Maximum Performance Evaluation Criterion Research Articles

Thermo-hydraulic performance evaluation of heat transfer tubes with different configuration forms

Fluid mixing induced by changes in tube direction is an effective method to enhance the heat transfer performance of heat transfer tubes. This study proposes three types of configuration forms for heat transfer tubes that improve their thermo-hydraulic performance, named cases 1, 2, and 3. Case 1 is distributed on the same plane and has the following configuration form: horizontal to vertical upward to horizontal to vertical downward to horizontal. Cases 2 and 3 transform the front and rear tubes into two parallel planes through the middle horizontal tube, with a 180° difference at the outlet direction. The thermo-hydraulic performance of heat transfer tubes with different configuration forms is evaluated by quantitative comparison of the Nusselt number (Nu), friction coefficient (f), and performance evaluation criterion (PEC), within a Reynolds number range of 5000–40 000. The distribution results of velocity, streamline, turbulent kinetic energy, skin friction coefficient, and so on are analyzed to reveal the underlying mechanisms of difference in the thermo-hydraulic performance of heat transfer tubes with different configurations. The results show that the thermo-hydraulic performance of heat transfer tubes with different configurations is better than that of a straight tube due to induced fluid mixing within the tube. In addition, case 1 rather than cases 2 and 3 has a more significant influence on the thermo-hydraulic performance of heat transfer tubes, especially at high Reynolds numbers, and the maximum PEC of case 1 exceeds cases 2 and 3 by 6% and 8.5%, respectively. Furthermore, the decrease in connection length of case 1 improves the heat transfer performance, which is more pronounced at high Reynolds numbers. These research findings serve as a valuable reference for designing heat transfer tube configurations to enhance heat transfer efficiency.

Numerical investigation of the thermal-hydraulic performance of a novel parabolic trough wavy tubular receiver by using FMWNCT/oil-nanofluid coupled with fins

This study employs a computational fluid dynamics (CFD) approach to assess the performance of a novel wavy profile tube receiver. It integrates rectangular fins and an Oil-based nanofluid, specifically utilizing Thermodyne GG-03 synthetic oil combined with Functionalized Multi-Wall Carbon Tubes (FMWNCT). The synthesis involves rigorous experimental procedures to characterize the thermophysical properties of the oil and nanofluid. Empirical correlations, validated against Bitam et al.'s model [1], guide the numerical analysis. The investigation, utilizing a steady-state κ - ω SST turbulence model with a non-uniform Gaussian thermal flux distribution, explores thermohydraulic performance in fully developed turbulent flow (Reynolds number range: 2 × 104 – 5 × 104). Comparative analysis with Bitam et al.'s work, employing Syltherm 800 oil as a reference, reveals a 25.76% average Nusselt number enhancement with Thermodyne GG-03. Additional improvements are observed: 124.69% with FMWNCT/oil-nanofluid, 137.04% with fins, and 236.54% with combined FMWNCT/oil-nanofluid and fins. These enhancements lead to increased heat transfer coefficients and rates. The friction coefficient rises by less than 60%, mainly attributed to the Nusselt number improvement. At RE = 20000, the Maximum Performance Evaluation Criteria (PEC) is 5.5, signifying significant improvement. Notably, a 300% PEC enhancement is observed compared to Roger and Mayhew's curved tube model [1]. In conclusion, these findings offer valuable insights for efficiently designing wavy tubular receivers in PTR collectors.

Thermal Performance Analysis of Porous Foam-Assisted Flat-Plate Solar Collectors with Nanofluids

This study proposed a model of a porous media-assisted flat-plate solar collector (FPSC) using nanofluid flow. The heightened thermal efficiency of FPSC undergoes numerical scrutiny, incorporating various factors for analysis, including aspects like the configuration of the porous block introduced, Darcy number (Da = 10−5~10−2), types of nanoparticles, volume fraction (φ), and mixing ratio (φc). The numerical findings indicate that the dominant factor in the channel is the global Nusselt number (Nug). As the Darcy number rises, there is an improvement in the heat transfer performance within the channel. Simultaneously, for the case of Re = 234, φ = 3%, and φc = 100%, the Nug in the channel reaches a maximum value of 6.80, and the thermal efficiency can be increased to 70.5% with the insertion of rectangular porous blocks of Da = 10−2. Finally, the performance evaluation criteria (PEC) are employed for a comprehensive assessment of the thermal performance of FPSC. This analysis considers both the improved heat transfer and the pressure drop in the collector channel. The FPSC registered a maximum PEC value of 1.8 when rectangular porous blocks were inserted under conditions of Da = 10−2 and Re = 234 and the nanofluid concentrations of φ = 3% and φc = 100%. The findings can be provided to technically support the future commercial applications of FPSC. The findings may serve as a technical foundation for FPSC in upcoming porous media and support commercial applications.

Investigations of thermohydraulic performance in heat exchanger tube with rectangular vortex generators

To demonstrate the rationalization of multi-longitudinal swirls (MLSs) in heat exchanger tubes, this paper investigates the thermohydraulic performance of heat exchanger tube with rectangular vortex generator using numerical simulation. Comparative analyses of rectangular vortex generators and their different slotted structures are conducted, along with the investigation of the effect of the longitudinal pitch (P = 0.1 m, 0.2 mand0.3 m) of the rectangular vortex generators on the thermohydraulic performance. The research reveals that the MLSs induced by the vortex generator inside the tube accelerate the exchange of cold and hot fluids, improve the field synergies of velocity vectors and temperature gradients, and enhance the heat transfer efficiency of the heat exchanger tube. The slotted structure reduces the flow resistance and lowers the degree of disturbance to the fluid, which reduces the strength of the MLSs, thus weakening the overall performance of the heat exchanger. The strength of the MLSs has a direct influence on the overall performance of the heat exchanger tube. With the increase of P, the performance evaluation criteria (PEC) of the heat exchanger tubes decreases, and the maximum PEC = 1.44 is obtained for P = 100 mm at the studied Reynolds number range.

Effect of triangular ribs on the flow and heat transfer characteristics of heat exchanger tube

To improve the heat exchange tube?s comprehensive performance and achieve enhanced heat transfer with lower flow resistance. The flow and heat transfer characteristics of a newly enhanced tube with triangular ribs were studied by numerical simulation. The results show that the multi-vortex longitudinal swirl developed in the triangular rib enhanced tube can enhance the cold and hot fluid mixing, and make the temperature distribution in the tube more uniform. The field synergy of velocity and temperature gradient was improved and the heat transfer capacity was enhanced. In the triangular rib enhanced tube, reducing the dimensionless pitch ratio of triangular ribs (P* = 0.5, 0.75, 1, and 1.25) and appropriately increasing the area of triangular ribs (A = 8, 12, 16, and 20 mm2) can improve the performance evaluation criteria (PEC). When Re = 8475, P* = 0.5, and A = 20 mm2, the maximum PEC = 1.324 is obtained.

Computational investigation of cross flow heat exchanger: A study for performance enhancement using spherical dimples on fin surface

Performance improvement of a heat exchanger is a vast topic for research work right now. This paper presents a numerical analysis of cross flow heat exchanger using CFD software package ANSYS FLUENT. To improve the performance of a traditional smooth fined heat exchanger, dimples are used on the fin surfaces. A cross flow heat exchanger with spherical dimples on the surfaces of the fins was modelled and effect of dimples on the performance of the heat exchanger was numerically investigated. Numerical investigations were carried out for different dimple depths such as 3 mm, 4 mm, 5 mm, 5.5 mm dimples on different positions such as on one side, on both side; and different number of dimples such as 32, 26, 20. Boundary conditions were considered as constant tube outer surface temperature, Reynolds number of 3553, inlet air temperature Ti = 299.45 K. Considering balance between heat transfer enhancement and pressure drop, performance evaluation criterion (PEC) was estimated to observe the optimal result. PEC value greater than 1 means there is better performance in consideration of both heat transfer rate and frictional loss. The case of 26 dimples on both sides of fin with 5.5 mm dimple depth provides highest 7.33 % increases of Nusselt number compared to smooth fin. The maximum PEC value 1.034 was found for the case of 32 dimples on both side of fin with 3 mm dimple depth. From the PEC analysis, it was observed that the case of 32 dimples on both sides of the fin with 3 mm dimple depth is the optimum case among all other cases with 5.71 % higher Nu and 6.75 % higher friction factor than smooth fin. To compare the heat exchanger performance, temperature effectiveness has also been evaluated. The case of 32 dimples and 26 dimples on both side of fin with 5.5 mm dimple depth have same and highest value of temperature effectiveness which is 11.45 %, where that value for smooth fin is 10.16 %. Furthermore, the results have been analyzed with the variation of Reynolds numbers.

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.

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.

Experimental and numerical investigations on the effects of insertion-type longitudinal vortex generators on flow and heat transfer characteristics in square minichannels

Longitudinal vortex generator (LVG) is an effective device for enhancing heat transfer in micro/mini-channel thermal systems. In this study, a new insertion-type LVG (ITLVG) is designed and the effects of length and arrangement of ITLVG on flow and heat transfer characteristics in square minichannel are explored using experimental and numerical methods under Reynolds number of 414–1042. Results show that the vortex flow is generated in both sides of ITLVG and behind ITLVG, thereby intensifying flow disturbance and reducing the thermal boundary layer. The friction factors and Nusselt numbers in the minichannels with ITLVGs increase by 85.5%–246.1% and 39.2%–102.0% on average, respectively, compared to smooth minichannel. The ITLVG arrangement has a significant effect on the flow and heat transfer, while the ITLVG length has a slight effect. The ITLVG with the length of 20 mm and arranged simultaneously in upstream, midstream and downstream shows the highest performance evaluation criterion (PEC) values at most of Reynolds numbers, as well as maximum PEC value reaches 1.50 at the Reynolds number of 1042. Moreover, the correlations for Nusselt number and friction factor are developed. Overall, the new ITLVG performs beneficial effect for comprehensive performance improvement in minichannel to increase energy conversion efficiency.

A Novel Ladder-Shaped Bridge Finned Tube for Convective Heat Transfer Enhancement

Abstract In order to improve the convective heat transfer efficiency of a shell-and-tube heat exchanger, a novel ladder-shaped bridge finned tube (LBFT) is presented. The LBFT possesses outer low helical integral fins, two layers of staggered transverse bridge, upper passage, middle passage, and bottom passage. The convective heat transfer performance of the LBFT is studied and experimental results show that the Nusselt numbers outside the tube and the overall heat transfer coefficients of the LBFT are significantly greater than those of the smooth tube. The bridges, bridge roots, and pores formed on the outer fins contribute to the larger heat transfer coefficient. Both the Nusselt number and the overall heat transfer coefficient decrease, while the friction resistance coefficient increases with outer helical fin pitch increasing and bridge width increasing. As the Reynolds number increases, the comprehensive performance evaluation criterion (PEC) decreases at first and then increases. The maximum PEC occurs at the Re number of 2300 and is up to 1.34.

A two-phase simulation for analyzing the hydraulic-thermal performance of Cu–Water nanofluid within a tube enhanced with W- and C-shaped ribs

The present study numerically investigated the simulation of two-phase nanofluid (NF) flow to examine the thermal performance of Cu–water NF within an enhanced tube with W- and C-shaped ribs in the heat exchangers (HEX). In this research, the effect of volume fraction (φ = 0.2, 0.4, 0.6, and 0.8%), and diameter (15, 20, 25 and 30 nm) of copper nanoparticles and the type and size of the turbulators (TRB) (W- and C-shaped ribs together), which were designed for the first time on Heat transfer (HT), were discussed. Heat transfer flow (HTF) entered the test section at Tin = 290 K in various velocities related to different Reynolds numbers (Re) 5000, 10000, 15000 and 20000. Based on the Eulerian-Eulerian two-phase method, the governing equations were solved. Different rib geometrical parameters were determined, and the optimization was performed to achieve the maximum performance evaluation criteria (PEC). According to obtained results, the PECs were more than 1, which indicated that these TRB were impressive from a hydraulic-thermal performance. Furthermore, the PEC variations of C- and W-shaped models were not similar. For the C-shaped configuration, the PEC values always enhanced with Re enhancement, while for the W-shaped model, the PEC values enhanced till Re = 10000, and then decreased till Re = 20000. The PEC values of the optimum model (W-shaped, NB = 6 and R = 15 mm) filled by NF at φ = 0.8% and dnp = 30 nm in Re = 5000, 10000, 15000 and 20000 are 1.491, 1.498, 1.482 and 1.469, respectively.

Shape memory alloys enabled smart heat exchangers

Modern heat exchangers encounter the paradox between the high performance and low flow resistance while most of the tasks feature in wide operating conditions where great functional flexibility is required. In this paper, we propose to tackle the dilemma by integrating shape memory alloys into the design of heat exchangers, utilizing a two-way shape memory alloy (SMA) strip as the self-adjusting vortex generator (VG) for heat transfer enhancement. The SMA based vortex generators are trained with predetermined deformation according to the temperature of the working media. To be specific, at low temperature, the SMA strip is flat to reduce the flow resistance. While the temperature is high, the SMA strip is curved to form a rectangular wing vortex generator to enhance the heat transfer. This concept was firstly verified via the experimental study followed by detailed numerical investigation focusing on the mechanism explorations. The deformation characteristic was verified by water bath. With the increase of the temperature of fluid, the heat transfer is increased by 110 ∼ 125 %. On the other hand, the Darcy friction factor can be reduced by 74 ∼ 90 %, when the heat transfer demand decreases based on the concept proposed. The details of flow and heat transfer are given and analyzed by using numerical simulation. And the numerical results are in good agreement with the experimental ones with the relative error of 11 % ∼ 3 % (on heat transfer, Re=8004400) and the warping height ΔZ=4/5 hydraulic diameter (Dh)). The ratio of heat transfer and flow resistance are positively related to the warping height (ΔZ) of VG. Under six calculated Reynolds numbers (Re), the maximum heat transfer enhancement coefficient can be reached at Re = 400 and 800, respectively, with the values ranging from 1.18 ∼ 2.68 for different ΔZ. In the case that ΔZ equals to 4 / 5 hydraulic diameter (Dh), the best performance can be achieved with Re≤1600. If Re≤800, the design can always maintain better performance than the original flat channel, and the maximum performance evaluation criteria (PEC) achieved is 1.32. Based on our research, the smart heat exchanger is expected to satisfy the heat transfer requirements of specific variable working conditions in the future.

Thermo-convective behavior and entropy generation studies on Alumina and Titania nanofluids flowing through polygonal ducts

The current study emphasizes the thermal performance of 0.05, 0.1, and 0.2% volume concentrated Al2O3/DI water and TiO2/DI water nanofluids flowing through three different ducts (equilateral triangle, square, and hexagonal shaped) were compared with circular tubes. The thermo-convective experiments were carried out in the turbulent regime (5000≤ Re ≤ 10,000) at iso-heat flux conditions. The experimental outcome reveals that the maximum Nusselt number of 78, 74, and 71 were achieved when 0.2% Al2O3/DI water flowed through hexagonal, square, and triangular ducts, respectively. Similarly, the desired lowest friction factor of 0.03692, 0.03688, and 0.03686 was achieved by the same nanofluid through those orientations, which ensured that the Al2O3/DI water outperformed TiO2/DI water. The maximum Performance Evaluation Criteria (PEC) was 1.102 when comparing the 0.2% Al2O3/DI water nanofluid flow through a hexagonal duct with water through a circular tube, and 1.169 when the flow through the duct is compared with DI water flow through the same hexagonal duct. When evaluating the performance of all these augmented flow orientations by Entropy Performance Evaluation Factor (EPEF), the maximum values of 665, 572, 635, and 654 were achieved by 0.2% Al2O3/DI water and 660, 531, 561, and 628 by 0.2% TiO2/DI water while flowing through the circular tube, triangular, square, and hexagonal ducts, respectively. Correlations for Nusselt number and friction factor employable to these orientations were derived based on the dominant dependant parameters.

Intensification of thermal efficiency of a cross-flow heat exchanger under turbulent flow conditions using CuFe2O4/water nanofluid

The use of nanofluids has opened new intellectual horizons in improving the performance of heat exchangers. Therefore, in this work an experimental study was conducted for investigating the effect of CuFe2O4/water nanofluid on the heat transfer rate enhancement in a cross-flow type heat exchanger under turbulent flow conditions. Heat transfer rate were examined at different volume percentages of CuFe2O4 nanoparticle (0≤ φ ≤ 0.9% vol.) with a nominal diameter of 28 nm at three inlet fluid temperatures of 72, 80 and 88 °C, water pump rotational speeds of 2000 rpm and 3000 rpm, and cross-flow fan speeds of 1500, 2000 and 2500 rpm. According to the results, the heat transfer rate in the case of using nanofluids with a volume percentage of 0.1% was significantly higher than that of distilled water in all test conditions. The highest relative increase in the universal heat transfer coefficient (U) equal to 92.3%, compared to the use of water (φ = 0) was obtained at 0.1% vol% of nanoparticles, the lowest temperature of fluid entering the heat exchanger (72 °C), medium pump speed (2000 rpm) and low fan speed (1500 rpm). The maximum Performance Evaluation Criterion (PEC) improvement of 44.46% also occurred at this working condition.

Experimental and numerical study on the heat transfer and flow characteristics of convex plate heat exchanger based on multi-objective optimization

The convex plate heat exchanger is one of the new types of plate heat exchangers that have specific functional properties compared to conventional plate heat exchangers, the structural parameters of convex plate heat exchangers are important in affecting the heat transfer performance. In this paper, based on two-layer multi-objective optimization which is aimed at maximum performance evaluation criterion (PEC) and maximum field synergy number (Fc), the heat transfer and flow characteristics of convex plate heat exchanger are investigated experimentally and numerically. The optimization findings are broken down into single factor, response surface, and sensitivity analysis. The optimal results under different objective functions are analyzed and the optimal structural parameters obtained which are the welding hole radius (R) is 5.81 mm, the ellipse radius (L) is 5.02 mm, and the welding hole spacing (P) is 64.00 mm; Compared to the structure before optimization, the size-optimized structure may enhance the temperature differential between the inlet and outflow of the cooling water by less than 8.27%, the heat transfer performance is increased by 20.43%, and the comprehensive performance is improved by 2.3∼19.59%.

Numerical investigation into heat transfer augmentation in a square minichannel heat sink using butterfly inserts

Heat transfer augmentation in a square minichannel heat sink through introduction of various butterfly insert configurations is numerically investigated for a range of Reynolds numbers (200 – 900). The present study also examines the individual effects of insert, pitch of the insert, and perforations in the wings of the butterfly insert on the thermohydraulic performance of minichannel heat sinks. Incorporating any kind of insert in a typical square minichannel is found to have a positive influence on the overall thermohydraulic performance, yielding performance evaluation criteria consistently over unity for the whole range of tested Reynolds numbers. The effect of pitch is tested for unperforated inserts, wherein a reduction of pitch distance from 10 mm to 5 mm is found to increase heat transfer performance by 15.08 - 46.39% for the studied range of Reynolds numbers. Perforations in the wings of butterfly inserts are found to result in a reduction of friction factor, with a 4.01 – 20.78% decrease, when compared with an unperforated insert having an identical pitch. However, this reduction is achieved at the cost of a lower heat transfer performance (5.07 – 16.17%). Therefore, unperforated butterfly inserts are deemed to be superior in terms of the overall thermohydraulic enhancement. In all enhanced minichannel configurations, a redistribution of velocity and temperature fields due to the formation of a primary vortex pair and thinning of thermal boundary layers due to a second pair of secondary vortices are thought to be the major contributors behind the observed thermohydraulic enhancement. • Introduction of a butterfly insert with 10 mm pitch is found to enhance heat transfer performance in MCHS by 42.02% to 109.31% for the tested range of Reynolds numbers. • A reduction in pitch from 10 mm to 5 mm in an MCHS with unperforated butterfly inserts is observed to yield an augmentation of average Nusselt number by 15.08% to 46.39% for the studied range of Reynolds numbers. • Perforation on insert wings is found produce a reduced enhancement in average Nusselt number, i.e., 5.07%–16.17%, for the investigated range of Reynolds numbers. • Observed thinning and disruption of thermal boundary layers and enhanced fluid mixing at the central region of the minichannel due to a pair of primary vortices are thought to be the major reasons for enhanced thermal performance. • A maximum performance evaluation criterion of 1.66 is observed for the case of unperforated butterfly inserts with 5 mm pitch at a Reynolds number of 900.

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.

Numerical investigation on the Thermal-hydraulic performance of the modified channel supercritical CO2 printed circuit heat exchanger

Printed circuit heat exchangers (PCHE) are designed to improve heat recovery and energy saving in supercritical CO2 (S-CO2) power cycles. In the current study, a modified channel PCHE is proposed based on the regular straight channel and a zigzag channel. The thermal–hydraulic performance of four different types of PCHE is numerically investigated and the methods are verified by both experimental and numerical results. The numerical results are presented for a Reynolds number based on the inlet conditions between 5 000 and 25 000. From the numerical results, the local pressure loss and local heat transfer coefficients are analyzed and discussed. Subsequently, the global Nusselt number and Fanning friction coefficients are discussed. It is found that the inserted straight section contributes to uniform flow, resulted in significant pressure loss reduction with a slight decrease in heat transfer. The modified channel can reduce the Fanning friction coefficient by 33.1%-84.7% while the global Nusselt number reduction is about 3.6%-30.3%. This leads to a maximum performance evaluation criterion (PEC) enhancement of 45.9%.

CFD analysis and environmental assessment on the heat transfer and flow of the pure water or water/silver Nano fluid coolants in a plate-fin heat sink applying two-phase mixture model

Environmental impacts are the consequences caused by the elementary flows on human health, plants, and animals (ecological health) or by the future availability of natural resources (resource depletion). The heat transfer characteristics of a plate-fin heatsink were investigated using a 3-dimensional numerical analysis based on the two-phase mixture model. The effect of using NF, fin spacing, and fin height on the performance of the system were studied considering the constant heat flux of 100 kW/m2 at the bottom of heatsink and NF inlet temperature of 300 K. The results showed that the increase in the secondary fin height (hsf) from 5 mm to 17.5 mm leads to increase in the pressure drop by 11.6%, 52%, to improve the heat convection coefficient (h) by 32.92%-23.84%, and consequently reduces the central processing unit (CPU) mean temperature by 4.31% and 2.34% for Re=500-2000. The maximum performance evaluation criterion (PEC) was obtained as 1.11-1.05 at Re numbers of 500-2000 for heatsink with hsf=12.5 mm. In addition, the optimum location for the secondary fin was determined to be at the mid-space of two primary fins (dsf=0.5 mm) which leads to improving h by 18%-5% at Re numbers of 500-2000 as compared to other fin spacing scenarios. Moreover, the intensification of nanoparticle concentration (ψ) leads to improve h by 15.71%-17.21% for Re=500-2000. Besides, the escalation of ψ decreases the pressure drop by 14.18% for all Re numbers. The PEC of the system with hsf=12.5 mm, ψ=1%, at Re=2000 was obtained as the highest PEC of 1.226 among the other studied cases. According to the design, the heat sink has an environmental impact of 0.5233.