Counter-flow Double-pipe Heat Research Articles

Experimental investigation of the performance attributes of a double pipe heat exchanger equipped with baffles of conventional or flower layouts

In industrial heat management, the design of baffles within heat exchangers is crucial. They guide fluid flow and enhance turbulence, optimizing heat transfer. Yet, their configuration must be carefully considered to balance thermal efficiency with energy expenditure and pressure management. This research conducts practical tests on the hydrothermal attributes of a counter-flow double-pipe heat exchanger. It evaluates two baffle layouts: segmental and flower, considering baffle cut-off ratio (16.7 %≤δ ≤ 50 %), pitch ratio (8.3 %≤λ ≤ 22.2 %), flower-design relative angle (30°≤γ ≤ 90°), and operating conditions of annulus-side (2660 ≤ Rean ≤ 13110, 5.21 ≤ Pran ≤ 7.48). The findings assure that installing the baffles results in notable increases in both Nu¯an and fan. Besides, lowering baffle cut-off and pitch ratios, and increasing the relative angle of flower baffles lead to additional increases. Moreover, raising the annulus-fluid temperature reduces Nu¯an with a negligible effect on fan. Increasing Rean leads to a reduced fan and greater Nu¯an. Compared with no baffles, the maximum recorded increases in the Nu¯an and fan are 147.4 % and 60.2 %, respectively, realized by incorporating flower layout. On average, the flower baffles boost the Nu¯an by 20.8 % more than those using conventional baffles, with an average increase of 4.3 % in the fan. To judge the benefit of utilizing baffles, the Hydrothermal Performance Index (HTPI) is calculated, and its highest value is recorded as 2.23, attained by running the annular pipe at the lowest flow rate and temperature, with inserting flower baffles (δ = 16.7 %, λ = 8.3 %, γ = 90°). Finally, correlations for Nu¯an, HTPI, and fan prediction are suggested.

CO2-Free Hydrogen Production by Methane Pyrolysis Utilizing a Portion of the Produced Hydrogen for Combustion

Air pollutants such as carbon dioxide and nitrogen oxides emitted by the combustion of fossil fuels have become the subject of increasing concern. Hydrogen has accordingly emerged as a promising low-emission alternative energy source. Among the various methods for hydrogen production, methane pyrolysis, which produces hydrogen without emitting carbon dioxide, has gained substantial attention. This study evaluated the self-sustainability of a new hydrogen production system based on methane pyrolysis, in which a portion of the hydrogen produced is used as combustion fuel rather than relying on catalysts and electrical heating. Coupled heat transfer and one-dimensional reaction simulations employing two plug-flow reactors of a counterflow double-pipe heat exchanger were conducted to investigate the feasibility and efficiency of the proposed system, as well as the influence of flow conditions on hydrogen production. The results confirmed system viability, informed the estimation of hydrogen production rates, and provided methane conversion rate data emphasizing the critical role of low-flow conditions and residence time in system efficiency. Additionally, the production of carbon constituted a significant aspect of system efficiency. These findings indicate that the proposed system can produce environmentally friendly hydrogen, contributing to its potential utilization as a sustainable energy source.

Investigation on the enhancement of heat transfer in counterflow double-pipe heat exchanger using nanofluids

Particles less than 100 nanometers in size are suspended in a base fluid such as water, oil, and ethylene glycol. These nanoparticles are floating in the nanofluid. The purpose of this study is to research the operation of a counter-flowing, double-pipe heat exchanger using two distinct nanofluids as cooling media. Titanium carbide and carbon nanotubes combine to form alkaline water, a basic fluid. The purpose of this research was to assess the performance of a counterflow double-pipe heat exchanger using water with different concentrations of titanium carbide and carbon nanotubes. Alkaline water had a particle volume concentration of 0.06, and its nanofluid-flow rate was 0.03. Using a heat exchanger, water is heated to 65?C while nanofluids are heated to 35?C, both at a constant input velocity. The speed of both fluids is constant. The findings demonstrate that nanofluid outperforms water in heat absorption across a broad range of flow speeds. Heat exchangers benefit from the improved thermal characteristics of nanoscale fluids.

Optimization of ultrasonic-excited double-pipe heat exchanger with machine learning and PSO

Two intelligent optimization methods, artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS), with particle swarm optimization (PSO), were employed in this study to forecast the heat transfer rate, Nusselt number, number of transfer units (NTU), and effectiveness of a double-pipe counter-flow heat exchanger. The experiments are related to hot flow rate (113–257 l/h), hot fluid inlet temperature (40–60 °C), ultrasonic excitation power level (0 or 60 watts), and volume fraction of nanoparticle (0–0.8%). The findings of the ANN, ANFIS, ANN-PSO, and ANFIS-PSO methods were verified through experimental studies. The ANN model, the multilayer perceptron/backpropagation with three different learning algorithms, the Levenberg Marquardt (LM), the scaled conjugate gradient (SCG), the Bayesian regularization algorithm (BR), and the ANFIS model were developed with backpropagation and the optimal hybrid method. Finally, these two models were optimized using the PSO algorithm. The experimental and predicted data were compared, and both models were found to be accurate. The correlation coefficients of both models were greater than 94.84%, with the ANN-PSO model slightly outperforming the ANFIS-PSO model. Also, the maximum amount of MSE is equal to 2.592, which shows the model has good performance in predicting results.

Design Optimization of Counter-Flow Double-Pipe Heat Exchanger Using Hybrid Optimization Algorithm

Double-pipe counter-flow heat exchangers are considered more suitable for heat recovery in the heat transfer industry. Numerous studies have been conducted to develop static tools for optimizing operating parameters of heat exchangers. Using this study, an improved heat exchanger system will be developed. This is frequently used to solve optimization problems and find optimal solutions. The Taguchi method determines the critical factor affecting a specific performance parameter of the heat exchanger by identifying the significant level of the factor affecting that parameter. Gray relational analysis was adopted to determine the gray relational grade to represent the multi-factor optimization model, and the heat exchanger gray relation coefficient target values that were predicted have been achieved using ANN with a back propagation model with the Levenberg–Marquardt drive algorithm. The genetic algorithm improved the accuracy of the gray relational grade by assigning gray relational coefficient values as input to the developed effective parameter. This study also demonstrated significant differences between experimental and estimated values. According to the results, selecting the parameters yielded optimal heat exchanger performance. Using a genetic algorithm to solve a double-pipe heat exchanger with counterflow can produce the most efficient heat exchanger.

Nanofluid as the working fluid of an ultrasonic-assisted double-pipe counter-flow heat exchanger

Nanofluid as the working fluid of an ultrasonic-assisted double-pipe counter-flow heat exchanger

Thermal performance analysis of a counter-flow double-pipe heat exchanger using titanium oxide and zinc oxide nanofluids

In a nanofluid, metals, oxides, or carbides with a diameter of less than 20 nm are combined as one with a base liquid, like water or an oil. Many examinations have recently been completed to inspect the effect of nanofluid on the speed increase of heat transfer rates in various heat exchangers. Heat transfer improvement using nanofluid is dependent on a variety of factors, among them the kind of nanoparticles, their size, shape, and concentration in the base fluid. The proposed article is aimed to study experimentally how a twin-pipe heat exchanger with counter-flow arrangements and two kinds of nanofluid cooling fluid performed. Zinc oxide (ZnO) and titanium oxide (TiO2) are used as base fluids with ethylene glycol (EG) and alkaline water. This study looked at the heat transfer capabilities of a two-pipe heat exchanger with a counter-flow configuration when various quantities of TiO2 and ZnO nanoparticles were combined with EG alkaline water. Alkaline water and nanofluid nanoparticle volume concentrations were 0.5, 0.75, and 1.25. The constant intake temperatures of 60 °C for water and 30 °C for nanofluid in a heat exchanger result in two fluids running at a constant inflow velocity. It was found that nanofluid had higher heat absorption at low flow rates than EG alkaline water and hence improved heat exchanger thermal performance. It was also noticed that when the concentration of nanoparticles increases, the heat transmission rate increases.

Hybrid CFD-ANN approach for evaluation of bio-inspired dolphins dorsal fin turbulators of heat exchanger in turbulent flow

The central aim of the present investigation is to evaluate the effects of bio-inspired Dolphin’s dorsal fin turbulators (DFTs) with a hybrid CFD-ANN approach in a counter flow double pipe heat exchanger. The DFT’s physical model is adapted from the infrared thermal image of a bottlenose dolphin dorsal fin. The effects of different influential parameters, such as the length scale (D) of DFTs including 4, 8, 12 mm and the number of turbulators (N) including 6, 10, and 14 are numerically examined at different Reynolds numbers. Also, using CFD data, the neural network is trained with great accuracy of R2 above 0.999. Important parameters such as Nu, f, Ɛ, NTU can be predicted in different conditions by the ANN method. This method greatly reduces the costs of CFD solutions, which is advantageous. The results indicate that the DFT's streamlined geometry could significantly reduce friction loss by streamlining the fluid flow. Also, colliding the fluid stream with the DFTs improves heat transfer by boundary layer destruction. The UA Ratio (UAR) of the Dolphin’s dorsal fin turbulator heat exchanger (DFTHE) to the simple heat exchanger (SHE) is between 1.02 and 1.74. Also, the ratio of Nu, Ɛ, NTU for the DFTHE to the SHE is equal to 2.48, 1.63, and 1.74, respectively.

Analisis Perpindahan Kalor Pada Double Pipe Heat Exchanger Beraliran Lawan Arah Menggunakan Sirip Trapesium Dengan Fluida Cair

<p><em>This study aims to analyze the counter flow performance of a double pipe heat exchanger using an experimental method with the influence of the flow rate of hot and cold substances. The results showed that the counter-flow double-pipe heat exchanger produced a total heat transfer coefficient of 69.229 W/m2</em><em>℃</em><em>. The double pipe heat exchanger produces Reynolds number of 82.17 and Nusselt number of 1.18 in hot fluids, while in cold fluids it produces Reynolds number of 4.528.42 and Nusselt number of 31.52. The double pipe heat exchanger has an effectiveness rate of 116.16%.</em></p>

Analysis study of nano fluids and longitudinal fins on the heat transfer in the counter flow double pipe heat exchanger

In this paper, the heat transfer enhancement in a counter-flow double pipe heat exchanger with longitudinal rectangular fins on the outer surface of the inner tube was numerically investigated by ANSYS 20.R1 software using CFD package and finite volume method. Hot water flows in the inner tube at 60℃ while cold water flows in the outer tube at 25℃. The flow is laminar with five mass flow rates from 0.012kg/s to 0.02kg/s) for hot side and from 0.01kg/s to 0.03kg/s for cold side. Two types of nanoparticles Al₂O₃ and SiO₂ have been added to produce nanofluids as heat transfer fluid in the external channel (cold fluid flow) with four different concentrations from 0.04% to 1%. Results showed, as the concentration of Nanofluids increased, the heat transfer rate also increased. At 1% concentration, the maximum heat transfer coefficient was belonged to Al₂O₃/water nanofluid by 22.3% enhancement in comparison with distilled water, while the SiO₂/water nanofluid has enhancement of 19% in heat transfer coefficient in comparison with the distilled water. Both nanofluids show higher pressure drop compared with distilled water where the SiO₂/water nanofluid gives a higher drop of (33.2%), while the Al₂O₃/water nanofluid has (32.1%) of the pressure drop.

Modelling and Analysis of Viscoelastic and Nanofluid Effects on the Heat Transfer Characteristics in a Double-Pipe Counter-Flow Heat Exchanger

This study computationally investigates the heat transfer characteristics in a double-pipe counter-flow heat-exchanger. A heated viscoelastic fluid occupies the inner core region, and the outer annulus is filled with a colder Newtonian-Fluid-Based Nanofluid (NFBN). A mathematical model is developed to study the conjugate heat transfer characteristics and heat exchange properties from the hot viscoelastic fluid to the colder NFBN. The mathematical modelling and formulation of the given problem comprises of a system of coupled nonlinear partial differential Equations (PDEs) governing the flow, heat transfer, and stress characteristics. The viscoelastic stress behaviour of the core fluid is modelled via the Giesekus constitutive equations. The mathematical complexity arising from the coupled system of transient and nonlinear PDEs makes them analytically intractable, and hence, a recourse to numerical and computational methodologies is unavoidable. A numerical methodology based on the finite volume methods (FVM) is employed. The FVM algorithms are computationally implemented on the OpenFOAM software platform. The dependence of the field variables, namely the velocity, temperature, pressure, and polymeric stresses on the embedded flow parameters, are explored in detail. In particular, the results illustrate that an increase in the nanoparticle volume-fraction, in the NFBN, leads to enhanced heat-exchange characteristics from the hot core fluid to the colder shell NFBN. Specifically, the results illustrate that the use of NFBN as the coolant fluid leads to enhanced cooling of the hot core-fluid as compared to using an ordinary (nanoparticle free) Newtonian coolant.

Design and analysis of the helium purification system for the NSRRC cryogenic system

Helium is an expensive consumable in cryogenic facilities and is used widely in space, medical and energy research. At NSRRC, liquid helium is used as a coolant for superconducting magnets and SRF cavities . Minor contaminants such as nitrogen, oxygen, moisture and oil will be picked up when liquid helium circulates in large scale cryogenic systems and such contaminants can crystalize and cause damage to the cold box turbo expanders resulting in system damage and failure . Therefore, a helium purification system is designed as an integral part of the cryogenic system to conserve helium by providing 99.9995% pure helium to the liquefier after eliminating contaminants. The NSRRC helium purification process is based on two principles, the first one being a cryo-sorption device using activated charcoal and a molecular sieve and the other being a cryo-condensation unit using a tubular heat exchanger. The purifier has been designed to purify impure helium with overestimated contaminants of as much as 2.5% nitrogen and 2.5% oxygen with a mass flow rate of 475 nm3/hr and delivering a pressure of 17 bar(a) of impure helium to the purifier, the actual impurity will be much lower than the actual design contaminants. In this paper, calculation and design of the helium purification system and components composed of one double pipe counter flow heat exchanger, one vessel and tube heat exchanger, one pre-cooler and one charcoal vessel will be discussed together with charcoal mass requirement calculations and design of other components. In NSRRC, helium is liquefied and is used as a coolant for the SRF system and for cryogenic undulators. During a cryogenic cycle in the cryogenic system, helium may pick up contaminants such as moisture, oxygen, oil, and nitrogen, which have a higher freezing point than liquid helium and will crystalize. These frozen impurities will then affect plant capacity and operation such as alternating flow characteristics, damaging moving parts like turbines in the cold box causing the overall cooling efficiency to drop. Eliminating the contaminants is therefore very important for the cryogenic system.

Performance of a double-pipe heat exchanger with different met-al foam arrangements

This paper contributes to the field of improving the performance of heat exchangers using metal foam (MF) full-filled and partially/periodically-filled within the gap between the two pipes. The effect of configuration and arrangement of copper MF (15PPI and porosity of 0.95) installed on the outer surface of the inner pipe of a counter-flow double-pipe heat exchanger on the thermal and hydraulic performance was studied experimentally. The test section consisted of concentric two pipes; the inner pipe which was made of copper while the outer pipe was a Polyvinyl chlo-ride. Air was used as a working fluid in both hot and cold sides. A wide cold air flow rate range was covered from 3 to 36 m3/h which corresponds to Reynolds number (Re) range from 2811 to 31,335. The hot air flow rate was kept constant at 3m3/h. The temperature difference (ΔT) be-tween the inlet hot air and inlet cold air was adopted to be (20°C, 30°C, 40°C, and 50°C). The re-sults revealed that the higher Nusselt number (Nu) was at ΔT= 50°C and the thermal performance of the heat exchanger with the MF for all the arrangements was greater than the smooth heat exchanger. The highest and lowest friction factor was 1.033 and 0.0833 for the case 1 and 8, re-spectively, and the optimal performance evaluation criteria (PEC) was 1.62 for case 7 at Re = 2800. The Nu would be increased with a moderate increase in the friction factor by optimizing the arrangement of the MF. The two essential parameters that played an important role for in-creasing the PEC were the MF diameter and the MF arrangement along the axial length of the cold air stream.

Numerical Investigation of Hydraulic-Thermal Performance for a Double-Pipe Heat Exchanger Equipped with 45°-Helical Ribs

In this paper, the hydraulic-thermal performance of a double-pipe heat exchanger equipped with 45°-helical ribs is numerically studied. The ribbed double-pipe heat exchanger is modelled using three heights (H = 0, 2.5, 3.75, 5 mm) of 45°-helical ribs. Two numbers (4-ribs and 8-ribs) of 45°-helical ribs are attached on the outer surface of the inner pipe of the counter-flow double-pipe heat exchanger and compared with a smooth double-pipe heat exchanger. Three-Dimensional computational fluid dynamics (CFD) model for a laminar forced annular flow is performed in order to study the characteristics of pressure drop and convective heat transfer. In addition, the influence of rib geometries and hydraulic flow behaviour on the thermal performance is system-atically considered in the evaluations. The annular cold flow is investigated with the range of Reynolds numbers from 100 to 1000, with three heights of ribs at the same width (W = 2 mm) and inclined angles of (θ = 45°).The results illustrate that the average Nusselt number and pressure drop increase with an in-creasing number of ribs, the height of ribs and Reynold number, while the friction factor decreas-es with increasing Reynolds numbers. The percentage of averaged Nusselt number enhancement for three rib heights (H = 2.5, 3.75 and 5 mm) at 4-ribs is (34%, 65% and 71%), respectively, While for 8-ribs the enhancement percentage is (48%, 87% and 133%) as compared with the smooth double-pipe heat exchanger at Re = 100. The best performance evaluation criteria of (PEC) at (8-ribs, and H = 5 mm) is 2.8 at Re = 750. The attached 45-helical ribs in the annulus path can generate kind of secondary flows, which enhance the fluid mixing operation between the hot surface of the annular gap and the cold fluid in the mid of the annulus, which lead to a high-temperature distribution. Increasing the height of 45°-helical ribs lead to an increase in the sur-face area subjecting to convective heat transfer.

An Approximate Transfer Function Model for a Double-Pipe Counter-Flow Heat Exchanger

The transfer functions G(s) for different types of heat exchangers obtained from their partial differential equations usually contain some irrational components which reflect quite well their spatio-temporal dynamic properties. However, such a relatively complex mathematical representation is often not suitable for various practical applications, and some kind of approximation of the original model would be more preferable. In this paper we discuss approximate rational transfer functions G^(s) for a typical thick-walled double-pipe heat exchanger operating in the counter-flow mode. Using the semi-analytical method of lines, we transform the original partial differential equations into a set of ordinary differential equations representing N spatial sections of the exchanger, where each nth section can be described by a simple rational transfer function matrix Gn(s), n=1,2,…,N. Their proper interconnection results in the overall approximation model expressed by a rational transfer function matrix G^(s) of high order. As compared to the previously analyzed approximation model for the double-pipe parallel-flow heat exchanger which took the form of a simple, cascade interconnection of the sections, here we obtain a different connection structure which requires the use of the so-called linear fractional transformation with the Redheffer star product. Based on the resulting rational transfer function matrix G^(s), the frequency and the steady-state responses of the approximate model are compared here with those obtained from the original irrational transfer function model G(s). The presented results show: (a) the advantage of the counter-flow regime over the parallel-flow one; (b) better approximation quality for the transfer function channels with dominating heat conduction effects, as compared to the channels characterized by the transport delay associated with the heat convection.

PERFORMANCE OPTIMIZATION OF COUNTER FLOW DOUBLE PIPE HEAT EXCHANGER USING GREY RELATIONAL ANALYSIS

Among various classifications of the heat exchanger, counter flow double pipe heat exchanger (CF-DPHE) is more suitable for many industrial heat transfer applications. In general, numerous research works are carried out to find optimal operating parameters for heat exchangers. In this study, grey relational analysis (GRA) is used to optimize the heat exchanger system output parameters such as the cold water outlet temperature (t2), the hot water outlet temperature (T2) and the effectiveness (ϵ). Such output parameters are the functions of the mass flow rate of cold fluid (mc), cold water inlet temperature (t1), the mass flow rate of hot fluid (mh), and hot water inlet temperature (T1). The application of this GRA method is capable of increasing counter flow double pipe heat exchanger effectiveness by 12.06%.

Application of experimental data to model local fouling resistances

Fouling is a problem that varies in space and time, but a fouling situation is commonly quantified using the integral thermal fouling resistance based on the integral heat balance and an area-averaged heat transfer assessment. However, current modeling does not take into consideration the local differences, such as constrictions, that can affect the integral fluid dynamic behavior. This work shows experimental and analytical results of local investigations of a fouled counterflow double-pipe heat exchanger. The determined local parameters are used to calculate different local fouling resistances as part of a holistic modeling approach with the aim of modeling and linking local and integral fouling resistances as well as the thermal and the mass based approaches. Therefore, mass based parameters are utilized to recalculate the obtained local thermal fouling resistances as a way to account for the heat transfer increases caused by local surface roughness and/or local constrictions. The aim of this procedure is to explain and eliminate apparent negative fouling resistances on a local basis. The local thermal fouling resistances are determined by measuring the local temperatures and then used for quantification of the local overall heat transfer coefficients. Modeling of the local mass based fouling resistances requires knowledge of the density and thermal conductivity of the local material, as well as the local layer thickness and/or the local fouling mass. The local thermal fouling resistances are recalculated using the local friction coefficients and local flow velocities resulting from local constrictions. All experimental and theoretical approaches are merged into the model presented here for the determination of local fouling resistances.

Influence Of Coiled Wire Presence On The Convective Heat Transfer Coefficients In R-600 Condensers

An experimental investigation has been performed to examine the heat transfer enhancement achieved by helically coiled wire inserts during forced convective condensation of R-600 vapor inside horizontal tubes. The experimental setup is a vapor-compression refrigeration cycle. This system includes a main condenser which is a coaxial double-pipe counter-flow heat exchanger with water as a coolant. To reach the favorable vapor qualities, pre-condenser and after-condenser systems were invoked. Experiments were carried out for plain tube and five different coiled wire inserted tubes. At each test, various parameters were measured like refrigerant mass flow rate, inlet and outlet water temperature of the condenser, refrigerant pressure, etc. Using the acquired data, heat transfer coefficients were calculated for different tubes. Investigation of the results showed that increasing the thickness of the wires can augment the heat transfer rate. Also, it is seen that reducing the coil pitch can enhance the heat transfer rate as high as 31.6%. Also, it was seen that employing coiled wire inserts inside the tube, increases the average heat transfer coefficient up to approximately 80% regarding the plain tube results.

Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2–66.2% and 42.1–68.7% over the Reynolds number ranging 250–1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

Design and analysis of double-pipe heat exchanger with new arrangements of corrugated tubes using honeycomb arrangements

Double-pipe heat exchangers are utilized as a part of mechanical procedure to recuperate heat between two process liquids. The main objective of this project to augment the heat transfer in a counter flow double-pipe heat exchanger filled with inner tube of honeycomb arrangements. To increase the efficiency of double-pipe heat exchanger is made up of concave and convex corrugated type of outer and inner tubes. Hot water (inner tube) and cold water (outer tube) inlet temperatures were maintained at 40°C and 8°C, respectively. Investigation were performed for inward tube (high temperature water) and external tube (cool water) volume flow rate was kept at 15 L per minute and 20 L per minute. Different parameters such as overall heat transfer coefficient, Nusselt number, pressure drop, friction factor, convective heat transfer coefficient, and effectiveness were obtained and compared for new arrangements of corrugated tubes filled with and without honeycomb arrangements. The analysis was carried out for porosity range is 0.8 and pore density (greater than 9 parts per litre) to ensure high effectiveness. Maximum effectiveness was obtained for heat exchanger made of concave corrugated outer tube and convex corrugated inner tube with honeycomb structure. <br><br><font color="red"><b> This article has been corrected. Link to the correction <u><a href="http://dx.doi.org/10.2298/TSCI200331157E">10.2298/TSCI200331157E</a><u></b></font>