. Part of the heat created is absorbed by the PCM heat sink, which absorbs 22.5 % of the thermal energy. Under the same volume, the PCM heat sink with a lower height (H p = 0.012 m) absorbs 14 % more heat compared to H p = 0.02 m. Thus, a lower-height PCM heat sink has a better heat dissipation effect. [ABSTRACT FROM AUTHOR]

Highlights • Transient characteristics of nanofluid in a minichannel heat sink with MEPCM layer in its ceiling are studied. • The wall temperature rises sharply after sudden heat-pulse and then tend to rise slowly. • The dispersion of nanoparticles inside water leads to the clear decrement of wall and temperature. Abstract In this work, transient thermal characteristics of pure water or Al 2 O 3 /water nanofluid with 2–8 wt% concentrations as coolant flowing through a minichannel heat sink with MEPCM layer in its ceiling are experimentally investigated. The heat sink consists of eight minichannels with length, height, and width of 50 mm, 3 mm, and 1 mm for each minichannel, respectively. A uniform heat flux in the range of 1.2–6.8 W/cm2 is imposed to heat the heat sink and a heat pulse amplitude of 8 W/cm2 is suddenly applied for 10 min after steady-state heating condition and then the heating power is cut off immediately. The dimensionless wall temperature distribution, temperature of MEPCM layer, maximum wall temperature suppression, and heat transfer effectiveness of the system are assessed under sudden heat-pulse conditions. The measured results reveal that the wall temperature and MEPCM layer temperature rise sharply after sudden heat-pulse and then tend to rise slowly. Moreover, it is observed that the latent heat absorbed by the MEPCM layer during melting process can reduce the severe temperature variation caused by sudden heat-pulse. Furthermore, it is concluded that the dispersion of alumina nanoparticles inside pure water and the increase of its concentration lead to the significant decrement of wall temperature and MEPCM layer temperature and increment of the maximum wall temperature suppression. Finally, the comparison of the results obtained from the employment of nanofluid and pure water in the heat sink shows that the nanofluid-cooled heat sink with MEPCM layer in its ceiling outperforms the water-cooled one with/without MEPCM layer. [ABSTRACT FROM AUTHOR]

This research aims to present the preparation, characterization and thermophysical properties of water-based microencapsulated n -eicosane PCM suspensions for thermal energy storage. n- eicosane PCMs are coated with urea–formaldehyde polymer shell. The microcapsules have been characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The differential scanning calorimetry (DSC) is also performed for measurement of the latent heat value, melting and freezing temperatures, and specific heat of MEPCMs. Then, the thermophysical characteristics of the MEPCM suspension including the thermal conductivity k m and viscosity µ m have been measured at different particle concentration (2, 5 and 10 wt%) and different temperatures from 25 to 50 °C. New correlations are developed to predict the thermophysical characteristics of MEPCM suspensions. Furthermore, the application performance of artificial neural network for predicting of k m and µ m is evaluated, and it is found that a neural network with the optimum structure of 2-4-4-2 provides a very accurate prediction of the experimental results. [ABSTRACT FROM AUTHOR]

An investigation into the effect of mass flow rate oscillation on the R-134a evaporation heat transportation in a horizontal annular duct was experimentally conducted. The experiments were performed at different amplitudes (10, 20, and 30%) and periods (20, 30, 60, and 120 s) of the mass flux oscillation in a duct with different gap sizes (1.0, 2.0 and 5.0 mm). In this regard, the time variations of evaporation heat transportation coefficient and the heated wall temperature were also analyzed for the thermal characteristics of the oscillatory evaporation heat transfer. Measured results showed that the amplitude and period of the mass flux oscillation insignificantly affected the time-average heat transportation coefficient for the R-134a oscillatory evaporation heat transfer. However, the larger amplitudes and longer periods of the mass flux oscillation led to stronger wall temperature oscillations. [ABSTRACT FROM AUTHOR]

This research study investigated the cooling performance of a minichannel heat sink that employed suspensions of microencapsulated phase change material (MEPCM) particles as the working fluid. The heat sink made from copper consisted of 10 rectangular minichannels, with a length of 50 mm, depth of 1.5 mm and a width of 1 mm. A uniform heat flux was used for heating the mini channel heat sink and the Reynolds numbers were in the range of 133–1515. The concentration of the MEPCM particles scattered in the water varied from 0 to 10 wt%. The experimental data showed that the wall temperature highly relied upon the Reynolds number and the increment of Reynolds number lead to the reduction of wall temperature for the coolant with or without MEPCM suspension in the minichannel heat sink. Moreover, the wall temperature got reduced for a coolant with MEPCM, compared to that without MEPCM especially at lower Reynolds numbers. Interestingly, the measured results revealed that the coolant with MEPCM particles was effective in cost performance than the pure coolant. The best cooling performance compared to that of pure water was observed for 2% MEPCM concentration within the considered range of flow rates. [ABSTRACT FROM AUTHOR]

• Plate-type membrane humidifier for PEMFC was analyzed with various channel sizes. • Water flux, water recovery ratio, and pressure loss were investigated. • Both width and depth of the channel must be taken into precise consideration. • Counter flow approach shows better performance rather than the parallel flow approach. In the present study, the performance of a planar membrane humidifier for proton exchange membrane fuel cell is evaluated experimentally for different channel structures. For this purpose, three performance indices including water flux, water recovery ratio (WRR), and pressure loss are employed. The measured results disclose that the humidifier using counter flow approach and the channel with width of 1 mm and depth of 1.5 mm has the best overall humidification performance in this work. Increasing the channel depth increases the water flux and therefore increases the WRR of the humidifier. Moreover, the pressure loss decreases with increasing the channel depth because the friction factor at an identical flow rate decreases with increasing the hydraulic diameter of the flow channel. Increasing the channel width expands the contact area with the membrane, leading to an improvement of heat and water vapor transfer. Thus, a higher WRR and pressure loss can be obtained at elevated channel widths. Both depth and width of the channel must be taken into precise consideration in order to minimizing the pressure loss and maximizing the heat and mass transfer. [ABSTRACT FROM AUTHOR]