In this study, two methods of nano-particle coating, by boiling and electrophoretic, have been used to investigate the effect of surface modification on the Critical Heat Flux of stainless steel plates. In each of these two methods, the coating was performed for 20, 40, and 60 minutes while other parameters remained constant. The SEM1 and EDS2 images were captured and then the contact angles were measured using the Stadler technique to study the effect of surface properties on Critical Heat Flux. Finally, the boiling curves of the hydrophilic and superhydrophilic surfaces were obtained and then the Critical Heat Flux (CHF) is determined. The CHF values were compared with the existing experimental data and empirical correlations. It was found that the CHF for nanoparticle coating by pool boiling, is significantly higher than those of electrophoretic coating. Also, a comparison of the present Critical Heat Flux results with those obtained by the empirical correlations that are a function of surface properties showed better agreement.

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.

In this paper, an inverse Heat conduction problem in one-dimensional infinite domain will be considered. By employing inverse Heat fundamental solution, and an over specified condition, the temperature and its Heat Flux will be identified.

A helical double-pipe Heat exchanger filled with a porous material under asymmetric Heat Flux is studied analytically. Momentum and energy equations are transformed to the Germano? s coordinate and then expressions representing the velocity and temperature fields are obtained based on the powers of dimensionless curvature using perturbation analysis. To be more insightful، contours of velocity and temperature fields are presented. Results reveal an asymmetric axial velocity profile arising from the curved geometry. The Nusselt number increases with respect to the dimensionless curvature increment as well as the inner to outer radius ratio increase.

In this study, some parameters such as quenching and boiling curves of a stainless steel cylindrical rod 80 mm long and having a diameter of 15 mm were experimentally obtained in saturate pure water and two nanofluids (SiO2 and TiO2) with 0. 01 wt%. The cylinder was vertically lowered into the pool of saturated water and its temporal center temperature was measured by a thermocouple. The boiling curves were then obtained by solving a transient one-dimensional inverse Heat conduction model and measuring the temperature at the center of the cylinder. The images of the surface morphology and uniformity of the deposited SiO2 and TiO2 nano particles were captured by the scanning electron microscope (SEM). The cooling time during quenching of the cylinder was decreased about 50% by nanoparticles deposition. However, the SiO2 and TiO2 nano particle deposition have similar Critical Heat Flux increment (up to 120%). Film boiling Heat transfer rate increased by repetitive quenching in SiO2 nanofluid.

Boiling Heat transfer is one of the most applicable Heat transfer processes in the industry. In recent years, many studies have been investigated in nanofluid pool boiling field and reported some contradictory results. This research is a qualitative and quantitative investigation to understand the behavior of nanofluid during pool boiling Heat transfer. For this purpose, a low concentration (up to 1000mg/l) of CuO-water nanofluid and a copper plate surface Heater with a diameter of 10 mm and surface roughness of 7.5 nm were used. CuO-water nanofluids have been created by 40nm nanoparticles and 1 to 1000 mg/l of concentrations are used in this research. The measurement of Critical Heat Flux at different concentrations of nanofluid showed that Critical Heat Flux has improved 92% in optimized concentration of 100 mg/l compared to distilled water. Atomic force microscopy, scanning electron microscopy and contact angle measurements have been done for analyzing properties of surface and nanocoated which are formed after nanofluid boiling. Results demonstrate that there is a positive effect in increasing roughness and a negative impact of thickness enhancement on Critical Heat Flux.

The necessity and importance of a high Heat removal potential in various areas particularly in nuclear applications are in a direct relationship with the excessively applied Heat Flux level. One way to increase the Heat transfer performance and subsequently enhance the threshold of the Critical Heat Flux is to employ spacer grids accompanied by mixing vanes. In this study, the effect of the spacers with mixing vanes on the Critical Heat Flux characteristics in the dryout condition has been numerically investigated employing the benefits of the Eulerian- Eulerian framework. In the current research, several vane angles, including vane with 0, 15 and 25 degrees in comparison with the effect of the bare spacer without any mixing vanes on the flow characteristics were examined. It was shown that the existence of the spacer alone, delays the temperature jump under Critical Heat Flux conditions. It was also concluded that increasing the angle of the mixing vanes, further improves the Heat transfer performance of the system by postponing the sudden temperature jump occurring in the channel; however, the presence of the spacers and vanes in the flow field imposes an increase of the pressure drop due to the constriction on the coolant flow area.

In order to justify the operating limits at actual nuclear plants, development of a design ,limit is a necessity. This paper describes the techniques involved in development of Critical, Heat Flux correlation (regression model) and its design limit for safety purposes of nuclear water reactors. The procedure involves all conservative statistical modelings. The method uses the basic relationship between Critical Heat Flux and local equilibrium quality which are ,linearly dependent on each other. The technique that is required to optimize the correlation is a non-linear regression process. Detection of outliers, collinearity check, and biasing toward a variable are considered. Checks for equality of standard variations, means, normality, and design limit of subgroups of samples and / or whole correlation data are also considered.