Numerical investigation of critical heat flux in subcooled flow boiling of nanofluids

et al. 2020

IJE

One of the major industry problems is the flow boiling, where reaching to the critical heat flux (CHF) condition can lead to a temperature jump and damage of the systems. In the present study, the effects of a uniform change in tube diameter on subcooled flow boiling and CHF was numerically investigated. The Euler-Euler model was used to investigate the relationship between the two liquid and vapor phases. The ANSYS Fluent code was used for simulation. According to the results, a linear increase in the tube diameter leads to increase of vapor volume fraction adjacent to the tube wall, as compared to a regular tube with a fixed-diameter, which leads to increase of the tube wall temperature due to the low value of the heat transfer coefficient. At CHF conditions, where the tube wall temperature is much higher than that in subcooled flow boiling, an increase in tube diameter may lead to higher tube wall temperature before the temperature jump, as compared to the post-jump temperature of a tube with a constant diameter. The best approach for decreasing the tube wall temperature was found to be a linear decrease in tube diameter. For the tube diameter change angles of θ <-0.0383°, tube wall temperature exhibited a decreasing trend from the inlet of the tube to its end.

Section: Mathematical Modellingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Effect of Linear Change of Tube Diameter on Subcooled Flow Boiling and Critical Heat Flux

DolatiAsl

Bakhshan

et al. 2020

IJE

“…In many cases in the industry, it is necessary to transfer a large amount of heat rapidly, which the boiling is one of the ways to transfer heat efficiently, which there are numerous experimental and numerical studies in this field. 1,2 By increasing the amount of heat flux applied to the hot surface, the amount of vapor generated near the wall may rise to the extent that the entire surface of the wall is covered by vapor. 3 In these cases, the coefficient of heat transfer from the wall to the fluid decreases; and as a result, the wall temperature suddenly increases, which can lead to the destruction of the wall, that investigated as critical heat flux (CHF).…”

Section: Introductionmentioning

confidence: 99%

Visualization of pool boiling and occurring critical heat flux on coiled wire

DolatiAsl

Bakhshan

Proceedings of the Institution of Mechanical Engineers, Part E:

2020

Self Cite

Pool boiling is used in various industries and play a significant role in heat transfer. So far, multiple studies have been carried out on investigating boiling and applying heat flux on the wire. In the present paper, the boiling of the coiled wire under atmospheric pressure conditions has been investigated. The fluid temperature inside the pool is considered under both constant (equal to saturation temperature) and variable temperature conditions. The value of the ring density in the coiled wire is considered to be variable. Based on the results, changing the pool liquid temperature changes bubble departure diameter and frequency. Also, increasing the density of the coil ring increases the diameter of bubbles. It has been observed that the bubbles are usually formed inside the coil, and after moving to the two ends of the coil, they leave the coil. However, by increasing the amount of heat flux and the pool liquid temperature, the size of bubbles will be larger; therefore, the bubbles must leave the coil from the empty spaces between the rings. By increasing the amount of applied heat flux, the coil was enclosed in a layer of vapor, which results in a decrease in the amount of heat transfer coefficient, and finally, a sudden increase in temperature on the wire will occur, which indicates the critical heat flux. Also, it has been observed that the critical heat flux always arises in the coil region of wire and not in the straight part of the wire.

“…Boiling can lead to the improved thermal performance of different sectors in industries and plant processes. 8,9 Boiling flow has two different flow regimes. Subcooled boiling is one of them capable of creating a very high heat transfer and is capable of producing good working conditions in different parts of the industries.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of flow boiling of refrigerant-based nanofluids and proposing correlations for heat transfer

Proceedings of the Institution of Mechanical Engineers, Part E:

Karachi

Jahromi

et al. 2020

Self Cite

The numerical simulation of subcooled flow boiling of R-113 working fluid has been done for two different nanofluids (R-113/Al2O3, R-113/TiO2) under different volume concentrations (0.5%, 1%, and 3%). The numerical results were compared with experimental results obtained by previous researchers, and the comparison shows that the numerical results are in good accordance. Nucleation site density, bubble departure frequency, and bubble departure diameter, which are three key parameters, are investigated in this study. The results express that these three parameters have the highest variation at low Reynolds numbers. The influence of different nanoparticles concentrations on the variation of the heat transfer coefficient is studied. The results indicate there is an insignificant difference between the effect of 1% and 3% concentrations on the heat transfer coefficient that means an increase of nanoparticles more than 1% concentration cannot improve heat transfer. The effect of different non-drag forces such as lubrication force, turbulent dispersion force, and lift force is also studied. Two correlations are proposed for predicting the convective heat transfer coefficient.