Pressure Drop ΔP Research Articles

A numerical investigation of microtube length effect on convective boiling

Abstract The microtube length significantly influences the convective boiling process and associated heat transfer characteristics. Other than high heat transfer, low pressure drop is also desired to improve the energy efficiency of the pumping system. This work numerically investigates the microtube length effect on heat transfer and pressure drops of convective boiling with the volume of fluid (VOF) method. The simulation results of vapor formation, heat transfer coefficient, and pressure drop are shown with different microtube lengths L = 2–20 mm. The onset of boiling is around 2 mm away from the mass flux inlet. The subcooled boiling regime can be observed between 2 and 10 mm. Three distinct regimes, liquid single-phase flow, bubbly flow, and plug flow, are shown in the longer microtubes (L = 15 mm and 20 mm). It is found that shorter microtubes can lead to less bubble formation with higher heat transfer and lower pressure drop. The average heat transfer coefficient can achieve 2432 W/(m2K) with a lower quasi-steady total pressure drop Δp|total of 32.8 Pa inside a 2-mm-long microtube. This work offers a detailed study of the impact of microtube length on convective boiling, along with pertinent physical insights. It may serve as an indicator for future microscale heat transfer application designs.

Determination of the Optimum Operating Conditions and Geometrical Dimensions of the Plate Fin Heat Sinks Using Teaching-Learning-Based-Optimization Algorithm

Abstract Electronic devices must be effectively cooled for long-term reliability and safe operation. It is essential to determine operating conditions and optimum dimensions of cooling devices in terms of device weight, space, cost, and sound limits. Plate fin heat sinks (PFHSs) are frequently used for cooling electronic devices. Optimum thermal designs of PFHSs are explored in this study using a teaching-learning-based-optimization (TLBO) algorithm where entropy generation (S˙gen) minimization, profit factor (J) maximization, base plate temperature excess (θb) minimization, total mass (mass) minimization, and total volume (volume) minimization are the objective functions of the constrained single-objective optimization problems. For further investigations of the entropy generation minimization method, three different optimization problems are also studied: minimization of thermal resistance (Rth), minimization of pressure drop (ΔP), and minimization of pumping power (W˙pump). Each optimization problem is subjected to a constraint, namely, temperature excess of base plate temperature (θb) should be lower than 10 K. Four optimization variables are considered which are the number of plate fins (N), freestream velocity (Vf), the thickness of the fin (tfin), and height of the fin (Hfin). Optimum configurations belonging to the different optimization problems are compared, and the effect of each optimization variable on the objective functions is discussed in detail. It is found that one can obtain optimum operating conditions and geometrical dimensions of the PFHSs according to the design objective, i.e., minimum mass requirement, space limitation, minimum base plate requirement, etc. As a result, the optimum designs of the studied cases are different which are superior to each other in terms of design targets.

Effect of surfactants on the convective heat transfer and pressure drop characteristics of ZnO/DIW nanofluids: An experimental study

The advancement of nanotechnology has demonstrated the ability of metal-oxide-based nanofluids (NFs) to produce high heat flux in microscale thermal applications. Convective heat transfer (HTC) and flow characteristics (pressure drop (ΔP) and friction factor (f)) of aqueous ZnO NFs' within a circular mini tube (Di = 1.0 mm, L = 330 mm) were analyzed. Experiments were carried out under steady-state and varying flow rates using 0.012–0.048 wt % of NFs and sodium hexametaphosphate (SHMP) and acetylacetone (ACAC) as surfactants (SFs). Laminar flow and constant wall heat flux conditions were used to assess NFs heat transfer properties, ΔP and f. The viscosity (VC) and thermal conductivity (TC) of NFs exhibited a strong dependence on the operating temperature and NFs concentration. VC and TC increased by increasing the NFs concentration and decreased by increasing the operating temperature. Maximum VC and TC enhancement of 16.75% and 23.70% were achieved for SHMP-stabilised NFs, respectively. The average HTC increased by increasing NFs loading and flow rate, with HTCmax of 17.0% noticed for ACAC-stabilised NFs. The ΔPmax and fmax were 16.0% and 12.0%, respectively. Experimental and theoretical results showed a maximum deviation of ±7.0% and ±4.0%, respectively.

Investigation of the effect of magnetic field on the PEC and exergy of heat exchanger filled with two-phase hybrid nanofluid, equipped with an edged twisted tape

In this study, the effect of using hybrid nanofluid and helical twisted tape (HTT) on the exergy efficiency and thermo-hydraulic performance of a heat exchanger is investigated numerically using the finite volume method (FVM). Also, Solidworks is used to sketch the geometry. The study is carried out by assuming the steady state flow using the pressure-based solver. Simulations of Cu-ZnO/water hybrid nanofluids are based on the mixture model. The Reynolds number (Re) changes from 10,000 to 40,000, volume fraction (φ) vary from 1 to 5%, and pitch ratio (PR) is of 1, 2, 3, and 4. The results demonstrate that the average Nusselt number (Nuav) and thermal performance of the heat exchanger are enhanced with Re and φ. At φ = 5% and Re = 40,000, placing a HTT with a PR of 4 causes the pressure drop (ΔP) to enhance by 180.97% In comparison with a collector without a solar panel a turbulator. In addition, in the heat exchanger with a HTT with a PR of 4 and φ = 5%, the exergy efficiency is increased by 38.89% as Re is enhanced from 10,000 to 40,000. The use of a magnetic field causes the PEC in the heat exchanger to become greater than 1 in all cases. Also, the maximum exergy efficiency occurs when a magnetic field is applied at Re = 20,000 and a Hartmann number (Ha) of 150.

Comparison of the Haemodynamic Performance of Various Treatment Options for Aorto-Iliac Occlusive Disease

Several surgical and endovascular techniques are used during the treatment of aorto-iliac occlusive disease. Aortobifemoral bypass (AoBFB) is the standard of care, but other options such as axillobifemoral (AxBFB) bypass, aorto-iliac kissing stents (KS), and covered endovascular reconstruction of aortic bifurcation (CERAB) are also available. This study aimed to perform a computational comparison of these four modalities to investigate their haemodynamic performance. Eight patient specific anatomies were analysed, with each of the abovementioned techniques used to treat two anatomies. The CT angiograms were segmented from the renal (or axillary) to common femoral arteries and the 3D geometries were exported. A commercial finite volume solver was implemented for numerical simulations. Outcomes that were assessed were pressure drop (ΔP) between the inlet and the outlet for every configuration and haemodynamic indices of Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), and Relative Residence Time (RRT) as markers of a thrombogenic environment. The results indicate that maximum ΔP was observed at peak systole for all models, with values ranging between 12mmHg and 21mmHg for the AoBFB, 64mmHg and 96mmHg for the AxBFB, 31mmHg and 46mmHg for the KS, and 43mmHg and 46mmHg for the CERAB configuration. TAWSS, OSI, and RRT varied among different configurations, mostly presenting values well above thrombogenic thresholds. Regarding RRT, the percentage of total surface area presenting such values is 2.5%, 3.2%, 2%, and 4.3% for the AoBFB, AxBFB, KS, and CERAB configurations, respectively. Computational modelling indicates a favourable haemodynamic performance of AoBFB compared with the other configurations. This leads to a smaller pressure drop and sconsequently a higher pressure in the outlet of the conduit, which is the perfusion pressure of the limb. Notably, lower patency rates of the latter modalities cannot be explained based on haemodynamic indices.

An Optimization Study on the Operating Parameters of Liquid Cold Plate for Battery Thermal Management of Electric Vehicles

The development of electric vehicles plays an important role in the field of energy conservation and emission reduction. It is necessary to improve the thermal performance of battery modules in electric vehicles and reduce the power consumption of the battery thermal management system (BTMS). In this study, the heat transfer and flow resistance performance of liquid cold plates with serpentine channels were numerically investigated and optimized. Flow rate (m˙), inlet temperature (Tin), and average heat generation (Q) were selected as key operating parameters, while average temperature (Tave), maximum temperature difference (ΔTmax), and pressure drop (ΔP) were chosen as objective functions. The Response Surface Methodology (RSM) with a face-centered central composite design (CCD) was used to construct regression models. Combined with the multi-objective non-dominated sorting genetic algorithm (NSGA-II), the Pareto-optimal solution was obtained to optimize the operation parameters. The results show that the maximum temperature differences of the cold plate can be controlled within 0.29~3.90 °C, 1.11~15.66 °C, 2.17~31.39 °C, and 3.43~50.92 °C for the discharging rates at 1.0 C, 2.0 C, 3.0 C, and 4.0 C, respectively. The average temperature and maximum temperature difference can be simultaneously optimized by maintaining the pressure drop below 1000 Pa. It is expected that the proposed methods and results can provide theoretical guidance for developing an operational strategy for the BTMS.

Development and validation of thermal performances in a novel thermoelectric generator model for automotive waste heat recovery systems

Integrated thermoelectric generators (TEGs) and heat exchangers (HEX) can transform heat into electrical power by converting temperature gradients between heat sources and cold sinks. Predicting TEG thermal performances with compact HEX is crucial to designing efficient TEGs for automotive waste heat recovery. However, previous investigations mainly concentrated on TEG electrical performance, neglecting the thermal performances under high Reynolds numbers (Re) of exhaust gasses. This study utilizes the model-based development (MBD) method to develop a novel 1D TEG model, focusing heat transfer coefficient α and pressure drop ΔP inside a louvered corrugated fin HEX, component temperatures, and boundary heat flux, which affect electrical power from thermoelectric modules (TEM). The performance data are measured from 36 tests under different fin pitches Fp = 1.0 - 2.0 mm, Re = 4,000–14,000, and inlet gas conditions. Two methods are used to develop the model using user-defined functions (UDFs) for friction coefficient Cf and α, accounting for actual fin geometries. In Method 1, UDF multipliers for each Fp are required to calibrate the TEG model. In Method 2, simplified UDFs for Cf and α are implemented. Method 1 shows that the model is well-calibrated with maximum average relative errors δa< 6.7% but requires model fitting for each Fp. The fast-predictive TEG model with the novel calibration Method 2 can reproduce the thermal and electrical performances with δa< 20% without model tuning, which can be used for TEG redesign and integrated into vehicle-level MBD with a conventional and electrified powertrain, leveraging a fast driving-cycle simulation.

Numerical feasibility study of using ultrasonic surface vibration as a new technique for thermal management of the electronic devices

The suitable thermal management of electrical devices leads to their reliable operation and durability. The present study investigates the application of ultrasonic surface vibration in a pin–fin heatsink to improve hydrothermal performance. To this end, a totally 31 scenarios were examined by altering the location of the vibrating transducers at four lateral walls and the top plate of the heatsink. The numerical calculations were performed within Reynolds number (Re) ranges of 500–2000 and frequency magnitude (F) of 15–30 kHz. Our results showed that the heatsink with three transducers at the top plate and two lateral adjacent walls (near and the opposite side of the inlet), namely case#27, exhibits the highest heat transfer coefficient and performance evaluation criteria (PEC) of 1.38 over the base case without transducers (WOT) at Re = 2000 and F = 30 among the studied cases. In addition, case#27 has its highest heat transfer coefficient and pressure drop (ΔP) at Re = 2000, while its maximum PEC is obtained as 1.78 at Re = 1000 for F = 30 kHz over the base case without vibration. Moreover, the maximum heat transfer coefficient and the lowest ΔP for case#27 at Re = 2000 were obtained at = 25 kHz. In such a case, the PEC was obtained as 1.06 over the base case.

Performance Comparison of Mini-Rectangular Fin Heat Sinks Using Different Coolants: Supercritical CO2, Water and Al2O3/H2O Nanofluid

Mini-channel heatsinks have proven useful in removing high heat fluxes from microelectronic devices. However, further miniaturization of electronic devices requires significant enhancement in the mini-channel heatsinks’ thermohydraulic characteristics, which depend greatly on the coolant and geometrical configuration of the channel. Therefore, the current study explores the potential of mini-channel heatsinks’ using different coolants (water, nanofluid and supercritical carbon dioxide) and various channel configurations. The effect of various channel configurations on the thermohydraulic characteristics of the mini-channel heat sinks is evaluated numerically for different coolants employing three flow rates (17 g/s, 34 g/s and 50 g/s). Hence, the effects of fin height, spacing and thickness, and mass flow rate on the overall heat transfer coefficient (CHT) and pressure drop (ΔP) are reported for the abovementioned coolants. It is found that increasing the mass flow rate increases both the CHT and ΔP. It is also noted that increasing the fin height and spacing decreases both the CHT and ΔP, as opposed to increasing the thickness, which causes both the CHT and ΔP to increase. Among the three coolants used, the sCO2 shows superior performance compared to the water and nanofluid and this based on higher CHT and lower ΔP. Moreover, the performance evaluation criterion (PEC) for the sCO2 is higher than that for the water and nanofluid by 53% at 17 g/s flow rate and 243% at 50 g/s flow rate.

Response Surface Methodology and Artificial Neural Network modellings on hydraulic and thermal performances of a disk-shaped heat sink with tree-like microchannels

To cope with the increasing heat generation resulting from increased power in micro-scale devices, an optimum design of a tree-like microchannel heat sink is suggested utilizing Artificial Neural Networks (ANN) and Response Surface Methodology (RSM). Based on the numerical finite volume model, both ANN and RSM models were trained, and their performances were assessed using four distinct performance criteria. The results showed that both of the models are reliable for the purpose of this study, showing a significantly high adjusted R2 for both performance control variables pressure drop (ΔP) and Nusselt number (Nu). The adjusted R2 values observed for the RSM were 0.987 and 0.997, respectively, for the Nu and ΔP. These values were calculated as high as 0.997 for Nu prediction and 0.997 for ΔP prediction using the ANN. Finally, utilizing the calibrated RSM and ANN models, three optimum design configurations for three different purposes given the priority requirements of the heat sink implementations were suggested. The minimum ΔP configuration is suitable for the longevity of the heat sink, and the maximum Nu configuration is suitable for applications where heat transfer performance is more critical. For a balanced optimum design, the efficiency index was maximized.

A comparative numerical analysis and environment assessment to examine hydrothermal behavior of two serpentine heatsink with water/silver Nano fluid applying two-phase mixture model

In the present study, the hydrothermal characteristics of two different a) serpentine (Conf. A), and b) double serpentine (Conf. B) heatsinks with water/silver Nano Fluid (NF) were studied. To this end, the Finite volume method was performed, and the governing equations were discretized based on the second upwind approach and solved numerically applying the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) scheme. The results demonstrated that the thermal resistance (R) of Conf. A is lower than that of Conf. B at low Re numbers, and these two configurations have an identical R as Re increases to 2000. Also, the convective heat transfer in Conf. A is slightly higher than that in Conf. B and for Re=2000 both configurations have a same h value. Moreover, the increasing of nanoparticle concentration from 0% to 1% increases h by 12.55% and decreases the pressure drop (ΔP) by 4.25%. In addition, the CPU mean temperature of Conf. A is 0.8% and 0.1% lower than that of Conf. B for Res of 500 and 2000, respectively. On the other hand, ΔP in Conf. A is 74% higher than that in Conf. B. Besides, Conf. B exhibits a better temperature uniformity as compared to other configuration. The parameter of figure of merit was obtained as 1.47 to 1.52 at Res of 500 and 2000, respectively, which showed that Conf. B provides a higher hydrothermal performance over the other configuration.The environmental impact of the designed heat sink is equal to 0.5388.

Mass transfer characteristics of ferrofluids flowing through a microchannel under AC magnetic field

The gas absorption process in a Y-shaped microchannel utilizing magnetic nanofluids stimulated within an alternating current magnetic field (AC mf) was studied. Absorption of CO2 under different operation conditions, ferrofluid concentration, and magnetic field strengths were investigated to analyze the liquid-side overall mass transfer coefficient (KLa), CO2 absorption efficiency (E), nanoparticle enhancement factor (α), magnetic field enhancement factor (γ), and pressure drop (Δp). The magnetic field strengths were 7, 12.6, and 21 mT accompanied by various ferrofluid concentrations within 0.001–0.004 (v/v). The ferrofluids were water-based colloids of Fe3O4 magnetic nanoparticles. The gas-liquid flow patterns were Taylor flow regime in all experiments. Furthermore, the position of the microchannel in the magnetic field was studied as an effective factor in CO2 absorption enhancement. The position in which the microchannel was held on the top inside the magnetic field reflected more gas absorption compared to the other positions. While exerting magnetic field strength of 21 mT, a maximum enhancement of 72.2% was observed for KLa compared to the case in which the magnetic field was absent.

Nanocellulose-regulated robust particle-gel for conformance improvement in fractured tight reservoirs: A mechanistic investigation of transport behavior and EOR performance in fracture models

Owing to the interpenetration of high-modulus nanocellulose into polyacrylamide (HPAM), the mechanical properties of particle gel were substantially improved. Five transport patterns in fractures were demonstrated as defined by particle/aperture ratio. The pressure drop (ΔP) generated by nanocellulose-regulated particle gel (NPG) depended on particle/fracture ratio, followed by NPG content and strength. A numerical model was established to correlate the stable ΔP of NPG with four critical operating parameters. The placement of NPG significantly remedied the conformance of the fractured cores; therefore, the subsequent CO2 and ultralow IFT surfactant injection processes produced additional oil recoveries of 4.7% and 7.1% original oil in place (OOIP), respectively, with the ultimate oil recoveries of 10.8% and 12.2% OOIP. However, the matrix oil was hardly mobilized during brine injection even after conformance treatment due to the adverse wettability and high capillary pressure.

Optimization of block structure parameters of PEMFC novel block channels using artificial neural network

Flow channel design is critically important to the performance of proton exchange membrane fuel cell (PEMFC) due to its great influence on liquid water removal and mass and heat transfer. Block flow channel shows good prospect to improve liquid water removal and mass transport, benefiting the PEMFC performance. In this study, the block structures, namely the length, width and height of the block, are optimized for a novel block channel using data-driven surrogate model based on the artificial neural network (ANN). The training/test datasets are obtained from a three-dimensional multi-phase model based on the volume of fluid (VOF) method, with the water removal time (T) and the maximum channel pressure drop (ΔP) taken as the output and optimization objectives. The results show that the ANN prediction agrees well with the physical model results, with the coefficient of determination (R2) of T and ΔP are 0.99598 and 0.99677, respectively. The block parameters are further optimized using the comprehensive scoring method considering both T and ΔP. The block parameters with the length of 0.8 mm, width of 0.375 mm and height of 0.75 mm are found to be the optimum in terms of the highest score. The optimum parameters obtained from the data-driven surrogate model are verified by the physical model, indicating that the ANN model is an effective and fast method to optimize block structure of block flow channel from the perspective of liquid water removal and channel pressure drop.

Multi‐objective optimization of drainage‐plates in wave‐plate mist eliminators using experiment and data‐driven modelling for lower water loss and energy requirement

AbstractWave‐plate mist eliminators are widely employed as gas–liquid separation devices to prevent the liquid escaping from thermal power plants or other cooling towers. In this study, the wave‐plate mist eliminator with drainage plates was numerically analyzed and the effects between geometrical variables on two objectives, namely, pressure drop (ΔP) and separation efficiency (η), were revealed. Plate spacing, width, and length, as well as the relative position of the drainage plate, were thoroughly investigated. A combined strategy was developed for multi‐objective optimization of the wave‐plate mist eliminator by integrating computational fluid dynamics (CFD) simulation, response surface methodology (RSM), non‐dominated sorting genetic algorithm‐II (NSGA‐II), and a technique for order of preference by similarity to ideal solution (TOPSIS) method. The results demonstrated that the relative position of drainage plates has a greater impact on the overall performance, whereas the width of drainage plates has the minimum effect. With the implementation of NSGA‐II and the TOPSIS method, an optimal solution for the design of the mist eliminator was obtained. After comparing with the baseline case, the optimized case presents promising characteristics with high separation efficiency (enhanced by 3.6%~9.06%) and a low energy consumption coefficient (reduced by 72.30% at η = 45%).

Numerical Simulation of a Flat-Sheet Membrane-based Dehumidifier with Various Serpentine Flow Channels

In the present analysis, three potential serpentine flow channel designs for a flat-sheet membrane-based dehumidifier are designed and evaluated in terms of performance metrics such as dehumidification rate (DR), approach temperature (AT), pressure drop (ΔP), and coefficient of performance (COP). The dry side inlet air temperature and relative humidity (RH) are set at 27°C and 0%, and the wet side inlet air temperature and RH are fixed at 40°C and 85%. The inlet air flow rates of the dry and wet sides are both controlled in the range of 20-60 L min−1. The simulation results revealed that the geometrical design of the flow channels has a remarkable impact on the dehumidification performance of the dehumidifier. It is outlined that the water vapor concentration and temperature distribution at the outlet of all proposed serpentine flow channels are almost identical, showing the oversized design of the three- and six-inlet serpentine channels. Under the air flow rates of 30 ∼ 60 L min−1, it is seen that the DR, AT, and ΔP of three-, six-, and nine-inlet serpentine channels are in descending order. It is found that the size and quantity of the channel outlets and inlets have a great influence on the pressure drop. Moreover, the dehumidifier with nine-inlet serpentine flow channel can provide the highest COP with a limited increase in the pressure loss. Hence, this channel design can be a good candidate to be implemented in the flat-sheet membrane-based dehumidifier. The findings of this study could be beneficial for the design of novel dehumidifiers.

Influence of Self-Compaction on the Airflow Resistance of Aerated Wheat Bulks (Triticum aestivum L., cv. ‘Pionier’)

Aeration is a key post-harvest grain processing operation that forces air through the pore volume of the grain bulk to establish favorable conditions to maintain grain quality and improve its storability. However, during storage, grain bulk experiences self-compaction due to its dead weight, which alters the bulk properties and impedes the uniform flow of air during aeration. Thus, this study focused on investigating the effect of self-compaction on the pressure drop ΔP of wheat bulk (Triticum aestivum L., cv. ‘Pionier’, X = 0.123 kg·kg−1 d.b.) accommodated in a laboratory-scale bin (Vb = 0.62 m3) at a coherent set of airflow velocities va. Pressure drop ΔP was measured at bulk depths Hb of 1.0, 2.0, 3.0 and 3.4 m and storage times t of 1, 65, 164 and 236 h. For the semi-empirical characterization of the relationship between ΔP and va, the model of Matthies and Petersen was used, which was proficient in describing the experimental data with decent accuracy (R2 = 0.990, RMSE = 68.67 Pa, MAPE = 12.50%). A tailored product factor k was employed for the specific grain bulk conditions. Results revealed a reduction of in-situ pore volume ε from 0.413 to 0.391 at bulk depths Hb of 1.0 to 3.4 m after 1 h storage time t and from 0.391 to 0.370 after 236 h storage time t, respectively. A disproportional increase of the pressure drop ΔP with bulk depth Hb and storage time t was observed, which was ascribed to the irreversible spatio-temporal behavior of self-compaction. The variation of pore volume ε was modeled and facilitated the development of a generalized model for predicting the relationship between ΔP and va. The relative importance of modeling parameters was evaluated by a sensitivity analysis. In conclusion, self-compaction has proven to have a significant effect on airflow resistance, therefore it should be considered in the analysis and modeling of cooling, aeration and low-temperature drying of in-store grain bulks.

Machine learning-based optimization of air-cooled heat sinks

Machine learning-based models using Artificial Neural Network (ANN) and greedy search algorithm are used to optimize air-cooled parallel plate-finned heat sinks (PPFHSs) subjected to laminar flow over an extensive range of design parameters. The thermal and hydraulic performances of PPFHSs are represented by heat transfer coefficient h and pressure dropΔP, respectively. Optimization objectives for PPFHS designs can vary from industry to industry depending on their design priorities. The present study proposes a novel and generalized optimization method that defines practical optimization objectives and provides an accurate optimization process to design effective PPFHSs for a wide range of industrial applications with different design requirements. Three optimization objectives are presented in this study: (i) the largesth/ΔP, (ii) the largest h within a specified maximum allowed flow rate, and (iii) the lowest weight that maximizes h for operation within the maximum allowed flow rate. While the shortcoming of the first objective is demonstrated, the other two objectives are found to be suitable for designing effective heat sinks (HSs) across different applications. Results suggest a promising trend from the third objective to develop HSs with ∼ 37–68% lower weight, 80–85% reducedΔP, and negligible penalty in h compared with optimized HSs obtained from the second objective. However, since the third objective leads to HSs with thinner fins, structural analysis should be performed to ensure reliable operation of the HSs.

Heat transfer efficiency optimization of a multi-nozzle micro-channel heat sink utilizing response surface methodology

Optimum heat transfer in modern micro-channel heat sinks (MCHSs) plays a considerable role in ameliorating the efficiency and power of these devices. The response surface methodology (RSM) is one of the recently developed techniques to study and optimize the thermal and hydraulic behaviors of the MCHSs. In the current investigation, a multi-nozzle MCHS with circular fins on both sidewalls of the micro-channels was elected to analyze. The RSM method predicted the Nusselt number ( Nu ) of the MCHS and pressure drop (ΔP) of the coolant (the responses of the model). The diameter, the longitudinal pitch, and the transverse pitch of the circular fins were considered as the independent variables. These variables were changed in the ranges of 0.02–0.06 mm (diameter), 0.1–0.4 mm (longitudinal pitch), and 0.1–0.2 mm (transverse pitch). The impact of changing the mentioned variables on Nu and ΔP of the coolant to achieve the higher cooling capacity was studied. At first, Nu and ΔP values were calculated by the numerical procedure and then predicted by the RSM. Comparing the values derived by the numerical and the RSM models, it was observed that the values predicted by the RSM were close to the ones calculated by the numerical simulation. The RSM model with the coefficient of determination of 97.51% and 98.74% for Nu and ΔP could predict these responses accurately.

Experimental, statistical, and numerical investigations for influence of using vegetable oil with mineral oil to enhance the flow characteristics through a closed hydraulic circuit

The aim of this paper is to investigate the performance of a hydraulic system using an equi-volume percentage of vegetable oil and mineral oil as hydraulic fluids. The hydraulic system performance was tested at different operating conditions, such as temperature and velocity. A test rig with a definite pipe length and diameter was used. The experimental results showed that the presence of vegetable oil reduced the viscosity by 21, 18, 11, and 8% at 30, 40, 50, and 60 °C, respectively. The pressure drop (ΔP) through the hydraulic circuit was improved. The reason may be attributed to a reduction in viscosity. At 6 L/min and 60 °C, the maximum percentage of drag reduction (%Dr) was around 29%, while the maximum percentage of flow improvement (%FI) was around 21%. Statistical analysis was used to correlate %Dr as a function of dimensionless groups with a high correlation coefficient. Numerical analysis was conducted using ANSYS software. Experimental and numerical results were very close with high validity. A numerical model was used to study the effect of pipe geometry. Pressure drop was increased with pipe length and inclination angle, but it decreased with pipe diameter. In the literature, the experimental and numerical performance of hydraulic systems using a blend of vegetable and mineral oils as hydraulic fluid was limited. Therefore, the current study is quite new for the hydraulic system performance at different operating conditions.