Sudipto Mukhopadhyay

Abstract: Solar energy is a promising renewable source to support the growing energy demand. Sensible heat thermal energy storage (SHTES) is widely used, in practice, to supply the stored energy, in off-solar hours. These systems can be built using locally available and environment friendly materials. However, a good design as well as proper choice of materials is essential to construct an efficient and economical system. In this work, the secondary SHTES system of in-house solar air tower simulator (SATS) is investigated. The system uses hot air as heat transfer fluid and magnesium silicate pebbles as the storage material. The function of the secondary TES here is to store the waste energy from the hot air after it exits the solar convective furnace (SCF). The charging and discharging of the TES system are studied experimentally. It is observed that the secondary TES performance is satisfactory and serves as a proof of concept for future development.

Abstract: Solar energy is a promising renewable source to support the growing energy demand. This energy is widely harnessed for solar water heating systems to provide hot water for both domestic and industrial sectors thus reducing use of conventional energy sources. In this work, a concentrated solar water heater (CSWH) system is designed and fabricated at IIT Jodhpur. The main objectives are development of a point focus based direct solar water heating system and preliminary experiment based evaluation of the designed system. The system envisages a flux concentration of 100 Suns, which will enable receiver area reduction and the use of other heat transfer fluids like oil in future. The CSWH system consists of (a) receiver and (b) parabolic dish with two-axis sun tracking provision. In the conventional solar water heater system the irradiance from sun is directly collected by the collector whereas in concentrated solar water heater the reflected irradiance is received by the receiver. The reflector consists of a reflecting surface mounted on a parabolic structure and the cavity receiver consists of consists of a serpentine copper tube exposed to concentrated irradiance. The receiver will be insulated from top in order to prevent heat loss from one of its surface. An optical model of parabolic dish and receiver has been developed using TracePro software. This model is used as reference to generate the flux density distribution. The experimental setup consists of a parabolic dish, a receiver with thermocouples, a Coriolis flow meter, pump, water tank and NI DAQ. Coriolis flow meter is used to measure the mass flow rate in the system. K-type thermocouples are attached on to the receiver and the temperature is recorded using NI DAQ system. The theoretical geometric concentration ratio predicted is 115 but from the experiment a flux concentration ratio 94 is measured.

Abstract: Abstract Heat and mass transfer phenomena were studied in the sudden expansion region of a pipe under steady and pulsatile conditions. The Prandtl number was varied from 100 to 12 000 and the flow was characterized for both uniform and parabolic entrance velocity profiles. A uniform velocity profile was used for pulsatile flow. It was found that heat transfer in the recirculation region was maximal near the area where wall shear was minimal. Blunting of the inlet profile caused the point of maximum heat transfer to move upstream. There was a nonlinear effect of Prandtl number on heat transfer which plateaued for Pr > 10 3 . The wall shear rate in the separation zone varied markedly with pulsatile flows, but the wall heat transfer remained relatively constant. The time-averaged pulsatile heat transfer at the wall was approximately the same as with steady flow with the mean Reynolds number. However, the isotherms within the pulsatile flow were markedly different from steady flow. The results demonstrate the complexity of separation flows and identify characteristic regions of high and low heat/mass transfer for high Prandtl/Schmidt pulsatile flow.

Abstract: This paper investigates the opto-thermal and economic assessment of low-cost solar parabolic dish concentrators (PDC), focusing on the receiver position-induced uncertainties. An optical model of the proposed PDC system is developed in Tonatiuh optical simulation tool. The optical analysis is conducted by the Monte Carlo Ray Tracing method for different vertical and horizontal positions of the PDC’s receiver. In addition, An experimental test rig based on a locally manufactured PDC with a low-cost reflecting surface made of aluminum reflector foil is developed to achieve the purpose of this work. A cavity receiver made of a cylindrical-cone brass tube is used and tested under different positions of the focal point of the PDC. The impact of the uncertainties on the performance of the proposed PDC is experimentally estimated. A relatively simple mathematical model is utilized to evaluate the thermal and exergy performance for the different positions of the cavity receiver. The results showed that the proposed PDC could generate hot water at temperatures 77°C, 64°C, and 55°C for the three focal point positions, respectively. The collector efficiency of the PDC-cavity receiver system in the receiver position 1, 2, and 3 were 70.2%, 53.2%, and 24 % while the average values of exergy efficiency for the PDC at the receiver positions were 4.7%, 2.3%, and 0.93% respectively. This clearly shows the effect of the receiver positions on the performance of the parabolic dish solar concentrator and justifies the requirement of appropriate positioning of the receiver for the parabolic dishes.

Abstract: A comprehensive, multi-zone, unsteady heat transfer model is developed for a straight absorber pore-based open volumetric air receiver. This includes heat exchange between the porous absorbers, absorbers and receiver casing, and absorbers and return air. The validation revealed its predictive capability within an uncertainty of ±7%. The model is used for the scale-up of receiver design with several intermediate absorber layers. The major recommendations for scale-up are a) multiple absorber layers is beneficial for mitigating thermal stress, b) higher flux concentration is required for non-volumetric heating, to achieve the desired air temperature, compared to volumetric heating, c) air return ratio should be 0.6, d) absorber porosity should be 0.6 for volumetric heating and higher for non-volumetric heating, e) absorber gap to length ratio should be 0.15 -0.25, f) the radiative heat loss is substantial for non-volumetric heating; therefore, the exposed surface area to ambient should be reduced, and g) absorber diameter to length ratio should be 1-2. The developed approach is generic and adaptable for the different open volumetric air receiver designs.

Abstract: Abstract A mathematical model is presented to analyze the double diffusive transport of hybrid nanofluids in microchannel. The hybrid nanofluids flow is driven by the cilia beating and electroosmosis in the presence of radiation effects and activation energy. Cu–CuO/blood hybrid nanofluids are considered for this analysis. Phase difference in the beatings of mimetic cilia arrays emerge symmetry breaking pump walls to control the fluid stream. Analytical solutions for the governing equations are derived under the assumptions of Debye–Hückel linearization, lubrication, and Rosseland approximation. Dimensional analysis has also been considered for applying the suitable approximations. Entropy analysis is also performed to examine the heat transfer irreversibility and Bejan number. Moreover, trapping phenomena are discussed based on the contour plots of the stream function. From the results, it is noted that an escalation in fluid velocity occurs with the rise in slippage effects near the wall surface. Entropy inside the pump can be eased with the provision of activation energy input or by the consideration of the radiated fluid in the presence of electroosmosis. The results of the present study can be applicable to develop the emerging thermofluidic systems which can further be utilized for the heat and mass transfer at micro level.

Abstract: The influence of pulsatile flow on the oscillatory motion of an incompressible conducting boundary layer mucus fluid flowing through porous media in a channel with elastic walls is investigated. The oscillatory flow is treated as a cyclical time-dependent flux. The Laplace transform method using the Womersley number is used to solve non-linear equations controlling the motion through porous media under the influence of an electromagnetic field. The theoretical pulsatile flow of two liquid phase concurrent fluid streams, one kinematic and the other viscoelastic, is investigated in this study. To extend the model for various physiological fluids, we postulate that the viscoelastic fluid has several distinct periods. We also apply our analytical findings to mucus and airflow in the airways, identifying the wavelength that increases dynamic mucus permeability. The microorganism’s thickness, velocity, energy, molecular diffusion, skin friction, Nusselt number, Sherwood number, and Hartmann number are evaluated. Discussion is also supplied in various sections to investigate the mucosal flow process.