Heat transfer plays an important role in the conceptual and the detailed design of cooling systems in internal combustion (IC) engines and has considerable influences over its operational performance. The demand for higher possible heat transfer rates has led to use a controlled transition from a single-phase convection to a sub-cooled boiling flow in hot regions, through the cylinder head. In order to achieve controlled boiling over a wide range of operating conditions, detailed flow and heat transfer analysis are essential. The computational fluid dynamic (CFD) simulation, incorporating the boiling model, is an effective approach for the thermal analysis of IC engines. In this paper, the water jacket of the national turbo-charged engine was simulated with the AVL-FIRE software to consider effects of boiling phenomena in the water jacket. For the validation of calculated results was performed through a test validation in a horizontal heated duct with two models, Chen and BDL models. It showed that the Chen boiling model was in better satisfactory with experimental data than the BDL model under the same conditions and could be used for calculating the boiling heat transfer in cooling passages of the engine. Contours of the pressure, the velocity, the heat transfer coefficient were demonstrated with and without consideration of boiling. Results showed that when boiling occurs, the heat transfer coefficient was significantly enhanced.

Boiling heat transfer is one of the most applicable heat transfer processes within the industry. In this paper, the pool boiling heat transfer of Fe3O4 /water nanofluid (ferrofluid) in atmospheric pressure has been analyzed, experimentally. The nanofluid in this study, has been synthesized in a single step and retains high stability. The replication and accuracy of the testing machine has been studied for deionized water for three times, indicating an appropriate concordance with the literature. Considering different volume concentrations of the nanofluid has revealed that boiling heat transfer in high concentrations decreases with an increase of concentration, while it rises with the increase of concentration in low concentrations. Hence, boiling heat transfer coefficient in 0.1% volume concentration nanofluid has been measured to be the optimum value which increases up to 43%. The roughness of boiling surface was varied with the deposition of nanoparticles in various conditions of nanofluid concentration, and heat flux. It is noteworthy that in the present research, the effects of surface roughness changes due to nanoparticles deposition and the impact of passing time on boiling process have been investigated, for the first time. Therefore, several experiments have been designed in order to study the change of nanoparticles deposition due to the change of nanofluid concentration and boiling surface heat flux. The results indicate that boiling heat transfer of deposited surfaces at low heat fluxes decreases; while it rises at high heat fluxes.

This study aims to investigate the effect of nanoparticle deposition on the boiling surface in the presence of microchannel on the characteristics of boiling heat transfer. In this experimental study, the copper boiling surfaces including polished circular surface, rectangular and trapezoidal microchannels were used. The microchannels include feeding sub-channels perpendicular to the main channel, which increases the boiling surface and separates the downward cool fluid flow and upward hot bubbles. Nuclear boiling experiments on microchannel surfaces in the presence of a hybrid water-based nanofluid containing 70% titanium oxide and 30% OH-based multi-wall carbon nanotubes in volumetric concentrations of 0.1% and 0.5% have been conducted. The results of nanofluid boiling experiments on both microchannel surfaces show that with increasing concentrations, critical heat flux and heat transfer coefficient increases and the highest increase in critical heat flux and heat transfer coefficient is related to the hybrid nanofluid with 0.5 % volumetric concentration on the surface with trapezoidal microchannel and their values are 64.64% and 344.76%, respectively, compared to pure water boiling on the polished copper surface. Also, in boiling of pure water on the deposited surfaces with nanoparticles, the greatest increase in critical heat flux and heat transfer coefficient is related to the surface with trapezoidal microchannels with 0.1% volumetric concentration  and 0.5% and volumetric concentration  and  their values are 120.16% and 149.4% respectively, compared to pure water boiling on the polished copper surface.

In order to meet increased demand for dissipating high heat fluxes from electronic chips that are continually shrinking in size, development of new cooling technologies have been considered for the last two decades. Recent research efforts have shown that boiling two phase flow through the mini-channels can provide desired heat transfer coefficients. The occurrence of the dryout phenomenon followed by a sudden increase in temperature due to the critical heat flux is one of the most important challenges in this context. In this study, departure from nucleate boiling phenomenon due to the critical heat flux in a mini-channel has been examined using computational fluid dynamics. The governing equations solved are generalized phase continuity, momentum and energy equations. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model developed by Rensselaer Polytechnic Institute (RPI). To simulate the critical heat flux phenomenon, the RPI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases considering the existence of thin liquid wall film. It was observed that by applying high heat fluxes near to CHF, DNB occurred and a vapor layer formed adjacent to the wall while most of the flow field is still subcooled liquid.

The subcooled flow boiling occurs when the bulk temperature is less than saturation temperature of the liquid at that pressure while the surface temperature is higher. The most importance of boiling phenomenon is related to the high latent heat of fluid which could removes high heat flux at relatively low temperature difference between liquid and the hot surface. In this study, the impact of velocity and roughness on the subcooled flow boiling were investigated experimentally for pure water. An experimental setup was designed and manufactured. The experimental setup consists of a plexiglass channel with cross section 20×30 mm and the length of 120 cm. A cylindrical heater with diameter 12 mm made of copper is located on the bottom surface of the plexiglass channel. All the experiments were conducted for the surface roughness of 0.65, 2.5 and 4.4 µm at velocities of 0.5, 0.7 and 0.9 m/s. The experimental results show that the surface heat flux increases as the surface roughness and velocity increases. However, this affect of velocity enhancement was only observed for lower boiling surface temperature and opposite trend has taken place for higher boiling surface temperature. This is due to the simultaneous consideration of the convection and boiling terms along with the interaction between them which has not been presented experimentally yet. It appears that this kind of experimental study has not been carried out for copper type surfaces.

One of the main reasons of destruction of the coastal slopesand riverbanks is failure of side slopes under the rising water table or sliding of the side slopes under the drawdown of channel water. In this research, effect of variations of water table and channel water level (peak and drawdown conditions of flood, respectively) on the piping of coastal slopes was studied and effect of cutoff wall on the phenomenonwas investigated. Experiments were conducted in a seepage tank having a trapezoidal cross-section with the side slope of 1.5% and 0.58 mm mean diameter of the particles. Cutoff wall was fixed in the relative depths Z/d=0.5, 0.67, 0.83 and 1 (Z is the depth of cutoff wall and d is the depth of channel). Results of peak conditions of flood (rising the water table), under controled experiment showed the relative channel water level was equal to y/d=0.7. In the experiment with cutoff wall Z/d=1 and without occurrance of piping, exit flow gradient was decreased approximately 41 present with respect to the control experiment. Piping was occurred only in the relative channel water level equal to y/d=0.167. Results of drawdown conditions of flood showed, piping phenomenon occured in the all channel water level. In the experiments with cutoff wall, in the cases with high water table, despite of existence of cutoff wall, increasing the exit flow gradient caused piping phenomenon in the all of the experiments because of increasing hydraulic head. Other wise, in the experiment with the relative water table equal to h/d=0.933, piping was occurred in the all depths of cutoff.

Investigating of boiling process is one of the attractive fields for researchers, because of many applications in industry such as heat exchangers and air condition systems. One of the important and effective factors in pool boiling heat transfer is the heating surface geometry. In present article, pool boiling of dionized water and Fe3O4/water nanofluid at atmospheric pressure have been analyzed on smooth and grooved copper surfaces, experimentally. The effect of rectangular, circular and triangular grooves with the same pitch on boiling heat transfer is the main aim of present article. The results have showed that the boiling heat transfer coefficient of dionized water in circular and rectangular grooved surfaces has enhanced 92% and 48.9%, respectively, and has reduced 33.1% in triangular grooved surface toward the smooth surface. Also, the boiling heat transfer coefficient of Fe3O4/water nanofluid in circular grooved surfaces has increased 40.7% and has decreased 21.8% and 88.7% in rectangular and triangular grooved surfaces, respectively, toward the smooth surface. The corners existence in rectangular and triangular geometries causes thermal resistance increasing and heat transfer coefficient decreasing toward circular geometry. Also, the groove area, the mechanism of bubbles creation and nanoparticles deposition content on different surfaces are effective on the boiling heat transfer. For investigation of depth effect, the grooves depth was increased in different geometries. By adding depth, the boiling heat transfer coefficient of water and nanofluid has increased up to 43.5% and 40.6%, respectively, because of heat transfer surface and nucleation sites density augmentation.

Numerical simulation of boiling has always been a challenging problem in terms of the variety and effectiveness of two-phase models. Boiling is one of the efficient methods in high heat transfer. In boiling simulation, in addition to choosing an appropriate heat and mass transfer model, it will be important to evaluate the surfaces which boiling occurs on it. A problem of nucleate boiling of saturated liquid is numerically simulated in this investigation by use of VOF (volume of fluid) model together with the geo-reconstruction of the interface. One-dimensional Stephan problem as sucking interface problem is solved for verification the numerical solver. Two-phase change models of the Lee model and the Tanasawa model are used in order to calculate the rate of phase change and source terms. The results of nuclear boiling are investigated on the hydrophilic surface, hydrophobic surface, and the surface with contact angle 90 degrees. The results show that boiling on hydrophobic surfaces causes the detachment of larger bubbles with a larger heat transfer rate. Besides, bubble merging depending on the density of nucleation sites leads the nuclear boiling on hydrophobic surface to film boiling.