Effects Of Bubble Injection Research Articles

Numerical investigations on the effect of bubble injection on heat transfer of natural convection in laminar flows

AbstractIt was found that the injection of bubbles into liquid can effectively improve heat transfer efficiency, so it is important for industrial applications to investigate the effect of bubble injection on heat transfer. The effect of bubble injection on natural convective heat transfer in steady laminar flows in a vertical channel is investigated using the volume of fluid (VOF) method, and the effects of bubble diameter, Eötvös number (Eo), bubble arrangement, and bubble distance from a hot wall on the heat transfer between the hot wall and liquid are studied, respectively. The results show that bubble injection can effectively improve the heat transfer between the hot wall and liquid; an increase in bubble diameter and Eo can improve the enhancement effect of heat transfer and can expand the enhancement area of heat transfer; the closer to the hot wall a bubble is, the better the enhancement of heat transfer is; and the spacing and arrangement of bubbles also have important effects on the heat transfer between the hot wall and liquid. The comparison shows that the enhancement of heat transfer is the best for the vertical arrangement of double bubbles, which increases the local heat transfer coefficient by 3.2 times. The enhancement of heat transfer generated by bubble injection is related to the degree of disturbance of the local liquid phase caused by bubble injection. The more strongly the local liquid is disturbed, the thinner the local temperature boundary layer becomes, and the better the enhancement of heat transfer is.

Effects of Bubble Injection on Heat Transfer from a Volumetrically Heated Sulfate Salt Solution

The fissioning of uranium in an aqueous solution creates 99Mo, the precursor to 99mTc, but also generates large amounts of hydrogen and oxygen from the radiolysis of the water. When the dissolved gases reach a critical concentration, bubbles will form in the solution, affecting both the fission power and the heat transfer out of the solution. Magnesium sulfate (MgSO4) was chosen as a surrogate for uranium sulfate salt in an aqueous solution for the experiments. A high aspect ratio tank was constructed to measure heat transfer from the solution with internal gas and heat generation. A fritted glass air injection manifold allowed the exploration of bubble characteristics and flow patterns on heat transfer from the heated pool to the cold walls. Experimental data analysis provided heat transfer coefficient values as a function of axial position, power density, and the superficial gas velocity in the pool. Results, including a recommended correlation for average heat transfer coefficients, are provided for superficial gas velocities between 0 and 0.3 cm/s and power densities of 200 and 400 W/L in pH 7 and pH 1 MgSO4 solutions.

Optimization of heat transfer and pressure drop characteristics via air bubble injection inside a shell and coiled tube heat exchanger

Most recently, a couple of academic investigations have focused on air bubble injection (with a constant air flow rate) inside the shell-and-coiled-tube heat exchangers in order to increase the performance and effectiveness of these heat exchangers. However, the amount of air flow rate has great effects on these applications which have not been probed in previous studies. Moreover, in former papers, air flow has been injected inside the only shell side and not coil side of heat exchanger. Hence, in this experimental research, air bubbles is flowed inside the shell or coil side of heat exchanger with variant air flow rates to detect an optimum condition and also fill out this topic. Air flow rate was changed between 1LPM and 5LPM. Coil side water flow rate was kept at 1LPM (inlet temperature of 40°C) and shell side water flow rate was varied between 1LPM and 5LPM (inlet temperature of 15°C). Furthermore, pressure drop due to bubble injection is measured in this paper for aforesaid heat exchangers as another new parameter. Observations showed that the air flow rate and injection side (shell and coil) play key roles on the effect of bubble injection into the heat exchangers. Findings showed that, increment of air flow rate causes enhancement of overall heat transfer coefficient. Air injection into the shell side of the heat exchanger increased the overall heat transfer coefficient 6–187% depending on air flow rate.

Effects of Bubble Injection on Heat Transfer from a Volumetrically Heated Water Pool

The fissioning of uranium in an aqueous solution creates 99Mo, the precursor to 99mTc, but also generates large amounts of hydrogen and oxygen from the radiolysis of the water. When the dissolved gases reach a critical concentration, bubbles will form in the solution, affecting both the fission power and the heat transfer out of the solution. A high aspect ratio tank was constructed to measure heat transfer from a liquid pool with internal gas and heat generation. Different air injection manifolds allowed the exploration of various bubble characteristics and bubble patterns on heat transfer from the pool to the cold walls. Experimental data analysis provided heat transfer coefficient values as a function of axial position, power density, and the superficial gas velocity in the pool. Results, including a recommended correlation for average heat transfer coefficients, are provided for superficial gas velocities between 0 and 0.3 cm/s and power densities between 115 and 400 W/ℓ in water.

Effects of Bubble Size on Heat Transfer Enhancement for Laminar Natural Convection by Sub-Millimeter Bubbles

Sub-millimeter-bubble injection is one of the most promising techniques for enhancing heat transfer for the natural convection of liquids. So far, we have investigated experimentally the heat transfer enhancement by sub-millimeter bubbles. However, the effects of the bubble diameter on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of bubble diameter on the heat transfer enhancement by sub-millimeter bubbles for the laminar natural convection of water along a vertical heated plate. We conduct temperature measurements using thermocouples and velocity measurements using a Particle Tracking Velocimetry (PTV) technique. We also carry out two-dimensional numerical simulations to comprehensively understand the effects of bubble injection on the flow near the heated wall. Temperature measurements show that the heat transfer coefficient increases with a decrease in the bubble diameter. This is due to a significant increase in the bubble advection effect.