Research Projects
Experimental investigation on pulsating jet-impingement and spray cooling performance for high heat flux application using Infrared thermography technique
The continuous search for better and relatively effective thermal management techniques to cool the ever increasing power dissipated from microelectronic devices has greatly excelled both fundamental and applied knowledge of thermal management. As part of this endeavor, spray cooling has demonstrated superior cooling capabilities. However, some critical fundamental knowledge about spray cooling is still unknown, and systematic studies pertinent to identifying how to further enhance these techniques are very demanding.
I am currently focusing on developing and modifying an effective flow loop (see above figure) that will be implemented to create a pulsating spray cooling pattern on a heated surface. I am considering Indium Tin Oxide (ITO) as one of the potential heating surface due to its compatibility with heat transfer mapping using optical technique. I will pursue both smaller hot-spot (< 300 μm2) and comparatively larger area (< 1 cm2) surface heating configurations, By our Time-domain Thermoreflectance (TDTR) setup, we will map the Heat Transfer Co-efficient (HTC) around the heated the region. For background, the TDTR measurement principle is based on measuring heat removal rate from a metal thin-film by its surroundings. For instance, the cooling of a Ti thin-film (≈ 64 nm in thickness) by flowing, stagnant, or boiling water (top) and the FS substrate (bottom). TDTR is a well-established optical technique used by the thermal management engineers and scientists’ community to characterize micro- and nano-scale heat transport. In principle, TDTR technique uses two concentrically focused pump and probe laser beams to heat (with the pump) and then measure or map (with the probe) the temporal changes in thermal transport in a sample (ITO in our case).
Thus, we will provide experimental evidence for future success in the proposed pulsed spray cooling studies. My spray cooling setup integrated with TDTR heat transfer mapping technique will help researchers and scientists better understand the complex interaction of water droplets with heated surfaces and thus help the thermal management system designers take care of the high thermal loads of microelectronics with simpler manifold designs.
Enhancement of heat transfer using nanoscale fluids
We reported that inclusion of nanoparticles and ferroparticles, for instance Cu, CuO, Al2O3, Fe2O3, into base fluid (water) cause increment of surface area necessary for thermal transport. Therefore, micro-convection dominates over the other modes of heat transfer. Thermal gradient inside the problem domainis found to be higher. As a result , average Nusselt number at the heated surface tends to rise. Therefore more effective and significant thermal transport can be achieved. Galerkin method of finite element analysis has been used to solve the governing equations. Numerical accuracy of solution is ensured by the grid independency test.
Publication: S. Mojumder, K. M. Rabbi et al., Journal of Magnetism and Magnetic Materials, 407 (2016) 412-424.
Effect of external magnetic field on heat transfer process
We reported that, in presence of magnetic field, Lorentz force retards flow velocity and therefore, reduces convection current. The characteristic of the flow strongly depends on intensity and direction of the external magnetic field. The applied magnetic field manipulates the suspended particles and rearranges their concentration in the fluid which strongly changes heat transfer characteristics of the flow. Magneto hydrodynamic (MHD) flow has a wide variety of application in engineering such as cooling of nuclear reactor, electronic package, crystal growth in liquid, microelectronic devices, and solar technology.Thus, the more the Ha, the more the Lorentz force dominates on the buoyancy force. Therefore, the strength of flow and thermal field varies with the strength of magnetic field.
Publication: K. M. Rabbi et al., Procedia Engineering, 105 (2015), pp 73-80.
Non-Newtonian flow modeling under rotational effect
We reported that non-Newtonian ferrofluid in lid-driven cavity can be implemented to quantify heat transfer rate in rotating environment. Dilatant fluid (n > 1) shows more strong flow and thermal field at higher rotational speed of cylinder. Power law index, rotational speed, Richardson number and solid volume fraction has a significant impact on velocity profile. More than 46% better heat transfer has been recorded at higher rotational speed (Ω = 15) in case of dilatant ferrofluid. Non-Newtonian ferrofluid exhibits better heat transfer (more than 15%) than non-Newtonian fluid. Further investigation can be made to develop a critical range of different pertinent parameters in this regard.
Publication: K. M. Rabbi et al., AIP Conf. Proc. 1754, 040016 (2016).
Turbulent flow modeling in VVER-1000 reactor
We carried out a three-dimensional Computational Fluid Dynamics (CFD) analysis for turbulent flow in the interior subchannel of hexagonal fuel rod assembly of VVER-1000. The following remarks may be drawn from the study-The change in temperature and velocity profile in the sub-channel after a critical axial distance is insignificant. With the increase of Reynolds number, the minimum axial distance required to achieve a fully developed flow decreases. To remove more heat, sufficient length of sub-channel must be allocated for fully developed Nusselt number. So, for VVER-1000, Reynolds number ≥ 105 may be considered. Relative pressure drop is almost the same for various Reynolds numbers. Friction factor for the interior sub-channel of hexagonal fuel rod assembly of VVER-1000 is validated with the Prandtl correlation.
Publication: M. A. Ullah, K. M. Rabbi et al., 11th International Conference on Mechanical Engineering, Dhaka, Bangladesh (ICME) 2015.
Solar predictive modeling using Artificial Neural Network (ANN)
We investigated an artificial neural network (ANN) model can be used to predict the monthly solar energy potential in Bangladesh. Used data are taken from NASA database for the past 22 years average from 1983 to 2005 and eight divisional cities are considered in this study. A multi-layered feed forward ANN model of four layers with eight independent input variables i.e. average temperature, sunshine duration, wind speed, precipitation, humidity, elevation, cloud coverage and atmospheric pressure to predict the monthly solar irradiation. Data from six cities are used for training and the remaining two cities were considered for testing and validation. A solar irradiation map is developed by data mapping using GIS technology. From the illustrations, the predicted data show good agreement with the observed data. This indicates that, this model can be used to predict solar irradiation of Bangladesh and to provide sufficient information about the feasibility of solar powered projects.
Publication: K. M. Rabbi et al., 4th Int. Conf. on Developments in Renewable Energy Technology (ICDRET), Dhaka, Bangladesh, IEEE Explore 2015.
Computer Aided Design and Fabrication
We re-developed a concept of utilizing solar power in an efficient way along with present transportation system. Through the investigation researchers may come to know the advantages of it which eventually paves the way to its public acceptation. By further research, features of solar powered motorized rickshaw can be advanced with new mechanical designs and a system with better mileage. We also developed a framework using Computer Aided Design (CAD) modeling. Thus this framework can be applied to the world of practice by quenching the thirst of energy specially by energy harvesting and designing effective cooling system.
Publication: T Ahmad, K. M. Rabbi et al. ,The 15th Annual Paper Meet (APM), Institute of Engineers Bangladesh, 2013.
Full publication list and presentation list can be found here.
© 2020 Khan Mohammad Rabbi.