Browsing by Author "Yadav, Ajay Kumar"

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Computational and Experimental Study of Solar Air Heater With Various Duct Cross-Sections and Artificial Roughness
(National Institute of Technology Karnataka, Surathkal, 2022) K, Nidhul; Yadav, Ajay Kumar; S, Anish
Thermo-hydraulic performance and exergetic efficiency of solar air heater (SAH) with various duct cross-sections and artificial roughness have been investigated using numerical and experimental methodology. The RNG k- model with enhanced wall treatment is employed to study the turbulent flow behavior. Validation of the CFD results for smooth and artificially roughened SAH (triangular duct and duct with semi- cylindrical sidewalls) with theoretical correlations and experimental data indicates reasonable accuracy. In triangular duct SAH, the performance of inclined ribs and V-ribs have been studied e/D) and pitch (P/e). It is observed that V-ribs in triangular duct provides a maximum thermo- hydraulic performance parameter (THPP) of 2.01 with a 23% enhancement in exergetic efficiency compared to smooth SAH. Further, the performance of triangular duct SAH with inclined ribs in an indirect type solar dryer is studied. Dryer with ribbed triangular duct SAH exhibits a 60.4% and 55% reduction in moisture ratio for food samples robusta and nendran, respectively, for the same drying time compared to a dryer with a ribbed rectangular duct SAH. In addition, the design enhances the drying characteristics with 93.3% increase in average diffusivity coefficient for banana food samples. CFD analysis of SAH design with semi-cylindrical sidewalls and continuous W-baffles provides THPP in the range of 1.70 to 2.27. Maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, relative to conventional SAH at Re = 5000. Based on the optimum results obtained from CFD, an experimental setup for SAH with semi-cylindrical sidewalls and multiple discrete inclined baffles is fabricated. The experimental results indicate that THPP is further enhanced for discrete inclined baffles with the gap at the trailing apex, with a peak value of 2.69. This design has higher collector efficiency (55 to 70%) compared to ribbed rectangular SAH design exhibiting 30 to 55%. Further, the design exhibits higher exergetic efficiency owing to lower exergy losses and higher collector efficiency. Maximum exergetic efficiency of 2.2% is obtained at lower Re, higher than that obtained for rectangular duct SAH with a similar kind of artificial roughness. In addition, at low Re, this SAH design has a higher coefficient of performance (COP) than conventional SAH designs. Hence, a SAH design having lower number of sharp corners and artificial roughness capable of generating multiple secondary flow can enhance the heat transfer rate with higher thermo-hydraulic performance.
Effect of High Temperature Biodiesel Injection In Compression Ignition Engines
(National Institute of Technology Karnataka, Surathkal, 2022) Kodate, Shankar; Yadav, Ajay Kumar; G. N., Kumar
Extensive research is being done to produce and utilise a variety of renewable fuels to meet the growing global energy demand and combat many issues such as environmental pollution, high costs of fossil fuels, and dependence on foreign energy sources. The current research aimed to extract and characterize Vateria indica and Karanja biodiesels through the transesterification process. The use of extracted biodiesels in a diesel engine leads to lesser brake thermal efficiency (BTE) and increased brake specific energy consumption (BSEC) due to higher viscosity and lower calorific value of biodiesels. This problem of higher viscosity is resolved by fuel preheating before injecting into the engine cylinder. The current research aims to evaluate the engine performance, emission, and combustion characteristics of Karanja oil methyl ester (KOME) and Vateria indica methyl ester (VIME) biodiesels blended with diesel at elevated fuel inlet temperatures ranging from 35 °C to 95 °C. The tests are carried out using two different engines, mainly the conventional DI engine (low-pressure injection at 180 bar) and CRDI engine (high-pressure injection at 1000 bar). In the CRDI engine, the effects of fuel injection timings and exhaust gas recirculation (EGR) rates on the engine parameters are also investigated. Results are obtained in terms of brake thermal efficiency, brake specific energy consumption, in-cylinder pressure, heat release rate, exhaust emissions of carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOX), carbon dioxide (CO2), and smoke opacity. It is observed from the findings of both the engines that the preheating of blends decreases viscosity which enhances engine performance, lower CO, HC, and soot emissions with a slight increase in NOX emissions. It is found that advancing the injection timing to 15° bTDC in a CRDI engine improves engine performance and reduces CO, and HC emissions with an increase in NOX emission compared to standard injection timing of 12° bTDC and retarded injection timing of 9° bTDC. As the EGR rate increases, engine performance decreases, and exhaust emissions like CO and HC increase with a reduction in NOX emission.
Experimental Investigation of Coffee Husk Biodiesel as A Renewable Fuel In Compression Ignition Engine
(National Institute Of Technology Karnataka Surathkal, 2023) Emma, Addisu Frinjo; A, Sathyabhama; Yadav, Ajay Kumar
In the present study, coffee husk (CH) and spent coffee ground (SCG) are used for the production of biodiesel. The CH is a by-product of the coffee processing industry, and SCG is obtained after the coffee is brewed. Field Emission Gun Scanning Electron Microscope (FEG-SEM) is used to investigate the elemental composition of the CH and the SCG samples and identify the presence of different elements with their distribution and concentration. The compositional analysis indicates that the CH comprised 49.84% of carbon and 48.06% of oxygen by weight. On the other hand, it is found that the SCG had 67.72% of carbon and 26.18% of oxygen by weight. The CH is selected for further study for the production of oil due to its higher oxygen distribution than SCG. From 1Kg of CH, 250g of oil is produced. By using the transesterification process, the produced oil is converted into biodiesel. Subsequently, 700 mL of coffee husk oil methyl ester (CHOME) biodiesel was produced from 1000 mL of coffee husk oil. After characterization of obtained biodiesel, the experiments are conducted in a single-cylinder direct injection diesel engine at a constant speed by varying the loads (0%, 25%, 50%, 75%, and 100%) for different biodiesel-diesel blends (B10, B20, B30, B40, B50, B80, and B100), and the results are compared with the baseline diesel. The brake thermal efficiency (BTE) of the blends, B10, B20, B30, and B50, is reduced by 0.6, 0.7, 1.29, and 3%, respectively, compared to the regular diesel. Similarly, the brake specific energy consumption (BSEC) is increased by 0.1, 0.3, 0.44, and 0.77% for B10, B20, B30, and B50, respectively. Exhaust gas emissions are reduced for all biodiesel-diesel blends with a marginal increase in NOx emission. Compared to regular diesel, at full load, CO, HC, and smoke opacity of B30 are reduced by 13.2%, 4%, and 12%, respectively. Whereas NOx and CO2 of B30 at full load are increased by 3.8% and 8.63% respectively The viscosity of CHOME biodiesel is found to be higher than diesel; hence a preheating mechanism is set to reduce the viscosity and density of the fuel before injecting it into the combustion chamber. Preheating the neat CHOME biodiesel (B100) to 95 °C decreased its viscosity and density by 49.5% and 3.7%, respectively. Running the engine with preheated B100 reduces CO, HC, and smoke opacity by 34%, 34%, and 35%, respectively, compared to unheated regular diesel. The percentage of CO2 in the exhaust gas is increased by 45.5% for preheated B100 compared with unheated B0 at 100% load. Furthermore, the injection timing of the engine is altered to find the optimum injection timing of the biodiesel-diesel blend. The BSEC is increased by 0.53 kg/kWh and reduced by 1.4 kg/kWh for advanced and retarded injection timing, respectively. By advancing injection timing, the HC, CO, and smoke opacity were reduced by 7.4%, 36%, 5.7%, and 7%, respectively, compared to the B30 at standard injection timing.
Experimental Study of Natural Composite Desiccant-Based Dehumidification System
(National Institute Of Technology Karnataka, Surathkal., 2024) Dasar, Sangappa R; S, Anish; Yadav, Ajay Kumar
This study investigates the sorption and desorption characteristics of a natural com- posite desiccant based on dried cow dung (DCD). The first part of the study focuses on finding out an effective binding material for DCD. For this Polyvinyl Pyrrolidone (PVP) and clay are selected as binders. The moisture uptake capacity of composite desiccants is measured with an isotherm experiment under different DCD-to-binder ratios. Based on their isotherms, composite desiccants are chosen for the study under different humid conditions and compared with available literature data. Brunauer-Emmett-Teller and Barrett-Joyner-Halenda analyses are carried out to understand the physical properties of DCD, DCD+PVP (3:1 ratio) and DCD+Clay (3:1 ratio). Total heat load reduction, exergy efficiency and power required for these dehumidification systems are calculated for different inlet conditions. Desorption characteristics are tested at 328 K and 6% RH. Results show the maximum moisture uptake capacity of DCD and DCD+PVP as 9.87 and 9.01 g/100 g, respectively. The maximum exergy efficiency of the DCD+PVP dehumidification system is found to be 55%. The desorption time for DCD+PVP desic- cant is 17 minutes, which is 4 and 2 minutes higher compared to DCD, and DCD+Clay, respectively. In the second phase of the study, a natural composite desiccant, in which the unuti- lized portion of the spherical desiccant material is replaced with a metallic ball, is pro- posed. Stainless steel balls with a diameter of 4.75 and 6.35 mm are used to make different thickness ratios (TR = 1, 0.525, and 0.365) of metal-embedded natural com- posite desiccants (MENCDs). The natural composite desiccant is prepared from dried cow dung and polyvinyl pyrrolidone with a ratio of 3:1. Experiments are conducted to find theoptimumthicknessratioofMENCDs.Thetotalmoisturesorption,moisture sorption rate,totalheatloadreduction,andexergyefficiencyofthesedehumidification systems areinvestigatedunderdifferentrelativehumidities(RH=65%,75%and85%), and ataconstanttemperatureandvelocity.Desorptioncharacteristicsaretestedat328 K and5%RH.ThemaximummoistureupatakecapacityofMENCDswithaTRof 0.365 isfoundtobe11.84g/100g,whichis17%highercomparedtonaturalcomposite desiccants (i.e.,TR=1)at85%RH,whereas,thetotalmoisturesorptionrateis0.4 g/100 g·min, whichis20.57%higherforTRof0.365comparedtoTR=1.Themois- ture desorptionrateforTR=0.365is16.66%highercomparedtoTR=1.Thesystems exhibitanaverageexergyefficiencyof60%.However,whenemployingcompositedes- iccants withaTRof0.365,theiraverageexergyefficiencyimprovesby9.6%compared to thesystemsoperatingwithTR=1.Furthermore,theaveragereductionintotalheat load withTR=0.365is24%highercomparedtothoseutilizingTR=1. Further studiesarecarriedouttoreducethepressurelossacrossthedehumidifica- tion bedandincreasethemoisturesorptioncapacity.Toachievethisthedehumidifi- cation bedisdesignedwithstaggeredhexagonalaluminiumchannels(SHACs).The natural compositedesiccant(NCD)waspreparedbycoatingthemixtureontothechan- nels witha2:1ratioofDCD:PVPduetobettercoatability.Theresultsofthestudyshow that theNCD-coatedSHACsdehumidificationsystemhadahighmoisturesorptionca- pacity,withmaximummoisturesorptionvaluesrangingfrom8.34to14.31g/100gat differentRHandtemperatureconditions.Thesystemalsoshowsanaveragemoisture sorption rateof0.26g/100g·min andadesorptionrateof0.51g/100g·min. Further- more, themoistureflowdesignoftheNCD-coatedSHACsbedresultsinalow-pressure drop of0.13kPa, whichissignificantlylowerthantheNCD-packedbed.
Flow Instability and Its Mitigation In Supercritical Co2 Based Natural Circulation Loops: Numerical and Experimental Study
(National Institute of Technology Karnataka, Surathkal, 2022) Wahidi, Tabish; Yadav, Ajay Kumar
A natural circulation loop (NCL) is a thermal energy transport system in which circu- lation solely occurs due to density gradient from a high-temperature source to a low- temperature sink without using any prime mover. Due to thermal imbalance in NCL, fluid flow oftenly subjects to instability in the form of oscillatory behaviour and flow reversal which may lead to catastrophic incidences. The underlying physics of instabil- ity for supercritical CO2 based NCL is complex. Hence, numerical and experimental investigations are carried out for supercritical CO2 based NCLs focus on the flow insta- bility and its mitigation. Three-dimensional computational fluid dynamics (CFD) simulation for super- critical CO2 based NCL is carried out to explore the effects of pressure and heat inputs on instability and determine the possible cause of its occurrence. Investigation shows that for supercritical CO2, there is a threshold point that decides the nature of flow. A heat input lower than a threshold value causes repetitive-reversal flow, while at higher heat input, the flow changes to stable or unidirectional flow. With an increase in heat input, the system attains stability for a given operating pressure. In addition, a possible mechanism for continuous flow oscillation and measurement of instability with differ- ent pressure in unstable loops is also proposed. The novelty of this investigation emphasizes the design of a modified Tesla type valve and its integration in the loop to assist the unidirectional flow of loop fluid, and in turn, reduces the instability. Results show that the use of a single modified Tesla valve leads to better stabilization for all supercritical pressures and heat inputs. It is also found that a loop with a single Tesla mitigates the temperature and velocity oscillations with a marginal reduction (8%) in the heat transfer performance. However, the use of a single modified Tesla type valve in NCL is not capable of mitigating the instability in the case of low heat inputs with operating pressures far away from the pseudocritical point. NCL integrated with two modified Tesla type valves is used to promote the uni- directional circulatory movement of loop fluid and to decrease the magnitude of insta- bility. Results are obtained with supercritical CO2 based twin Tesla-NCL and compared with regular-NCL and single Tesla NCL at different heat inputs and operating pressures. It is found that an increase in the number of Tesla valves, mitigates the instabilities in the NCL operated away from pseudo-critical region at lower heat inputs. However, the use of twin Tesla type valves in NCL drops the heat transfer capability by 15% com- pared to regular NCL. To validate the simulation results and check the practical feasibility, an experi- mental setup of NCL integrated with a modified Tesla valve is designed and developed. Experiments are carried out to comprehend the instability in supercritical CO2 based NCL. Experimental results show that the unidirectional fluid flow circulation can be achieved in the loop with the Tesla valve, which makes it an efficient technique to com- bat instability.
Suitability of Biofuels and Plastic Oil Blended With Diesel in CRDI Engine
(National Institute of Technology Karnataka, Surathkal, 2017) Lamani, Venkatesh T.; Yadav, Ajay Kumar; Kumar, G. N.
Nitrogen oxides and smoke are the substantial emissions for the diesel engines. Fuels comprising high-level oxygen content can have low smoke emission and higher efficiency due to better combustion. The objective of this research is to assess the potential to employ oxygenated fuels such as dimethyl ether, ethanol and butanol, and waste plastic oil in direct injection engine as alternative fuels for diesel. To reduce NOX, exhaust gas recirculation technology for various fuels is studied. Computational fluid dynamics (CFD) studies on combustion and emission characteristics of common rail direct injection (CRDI) engines using oxygenated fuel-diesel blends are less developed and still under intense study. In view of that detailed CFD simulation is carried out in present study and also validated with experimental results. Ethers are favourable alternative for diesel engine due to their chemical structure. Presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), cause less pollution in DME operated engine compared to diesel engine. Study emphasizes the effect of various EGR rates (0-20%) and DME-diesel blends (0-20%) on combustion characteristics and exhaust emissions of CRDI engine using CFD simulation. Results show that, due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increase in DME- diesel blends. Ethanol is an attractive alternative fuel because it is oxygenated, renewable and bio-based resource; thereby it has potential to reduce smoke emissions in compression-ignition engines. CFD simulation is carried out to study the effect of EGR and injection timing on the performance, combustion and exhaust emission characteristics of CRDI engine fuelled with bioethanol-diesel blends. The results indicate that the mean CO formation and ignition delay increase whereas mean NOX formation and in-cylinder temperature decrease with increase in the EGR rate. Further, CFD simulation is carried out to find optimum injection timing for bioethanol-diesel blends (0-30% ethanol). Optimum injection timing is obtained for maximum ITE. Obtained CFD results are validated with experimental data available in literature and found good agreements.Several second generation biofuels (e.g., n-butanol) are also promising alternative to diesel fuel. The experimental and CFD simulation is carried out to estimate the performance, combustion and exhaust emission characteristics of n-butanol-diesel blends (0 to 30%) for various injection timings and various EGR rates using modern twin-cylinder, four-stroke, CRDI engine. Experimental results reveal the increase in brake thermal efficiency (BTE) for n-butanol-diesel blends. Attention is also focused to counter plastic waste disposal problem and to find alternate fuel to diesel by waste to energy retrieval. Present range of investigation evaluates the prospective use of waste plastic oil (WPO) as an alternative fuel for diesel engine. Experiments are conducted for various injection timings and for different EGR rates. Combustion, performance and tail pipe emissions of CRDI engine are studied. The NOx, CO and soot emissions for waste plastic oil-diesel blends are found more than neat diesel. To reduce NOx, EGR is employed which results in reduction of NOx considerably. Brake thermal efficiency (BTE) of blends is found to be higher compared to diesel. The higher NOx emitted by engine operated with WPO-Diesel blends are treated by multiple injection strategies. Experiments are carried out for various pilot injection timings and different main injection timings. The remarkable reduction in nitrogen oxide is observed by retarding main injection timing and injecting more fuel in pilot injection compared to single injection.