Double Pipe Heat Exchanger Research Articles

Thermal performance analysis of molten salt based on a novel experimental rig

In the field of medium and high temperature solar heat utilization, molten salt is widely used. Besides, the thermal performance of molten salt is very important for solar heat utilization. However, current studies were mainly conducted by simulation, supplemented by experiment. Therefore, a novel experimental rig was designed and established, in order to investigate the performance of commercial molten salt in the typical heat transfer process. The tests under 24 conditions were conducted. Gnielinski empirical formula was modified by experiments to describe the thermal performance of molten salt more accurately. 400 groups of randomized tests with different heat exchangers were carried out to confirm the application conditions and accuracy of the modified empirical formula. The average relative deviation between the experimental and the calculated comprehensive heat transfer coefficient was 3.09% in the molten salt -oil double-pipe heat exchanger, and was 3.42% in the molten salt -oil 1–1 tube-shell heat exchanger. The research result could provide theoretical and experimental support for thermal performance analysis of molten salt. This modified empirical formula with wider range of utilization conditions could accurately describe the thermal performance of molten salt in common commercial heat exchangers of practical engineering.

Multi-objective optimization of thermo-hydraulic behavior of heat exchanger with v-cut twisted tape in axial and radial direction using NSGA-II

ABSTRACT In pursuit of optimizing the thermo-hydraulic behavior of a heat exchanger, this study employs twisted tape inserts, a well-known method for enhancing heat transfer rates in heat exchange devices compared to plain tubes. Experiments involving v-cut twisted tapes with v-angles of 15°, 30°, and 45° in both axial and radial directions were conducted within a double pipe heat exchanger, encompassing a Reynolds number range from 5500 to 10,000, with water as the flowing medium. As part of the modeling approach, response surface methodology (RSM) was harnessed to construct mathematical models for the heat transfer rate, quantified as the Nusselt number, and the friction factor. This modeling accounted for independent variables including Reynolds number, Prandtl number, axial angle, and radial angle. The RSM models demonstrated high statistical significance and reliability, yielding an R-squared value exceeding 97%, with the linear terms of Reynolds number and cut angles identified as the most influential factors. To attain optimization, a multi-objective approach was adopted, employing the NSGA-II algorithm. This algorithm efficiently explored the design parameter space, seeking the optimal combination that maximizes heat transfer rate and minimizes the friction factor simultaneously. Quantitative results from the experimentation revealed that, at a Reynolds number of 10,000, the Nusselt number achieved its peak value of 96.51. Conversely, the highest friction factor (0.0582) and performance evaluation criteria (PEC) of 1.65 emerged at a Reynolds number of 5500, specifically when employing a 45-degree radial v-cut angle. Notably, this configuration led to substantial enhancements: the Nusselt number increased by 98.7%, the friction factor by 38.9%, and the PEC by 39.4% compared to a plain tube. These findings underscore both the effectiveness of the NSGA-II algorithm in optimizing heat exchanger designs and the valuable insights gained into the influence of twisted tape insert parameters on heat transfer performance and hydraulic behavior. The optimized design parameters obtained through this study hold significant potential for enhancing heat transfer efficiency across diverse industrial applications. Overall, this research advances heat exchanger optimization techniques and provides a framework for further investigations in this field.

A comparative analysis of dovetail and rectangular fins with insulated tips wetted with ZnO-SAE 50 nanolubricant for energy transfer process

This study focuses on exploring innovative methods of energy conservation specifically through the nonlinear fin equation. To improve the heat transfer efficiency in cooling systems, the research suggests utilizing nano lubricants that possess superior thermo-physical properties. Unlike other nanofluids, the use of nanolubricants can decrease corrosion and abrasion in operational parts such as the bore-piston, gasket, and valve mechanisms. The study concentrates on the temperature distribution in both rectangular and longitudinal dovetail fins utilized in double-pipe heat exchanger applications. The energy equation is formulated to consider radiation, temperature-dependent internal heat generation, and wetted conditions, and is subsequently transformed into a dimensionless form. Numerical solutions to the resulting differential equation are obtained through the utilization of the collocation method. The study explores the use of a specific heat transfer liquid (ZnO-SAE 50) nanolubricant to analyze thermal dispersion in both straight rectangular and dovetail fins. Additionally, it investigates how temperature-dependent internal heat generation impacts convection-conduction heat transfer. The study finds that an increase in surface emissivity results in greater heat transfer through the fin's surface in the presence of nanolubricant.

Performance analysis of groove-cut tube based double-pipe heat exchanger using microencapsulated phase change material slurry

It is commonly accepted practice to improve a thermal-fluid device by adopting surface enhancement techniques for better heat transfer. On the other hand, Microencapsulated phase change material (MPCM) slurry has been used as a heat transfer fluid (HTF) due to its improved heat capacity and heat transfer performance. The current paper attempted to study the combined effect of the two enhancement methods in a double-pipe heat exchanger. The results were first validated with experimental work taking into account the hydraulic and heat transfer characteristics of the MPCM slurry flow. Groove-cut geometrical models of MGGC, RGC, CGC, and TGC were proposed to modify heat transfer tube geometry. The effect of the number of helical turns (3, 4, 5, and 6-turns) and various Reynolds numbers were also considered for the investigation. The result showed that the proposed groove-cut models demonstrate enhanced flow mixing for MPCM slurry but with a higher friction factor, which increases with increasing helical turns. The impact was also manifested by improving the heat transfer by facilitating a uniform melting of MPCM particles, and the RGC model shows higher performance. The overall thermohydraulic performance assessment showed that the groove-cut tube models outperformed the corresponding plain tube. The highest performance factor value of 1.24 was observed for the RGC model, while the TGC model shows only 1.14 for the 6-turns. Similarly, the Q/Wp ratio indicates that the groove cut models transport more heat than the pumping power requirement for MPCM slurry.

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.

Cryogenic cold energy recovery in liquid hydrogen refueling station with double-pipe heat exchanger

Recovering the cryogenic cold energy of liquid hydrogen (LH2) for precooling high-pressure hydrogen gas before refueling can significantly reduce the electricity and energy consumption of liquid hydrogen refueling stations. Existing methods, such as blending, require continuous cryogenic pump operation and are not suitable for various operating conditions. This work proposes a novel method to recover LH2 cryogenic cold energy using a double-pipe heat exchanger, which can decouple the compression and refueling process and meet the fluctuating demand for the cryogenic cold energy required by the hydrogen dispenser. The lumped parameter method and temperature partition method were adopted to design the heat exchanger structure. Numerical simulations of a 2D axisymmetric swirl model were done to verify the accuracy of the temperature partition method applied to high-pressure cryogenic hydrogen. Due to the low temperature of LH2, the secondary refrigerant dichloromethane (CH2Cl2) risks freezing. Comparing the outer wall surface temperature of the inner pipe with the CH2Cl2 freezing point temperature, the optimal anti-freezing condition is that the outer pipe nominal diameter should be selected as 0.032 m and CH2Cl2 mass flow rate should be at least 1.72 kg s−1. Recovery efficiency can reach over 75.39% without freezing.

Numerical and experimental investigation of the thermal performance of the double pipe-heat exchanger

Numerical and experimental investigation of the thermal performance of the double pipe-heat exchanger

Enhancement in heat transfer characteristics by using truncated conical turbulators in a double pipe heat exchanger under turbulent conditions

Enhancement in heat transfer characteristics by using truncated conical turbulators in a double pipe heat exchanger under turbulent conditions

Numerical analysis of fluid type and flow mass rate on logarithmic temperature difference and heat transfer coefficient of double pipe heat exchanger

This CFD and statistical article aims to evaluate the impact of fluid type and flow mass rate on the log-mean temperature difference (ΔTLM) and the heat transfer coefficient (Ushell) in a double tube heat exchanger (DPHEX) using computational fluid dynamics (CFD) and statistical analysis. ANSYS Fluent software was utilized to conduct CFD calculations. CFD analyses were implemented using Taguchi L8 orthogonal array containing two variables such as the fluid types and the flow mass rates. The levels of fluid types were considered as water-liquid, ethylene-glycol, engine-oil, and benzene-liquid. The levels of fluid types were decided as 1.1 kg/s to 1.5 kg/s. To determine the optimal levels of variables and their impacts on the ΔTLM and Ushell in DPHEX, analysis of Signal to Noise (S/N) ratio was employed. Analysis of Variance (ANOVA) was also utilized to decide the effective variables and their percentage contribution rates on the outcomes. The CFD result obtained using the optimum levels of variables were compared with Taguchi estimation result. According to the study, the highest effects were obtained using ethylene-glycol, engine-oil, water-liquid, and benzene-liquid on the highest log-mean temperature difference values, respectively. In addition, the highest heat transfer coefficient values were found utilizing water-liquid, benzene-liquid, ethylene-glycol, and engine-oil, respectively. Increasing flow mass rate from 1.1 kg/s to 1.5 kg/s causes an increase in both outcomes. The study provides a reference for resolving issues that may arise in the production of experimental DPHEXs.

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.

Augmenting the double pipe heat exchanger efficiency using varied molar Ag ornamented graphene oxide (GO) nanoparticles aqueous hybrid nanofluids

The optimization of heat transfer in heat exchanging equipment is paramount for the efficient management of energy resources in both industrial and residential settings. In pursuit of this goal, this empirical study embarked on enhancing the heat transfer performance of a double pipe heat exchanger (DPHX) by introducing silver (Ag)-graphene oxide (GO) hybrid nanofluids into the annulus of the heat exchanger. To achieve this, three distinct molar concentrations of Ag ornamented GO hybrid nanoparticles were synthesized by blending GO nanoparticles with silver nitrate at molarities of 0.03 M, 0.06 M, and 0.09 M. These Ag-GO hybrid nanoparticles were then dispersed in the base fluid, resulting in the formation of three distinct hybrid nanofluids, each with a consistent weight percentage of 0.05 wt%. Thorough characterization and evaluation of thermophysical properties were performed on the resulting hybrid nanomaterials and nanofluids, respectively. Remarkably, the most significant enhancement in heat transfer coefficient, Nusselt number, and thermal performance index (62.9%, 33.55%, and 1.29, respectively) was observed with the 0.09 M Ag-GO hybrid nanofluid, operating at a Reynolds number of 1,451 and a flow rate of 47 g/s. These findings highlight the substantial improvement in thermophysical properties of the base fluid and the intensification of heat transfer in the DPHX with increasing Ag molarity over GO. In summary, this study emphasizes the vital importance of optimizing the molarity of the material, which also plays a significant role in nanoparticle synthesis to achieve the optimal amplification of heat transfer.

Geometry modification of a vertical shell-and-tube latent heat thermal energy storage system using a framed structure with different undulated shapes for the phase change material container during the melting process

This study aims to modify the melting performance of a vertical latent heat double-pipe heat exchanger by geometry modification of the phase change material (PCM) container. To modify the configuration of the PCM container placed in the outer tube, a framed structure is embedded in the inner surface of the outer tube. Different framed structures i.e. smooth, arc-shaped, reverse arc-shaped, and zigzag-shaped structures are examined and compared with that of the unframed enclosure. Moreover, different numbers of pitches are also examined. The results show that the melting duration drops by almost 55 % and the thermal energy storage rate improves by 115 % using a smooth framed structure for the PCM container compared with that of using an unframed structure. The thermal energy storage rate and melting time are ∼9.5 W and 244.4 min, respectively, for the system using an unframed structure. The analysis of the pitch number for the zigzag-shaped structure reveals that increasing the number of pitches from 0 to 11 enhances the thermal energy storage rate by 36.5 %. The evaluation of different shapes of the framed structure shows that the case with reverse arc-shaped structure is the most enhanced unit which has the thermal energy storage rate of ∼34 W and melting time of 63.15 min heated by water at the Reynolds number 1000 and inlet water temperature of 50 °C. The sensitivity analysis of the HTF characteristics reveals that by increasing the Re from 1000 to 2000, the thermal energy storage rate increases by around 6 W. Furthermore, by increasing the inlet temperature of HTF from 50 °C to 55 °C, the thermal energy storage rate enhances by around 10 W. This paper shows the capability of geometry modification in enhancing the thermal energy storage rate of the systems.

Air-Purge Regenerative Direct Air Capture Using an Externally Heated and Cooled Temperature-Swing Adsorber Packed with Solid Amine

CO2 capture from air is crucial in achieving negative emissions. Based on conventional or newly developed high-enriching processes, we investigated the rough enrichment of CO2 from air via an externally heated or cooled adsorber (temperature-swing adsorption, TSA), along with air purge using double-pipe heat exchangers packed with low-volatility polyamine-loaded silica. A simple adsorption–desorption cycle was attempted in a TSA experiment, by varying the temperature from 20 °C to 60 °C using moist air, yielding an average CO2 concentration of product gas that was ~17 times higher than the feed air, but the CO2 recovery rate was poor. A double-step adsorption process was applied to increase CO2 adsorption and recovery simultaneously. In this process, substantial-CO2-concentration gas was used as the product gas, and the remaining gas was used as the reflux feed gas for adsorber. This method can provide a product gas with ~100 times higher CO2 concentration than raw gas, with a recovery ratio ~60% under the shortest adsorption/desorption time and the longest refluxing time of cycle operation. Therefore, the refluxing step significantly helped to enhance CO2 capture via adsorption from elevated-CO2-concentration recirculating gas. With this CO2 concentration, the product gas can serve as the CO2 supplement for the growing plant processes.

Numerical solution for optimization of curved turbulator geometry in a double-pipe heat exchanger containing two-phase Cu-GO/Therminol VP-1 hybrid nanofluid to achieve maximum exergy efficiency

In industry, heat exchangers (HE) either remove excess heat from a device to cool it or keep a reaction warm within a certain temperature range. Most of the HEs used in oil, gas, and petrochemical industries are double-pipe types. The present study was carried out in steady state and utilizing the pressure-based finite volume method (FVM). The Two-phase Cu-GO/Therminol VP-1 (copper-graphene oxide) hybrid nanofluid (HN) is modeled utilizing the mixture model. The turbulence model is the k-ε model. The range of changes of Re and φ of GO and Cu nanoparticles is 17000 to 41000 and 0 to 3%, respectively. Also, the study is done for different geometric shapes of the novel turbulator with the curvature angles of β = 0⁰, 45⁰, 90⁰, and 135⁰. The numerical results demonstrate that an increment in Re, i.e. an increase in the HN velocity, enhances the Nusselt number (Nu) and convective heat transfer coefficient (HTC). The maximum amount of thermal performance in the double-pipe exchanger is related to the use of the turbulator with β = 135⁰ and φ = 3%. In addition, for all cases, the values of the performance evaluation criteria (PEC) is greater than 1. Therefore, it is appropriate to use the innovative turbulator (IT) and change its curvature angle in the HE in terms of PEC. For all values of β, the exergy efficiency is improved with φ and Re and is reduced with β.

Comparative study of different meta-heuristics on optimal design of a heat exchanger

AbstractThe paper compares different metaheuristics for using heat exchangers as a benchmark to estimate the best design parameter values using optimization efficient algorithms. Many MATLAB algorithms are used in this study. Also, an engineering equation solver, which is commercial software, is used to solve the issue. The design calculates three variables, which are the length, and inner and outer pipe diameter of the heat exchanger. The results showed that the best algorithms are particle swarm optimization, and when using this algorithm, the optimal design of the double pipe heat exchanger is as follows: the pipe length is 5.6734·10−1 m, the pipe inner diameter is 8.0203·10−3 m, and the pipe outer diameter is 2.2439·10−2 m.

Thermal enhancement techniques for a lobed-double pipe PCM thermal storage system

In this paper, the simultaneous harvesting and storing of solar thermal energy using a lobed double-pipe heat exchanger with Phase Change Materials (RT82), in a solar collector energy storage unit, has been simulated. The storage unit is a double pipe system, where it is contained within the inner pipe with RT82, while the outer pipe contains water as the heat transfer fluid. To improve the system efficiency in terms of PCM thermal performances, solutions like lobed geometries, metal foam, dispersed nanoparticles, have been considered, together with a carbon nanotube-based hybrid nano powder for the heat transfer fluid. Temperatures evolution have been evaluated with a 3D mathematical model that considers paraffin phase changes, nanoparticles, and porous media modeling. Various Stefan numbers were examined as input variables to evaluate thermal performances in terms of melting/solidification times, stored/released energy, and so on. The outcomes illustrate that, for whom wants to improve the efficiency of the system via geometry improvements, a six-lobed surface decreases the charging and discharging time by 18.32% and 11.40%, respectively, when compared to a one-lobe one. By combining all the enhancement techniques in Case F, and by using the lowest investigated porosities for the foam, the charging and discharging times are reduced by 66.68% and 81.62%, respectively, in comparison to Case A with pure RT82; on the other hand, it has been also shown that the main contribution to this comes from metal foam inclusion. Also, the rate of heat energy harvesting, and storage becomes 198.95 W and 169.78 W, and 0.0503 and 0.0268 in the scaled form, respectively.

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

Genetic algorithm optimization for double pipe heat exchanger PCM storage system during charging and discharging processes

Nowadays, world faces an energy crisis and residential buildings in developed countries account for 20–40% of the world's total energy demand. Therefore, reducing energy consumption in this sector is crucial for sustainable energy systems. Using phase change materials (PCMs) in energy systems is one of the most reasonable solutions. This study investigates PCMs in a dual-pipe latent heat exchanger system for thermal energy storage. The outer pipe of the exchanger contains the salt hydrate TH29 PCM, while the inner pipe carries water. The system is charged using hot water at 70°C and discharged with cold water at 8°C. An adiabatic time interval is introduced to optimize the charging and discharging operations during which the pump power is cut off and the water flow is stopped. The stored energy and exergy destruction during one hour of system operation is investigated by varying the adiabatic time interval. The Genetic algorithm is implemented to maximize the stored energy or minimize the destruced exsergy in the heat exchanger. The algorithm starts with 20 initial samples and 50 number of samples per iteration. The results show that the stored energy is a function of adiabatic time and maximizes to 25,312 J with an adiabatic time interval of 2150 s (out of 1 hour). Furthermore, the exergy destruction is minimized by an adiabatic time interval of 2249 s.

The Impact of Gas-Liquid Dispersed Flow on Heat Exchanger Performance with Improvement Using CuO Nanofluid

Both the air-water dispersion coefficient and the air-nanofluid (CuO) dispersion coefficient were studied and measured in a double-pipe heat exchanger. Pumping air into a tank fitted with a Rushton turbulent impeller resulted in gas-liquid dispersion. In order to test the effects of varying operating conditions on the air-water and air-nanofluid dispersions, they were heated and pumped into the tube of a double-pipe heat exchanger. Reynolds numbers of Rec= 4750-13100 on the shell side and Reh=19900-64000 on the tube side were used to get the total heat transfer coefficient (Uo). The dispersion in the hot fluid tank was achieved by combining the two-phase fluids using a Rushton turbine impeller. It was discovered that the conscious phase saw a significant drop in the heat transfer coefficient when the air bubbles dissipated. Because the impeller's agitation speed affects the rate at which air bubbles are broken, the heat transfer coefficient in the case of dispersion rises as Reh and Rec rise. For all examined parameter values, CuO nanofluid showed significant heat transfer improvement. The heat transfer rate of gas-liquid dispersion increases by nanofluid by as much as 135.5% compared to gas-liquid dispersion which is considered the first attempt for heat transfer enhancement of two phase flow (gas-liquid dispersion) using Nano fluid.

CFD ANALYSIS OF DOUBLE PIPE HEAT EXCHANGER

CFD ANALYSIS OF DOUBLE PIPE HEAT EXCHANGER