The influence of particle size on the viscosity of water based ZnO nanofluid

This experimental work investigated, the effect of ZnO particles’ size on the water-based nanofluid viscosity. Nanofluid samples with 0.5, 0.75, and 1% volume concentrations were prepared using 20  and 50∼150 nm ZnO nanoparticle sizes. Their viscosity was determined at 20, 30, 40, 50, and 60°C. Scanning electron microscopy was employed to investigate the morphology of the nanoparticles. The maximum relative viscosity was measured for 1% ZnO (50∼150 nm) as 1.35 times water. The stability of samples was evaluated for 1% ZnO (20 nm) and 1% ZnO (50∼150 nm) by measuring their Zeta potential values which were −21.4 mV and –23.1 mV, respectively. The correlation for the dynamic viscosity using measured data was compared with well-known ones. The offered correlation has R2 = 0.988, Radj2 = 0.987, and ±5.58% maximum deviation. The results showed that 12.8% reduction in viscosity is possible by varying nanoparticle sizes. The current study proposes additional new findings on the nanofluids' usability

Optimization of the finned double-pipe heat exchanger using nanofluids as working fluids

The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost. Increasing fin dimensions increases the annulus hydraulic diameters. Even though the total volume of the heat exchanger remains unchanged between the finned and bare designs, the heat duty increases with increased heat transfer area for the finned design. The fins should be designed, and the dimensions should be calculated with special attention for different flow rates and heat exchanger dimensions. In this study, number, geometry and dimensions of the fins are determined using the algorithms available in the literature. The operational condition optimization is carried out accompanied with the cost analysis. In addition, the effects of the types of working fluids and fouled and clean cases are investigated for the total heat transfer enhancement in parallel with performance, lifetime and cost issues. A detailed analysis is presented for finned and unfinned double-pipe heat exchanger models for pure engine oil and its nanofluid mixtures with Ti, TiO2, Cu, CuO, Al and Al2O3 nanoparticles, multi-wall carbon nanotubes and graphene nanosheet having a constant particle concentration in the liquid phase. The nanofluid is flowing in annulus side, whereas the seawater is flowing in the tube side. It is observed that both the pressure drop and the pumping power increase with the increasing fin number and decrease with the cleanliness factor, whereas the total tube number decreases with increasing fin number. It is found that different types of nanofluids affect the cost and optimum annulus side velocity significantly. The results are summarized in several figures that consider the increasing Reynolds number with the cleanliness factor, the heat transfer coefficient and the pressure drop, the friction factor with changing mass flow rate and the cost values with corresponding annulus side velocities. Finally, the overall characteristics of the trend lines are provided in the figures

A model of energy management analysis, case study of a sugar factory in Turkey

WOS: 000429178800003This study presents a case study of energy management in a sugar factory in Turkey. The main idea of the study is to analyse energy consumption, the quantity of material production, and figure out a suitable energy efficiency for the case study of a sugar factory subsequently. Firstly, a material production and energy consumption audit were performed for the sugar factory. Secondly, energy efficiency was calculated from the energy data. The SPSS (Statistical Package for the Social Sciences) statistical software was used to ensure the accuracy of the data. The factory's energy consumption was calculated as 43,590.25 toe (tons of oil equivalent) over the last year. These results were used for CUSUM (Cumulative Sum Deviation Method) graphics. This research poses the consumption of energy, cost of energy and the relationship between energy usage and material production of sugar. The unit of energy cost was 688.22 [$/toe] for the last year. This result showed that the factory decreased the unit of energy by optimisation. The results indicated that the investigated sugar factory should pay attention to the energy management issue in order to comply with the Energy Efficiency of Turkish Law and Directives

Parametrıc study of energy, exergy and thermoeconomıc analyses on a vapor-compressıon system cascaded wıth lıbr/water and nh3/water absorptıon cascade refrıgeratıon cycles

Taner, Tolga (Aksaray, Yazar)Energy savings on cooling systems can be achieved using novel refrigeration cycles. To this end, vapor-compression/vaporabsorption cascade refrigeration systems may be a substitute for single-stage vapor-compression refrigeration systems. These cycles can use renewable energy sources such as geothermal and solar heat energy as well as waste heat from processes to provide cooling, and they also require less electrical energy than vapor-compression cycles with alternative refrigerants. In this study, vapor-compression and vapor-absorption cascade systems undergo second-law analysis for various cooling capacities. While lithium bromide-water and NH3/H2O are the working fluids in the vapor-absorption part, various refrigerants are used in the vapor-compression section. The refrigerants R134a and R600a as well as R410A and R407C are tested in the study. The effects on the coefficient of system performance (COP) of alterations in cooling capacity, superheating, and subcooling in the vapor-compression part; temperature in the generator and absorber; and degree of overlap in cascade condenser in the vaporabsorption part. The results were validated by values given in the literature. Improvements in the COPs of the vapor compression, vapor absorption, and cascade systems were obtained separately. According to the analyses, cascade systems' COP increases with generator and evaporator temperatures and also increase as condenser and absorber temperatures decrease. Moreover, the generator had the highest exergy-destruction rates, followed by the condenser and absorber, respectively. Electricity consumption and payback period were also determined by considering the various parameters of the study

Effect of hydrogen–diesel dual-fuel usage on performance, emissions and diesel combustion in diesel engines

Diesel engines are inevitable parts of our daily life and will be in the future. Expensive after-treatment technologies to fulfil normative legislations about the harmful tail-pipe emissions and fuel price increase in recent years created expectations from researchers for alternative fuel applications on diesel engines. This study investigates hydrogen as additive fuel in diesel engines. Hydrogen was introduced into intake manifold using gas injectors as additive fuel in gaseous form and also diesel fuel was injected into cylinder by diesel injector and used as igniter. Energy content of introduced hydrogen was set to 0%, 25% and 50% of total fuel energy, where the 0% references neat diesel operation without hydrogen injection. Test conditions were set to full load at 750, 900, 1100, 1400, 1750 and finally 2100 r/min engine speed. Variation in engine performance, emissions and combustion characteristics with hydrogen addition was investigated. Hydrogen introduction into the engine by 25% and 50% of total charge energy reveals significant decrease in smoke emissions while dramatic increase in nitrogen oxides. With increasing hydrogen content, a slight rise is observed in total unburned hydrocarbons although CO 2 and CO gaseous emissions reduced considerably. Maximum in-cylinder gas pressure and rate of heat release peak values raised with hydrogen fraction

Performance of refrigerants employed in rooftop air-conditioners

Unlike earlier studies, this study examines six refrigerants with various properties using the same rooftop air conditioning system of a building to evaluate performance. Performance metrics such as cooling capacity, energy consumption, temperature, and pressure were calculated. Laboratory testing of a rooftop air conditioner with R410a was performed to validate the simulation program's predicted data. Six distinct refrigerants' carbon emissions in two different scenarios were calculated using the Life Cycle Climate Performance technique, which was evaluated for environmental studies. These experimental tests were carried out at temperatures of 20 °C, 25 °C, 30 °C, and 35 °C, respectively. Maximum discrepancies between simulated and experimental results for cooling capacity, energy consumption, and energy efficiency were calculated to be 2.8%. The study found the lowest value in the R1234yf carbon emission at 51.30 kg CO2e. The highest cooling capacity was 154760.34 W in R454b, and the lowest cooling capacity was 76949.94 W in R1234yf. The highest EER value was 3,018 in R454b, while the lowest released was 2.257 in R22. The SEER value was 4.101 for R32 and 2.298 for R1234yf. The simulations concluded that R410a, R454b, and R32 refrigerants have superior cooling capacities

Effect of the segmented fin height on the air-side performance of serrated welded spiral fin-and-tube heat exchangers

Serrated welded spiral fin-and-tube heat exchangers (SWSFTHXs) are experimentally investigated. The work primarily focuses on the effects of the segmented fin height (h(s)) with various fin pitches (f(p)) on the air-side performance (ASP). Experimental results show that SWSFTHXs provide a higher air-side heat transfer coefficient than the plain welded spiral fin-and-tube heat exchangers (PWSFTHXs) at the same f(p). The h(s) has a significant effect on the Nusselt number (Nu) and Colburn factor (j), whereas f(p) clearly has a greater effect on the friction factor (f) and Euler number (Eu) than h(s). Furthermore, the Nu, j, f, and Eu correlations for PWSFTHXs and SWSFTHXs are also proposed

Prediction of heat transfer characteristics in a microchannel with vortex generators by machine learning

Because of the prompt improvements in Micro-Electro-Mechanical Systems, thermal management necessities have altered paying attention to the compactness and high energy consumption of actual electronic devices in industry. In this study, 625 data sets obtained numerically according to the change of five different geometric parameters and Reynolds numbers for delta winglet type vortex generator pairs placed in a microchannel were utilized. Four dissimilar artificial neural network models were established to predict the heat transfer characteristics in a microchannel with innovatively oriented vortex generators in the literature. Friction factor, Nusselt number, and performance evaluation criteria were considered to explore the heat transfer characteristics. Different neuron numbers were determined in the hidden layer of each of the models in which the Levethenberg-Marquardt training algorithm was benefited as the training algorithm. The predicted values were checked against the target data and empirical correlations. The coefficient of determination values calculated for each machine learning model were found to be above 0.99. According to obtained results, the designed artificial neural networks can provide high prediction performance for each data set and have higher prediction accuracy compared to empirical correlations. All data predicted by machine learning models were collected within the range of +/- 3% deviation bands, whereas the majority of the estimated data by empirical correlations dispersed within & PLUSMN;20% ones. For that reason, a full evaluation of the estimation performance of artificial neural networks versus empirical correlations data is enabled to fill a gap in the literature as one of the uncommon works

Effect of the use of natural gas–diesel fuel mixture on performance, emissions, and combustion characteristics of a compression ignition engine

A compression ignition engine with a mechanical fuel system was converted into common rail fuel system by means of a self-developed electronic control unit. The engine was modified to be operated with mixtures of diesel and natural gas fuels in dual-fuel mode. Then, diesel fuel was injected into the cylinder while natural gas was injected into intake manifold with both injectors controlled with the electronic control unit. Energy content of the sprayed gas fuel was varied in the amounts of 0% (only diesel fuel), 15%, 40%, and 75% of total fuel’s energy content. All tests were carried out at constant engine speed of 1500 r/min at full load. In addition to the experiments, the engine was modeled with a one-dimensional commercial software. The experimental and numerical results were compared and found to be in reasonable agreement with each other. Both NO x and soot emissions were dropped with 15% and 40%, respectively, energy content rates in gas–fuel mixture compared to only diesel fuel. However, an increase was observed in carbon monoxide emissions with 15% natural gas fuel addition compared to only diesel fuel. Although smoke emission was reduced with natural gas fuel addition, there was a dramatic increase in NO x emissions with 75% natural gas fuel addition

CFD analyses on the thermal comfort conditions of a cooled room: A case study

Taner, Tolga ( Aksaray, Yazar )This study examined a room with a surface of 1.8 x 1.8 x 2.85 (m) and a well-insulated floor (adiabatic condition) and examined the heat exchange from the side surfaces and ceiling. In this closed room, the heat transfer effects with radiation were investigated while bringing them to comfort conditions ranging from 30 (degrees C) air temperature to 20-24 (degrees C). A computer with a power of 25 (W) as a source of heat, a person with an average metabolic activity of 50-70 (W) and a table were found in this closed room. In this study, the cooling of the room from the floor, ceiling and air conditioner was inquired while the computer was running, in a closed area under the specified heat transfer conditions. As a scenario, the air exchange coefficient was modeled via Ansys Fluent, fed with air of 15 (degrees C) with 1, 3, 5, 10, 15 air. In addition, the comfort values of the human wrist (the distance of 0.1 m) and the shoulder (the distance of 1.1 m) were researched according to ASHRAE-55. The obtained results were analyzed as a comparison of ACH results, and the comfort parameter values were analyzed by reading the sections taken from the ankle shoulder level and velocity, temperature, values according to ANSI/ASHRAE-55. The relative humidity was 50% in the room, while the metabolic activity is 1.2 (met). These parameters corresponded to the sitting position; the clothing effect was found to be 0.67 (clo). The novelty of this study encourages the production of the ideal CFD analysis on the thermal comfort conditions of a cooled room, the task of engineering