Experimental study of slug flow for condensation in a single square microchannel (original) (raw)

Measurement and modeling of R141b condensation heat transfer in silicon rectangular microchannels

Journal of Micromechanics and Microengineering, 2008

A special test apparatus for microchannel condensation was designed and fabricated based on silicon microfabrication processes, in which the condensing die was sandwiched by two cooling dies on both sides. Micro thermal sensors were integrated on both the surfaces of the condensing die to measure the wall temperature. Experimental investigations of R141b condensation were carried out in rectangular microchannels with hydraulic diameters of 117.3 µm, 92.3 µm and 66.7 µm, and with the mass velocity ranging from 50 to 500 kg m −2 s −1 . Characteristics of the heat transfer and pressure drop in microchannel condensation were analyzed and discussed. With the annular flow and slug/bubbly flow of microchannel condensation considered, by introducing a parameter of flow-pattern fraction, a model was developed to predict the characteristic of condensation heat transfer in microchannels with hydraulic diameter below 200 µm. It shows that the measured Nusselt number depends heavily on both the condensate mass velocity and the condensation heat flux, but depends less on the hydraulic diameter of the microchannels of the present study. The results show that the Nusselt number predicted by the model has a good accordance with the measured results, with a maximum deviation of 20%.

Flow and heat transfer in slug flow in microchannels: Effect of bubble volume

International Journal of Heat and Mass Transfer, 2019

Flow and heat transfer in gas-liquid slug flow in small diameter channels have been studied extensively in the last few decades because of its unique ability to segment the flow and enhance heat transfer by the internal recirculation in the liquid phase. The segmentation of the continuous liquid phase is achieved by the gas bubble of the size of the channel. While the hydrodynamics and heat transfer for long Taylor bubbles having volume more than that of a sphere that can fit in the channel has been studied extensively, very little attention has been paid to the bubbles having smaller volume but almost spanning the channel. The bubble volume can be represented by a non-dimensional equivalent sphere radius, ratio of the radius of a sphere having same volume as that of the bubble and channel radius. In this work, we study the hydrodynamics of the slug flow for a range of bubble volumes keeping all other parameters constant for non-dimensional equivalent sphere radius close to 1, between 0.72 and 1.55. The bubble shape, pressure distribution, bubble velocity and flow field in the liquid slug has been investigated. The effect of Reynolds number on the bubble shape for short as well as Taylor bubbles has also been studied. Heat transfer without phase change for constant heat flux boundary condition at the wall has been investigated and the Nusselt number is found to be highest for the non-dimensional equivalent sphere radius close to one. The heat transfer results have also been compared with a simple phenomenological model available in literature for heat transfer in slug flow.

Numerical study of vapor bubble effect on flow and heat transfer in microchannel

International Journal of Thermal Sciences, 2012

Flow boiling in a microchannel is characterized by nucleation and dynamic behavior of vapor bubbles in the channel. In the present study, the effect of vapor bubble on fluid flow and heat transfer in a microchannel is investigated via lattice Boltzmann (LB) modeling. With respect to boiling flow in a single microchannel, the bubble nucleation, growth, and departure are simulated by using an improved hybrid LB model. Relating bubble behavior with fluid flow and boiling heat transfer provides some insight into the relevant fundamental physics on flow boiling in the microchannel. It is found that the bubble growth before its departure from the wall induces an obvious resistance to the fluid flow. The processes of nucleation and motion of different bubbles interact, leading to an alternate, either enhanced or weakened, effect of bubble behavior on the flow boiling.

Condensation flow patterns and heat transfer in horizontal microchannels

Experimental Thermal and Fluid Science, 2018

An experimental investigation was carried out to study the effect of refrigerant mass flux, local vapour quality, coolant flow rate and inlet coolant temperature on the local condensation heat transfer coefficient. Flow visualization was also conducted to capture flow patterns during flow condensation using a high-speed camera integrated with a microscope. HFE-7100, a dielectric and eco-friendly refrigerant was used in rectangular multimicrochannels with a hydraulic diameter of 0.57 mm. Experiments were performed at a saturation temperature of 60°C, mass flux range 48-126 kg/(m 2 s), coolant flow rate range 0.5-1.1 L/min and inlet coolant temperature range 20-40°C. The results showed that the local condensation heat transfer coefficient increases with increasing mass flux and decreases with decreasing local vapour quality. A negligible effect of the coolant side conditions, saturation-to-wall temperature difference, on the local condensation heat transfer coefficient was found. The main flow regime was annular flow, while slug and bubbly flow were found at some operating conditions. The experimental results were compared with the existing correlations for heat transfer rates. Also, two existing flow pattern maps, for conventional and mini/microchannels, were used to compare the current flow pattern results.

An experimental investigation on pressure drop of steam condensing in silicon microchannels

International Journal of Heat and Mass Transfer, 2008

Experiments are carried out to study the two-phase pressure drop for water vapor condensation in four smooth trapezoidal silicon microchannels having hydraulic diameters of 109 lm, 142 lm, 151 lm, and 259 lm, respectively. It is found that two-phase frictional pressure drops in the microchannels are greatly influenced by the hydraulic diameter, mass flux and vapor quality. The two-phase pressure drop data in microchannels are compared with existing correlations for macro-and mini-channels based on the homogenous model and the separated flow model to determine their applicability to condensing flows in microchannels. A modified correlation for the Matinelli-Chisholm constant, taking into consideration of surface tension and diameter effects, is developed in the form of the Lockhart-Martinelli correlation for the pressure drop in steam condensation in microchannels. The resulting condensation pressure drop correlation equation is within ±15% of the experimental data.

Prediction of heat and fluid flow in microchannel condensation

E3S Web of Conferences

The condensing flow inside the microchannel has gained importance as the microchannel heat exchangers are widely used in the industry. In this study, a number of numerical simulations on condensing flow inside the microchannel were conducted to investigate heat transfer characteristic. Circularmicrochannel geometries with the various diameters were considered. The Volume of Fluid model was used to model twophase flow. The phase change at the saturation temperature was modeled by the Lee model.In the considered geometries, different from the conventional channels, surface tension forces can be importantcomparedto other forces. Therefore, surface tension was considered in the simulations. Constant wall heatflux and constant saturation temperature were applied as simulation conditions, similar to actual operating conditions. The predictions were validated by comparisons with the experimental results that exist in the literature. A satisfactory agreement of the present predictions with ...

Thermal Performance Analysis of Slug Flow in Square Microchannels

Thermal Performance Analysis of Slug Flow in Square Microchannels, 2020

Thermal performance enhancement of microchannel heat sinks for electronics cooling is becoming more and more necessary. To this end, microchannels with noncircular cross-sections conveying immiscible droplets have been employed in this study and geometric manipulations are applied to enhance fluid mixing and consequently achieve a higher rate of heat removal. Three-dimensional numerical simulations are performed using volume of fluid method for channels of 100 mm hydraulic diameter. Constant wall temperature is chosen as the boundary condition for heating section of the channels. Effects of parameters such as adding curvature to the side walls and varying the entering velocity of the base liquid on heat transfer rate are studied. A performance coefficient is used to evaluate the relative impact of increase in both the Nusselt number and pressure drop as a result of adding curvature to the channel walls. Results of the study showed that slug flow in curved channels is capable of improving the thermal performance in comparison with single liquid flow in straight channels and in best case, can improve the performance up to 50%.