Bamido Alaba | Texas A&M University (original) (raw)

Papers by Bamido Alaba

Thermal energy storage (TES) can be utilized as supplemental platforms for improving operational ... more Thermal energy storage (TES) can be utilized as supplemental platforms for improving operational reliability and systemic efficiency in variety of industries, such as for reducing water usage in power production (food-energy-water/ FEW nexus), chemical and agro-process industries and for improving sustainability (e.g., desalination), etc. Phase change materials (PCMs) can be used in Original Research Article Shettigar et al.; JERR, 20(4): 70-84, 2021; Article no.JERR.65675 71 TES due to their high latent heat storage capacity during phase transformation. Inorganic PCMs typically have the highest latent heat capacity and are attractive for their ability to store the larger quantities of thermal energy in small form factors while conferring respectable power ratings (however, they suffer from compromised reliability issues, that often arise from the need for subcooling). Subcooling (also known as supercooling) is a phenomenon where the temperature needs to be reduced substantially bel...

In recent times, goals for industry standards and national mandates have resulted in attempts to ... more In recent times, goals for industry standards and national mandates have resulted in attempts to reduce the environmental impact of transient thermal processes (e.g., thermal management) in a multitude of applications ranging from industry to domestic use (consumer markets). A potential cheap, efficient and reliable solution is the implementation of a thermal energy storage (TES) unit which can serve as a primary or supplemental option, i.e., as a source of heating and/or cooling. Phase change materials (PCMs) can be used in TES due to their high latent heat storage capacity during phase transformation. Inorganic PCMs typically have the highest latent heat capacity and are attractive for their ability to store the highest amounts of thermal energy in small form factors while conferring respectable power ratings (however, they suffer from compromised reliability issues, that often arise from the need for subcooling). Subcooling (also known as supercooling) is a phenomenon where the t...

Volume 3: Fluid Mechanics; Micro and Nano Fluid Dynamics; Multiphase Flow

A normally-open thermally-actuated microvalve was designed (using microfabrication/soft-lithograp... more A normally-open thermally-actuated microvalve was designed (using microfabrication/soft-lithography techniques involving 3D Printed molds), assembled and tested. The motivation of the research work is to develop an array of microvalves for precise delivery of water to individual plants in a field (with the goal of developing smart irrigation systems for high value cash-crops in the agricultural sector). It is currently impossible to control application of irrigation-water at the level of a single plant. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the output of every plant in a farm field could be optimized (i.e., food-water-energy nexus in sustainability applications). The aim of this study is to develop and test a microfluidic system (consisting of a microvalve array) that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. Two ty...

2021 20th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (iTherm), 2021

Polydimethylsiloxane (PDMS) is a soft polymer that is primarily used for soft lithography (e.g., ... more Polydimethylsiloxane (PDMS) is a soft polymer that is primarily used for soft lithography (e.g., microfluidics and labon-chip devices) and also has wide range of applications, such as for thermomechanical actuators. The unique material properties of PDMS (such as the low values of Young's modulus) renders it to be an attractive material for applications where large range of deformations can be achieved with small variations in the actuating pressure (or actuating forces) thus providing good mechanical advantage. PDMS has been reported in the literature for microfabricating and testing thermally actuated microvalves (for microfluidics applications). These microvalves involve the thermal expansion of a fluid resulting in the deformation of a flexible PDMS membrane. Accurate numerical modeling of such thermo-mechanical actuators made from PDMS necessitates the knowledge of the temperature dependent mechanical properties of PDMS (such as Young's modulus) which is currently lacking in the literature. In this study large deformations were obtained for a thin flexible PDMS membrane (with a square footprint of 7.2 mm and thickness of 200 microns) that was microfabricated on the top of a hermetically sealed cavity (that was 3 mm deep) by subjecting the membrane to thermo-pneumatic pressure arising from the thermal expansion of air trapped in the hermetically sealed cavity and heated from below. This enabled the experimental determination of maximum displacement of the membrane as a function of actuating temperature and therefore the estimation of the temperaturedependent mechanical properties (e.g., Young's Modulus and Poisson's ratio) using parametric simulations using the finite element method (FEM) and based on linear elastic assumption for the deformation of PDMS. Using digital images of the convex shape of the deformed PDMS membrane the maximum deformation was measured as a function of temperature under steady state conditions. Computational Fluid Dynamics (CFD) based commercial solver (Ansys™ 2019R1®) was used to estimate the air pressure inside the hermetically sealed chamber as a function of temperature under steady state conditions (which was verified by analytical calculations). The values of pressure (obtained from CFD simulations) was used as the boundary condition in the FEM model (Ansys™ 2019R1®) for a fixed value of the Young's Modulus and Poisson's ratio to estimate the maximum deformation of the PDMS membrane. By parametric variation of the Young's Modulus and Poisson's ratio (for a particular operating temperature) the actual values were determined based on the computational result that matched the experimental data. The results show that the material

ASME Summer Heat Transfer Conference, 2020

Analytical and computational studies were performed to compare the convective heat transfer chara... more Analytical and computational studies were performed to compare the convective heat transfer characteristics of a supercritical fluid in a circular pipe for horizontal flow configuration. The motivation of this study was to explore the efficacy of heat exchangers involving forced convective heat transfer of supercritical fluids (tube side) integrated with air cooling (i.e., in free convection). The goal of this study was to determine the forced convective heat transfer characteristics of supercritical carbon dioxide (sCO2) in air-cooled tube heat-exchangers. The scope of this study was limited to the values of Reynolds number (Re) varying from 10 ~10 4 (i.e.,involving both laminar and turbulent flow correlations for analytical formulations and computational models). The predictions for the forced convection heat transfer characteristics (e.g., heat transfer coefficient, pressure drop, volume flow rate, mass flow rate, pump penalty/ pumping power/ required compressor ratings, Nusselt number (Nu) etc.) were obtained using analytical formulations and compared with that of computational models. The flow configurations involved a horizontal circular pipe of 1 m length and with different diameters (ranging from 1 mm-10 mm). The supercritical properties of the working fluid were investigated at a fixed value of reduced pressure (Pr = 1.1) and a fixed range of temperatures, i.e., T, varying from 550 to 750 [K]. The fluid properties were gleaned from the NIST property database (available online at the NIST website). For the second part of this study, the forced convective heat transfer characteristics of sCO2 flowing in a horizontal tube with circular cross-section were studied using analytical correlations (e.g., Dittus-Boelter and Gnielinski correlation) and validated using commercial tools for Computational Fluid Dynamics (CFD)/ Computational Heat Transfer (CHT), i.e., using Fluent® (Ansys®). Validation of the analytical predictions using CFD/ CHT tools was performed to ascertain the level of uncertainty in the predicted results due to acute variation of the thermo-physical properties as a function of temperature and pressure (since the thermo-physical properties are expected to oscillate widely in the vicinity of the critical point). In the simulations, the inlet temperature for the supercritical fluid (sCO2) was fixed (at Tin = 700 [K]), and the ambient temperature was also fixed (at Tamb = 300 [K]), for the purpose of determining the values of the natural convection coefficients (external to the tube). Constant values of the thermo-physical properties of sCO2 at the mean film temperature (and corresponding to the inlet pressure values) were assumed for obtaining the analytical predictions. The results from the CFD / CHT simulations helped to quantify the level of uncertainties in the assumption of constant properties (in the analytical model) at different values of Reynolds number (i.e., for both laminar and turbulent flow regimes).

ASME Summer Heat Transfer Conference, 2020

It is currently impossible to control irrigation at the level of a single plant. Even with drip i... more It is currently impossible to control irrigation at the level of a single plant. Even with drip irrigation, in which emitters could conceivably be placed on a plant-by-plant basis, there is no way to control the amount of water emitted according to the needs of the individual plants. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the water input for every plant in a farm (or field) could be optimized. Therefore, we are exploring the possibility of developing a microfluidic system that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. The principal aim is to show proof of concept by building and testing a prototype to produce data suggestive of the potential for multiple individually controllable microfluidic ports along a pressurized tube of water. Hence, in this study we perform experiments using a thermally actuated microvalve for irrigation in precision agriculture applications. The microvalve was manufactured using soft-lithography techniques, i.e., using polydimethylsiloxane (PDMS). The active microvalve was designed for a "normally open" configuration and consists of two layers: (1) a flow layer and (2) a control layer. The flow layer contains the water inlet, outlet, and the flow channels for passage of water. The control layer contains an enclosure (chamber) which expands upon heating, which in turn deforms a thin membrane into the flow layer and thus impedes (or reduces) the water flow rate in the flow layer. Both layers are bonded together and then on a glass substrate. The bonded PDMS microvalve and glass assembly is heated to different temperatures for enabling the actuation of the microvalve. Experiments were performed using two microvalves of identical design but with two different actuation fluids. The first design used the control chamber filled the air while the second design used the control chamber containing a Phase Change Material (PCM). Experiments were performed to determine the reduction of water flowrate as the membrane deforms with increase in temperature. Water flows into the inlet of the microvalve from a syringe barrel, with a hydrostatic pressure head of about 0.62 [m]. The water from the microvalve outlet was collected in a 10[ml] pipette. The results show that the water flowrate decreased as the temperature at the base of the microvalve was increased. There was a 60% and 40% reduction in the water flowrate through the microvalve design with control chamber containing air and PCM (phase change material) respectively.

Volume 3: Fluid Mechanics; Micro and Nano Fluid Dynamics; Multiphase Flow

2021 20th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (iTherm), 2021

ASME Summer Heat Transfer Conference, 2020