Enhancement Of Heat Transfer Coefficient Research Articles

Effectiveness study in shell and tube heat exchanger at various concentrations of CuO nanofluid for parallel flow

Nanoparticles enhances the heat transfer between particles and the fluids due to their high specific surface area and adjustable properties, including thermal conductivity and surface wettability, by varying particle volume concentrations in the base fluid to suit different applications. This article is an experimental study on the effectiveness and overall heat transfer coefficient in STHE (shell and tube heat exchanger), comprising baffle cut 25% with a nanofluid at 0.05, 0.1, and 0.2 percentage concentrations of CuO nanoparticles in the DW (distilled water) base-fluid. The inclusion of 0.15% SDBS (Sodium dodecyl-benzene sulphonate) by a two-step method as a surfactant improves the stability of dispersed CuO nanoparticles. The CuO/DW nanofluid thermo-physical properties such as thermal conductivity (k), density (ρ), and dynamic viscosity (μ), have increased. However, the nanofluid's specific heat (Cp) reduces as the nanoparticles proportion rises in the DW base fluid. There is an enhancement of the overall heat transfer coefficient and effectiveness compared to water during parallel flow variation. The maximum heat exchanger effectiveness was 3.01%, 4.01%, and 5.94% higher than water at 0.6 lpm mass flow rate and temperature T = 80 °C for volume fractions of 0.05, 0.1, and 0.2 percentage of CuO/DW nanofluid respectively during parallel flow.

A study on heat transfer characteristics by impinging jet with several velocities distribution

Impinging jet is well known as the most effective cooling method of a heated surface, since it has a high heat transfer coefficient. In this paper, the heated plate surface is going to be cooled by impinging jet through the heat transfer coefficient enhancement. An air flow with several patterns of velocities is suitable for rapid cooling. Therefore, this method is treated as cooling of thermal systems.The objective of this research consists of improving the heat transfer by air jet flow at proper velocity and adequate distances of collision in order to ensure efficient cooling.In this paper, the measurement of velocity distribution by pitot tube is going to be investigated, the flow visualization by high speed camera and finally the heat transfer characteristics on the heated surface by the impinging jet when changing the distance to the collision plate X/D and the air flow velocities distributions. The experimental results indicate that, the collisions distances X/D = 4, 7 and 9 at velocity 15 m/s compare to others values have the highest heat transfer coefficient rate.

Similar Characteristics of Heat Transfer in Different Scale Cooling Channel with Ribs

The gas turbines are highly demanded in modern industries, and the improvement of the performance derives from the increase of the turbine inlet temperature. Various cooling structures are used, such as ribs, pin fins, to improve heat transfer performance and extend the lifespan of the blade. Due to the limitations of the measurement technique, magnified geometry models have been tested with similarity theory in the past. In this paper, a thermochromic liquid crystal experiment was conducted to investigate the heat transfer performance of a magnified rectangular channel with ribs, supplemented with numerical simulation. The results indicated that the vortex and secondary flow generated by the ribs enhance the local heat transfer. Moreover, the thermal performance of the rib-roughed rectangular cooling channel was calculated under different scale factor conditions. The quantitative correlation equations of Nusselt number and friction coefficient versus the scale factor were established. Nusselt number showed an exponential growth with the increase of scale factor, while the friction coefficient displayed an exponential decay. Compared with the baseline, the enhanced heat transfer coefficient is improved by 18.7% and the normalized friction coefficient is dropped by 8.2% with geometry scaled up 10 times.

Enhanced flow boiling of HFE-7100 in picosecond laser fabricated copper microchannel heat sink

The enhanced flow boiling heat transfer of HFE-7100 in wavy copper microchannel heat sink was experimentally studied, which was fabricated with the picosecond laser technique. The micro porous structures were naturally formed on the sidewall and bottom of microchannel during the laser fabrication process, which increase the wall surface roughness. In single-phase flow region, the evaluation of performance evaluation criteria (PEC) proves the heat transfer enhancement overcomes the pressure-drop penalty in present wavy microchannel. In two-phase flow region, the flow patterns including bubbly flow, slug flow and annular flow were captured with the visualization technique, three heat transfer modes including heat convection, nucleate boiling and thin film evaporation were analyzed in detail. In wavy microchannel, the nucleate bubble on concave channel sidewall has a different apparent shape with a larger growth rate compared to that on convex one. In the thin film evaporation stage, the thickness of liquid film varies and it depends on the difference in curvatures between bubbles and sinusoidal channel sidewall. Compared to the straight channel, an increase of 28.89% for CHF can be achieved in wavy one, and the heat transfer coefficient enhancements of 60.76% and 52.71% are obtained in wavy one at the nucleate boiling stage and thin film evaporation stage, respectively.

Numerical investigation on natural convection of hybrid nanofluid Al2O3 – MWCNT/water inside a vertical annulus

A numerical inspection on natural convection inside a vertical annulus interior of which water based (Al2O3 + MWCNT) (7:3) hybrid nanofluid has presently been carried out using CFD solver Ansys Fluent. Finite volume method (FVM) is used to perform the numerical simulations at constant heat flux of 3kW/m2 and various volume fraction (0-0.04) of nanoparticle. The thermal conductivity and viscosity of hybrid nanofluid is computed by modified Maxwell model and Batchelor model respectively. The paper carried explicit analysis on effect of nanoparticle concentration, Nu number and heat transfer coefficient. The maximum enhancement in average heat transfer coefficient found to be 73.67% when gauged on volume fraction of 0.04.

Systematic micro heat sink optimization based on hydrofoil shape pin fins

Multi-objective optimization of the hydrofoil shaped pin fins for micro heat sinks was studied. Optimization tool utilized a multi objective genetic algorithm (MOGA) and a numerical model that was validated against previously obtained experimental single-phase heat transfer results on a hydrofoil shape micro scale pin fin. The numerical model was built using StarCCM + software. Several turbulence models were examined against single-phase experimental data and the Lag-EB k-epsilon turbulence model was chosen for validation. Optimization tool varied the shape of the hydrofoil pin fin through flexible parametrization utilizing an ellipse and polynomials. An algorithm coupling pin fin parametrization code, validated the 3D CFD solutions and a MOGA interface was implemented. Subsequently, multi-objective optimization was performed to maximize the heat transfer coefficient while minimizing pressure drop. A broad range of novel geometries were obtained with a tradeoff between thermal and hydraulic performance for low Reynolds number. Novel pin fin shape, bird design, is proposed as a result of the study. Additional 3D steady state conjugate CFD simulations including the bird design pin fin were performed using already verified setup, and it was shown that the enhancement in the average heat transfer coefficient dominates over the pressure drop increase at higher Reynolds numbers.

CFD study on heat transfer and pressure drop of nanofluids (SiO2/H2O, Al2O3/H2O, CNTs/H2O) in a concentric tube heat exchanger

In this work, a computational fluid dynamics (CFD) analysis has been carried out over a concentric tube heat exchanger for analysing the overall heat transfer coefficient, heat transfer rate and pressure loss of SiO2/water, Al2O3/water and CNTs/water nanofluids at different volume concentrations (1 %, 2% and 3%) under turbulent flow condition (Reynolds number range 2000–10000). Analysis resulted in 23.6%, 26.83% and 37.25% enhancement of the overall heat transfer coefficient and 20.71%, 23.72% and 32.65% enhancement in the heat transfer rate with 3% volume concentration of SiO2/water nanofluid, Al2O3/water nanofluid and CNTs/water nanofluid when compared with base fluid, respectively. Despite all these enhancements, a little increment in pressure loss is also observed. It has been concluded that the overall heat transfer coefficient and heat transfer rate increases with the increase in the Reynolds number as well as volume concentration of nanofluids.

A critical review on nanorefrigerants: Boiling, condensation and tribological properties

A major amount of domestic energy consumption is spent on refrigeration and space cooling appliances. The performance of the refrigeration system depends on the thermophysical properties of the refrigerant. Altering the properties by additives such as nanoparticles has proven to be an effective solution to improve the performance of the system. This work swivels around flow boiling, pool boiling, tribological and condensation characteristics of nanorefrigerants in Vapour Compression Refrigeration System (VCRS) and Vapour Absorption Refrigeration System (VARS). An evolutionary timeline of nanorefrigerants is presented. Energy savings on compressor work by addition of nanolubricants is discussed. A sum of thirteen refrigerants and twelve nanoparticles in various combinations were encountered during this review process. CNTs performed better than metallic (Al, Cu, Au, Ag) and ceramic (Al 2 O 3 , TiO 2 , SiO 2 , ZnO) counterparts. Majority of the work reported enhancement in heat transfer rate and coefficient of performance (COP), however, few studies presented that CuO nanoparticles have shown negative correlation between HF, COP and volume fraction of nanoparticle. The review presents a broad idea on dispersion techniques, stability, properties of boiling and condensation, migration phenomenon of nanoparticles and various novel techniques to improve the performance of the refrigeration systems.

A Critical Review on Thermo-Hydraulic Performance of Wire Screen Matrix Packed Solar Air Heaters

Solar air heaters (SAHs) have an important role in applications such as spaceheating and industrial drying worldwide. The packing of SAH bed not onlyincreases the heat transfer area but also increases the pumping power lossesthereby limiting the thermo-hydraulic performance. In the present study,efforts have been made for a critical assessment of the literature dealingwith the impact of collector bed and operating parameters over thermal andthermo-hydraulic performance for different configurations of wire screenmatrix packed SAH. The porosity of bed and mass flow rate of the air have amajor influence on the thermo-hydraulic performance of wire screen matrixpacked SAH. It is found that the enhancement in the volumetric heat transfercoefficient due to a decrease in bed porosity is obtained at the expense ofincrease in pumping power which ultimately affects the thermo-hydraulicperformance of wire screen matrix packed SAH. In general it is observedthat porosity is an important parameter that affects the thermo-hydraulic performance. It is seen that matrix having porosity 0.937 yields thermo-hydraulic performance of 68% at mass flow rate 0.023 kg/s where as for thesame mass flow rate porosity of 0.887 results thermo-hydraulic performanceof only 42%.

Forced Convective Boiling in a Vertical Annular Test Section With Seawater Coolant

Abstract In case of some nuclear reactors, seawater is used as an emergency resource to remove the decay heat from the reactor core. This study aims to improve the understanding of boiling heat transfer with seawater coolants. Under the boiling conditions with seawater, the mass transfer of the dissolved impurities to the heated surface is expected to significantly impact the heat transfer characteristics. The focus of this experimental work is to measure the differences of the heat transfer performance between seawater and tapwater with electrically heated cylindrical section in a vertical annulus. High speed visualization is performed to quantify and characterize the bubble dynamics parameters. The experimental results indicate an enhanced heat transfer coefficient with seawater in the initial transient under saturated boiling followed by an asymptotic reduction to values similar to tapwater. Under subcooled boiling, a consistent reduced heat transfer coefficient was observed in seawater for a range of heat fluxes. The high speed visualization of subcooled boiling showed fewer and smaller bubbles nucleating off the heat transfer surface in seawater indicating a lower evaporative flux as compared to tapwater.

Steam condensation heat transfer on lubricant-infused surfaces

SummarySteam condensation is fundamental to several industrial processes, including power generation, desalination, and water harvesting. Lubricant-infused surfaces (LISs) promote sustained dropwise condensation, leading to significantly higher heat transfer performance that trades off with durability. Here, we present a systematic study on lubricant-infused copper tubes in a partial vacuum environment typical of power plant condensers to elucidate the influence of the design parameters—texturing, functionalizing agent, and lubricant viscosity—on condensation heat transfer performance and durability. Heat transfer effectiveness is introduced as a relevant parameter to quantify the effects of condensation heat transfer coefficient enhancement on the overall system heat transfer performance. Analytical expressions are developed for lubricant retention fraction and heat transfer effectiveness in terms of Bond number, viscosity ratio, and a dimensionless logarithmic mean temperature difference that can be used for predicting the performance of a LIS or for designing surfaces for a desired performance.

Heat Transfer and Second Law Analysis of Ethylene Glycol-Based Ternary Hybrid Nanofluid Under Laminar Flow

Abstract Experiments were conducted to evaluate the thermal entropy generation, frictional entropy generation, and exergy efficiency of reduced graphene oxide (rGO)–Fe3O4–TiO2 hybrid nanofluid flow in a circular tube under laminar flow. The ternary nanoparticles were synthesized using the sol–gel technique and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). The stable ethylene glycol-based ternary hybrid nanofluid was prepared and its thermophysical properties, heat transfer, friction factor, and pumping power at various values of particle weight concentrations (0.05–0.2%) and Reynolds number (211–2200) were studied experimentally. Nusselt number, heat transfer coefficient, friction factor, and exergy efficiency augment with increasing values of particle loading and Reynolds number. Results show the thermal conductivity and viscosity increase, as compared to the base fluid, by 10.6% and 108.3% at ψ = 0.2% and 60 °C. Similarly, for ψ = 0.2% and Reynolds number of 1548, and in comparison to the base fluid data, the Nusselt number and heat transfer coefficient enhancement are 17.78% and 24.76%, respectively, the thermal entropy generation reduction is 19.85%, and the exergy efficiency enhancement is 6.23%. At Reynolds number of 221.1, the rise in pressure drop, pumping power, and friction factor is 13.65%, 11.33%, and 16%, respectively, for ψ = 0.2% as compared to the base fluid data. The overall thermal performance of the system is enhanced by 14.32%. New equations are developed for the evaluation of the thermophysical properties, Nusselt number, and friction factor.

Numerical Assessment of Nanofluids in Recharging Microchannel: Thermo-Hydrodynamic and Entropy Generation Analysis

Abstract Three-dimensional numerical study is presented in this work that deals with thermo-hydrodynamic and entropy generation analysis of water-based nanofluids in recharging microchannel (RMC). Four different water-based nanofluids (Al2O3, CuO, SiO2, and ZnO) are considered with volume concentrations of 1–5% and nanoparticle diameters of 10–50 nm to understand their effect on thermo-hydrodynamic performance and entropy generation. Substrate bottom surface is subjected to a constant wall heat flux of 100 W/cm2 while coolant with Reynolds number range of 100–500 flows through the RMC. It is revealed that among all the nanofluids under investigation, water/Al2O3 provides enhanced thermal performance with higher effectiveness parameter (η), and it also shows reduced entropy generation. With increasing volume concentration of water/Al2O3 nanofluid, heat transfer coefficient increases, effectiveness parameter increases, and entropy generation reduces. Water/Al2O3 nanofluid with smaller nanoparticle diameter shows enhanced heat transfer coefficient and reduced entropy generation, whereas it shows decreased effectiveness parameter. This is attributed to increased pressure drop with decreasing particle diameter. This study suggests that an optimized combination of particle diameter and volume concentration should be chosen for using nanofluid-based coolants for high heat flux removal.

Microtube Surfaces for the Simultaneous Enhancement of Efficiency and Critical Heat Flux during Pool Boiling.

Boiling is an essential process in numerous applications including power plants, thermal management, water purification, and steam generation. Previous studies have shown that surfaces with microcavities or biphilic wettability can enhance the efficiency of boiling heat transfer, that is, the heat transfer coefficient (HTC). Surfaces with permeable structures such as micropillar arrays, in contrast, have shown significant enhancement of the critical heat flux (CHF). In this work, we investigated microtube structures, where a cavity is defined at the center of a pillar, as structural building blocks to enhance HTC and CHF simultaneously in a controllable manner. We demonstrated simultaneous CHF and HTC enhancements of up to 62 and 244%, respectively, compared to those of a smooth surface. The experimental data along with high-speed images elucidate the mechanism for simultaneous enhancement where bubble nucleation occurs in the microtube cavities for increased HTC and microlayer evaporation occurs around microtube sidewalls for increased CHF. Furthermore, we combined micropillars and microtubes to create surfaces that further increased CHF by achieving a path to separate nucleating bubbles and rewetting liquids. This work provides guidelines for the systematic surface design for boiling heat transfer enhancement and has important implications for understanding boiling heat transfer mechanisms.

Numerical Study of Single-Phase Heat Transfer Performance of a Mini/Micro-Channel Integrated With Multiple Bypass Micro-Nozzles

Abstract Surface temperature uniformity is an important factor in the thermal management of electronics. The present numerical study investigates the influence of multiple bypass injections on the wall temperature distribution of a single-phase mini/micro-channel. The proposed scheme consists of sending a fraction of the coolant through the inlet of a 0.6 mm deep, 2.5 mm wide, and 25 mm long channel and injecting the remaining coolant through multiple bypass inlets on top of the channel positioned at different axial locations. The study explores four different configurations: the first one being three equispaced bypass micro-nozzles or bypass inlets of uniform diameter (1 mm), the second one being three equispaced bypass micro-nozzles of varying diameter (2 mm, 1 mm, and 0.5 mm), the third one being five equispaced bypass micro-nozzles of varying diameter (2 mm, 1 mm, 0.5 mm, 0.25 mm, and 0.125 mm), and the fourth one being five bypass micro-nozzles, but with three equispaced bypass inlets of varying diameter (2 mm, 1 mm, and 0.5 mm), and the last two bypass inlets of the same diameter as that of the third inlet (0.5 mm). Water is considered as the coolant in the study and the simulations are carried out for two mass fluxes of 465 kg/m2s and 930 kg/m2s and two heat fluxes of 25 kW/m2 and 125 kW/m2. The thermal performance of the channel is evaluated for bypass percentages of 25%, 50%, and 75%, with the Reynolds number varying from 150 to 900 at the primary channel inlet and at the secondary channel inlet, and the range of the nozzle Reynolds number varying from 10 to 707. The fourth configuration results in a near uniform wall temperature distribution, with 82–89% reduction in the wall temperature nonuniformity compared with the no-bypass case. The reductions for the third, second and first configurations are 65–71%, 53–76%, and 54–74%, respectively. The third configuration results in an average heat transfer coefficient enhancement of up to 49%. On the whole, the improvement in the wall temperature uniformity is higher than the increase in the pressure drop, and the increase in the channel heat transfer coefficient is higher than pressure drop for some cases.

Experimental Investigation on Enhancement of Convective Heat Transfer Coefficient in Parabolic Collector Using Nanofluids

Experimental Investigation on Enhancement of Convective Heat Transfer Coefficient in Parabolic Collector Using Nanofluids

Experimental Study of Forced Convection Heat Transfer through Porous Media inside a Rectangular Duct of Fully Developed Region

This prospective study was designed to experimentally investigate the effects of inserting copper mesh in fully developed turbulent flow on the flow and heat transfer characteristics. Experimental work includes designing and manufacturing the test section of rectangular duct with dimensions of (30*3*40 cm) with aspect ratio and hydraulic diameter of 10 and 5.45 mm respectively. A constant heat flux ranged (1.5*102 – 1.8*102 W/m2) was applied to the lower surface of duct with Reynolds number range (3.3*104 – 4.8*104). The porosity rang of (0.98 – 0.99). Also, the effects of porous height ratio (full and partial filling) were considered and considered air as working fluid. The results indicate that inserting mesh wire leads to enhance heat transfer coefficient and increase pressure drop. Taken together, these results show that the obtained values of performance enhancement criteria (PEC) ranged (1.01 -1.98 ), the enhancement in heat transfer coefficient is 315% duo to wire mesh insert. Also, from obtained results empirical correlation for friction factor and Nusselt number were suggested.

Optimization of Thermophysical and Rheological Properties of Mxene Ionanofluids for Hybrid Solar Photovoltaic/Thermal Systems.

Since technology progresses, the need to optimize the thermal system’s heat transfer efficiency is continuously confronted by researchers. A primary constraint in the production of heat transfer fluids needed for ultra-high performance was its intrinsic poor heat transfer properties. MXene, a novel 2D nanoparticle possessing fascinating properties has emerged recently as a potential heat dissipative solute in nanofluids. In this research, 2D MXenes (Ti3C2) are synthesized via chemical etching and blended with a binary solution containing Diethylene Glycol (DEG) and ionic liquid (IL) to formulate stable nanofluids at concentrations of 0.1, 0.2, 0.3 and 0.4 wt%. Furthermore, the effect of different temperatures on the studied liquid’s thermophysical characteristics such as thermal conductivity, density, viscosity, specific heat capacity, thermal stability and the rheological property was experimentally conducted. A computational analysis was performed to evaluate the impact of ionic liquid-based 2D MXene nanofluid (Ti3C2/DEG+IL) in hybrid photovoltaic/thermal (PV/T) systems. A 3D numerical model is developed to evaluate the thermal efficiency, electrical efficiency, heat transfer coefficient, pumping power and temperature distribution. The simulations proved that the studied working fluid in the PV/T system results in an enhancement of thermal efficiency, electrical efficiency and heat transfer coefficient by 78.5%, 18.7% and 6%, respectively.

A Combined Experimental and Numerical Characterization of the Flowfield and Heat Transfer around a Multiperforated Plate with Compound Angle Injection

The aerodynamic and thermal behaviour of multiperforated zones in combustors is essential to the development of future combustion chambers. Detailed databases are therefore crucial for the validation of RANS/LES solvers, but also regarding the derivation of heat transfer correlations used in 0D/1D in-house codes developed by engine manufacturers. In the framework of FP7 EU SOPRANO Program, the test-rig used in a previous study is modified to be compatible with anisothermal conditions. The plate studied is a 12:1 model with a 90∘ compound angle injection. A heating system is used to generate a moderate temperature gradient of about 20 K between the secondary hot flow and the main cold flow. The aerodynamic field is acquired by a PIV 2D-3C (Stereo Particle Image Velocimetry) system. The surface heat transfer coefficient is derived based on surface temperature distribution acquisitions. Several heating power levels are tested, which allows evaluating the convective heat transfer coefficient and reference temperature through a linear regression. Measurements are conducted on both sides of the plate, which also gives access to those quantities on the injection/suction sides. From a numerical point of view, the configuration is studied using the unstructured ONERA in-house CEDRE solver with an advanced Reynolds Stress Model. A systematic comparison is presented between the experimental and numerical database. Due to the high blowing ratio, the film protection is low in the first rows, with a convective heat transfer coefficient enhancement around three, and freestream cold air brought close to the wall by vortices created at injection. After four rows, the film is building up, leading gradually to a better insulation of the wall. The comparison with the numerical simulation exhibits a qualitative agreement on the main flow structures. However, the mixing between the jets, the film and the freestream is underestimated by the calculation.

Hybrid microchannel/multi-jet two-phase heat sink: A benchmark and geometry optimization study of commercial product

In this paper, an experimental study of two-phase cooling heat sink using the dielectric working fluid Novec/HFE-7000 is performed. The liquid flow is directed into microchannel fins through multiple impinging jets. A copper microchannel heat sink with a fin height of 3mm, fin thickness of 0.1 mm and channel width of 0.1 mm was used for removing heat flux from the heated surface. A copper block was used to mimic computer chip with a surface area of 1” x 1” (6.45 cm2). The experiment was performed at heat flux from 5 W/cm2 to 80 W/cm2, subcooling of 5 °C, 15 °C, 25 °C, and flow rates 1, 1.25 and 1.75 lpm. The results in the two-phase regime for high heat fluxes are compared with analytical correlations. Reduced subcooling can results in enhancement of heat transfer coefficient by 25 % but will increase the pressure drop through the heat sink. Heat transfer coefficient increases with flow rate in the single-phase region and in the convective boiling region. In nucleate boiling region, heat transfer coefficient increases with heat flux rather than flow rate. Geometry optimization of heat sink was carried out considering effects of fin height on thermal and hydraulic performance. It is found that thermal resistance variation with fin height shows a parabolic trend and an improvement of 46 % in thermal performance can be obtained. A new correlation was also developed to predict results of experimental data with mean absolute error of 7 %. The inclusion of Reynolds number and hydraulic diameter was found to considerably reduce error when compared to values obtained with the previously available correlation, in which only the subcooling and heat flux were the parameters for modelling the heat transfer.