In this investigation, nucleate boiling heat transfer coefficients were experimentally measured during Pool boiling of mixtures, consisting of water/monoethanolamine and water/diethanolamine on a horizontal heating rod, under atmospheric pressure. The experiment was carried out below 205 kW.m-2 heat flux, over a wide range of concentrations. These experiments include, measurement of Pool boiling heat transfer coefficient and also visual information. Applicability of the existing main correlations is briefly discussed, with the present experimental data. The major predictions (over and/or under) were observed in some parameter range by the existing correlations. In this investigation the correlations of Fujita et al and Inoue et al, which are structurally the same but have different tuning parameters were modified for this system and the average error has been significantly reduced.

The phenomenon of nuclear boiling has always been recognized suitable for heat transfer between different boiling regimes. Study on boiling is considered as a new field which meets different research and industrial needs such as heat transfer in nuclear reactors, cooling units, rocket motors, electronic equipment cooling, batteries, etc. In this study, a chamber with immiscible fluid, water, steam, and air, having a side wall with uniform heat flux has been studied in 3D. To do so, we first considered the prediction of the heat flux interval for which the boiling occurs in the form of nuclear boiling. In this study, two-phase fluid volume (VOF) approach was used for modelling boiling on the vertical wall and two-phase flow. In this research, Ansys software package was used for numerical modelling and numerical simulation. Distribution of the velocity field follows more uniform pattern in dimensionless heights less than 0.9. In this study, bubbles are only present near a wall with heat flux that has a lower Rayleigh number. Also, existence of these bubbles on the wall, which prevents fluid infiltration, affects vortices caused by natural convection. However, the general and uniform patterns of vortices remain unchanged in most part of the fluid, which is because of the limited amount of bubbles near the wall with heat flux. Natural convection increases the height of fluid inside the chamber, which leads to the formation of stronger vortices at a dimensionless height of 0.9 that has a high Raleigh number due to high heat flux. In this case, the continuous use of heat flux gives rise to the production of bubbles over time.

In recent decades, thermal-fluid specialists have made considerable efforts to investigate the boiling heat transfer process. Pool boiling of pure liquids and nanofluids has been widely studied in the last decade, but the existing knowledge on modeling of nanofluids Pool boiling process is still limited. The boiling of fluids containing tinny solid particles is very complicated due to the interaction between the existing phases, their interface, and the heating surface. Some new research shows that many factors are effective in Pool boiling of nanofluids. Among these factors, we can mention particle size, concentration, the structure of the boiling surface, and the dynamics of bubbles. In this research, the film Pool boiling process of pure ethanol was numerically simulated. Then, the film Pool boiling of nanofluids including two types of nanoparticles 〖Al〗_2 O_3 و SiO_2 and ethanol base fluid with two volumetric concentrations of 0.1% and 0.3% have been simulated. The results show that the presence of nanoparticles in film boiling in the base fluid has increased the heat transfer coefficient. The highest value coefficient for alumina and silica nanofluids with a volumetric concentration of 0.3% was obtained, respectively 0.32 (kW/m2°C) and 0.3 (kW/m2°C). In addition, the presence of nanoparticles in the boiling process has significantly increased the minimum heat flux. According to the results of numerical simulation, the minimum heat flux value in boiling of pure ethanol is 28.99 (kW/m2), in boiling of alumina-ethanol nanofluid with volumetric concentrations of 0.1% and 0.3%, is 37.11 (kW/m2) and 38.84 (kW/m2), respectively and in boiling of silica-ethanol nanofluid with volumetric concentrations of 0.1% and 0.3%, is 35.81 (kW/m2) and 38.31 (kW/m2), respectively. The highest heat transfer coefficient is achieved by alumina nanofluid with 0.3% concentration, while the highest minimum heat flux is achieved by silica nanofluid with 0.3% concentration. The numerical results are in good agreement with the experimental results. By comparing these values with the experimental results, there is a good consistency between the results.

Today, Pool boiling heat transfer is used in many industrial equipment and engineering applications. Pool boiling heat transfer compared to single-phase heat transfer has a higher heat transfer capacity due to the use of latent heat evaporation of liquids. Therefore, in this study, the Pool boiling heat transfer on a flat vertical plate and plate with triangular and circular grooves have been investigated using numerical simulations. In studies, the effect of adding two types of triangular grooves, two types of circular grooves with different dimensions, and four heating surface temperatures has been investigated. In order to simulate the two-phase flow in this study, the volume of the fluid method was used and the governing equations were solved using the finite volume method. The obtained results showed that adding triangular and circular grooves on the heating surface will increase the average heat flux. In the triangular grooved surface case, the average heat flux which entered liquid increased from 128% to 177%. By using a circular groove, the average heat flux augments about 69% to 105%.  Also, the water vapor value in the triangular grooved surface case increased from 160% to 340%, and in the circular grooved surface case rises 101% to 155%.

The use of nanofluids to increase the safety margin of high heat flux thermal systems in nuclear power plants through the enhancement of the critical heat flux (CHF) has been considered recently by researchers. To investigate the CHF characteristics of nanofluids, Pool boiling experiments of nanofluids with various concentrations of TiO2, Al2O3 and SiO2 nanoparticles were carried out using a 0. 2 mm diameter cylindrical Ni– Cr wire under the atmospheric pressure. The results showed that the CHF of SiO2 nanofluid is significantly enhanced by 56% compared with that of pure water by increasing the nanoparticle concentration to 0. 05 wt%. Microscopic images, subsequent to the CHF experiment of SiO2 nanofluid, revealed that nanoparticles are deposited on the wire surface during the Pool boiling of the nanofluid. The CHF of pure water was measured on a nanoparticle-coated wire which was produced during the Pool boiling experiments of SiO2 nanofluids. The results of these experiments showed clearly that the main reason for the CHF enhancement of the nanofluid is the modification of the heating surface by the SiO2 nanoparticle deposition during the Pool boiling.

boiling is used in processes with high heat transfer rate given the large amount of heat flux involved in the phenomenon. Devising a groove on the surface can improve the bubble formation and increase the heat transfer of the boiling. Accordingly, the Pool boiling phenomenon on a horizontal surface is numerically simulated using the Eulerian-Eulerian method in this study. Four surfaces: smooth, with rectangular groove, with triangular groove, and with circular groove are examined to this end. Numerical simulation results are compared with available experimental data. The results indicate that the surfaces with rectangular and circular grooves render approximately 50 and 90% more heat flux than the smooth surface, respectively. However, the surface with a triangular groove rendered approximately 37% less heat flux than the smooth surface.

In this investigation, the performance of coolant in various operating conditions was examined through an energy analysis of experimental data. A novel method was introduced for presenting Pool boiling test results, facilitating coolant performance assessment across distinct operational scenarios and enabling comparative energy analyses between transient and steady-state boiling. Leveraging principles of thermal science, distinct correlations were formulated to elucidate Pool boiling phenomena in transient mode. analysis was based on experimental results from transient Pool boiling tests conducted over predefined time intervals. analysis indicates a direct correlation between the heater's energy output and test duration. Notably, in a steady state, the energy rate produced as a result of Joule heating effects reached its maximum value, which is reflective of the extended duration of this state relative to transient state tests. Specifically, energy yield from the wire heater increased by 75% when the test duration was extended from 1s to 5s. Furthermore, extending duration to 10 s increased energy outputs by 62% and 186% compared to 5s and 1s durations, respectively. Performance decreases as a vapor film forms temporarily, before increasing and becoming nearly constant during film boiling.

Subcooling degree and surface roughness are two major parameters that have a considerable effect on boiling heat transfer. In the present study, the effects of subcooling degree on Pool boiling heat transfer coefficient and surface temperature distribution are investigated experimentally. Tests are conducted for saturated and subcooled water with different subcooling degrees in the local atmospheric pressure (863 mbar) around a horizontal stainless steel cylinder with specific surface roughness. The test section is a Pool with dimensions of 120×400×550 mm3 and test case is a circular cylinder with 80 mm length, 9 mm diameter and 0.794 mm average surface roughness. In this research, experiments are performed for the degrees of subcooling between 5.5°C to 45.5°C and for the heat fluxes between 0.31 kW/m2 to 125.62 kW/m2. Results show that by increasing the degree of subcooling for a specific average surface roughness, average surface temperature is decreased and due to changes in the mechanism of heat transfer from nucleate boiling to natural convection, heat transfer coefficient is also decreased. In the region of natural convection, the variation of heat transfer coefficient with heat flux is low and when boiling process begins, this variation is more considerable. Furthermore, for lower heat fluxes (less than 5 kW/m2), the temperature difference between upper and lower sides of the test case is less than 1°C which increases for higher heat fluxes so that for more than 100 kW/m2, it reaches to 6°C.

The Pool boiling heat transfer coefficient of pure liquids were experimentally measured on a horizontal bar heater at atmospheric pressure. These measurements were conducted for more than three hundred data in thermal currents up to 350 kW. m-2. Original correlations and the unique effect of these correlations on experimental data were discussed briefly. According to the analysis, a new empirical relationship implying a performance superior to other available correlations is presented.