Flow Double-pipe Heat Exchanger Research Articles

Experimental and numerical investigation of heat transfer and flow of water-based graphene oxide nanofluid in a double pipe heat exchanger using different artificial neural network models

In this study, a water-based graphene oxide nanofluid was utilized in a counter-current flow double pipe heat exchanger (DPHE). The inner pipe carried the hot fluid (deionized water-based fluid). In the outer pipe, the cold fluid was flown, in which the experiments were performed once for deionized water-based fluid and once for graphene oxide nanofluid. These experiments were conducted at various inlet hot fluid temperatures of 35, 45, and 55 °C, volumetric concentrations of 0.01, 0.055, and 0.1% for nanofluid, and cold fluid flow rates of 14.4, 18.9, and 23.4 ml/s to evaluate the thermohydraulics of the DPHE. The results demonstrated that an increase in the flow rate and concentration of nanoparticles led to an improvement in the heat transfer coefficient (HTC) . It is also observed that inlet hot fluid temperature had a negligible effect on this coefficient compared to the concentration and flow rate. Additionally, the results showed that the friction factor and pressure drop of nanofluid were higher than those of the basefluid and their values were increased by increasing the concentration. The maximum increase compared to the basefluid was 72% for the friction factor and 111%, for the pressure drop. Besides, radial basis function neural network (RBFNN) and multi-layer perceptron neural network (MLPNN) models were designed for estimating the HTC. Both models accurately predicted the coefficient, but the RBFNN model exhibited higher accuracy than the MLPNN model. The results further indicated that the nanofluid outperformed the basefluid in terms of HTC. Due to the exceptionally high thermal conductivity of graphene nanoparticles, the HTC of the nanofluid was improved by up to 85% compared to the basefluid. The optimum value of HTC was achieved at a temperature of 55 °C, a volume concentration of 0.1%, and a flow rate of 23.4 ml/s.

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.

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.

Experimental and CFD Analysis of GW70 based Cu Nanofluids in a Parallel Flow Heat Exchanger

The Nusselt number, overall heat transfer, and convective heat transfer coefficients of glycerol-water-based Cu nanofluids flowing in a parallel flow double pipe heat exchanger are estimated using CFD analysis. Single-phase fluid approach technique is used in the analysis. Ansys 19.0 workbench was used to create the heat exchanger model. Heat transfer tests with nanofluids at three flow rates (680<Re<1900) are carried out in a laminar developing flow zone. For testing, a 500 mm long concentric double pipe heat exchanger with tube dimensions of ID=10.2 mm, OD= 12.7 mm, and annulus dimensions of ID=17.0 mm, OD= 19.5 mm is employed. Copper is utilized for the tube and annulus material. This study employed three-particle volume concentrations of 0.2 percent, 0.6 percent, and 1.0 percent. The mass flow rates of hot water in the tube are 0.2, 0.017, and 0.0085 kg/s, while the mass flow rates of nanofluids in the annulus are 0.03, 0.0255, and 0.017 kg/s. The average temperature of nanofluids is 36°C, whereas hot water is 58°C. In comparison to base liquid, the overall heat transfer coefficient and convective HTC of 1.0 percent copper nanofluids at 0.03 kg/s are raised by 26.2 and 46.2 percent, respectively. The experimental findings are compared to CFD values, and they are in close agreement.

Experimental and Mathematical Research of Convection Heat Transfer for a High Integral Finned Tube Heat Exchanger

This research exhibits an experimental and numerical investigation for the characteristics of heat transfer by utilizing an integral and smooth high finned tube and shows how the integral high fins affect in improving the transfer of heat. In the experimental work, the experimental rig consists of a cold water loop, a hot air loop and the trial part which is a concentric parallel flow double pipe heat exchanger. The first test smooth tube made of brass has external and internal diameter (32 mm) and (22 mm), respectively, the second test section made of the same material has external fins, the third test section possesses internal fins, and the fourth test section has internal and external fins. The dimensions of the fin are (2 mm) in thickness, (2 mm) in height and pitch (2.5 mm) center to center. And, the water flow rates are (6, 8, 10, 12 and 14 L/min). The inlet water to the trial tube was at temperatures (15, 25, 35, and 45oC). The investigational results manifested that the air side heat transfer coefficient of the smooth tube was lesser than the integral high finned tube. The ratio of improvement when using the integral high finned tube was (47.5%, 60.5% and 67.5 %). Numerical simulation was applied on the current heat exchanger to study both the transfer of heat and the field of flow by using ANSYS, FLUENT15 package. Steady state, Newtonian flow, incompressible and three dimensional analyses were assumed. The comparison between experimental work and numerical results elucidated a good agreement.

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%.

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>

Effect of Al2O3/water nanofluid on heat transfer of turbulent flow in the inner pipe of a double-pipe heat exchanger

In this paper, an experimental study was carried out in order to investigate the effects of Al2O3/water nanofluid with a mean diameter of 50 nm on heat transfer performance in a counter flow double-pipe heat exchanger. The nanofluid was used as cold side fluid and passed through the inner pipe of the double-pipe heat exchanger considering fully developed turbulent flow regime with different Reynolds numbers ranging from 20,000 to 60,000. Experiments were conducted in various cold side fluid flow rates ranging from 1.1 to 3.9 m3/h, inlet temperatures of 40 °C and 50 °C at cold side, and Al2O3/water nanofluids of 0.25% and 0.5% nanoparticles volume concentration. Results indicate that the Nusselt number increases with increasing nanoparticles volume concentration and Reynolds number but decreases with the inlet temperature at cold side of double-pipe heat exchanger. The maximum increase of Nu are respectively 23.2% and 32.23% for inlet temperature of 40 °C and 50 °C. In addition, the single-phase model in CFD (Computational Fluid Dynamics) is adopted to simulate the heat transfer performance by ANSYS Fluent commercial software. It is found that the simulated results show a good agreement with the experimental results and results derived from Gnielinski correlation. The maximum error between experimental Nusselt numbers and simulated results are found to be 12.8%. It is concluded that the CFD approach gives good prediction for heat transfer performance in a double-pipe heat exchanger using Al2O3/water nanofluids.

Effect of surface roughness on the performance of heat exchanger

In this research work, double-pipe counter flow heat exchanger has been analyzed with various roughnesses of steel, aluminum and copper pipes and also with two different cold fluids: water and ammonia at same flow rates. Dimensions of the heat exchanger are inner and outer diameters of inner pipe being 0.034 and 0.042 m, whereas diameters of outer pipe are 0.054 and 0.06 m, respectively, and length of heat exchanger is 1.8 m. In K-ℇ modeling, computational fluid dynamics tool has been used for performance analyses and this computational work has been validated by entropy, exergy and entransy analyses. After computational numerical analyses, this investigation has concluded that maximum rate of heat transfer through heat exchanger has been found with copper–ammonia combination with smooth surface. Minimum rates of entropy generation, exergy destruction, entransy dissipation-based thermal resistance and entransy dissipation number have been obtained with copper–water combination, and minimum entropy generation number and maximum effectiveness have been obtained with copper–ammonia combination. Percentage changes in the parameters/properties have also been calculated at different operating conditions. Copper as inner pipe material with smooth surface and ammonia as cold fluid have been recommended for counter flow double-pipe heat exchanger. Computer software has been developed for hassle-free analyses of heat exchanger.

Investigation of turbulent heat transfer and nanofluid flow in a double pipe heat exchanger

In present study, heat transfer and turbulent flow of water/alumina nanofluid in a parallel as well as counter flow double pipe heat exchanger have been investigated. The governing equations have been solved using an in-house FORTRAN code, based on finite volume method. Single-phase and standard k-ε models have been used for nanofluid and turbulent modeling, respectively. The internal fluid has been considered as hot fluid (nanofluid) and the external fluid, cold fluid (base fluid). The effects of nanoparticles volume fraction, flow direction and Reynolds number on base fluid, nanofluid and wall temperatures, thermal efficiency, Nusselt number and convection heat transfer coefficient have been studied. The results indicated that increasing the nanoparticles volume fraction or Reynolds number causes enhancement of Nusselt number and convection heat transfer coefficient. Maximum rate of average Nusselt number and thermal efficiency enhancement are 32.7% and 30%, respectively. Also, by nanoparticles volume fraction increment, the outlet temperature of fluid and wall temperature increase. Study the minimum temperature in the solid wall of heat exchangers, it can be observed that the minimum temperature in counter flow has significantly reduced, compared to parallel flow. However, by increasing Reynolds number, the slope of thermal efficiency enhancement of heat exchanger gradually tends to a constant amount. This behavior is more obvious in parallel flow heat exchangers. Therefore, using of counter flow heat exchangers is recommended in higher Reynolds numbers.

Numerical Study of Heat Transfer Enhancement in Heat Exchanger Using AL2O3 Nanofluids

In this study, the flow and heat transfer characteristics of Al2O3-water nanofluids for a range of the Reynolds number of 3000, 4500, 6000 and 7500 with a range of volume concentration of 1%, 2%, 3% and 4% are studied numerically. The test rig consists of cold liquid loop, hot liquid loop and the test section which is counter flow double pipe heat exchanger with 1m length. The inner tube is made of smooth copper with diameter of 15mm. The outer tube is made of smooth copper with diameter of 50mm. The hot liquid flows through the outer tube and the cold liquid (or nanofluid) flow through the inner tube. The boundary condition of this study is thermally insulated the outer wall with uniform velocity at (0.2, 0.3, 0.4 and 0.5 m/s) at the cold loop and constant velocity at (0.5 m/s) at the hot loop.&#x0D; The results show that the heat transfer coefficient and Nusselt number increased by increasing Reynolds number and particle concentration. Numerical results indicate that the maximum enhancement in Nusselt number and heat transfer coefficient were 9.5% and 13.5% respectively at Reynolds number of 7100 and particles volume fraction of 4%. Results of nanofluids also showed a good agreement with the available empirical correlation at particles volume fractions of 1%, 2% and 3%, but at volume fractions of 4% a slight deviation is obtained.&#x0D;

Experimental Investigation of Relative Performance of Water Based TiO2 and ZnO Nanofluids in a Double Pipe Heat Exchanger

This paper deals with experimental determination of convective heat transfer coefficient in a counter flow double pipe heat exchanger using water based TiO ZnO nanofluids with 0.002% & 0.004% volume concentrations. Experiments are 2, conducted at various Reynolds numbers ranging from 1600 to 6100. From the experimental results it is found that heat transfer coefficient increases with increase of volume concentration of nanoparticles as well as Reynolds number. Enhancement of heat transfer coefficient between nanofluids with 0.002% volume concentration of TiO ZnO and the 2, inner walls of copper tube in a double pipe heat exchanger increased up to 30.37% and 57.31% respectively. The enhancements are as high as 66.12% and 78.30% when the volume concentration is 0.004% of TiO and ZnO 2 respectively for same set of operating conditions when compared to pure water at Reynolds number 6100. The experimental results are presented in graphical form. The variation of heat transfer coefficient in both dimensional and non-dimensional form are presented as a function of Reynolds number for different volume concentrations of nanofluids. The effectiveness of heat exchanger is also presented as a function of volume concentration of nanofluids.

Aqueous Al2O3 nanofluids: the important factors impacting convective heat transfer

A high accuracy, counter flow double pipe heat exchanger system is designed for the measurement of convective heat transfer coefficients with different nanofluids. Both positive and negative enhancement of convective heat transfer of alumina nanofluids are found in the experiments. A modified equation was proposed to explain above phenomena through the physic properties of nanofluids such as thermal conductivity, special heat capacity and viscosity.

Simulation Study for Heat Transfer Performance of Spiral Flow Double-Pipe Heat Exchanger

In this article, simulation analysis has been performed for the flow and heat transfer performance of spiral flow double-pipe heat exchanger using finite volume method, respectively for the relationship between Nu and the average shear force on inner pipe outer wall at different turbulent flow Re with different radial offset of inlet and outlet pipes and different spacing of inlet and outlet pipes. The results show that, as compared with an ordinary double-pipe heat exchanger, in a spiral flow double-pipe heat exchanger, both inner pipe convective heat exchange coefficient and inner pipe wall surface shear force are lower, with the magnitude of reduction related to a number of factors such as radial offset of inlet and outlet pipes and Re. The study in this article has provided theoretical basis for further engineering application of spiral flow double-pipe heat exchangers.

Numerical study of conjugated heat transfer in metal foam filled double-pipe

The two equation numerical model has been applied for parallel flow double-pipe heat exchanger filled with open cell metal foams. The model fully considered solid–fluid conjugated heat transfer process coupling heat conduction and convection in open cell metal foam solid matrix, interface wall and fluid in both inner and annular space in heat exchanger. The non-Darcy effect and the wall thickness are also taken into account. The interface wall heat flux distribution along the axial direction is predicted. The numerical model is firstly verified and then the influences of solid heat conductivity, metal foam porosity, pore density, relative heat conductivity and inner tube radius of the heat exchanger on dimensionless temperature distribution and heat transfer performance of heat exchanger are numerically studied. It is revealed that the proposed numerical model can effectively display the real physical heat transfer process in the double pipe heat exchanger. It is expected to provide useful information for the design of metal foam filled heat exchanger.

Entropy Generation in Counter Flow Gas to Gas Heat Exchangers

Analysis of heat transfer and fluid flow thermodynamic irreversibilities is realized on an example of a counter flow double pipe heat exchanger utilizing turbulent air flow as a working fluid. During the process of mathematical model creation and for different working and constructing limitations, total thermodynamic irreversibility is studied. The present work proves that the irreversibility occurred due to unequal capacity flow rates (flow imbalance irreversibility). It is concluded that the heat exchanger should be operated at effectiveness, ε, greater than 0.5 and the well operating conditions will be achieved when ε approaches one where low irreversibility is expected. A new equation is adopted to express the entropy generation numbers for imbalanced heat exchangers of similar design with smallest deviation from the exact value. The results obtained from the new equation are compared with the exact values and with those obtained by Bejan (Bejan, A., 1997, Advanced Engineering Thermodynamics, Wiley, New York).

FEM analysis of multifluid heat exchangers

Heat exchangers are devices for exchanging energy between two or more fluids. They find applications in various industries like power, process, electronics, refining, cryogenics, chemicals, metals and manufacturing sector. Even though heat exchanger designs have been reported quite extensively, they are generally limited to steady‐state performance, single phase fluids, a few of the many possible flow arrangements and only two fluid heat exchangers. While these designs encompass the majority of the heat exchanger applications, there are some designs, which involve several fluids such as in cryogenics or fault‐tolerant heat exchangers. The governing differential equations for a three‐fluid heat exchanger are written based on the conservation of energy. The finite element method is used to solve the governing differential equations along with the appropriate boundary conditions. The case of a Buoyonet heat exchanger (used for pasteurizing milk) is analysed and the results are compared with the analytical solution available in the literature. The Buoyonet heat exchanger, treated as a three‐fluid heat exchanger is also analysed. The effect of heat loss to the ambient from a parallel flow double pipe heat exchanger is also investigated and the results are compared with those available in the literature. The results are presented both in terms of the temperature distribution along the length of the heat exchanger and the variation of effectiveness with NTU. The methodology presented in this paper can be extended to heat exchangers with any number of streams and any combination of the flow arrangements.

Analytical and experimental response time to flow rate step along a counter flow double pipe heat exchanger

Temperatures transient response along a tubular counter flow heat exchanger is investigated when mass flow rate is subjected to sudden change. The dynamic behaviour is approximated by a first order response with a time constant. The hot fluid subjected to the flow rate step presents a decreasing linear time constant according to flow axis. The cold fluid, which is not submitted to the flow rate step, shows two types of transient response. The first one corresponds to a linear spatial increasing function of time constant while the second one presents a uniform time constant along the heat exchanger. Considering the conditions of the transient response on the boundaries of the heat exchanger, analytical expressions of time constants are obtained for each case. The comparison of the theoretical results with experimental data allows to validate the analytical expressions, which depend on initial and final steady-states. The influence of the flow rate step magnitude on transient behaviour is studied by maintaining the initial steady-state.

Transferts de chaleur lors de la condensation du mélange HFC23/HFC134a à l'intérieur d'un tube lisse horizontal

The environmental effects of the depletion of stratospheric ozone due to refrigerants containing chlorine, have resulted in international treaties, laws and amendments (Copenhagen, 1992, to the Montreal protocol, 1987) to phase out and eliminate many common refrigerants. HCFC22 is one of these refrigerants and no such single component alternative has been discovered for this fluid. Zeotropic refrigerant mixtures (binary or ternary) are being considered as potential replacements for HCFC22. Evaporation and condensation heat-transfer characteristics, and inside tubes of heat exchangers, due to the use of zeotropic refrigerant mixtures, have been a subject of fundamental importance in evaluating the heat exchanger performances in the refrigeration and air-conditioning industry. In this study, it is proposed to determine the heat transfer and pressure drop coefficients during in-tube condensation of zeotropic mixture HFC23/HFC134a in a smooth copper tube with an inside diameter of 8.92 mm. The test section of three passes of 2 m each; it is a counter flow double-pipe heat exchanger with water flowing in the annulus and refrigerant in the inner tube. This test section is instrumented with temperature and pressure sensors. We have tested HCFC22, HFC134a, and three refrigerant mixtures of HFC23/HFC134a at different compositions to appreciate the effect of glide on heat transfer. The quality was from 1 to 80%, the heat flux ranged from 2 to 50 kW m −2 and mass flux varied from 80 to 480 kg m −2s −1. In these conditions, no effect of a glide on the heat-transfer coefficient was observed; this result was confirmed by using an equilibrium condensation curve analysis. The pressure drop can be calculated with classical correlations but with physical properties of the mixture.