R. Thundil Karuppa Raj

Experimental and numerical analysis using CFD technique of the performance of the absorber tube of a solar parabolic trough collector with and without insertion

In this work, numerical analyses have been conducted for the flow of fluid in the absorber tube of a cylindrical parabolic trough collector through CFD technique. The efficiency of the absorber tube can be improved by increasing the overall surface area, which increases the heat transfer to the working fluid. Analyses of the same have been done to see to what degree the insertions cause an improvement in heat transfer and as a result in increasing the outlet temperature of the working fluid. This has been carried out numerically by commercial CFD code Ansys CFX 12.0. The analysis has been carried out to study the effect of heat transfer in absorber tubes with and without insertions. The study also takes care in distributing different heat flux along the walls of the absorber tubes. The numerical analysis of the absorber tube without any insertions (plain tube) is validated with the experiments carried out on the absorber tube of a solar parabolic trough collector. After validating the numerical analysis, it is extended to study the effect of insertion in the performance of the absorber tube. The working fluid in all these studies is taken as water with different mass flow rates of 33 kg/hr, 63 kg/hr and 85 kg/hr. The temperature at the exit, pressure drop across the absorber tube, wall temperature and velocity along the mid-plane are plotted.

Performance analysis and emissions profile of cottonseed oil biodiesel–ethanol blends in a CI engine

ABSTRACT Biodiesel is identified as a likely alternative fuel for Compression Ignition (CI) engines as it leads to an effective reduction in consumption of petroleum diesel, and of engine exhaust emissions. In the current study, the effects of preheating of intake air on performance, emissions and combustion behavior have been studied for various compositions of cottonseed oil biodiesel–ethanol blends in a compression ignition engine. The characteristics were compared for intake air temperatures of 30°C and 80°C, respectively. An increase in the air intake temperature caused variations in the ignition delay period of the biodiesel–ethanol blend by improving the vaporization characteristic of ethanol, and provides a better combustion. It was found experimentally that the carbon monoxide (CO) as well as the unburned hydrocarbon (HC) emissions decreased with an increase in the preheat temperature, and were found to be slightly lower than those of biodiesel-fueled CI engines. An increase in the relative amount of ethanol blended with the biodiesel was also found to decrease CO and HC emissions. However, in comparison with biodiesel fuel, the ethanol–biodiesel blends resulted in higher emissions of oxides of nitrogen (NOx).

Influence of Dual Fuel Twin Injection on Diesel Engine Combustion and Emission Characteristics

The objective of this study is to investigate the feasibility of two-stage injection on combustion and exhaust emission characteristics in diesel (main fuel) ethanol (pilot fuel) fuelled single cylinder diesel engine. The pressure crank angle and net heat release rate diagrams revealed that increase in the ethanol pilot quantity causes an increase in the ignition delay in the pilot combustion and hence the main combustion due to diesel fuel is slightly influenced by the ethanol pilot fuel. The increase in the pilot injection decreases the NOx considerably. The concentration of soot emissions also decreases with increase in pilot injection. The CO emissions increases with increase in pilot injection and a slight increase in HC emission is observed.

Numerical Investigation of Transverse Jet in Supersonic Cross-Flow Using CFD Techniques

High speed jets in cross flows are central to fuel injection in supersonic combustion scramjet engines. In supersonic combustion scramjet engines, the sonic under expanded transverse jet of fuel is injected into a supersonic cross flow of air, where efficient mixing of fuel and air is one of the major critical issues. Due to the limited flow residence time inside the combustion chamber, the enhancement of supersonic turbulent mixing of jet fuel and cross-flow air is a critical issue in developing supersonic air-breathing engines. The accurate estimation and detailed physical understanding of the turbulent mixing mechanisms plays an important role in combustor design of scramjet engines. This numerical study aims at understanding the complex physical phenomenon involved in mixing of fuel jet and air and the associated turbulence characteristics, boundary layer capture and flow separation. In the current study the flow field resulting from the transverse injection of fuel jet into cross-flow of air is simulated numerically by solving the appropriate governing equations for a 2-dimensional flow. Numerical simulations are used to study an under-expanded jet injected into a supersonic cross flow. This study examines the flow structure, separation topology and performance characteristics of an under expanded transverse jet issuing normally into supersonic free stream. The influence of the compressibility effect on the shock wave structure and on the vortex system ahead and behind of the jet are studied by solving Favre averaged Navier Stokes (FANS) equations with SST k-ω turbulence model. The influence of the jet Mach number and jet-to-cross-flow pressure ratio on shock wave structure of the flow and jet penetration depth are studied. The simulated numerical results are compared with the experimental data available in the literature. Grid independence study is carried out for all the simulations carried out in the work to have good accurate results. It was found out that wall pressure profile of transverse jet injection for the high jet-to-cross-flow pressure ratio is predicted more accurately by the SST k-ω turbulence model. The jet penetration depth found out to be increasing with the increase in jet-to-cross-flow pressure ratio and fuel jet slot width.Copyright

A Numerical Investigation on the Performance of an Earth Air Heat Exchanger System for the Indian District of Nagpur

The performance of an Earth-Air Heat Exchanger (EAHE) system to be operated in climatic and soil conditions prevailing in the Indian district of Nagpur is modeled numerically. To do so, a CFD model is developed in ANSYS Fluent 12.1. The validation of the CFD model is carried out using data obtained from published literature and good agreement is established between the simulation results and published experimental data. An earth pipe of length 60 m and internal diameter 0.1 m is chosen for validating the model and this validated model is used to further investigate for three different lengths of the pipe - 40 m, 35 m and 30 m. The 3-dimensional flow field through the earth air heat exchanger is studied numerically by solving the appropriate governing equations namely: continuity, momentum and energy equations and a finite volume CFD code is employed for solving the same. An air inlet velocity of 2 m/s is maintained and the inlet temperature was varied between 308.1 K and 315 K for each chosen length. The decrease in temperature and flow distribution along the pipe length is plotted.

Effect of Convergent Angle on Flow Characteristics of Y-Shaped Diffusers Using CFD

Diffusing ducts are used in fluid flow systems, mainly in aeroplane engine inlets to decelerate the flow and to correspondingly increase the static pressure. The main problem in achieving a high pressure recovery is the flow separation which results in non-uniform distribution and excessive losses. The present work is aimed to study the flow characteristics in Y-shaped diffusing ducts. The Y-shaped diffuser has rectangular inlets and the outlet is circular with a certain settling length for the flow to be stabilized. The diffuser is modeled in CATIA V5 and further discretized using ICEMCFD12.1. Hexahedral mesh is generated for all diffuser cases, which have been used to capture the hydrodynamic boundary layers. ANSYS CFX 12.1 based on finite volume technique, using k-ε turbulence model is adopted for predicting the flow. The flow field through the 3-dimensional domain is captured by solving the appropriate governing equations namely, the continuity equation and the momentum equation. The convergence criterion is set to 10E-06 for mass and momentum. The whole investigation is done in two phases: in the first phase a commercial CFD code is validated for the results obtained for an S-shaped diffuser and in the second phase the same idea is then extended for the analysis of Y-shaped diffuser. The coefficient of static pressure, cross flow and axial flow velocity distributions are calculated based on the mass averaged quantities for the Y-shaped diffusers (30o and 40o).

Numerical Investigations of Spray Droplet Parameters in a Direct Injection Diesel Engine Using 3-Z Extended Coherent Flame Model

Diesel engine combustion modeling presents a challenging task as the injection starts with the spray formation and breakup of spray into droplets. The computation involved in predicting the in-cylinder fluid mixture during combustion using eulerian and lagrangian approach is rather a cumbersome task. In this work, 3D-CFD computations are performed to understand the behaviour of spray droplet variables on combustion process and emissions in a direct injection diesel engine. The study involves the computation of turbulent flow-field quantities, modelling various processes such as fuel spray distribution, atomization, collision, evaporation, combustion and pollutant formation using a commercial CFD code. Grid independence and time independent studies are carried out for finding the optimum grid size and time step. The numerical results predicted using CFD code is validated with the experimental data available from the literature. The process of combustion and emission characteristics is investigated numerically with respect to spray characteristics. The work is further extended to study the effect of swirl ratio and injection timing on droplet parameters.