Search

A 2D numerical analysis was executed using ANSYS Fluent 16.0 to optimize the dimensions of pentagonal corrugations (corrugation pitch p and angle α) in the absorber plate of a solar air collector of an indirect solar dryer. Initially, α and corrugation height (e) were kept constant and varied the p from 50 to 175 mm, and optimized p was found. Hence, there are 36 sets of results (part-A). This optimized p was used in the second set of simulations where α is varied from 10° to 37.5° with an increment of 2.5°. It has 72 sets of results (part-B). The performance parameters such as Nusselt number (Nu), friction factor (f), Nu ratio, f ratio and thermohydraulic performance parameter (Thp) were determined for both sets. Nu ratio was from 1.81 to 3.126, which implied that the heat transfer was enriched up to 3.126 times. The maximum Thp was 1.748 at p = 150 mm. Hence, p = 150 mm is proposed from part-A simulations. In the part-B simulations, the maximum of Thp was noticed at α = 35° and 37.5°. Considering the material requirement, dimensions of p = 150 mm and α = 37.5° are proposed. [ABSTRACT FROM AUTHOR]

This work concentrates on the design parameters of a turbine blade for a small-scale solar chimney plant. The pitch angle (θ), relative wind angles (ϕ and ψ), lift force (FL) and relative chord length (lcr) of the turbine blade are determined. Betz and Bernoulli's theories were used for estimating and optimizing the above blade parameters. The coefficients of power, drag, lift and thrust forces are estimated and analyzed. Two wind speeds were considered. One represented higher speed (10 m/s) and the other for lower speed (2 m/s). At 10 m/s, the required rotor diameter is drastically reduced for producing the same power output. At 2 m/s, θ, ϕ, ψ and FL were optimized and they are; θ = 18.4°, ϕ = 26.4°, ψ = 75.6° and FL = 0.0073 N for maintaining the maximum power (P) of 0.026 W. The required diameter for the rotor blade is estimated and is varied from 0.66 to 6.56 m for producing a power range of 1–100 W. At 10 m/s, the optimized parameters are; θ = 42.9°, ϕ = 50.94° and ψ = 20.39° and FL = 0.4082 N for reaching the maximum P of 2.538 W. The estimated results were validated with existing studies and observed a good match. [ABSTRACT FROM AUTHOR]

In the present study, an indirect solar dryer (ISD) was analyzed without thermal energy storage (TES) device (case-1) and with a TES device (case-2) during drying guava slices to appraise the quality of the dryer. The average drying efficiency was 5.41% and 9.29% in case-1 and case-2, respectively, with an improvement of 71.4% in case-2. A 42.86% decrement in specific energy consumption and a 75.02% increment in specific moisture extraction rate were observed in case-2 due to the TES device than case-1. The drying time was saved by 9 h in case-2. The average drying rate was 0.3062 and 0.3392 kg/h in cases-1 and 2, respectively, with an improvement of 10.77% in case-2. The average effective diffusion, mass and heat transfer coefficients were 7.75 × 10−9 and 7.58 × 10−9 m2/s, 0.0040 and 0.0039 m/s, 4.645 and 4.503 W/m2K, for cases-1 and 2, respectively. The activation energy was calculated as 136.98 and 130.72 kJ/mol in cases-1 and 2, respectively. Case-2 performed well with better drying efficiency and drying was completed within a day, whereas case-1 took two days. The TES device installed in case-2 improved the thermal and performance parameters of ISD. [ABSTRACT FROM AUTHOR]

The current study evaluated the performance parameters and drying characteristics of muskmelon slices in the indirect forced convection solar dryer (IFCSD) without thermal energy storage (TES) device (case-A) and with a TES device (case-B). The average collector and drying efficiencies (ηSAC and ηdr) were 66.37 and 11.37% in case-A and 67.82 and 16.93% in case-B, respectively. The ηSAC of both setups was not affected by the TES as it was installed in the drying cabinet, whereas ηdr of case-B setup was improved because the stored and released heat was more, also, the drying completed within a day compared to case-A. The six sunshine hours were saved, and a 53.98% average drying rate was improved by case-B. The specific moisture extraction rate was improved by 74.19%, and the specific energy consumption was decreased by 42.56% compared to case-A due to the higher quantity of moisture removal per input solar radiation in case-B. Two-term exponential and Page models were appropriately suited for drying muskmelon slabs in case-A and case-B, respectively. The values of effective moisture diffusivity, heat and mass transfer coefficients (averages) were improved slightly by TES device in case-B. The temperature of the drying cabinet could be continued 4.5 to 8.9 °C greater than the atmospheric temperature in case-B after the sunset. The performance of IFCSD was better in case-B compared to case-A, and the final moisture content was achieved within a day in case-B. [ABSTRACT FROM AUTHOR]

The performance, thermal parameters and drying kinetics of muskmelon are calculated in an indirect natural convection solar dryer (INCSD) and indirect forced convection solar dryer (IFCSD). The initial moisture content (MC) of muskmelon slices was 12.4156 kg/kg of db (db) and it declined to 0.1605 db in 15, 18 and 22 h in IFCSD, INCSD and open sun drying (OSD), respectively. The estimated collector and drying efficiencies (ηcl and ηdr) were 58.5 and 9.39% in INCSD and the same were 66.37 and 12.11% in IFCSD, respectively. The specific moisture extraction rate (SMER) was 0.544 and 0.6204 kg/kWh in INCSD and IFCSD, respectively. The Verma model was relevant to fit the drying characteristics of muskmelon in INCSD, IFCSD and OSD. The thermal parameters such as effective moisture diffusivity (Defm), surface transfer coefficients (hht and hmt) and activation energy (Eac) were also determined for both setups. The average increment of 13.45% on ηcl, 28.97% on ηdr, 14.04% on SMER, 24.08% on Defm, 55.36% on hht, 55.16% on hmt, and 24.83% on Eac were observed in IFCSD than INCSD. The Eac of muskmelon slices was 38.06 and 28.61 kJ/mol in INCSD and IFCSD, respectively. Uncertainty analysis was performed and error bars were included in all the plots. [ABSTRACT FROM AUTHOR]

A 2D numerical solution was developed to estimate the temperature and moisture distribution of a spherical moist product. The object used in the study is cranberry (Vaccinium macrocarpon). Robin boundary condition was incorporated as the heat and mass transfer takes place from the object by convection. The governing transient partial differential equations were discretized by the finite difference method. The transient terms were discretized using an implicit scheme. A computer program was generated to solve the heat and moisture transport expressions simultaneously. The diffusion coefficient was assumed as temperature dependent which allowed solving of the heat and moisture transport expressions simultaneously. Temperature and moisture profiles were calculated at various drying times and hot air temperatures ranged from 313 to 348 K. Mean and center temperature and moisture content were calculated. The average moisture content was reduced from 7.49 to 2.58, 0.65 and 0.24 kg (kg of db)−1 at drying time of 10 h and hot air temperatures of 313, 333 and 348 K, respectively. The product needed to be dried up to 2, 3 and 5.5 h at drying temperature of 348 K to maintain 50%, 30% and 10% of its initial moisture content. The results obtained were compared to existing work, and it was in good agreement. [ABSTRACT FROM AUTHOR]

A computational model is generated to analyse the influence of shrinkage on convective drying problems. The object considered here is cranberry which is assumed as 100% spherical. The drying air temperatures were considered from 313 to 348 K. There were four models used in this study, namely one-dimensional models without and with shrinkage, two-dimensional models without and with shrinkage. A finite difference scheme was used to discretize the heat and mass transport equations. Four separate computer codes were written in MATLAB to solve the discretized equations. The Arrhenius model is used to couple the heat and moisture transport equations and solve them simultaneously. The Gauss–Seidel iterative method was used to solve the equations. An empirical shrinkage model was used to calculate the shrinkage effect. The temperature and moisture distributions of cranberry were obtained with drying time. Moisture distributions without and with shrinkage results were calculated and compared to identify the effect of shrinkage. The cranberry lost a maximum of 35% of its size during drying. There was not much variation found in the results between 1- and 2D models. The maximum difference in centre moisture content of cranberry without shrinkage model was 56%, and the difference in mean moisture content was 49.2%. The numerical outcomes were validated with experimental data, and the model with shrinkage was a good fit with them than without shrinkage. Therefore, shrinkage needs to be considered in convective drying phenomena. [ABSTRACT FROM AUTHOR]

A numerical analysis has been performed to examine and assess the flow and performance characteristics of the solar updraft tower (SUT) power plant. A realistic domain (geometry and mesh) of the flow model was generated and simulations were run with the help of ANSYS FLUENT 16.0 CFD package. A turbulent, realizable (k–ε) and discrete ordinates radiation techniques were taken into consideration to solve the governing equation. The maximum air velocity of 3.27 m s−1 was noticed at 200 mm above the chimney base (CB). The mean velocity at CB was 1.8 m s−1. The highest air temperature of the absorber plate was 323 K, and it was at the centre of the absorber plate. The average air temperature inside the setup was 306.7 K. The power generated from the plant, chimney efficiency and overall efficiency of the SUT setup were evaluated to be 0.38 W, 0.018% and 0.005%, respectively. 24% velocity increase and 70% power output increase were noticed when solar flux increased from 650 to 1150 W m−2. Exergy analysis was performed. The results were compared with existing studies and were found to be in good agreement. [ABSTRACT FROM AUTHOR]

Diesel engines are frequently employed in industries, transport and agriculture. The rapid consumption of fossil fuel in the transportation sector compels a search for alternative sources of fuel for internal combustion engines. Lower volatility, unsaturated fats and higher viscosity of crude oil are major problems to use vegetable oil straight away as fuel. The present work aims to conduct the experiments with different proportions of Azadirachta indica oil with diesel. The biodiesel used for the experimentation is prepared by two-step transesterification process considering the optimized parameters such as reaction time and concentration of catalyst. With different trials, the reaction time (90 min) and the concentration of catalyst (1%) were finalized. Experiments were conducted on a variable compression ratio diesel engine to determine various performance parameters and its exhaust emissions for different blend proportions at various loads. The brake thermal efficiency of biodiesel blends is very similar to that of diesel up to partial loads. Higher brake-specific fuel consumption (BSFC) is noticed for biodiesel blends than mineral diesel. At maximum load, BSFC is the same for all percentage of blends along with mineral diesel. The exhaust emissions such as CO and UHC are lower for different blends, while NOx emission is more. By analyzing all the results with different blends of Azadirachta indica biodiesel, it is evident that it can be used as a promising alternative fuel for a diesel engine without further modifications in engine adjustments. Uncertainty analysis and repeatability tests were performed to check the accuracy of the results. [ABSTRACT FROM AUTHOR]

Effect of thermal energy storage (TES) system of solar updraft tower (SUT) is studied in this work. A 3D numerical model was developed to analyze the same and estimate the performance parameters. Two models were developed: case-I and case-II. Case-I is without TES system and the case-II with TES system. The collector diameter 3.5 m, chimney height 6 m, chimney diameter 0.6 m, inlet gap 0.15 m, slope of the collector 30° were the dimensions considered for the model of case-I. Case-II consisted of same dimensions of case-I with additional storage material of thickness 0.15 m and diameter of 3.5 m. Steady-state pressure-based solver with realizable k-ɛ turbulent model and solar ray-tracing algorithm were employed. SIMPLE scheme was used for pressure-velocity coupling and in spatial discretization; first order upwind for momentum and second-order upwind for energy were used. Flow parameters such as velocity, pressure, density, and temperature were estimated for both the cases. Results from the numerical simulations showed that adding TES to the SUT plant decreases the pressure, velocity, and temperature of air because certain amount of heat energy was stored in case-II setup. [ABSTRACT FROM AUTHOR]

Solar updraft tower (SUT) is a viable option to produce electrical energy from solar energy. Extensive studies needed to estimate the flow parameters and analyse this set-up. A 3D numerical model is developed to analyse the flow parameters such as pressure, temperature and velocity of SUT plant. Effect of geometrical parameters such as chimney height and collector roof angle is studied numerically in this work. The diameter of absorber plate and chimney as 3.5 m and 0.6 m and the collector roof angle, chimney height and inlet gap as 30º, 6 m and 0.1 m, respectively, are selected for numerical simulation. A parametric study is performed for varying chimney heights from 3 to 8 m and collector roof angle 20º-35º with an increment of 5º each case. The airflow inside the SUT is turbulent, renormalization group (RNG) k-ε model is selected, and (discrete ordinates) DO model is incorporated for evaluation of radiation effect inside the domain. From the simulation results, it is concluded that when collector roof angle is increased, air velocity is increased and also air temperature is slightly dropped. It is found that there is 31% velocity enhancement when the chimney height is increased from 3 to 8 m. [ABSTRACT FROM AUTHOR]

A simultaneous heat and mass transfer model for convective drying of moist food materials has been developed. Cartesian, cylindrical, and spherical coordinate systems are taken for the analysis, as food materials dried in industries are of different shapes. The governing transient partial differential equations describing heat and mass transfer are discretized, using the finite difference method, and sets of algebraic equations are obtained. The diffusion coefficient is a temperature function, and, therefore, the heat and moisture transfer equations are solved simultaneously. A MATLAB computer code is developed to solve them. Transient temperature and moisture profiles during convective drying are estimated. The present results are compared with the existing experimental data, and it is observed that there is good agreement. [ABSTRACT FROM AUTHOR]