Heat Transfer Enhancement Methods Research Articles

ИСПЫТАНИЯ ЛАБОРАТОРНОЙ УСТАНОВКИ ДЛЯ ИССЛЕДОВАНИЯ ТЕПЛОПЕРЕДАЧИ НА ГОРИЗОНТАЛЬНОЙ ТЕПЛООБМЕННОЙ ТРУБЕ

Tests of a laboratory setup for the study of new methods of heat transfer enhancement were performed. The experimentally determined heat transfer coefficients are in good agreement with those calculated by known equations, which indicates the reliability of the research methods used.

A Review on Design and optimization of shell and tube heat exchanger by varying parameters

In recent years, thermal control systems performance has improved in numerous ways due to developments in control theory and information technology. Efforts have been made to produce more efficient heat exchangers by employing various methods of heat transfer enhancement. An increase in heat exchanger performance can lead to a more economical design of heat exchanger which can help to make energy, material & cost savings related to a heat exchange process. Compact heat exchangers (CHEs) technologies are expected to be one of the solutions for the new generation heat exchanger. In this paper are presented of the compact heat exchanger, Plate-fin heat exchanger, and Printed Circuit Heat Exchanger. And computation fluid dynamic is used which offers an alternative to the quick and inexpensive solution for the design and optimization of compact heat exchangers.

Numerical investigation of magnetic field effect on nanofluid heat transfer in microchannel with hydrophobic surface using incompressible pre conditioned lattice Boltzmann method

The flow concerning water/alumina nanofluid is studied by pre-conditioned incompressible version of Lattice Boltzmann method. The geometry at hand is a rectangular microchannel. The volume fraction of the nanoparticles is in the range of 0–2%. The present study aims to combine the heat transfer enhancement methods such as application of smooth surfaces with a slip velocity coefficient of 0–0.06 and linear magnetic field with Hartmann number of 0–40. The results of this study show that as the wall slip increases, the amount of solid blocking the fluid motion decreases. Hence, the fluid moves with less momentum drop and it moves the path along the microchannel with less momentum dissipation. Upon applying a linear descending magnetic field to a flow, the Lorentz force and the flow behavior will change. It can also be concluded that Lorentz force reduces the slippage of the fluid layers. This will eventually reduce the effects of the hydrodynamic boundary-layer and the formation of the viscous regions. As this coefficient increases, the fluid flows easier, and the effects of the isotherms penetration in the central region of the flow can be smooth. The wall slip presence in the microchannel has also boosted the motion of the fluid and reduced the velocity gradients due to the presence of solid surfaces.

CFD analysis of second law characteristics for flow of a hybrid biological nanofluid under rotary motion of a twisted tape: Exergy destruction and entropy generation analyses

The main goal of the current study is to evaluate the effects of a hybrid heat transfer enhancement method, i.e. simultaneous deployment of active and passive techniques, with employing an ecofriendly-produced graphene nanoplatelets nanofluid from the viewpoint of the second law of thermodynamics. The numerical simulations are performed for the tubes enhanced with the innovative rotary twisted tape. Employing the rotary twisted tape intensifies the flow mixing, disrupts the thermal boundary layer, and reduces the temperature gradients dramatically. The total entropy generation and total exergy destruction of nanofluid extremely diminish by the rotational speed elevation. The maximum decrement in the total entropy generation is 87.38%, which occurs by elevating the rotational speed from 0 to 900 rpm. The concentration increase considerably contributes to the exergy destruction decrement besides total entropy generation reduction. The lower twisted ratio exhibits the smaller thermal irreversibility, and the best second law efficiency equals to 0.932.

Entropy generation and exergy destruction for flow of a biologically functionalized graphene nanoplatelets nanofluid within tube enhanced with a novel rotary coaxial cross double-twisted tape

Abstract The second law performance of the ecofriendly graphene-based nanofluid inside the tubes fitted with novel rotary coaxial cross double-twisted tape (RCCDTT) is studied. Indeed, this study examines the effects of using both active and passive heat transfer enhancement methods simultaneously. Several weight fractions are examined and effects of the twisted ratio are also considered. The combination of these two techniques results in great decrement in the total entropy generation and exergy destruction, such that at weight fraction of 0.025% and twisted ratio of 3.5, the thermal entropy generation decreases up to 80% by rising the angular velocity from 0 to 900 rpm. Increasing the concentration results in the less irreversibility and the maximum decrement in the exergy destruction rate is about 24%. Moreover, the twisted ratio increment augments the entropy generation caused by heat transfer. The entropy generation due to the friction has a minute contribution and increases slightly by rising the angular velocity and weight fraction. The second law efficiency has ascending trend by the weight fraction increase and profoundly augments with increasing the angular velocity. The highest second law efficiency is attained 0.935 at concentration of 0.1%, angular velocity of 900 rpm, and twisted ratio of 2.5.

Numerical study of tube arrangement and fin effects on improving the ice formation in ice-on-coil thermal storage systems

Abstract Heat storage systems are used as a method for transferring and controlling the cold load in hot seasons. In this paper, to analyze the phase changes of an ice-on-coil thermal storage tank, the process of ice formation in a cavity with refrigerant carrier tubes is carried out using numerical simulation. Moreover, performance of some heat transfer enhancement methods including usage of fins around tubes with various dimensions and numbers and various tube number and arrangement, are compared. In this study, the inlet temperature is considered to be 275 K, which the temperature decrease up to 10 K due to freezing is observed. According to the results, the fin height is a very effective parameter in increasing the freezing rate. Also, upon increasing the tube number with smaller diameter, ice is formed with a higher speed due to their uniform distribution. So, with the tube number increasing from 9 to 16 in these systems at the same time interval, the fluid temperature drops from about 275 to 269 K, as well as the volume fraction of liquid decrease from about 0.4 to 0.22. Finally, by changing the tube arrangement from rectangular to triangular, faster rate of ice formation are observed.

Heat transfer enhancement in concentric tube heat exchanger with tangential injection and twisted tape inserts

Heat exchanger has many engineering applications such as air conditioning, chemical reactor and refrigeration systems, etc. The performance of this industries mainly depends on the performance of heat exchanger. So, to increase the performance of heat exchanger many techniques have been investigated on enhancement of heat transfer rate and decrease the size and cost of the heat exchangers. In most of applications and key areas like power plants, process & chemical industries uses surface enhancement methods. Present work mainly emphasis on the both passive and active methods of heat transfer enhancement. In this work, to enhance the heat transfer rate with the help of twisted tape insert in passive method in which aluminium twisted tapes are used. In the active method fluid is injected in annulus space to generate turbulence through tangential injectors. There are six injectors are used to generate turbulence. Water is used as a working fluid in both types of heat exchanger. From the experiment it shows that, as Reynolds number increases heat transfer coefficient also increases

Laminar convective heat transfer in helical tube with twisted tape insert

Tape insert has been commonly adopted as heat transfer enhancement method in a thermal system. Most studies dealing with tape insert have been focused on straight tube. Helical coil tube, on the other hand, has been proven to have higher heat transfer than straight tube. It is of interest to combine both enhancement methods and obtain the optimum heat transfer enhancement. The main objective of this study is, therefore, to numerically investigate flow behaviour and the corresponding heat transfer in helical tube with twisted tape insert subjected to constant wall temperature. A three-dimensional computational model is developed based on conservation equations of mass, momentum, and energy, and is validated against the established empirical correlations. Good agreement is achieved between the numerical prediction and the empirical correlation calculation within the considered range of Reynolds (Re=100−2000) and Dean Numbers (De=25−1200). The effects of twist ratio, inlet Reynolds number and wall temperature are evaluated and discussed in the light of numerical result. It is found that adding twisted tape insert in helical heat exchanger can enhance heat transfer performance by up to four times as compared to conventional straight tube heat exchanger, at a cost of higher frictional pressure drop. Lower twisting ratio gives rise to a higher heat transfer enhancement as it promotes higher secondary flow. At low Pr (air), heat transfer enhancement ratio increases as Re is increased; however, at high Pr (water), heat transfer enhancement ratio is higher at Re 500–1000. Finally, Nu and f correlations are developed to predict heat transfer and pressure drop for practical applications.

Experimental and Numerical Examination on Heat Transfer Enhancement using Twisted Tapes

Recent years amply of researchers doing research in enhancement of heat transfer by applying passive heat transfer technique. Recently usage of twisted tape insert to increase the heat transfer surface area is the most preferable passive technique followed by numerous researchers. To increase the complexity of the situation and properly implement the heat transfer enhancement method creating geometrical changes on the twisted tape is leading to a various study of flow physics. In this present review enhancement of heat transfer using insertion of twisted tape investigated numerically and experimentally is reported based on the past decade researches. This review will enable the researchers to involve in diversified usage of twisted tape inserts in the flow field to report the flow physics in detailed manner. This review depicts the findings of experimentally and numerically investigated research works of influence of twisted tape inserts on heat transfer enhancements.

The enthalpy-based lattice Boltzmann method (LBM) for simulation of NePCM melting in inclined elliptical annulus

Constrained melting of ice as a PCM11Phase Change Material. in inclined elliptical annulus should be studied. Efficiency of heat transfer enhancement methods such as insertion of Cu nanoparticles and metallic porous matrix in this heat storage system must be determined. Porous material is made of alloys of Nickel and Steel. The enthalpy-based LBM22Lattice Boltzmann Method. with a D2Q9-DDF33Double Distribution Function. model at the REV44Representative Elementary Volume. scale is implemented. There is thermal equilibrium condition between porous media and PCM. Also, for NEPCM55Nanoparticles-Enhanced PCM. melting, the single phase flow model is adopted. Particle diameter in nanofluid is equal to 100 nm. The sub-cooling of solid PCM is ignored. Prandtl number, Stefan number, Rayleigh number and Darcy number are 6.2, 1, 2×105 and 10−3, respectively. The volumetric concentric of the nanoparticles is between 0 and 0.02. Porosity is between 1 and 0.9. It is found that inclination of the elliptical annulus does not engender any change in the liquid fraction. Inserting nanoparticles is best effective technique to enhance liquid fraction in oblate annulus due to enhanced conduction heat transfer. Use of porous matrix is recommended for prolate and inclined configurations. It obviates considerably stable stratification at bottom of elliptical annulus as a thermal storage unit.

Effect of porous medium and nanoparticles presences in a counter-current triple-tube composite porous/nano-PCM system

To solve the problem of low thermal conductivity of phase change materials (PCMs), three different methods including geometry modification, adding nanoparticles and metal foam are studied in a triple-tube latent heat storage system (LHS). PCM is enclosed in the middle tube while water passes through the inner and outer tubes as the heat transfer fluid (HTF). Different nanoparticles concentrations and metal foam porosities are examined. Different HTF flow directions in the inner and outer tubes related to the gravity direction are assessed. The results show the advantage of the system with counter-current flow of the HTF when the HTF flow in the outer tube is in the gravity direction. By adding 5% copper nanoparticles, the melting/solidification time reduces by 25.9/28.2%. By adding a 95% porous metal foam, the melting/solidification time reduces by 83.7/88.2% showing the advantage of adding a metal foam compared with adding nanoparticles. Increasing the volume fraction of nanoparticles or reducing the porosity of the metal foam reduce the melting/solidification time. Simultaneous usage of the nanoparticles and metal foam show that in the presence of metal foam, the effect of adding nanoparticles is almost negligible. For the porous/nano-PCM case with 95% porosity of the metal foam and 5% volume fraction of nanoparticles, the melting/solidification time reduces by 84.2/88.8% compared with the pure PCM system. This paper provides a clear and comprehensive vision of the simultaneous effects of different heat transfer enhancement methods inside the PCM in triple-tube LHS systems.

A Review of Modern Methods for Enhancing Nucleate Boiling Heat Transfer

The main results obtained for the last decade in studying the possibilities of enhancing boiling heat transfer and increasing critical heat fluxes are reviewed. Heat transfer enhancement methods involving the use of a modified/structured boiling surface obtained by means of mechanized processing, electrochemical technologies, plasma and ion deposition, laser emission, and subcooled liquid boiling are considered.

Analysis on thermal and flow behavior of triple concentric tube heat exchanger handling MWCNT-water nanofluids

Design of heat exchangers and heat transfer enhancement methods are struggling to meet out the cooling demand of present scenario. Many researchers suggested that the addition of nanosized solids particles into traditional base fluids resulting the higher heat transfer rate than the existing coolants and named the new fluids as nanofluids. In this investigation, the effect of microwave carbon nanotube (MWCNT)-water nanofluids on heat transfer rate, pressure drop and pumping power of a triple concentric tube heat exchanger are experimentally investigated and compared the results of MWCNT-water nanofluids with water. The MWCNT-water nanofluids were prepared by two step method at the volume concentrations of 0.2%, 0.4%, and 0.6%. The range of target fluid mass-flow rate is in the range of 0.026 to 0.039 kg per second and the constant heat flux condition is considered. On experimentation, it is noted that the effectiveness and presure drop of 0.6% MWCNT-water based nanofluids are 27% and 21% greater than water at the maximum mass-flow rate. The reason for improved heat transfer rate of nanofluids is because of higher thermal conductivity, Brownian motion, lower boundary-layer thickness, and lower specific heat capacity of nanofluids. Also found that the pumping power increases with increasing volume concentration and pumping power is 25% higher than water at the 0.6% nanofluids. Therefore, the MWCNT-water nanofluids are good choice for replacing water as coolant in triple concentric tube heat exchanger.

On heat transfer and flow characteristics of jets impinging onto a concave surface with varying jet arrangements

The increase in hot gas temperature is helpful for the turbine efficiency improvement and energy-saving. The significantly curved leading edge suffers the highest thermal load in a turbine blade. Jet impingement is one of the popular heat transfer enhancement methods, which has been widely used in blade leading edge. In this study, the flow structure and heat transfer characteristics of jets impinging onto a curved surface with varying jet arrangements and Reynolds number (10,000–40,000) are numerically investigated. The relative jet-to-target spacing equals 1, and relative surface curvature equals 10. An array jets arrangement is provided as baseline. Concerning three array cases, jet holes are positioned in inline and staggered patterns with changing jet-to-jet spacing. In this work, streamlines of different sections, limiting streamlines near target wall and vortex, are obtained. Local Nusselt number contour, local Nusselt number curves and surface-averaged Nusselt number are also presented. Local heat transfer characteristics are analyzed with fluid flow. It is also shown that the heat transfer uniformity of both inline and staggered cases is significantly enhanced by comparing with an array jets case. The whole curved surface-averaged Nusselt number increases with increasing jet-to-jet streamwise spacing at inline arrangement.

Perspectives and problematic issues in the development of heat transfer enhancement methods at boiling and evaporation

The paper presents an analysis of modern methods of heat transfer intensification and critical heat flux increase during boiling and evaporation using micro-nanostructuring of surface. Special attention is paid to the analysis of such promising methods of modifying heat-transfer surfaces as the application of combined microstructured surfaces/coatings by SLM/SLS (3-D printing), the organization of structures with contrast wettability on the micro-scale. The conclusions formulated on the basis of generalization of results of complex research on studying of heat transfer, transitional and crisis phenomena at boiling in the conditions of free convection, at evaporation and boiling in flowing down films and in thin horizontal layers of liquids at use of various types of microstructuring of heat- transfer surfaces are presented.

Numerical Study of Flow and Heat Transfer with ZnO-Water Nanofluid in Flattened Tubes

AbstractThe usage of nanofluids and modification of tube geometry are the two most prominent heat transfer enhancement methods employed to improve the performance of thermal devices. In this work, the combined effect of these methods has been studied by CFD modelling of developing and Graetz laminar flow in flattened tubes with ZnO – water nanofluid. For the purpose of comparison, simulation with water and circular tube has also been carried out. Performance evaluation has been done using PEC, PER and entropy generation. Results reveal that tube flattening has more pronounced effect on both heat transfer and flow compared to that of nanofluid. An optimum tube flattening in terms of aspect ratio and nanofluid concentration has also been identified for this kind of flow. Flattened tube with aspect ratio 6 with 1 % ZnO-water nanofluid has been found to yield the highest entropy generation reduction of 13.24 %

Review of Heat and Mass Transfer Enhancement Techniques and Current Advancement for Adsorption Heating/Cooling Systems

Abstract Adsorption heating/cooling became an alternative to vapour compression system due to low ozone depletion potential (ODP) and global warming potential (GWP). However, more investigation is required due their low efficiency when compared to conventional heating/cooling systems. This review emphasizes on the mathematical modelling simplification and heat transfer enhancement method that applied by many researchers to improve the performance of adsorption heating and cooling technologies. Various techniques investigated by many researchers on solving low thermal conductivity and the different methods for enhancing heat and mass transfer in the adsorbed bed/pipe also discussed. Common techniques used to enhance heat and mass transfer in the adsorbed bed/pipe include the fin type adsorbent tube/ heat exchanger, amalgamated adsorbent bed with a metal foam, consolidated adsorbent, adsorbent coating and adsorbent with multi cooling tubes. Other than that, recent advancements in adsorption cooling/heating systems also discussed in this review.

Thermo-economic performance evaluation of emerging liquid-separated condensation method in single-pressure and dual-pressure evaporation organic Rankine cycle systems

Liquid-separated condensation is an emerging and effective heat transfer enhancement method to reduce the condenser cost, which can help with the widespread application of organic Rankine cycle (ORC) systems. However, few related studies have focused on the shell-and-tube condenser even if it is widely used in ORC systems. The thermo-economic performance superiorities and applicable working conditions of shell-and-tube liquid-separated condenser should be investigated, especially in novel ORCs. This study introduced the liquid-separated condensation method into single-pressure and dual-pressure evaporation ORC systems with shell-and-tube condenser. R245fa, R600a, and R1234ze(E) were used as working fluids. Optimal liquid-separated thermodynamic states and decrements in condenser heat transfer area of one to four stages liquid-separated condensations were provided. Decrements in specific investment cost (SIC) of ORC system by adopting the liquid-separated condensation method were evaluated. Results show that the liquid-separated condensation method is more suitable for low tube diameter, low inlet velocity in tubes, high inlet velocity outside tubes, and low cooling water temperature rise. Optimal liquid-separated thermodynamic states remain constant with increasing the tube diameter and inlet velocities. The SIC of ORC system can be reduced by 4.6% at most by adopting the liquid-separated condensation over the conventional condensation method. Increasing the mass flow rate of heat source fluid and pinch point temperature difference during heat absorption process is beneficial to increase the superiority of liquid-separated condensation method. Compared with dual-pressure evaporation ORC, the effects of liquid-separated condensation method on reducing the SIC are more remarkable in single-pressure evaporation ORC.

Thermal performance of a new nanofluid containing biologically functionalized graphene nanoplatelets inside tubes equipped with rotating coaxial double-twisted tapes

This research attempts to investigate the benefits of utilizing two heat transfer enhancement methods simultaneously. These techniques include employing biological graphene-based nanofluid and using rotating coaxial double-twisted tapes (RCDTT) to enhance heat transfer inside tubes. Using the nanofluid is desirable such that at twisted ratio of 2.5 and rotational speed of 0 rpm, the heat transfer coefficient improves about 16.3% by increase of the concentration from 0 to 0.1%. Furthermore, higher rotational speed is suggested such that its increase from 0 to 900 rpm, at twisted ratio of 3.5 and concentration of 0%, causes a 77% increment in the heat transfer coefficient. Lower twisted ratios are also more effective for enhancing heat transfer rate. The rotational speed increment has the great impact on the pressure drop, such that a 34% increment in the pressure drop occurs with increasing the rotational speed from 300 rpm to 900 rpm at weight fraction of 0.075% and twisted ratio of 3.5. Owing to the more intense disturbances generated by greater rotational speeds, the particle residence time becomes greater leading to pumping power increment. The figure of merit for all the cases is higher than 1, which is an excellent outcome from energy efficiency viewpoint.

Effects of wavy wall and Y-shaped fins on solidification of PCM with dispersion of Al2O3 nanoparticle

In current modeling, solidification process within a three-dimensional triplex tube was numerically studied. In two sides, the cold water flow is used while the middle tube contains RT82. The purpose of the current article is investigating the impacts of using nanoparticles, fin, and the combination of both of them on thermal characteristics during solidification in an energy storage unit. Also, the amount of stored energy has been investigated over time, and the influences of temperature and water velocity were scrutinized. The results revealed some substantial improvements in the solidification rate by adding fins or nanoparticles. It was indicated that using a combination of these two heat transfer enhancement methods presents a better enhancement compared to when either of these two methods is employed alone.