Convective Heat Transfer and Pumping Power Analysis of MWCNT + Fe3O4/Water Hybrid Nanofluid in a Helical Coiled Heat Exchanger with Orthogonal Rib Turbulators

Utilizing nanofluids in heat exchangers can lead to improved thermal performance. Nanofluids with suspended carbon nanotubes are specifically desirable in thermal systems because of their unique capabilities. In this study, convective heat transfer and required pumping power are studied simultaneously for a helical coiled heat exchanger with laminar water flow while incorporating 0.1 and 0.3 percent volume fraction of the hybrid nanofluid MWCNT + Fe3O4/water. Two different geometries of bare and ribbed tubes are used for the heat exchanger part. The ribs are chosen to be orthogonal, i.e., 90° with respect to the inclined ones. Three different Reynolds numbers are selected for investigation, all in laminar flow regime based on the non-dimensional M number defined in coiled tubes. Computational fluid dynamics is used to study thermal and fluid behavior of the problem. The convective heat transfer coefficient can serve as a criterion to measure the effectiveness of utilizing nanofluids in heat exchangers by taking the pressure drop and pumping power of the system into consideration. Finally, the artificial neural network curve fitting tool of MATLAB is used to make a good fit in the data range of the problem. It is shown that for most cases of the study, the pumping power ratio is less than 1 that can be considered appropriate from energy consumption viewpoint.publishedVersio

Enhancing diesel engine cooling efficiency: A comprehensive numerical study on nanofluid coolants with exergy and economic analysis

This research focuses on improving the efficiency of four-stroke diesel engines, widely used in land transport. The study looks at how using nanofluids and different coolant combinations can impact thermophysical properties, such as convective heat transfer coefficient, Nusselt number, and entropy values. The Mercedes-Benz OM502 v8 2023 engine is used in the study. The goal is to improve radiator cooling processes and achieve economic savings. Causing more improvements in nanofluids thermophysical specifications according to available literature has led us to consider titania (TiO2), silica (SiO2), and alumina (Al2O3) nanoparticles. Nanofluids with the mentioned compositions, besides nanoparticles with 0.2%–0.8% vol. concentrations, have been studied, and eventually, the most efficient nanofluid composition has been selected as the optimal coolant. The validity of the utilized numerical technique is verified by comparing the method output with the Mercedes-Benz OM502 V8 2023 engine catalog. Results of our numerical studies show a 75.1% and 128.1% improvement in heat transfer rate along with a coolant temperature drop at the outlet by 23.8 °C and 21.4 °C at coolant's inlet temperatures of 85 °C and 95 °C. Furthermore, economic analyses have demonstrated that the use of optimal coolant composition can yield annual cost savings of approximately $2700

Effect of Excess Air Ratio and Temperature on NOx Emission from Grate Combustion of Biomass in the Staged Air Combustion Scenario

The combustion of biomass, in this case demolition wood, has been investigated in a grate combustion multifuel reactor. In this work a temperature range of 850-1000 degrees C is applied both for staged air combustion and nonstaged combustion of biomass to investigate the effects of these parameters on the emission levels of NOx, N(2)O, CO, hydrocarbons (C(x)H(y)),) and different other components. The composition of the flue gas is measured by four advanced continuous gas analyzers including gas chromatograph (GC), two Fourier transform infrared (FTIR) analyzers, and a conventional multispecies gas analyzer with fast response time. The experiments show the effects of staged air combustion, compared to nonstaged combustion, on the emission levels clearly. A NOx reduction of up to 85% is reached with staged air combustion. An optimum primary excess air ratio of 0.8-0.95 is found as a minimizing parameter for the NOx emissions for staged air combustion. Air staging has, however, a negative effect on N(2)O emissions. Even though the trends show a very small reduction in the NOx level as temperature increases in nonstaged combustion, the effect of temperature is not significant for NOx and C(x)H(y), neither in staged air combustion or nonstaged combustion, while it has a great influence on the N(2)O and CO emissions, with decreasing levels with increasing temperature

Experimental Investigation on NOx Reduction by Primary Measures in Biomass Combustion: Straw, Peat, Sewage Sludge, Forest Residues and Wood Pellets

An experimental investigation was carried out to study the NOx formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NOx level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO2, CxHy, O2, NO, NO2, N2O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NOx reduction of 50–80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NOx emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NOx showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1–25% of the fuel-N content is converted to NOx depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NOx reduction and low fuel-N conversion to NOx. Tops and branches did not show desirable NOx reduction and made the combustion also more unstable. N2O emissions were very low, typically below 5 ppm at 11% O2 in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere

Refrigeration components sizing tool for design of domestic refrigerators (ReSiCo): Demonstration in full scale

Domestic refrigerators have caused various energy-related issues for years. Replacing old refrigerants, using more flexible components, and reducing power consumption have been the main concerns of manufacturers. It is an improper use of energy and resources to implement each new change in the construction of the refrigeration cycle by trial and error. Therefore, virtual labs can assist designers in investigating potential changes before implementing that in practice. This work describes the procedure by which a flexible software is developed to simulate each component of the refrigeration cycle and predict the desired variables in an efficient time. In this software, the amount of refrigerant charge and the degree of superheat are provided as input variables; geometrical parameters for each component are considered in detail. The tube-by-tube and map-based methods are implemented to model the heat exchangers and compressor, respectively. Heat transfer between the suction line and capillary tube is simulated as well. Eventually, the performance parameters with all thermodynamic properties of the cycle at any arbitrary location can be reported as outputs. The case studies showed that the coefficient of performance will increase from 1.58 to 2.1, and from 2 to 2.2 by tuning the suction-line-heat-exchanger and evaporator fan speed, respectively

Numerical simulations of staged biomass grate fired combustion with an emphasis on NOx emissions

In the present paper NOx emissions from biomass combustion was studied, with the objective to demonstrate the applicability of stationary computational fluid dynamics simulations, including a detailed representation of the gas phase chemistry, to a multi-fuel lab-scale grate fired reactor using biomass as fuel. In biomass combustion applications, the most significant route for NOx formation is the fuel NOx mechanism. The formation of fuel NOx is very complex and sensitive to fuel composition and combustion conditions. And hence, accurate predictions of fuel NOx formation from biomass combustion rely heavily on the use of chemical kinetics with sufficient level of details. In the present work we use computational fluid dynamics together with three gas phase reaction mechanisms; one detailed mechanism consisting of 81 species and 1401 reactions, and two skeletal mechanisms with 49 and 36 species respectively. Using the detailed mechanism (81 species), the results show a high NOx reduction at a primary excess air ratio of 0.8, comparable to the NOx emission reduction level achieved in the corresponding experiment, demonstrating both the validity of the model and the potential of NOx reduction by staged air combustio

NOx emission reduction by staged combustion in grate combustion of biomass fuels and fuel mixtures

NOx and N2O emissions have been investigated for different pelletized biomass fuels and fuel mixtures thereof both with and without air staging in a grate fired multi-fuel reactor. The fuels investigated are wood, demolition wood and coffee waste, and selected mixtures of these. The multi-fuel reactor was operated at close to constant operating conditions due to impactor (ELPI) measurements, with a total excess air ratio of about 1.6, and a primary excess air ratio of about 0.8 in the air staging experiments. The reactor set point temperature was held constant at 850 degrees C. NOx emission levels as a function of air supply mode and fuel nitrogen content are reported, showing a large NOx reduction potential, up to 91% and corresponding to less than 20 ppm NOx at 11% O-2 for a fuel containing about 3 wt.% fuel-N, using air staging. The effect on N2O, however, is adverse at the selected set point temperature and optimum primary excess air ratio for NOx reduction. The effect of fuel mixing and fuel nitrogen content on the conversion of fuel nitrogen to NOx is also reported and discussed. Fuel mixing has a positive influence on the NOx emission level, but a negative influence on the overall conversion factor for fuel-N to NOx and N2O