Heat Transfer In Exchanger Research Articles

Evaluating two-phase fluid flow and heat transfer in pillow-plate heat exchangers with nanofluids for organic Rankine cycle in municipal solid waste power plant: A numerical simulation study

One of the key considerations in the design and operation of process industries nowadays is reducing energy waste. The purpose of this research is to assess fluid flow and heat transfer in pillow-plate heat exchangers (PPHEs) using nanofluids for the Organic Rankine Cycle (ORC) in Municipal Solid Waste (MSW) power plants. The thermal performance and hydraulic features of the PPHE were investigated using a two-phase numerical modeling approach. three nanoparticles of Cu, TiO2, and Al2O3 were examined. To precisely determine the temperature distribution within the heat exchanger, various boundary conditions were used. The results demonstrate a strong correlation between the velocity field and temperature, underlining the importance of boundary conditions in determining the temperature profile. Furthermore, the two-phase model illustrates that nanofluids are extremely reliant on inlet velocity and volume fraction. such that at a 2 m/s inlet velocity, increasing the volume percentage to 12.8% contributes to heat transfer coefficient improvements of 7.57%, 12.15%, and 2.71% for water_TiO2, water_Al2O3, and water_Cu, respectively. These findings give significant insight into the fluid flow and heat transfer properties of PPHEs, as well as prospective pathways for increasing thermal performance and decreasing pump power in ORC systems using nanofluids in MSW-generating plants.

Performance improvement of a double tube heat exchanger using novel electromagnetic vibration (EMV) method in the presence of Al2O3-water and CuO-water nanofluid; An experimental study

In this research, the novel approach of the electromagnetic vibration (EMV) method was utilized for the first time to increase heat transfer in a double-tube heat exchanger (DTHEX). In this method, a magnetic turbulator (comprising a magnet and an oscillator) was installed inside a central tube that vibrated using an AC magnetic field. The influences of various parameters such as the geometry of the oscillator, magnet position, employing nanofluids, and fluid flow were assessed on the thermal-frictional behavior. The thermal enhancement factor (TEF) was assessed to select the optimal option. The studied options were economically evaluated based on energy efficiency. According to the results, the maximum heat transfer rate could be achieved when the magnet is positioned at 0.374. L from the tube inlet. The highest value observed for overall heat transfer was related to CuO-water 1% nanofluid, which was 277.5% more than simple heat exchanger. Also, the findings showed that heat transfer can be increased up to 13.3 times the energy used and reached to TEF = 3.92, which is a very significant number. Regarding the high potential of the EMV in reaching high thermal performance, it can be utilized as a game changer to save materials, energy, and compaction of the heat exchangers and solar systems.

Numerical Investigation of Heat Transfer and Pressure Drop Characteristics in a Double Pipe Heat Exchanger with Corrugated Tubes and Rod Baffles at Various Reynolds Numbers

Numerical Investigation of Heat Transfer and Pressure Drop Characteristics in a Double Pipe Heat Exchanger with Corrugated Tubes and Rod Baffles at Various Reynolds Numbers

Review of Developments in Plate Heat Exchanger Heat Transfer Enhancement for Single-Phase Applications in Process Industries

A plate heat exchanger (PHE) is a modern, effective type of heat transfer equipment capable of increasing heat recuperation and energy efficiency. For PHEs, enhanced methods of heat transfer intensification can be further applied using the analysis and knowledge already available in the literature. A review of the main developments in the construction and exploration of PHEs and in the methods of heat transfer intensification is presented in this paper with an analysis of the main construction modifications, such as plate-and-frame, brazed and welded PHEs. The differences between these construction modifications and their influences on the thermal and hydraulic performance of PHEs are discussed. Most modern PHEs have plates with inclined corrugations on their surface that create a strong, rigid construction with multiple contact points between the plates. The methods of PHE exploration are mostly experimental studies and/or CFD modelling. The main corrugation parameters influencing PHE performance are the corrugation inclination angle in relation to the main flow direction and the corrugation aspect ratio. Optimisation of these parameters is one way to enhance PHE performance. Other methods of heat transfer enhancement, including improving the form of the plate corrugations, use of nanofluids and active methods, are considered. Future research directions are proposed, such as improving fundamental understanding, developing new corrugation shapes and optimisation methods and area and cost estimations.

A Numerical Study of Heat Performance of Multi-PCM Brick in a Heat Storage Building

Modern technologies of thermal power engineering make it possible to design and build systems using renewable energy sources. Often, energy accumulation and storage require the development and adaptation of appropriate systems, the simplest of which are passive systems based on phase-change materials. In this study, a numerical analysis of heat transfer in a brick wall containing several materials with different melting temperatures is carried out. The unsteady two-dimensional conjugate problem of phase transitions is considered, taking into account natural convection in the melt, which has been solved using the developed in-house finite difference technique. A numerical experiment has been carried out for a brick block with several rectangular inserts filled with PCMs under various external thermal conditions. As a result of the numerical analysis, it has been shown that the relative arrangement of materials with different melting points has a significant impact on the heat transfer and heat exchange between the environment and the room.

HENS Unchained: MILP Implementation of Multi-Stage Utilities with Stream Splits, Variable Temperatures and Flow Capacities

In this paper, we present an extended heat exchanger synthesis superstructure (HENS) formulation to consider streams with variable temperatures and flow capacities using mixed-integer linear programming (MILP). To keep the problem tractable and to leverage the potential of state-of-the-art MILP solvers, piecewise-linear models with logarithmic coding are used. Allowing for variable utility parameters within a feasible technical range, instead of a priori defined ones, removes limitations of the HENS. Increasing the utility’s degree of freedom offers advantages when sensible heat from, for example, flue gas, thermal oil, or water is used. Moreover, utilities are no longer limited to single-stage heat transfer without stream splits at the stream ends, generating opportunities for efficiency enhancement. We consider three representative case studies to evaluate the performance of the unchained HENS method. Our results show that representing utilities as streams in the HENS optimization problem leads to lower total annual costs (TAC). Significant cost savings arise due to more efficient utility placement, heat transfer, and smaller heat exchanger areas. The results indicate that this method can lead to cheaper and more resource-efficient HEN and thus positively contribute to the environment.

Experimental and numerical analysis of heat transfer in a dimple pattern heat exchanger channel

In contrast to the predominant herringbone shape of heat plates, a microplate heat exchanger has an array of relatively small dimples. Its number and shape define the characteristics of such a plate heat exchanger. Literature, however, of the flow characteristics in such kinds of channels is scarce. Precise knowledge of the flow specifics in such a channel is of key importance to develop efficient new products. Single-phase water flow and heat transfer in microplate heat exchanger was investigated with the laboratory experiments and use of computational fluid dynamics simulations. A novel and innovative laboratory experiment was developed where flow characteristics and heat transfer in the microplate heat exchanger were measured. Experimental results were directly used as boundary conditions in numerical simulations. With this approach a direct validation of the results of numerical simulations were obtained. Heat transfer simulations were performed with three turbulence models: k- ε, k-ω SST and the Reynolds stress model. The most reliable results in heat transfer analysis were obtained using the Reynolds stress model where results are on average 7.05% lower compared to the results of the laboratory experiment. When all experimental uncertainty contributions were analysed, the simulation results were in the band between − 11% and 1.8% compared to the results of the laboratory experiment. Numerical simulations show that the heat transfer coefficient in the channel is proportional to Re0.64 in the analysed geometry of a microplate heat exchanger. The heat transfer coefficient was calculated and was between 9740 and 21990 W/m2K at Reynolds numbers 1170 and 4170 respectively.

Experimental analysis of thermal performance factor for double pipe heat exchanger with ZnO–water nanofluid

Nanofluid has attracted a large number of researchers in recent decades due to its exceptional heat transfer properties. In this study, a ZnO–H2O nanofluid with surfactant sodium dodecyl benzene sulphonate has been investigated to quantify heat transfer and frictional loss in a double-pipe heat exchanger. The turbulent zone was studied, with Reynolds numbers ranging from 5500 to 16,000 for fully developed flow. Volume fractions employed were 0.005%, 0.01%, 0.03% and 0.06%. Brownian motion and the interfacial layer, in addition to thermal conductivity, are the primary factor to influence heat transfer in heat exchangers. The maximum enhancement in Nusselt number and thermal performance achieved for a volume fraction of 0.06% at Reynolds number 5500 is 35% and 1.15, respectively.

Simulation of heat transfer and effectiveness in a helical heat exchanger made from thermally enhanced polymer material for use in absorption cooling

Heat exchangers in absorption chillers are usually made of copper material. However, prob-lems of corrosion are usually encountered, especially in the solution heat exchanger. In this study a numerical investigation of the heat transfer effectiveness in a double pipe helical heat exchanger made from a thermally enhanced polymer material was conducted. The material consists of a Liquid crystal polymer (LCP), (Vectra A950) as the matrix material, while carbon fibre is the filler material. The resulting composite has a carbon fibre weight fraction of 74%. The heat exchanger was modelled as a counter flow solution heat exchanger to be used in a lithium bromide – water absorption chiller of 3 kW capacity. The numerical software ANSYS fluent (version 14.5) was used for the modelling and simulation. Thermal and mechanical properties of the thermally enhanced polymer were used in the modelling and simulation. The viscous laminar model was used, while employing a second order upwind solution method. Results indicate that the heat exchanger was able to perform the required duty by reducing the strong solution temperature from 90oC at inlet to 57oC at outlet, while increasing the weak solution temperature from 40oC at inlet to 67oC at outlet. The effectiveness of the heat ex-changer was 77.4%. Results were numerically compared to a corresponding heat exchanger of same geometry and flow conditions, made of copper. It was observed that the polymer heat exchanger attained 89.2% effectiveness of the copper heat exchanger.

Prediction of Friction Factor and Heat Transfer Coefficient for Single-Phase Forced Convection Inside Microfin Tubes

Microfin tubes are widely used to enhance heat transfer in heat exchangers in order to reduce volumes, costs and refrigerant charge. Much experimental work has been published for the flow of liquids, while some experimental work is available for the flow of gases for the chemical, refrigeration and air conditioning industry. This work reviews the literature and presents new experimental friction factors for the flow of the superheated vapor of R1234ze(E) in a 5 mm outside diameter microfin tube. The authors have also collected an extensive data bank of heat transfer coefficients (around 648 points from different research laboratories) and friction factors (around 536 points), covering 45 different geometries of inner finned tubes. After comparing the predictions from available correlations with experimental data, the present paper suggests the best performing equations for the calculation of the friction factor and of the Nusselt number during forced convection flow of liquids and gases. The suggested model for friction factor estimates the experimental values with a relative and absolute deviation of −0.3% and 7.9%, respectively, whereas the suggested model for the heat transfer coefficient predicts the experimental data bank with a relative and absolute deviation of −3.3% and 13.9%, respectively. The validity range of the two correlations is extremely wide, covering microfin tubes with diameters from 2.6 mm to 24.4 mm, and Reynolds number from about approximately 1000 to 300,000 for the friction factor, and from 3000 to 1,000,000 for the heat transfer coefficient.

CFD Modeling of Heat Exchanger with Small Bent Radius Coils Using Porous Media Model

The efficiency of heat transfer in air-cooled heat exchangers of various industrial facilities depends on the flow rate of the coolant, its inlet temperature and ambient temperature. These parameters are transient and depend both on the features of the technological process and on weather conditions. One option for a compact design of heat exchangers is the use of close-packed coils with a small bending radius. In this case, heat transfer in the complex geometry of the annular space cannot be described by simple one-dimensional dependencies. To solve this problem, it is necessary to consider the three-dimensional spatial structure of the heat exchange surface. Since the size of the grid elements will be several orders of magnitude less than the size of the facility, the size of the computational grids for CFD modeling full-scale heat exchangers will be billions of finite volumes, and even on powerful supercomputers, the solution time will be about a month. One way to reduce computational costs is to use reduced order models, in which the computational domain is not modeled directly; instead, simplified models, such as a porous medium model, are used to describe it. However, such models require additional closing relations and coefficients that characterize the actual channel geometry. This paper presents a technique for creating a digital twin of a heat exchanger with small bend radius coils based on a porous medium model. The values of heat transfer coefficients and hydraulic resistance depend on the speed of air movement in the space between the coils. The calculated value of the thermal power obtained using the strengthened model was 529 kW, which corresponds to the passport data of 500 kW, with less than 6% deviation for the heat exchanger under study. This confirms the correctness of the calculation with accepted simplifications. The calculation time in this case was only a few minutes when using a personal computer. The developed numerical model allows for the resolution of performance characteristics based on the temperature of the cooled medium at the inlet, air temperature, and fan speed. Analyzing the different modes of turning on the cooling fans made it possible to determine the values of the thermal power when turning off the fans or reducing the number of revolutions.

First analysis of a novel design of a solar chimney with absorber elements distributed in the air channel

The study of solar chimneys arouses great interest because of the wide variety of its applications, above all passive heating, cooling and ventilating of buildings. Mathematical models to predict the obtainable air flow rates and the conversion efficiency have been developed. Some studies focused on the possibility of increasing the amount of heat transferred to the air, and thus the efficiency, through an increase of the absorbing surface area inside the channel. The present work arises in this research line, and in this study a never investigated novel solar chimney configuration is proposed, with four arrays of cylindrical absorber elements in the air channel. Aim of this system is not only to increase the absorbing surface, but also the convection exchange coefficient between absorber surface and air, thus increasing thermal efficiency compared to a traditional system. A numerical model has been developed to investigate the proposed system, with an accurate approach to the radiative heat transfer exchanges, that have usually been rather neglected in previous studies. Convection heat transfer coefficient have been calculated and simulations have been conducted both in the hypothesis of natural and mixed convection. Head losses have also been taken into account. Thermal efficiency and air flow rate have been calculated for different values of the solar height. Results show that in the investigated configuration (a direct power equal to 669.1 W has been considered) the efficiency is always higher than in the traditional system, reaching values up to 61%. Moreover, efficiency value does not decrease as solar height increases, as it happens in the traditional system, where efficiency maximum value is 38% for a 10° solar altitude. Compared to the traditional system efficiency values, the proposed system values result increased, between a minimum of 47% at a solar altitude equal to 3 3° and a maximum of 128% at a solar altitude equal to 71°. Also airflow rates are higher, from a minimum of 7% to a maximum of 21% respectively for the solar altitude values of 33° and 71°. With reference to the average of the efficiency values (in the ten solar altitude values examined in the range 10°-71°), it has been verified that is 68% higher for the configuration with cylinders than for the traditional one. The average air flow rate is 11% higher.Also the power lost by the glass surface do not depend on solar height, and results much lower in the proposed system than in the traditional; the power loss due to the direct power on the inlet opening in the proposed system is lower than in the traditional system, especially for high solar altitudes, having a value up to 135 W, while in the traditional system it reaches 280 W. Moreover, the proposed system efficiency values in several cases results also higher than those found with solutions presented in other studies to increase the absorbing surface.Results therefore show considerable advantages in adopting a novel solar chimney system such as the one proposed in the present work, and its performance appears to be worthy of further investigation, focusing on convection mode and on the optimization of the arrangement of the cylinders (position, number of arrays,..) with respect to the solar height.

Numerical analysis of pumped two-phase loop: Characterization of steady-state performance

With growing heat dissipation from advanced electronics, two-phase cooling promises effective and unmatched cooling. A pumped two-phase loop (P2PL) can acquire high power and heat flux from the electronics (heat source) and transport and dissipate it to a heat sink with small total thermal resistance at negligible pumping power consumption because of highly effective phase change (boiling and condensation) heat transfer. Owing to many advantages, in recent years, extensive research efforts have been dedicated to understanding fundamental mechanisms of heat and mass transfer in phase change heat exchangers (evaporators or condensers) at a component level. However, there is little work done for an entire two-phase cooling system as a closed loop which is essential to study the system performance characteristics and the contributions/interactions of each component to the system performance. A comprehensive thermal–hydraulic flow network model was developed to study the system performance characteristics. The pressure variation of the P2PL was calculated by considering the compressibility of the vapor volume in the P2PL to account for the effect of the amount of vapor in the system. The numerical results on the thermal and hydraulic performance characteristics of the P2PL for various operating and design parameters – evaporator heat load, mass flow rate, heat sink temperature, and microchannel dimensions – are discussed. It was found that the numerical results match well with the measured steady-state temperature and pressure profiles of the P2PL. The study also highlights the trade-off between the total system thermal resistance reduction and the increased pressure drop (pumping power) with an increase in mass flow rate. It was also found that the microchannels with smaller hydraulic diameters had significant heat transfer enhancement in the evaporator but poor system performance.

Numerical investigation of turbulent nanofluid flow behavior in a multi-stream plate-fin heat exchanger with a novel design of fractal fins

Plate heat exchangers are widely used in various industries. This study considers using a novel design of fractal shape fins with a new structure on the performance of multi-stream plate-fin heat exchangers for the first time, which has not been studied by researchers before. The numerical study is done with a 3D finite volume method. The effect of using Oil/MWCNT nanofluid and using various configurations of fractal fins with different attack angles ranging from 30 degrees to 100 degrees with the range of Reynolds number of 10,000–40,000, have been studied in the current research. These changing parameters have a significant impact on the flow field and heat transfer in the heat exchanger. The results of this study show that increasing the angle of attack of fractal fins creates more flow deflection and higher fluid mixing. The rise of the Reynolds number creates stronger vortexes as the flow passes over the fins, thereby it can augment the fluid mixing in the areas which are close to the finned. As the Reynolds number rises, the growth of the thermal boundary layer diminished. It can also be seen that as the fluid impacts the fractal fins at higher angles of attack, the temperature distribution becomes more uniform in the heat exchanger. Increasing the Reynolds number from 10,000 to 40,000 increases the heat transfers up to 63 %. At the constant Reynolds numbers, increasing the fraction of solid nanoparticle volume up to 4 % in the cooling fluid augment the heat transfer rate by 48 % compared to the base fluid. Increasing the fluid velocity results the amplification of longitudinal vortex formation. Therefore, the pressure loss is higher at the increased Reynolds numbers. At the lower Reynolds numbers, the pumping power has a weaker dependency on the nanofluids concentration. Increasing the angle of attack of fractal fins increases the pumping power by 50 % compared with the angle of attack of 30 degrees. Increasing the fractal fin angle of attack compared with 30 degrees increases friction by 45–85 %. Changes in the Colburn factor show that considering all parameters that increase heat transfer, the Colburn factor increases by 23–42 % compared with the base scenario with Re = 10,000 and angle of attack = 30 degrees.

Studies on the Enhancement of Heat Transfer in the Counter-Flow Heat Exchanger(HX)- A Review

Studies on the Enhancement of Heat Transfer in the Counter-Flow Heat Exchanger(HX)- A Review

Design optimization of a novel annular fin on a latent heat storage device for building heating

The poor heat transfer performance of the heat exchanger leads to low heat storage efficiency of the latent heat storage device. To improve the heat transfer performance of the heat exchanger, a novel annular fin with inclined angle is proposed to enhance heat transfer of the heat exchanger. 12 fins with different structural parameters are designed and welded to the inner tube wall of the heat exchanger. The simulation model is in good agreement with the literature and the model is considered to be reliable. Based on the enthalpy-porosity model, the liquid fraction, temperature distribution, melting front, energy storage density and heat storage rate were used to compare and optimize the structural parameters of the annular fins. Results demonstrated that the difference in complete melting time due to the number of fins, fin arrangement, fin length and fin angle were 43 min, 85 min, 17 min and 10 min, respectively. The fin arrangement was the most significant in reducing the heat storage time. Compared to N = 4 and uniformly distributed fins, non-uniformly distributed fins reduced the total melting time of stearic acid by 53.13 % and 20.54 %. To be conclusive, the addition of non-uniformly distributed annular fins with 70° inclination enhanced the heat transfer in the heat exchanger and saved a significant amount of heat storage time.

Numerical Simulation on Enhanced Heat Transfer and Flow Characteristics in Direct-Contact Heat Exchanger: A Novel Kenics Static Mixer

In this paper, a novel Kenics static mixer applied in a direct-contact heat exchanger (DCHE) was proposed in order to enhance the heat transfer efficiency. The computational fluid dynamics (CFD) simulation method was adopted to investigate the effect of the continuous phase and dispersed phase on direct-contact heat transfer (DCHT) in the Kenics static mixer. The perforation index (PI) was introduced to depict the performance of the Kenics static mixer, and the effect of different numbers of openings at three initial heat transfer temperature differences (at the inlet of the continuous and dispersed phases) was studied. The simulation results showed that under the same working conditions, a larger initial temperature difference would result in greater differences in the fluid uniformity index (UI), turbulence intensity, and time evolution of a gaseous working substance. The increase of hole numbers and decrease of hole diameters can optimize the DCHT. Under three initial temperature differences, the heat transfer efficiency for the 6-hole and 9-hole Kenics DCHEs was about 20% higher than the Kenics DCHE without holes.

Experimental study of the hydrothermal characteristics of copper tube in the presence of the multi-string and multi-strip magnetic turbulator

Electromagnetic vibration (EMV) is a novel active method to enhance heat transfer in heat exchangers. This method installs a magnetic turbulator vibrating at a specific frequency inside a tube. Recent studies have used a single turbulator inside the tube. This paper is the first exploration of the effect of using multiple turbulator on hydrothermal parameters. In this regard, a turbulator with strip or string geometries with three different arrangements of double, triple, and quadruple turbulators was placed inside the tube to investigate its effect on heat transfer and pressure drop. Experiments were performed for the Reynolds number range from 500 to 1500. The results indicated the significant effect of the geometry and the magnetic turbulator arrangement on hydrothermal parameters. The highest heat transfer and thermal enhancement factor (TEF) were observed in a quadruple strip turbulator. In the presence of this turbulator, heat transfer was up to 3.02 times that of the plain tube, and TEF was 2.01.

Numerical investigation of the heat transfer in a meandering millichannel by a coupled 1D-flow-channel / 3D-surrounding-solid model

Heat exchanger/reactors with corrugated channels are used to implement especially exothermal chemical reactions. Heat conduction effects in their solid material are not negligible and induce in particular heat flows between adjacent channels. In this context, this work proposes a model of a plate-type heat exchanger/reactor with a 2D-meandering millichannel, taking into account these conduction effects by coupling a 1D approach for the channel flow, with correlations for the friction factor and the Nusselt number, to a 3D approach for the solid part. This model is a compromise between the 1D classical reactor models that don’t account for 3D conduction effects in the solid and the 3D simulations of the channel flow with the surrounding solid which are computationnally expensive or unachievable for a large reactor. In the tested case, the 1D/3D and 3D CFD results are in good agreement (5 min vs 4 h computational time), which suggests valid model assumptions and internal model consistency. Simulated and experimental conversion rates of a fast highly exothermic reaction are then compared, showing the relevancy of the model. Further investigations are performed to highlight the effect of conjugate heat transfer in millistructured heat exchangers and to quantify its limitations versus the 1D/3D model.

EXPERIMENTAL ANALYSIS ON ENHANCEMENT OF HEAT TRANSFER IN COMPACT HEAT EXCHANGER USING NANO PARTICLES

This study aims to experimentally investigate the enhancement of heat transfer in a compact heat exchanger (CHE) using nano particles, without considering the Reynolds number effect. In recent years, nanofluids have attracted attention as a promising alternative to traditional heat transfer fluids due to their improved thermal conductivity. The experimental setup consisted of a counter-flow CHE with a nanofluid circulating through the tubes. The nanofluid was prepared by dispersing Aluminium Oxide (Al2O3) and Copper (II) oxide (CuO) nanoparticles into distilled water. The effects of various parameters such as nanoparticle concentration and heat flux on heat transfer enhancement were investigated. Results showed that the addition of nanoparticles significantly increased the heat transfer rate compared to the base fluid. Moreover, the enhancement was found to be more significant at higher concentrations of nanoparticles and heat fluxes. The results also showed that the increase in heat transfer was due to the improved thermal conductivity of the nanofluid. Overall, the study demonstrated that the use of nanofluids in CHEs can significantly improve their performance, making them more efficient and compact for a wide range of industrial applications, even without considering the Reynolds number effect