Nirmalendu Biswas

Influence of Heater Aspect Ratio on Natural Convection in a Rectangular Enclosure

Analysis of natural convection with heating source protruding from the nonheated lower surface of a rectangular enclosure has been performed using experimental apparatus of a two-dimensional particle image velocimetry system. Results obtained from the experiments are used to validate the numerical simulations. Extensive numerical simulation is carried out using in-house code based on the finite-volume method and the SIMPLE algorithm. Heat transfer and entropy generation are estimated numerically for a protruding heater of different perimeters and aspect ratios, Rayleigh number, and Prandtl number. It is found that the Rayleigh number, Prandtl number, and heater sizes have strong influence on the flow fields, thermal mixing, heat transfer characteristics, and entropy production rate in the enclosure. The analysis indicates that a high thermal mixing may not be the most favorable situation for achieving higher degree of temperature uniformity. The effect of Bejan number is discussed.

Mixed Convection Heat Transfer in a Grooved Channel with Injection

Improved heat transfer is very important for the energy efficiency, higher performance, and size reduction of a system. In this context, the paper presents an efficient way for improving mixed convection heat transfer in a grooved channel by dividing total flow into main flow and injection under the assisting flow configuration. The influences of the pertinent injection parameters (e.g., position, size, and injection flow) are investigated systematically for Richardson number 0.1–10 and Reynolds number 50–200 using an in-house CFD code. The results reveal that performance with injection is always superior and heat transfer enhancement is found to increase from 50 to 218% depending upon injection, Richardson number, and Reynolds number.

Numerical Simulation of Laminar Confined Radial Flow Between Parallel Circular Discs

In this work, a fluid jet is issued axially from a short, circular nozzle and then fed radially outward through the clearance of two parallel circular discs. The disc assembly was considered fully submerged within a fluid in a horizontal plane. Axisymmetric computational domain is chosen for the analysis considering steady, laminar flow. The numerical simulation is carried out by an in-house CFD code developed following the finite volume method and SIMPLER algorithm. The effects of flow rate and channel dimensions are analyzed to understand the characteristics of submerged radial flow. It is found that the flow field consists of several features like toroidal recirculation, annular separation bubble and flow reattachment, which are strongly influenced by the clearance between the two parallel discs and the flow rate.

PIV Measurements and POD Analysis during Natural Convection with Protruded Heater in a Rectangular Enclosure

An extensive measurement using 2-D Particle Image Velocimetry (PIV) technique has been carried out during natural convection with a heating sources protruded on the non-heated lower surface of a rectangular enclosure. A time-resolved data series have been captured to analyse the effect of different Rayleigh number on flow fields for fluid of Prandtl number 0.71. A fast and efficient data analysis tool based on the Proper Orthogonal Decomposition (POD) technique has been used to create low dimensional approximations of high dimensional systems for predicting the dominant flow structures. This includes interpolating results at off-design parameters, along with knowledge about contours of different higher modes as well as obtaining information about the energy content in each specific mode. The mean non fluctuating mode showed maximum energy and the same decreased with increasing mode number. This allowed a clear detailed understanding about the complex non-linearities in the problem using a linear decomposition technique

Mixed Convection in a Ventilated Enclosure with Different Heater Position

A comprehensive investigation on mixed convection in a ventilated enclosure has been carried out numerically for different positions of heat sources at the sidewalls. The relative position of the isothermal heat source and heat sink on both vertical walls influences the heat transfer process. Different configurations are simulated using an in-house developed CFD code, based on finite volume method. The characteristics of heat transfer, flow complexity and entropy generation are calculated as a function of Richardson number (Ri = 0.01–100) and Reynolds number (Re = 100). The results for different position of heat sources and heat sinks are presented along with isotherms, streamlines and Bejan number. The results show that the performance with middle-middle position of heat source is always superior.

Experimental studies of flow through radial channels using PIV technique

In the present work a confined, submerged, laminar water jet is issued axially from a short, circular nozzle and fed radially outward through the clearance of two parallel circular discs. The disc assembly was fully submerged into the water-filled tank. Water has been used as the experimental fluid and flow diagnosis has been performed using 2D particle image velocimetry (PIV) technique. Effect of inlet flow rates, disc radius and clearance between the two parallel discs have been investigated to understand the characteristics of submerged radial flow. It is observed that the flow field consists of several interesting features like toroidal recirculation, annular separation bubble around the inlet corner and flow reattachment, which are strongly influenced by the clearance between the two parallel discs and the flow rate. The present observations reveal distinct flow structure between two parallel discs and provide insights for understanding of radial flow structure. The numerical results simulated from PIV experiments are also included in the form of vector plots and from it a close consistency between the two results is clearly visible.Graphical Abstract