Suvanjan Bhattacharyya

Simulation of heat transfer enhancement in tube flow with twisted tape insert

Heat transfer behaviour in a tube with inserted twisted tape swirl generator is investigated numerically, for different values of the twist ratio and diameter ratio and for Reynolds numbers within the range 100-20,000. The transition-SST model is used as the turbulence model. The computational model is validated, first, on a plain tube, where a good agreement is achieved with the correlations. The subsequent analysis of the tube with twisted tape indicates that the use of twist tape enhances heat transfer generally, which is accompanied by a higher pressure drop. It is observed that an improvement of the thermal-hydraulic performance can only be observed for certain configurations and Reynolds numbers.

Numerical Investigation of Thermohydraulics Performance in Elliptical Twisted Duct Heat Exchanger

Heat transfer behaviour in twisted elliptical duct swirl generator is investigated numerically. Twisted geometry is a widely used technique for heat transfer enhancement. This work presents the investigation of a elliptical twisted duct (ETD) for turbulent heat transfer in air using computational fluid dynamics (CFD) modelling. In the present paper, transition—SST model which can predict the change of flow regime from laminar through intermittent to turbulent has been used for numerical simulations. While the aspect ratio of major and minor axes of the elliptical duct is 0.5, the pitch length (Y) is varied between 0.5 and 1.0. The results indicate that the smaller pitch length yields a higher heat transfer value with relatively lower performance penalty. The transition from laminar to turbulent regime is observed between Reynolds numbers of 1000–3500 for all cases. For all investigated cases, heat transfer enhancement (η) tends to increase with the increase of Reynolds number. This result is useful for the design of solar thermal heaters and heat exchangers.

Investigation of Inclined Turbulators for Heat Transfer Enhancement in a Solar Air Heater

ABSTRACT In the present study, the effect of forward inclined turbulators on the heat transfer enhancement in a duct is investigated, for forced convection. Turbulator configurations with three different pitch ratios and three different inclination angles are investigated for seven Reynolds numbers within the range 500–50,000. Investigations are performed experimentally as well as computationally, within a computational fluid dynamics framework. A distinguishing feature of the latter has been the employment of a turbulence model, the transitional shear stress transport model that is applicable throughout the presently considered range of Reynolds numbers containing laminar, transitional, and turbulent regions. At the beginning of the study, measurements and predictions are validated against analytical and empirical expressions known for a plain duct. The results obtained for turbulators configurations indicate that Nusselt number increases with the inclination angle but decreases with the pitch ratio. The influence of the inclination angle on the Nusselt number and thermal enhancement factor is found to be stronger than that of the pitch ratio. For all Reynolds numbers and for all configurations, the thermohydraulic performance is observed to increase, leading to thermal enhancement factors within the range 2–5. In all cases, a quite good agreement of the predictions and experiments is observed, which increases the confidence in the accuracy of both approaches.

Computational investigation of heat transfer enhancement by alternating inclined ribs in tubular heat exchanger

This paper encapsulates results of a numerical investigation on flow and heat transfer of an incompressible medium with constant properties through an isothermal circular tube with alternating inclined ribs. Simulations are conducted for laminar, transitional, and turbulent flow regimes. As turbulence model, the transitional shear stress transport model is employed. The problem is investigated for four rib angle of attack values, as well as for a plain tube without any ribs. All configurations are observed to lead to a thermal performance factor close to or greater than unity. Within the investigated range, the larger thermal performance factors are observed to occur for the intermediate Reynolds numbers. Maximum values in the range 2.0-2.5 are predicted for the Reynolds number of 2,000, where a subsequent drop to values within the range 1.0-1.5 are found to occur for Reynolds numbers around 3,000-4,000, which may be attributed to the transitional effects.

Performance Analysis of a Geothermal Air Conditioner Using Nanofluid

Energy Saving is a serious challenge faced by mankind due to rapid increase in energy depletion. Geothermal energy along with nanotechnology is used in the proposed air conditioning model. This paper reports the design and experimental investigation of a vertical closed loop geothermal air conditioner. The system operates under different ground water condition at different mass flow rate. Nanofluid Al2O3R134a has been used as a working fluid. The result reports that the geothermal air conditioning system using refrigerant R134a is better than the conventional air conditioning system both in terms of performance and power saving. Although the best output characteristics are achieved by using geothermal air conditioner by means of nanofluid. The COP is showing some promising results and shows outgrowth of nanotechnology in renewable energy system.