Counterflow Double Tube Heat Exchanger Research Articles

Property of water-nanoparticle flow and heat transfer in the double-tube heat exchanger with nanofluid

The three-dimensional numerical simulation is conducted to study the impact of Al2O3/water nanofluid on the flow property and heat transfer of a counter flow double-tube heat exchanger where a laminar flow of cold water is in the outer tube, and in the inner tube there is a turbulent flow of hot nanofluid with particle volume concentrations ranging from 0.05% to 3%. The effects of temperature, flow rate, and particle volume concentration on the property of nanofluid flow and heat transfer are explored. The results show that the friction factor decreases with the increase of temperature and flow rate, and the pressure drop increases with increasing particle volume concentration. The temperature of the nanofluid at the outlet first decreases rapidly with time and then increases gradually to a stable value. Along the flow direction, the temperature of nanofluid decreases slowly at x/D < 10, and the axial temperature gradient increases at the full development stage. At a constant Reynolds number, the lower the temperature or the larger the particle volume concentration, the stronger the heat transfer. The local heat transfer coefficient on the wall of the inner tube decreases rapidly after reaching the peak x/D = 2.3, and then increases slowly until the outlet. The particle number density decreases sharply at x/D < 5, and then slowly decreases, while the change of the geometric mean diameter of particles is just the opposite. Increasing the flow rate or the temperature will strengthen particle coagulation, resulting in the decrease of particle number density and the increase of geometric mean diameter of particles.

Performance investigation of a concentric double tube heat exchanger using twisted tape inserts and nanofluid

A horizontal double-tube counter-flow heat exchanger with and without twisted tape inserts (twist ratio of 3.2, 4, and 6) has been investigated experimentally using TiO2-H2O nanofluid. In this study, the heat transfer coefficient and friction factor of turbulent flow of TiO2-H2O nanofluid have been determined for Reynolds’ number varying from 5,000 to 25,000. Convective heat transfer coefficient for TiO2-H2O nanofluid (0.05% by vol.) is found to be higher than base fluid (4–6%). Also, an increase in the heat transfer coefficients up to 6%, 10.9%, 17.4%, and 23.4% are observed numerically for the 0.05%, 1%, 2%, and 3% volume concertation of nanoparticles of TiO2. On the other hand, when TiO2-H2O nanofluid (0.05% by vol.) is investigated using twisted tape inserts of twist ratio 3.2, the heat transfer coefficient is found to be increasing by 45%. The variation of the heat transfer coefficient for different types of nanofluids such as; TiO2-H2O, Al2O3-H2O, and CuO-H2O with 1% concentration of nanoparticles (by vol.) has also been studied at different Reynolds’ numbers. The simulated results show no significant effect of the size (30 nm and 50 nm) of nanoparticles (TiO2) on the heat transfer coefficient values of TiO2-H2O nanofluid at 0.05% volume concentration.

Experimental Validation of ANSYS CFX for Transient Flows With Heat Transfer in a Tubular Heat Exchanger

Abstract Within the European SESAME project, extensive experimental work was performed and complemented by the development, application, and validation activities of thermal-hydraulic simulation tools for different scales. The TALL-3D experimental facility, operated by KTH Royal Institute of Technology in Stockholm, is designed for thermal-hydraulic experiments with lead-bismuth eutectic (LBE) coolant at natural and forced circulation conditions. The heat generated in the primary TALL-3D circuit is transferred via a double-tube counter-flow heat exchanger (HX) to the secondary side, which is cooled by glycerol oil. Validation calculations with the coupled simulation code ATHLET-ANSYS CFX within the European THINS project showed that one of the major challenges for this one-dimensional–three-dimensional (1D–3D) simulation of the experimental facility lies in the calculation of the HX with ATHLET. This is due to the fact that glycerol oil properties are not yet available for ATHLET. In order to better understand the flow and heat transfer phenomena inside the HX, 3D stand-alone calculations with ANSYS CFX were carried out for the SESAME experiment TG03.S301.03. The data generated in this experimental run is challenging for validation of computational fluid dynamics (CFD) codes, because the test combines heat transfer between buoyancy-driven LBE flow in the primary circuit and a turbulent oil flow in the secondary TALL-3D side. Moreover, the validation gets even more difficult for the CFD approach due to the fact that both coolants are nonunity Prandtl fluids, and this requires a careful modeling of the turbulent heat flux. In this paper, the TALL-3D HX behavior during test TG03.S301.03 is analyzed, and the results of the ANSYS CFX calculations are compared with measurements.

Heat transfer performance and friction factor of various nanofluids in a double-tube counter flow heat exchanger

Experimental research was conducted to reveal the effects of nanofluids on heat transfer performance in a double-tube heat exchanger. With nanoparticle weight fraction of 0.5-2.0% and Reynolds number of 4500-14500, the flow resistance and heat transfer were analyzed by using six nanofluids, i.e., CuO-water, Al2O3-water, Fe3O4-water, ZnO-water, SiC-water, SiO2-water nanofluids. Results show that SiC-water nanofluid with a weight concentration of 1.5% provides the best improvement of heat transfer performance. 1.0% CuO-water and 0.5% SiO2-water nanofluids have lower friction factors in the range of Reynolds number from 4500-14500 compared to the other nanofluids. Based on test results of heat transfer performance and flow resistance, the 1.0% CuO-water nanofluid shows a great advantage due to a relatively high heat transfer performance and a low friction factor. Finally, empirical formulae of Nusselt numbers for various nanofluids were established based on experimental data tested in the double-tube heat exchanger.

Experimental analyses on heat transfer performance of TiO2–water nanofluid in double-pipe counter-flow heat exchanger for various flow regimes

Nanofluids are widely used in heat transfer applications. This article presents the effect of heat transfer and pressure drop of the TiO2–water nanofluids flowing in a double-tube counter-flow heat exchanger with various flow patterns. In this experimental work, performance of TiO2–water nanofluid on heat transfer in three different cases such as laminar, transition and turbulent flow region were analyzed. TiO2 nanoparticles with average diameters of 20 nm dispersed in water with three volume concentrations of 0.1, 0.3 and 0.5 vol% were used as the test fluid. The results show that the heat transfer of nanofluids is higher than that of the base liquid (water) and increased with the increase in Reynolds number and particle concentrations. The heat transfer rate of nanofluid with 0.5 vol% was 25% greater than that of base liquid, and the results also show that the heat transfer coefficient of the nanofluids at a volume concentration of 0.5 vol% was 15% higher than that of base fluid at given conditions. Pressure drop of nanofluid was increased with increase in volume concentration, and it is slightly higher than that of the base fluid.

Estimation of Heat Transfer Coefficient and Thermal Performance Factor of TiO2-water Nanofluid Using Different Thermal Conductivity Models

Background: Enhancement of heat transfer rate is one of the most important aims in industrial applications. The conventional fluids including oil, water and ethylene glycol have poor thermal properties compared to those of most solids. With this information, it leads to the idea that, if we disperse very small particles and let them suspend stably in base fluids, thermal conductivities of that base fluids should be higher. In previous study of the authors, the effects of different thermal conductivity models on heat transfer and pressure drop of nanofluids were not carried out. In view of that consequence, this article is aimed at reporting the effect of different thermal conductivity models on the prediction of convective heat transfer coefficient and thermal performance factor of nanofluids experimentally. Method: An experimental study was performed for TiO2 -water nanofluid with a volume fraction between 0.002 and 0.02 and Reynolds number (Re) from 8,000 to 51,000. The experimental apparatus is a horizontal double tube counter-flow heat exchanger. Results: It shows that by growing the Re or nanoparticle volume fraction value, the Nusselt number enhances for all models studied. All equations used to calculate the thermal conductivity of nanofluid show same trends regarding the Nusselt number when Re or nanoparticle volume concentration changes. Some models could show more variation or low changes in the Nusselt number when the Re or nanoparticle volume concentration changes, however. Meanwhile, all nanofluids have a higher Nusselt number compared to distilled water. Conclusion: The nanofluid Nusselt number significantly enhances with growing Re and volume concentration for all thermal conductivity models studied in this work. By applying the nanofluid at a 0.02 nanoparticle volume fraction and Re equal to 47,000, the maximum thermal performance factor of 1.86 is found, based on Yu and Choi's and Jang and Choi's models. At low Re, all models show approximately same Nusselt numbers for all nanoparticle volume concentration. For moderate and high Re, the difference between the Nusselt numbers calculated by different models enhances. The thermal performance factor is higher than the unity for all Re and all volume concentration in this study, based on every thermal conductivity model. Keywords: TiO2-water nanofluid, thermal conductivity model, Nusselt number, thermal performance factor, turbulent flow, counter-flow heat exchanger.

Experimental study on the heat transfer and flow properties of γ-Al2O3/water nanofluid in a double-tube heat exchanger

Double-tube heat exchanger is primarily adapted to high-temperature, high-pressure applications due to their relatively small diameters. An experimental study performed to investigate the effects of Al2O3/water nanofluid on the hydrodynamics and convective heat transfer of a counter flow double-tube heat exchanger. The nanofluid was used as hot fluid and passed through the inner tube of the heat exchanger considering fully developed turbulent flow regime. Experiments were conducted at the nanofluid flow rates of 7, 9, and 11 L min−1, nanofluid inlet temperatures of 45, 55, and 65 °C, and dilute nanoparticle concentrations of 0.05 and 0.15 vol%. Local convective heat transfer coefficient in double-tube heat exchanger has been measured experimentally for the first time. Results showed that nanofluids had higher Nusselt number than pure water. Also, the Nusselt number increased by increasing particles volume fraction, flow rate as well as temperature of nanofluid. However, increasing the convective heat transfer coefficient of the nanofluids was not sensible with increasing the concentration. In addition, the ratio of the heat transfer coefficient of nanofluid to that of the base fluid decreased by increasing Reynolds number. Adding γ-Al2O3 nanoparticles to the base fluid increased the friction factor. In this study, the greatest enhancement in the heat transfer coefficient and the friction factor obtained at 0.15 vol% concentration of nanoparticles which were 23 and 25 %, respectively.

Experimental study of Cu–water nanofluid heat transfer and pressure drop in a horizontal double-tube heat exchanger

This article reports an experimental study on the performance of horizontal double tube counter-flow heat exchanger. Due to the modicum in the heat transfer surface area, the overall heat transfer coefficient is enhanced. Cu-nanoparticles are added to the cold water in the annulus of the heat exchanger, however, the inner tube that contains the hot water is rotated. The inner tube is made of copper with 25.4mm outer diameter with a thickness of 2mm, while the outer tube, which is made of transparent Acrylic Plexiglass, has an outer diameter of 76.2mm and 5mm thickness. Cu–water nanofluid is prepared at volume fractions of 1–3% and the inner tube is rotated with speed from 0 to 500rpm. Results demonstrated a remarkable enhancement in the rate of heat transfer due to the nanoparticles addition as well as the inner tube rotation. Consequently, the effectiveness and the transfer number units (NTU) of the heat exchanger are augmented. Optimization between heat transfer augmentation and the pressure drop penalty is carried out. Finally, the use of the nanofluid has a little penalty in pressure drop in compared with the inner tube rotation.

Experimental study of the effect of solid volume fraction and Reynolds number on heat transfer coefficient and pressure drop of CuO–Water nanofluid

This study presents an experimental study of the effect of solid volume fraction and Reynolds number on heat transfer coefficient and pressure drop of CuO–Water nanofluid. Pure Water and nanofluid with particle volume fractions of 0.0625%, 0.125%, 0.25%, 0.5%, 1%, 1.5% and 2% are used as working fluids. Nanofluids were flowed inside a horizontal double-tube counter flow heat exchanger under turbulent flow regime. Flow Reynolds numbers of each volume fraction of nanofluid were between from 2900 to 18,500 during the experiments. The Result shows that generally heat transfer coefficient of nanofluids is higher than that of base fluid. Moreover, it is observed that heat transfer coefficient and Nusselt number of nanofluids increases with an increase in solid volume fraction and Reynolds number. But the rate of this increase in low Reynolds numbers was more than that at high Reynolds numbers. The measurements also show that the pressure drop of nanofluid is slightly higher than that of the base fluid and increases with an increase in the nanoparticles volume fraction. But the rate of this increase in low Reynolds numbers was more than that at high Reynolds numbers. Therefore, it can be concluded that the effect of increasing percentage of nanoparticle in low Reynolds number of this research is stronger than that of high Reynolds number. Moreover, friction factors were calculated and compared with blasious correlation. Finally, in order to find the optimum condition of this nanofluid for practical applications, thermal performance factor was defined to consider increasing Nusselt ratio besides increasing friction ratio simultaneously. The results show that the maximum thermal performance factor of this nanofluid was 1.266, which was calculated for 2% nanoparticle volume fraction at Reynolds number 3677.

The black box model of a double-tube counter-flow heat exchanger

Variable working conditions of a double-tube counter-flow heat exchanger were analysed. During operation of the heat exchanger, the parameters (temperatures and mass flow rates) of both fluids at its inlet change, which leads to a change in its performance. Heat transfer effectiveness is commonly used to assess the heat exchanger performance, defined as the ratio of the actual to the maximum heat flow rate. In the present paper, the heat exchanger was considered to be a ‘black box’, and the aim was to investigate how the inlet parameters (temperatures and mass flow rates of both fluids) affect the outlet ones (temperatures of both fluids), and thus to attempt to introduce a new relation for the heat transfer effectiveness of a counter-flow heat exchanger as a function of only inlet parameters. Following the analysis, a relation for the heat transfer effectiveness as a function of inlet parameters with five constant coefficients was obtained. These coefficients depend on the heat exchanger geometry and on the properties of the heat transfer fluids; they are not general-purpose, but specific to a counter-flow heat exchanger. The form of the proposed relation for the heat transfer effectiveness of a counter-flow heat exchanger is not satisfactory as it involves five constant coefficients; therefore, a new approach was chosen, consisting in analysing a parameter defined as the ratio of the minimum to the actual arithmetic mean temperature difference. Using the parameter defined in this way, the relation for the heat transfer effectiveness of a counter-flow heat exchanger was obtained as a function of two parameters: the ratio of the heat capacity rates of both fluids, and NTU, with no constant coefficients. The proposed relations were verified against the data produced by a simulator of a double-tube counter-flow heat exchanger.

Experimental investigation of diameter effect on heat transfer performance and pressure drop of TiO2–water nanofluid

In this paper, an experimental study performed to investigate the convection heat transfer characteristics in fully developed turbulent flow of TiO2–water nanofluid. The effect of mean diameter of nanoparticles on the convective heat transfer and pressure drop studied at nanoparticle volume concentration from 0.01 to 0.02 by volume. The experimental apparatus is a horizontal double tube counter-flow heat exchanger. The nanoparticles of TiO2 with diameters of 10, 20, 30 and 50nm dispersed in distilled water as base fluid. The results indicated higher Nusselt number for all nanofluids compared to the base fluid. It is seen that the Nusselt number does not increase by decreasing the diameter of nanoparticles generally. In this study both Nusselt number and pressure drop were considered in definition of thermal performance factor. The results show that nanofluid with 20nm particle size diameter has the highest thermal performance factor in the range of Reynolds number and volume concentrations were studied.

Experimental study on the effect of TiO2–water nanofluid on heat transfer and pressure drop

An experimental study performed to investigate the effect of nanoparticle volume fraction on the convection heat transfer characteristics and pressure drop of TiO2 (30nm)–water nanofluids with nanoparticle volume fraction between 0.002 and 0.02, and Reynolds number between 8000 and 51,000. The experimental apparatus is a horizontal double tube counter-flow heat exchanger. It is observed that by increasing the Reynolds number or nanoparticle volume fraction, the Nusselt number increases. Meanwhile all nanofluids have a higher Nusselt number compared to distilled water. By use the nanofluid at high Reynolds number (say greater than 30,000) more power compared to low Reynolds number needed to compensate the pressure drop of nanofluid, while increments in the Nusselt number for all Reynolds numbers are approximately equal. Therefore using nanofluids at high Reynolds numbers compared with low Reynolds numbers, have lower benefits.

Performance Evaluation of AI2O3/Water Nanofluid as Coolant in a Double-Tube Heat Exchanger Flowing under a Turbulent Flow Regime

Nanofluids are expected to be a promising coolant candidate in chemical processes for water waste remediation and heat transfer system size reduction. This paper focuses on the potential mass flowrate reduction in exchanger with a given heat exchange capacity using nanofluids. Al2O3 nanoparticles with diameters of 7 nm dispersed in water with volume concentrations up to 2% are selected as a coolant, and their performance in a horizontal double-tube counterflow heat exchanger under turbulent flow conditions is numerically studied. The results show that the flowrate of nanofluid coolant decreases with the increase of concentration of nanoparticles in the exchanger with a given heat exchange capacity. The mass flowrate of the nanofluid at a volume concentration of 2 vol.% is approximately 24.5% lower than that of pure water (base fluid) for given conditions. For the pressure drop, the results show that the pressure drop of nanofluid is slightly higher than water and increases with increase of volume concentrations. In addition, the reduction of wall temperature and heat transfer area is estimated.

An experimental investigation of thermo-physical properties and heat transfer performance of Al2O3-Aviation Turbine Fuel nanofluids

Aviation Turbine Fuel (ATF)-Al2O3 nanofluids are investigated for better heat transfer performance in a potential application of regeneratively cooled semi-cryogenic rocket engine thrust chambers. The volume concentration of Al2O3 nanoparticles is varied between 0 and 1%. To ensure a realistic evaluation, all properties of the nanofluids are experimentally measured rather than resorting to available formulae or empirical correlations. Among the thermo-physical properties, thermal conductivity and specific heat are measured separately using experimental set-ups fabricated in-house whereas the viscosity is determined using a commercial viscometer. The heat transfer coefficient is determined using a horizontal double tube counter-flow heat exchanger under turbulent flow conditions. At 1% particle volume concentration, the enhancement in the thermal conductivity is 40%, whereas the viscosity increases by 38%. The measured specific heats of the nanofluids do not exhibit appreciable difference within the range of the particle volume concentrations investigated. The heat transfer coefficient increases by 30% at 1% particle volume concentration and correspondingly leads to an enhancement of 10% in the Nusselt number. For the same value of pressure drop, the heat transfer performances of nanofluids are compared with those of ATF. The experimental results show that the maximum enhancement in the heat transfer coefficient observed for the same pressure drop is 28% and even the least enhancement obtained is 2%.

Numerical investigation on the single phase forced convection heat transfer characteristics of TiO 2 nanofluids in a double-tube counter flow heat exchanger

In this study, forced convection flows of nanofluids consisting of water with TiO 2 and Al 2O 3 nanoparticles in a horizontal tube with constant wall temperature are investigated numerically. The horizontal test section is modeled and solved using a CFD program. Palm et al.'s correlations are used to determine the nanofluid properties. A single-phase model having two-dimensional equations is employed with either constant or temperature dependent properties to study the hydrodynamics and thermal behaviors of the nanofluid flow. The numerical investigation is performed for a constant particle size of Al 2O 3 as a case study after the validation of its model by means of the experimental data of Duangthongsuk and Wongwises with TiO 2 nanoparticles. The velocity and temperature vectors are presented in the entrance and fully developed region. The variations of the fluid temperature, local heat transfer coefficient and pressure drop along tube length are shown in the paper. Effects of nanoparticles concentration and Reynolds number on the wall shear stress, Nusselt number, heat transfer coefficient and pressure drop are presented. Numerical results show the heat transfer enhancement due to presence of the nanoparticles in the fluid in accordance with the results of the experimental study used for the validation process of the numerical model.

Experimental investigation of twisted tape inserts performance on condensation heat transfer enhancement and pressure drop

A comprehensive experimental investigation is conducted on the augmentation of heat transfer coefficients and pressure drop during condensation of HFC-134a in a horizontal tube at the presence of different twisted tape inserts. The test section is a 1.04 m long double-tube counter-flow heat exchanger. The refrigerant flows in the inner copper and the cooling water flows in annulus. The experiments are performed for a plain tube and four tubes with twisted tapes inserts of 6, 9, 12 and 15 twist ratios. The pressure drop is directly measured by a differential pressure transducer. It is found that the twisted tape with twist ratio of 6 gives the highest enhancement in the heat transfer coefficient and the maximum pressure drop compared to the plain tube on a nominal area basis. For this case the enhancement in heat transfer and the pressure drop are increased by 40 and 240% in comparison with to the plain tube. It is observed that the twisted tape with the twist ratio of 9 has the best performance enhancing the heat transfer with the minimum pressure drop. Also empirical correlations are developed to predict smooth tube and swirl flow pressure drop. Predicted results are compared to experimental data and it is found that these correlations are reliable for pressure drop estimation.

An experimental study on the heat transfer performance and pressure drop of TiO 2-water nanofluids flowing under a turbulent flow regime

Nanofluid is a new class of heat transfer fluids engineered by dispersing metallic or non-metallic nanoparticles with a typical size of less than 100 nm in the conventional heat transfer fluids. Their use remarkably augments the heat transfer potential of the base liquids. This article presents the heat transfer coefficient and friction factor of the TiO 2-water nanofluids flowing in a horizontal double tube counter-flow heat exchanger under turbulent flow conditions, experimentally. TiO 2 nanoparticles with diameters of 21 nm dispersed in water with volume concentrations of 0.2–2 vol.% are used as the test fluid. The results show that the heat transfer coefficient of nanofluid is higher than that of the base liquid and increased with increasing the Reynolds number and particle concentrations. The heat transfer coefficient of nanofluids was approximately 26% greater than that of pure vol.%, and the results also show that the heat transfer coefficient of the nanofluids at a volume concentration of 2.0 vol.% was approximately 14% lower than that of base fluids for given conditions. For the pressure drop, the results show that the pressure drop of nanofluids was slightly higher than the base fluid and increases with increasing the volume concentrations. Finally, the new correlations were proposed for predicting the Nusselt number and friction factor of the nanofluids, especially.

Heat transfer enhancement and pressure drop characteristics of TiO 2–water nanofluid in a double-tube counter flow heat exchanger

This article reports an experimental study on the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and 0.2 vol.% TiO 2 nanoparticles. The heat transfer coefficient and friction factor of the TiO 2–water nanofluid flowing in a horizontal double-tube counter flow heat exchanger under turbulent flow conditions are investigated. The Degussa P25 TiO 2 nanoparticles of about 21 nm diameter are used in the present study. The results show that the convective heat transfer coefficient of nanofluid is slightly higher than that of the base liquid by about 6–11%. The heat transfer coefficient of the nanofluid increases with an increase in the mass flow rate of the hot water and nanofluid, and increases with a decrease in the nanofluid temperature, and the temperature of the heating fluid has no significant effect on the heat transfer coefficient of the nanofluid. It is also seen that the Gnielinski equation failed to predict the heat transfer coefficient of the nanofluid. Finally, the use of the nanofluid has a little penalty in pressure drop.

Effect of thermophysical properties models on the predicting of the convective heat transfer coefficient for low concentration nanofluid

The term of nanofluid refers to a solid–liquid mixture with a continuous phase which is a nanometer sized nanoparticle dispersed in conventional base fluids. In order to study the heat transfer behavior of the nanofluids, precise values of thermal and physical properties such as specific heat, viscosity and thermal conductivity of the nanofluids are required. There are a few well-known correlations for predicting the thermal and physical properties of nanofluids which are often cited by researchers to calculate the convective heat transfer behaviors of the nanofluids. Each researcher has used different models of the thermophysical properties in their works. This article aims to summarize the various models for predicting the thermophysical properties of nanofluids which have been commonly cited by a number of researchers and use them to calculate the experimental convective heat transfer coefficient of the nanofluid flowing in a double-tube counter flow heat exchanger. The effects of these models on the predicted value of the convective heat transfer of nanofluid with low nanoparticle concentration are discussed in detail.

Effect of EHD on heat transfer enhancement during two-phase condensation of R-134a at high mass flux in a horizontal smooth tube

In this study, effect of electrohydrodynamic (EHD) on the condensation heat transfer enhancement and pressure drop of pure R-134a are experimentally investigated. The test section is a 2.5 m long counterflow double tube heat exchanger with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is made from smooth horizontal copper tubing of 9.52 mm outer diameter. The electrode is made from stainless steel wire of 1.47 mm diameter. The test runs are performed at average saturated temperatures ranging between 40 and 60°C, mass flux ranging between 200 and 600 kg/m2 s, heat flux ranging between 10 and 20 kW/m2 and applied voltage at 2.5 kV. For the presence of the electrode, the experimental results indicate that the maximum heat transfer enhancement ratio is around 30% while the maximum increase in pressure drop is about 25%.