Dr. Hisham E. Hegab Profile

Dr. Hisham E. Hegab

Assistant Professor at Louisiana Tech Univ

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Proceedings Article | 28 September 2001 Paper

Experimental investigation of flow and heat transfer characteristics of R-134a in microchannels

Hisham Hegab, Abdullahel Bari, Timothy Ameel

Proceedings Volume 4560, (2001) https://doi.org/10.1117/12.443049

KEYWORDS: Microfluidics, Aluminum, Temperature metrology, Surface roughness, Convection, Adhesives, Glasses, Silicon, Epoxies, Uncertainty analysis

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Fluid flow and heat transfer characteristics of single-phase flows in microchannels for refrigerant R-134a were experimentally investigated. Experiments were conducted using rectangular channels micro-milled in aluminum with hydraulic diameters ranging from approximately 112-mm to 210-mm and aspect ratios that varied from 1.0 to 1.5. Using overall temperature, flow rate, and pressure drop measurements, friction factors and convective heat transfer coefficients were experimentally determined for steady flow conditions. Reynolds number, relative roughness, and channel aspect ratio were the parameters examined in predicting friction factor and Nusselt number for the experiments. Experiment results indicated transition from laminar to turbulent flow occurred between a Reynolds number of 2,000-4,000. Friction factor results were consistently lower than values predicted by macroscale correlations. Nusselt number results indicated channel size may suppress turbulent convective heat transfer. Results also indicate that surface roughness may affect heat transfer characteristics in the turbulent regime.

Proceedings Article | 18 August 2000 Paper

Fluid flow modeling of micro-orifices using micropolar fluid theory

Hisham Hegab, Guohua Liu

Proceedings Volume 4177, (2000) https://doi.org/10.1117/12.395670

KEYWORDS: Microfluidics, Systems modeling, Data modeling, Instrument modeling, Sensors

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Previous research has indicated that micropolar fluid theory may provide a better model of fluid flow in microfluidic devices than classical Navier-Stokes theory. Micropolar theory augments classical Navier-Stokes theory with additional equations that account for conservation of micro- inertia moments. In our work, a two-dimensional numerical model based on micropolar fluid theory is used to examine flow behavior in micro orifices. This particular flow geometry has many application within microfluidic systems and devices such as flow sensors and micro valves. The numerical model is validated by comparison to experimental data and an analytical solution determined for fully developed flow conditions in microchannels. The numerical model was used to examine the effect of orifice geometry on pressure drop and the size of the recirculation region. Simulations were performed for orifice contraction ratios of 0.2, 0.44, and 0.6. The numerical results indicate an increase in the pressure drop when compared to traditional macroscale theory predictions and a decrease in the size of the recirculation zones after the orifice. The results provide further evidence that micropolar fluid theory may provide a better approximation for the observed increases in friction that have been reported in the literature for experiments on microchannel flows.

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