Showing papers in "Heat and Mass Transfer in 2019"

Performance, emission and combustion study on neat biodiesel and water blends fuelled research diesel engine

Abstract: This work investigates the experimental study to examine the operation characteristics of an orange peel oil biodiesel (BD100) along with water as an oxygenated additive in various volume fractions. Hard water is mixed into 100% of BD100 at 4 and 8% volume. Span 80 was employed as a nonionic surfactant, which emulsifies water into biodiesel. The experimental investigation on diesel engine reveals that the addition of water to BD100 resulted in enhancement of brake thermal efficiency (BTE) with a reduction in brake specific fuel consumption (BSFC). The tested emission parameters such as CO, HC, NOx and smoke were decreased by 11.4, 9.89, 3.36 and 5.14% for BD94W4S2 (94% volume of biodiesel) + (4% volume of water) + (2% volume of surfactant) and 12.22, 10.11, 4.85 and 6.18% for BD90W8S2 (90% volume of biodiesel) + (8% volume) + (2% volume) respectively when compared to BD100. Further, the cylinder pressure and heat release rate and were enhanced by adding water to base fuel (BD100). Overall, improvement in ignition characteristics of the engine was finer by adding, 4 and 8% volume of water to BD100 on account of its chemical properties.

Research on heat transfer enhancement and flow characteristic of heat exchange surface in cosine style runner

Abstract: The steady state heat transfer and flow resistance performance in cosine style runners with different amplitudes are studied numerically and experimentally in this paper. The results show that: When the Reynolds numbers (Re) range from 1210 to 5080, the core volume goodness factor (ηohstdα) is used to compare the overall heat transfer performance of the two runners, and the ηohstdα value in the cosine style runner is 7–25% larger than that of the equal cross section runner, so that the cosine style runner has better overall heat transfer enhancement performance. When the amplitudes (2A) range from 5 to 9 mm, with the decrease of amplitude, the overall heat transfer performance is getting better. At the same amplitude, the convective heat transfer performance gradually increases as the inlet height (Fh) decreases; with the increase of Re, the thickness of the thermal and velocity boundary layers are both decreasing. Based on the field synergy principle, the heat transfer enhancement mechanisms with different parameters are evaluated, and we conclude that the smaller the amplitude is, its field synergy is better.

Investigation on behavior of diesel engine performance, emission, and combustion characteristics using nano-additive in neat biodiesel

Abstract: This work investigates the combustion, performance and emission characteristics of neat palm stearin biodiesel (PSBD) fuelled diesel engine with silver oxide as a additive in various mass fractions (5 and 10 ppm) and various particle size (10 and 20 nm) particles and the results compared with conventional diesel. Experiments were conducted in a natural aspirated, single-cylinder diesel engine at a constant speed and compression ratio of 1500 rpm and 18:1 respectively. Silver oxide (AgO) nano particles were added with neat biodiesel using ultrasonicator. The experimental investigation on diesel engine reveals that the addition of silver oxide nano-additives to PSBD resulted in enhancement in ignition characteristics because of enhanced surface area to volume ratio. Further, the addition of AgO nano-additive to PSBD resulted in enhancement in brake thermal efficiency (BTE) with a reduction in brake specific fuel consumption (BSFC). The experimental results also show that the AgO nanoparticles at 20 nm particle size and 10 ppm concentartion promote an improved level of hydrocarbon (HC), carbon monoxide (CO), smoke emissions and nitrogen (NOx) emission than neat biodiesel. Further, The AgO nano-additive inclusion at different 10 ppm significantly reduces the peak pressure and increases the net Heat Release rate values and its corresponding CA. An inclusion of 20 nm nano-additive at 10 ppm concentartion in PSBD reduces the In Cylinder Pressure and increases the Net Heat Release Rate values by 2.2 and 4.7% respectively than PSBD.

Evaluation of methyl ester derived from novel Chlorella emersonii as an alternative feedstock for DI diesel engine & its combustion, performance and tailpipe emissions

Abstract: This work examines the feasibility of fueling methyl ester derived from green algae species, Chlorella emersonii in a compression ignition engine. This work also proposes Chlorella emersonii methyl ester (CEME) as a potential alternative energy source since the above species is available extensively in freshwater, marine and aquatic ecosystems throughout the world. CEME was blended with petroleum diesel fuel at various volume proportions of 10%, 20%, 30%, 40% and 100% and their properties were analyzed as per ASTM standards for its application as biofuel. The prepared test fuels were analyzed experimentally in a single cylinder diesel engine at a constant speed (1500 rev/min) for its performance, combustion and emission (regulated and unregulated) characteristics. Test results indicated that, the characteristics of 20% CEME+80% DIESEL fuel blend was in par with neat DIESEL fuel in terms of thermal efficiency, THC (total hydrocarbon), CO (carbon monoxide) and smoke emissions. However, CEME blends resulted in slightly higher levels of CO2 (carbon dioxide) and NOx (oxides of nitrogen) emissions. In terms of unregulated emissions, CEME blends in DIESEL showed lowered toluene and acetaldehyde emissions. However, acetone and formaldehyde emissions increased with higher percentage of CEME in DIESEL blend. At full load, the attained cylinder pressure and heat release rate of CEME were comparatively lower than DIESEL fuel. Overall, it can be concluded that B20 (20% CEME +80% DIESEL fuel) blend can be a positive variant feedstock and it can be utilized in an unmodified diesel engine with minimal tailpipe emissions.

Numerical investigation of efficiency and economic analysis of an evacuated U-tube solar collector with different nanofluids

Abstract: In this paper, an evacuated U-tube tube solar collector (EUSC) was designed and simulated numerically. The thermal performance of the EUSC was analyzed under different operating conditions. In order to enhance the heat transfer efficiency and also collector efficiency, higher thermal conductivity working fluids were used. Ag, ZnO and MgO nanoparticles in 30%:70% (by volume) ethylene glycol-pure water (EG-PW) mixture and different nanoparticle volumetric concentrations were used as working fluids. The highest collector efficiency is found at 68.7% for 4.0 vol% Ag/EG-PW nanofluid which is 26.7% higher than EG–PW. Furthermore, using nanofluids in solar collectors helps to reduce the coal usage with CO2 and SO2 generation. The maximum values of reduction of coal usage and CO2 and SO2 generation are 855.5 kg, 2241.4 kg and 7.2 kg per year, respectively, when 30 solar collectors are installed with using 4.0 vol% Ag/EG-PW nanofluid. These findings reveal that the using of solar energy comprehensively is more beneficial for health of earth.

Improving the performance of a passive battery thermal management system based on PCM using lateral fins

Abstract: Phase-change materials (PCMs) combine the latent and sensible heat adsorption capabilities which makes them promising candidates in a wide range of heat transfer applications such as battery thermal management systems (BTMSs) in hybrid electric vehicles (HEVs), battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). PCM must preserve the battery cells in the desired temperature range. However, pure PCMs face some challenges due to their low thermal conductivities. To mitigate this issue, one possible solution is employing fins to enhance the heat transfer across the PCM. Since the PCM melting is affected by buoyancy forces, alignment of employed fins may have an essential role in the performance of BTMSs. In the current investigation, six different BTMSs using PCM with dissimilar fin alignments are simulated and evaluated. The time evolution of liquid fraction contours are depicted for simulated cases. The results indicate that the BTMS employing horizontal fins provides the best cooling effect with the largest melt fraction after a prescribed period of time. Besides, the results demonstrate that the breaking manner of solid PCM can be greatly affected by the alignment of fins.

Heat transfer enhancement of TiO 2 -water nanofluid flow in dimpled tube with twisted tape insert

Abstract: This paper deals with the thermo-hydraulic behaviors of dimpled tubes mounted with twisted tape inserts using TiO2-water nanofluids as the test fluids. The possible heat transfer mechanisms were discussed. Experiments were conducted using (1) the dimpled tubes with dimple angles (θ) of 0, 15, 30 and 45°, (2) the tapes having twist ratios (y/W) of 3.0, 4.0 and 5.0, and (3) TiO2-water nanofluids with ϕ = 0.05, 0.1 and 0.15 vol.%. The experimental results revealed that the dimpled tubes with twisted tapes yielded higher heat transfer rates than the dimpled tube alone. The results also indicated the strong influence of dimple angle, twist ratio and TiO2-water nanofluid concentration on the thermo-hydraulic performance. Among the tested dimpled tubes, the one with a dimple angle of 45° yielded the highest heat transfer enhancement. Heat transfer (Nu) increased with decreasing twist ratio (y/W) and increasing nanofluid concentration. Over the investigated range, the highest thermo-hydraulic performance of 1.258 was achieved by using the nanofluid with ϕ = 0.15 vol.% in the dimple angled having the dimple angle of 45°, inserted with twisted tape possessing the twist ratio of 3.0. In the present work, the Wilson plot method was employed to develop the Nusselt number correlation for the flow of TiO2-water nanofluid through the dimpled tubes mounted with twisted tape inserts. The predicted heat transfer rate, friction factor and thermo-hydraulic performance were found in good agreement with the experimental results.

Determination of the drying kinetics and energy efficiency of purple basil ( Ocimum basilicum L.) leaves using different drying methods

Abstract: In this work, the effects of different drying methods, namely sun, freeze, convective and microwave oven drying on the drying time, rate and kinetics were investigated in purple basil leaves. Additionally, the energy efficiencies of the driers were determined. All the drying processes took place mainly in the falling-rate period. Comparatively, higher drying rates were obtained from microwave oven drying of the samples. Eleven thin-layer drying models, (Lewis, Page, Modified Page I, Henderson and Pabis, Modified Henderson and Pabis, Logarithmic, Midilli, Modified Midilli, Two-Term, Two-Term Exponential, and Wang and Singh) were fitted to the experimental moisture ratio data. Handerson and Pabis for freeze drying, logarithmic for sun drying and Page for convective and microwave oven drying were found to be the best models for explaining the drying behavior of the purple basil leaves with the highest R2 and lowest RMSE values. The effective moisture diffusivity (Deff) values of the dried purple basil leaves were calculated with Fick’s diffusion model and ranged from 1.62 × 10−9 to 7.09 × 10−8 m2/s. The energy efficiency of microwave oven drying was higher than the other methods.

Study the effect of microwave power and slices thickness on drying characteristics of potato

Abstract: In the present work, the influence of microwave power and samples thickness on drying behavior, moisture diffusivity and energy consumption of potato slices was studied. The slices with thicknesses of 3.5, 5, 7 and 9 mm were dried as mono layers at four different power levels (200, 400, 600 and 800 W). The results showed that the process time was significantly (P < 0.05) decreased with increasing power and decreasing thickness. The curves of moisture removal rate included a short accelerating rate period at the beginning followed by a long falling rate period. Seven thin layer models were practiced to simulate the experimental drying kinetics and the Midilli model showed the best performance. The average values of effective moisture diffusivity were obtained to be in the range of 1.15510−8-6.654 × 10−8 m2 s−1, and increased significantly (P < 0.05) with both of the increasing microwave power and the samples thickness. The average activation energies changed from 1.423 W g−1 to 1.621 W g−1, and decreased with increasing samples thickness. Specific energy consumption for the process were ranged from 0.680 MJ kg−1water to 2.591 MJ kg−1water.

Nanoparticle shape effects on thermal-hydraulic performance of boehmite alumina nanofluid in a horizontal double-pipe minichannel heat exchanger

Abstract: The aim of the present study is an investigation of the impact of nanoparticle shape on the hydrothermal characteristics of boehmite alumina nanofluid flowing through a horizontal double-pipe minichannel heat exchanger. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes (i.e. cylindrical, brick, blade, platelet, and spherical) are dispersed in a mixture of water/ethylene glycol as the nanofluid. The effects of the Reynolds number and nanoparticle concentration on the heat transfer rate, overall heat transfer coefficient, effectiveness, pressure drop, pumping power, and performance index are numerically analyzed for different nanoparticle shapes. The results reveal that the nanofluids containing cylindrical and platelet shaped nanoparticles have the highest and lowest thermal conductivity, respectively. Additionally, it is found that the highest and lowest viscosity belong to the nanofluids with platelet shaped and spherical nanoparticles, respectively. Furthermore, it is depicted that, among the considered nanoparticle shapes, platelet shaped demonstrates better heat transfer characteristics, while performance index of the heat exchanger for nanofluid containing spherical nanoparticles is higher. Finally, it is inferred from the obtained results that the increase of Reynolds number and nanoparticle concentration result in a higher heat transfer rate, overall heat transfer coefficient, pressure drop, and pumping power and a lower performance index.

A 3-D numerical simulation of non-Newtonian blood flow through femoral artery bifurcation with a moderate arteriosclerosis investigating Newtonian/non-Newtonian flow and its effects on elastic vessel walls

Abstract: In this study, a fluid-structure interaction (FSI) simulation of the blood flow in the femoral artery with a small occlusion is presented. For a more accurate simulation of the real conditions, computerized tomography (CT) scan was used to obtain a 3-D model of leg blood vessels, while the vessel was modeled as an isotropic elastic wall. By assuming a heartbeat period of 0.5 s, the inlet condition was considered as a time-dependent pulse using a non-Newtonian flow model. Blood flow was assumed nonlinear and incompressible, and Carreau model was used for blood rheological model. By considering unstable blood flow at the inlet, the involved hemodynamic parameters are velocity profile, vortices shapes, pressure drop, and streamlines. Furthermore, to determine the relationship between flow geometry and the vascular wall, wall shear stress (WSS) was calculated. By taking the real geometry of the vessel and fluidity of blood into account, comparison of computational results indicated a significant difference in velocity distribution and shear stress depending on whether the fluid-structure interaction is considered Newtonian or non-Newtonian. The results showed that employing Newtonian models for the blood flow does not lead to promising results at occluded areas and beyond them.

Influence of injection timing on torroidal re-entrant chamber design in a single cylinder DI engine fuelled with ternary blends

Abstract: The present experimental work focuses on the influence of injection timing on torroidal re-entrant chamber design in a single cylinder diesel engine fuelled with ternary fuel (diesel-biodiesel-ethanol) blend. Ternary fuel is transformed to a high performance fuel (HPF) by addition of alumina nano additives. Experiments were conducted on HPF subjected to various injection timings of 21obTDC (Retarded injection timing), 22obTDC (Retarded injection timing), 23obTDC (standard injection timing) and 24obTDC (advanced injection timing) respectively at torroidal re-entrant combustion chamber design (TRCC) and were compared with base fuel diesel. Based on experimentation, it is observed that, BTE is lowered for 21obTDC and 24obTDC by 4.53% and 1.22% while highest BTE of about 33.8% is achieved for 22obTDC in comparison with other blends such as DIESEL-HCC23 (32.75%), HPF-TRCC21 (31.41%) and HPF-TRCC24 (32.53%). Lowest BSEC profile was achieved for HPF-TRCC22. HPF-TRCC22 resulted in lowered HC and CO emissions of about 9.18% and 16.83% in comparison with HPF-TRCC23. HPF-TRCC21 resulted in lowered NOx emissions by 22.53% along with higher HC and CO emissions by 6.13% and 20.51% in comparison with HPF-TRCC23. Cylinder pressure and HRR of HPF-TRCC22 stays at an acceptable range of 75.42 bar and 85.34 J/deg. CA in comparison with other test blends.

Citrullus colocynthis - an experimental investigation with enzymatic lipase based methyl esterified biodiesel

Abstract: The intensification of energy claim and inadequate fossil fuel wealth instruct the way to renewable-based energy development that is to say vegetable oils, seed oils, plants oil and animal fats and etc. The experimental study investigated the significance of biodiesel replaced for diesel. The biodiesel is obtained by two intrinsic methods from Citrullus colocynthis, one with methyl ester and other with enzymatic lipase-based methyl ester transesterification process. The process involves Fe3O4+ thermomyces lanuginosus lipase as a catalyst for transesterification. The fuel extruded from these methods is tested with a single cylinder four stroke DI diesel engine to investigate the performance emission and combustion parameters. Initially, Novel immobilization-based lipase transesterification method was involved in the extrusion of oil from Citrullus colocynthis seed and a yield of 90% with a time frame of 0 to 73 h, the extrusion was also escalated with conventional transesterification. The investigation shows that the fuel undergoes good combustion and the performance parameters were improved which in turns reflects the reduction of emission. The brake thermal efficiency of lipase immobilized biodiesel (Blend-L) is 29.86% at full load condition which is fairly less than diesel (31.33%) followed by a value of 28.93% at full load condition for conventional transesterified biodiesel. When the fuels are combusted the heat release rate and peak pressure is quite less than diesel fuel for Blend-L. The emission parameters such as PM and NOx are comparatively high than diesel and the remaining emission showed significantly reduced values.

Heat transfer and pressure drop characteristics of MgO nanofluid in a double pipe heat exchanger

Abstract: The present work aims to investigate the plausible application of MgO-ethylene glycol as a heat transfer fluid in a double-pipe heat exchanger. The nanofluid was prepared using a two-step method at weight concentrations of 0.1, 0.2 and 0.3%. The test rig provided conditions to measure the convective heat transfer coefficient, pressure drop and friction factor of the system. Influence of the different operating parameters such as flow rate, mass concentration of nanoparticles and inlet temperature of nanofluid to the heat exchanger on the heat transfer coefficient and pressure drop was experimentally investigated. Results showed that the heat transfer coefficient within the heat exchanger can be enhanced by 27% for wt.% = 0.3 in comparison with the base fluid (ethylene glycol). It was also found that the presence of MgO nanoparticles increased the pressure drop by 35% at wt.% = 0.3. The friction factor of the system decreased nonlinearly with an increase in the Reynold number and it followed the trend of 64/Re equation. An increase in the mass concentration of nanoparticles increased the friction factor and the maximum friction factor enhancement was 32% belonging to the nanofluid with mass concentration of wt.% = 0.3. Likewise, inlet temperature was found to have a very slight influence on the heat transfer coefficient and no effect on the friction factor and pressure drop of the system. The thermo-physical properties of MgO-ethylene glycol nanofluid was also experimentally measured at various temperatures.

Comparative study of flow characteristics of a single offset jet and a turbulent dual jet

Abstract: The present paper consists of a numerical investigation of dynamic and thermal characteristics of the flow field resulting from the interaction of dual-jet consisting of a wall jet and an offset jet and comparison with a single turbulent offset jet. The effects of velocity and offset ratios between two jets in the near field region have been simulated numerically using two-dimensional steady RANS equations. The simulation is carried out through the resolution of the different governing Navier–Stokes’ equations by means of the finite volume method. Two different closure models were tested: the standard k–e model and the Reynolds stress model (RSM) second order model. A non-uniform mesh system tightened close to the emitting nozzle and both the vertical and horizontal walls is also adopted. The confrontation of the numerical results with experimental data from literature shows satisfying agreement with the RSM model in the description of the handled flow; that’s why we adopted it for the rest of the paper. Once the model validated, a detailed discussion has been provided on the mean velocities, pressure field, Reynolds stress, and kinetic energy. The merge point, the combined point and the impact point have also been obtained and compared with other results. A similarity profile has been obtained in the downstream direction for different offset and velocity ratios.

Experimental investigation on pyramid solar still in passive and active mode

Abstract: In this research work pyramid solar still is experimentally researched on both passive and active mode. In active mode, the pyramid solar still is incorporated with straight tube and spiral tube solar water heater. The experiments were carried out by passive and active pyramid solar still at 1 cm water depth. It is found that the pyramid solar still incorporated with the spiral tube solar water heater operated at mass flow rate of water at least amount produced the higher productivity of 6.35 kg/m2/day with the daily energy and exergy efficiency of 15.25 and 3.22%, respectively. The pyramid solar still incorporated with the spiral tube solar water heater increases the productivity, energy and exergy efficiency of about 12.18, 14.58, and 18.76%, respectively as compared to the straight tube solar water heater.

Experimental investigation of thermal conductivity behavior of MWCNTS-Al 2 O 3 /ethylene glycol hybrid Nanofluid: providing new thermal conductivity correlation

Abstract: The present study investigates the thermal conductivity of Al2O3 hybrid with MWCNTs (multi-walled carbon nanotubes) nanoparticles dispersed in ethylene glycol (EG) as a base fluid. Seven different nanoparticles volume fractions, namely, 0.02%, 0.04%, 0.08%, 0.1%, 0.25%, 0.5% and 0.8% at temperatures ranging from 25 °C to 50 °C of the hybrid nanofluid are prepared without using any surfactant. Transient Hot Wire method (THM) using KD2 Pro device (Decagon Devices, Inc., USA) was used to measure the thermal conductivity of the nanofluids. The results show at most about 17% thermal conductivity enhancement for 0.8% nanoparticles volume fraction at 50 °C. Two new correlations are proposed to estimate the hybrid nanofluid thermal conductivity with high accuracy. The first one is a function of the nanofluid temperature and its volume fraction and the next one, with a higher accuracy, is in effect six expressions in terms of the nanoparticles volume fraction presented at temperatures 25 °C, 30 °C, 35 °C, 40 °C, 45 °C and 50 °C.

Investigation and recent developments in aerodynamic heating and drag reduction for hypersonic flows

Abstract: Investigation on new methods of drag reduction and thermal protection for hypersonic velocities are proposed based on the new technologies for shock reconstruction. In principle, a blunt vehicle flying at high speeds generates a strong bow shock wave ahead of its nose, which is responsible for the high drag and aero heating levels. There have been a number of efforts devoted towards reducing both the drag and the aero heating by modifying the flow field ahead of the vehicle’s nose. An introduction to the philosophy and recent development in hypersonic aerodynamic heating and drag reduction techniques are presented. These techniques are classified in four major group. Geometrical, mass injection, energy deposition, and magneto aerodynamic techniques. In this review, these new techniques and investigation of the philosophy and development procedure of these techniques are brought to the table and then the effects of each method on drag wave and aerodynamic heating reduction is shown. Geometrical techniques such as structural spike and aerodisk, cavity, multi-row disk (MRD) use to drag reduction. Mass injection techniques like arrays of micro jets, spike and jet, heat addition and plasma injection are very useful to aerodynamic heating reduction. Energy deposition techniques by using laser and plasma can reduce aerodynamic heating and wave drag of hypersonic flows. Magneto aerodynamic technique can reduce drag and aerodynamic heating, by the addition of the magneto technology in hypersonic flows. The present paper is devoted to surveying these studies and illustrating the contributions of the authors in this field. Not only do the paper criticize the previous investigations but also raises some of the areas in the field that need further investigations.

Performance investigation of PEMFC with rectangle blockages in Gas Channel based on field synergy principle

Abstract: This work, using three-dimension proton exchange membrane fuel cell (PEMFC) model combined with theoretical analysis, is mainly to improve the performance of PEMFC through optimizations of fuel cell structure, adding rectangle blockages in the gas channel. Performance comparison, velocity distribution, interface reactant concentration difference, and pressure drop have been studied in the paper. The result shows that, longitudinal vortices would appear and the performance could be improved with the addition of blockages in the gas channel, especially at high current density with closer arrangement. According to field synergy principle, average mass transfer synergy angle could prove the superiority of optimized structure in the ability of mass transfer. Besides, a novel physical quantity, effective mass transfer coefficient, has been proposed. The effective mass transfer coefficient, is the ability of mass transfer in the direction of electrochemical reaction in PEMFC, which could also give mechanism explanation for the performance improvement.

Liquid-liquid two-phase flow patterns in ultra-shallow straight and serpentine microchannels

Abstract: Water-butanol and water-hexane flows were visualized in ultra-shallow straight and serpentine microchannels with a cross-junction. At the inlet cross-junction, three major flow patterns including tubing/threading, dripping and jetting were mapped using the aqueous Capillary number versus the organic Weber number. Correspondingly, in the main microchannel, annular flow, slug flow and droplet flow were mapped using combined dimensionless numbers (Weber number times Ohnesorge number) of both phases. The flow pattern transitions were explained based on a force analysis, considering the phase flow rates, junction angle between the side feeding channels and the central feeding channel as well as aspect ratios. Compared to the straight microchannel, the dripping regime at the inlet junction and the slug flow occupy larger zones in serpentine microchannels because the centrifugal force tends to break up the organic annular core into slugs and droplets over the bends.

Experimental investigation on thermal performance of closed loop pulsating heat pipes with soluble and insoluble binary working fluids and a proposed correlation

Abstract: In this study, an experimental investigation was conducted from a thermal performance standpoint on closed-loop pulsating heat pipes (CLPHPs) with four different fluids and their water-based binary mixtures as working fluids with volume mixing ratios of 3:1, 1:1, and 1:3. Ethanol and acetone as two types of fluids that are soluble in water and, to unprecedentedly compare the behavior of insoluble mixtures with the soluble ones as the working fluids, toluene and hexane as two types that are insoluble in water were used. Additionally, to predict the thermal performance of the pure, soluble binary, and insoluble binary fluids simultaneously for the first time, a correlation was derived.

Characterization and thermal conductivity investigation of Copper-Polyaniline Nano composite synthesized by gamma radiolysis method

Abstract: In this study, Copper-Polyaniline nanocomposite (Cu-PAni) has been synthesized by gamma radiolysis as a novel method and was confirmed by different analytical techniques such as Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray powder diffraction (XRD). The copper nanoparticle completely covered by a layer of polyaniline with different thickness. The particle mean size was determined from XRD by using the Debye-Scherrer’s formula and the particle size was found to be 21 nm. The thermal conductivity of the nanofluid has been measured at different nanofluids volume fractions of 0.2%, 0.4%, 0.6%, 0.8% and 1.0%. The effect of nanofluid temperature on the nanofluid properties is measured in the range from 10 °C to 90 °C. The thermal conductivity ratio of the Copper-Polyaniline nanocomposites water nanofluid increases 107% at nanofluid temperature of 10 °C and 159% at 90 °C for a volume fraction of 1.0%. The Cu-PAni nanocomposite is a potential material for thermal conductivity enhancement of water based nanofluid.

Experimental study on the convective heat transfer performance and pressure drop of functionalized graphene nanofluids in electronics cooling system

Abstract: Cooling of electronic equipment has gained significant importance in thermal management systems as a result of the increase of power densities in micro-electronic equipment. This present work investigates the convective cooling performance of microwave assisted acidic functionalized graphene – deionized water nanofluid. The nanofluid possess high dispersion stability (Zeta potential < −40 mV) in the pH range (6–8) and a thermal conductivity enhancement of 55.38% compared to base fluid. The heat transfer performance of the nanofluid was studied by investigating the effect of volume fraction (0 to 0.2 vol.%) and flow rate (5 ml/s to 10 ml/s) on the convective heat transfer coefficient, processor core temperature, and pressure drop. An increase in the convective heat transfer coefficient of about 78.5%, a decrease in the core temperature of about 15% and an average increase of 5% in pressure drop were obtained for the maximum concentration and flow rate of the nanofluid. The results concluded that acidic functionalization of graphene nanoparticle has a significant influence on the increase in the thermo-fluid properties of nanofluid and thus can be used as an efficient heat transfer fluid, compared to conventional coolants.

A detailed review on various V-shaped ribs roughened solar air heater

Abstract: Solar air heater (SAH) is a popular and economical device which collects the solar energy and is employed for space heating, drying of agricultural products, food items, and leather, seasoning of timber, etc. Attachment of artificial roughness on the absorber surface is an appropriate method to augment the heat transfer from the heated surface to the air flowing through SAH duct. Use of artificial roughness has been an area of great interest for researchers as far as the cooling of turbine blades, and combustion chambers are concerned. This technique is effective in enhancing the heat transfer in a micro-channel heating/cooling system. Present paper holistically furnishes concise information about various kinds of V-shaped roughness geometries used in SAHs for improving its performance covering experimental, analytical, numerical and computational fluid dynamics (CFD) approaches. In this paper, 124 research articles have been referred, which provide a detailed comprehensive and comparative study revealing the effect of various geometrical parameters and different V-shaped roughness patterns on the performance of SAH. This article also brings in the information about the correlation developed by researchers for heat transfer and friction factor. This comprehensive review will be quite useful for technical persons and researchers working in the area of SAH.

Numerical study of heat transfer and flow characteristic of twisted tube with different cross section shapes

Abstract: In the present work, three dimensional numerical study is conducted to investigate the heat transfer and flow characteristics of twisted tubes of different cross section shapes with the Reynolds number ranging from 50 to 2000 The constant wall temperature condition is used in the simulation analysis The numerical results of twisted square tube are compared with the available previous experimental data The results indicate that the heat transfer performance of twisted tube is enhanced compared with the smooth tube, while the pressure drop increases as well One of the key findings is that the transition point of twisted square tube from laminar flow to turbulent flow is identified and located at Re = 500 It is also found that the cross section shape has little effect on the heat transfer of twisted tubes, while it has great influence on the flow pattern The results also reveal that the twist pitch has remarkable effects on the heat transfer performance of twisted tubes In addition, the maximum value of PEC of 269 is obtained in twisted pentagon tube with twist pitch ratio of 017, and the Reynolds number of 350 These results are significant because it will contribute to the development of compact twisted tube heat exchangers

Review of gas–liquid mass transfer enhancement by nanoparticles from macro to microscopic

Abstract: Gas–liquid mass transfer is an extremely common process in the chemical industry and enhancing this process can help achieve high efficiency and low energy consumption. The addition of nanoparticles in the liquid phase is an important method for enhancing such transfers. In this paper, the preparation methods of nanofluids are briefly described and the parameters associated with nanofluid transport, such as mass-transfer coefficient, liquid volumetric mass-transfer coefficient, mass transfer interface area, and gas holdup, are introduced. Then, the latest experiments and mechanisms for the effect of nanofluids on the gas–liquid mass transfer process are reviewed from the viewpoint of transport parameters. The reasons for the enhancement of gas–liquid mass transfer by nanofluids are given: shuttle effect, mixing of the gas–liquid boundary layer, and inhibition of bubble coalescence. Finally, the problems existing in current research are assessed and, toward enhancing gas–liquid mass transfer using nanoparticles, future research directions are proffered.

Saturated flow boiling heat transfer: review and assessment of prediction methods

Abstract: This paper presents a review of the correlations for saturated flow boiling heat transfer coefficients. Fifty correlations are systematically reviewed, which fall into seven categories. An experimental database for saturated flow boiling heat transfer was compiled from 67 sources. It contains 10,932 data points and covers 19 fluids, including eight pure halogenated refrigerants (R134a, R22, R123, R1234yf, R1234ze(E), R152a, R245fa, and R32), five refrigerant mixtures (R404A, R407C, R410A, R417A, and R507), four inorganic compounds (CO2, ammonia, water, and nitrogen), and two hydrocarbons (R290 and R600a). The parameter range of the database covers hydraulic diameters of 0.137–21 mm, mass fluxes of 20–1500 kg m−2 s−1, heat fluxes of 1.99–201 kW m−2, qualities of 0.001–0.999, and reduced pressures of 0.005–0.61. Fifty correlations of saturated flow boiling heat transfer coefficients are evaluated with the database, and the detail analysis of the evaluation results is performed. The work provides a guide to choosing a proper correlation for a given application and is helpful for understanding prediction methods of saturated flow boiling heat transfer coefficients.

Enhanced heat transfer in plate fin heat sink with dimples and protrusions

Abstract: The heat transfer and flow performance of the plate fin heat sink in a horizontal rectangular channel with dimples and protrusions on the fin surfaces has been experimentally investigated in forced convection. The Nusselt number and friction factor are obtained by varying the system parameters as depth and pitch of the dimples for inline and staggered arrangements. The Reynolds number is considered in the range of 6800 to 15,200. The effect of depth and pitch of dimples are examined under constant heat flux while keeping the constant diameter of dimples. Experimental results indicate that the heat transfer and flow performance of fin array are significantly influenced by increasing the depth of dimples. The heat transfer from fin array is enhanced and the flow resistance is increased by decreasing the pitch ratio (s/d) and increasing the depth ratio (D/d). The maximum fin performance of dimpled fin heat sink corresponds to the staggered arrangement of dimpled heat sink with dimple pitch ratio (s/d) of 2.5 and dimple depth ratio (D/d) of 0.5.

A reliable model to estimate the effective thermal conductivity of nanofluids

Abstract: The thermal conductivity is a key parameter to study the applicability of nanofluids for heat transfer enhancement of flowing liquids. This paper is an effort on implementing various methods to model the effective thermal conductivity of 26 nanofluids under different situations and evaluate the authenticity of the reported experimental data in the open literature. The most influential physical properties of nanofluids, such as the nanoparticle volume fraction, nanoparticle diameter, thermal conductivity of base fluid, temperature, and thermal conductivity of solid particle are considered as the input variables. With the purpose of introducing a comprehensive and pragmatic model with desired accuracy, a Multilayer Perceptron-Artificial Neural Network (MLP-ANN) approach is constructed and tested using data generated from 993 experiments. To appraise the creditability of the MLP-ANN model, a comparison with other 10 alternative techniques is carried out. The predictions made by the MLP-ANN yield excellent match with the experimentally generated samples against those of the other approaches. The coefficient of determination and relative root mean squared error are found to be 0.994 and 1.534%, respectively. Likewise, the results of the data analysis and the outlier detection method have proved that some of the data samples are significantly inconsistent with the remainder of the data set.

The effects of some exergetic indicators on the performance of thin layer drying process of long green pepper in a solar dryer

Abstract: In this study, exergy analysis of the thin layer drying process of long green pepper was performed in solar dryer with forced convection. The effects of some exergetic indicators on the performance of a thin layer solar drying system by using the experimental data in the literature for long green pepper (Akpinar and Bicer in Energy Convers Manag 49: 1367–1375, 2008) were investigated. For this purpose, the exergetic indicators such as exergetic efficiency, waste exergy ratio, environmental impact factor, exergetic sustainability index and improvement potential, previously used in the literature, were taken into account (Zisopoulos et al. in Crit Rev Food Sci Nutr 57(1):197–211, 2017, Midilli and Kucuk in Int J Exergy 16(3): 278–292, 2015, Van Gool 1997). The exergetic efficiency and improvement potential of the solar drying system decreased with the increase of drying time. The waste exergy ratio increased with the increase of drying time. The exergetic sustainability index increased with increasing the exergetic efficiency, decreased with decreasing the exergetic efficiency. The environmental impact factor decreased with increasing the exergetic efficiency.