• Energy Research

Abstract Heat transfer enhancement and pressure loss of a fin-and-tube heat exchanger with rectangular winglet pairs has been numerically investigated by solving the conservation equations of mass, momentum and energy. The flow is assumed to be laminar at different Reynolds numbers. The winglets are placed in common flow up configuration which increases the heat transfer in the wake region of the tube. It was found from the numerical investigation the rate of heat transfer is increasing with number of winglets. It was also found that the placement of winglets near the central tube is more effective in transferring heat compared to entrance and exit of the heat exchanger. Keeping other parameters fixed it was found from the numerical experiment that the heat transfer performance was increasing significantly with the attack angle (β) of winglets. There also exists an optimum stream wise distance (ΔX) for placement of winglets for which the heat transfer is found to be highest. An optimum value of span wise distance (ΔY) could be decided where the heat transfer to the fluid was found to be maximum.

The present work aims at optimizing the geometry of curved trapezoidal winglets to enhance heat transfer rates (expressed as Colburn factor, j) and minimize pressure losses (expressed as friction factor, f). A fin-and-tube heat exchanger was analyzed with winglets mounted on the alternate tube and on either side of the fins. Multi-objective optimization was performed using the genetic algorithm (GA) to maximize j and minimize f. Two surrogate models, viz. response surface methodology (RSM) and artificial neural network (ANN), were considered as inputs to GA. To reduce the number of runs, a sensitivity analysis was first performed to select the most influential geometrical parameters for optimization. The values of j and f in the design of the experiments table were computed using CFD. The Pareto front points elucidated a significant improvement compared with the reference model along with a broad choice for the designers, not only for the design condition but also for the off-design inlet condition.

Abstract The present work is aimed at optimizing the geometry of the curved trapezoidal winglets to enhance the overall performance of the heat exchanger. Prior to optimization, the most critical geometric entities are identified to reduce computational overheads. Based on the performance, three design parameters viz. arc radius (R), the angle subtended (θ), and winglet’s larger end height (h2) are chosen for optimization. By making use of the Latin hypercube sampling plan, the design of experiments has been conducted for the above mentioned variables. The required responses for different combinations of the independent variables – that include the Colburn factor (j) and friction factor (f) – are computed by making use of computational fluid dynamics. Both fluid and solid domains are discretized using hexahedral control volumes and the numerical simulations are performed by accounting the conjugate heat transfer approach. The SST k–ω (a 2-equation based) turbulence model is used as a closure model for Reynolds-averaged Navier-Stokes equations to evaluate the values of j and f. The data from DoE are used to train an artificial neural network for multiobjective optimization. Finally, the optimized data sets are generated using genetic algorithms and very encouraging results have been obtained. These Pareto front points range from an energy-efficient to a high-performance heat exchanger design. Therefore, the designers can make the choice(s) of the winglet geometry over a wide range depending on the desired performance of the heat exchanger.

Abstract In this work, the thermo-fluid performance of a biomass drying chamber with innovative tray configurations has been numerically investigated by solving the governing equations of mass, momentum, energy, and turbulence using Fluent 17. The effect of tray number, tray length, tray arrangement, and hole arrangement on the tray surface has been examined in detail. An enhancement factor has been presented to account for the heat transfer and the associated pressure drop. The results show that both the heat transfer and the pressure drop increase with an increase in tray number and optimum tray number is decided based on the highest enhancement factor. Six different tray arrangements have been examined and it has been found that alternative packed side and rear-front walls arrangement of trays is most effective from the thermo-fluid performance point of view. Based on the hole arrangement investigation, it has been revealed that compared to the inline hole arrangement, the staggered arrangement resulted in higher heat transfer performance with almost no addition to pressure drop. Correlations have been developed to predict the enhancement factor for different tray lengths, tray numbers, and inline and staggered hole arrangements, which help design an efficient and economic biomass drying chamber.