Performance Evaluation Criteria Research Articles

Partial response continuous phase modulation with a prolate spheroidal wave function for compass system in the S-band

Continuous phase modulation (CPM) has the characteristics of high power efficiency, spectral efficiency, and less out-of-band radiation, which is very suitable for the Compass S-band (2483.5–2500 MHz) with limited power and bandwidth. However, as more and more navigation systems share the S-band, the mutual interference between different systems is gradually increasing, and the compatibility of CPM signals with rectangular or raised cosine pulses needs to be further improved. To enhance the navigation performance and compatibility of current CPM candidate signals, we propose to apply continuous phase modulation with prolate spheroidal wave function (CPM-PSWF) to S-band navigation. The proposed modulation scheme selects PSWF with excellent time-frequency energy aggregation and flexible time-bandwidth product as the frequency pulse function of CPM. Then, the influence of key modulation parameters such as M, L, h, and C on CPM-PSWF power spectral density is analyzed, and a specific partial-response CPM-PSWF signal is proposed as the S-band candidate navigation signal. Finally, the navigation performance evaluation criteria are derived, and the proposed signal scheme and existing candidate schemes are comprehensively evaluated. Theoretical analysis and simulation results indicate that compared with CPM with BM2RC(8), cos-phase binary offset carrier (BOCc(4,4)), sin-phase binary offset carrier (BOCs(4,4)), minimum shift keying-BOCs (MSK-BOCs(4,4)) and binary offset carrier (BPSK(8)), the proposed signal scheme not only delivers exceptional spectral performance but also exhibits superior performance in code tracking accuracy and multipath suppression. In addition, in the acquisition and tracking phase, compared with other candidate signals except for BOCc(4,4), the mutual interference between the proposed signal scheme and most S-band signals is the lowest, which is easier to realize the compatibility of the Compass system with IRNSS, Galileo, and Globalstar systems.

A comparative investigation on heat transfer performance of novel nanoaerosols in pipe flow: Experimental results

This paper describes the experimental analysis of aerosol heat transfer coefficient (AHTC), pressure drop, and friction factor of SiO2, TiO2, and MgO nanoaerosol in the pipe flow with the volumetric flow rate of 30 lpm, 40 lpm, and 50 lpm. The SiO2, TiO2, and MgO nanoparticles are characterized by using the field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) analysis. The SiO2, TiO2, and MgO nanoparticles are dispersed in the air at the particle volume concentrations of 0.5 %, 1.0 %, and 5.0 %, respectively. The thermo-physical characteristics of nanoaerosols are determined using empirical correlations. The variation in temperature, pressure, and flow rates are measured by using the thermocouples, pressure gauges, and flow meters installed in the experimental setup. The temperature readings are recorded by using the data acquisition system. The experimental results indicate the enhancement of forced convective AHTC with the increase in the nanoparticle volume concentration and the volumetric flow rate of the nanoaerosol. At volumetric flow rates of 30 lpm, 40 lpm, and 50 lpm, respectively, increasing the particle volume fraction from 0.5 % to 5.0 % improves the average heat transfer coefficient by 92 %, 84 %, and 91 % for SiO2 nanoaerosol, 72 %, 50 %, and 37 % for TiO2 nanoaerosol, and 50 %, 67 %, and 72 % for MgO nanoaerosol. The pressure drop of the nanoaerosol increases by 2, 2.33, and 3 times, respectively, and the friction factor decreases by 27.99, 15.99, and 11.1 times for SiO2, TiO2, and MgO nanoaerosol by increasing the flow rate from 30 lpm to 50 lpm. For the SiO2, TiO2, and MgO nanoaerosols, increasing the particle volume concentration from 0.5 % to 5.0 % increases the pressure drop by 6, 7.66, and 10 times, respectively, and the friction factor by 32.03, 19.08, and 5.67 times. By considering all of these factors, it is concluded that the performance evaluation criteria are lowest for 0.5 % TiO2 and highest for 5.0 % MgO. The significant finding of this research is that the AHTC increases with the increase in the particle volume concentration and volumetric flow rate. Whereas, the friction factor decreases with the increase in the volumetric flow rates.

Performance enhancement of fin and tube heat exchanger employing curved delta winglet vortex generator with circular punched holes

The generation of vortices has recently gained attention as a potential passive technique for improving air-side heat transfer in a fin and tube heat exchanger. This study proposes novel configurations of a curved delta winglet vortex generator (CDWVG) with and without circular holes to improve heat transfer in FTHEs. The present study utilizes a three-dimensional numerical analysis to investigate the thermal-hydraulic performance analysis of fin and tube heat exchanger (FTHE) with curved delta winglet vortex generators (CDWVG) with or without circular holes, operating across a wide Reynolds number range (i.e., from 400 to 2000). In addition to being arranged in vertical and horizontal configurations, the CDWVGs are oriented in the same way as the flow direction. Therefore, the pressure distribution, temperature distribution, and flow structure distribution of an FTHE with a four-in-line circular tube configuration are analyzed and compared between FTHE without vortex generator (VG) and five different configurations of CDWVG (i.e., CDWVG without hole, CDWVG with 1 hole, CDWVG with 2 holes, CDWVG with 3 holes and CDWVG with 6 holes). The pressure drop (ΔP), London area goodness factor (LAGF) (j/f), Nusselt number (Nu), and Colburn factor (j) are also used to evaluate the thermo-hydraulic performance of FTHE. The FHTE performance with CDWVGs can be affected by the number of punched holes, which is evaluated using a dimensionless number including Performance Evaluation Criteria (PEC), Colburn factor, etc. The thermo-hydraulic efficiency of the FTHE is improved significantly by using CDWVGs with circular punched holes. Nusselt number decreases across all the VG configurations (i.e., CDWVG without hole, CDWVG with 1 hole, CDWVG with 2 holes, CDWVG with 3 holes, and CDWVG with 6 holes) due to the lower flow resistance. Compared to other CDWVG configurations, the 6-hole configuration of CDWVG is the most effective. The Nusselt number of CDWVG with 6 holes increases by 77.25% and 42.51% at Reynolds numbers of 400 and 2000, with respect to fin and tube heat exchangers without vortex generator, respectively. On the other hand, friction is decreased by 5.11%. Therefore, when considering the London area goodness factor, CDWVG with six holes is found to be superior to other CDWVG configurations.

Numerical investigation of thermo-hydraulic performance in an annular heat exchanger with sinusoidal vortex generators

This study investigates thermal performance enhancement by utilizing vortex generators (VGs). VGs come in many designs, and this paper proposes optimizations for the sinusoidal vortex generator (SVG) when used in an annular conduit to improve heat transfer with minimal pressure drop. Two vital parameters of the SVG are analyzed, namely, blockage ratios (BRs) (0.1 and 0.2) and attack angles (α) (0–90°). The investigated fluid regime is turbulent, with the Reynolds number (Re) ranging from 5973 to 11,947. Three rows of SVGs are fitted on the surface of the inner pipe, where constant heat flux is applied, while the outer pipe wall is entirely insulated. The results indicate that the highest Nusselt number is enhanced by 20.4% over the smooth pipe when the case with BR = 0.2 and α = 90° is used at Re = 5973. However, the friction factor increases by 56.5% for the same case. Two types of transverse vortices are identified, where one type has its rotational axis normal to the inner pipe surface, and the other has its rotational axis parallel to the inner pipe surface. Those vortices with the axis perpendicular to the pipe surface merge with the fluid above the SVG to develop longitudinal vortices in different BRs and α. The case with BR = 0.2 and α = 15° yields the greatest average performance evaluation criterion (PEC) compared to other tested cases with a value of 1.054. This study finds that SVGs can contribute to a more efficient annular pipe-based heat transfer system.

Numerical investigation of turbulent flow and heat transfer characteristics in the improved Kenics static mixer

AbstractThis study focuses on using computational fluid dynamics to explore how well a modified static mixing component called the Kenics static mixer (KSM) increases heat transfer. The purpose of the study is to assess this new static mixer's pressure drop and heat transfer properties. Convective heat transport of water within the improved Kenics static mixer (IKSM) was examined using three‐dimensional turbulent, steady, and incompressible flow simulations. The Nusselt number and friction factor simulation results in the KSM are in good agreement with previous literature findings. Between the simulated outcomes of the IKSM, empty pipe, and standard KSM, a comparison analysis was done. The study considered a range of Reynolds number (Re) values from 2000 to 20,000 and investigated the effects of the Re, slit width configuration (), as well as an aspect ratio () on heat transfer and mixing. Based on the performance evaluation criteria and field synergy number characteristics, the hydrothermal efficiency of the IKSM was evaluated, allowing the geometry to be modified for better heat transmission while lowering the friction factor. Notably, in the 2000–20,000 Reynolds number range, the IKSM with four slits showed a 38%–52% greater heat transfer coefficient than the traditional KSM.

Numerical Assessment of Nanofluids in Corrugated Minichannels: Flow Phenomenon and Advanced Thermo-hydrodynamic Analysis

The current study addresses the influence of the amplitude of distinct corrugation patterns on heat transfer and the performance of nanofluids as a coolant. A novel combined approach has been presented here to optimize the heat transfer, incorporating both geometry modification and coolant optimization. The computational model evolved for single-phase, and turbulent flow conditions in three-dimensional corrugated minichannels (i.e. rectangular, sine-shaped, and V-shaped) with Reynolds number varying from 10,000 to 30,000. Considering a uniform heat flux of 10,000 W/m2, the investigation evaluates the thermal-hydraulic performance of single nanofluids (CuO/water, Al2O3/water, TiO2/water) and hybrid nanofluids (Al2O3CuO/water, Al2O3-TiO2/water), with volume fractions ranging from 1% to 3%. Various nanoparticle compositions exhibited a 25–30% increased heat transfer coefficient in the corrugated minichannel relative to the smooth one. An enhanced Nusselt number is evident due to the sophisticated corrugated arrangement dependent on the amplitude and patterns of the corrugations. The obtained energy ratio quantifies the effectiveness of a heat exchanger, whereas the Bejan number signifies the heat transfer being characterized by higher irreversibility, leading to a notable dissipation of energy. To account for the PEC (performance evaluation criterion) value above one, the corrugated geometries can outperform smooth channels. With an optimal thermal performance improvement of 22.19%, the 3% Al2O3CuO/water has been found to be the most effective nanofluid in the rectangular corrugated minichannel with the amplitude-to-wavelength ratio of 0.12.

Impact of fin and hybrid nanofluid on hydraulic-thermal performance and entropy generation in a solar collector using a two-phase approach

This research investigates the impact of cylindrical fins and a hybrid nanofluid (HNF) composed of water and copper-zinc oxide on the hydraulic-thermal performance and entropy generation of a solar collector (SC). Numerical simulations are conducted for steady flow utilizing the pressure-based solver. The HNF flow is modeled using the two-phase mixture approach, while the turbulent flow is represented using the standard k-ε turbulence model. The study explores varying inlet Reynolds numbers (Re) from 17,000 to 41,000, volume fractions of nanoparticles (φ) ranging between 1 and 3%, and cylindrical fin heights (λ) of 5, 10, and 15 mm. The results indicate that employing twisted tape in the SC leads to improved thermo-hydraulic performance compared to a SC without twisted tape. Also, the addition of cylindrical fins plays an important role in the flow field because the HNF flow separates after colliding with the fins. This causes the formation of swirling vortices and spatial and temporal fluctuations. The amount of the performance evaluation criterion (PEC) is similar in all cases and decreases with Re. The PEC is much higher than the desired one. Although this trend is decreasing, the results show that in this range of Re, the use of cylindrical fins creates a more reasonable pressure drop (Δp) compared to the enhancement in thermal performance. Finally, the thermal and total entropy generation are reduced and frictional entropy is enhanced by increasing Re. In other words, the increment in the height of the cylindrical fins in the solar system leads to a reduction in the entropy generation.

Single- and double-inlet PV curtain wall systems using novel heat recovery technique for PV cooling, fresh and supply air handling: Design and performance assessment

Building integrated photovoltaic (BIPV) technology has emerged as a promising solution for serving electricity and heat demands in buildings. However, PV overheating causes reduced production, increased space cooling load, and stagnation damage. To address overheating and save energy in air conditioning, this study proposed novel single- and dual-inlet ventilation PV curtain wall systems (SVPV and DVPV). In summer, the building exhaust is introduced into the channel to strengthen PV cooling, while incoming fresh air is used to preheat dew-point air. In winter, warm exhaust within the channel decreases heat loss through the facade and then raises the fresh air intake temperature. Mathematical models were developed for the systems, and a comprehensive performance evaluation criterion (PEC) was defined. Economic analysis was conducted using simple payback (SP) and net present value (NPV) models. Additionally, the impact of ambient temperature and solar radiation on system performance was investigated. The case study demonstrates that SVPV and DVPV reduced annual energy consumption by 957.23 kWh (28.07%) and 910.97 kWh (26.72%), respectively, compared to a conventional non-ventilated system. SVPV slightly outperformed DVPV, with an average PEC of 0.556 and 0.544, respectively. This study provides valuable insights for operational strategies and future large-scale promotion of BIPV applications.

Study on Thermal–Hydraulic Characteristics of Novel Channels for Printed Circuit Heat Exchanger Using Supercritical CO2

Abstract Two new types of printed circuit heat exchanger (PCHE) channels are proposed based on the typical airfoil fin PCHE channel proposed in literatures (standard channel) to further improve the thermal–hydraulic performances of airfoil fin PCHE channel. The small shuttle fins and oval fins are employed between the adjacent two airfoil fins of two novel channels, respectively. Using supercritical CO2 as the working fluid, the thermal–hydraulic performances and enhancement mechanisms of the novel channels are numerically investigated. The results show that the channel with shuttle fins has the best comprehensive performance. The Nusselt number of the channel with shuttle fins is 6.7–26% larger, and the f-factor is 8.3–18.6% larger than that of the standard channel under the selected conditions, which leads to a 3–19.1% increase in the PEC (comprehensive performance evaluation criteria). The Nusselt number of the channel with oval fins is 9–27.3% larger, and the f-factor is 26.6–43.4% larger than that of the standard channel, which leads to a 1–15.3% increase in the PEC. The applications of small fins between the adjacent two fins can effectively reduce the low-velocity region area and enhance the local disturbance, thereby effectively improving the thermal–hydraulic performance. The enhancement mechanism of the novel fin PCHE channel structure can be well explained by the principle of field synergy. It can be found that the synergies of the temperature gradient field and the velocity field in two novel channels are significantly improved.

Numerical Study on Thermo-Hydraulic Performance of Enhanced Tube With Crossed Helical Dimples

Abstract A numerical investigation was performed to study the thermo-hydraulic performance in an enhanced tube with crossed helical dimples. The simulations were carried out in the Reynolds number range of 5000–30,000 in crossed helical dimple tube of a period length with a constant wall temperature of 350 K. The thermal enhancement, friction factor, and performance evaluation criteria (PEC) were the primary focus of the present work. Moreover, geometric parameters such as spiral pitch, transverse length, and dimple depth were investigated for their effects on thermo-hydraulic performance. The results revealed that the shape of crossed helical dimple exerts positive effects on the heat transfer enhancement. This unique shape generated intensive transverse flow and induced a higher transverse velocity, leading to heat transfer enhancement. Therefore, the synthesized heat transfer performance was increased by 150–225% over that of the smooth tube. Furthermore, the heat transfer enhancement and friction factors increased with increasing dimple depth and declining spiral pitch and transverse length. Within the scope of this study, the maximum PEC = 2.25 was observed for Re = 30,000, P = 30 mm, L = 11.064 mm, and H = 3 mm.

Nanofluid turbulent flow in parabolic trough collector: Insulator roof, acentric absorber tube and SiC nanoparticles effects

The key purpose of the current study is to design a parabolic trough collector (PTC) having insulator roof and an acentric absorber tube, with nanofluid using single-phase and two-phase mixture models (TPM and SPM). The effects of employing the SPM and TPM on the fluid field and heat transfer of nanofluid (SiC nanoparticles (16–90 nm) and volume fraction (0–4%) to the water and EG-water) in the absorber tube is studied. Results of present investigation shown that for both proposed (novel) and conventional PTC arrangements, the pressure drop (3%), Nusselt number (5%), friction factor (3%), energy efficiency (3%), and performance evaluation criteria (PEC) (3%) employing the TPM are greater than that of SPM. In addition, it is shown that employing the novel PTC presents greater Nusselt number (25%), energy efficiency (30%), and PEC (50%). Temperature field inside the absorber tube and heat transfer fluid zone employing the TPM are greater than that of SPM. Maximum PEC for SiC/EG-water and EG-water nanofluid are 1.67 and 1.70, respectively, for sinusoidal-wavy minichannel having a nanoparticle volume fraction of 4%, nanoparticles diameter of 90 nm, and Reynolds number of 15,001.3. Furthermore, EG-water as base fluid with a nanoparticle diameter of 90 nm presents greater energy efficiency than water.

Numerical assessment of hydraulic behavior and thermal efficiency of multiphase hybrid nanofluid in a shell-and-tube heat exchanger with inclined baffles

Improving the thermo-hydraulic performance of shell-and-tube heat exchangers (STHE) has always been the focus of researchers due to their wide applications in recent decades. This numerical study investigates the hydraulic behavior and thermal efficiency of turbulent multiphase flow of Fe3O4−MWCNT/water hybrid nanofluid (HN) in a shell-and-tube heat exchangers (STHE). The Reynolds number (Re) is 5000, 7500, 10000, and 12500 and the volume fraction of nanoparticles (φ) is 0, 2, and 4%. Numerical simulations are conducted using the k-ε turbulence model, two-phase mixture model, finite volume method (FVM), and PISO algorithm. The maximum value of the friction coefficient (FC) is 1.45, which corresponds to a baffle angle of 180º, φ = 4%, and Re = 5000. As the baffle angle is enhanced, the value of the average Nusselt number (Nuave) is intensified for all cases. The maximum value of the performance evaluation criteria (PEC) is about 1.55, which is related to a baffle angle of 180º and Re = 7500. For all the examined situations, the value of PEC is greater than one, indicating the effectiveness of the application of nanofluid and baffles at different angles. Hence, it is recommended to utilize baffles. The maximum value of thermal efficiency is about 37%, which occurs when the baffle angle is180º, φ = 4%, and Re = 5000.

S-CO2 flow in vertical tubes of large-diameter: Experimental evaluation and numerical exploration for heat transfer deterioration and prevention

Heat transfer deterioration (HTD) problems can undermine the thermal safety of heating tubes for supercritical carbon dioxide (S-CO2) flows. Relevant experimental evidence is highly desired, but most cases were investigated for small tube diameters (below 10 mm) and under limited operation parameters, far from the industry-scale applications. In the present work, large tubes (24 mm) are investigated experimentally with pressures of 7.5–15 MPa, mass flow rates of 100–1200 kg·m−2·s−1 and heat fluxes of 30–350 kW·m−2. The seriousness of HTD in large tubes was experimentally confirmed, and the mechanism is explored via a carefully-designed comprehensive comparison between present numerical simulations and experimental tests. Detailed analysis of vapor-like film development inspires us to mitigate the problem using structured-inner-surface, from the viewpoint of “supercritical pseudo-boiling”. This inspiration is further evaluated numerically: five types of enhancement structures are proposed to interfere with the development of vapor-like film. It was found that the proposed methods can fully prevent HTD problems, and especially the conical strips can achieve a high heat transfer performance (with performance evaluation criteria PEC of 1.21–1.35) and are thus recommended for HTD prevention in vertical large-diameter tubes under near-critical conditions. Overall, the experimental tests and numerical explorations can deliver more evidence on the theory and applications of supercritical fluid flow and heat transfer.

Simulation of two-phase hybrid nanofluid flow in a flat plate solar collector equipped with spiral absorber tube under the influence of magnetic field: Hydraulic-thermal, energy, and exergy analysis

In this research, a flat plate solar collector (FPSC) equipped with a spiral absorber tube is numerically simulated. The aim of using the spiral tube in the FPSC is to enhance the amount of hybrid nanofluid (HN) mixing and turbulence and to improve the thermal efficiency of the FPSC. First, the FPSC geometry was prepared in SolidWorks software, and then the Design Modeler and Meshing module of Ansys software was used to evaluate the computational domain and meshing. MgO-MWCNT/Therminol VP-1 two-phase HN is simulated using a mixture model and the RNG k-ε turbulence model has been used to model the turbulent flow. The range of Reynolds number (Re) is from 9000 to 24,000 and the volume fraction (φ) of MgO and DWCNT nanoparticles changes from zero to 3% when the pitch ratio (α) of the absorber tube is 0.75, 1.50, and 2.25. Finally, the absorber tube of the FPSC is placed under a magnetic field with the Hartmann number (Ha) of 20 to 140. Based on the obtained results, an increment in the Re and φ leads to an increase in the thermal performance and pressure drop (Δp) of the FPSC. When φ = 3% and Re = 24000, the use of a spiral absorber tube with α = 2.25, the average Nusselt number (Nuave) and Δp are enhanced by 121.11% and 309.52% compared to the solar collector (SC) with a simple absorber tube. The energy efficiency is always improved with Re and φ. Also, the maximum energy efficiency corresponds to α = 2.25 for all amounts of Re and φ. The exergy efficiency has increased, increased and decreased with the increase of Re, φ, and α, respectively. In the f FPSC equipped with a spiral absorber tube with α = 0.75, the exergy efficiency is improved by 36.14% when Re increases from 9000 to 24,000 and φ = 3%. The performance evaluation criteria (PEC) index of the FPSC is more than 1 for all cases when the magnetic field is applied. Also, the maximum exergy efficiency occurs when the magnetic field is applied, Re = 14000, and Ha = 150.

Thermalhydraulic assessment and design optimization of incorporating flow obstructors in a supercritical minichannel heat sink

Modulation of the thermalhydraulic characteristics of the miniaturized heat sink by geometric alteration is a less explored topic, particularly in conjunction with the supercritical fluids, which can experience both enhancement and deterioration in performance based on the conditions. The present study appraises the response of a square minichannel by incorporating rectangular obstructions, with the primary aim of identifying an optimized orientation and design. A performance evaluation criterion, defined as a combined change in both heat transfer coefficient and pressure drop because of geometric modification, is selected as the primary variable. Installation of the baffles substantially augments the turbulent mixing among the fluid layers, realizing a lower wall-to-fluid temperature differential and enhanced heat transfer coefficient. A relatively lower level of temperature is maintained within the baffled section, thereby delaying the appearance of heat transfer deterioration. Obstructions, however, considerably increases the pressure losses, necessitating careful selection of the dimensions. The use of three pairs of baffles has been identified to be the most feasible option. Desirable values of the height, thickness, and inclination angle for individual plates in this orientation have also been identified, along with a detailed thermalhydraulic assessment about the role of the operating variables with the optimum design.

Thermohydraulic performance of ammonia, isopropanol, water and nanofluids as cooling fluid for lithium-ion 1C and 3C rating batteries

Cooling Lithium-ion batteries of different C ratings receive excellent attention amongst researchers in thermal management. The present study proposes to investigate the thermohydraulic performance of a wavy channel and compare the finding with the conventional straight channel. The full Navier Stokes equations and the energy equation were solved numerically using the finite element technique. Water is the cooling liquid used in the simulation. The flow is laminar and steady state. It is found that the average Nusselt number is higher as the waviness of the channel wall increases. The average Nusselt number for the wavy channel case was increased by up to 31% compared to the straight channel configuration. Also, the performance evaluation criterion increases by 23% compared to straight channel configuration. Thus, allowing the fluid to absorb more heat. However, at the expense of the pressure drop, the performance evaluation criterion is higher for the wavy wall channel mode than the straight channel wall. Amongst all fluids studied in this paper, including water, ammonia, isopropanol, Ammonia binary mixture and TiO2 nanofluid at different concentrations, ammonia is the most suitable liquid for cooling.

Structure Optimization and Cooling Performance of a Heat Sink With Discontinuous Triangular Ribs Impacted by Hybrid Nanofluid Confined Slot Jet Impingement

Abstract Due to the increased use of high heat flux electronic equipment, improving the heat transfer capacity and surface temperature uniformity of heat sinks have become a major concern. In this study, a novel confined slot jet impingement heat sink with discontinuous triangular ribs (CSJIHS-TR) in the wall impingement zone is proposed. The upper cover plate is angled to improve the ability of the heat sink to dissipate heat. A Cu-Al2O3/water hybrid nanofluid is chosen as coolant. The main structural parameters of CSJIHS-TR are optimized using multi-objective. The optimized CSJIHS-TR is investigated using the Re and φ of the hybrid nanofluid. The results show that the optimized CSJIHS-TR exhibits an improved heat transfer capacity. The optimized CSJIHS-TR achieves a 27.8% improvement in performance evaluation criterion (PEC) and a 91.0% reduction in temperature standard deviation (Tstd) compared to the confined slot jet impingement flat-plate heat sink (CSJIFPHS). As Re of the jet impingement and φ of the hybrid nanofluid increase, the heat transfer capacity and temperature uniformity of the optimized CSJIHS-TR increase; however, the flow resistance of CSJIHS-TR also increases. In addition, compared with the mononanofluid, the temperature uniformity and the heat transfer capacity of the CSJIHS-TR with hybrid nanofluid are significantly improved.

Swirling jet impingements for thermal management of high concentrator solar cells using nanofluids

Large intensity of irradiance in high concentrator solar cells leads to extremely high temperatures causing an adverse effect on the performance of solar cells. Efficient cooling systems are crucial for the optimal performance of high concentrator cells, which are typically required to operate within a prescribed temperature range (⁓ 110 °C). The implementation of effective cooling strategies poses a significant challenge for High Concentrator Photovoltaic Thermal (HCPV/T) hybrid systems to ensure sustained performance and longevity of the modules. This study proposes a novel method for the thermal management of High Concentrator Solar Cells (HCSC) using swirling nanofluid jets impinging on a heat sink. The study applies RANS (Reynolds-Averaged Navier-Stokes) method with the SST k-ω turbulence model and energy equation to resolve a conjugate heat transfer analysis for three different flow ratios: Qr = 0, Qr = 0.5 and Qr = 1 and two water-based nanofluids: Al2O3-Water and CuO-Water. The numerical results demonstrate a significant decrease in cell temperatures, reaching as low as 71 °C. At a mass flow rate of 50 g/min, the use of Al2O3-Water nanofluid increases the overall electrical efficiency by a maximum of 39.43%. In contrast, a minimum electrical efficiency of 39% for CuO-Water nanofluid is obtained for a lower mass flow rate (25 g/min). Al2O3-Water nanofluid yielded a maximum PEC (Performance Evaluation Criteria) of 116%, while CuO-Water nanofluid yielded about 113%. In addition, an increase of the mass flow rate results in an improvement of temperature uniformity, as demonstrated by a reduction of temperature variation from 6.8 to 5.2. These results suggest that the use of nanofluids is promising. The proposed swirling jet impinging on a heat sink in combination with nanofluid provides an effective cooling technique for HCSC, thereby potentially contributing to the improvement of the cell's performance and longevity.

Effect of Stress Ratio K due to Varying Overburden Topography on Crack Intensity of Tunnel Liner

A structural health assessment of the tunnel lining is carried out to investigate and mitigate the cause of defects in the tunnel lining to ensure user safety. Many factors affect the tunnel’s integrity, causing a wide range of defects. Identifying the possible cause and its relation with the degree of associated defect is essential for tunnel stability. In conjunction with defects of tunnel failure, liner cracks were found to be most critical because they could trigger other defects to form and jeopardize tunnel stability. Thus, this research acquires visual inspection followed by comprehensive mapping and quantification of liner cracks to enhance our understanding of the effect of varying overburden on the intensity of liner cracks. The numerical analysis was further performed to analyze the influence of varying topography (overburden) on the crack intensity of the liner using the stress ratio, K as a parameter in terms of the state of stress using induced stress (IS) and stress concentration factor (SCF) as a performance evaluation criterion. The work demonstrates that the shift in magnitude and position of liner cracks on the different portions of the tunnel liner implies the effect of a regionally external factor (varying overburden depth) on tunnel degradation. For advances in tunnel assessment based on the regional diversity of cracks along the longitudinal profile of the tunnel, the tunnel should be divided into zones based on the overburden to identify the varying intensity of the liner crack. This study shows the variable crack density of 575 m to 628 m, 650 m to 700 m, and 704 m to 724 m for shallow, intermediate, and deep zone, respectively. The findings of this study can provide scientific guidance to tunnel inspectors and engineers regarding the tunnel liner health assessment and identifying the subsequent method of repair.

Numerical simulation of dual-tube heat exchanger equipped with an innovative turbulator containing two-phase hybrid nanofluid: Hydrodynamic and exergy analysis

Due to the energy requirements of industries and the limitations of energy resources in the world, energy storage and prevention of energy loss are of particular importance. Therefore, energy loss and energy storage are among the most important new concerns of human beings. Heat exchangers (HE) are one of the most widely used heat transfer (HT) equipment that transfer heat from one fluid to another. For the simulation of water/silicon oxide-iron oxide hybrid nanofluid (HN), the mixed two-phase model has been used. The flow is turbulent and the turbulence model is RNG k-ε. The inlet Reynolds number (Re) and the volume fraction (φ) of SiO2 and Fe3O4 nanoparticles changes from 30,000 to 45,000 and 2% to 5%, respectively. Four different geometries of the novel turbulator with different values of pitch ratio (λ=0.15, 0.35, 0.55, 0.75) are modeled inside the HE and its effects on the average Nusselt number (Nuave), pressure drop (Δp), performance evaluation criterion (PEC), and exergy efficiency are examined. The results demonstrate that the use of water in the HE system leads to lower thermal performance compared to water/silicon oxide-iron oxide HN for all cases. Also, as λ and φ are enhanced, the values ​​of Nuave, Δp, and PEC are increased. In a dual-tube heat exchanger (DTHE) equipped with an innovative turbulator with maximum amounts of λ, using a HN with φ = 5% results in an enhancement in Nuave by 105.59% when Re changes from 30,000 to 45,000. Also, according to the values of the PEC, although the use of the turbulator leads to an increment in Δp, the enhancement of the thermal performance is higher. According to the exergy analysis, increasing the inlet velocity of the inner tube of the double-tube heat exchanger enhances the exergy efficiency. For all geometries, the maximum exergy efficiency corresponds to Re = 45,000.