Number Of Transfer Units Research Articles

Review and Thermal Calculation of a Shell and Tube Heat Exchanger with Baffles in Cross - Counter Flow Arrangement

In one pass shell and tube heat exchanger with baffles one fluid flows inside of parallel tubes and other fluid flows outside of tubes in perpendicular to tube axis changing alternately its direction. Passing the window of the baffles the shell side fluid deviates its flow direction rapidly. This creates just behind the window of each baffle a so-called “dead volume” which renders a stagnation of flow. This dead volume assumed to be triangular in shape causing the flow behind the window to be conical.In this thermal model the “dead volume” taken into account and change of temperature of the shell side fluid during its flow from tube to tube is considered. The thermal analysis of the cross- counter flow arrangement for any number of tube in bundle with progressive changes in tube length has been carried out. The numerical computations with different tube and baffle numbers are performed. It is found that at the beginning the effectiveness of the heat exchanger increases distinctly with increasing tube number and baffle number. But after certain number of tube and baffles the increasing rate weakens and it becomes very small. Due to the presence of “dead volume” there is reduction in the thermally active heat transfer surface area which leads to a smaller value of Number of Transfer Units (NTU). Hence, the results of computation obtained in this paper with the consideration of the “dead volume” will provide lower value of the effectiveness than that of without the consideration of it.

Evaluation of Counter Current Horizontal Screw Extractor’s Performance in Determining Leaching Equilibrium of Clitoria ternatea Anthocyanins

Anthocyanin compounds as natural coloring substances contained in Clitoria ternatea flowers have higher antioxidant activity than anthocyanins from other flower extracts. Obtaining anthocyanin extract from Clitoria ternatea flower can be done using the solid-liquid extraction method. The objectives of this study include making a leaching equilibrium diagram of Clitoria ternatea flowers and determining the optimum L/S ratio and the number of equilibrium stages in the counter current horizontal screw extractor. In the maceration process, a leaching equilibrium diagram is produced, which is then used to design and determine the number of equilibrium stages. The equilibrium diagram of anthocyanins from Clitoria ternatea flowers with a gradient slope to the right is in accordance with the literature so that the equilibrium diagram can be used in the design of the extraction unit and the calculation of the theoretical stage of the multi-stage extraction unit. Based on the equilibrium diagram, the Number of Transfer Units (NTU) of 4 stages and the Height of the Transfer Unit value of this process is 0.105 m.

Experimental and Comparative Heat Transfer Analysis of Heat Exchanger with Surface Modification

This research aims to enhance the heat exchanger performance by a surface modification approach. The shot peening effect on the heat transfer performance of shell and tube heat exchanger (STHE) is experimentally studied with different surface modifications of stainless steel (SS) tube-like plain SS tube, grinded surface and blast with copper, sand & iron surface. The effect of shot peening on the surface morphology of the SS outer surface is analyzed by scanning electron microscope, and it was found that the iron blast surface has a coarse grain structure. The optimum flow rate for STHE was experimentally studied by base SS tube, and its values are compared with analytical results of computational fluid dynamics and heat transfer research. The underwater medium maintained the higher and lower temperatures of 80 °C and 30 °C, respectively. Based on the logarithmic mean temperature difference, number of transfer units (NTU), overall heat transfer coefficient, effectiveness and exergy efficiency of SS and its modified surface are experimentally evaluated, and iron blasted surface offered maximum heat exchanger performance like 100% for Stanton number, 89% for Nusselt number, 89% for overall heat transfer coefficient, 89% for an NTU, 57% for effectiveness, and 148% for exergy efficiency, while compared to SS surface without modification.

Numerical and experimental investigation of the gyroid heat exchanger

This paper presents a study of a novel type of heat exchanger (HE) whose core is built based on a Triply Periodic Minimal Surface structure. The core of this exchanger is built as a periodic structure based on a gyroid-type lattice and is manufactured by laser powder-bed fusion technology. This solution is distinguished not only by an exceptionally favorable ratio of the heat exchange surface area to the volume occupied but also by a unique geometry that additionally turbulates the flow and intensifies the heat exchange process. This article contains the results of numerical analyses of the entire exchanger under different operating conditions and the results of analyses of small fragments of the core filled with cells of different sizes. Numerical analyzes of the lattice-type exchanger are performed on the basis of the experimentally validated numerical model. The objective of the study is to determine the performance of the gyroid HE under different operational conditions and select the best elementary cell size per exchanger core for the assumed operating conditions. The printed HE was compared with a plate HE that was 30% larger, although the lattice one managed to achieve 10.5% higher values in on average Number of Transfer Units (NTU) and on average 5% higher temperature effectiveness (TE) in the studied range of flow parameters.

ЭФФЕКТИВНОСТЬ КОНТАКТНЫХ ТАРЕЛОК РЕКТИФИКАЦИОННЫХ КОЛОНН

The methods of calculating the efficiency of fracking column plates are considered. The efficiency of cap plates was calculated when separating the methanol-water mixture according to two models based on the use of the number of transfer units and mass transfer coefficients

Design of continuous repeater power transmission coil for wireless power transfer system for EVs with consideration of vehicle deviation

In recent years, EVs have become increasingly popular around the world, and research on wireless power supply technology for EV driving has progressed accordingly. In order to realize this wireless power transfer system for EVs on a real scale, it is necessary to lengthen the power transfer section per power transfer unit and to secure a sufficient power transfer section with a small number of power transfer units as a whole. To solve this problem, the single coil method, in which one coil is lengthened, has been proposed. However, as the coil length increases, resistance loss increases and efficiency decreases. Therefore, a repeater coil system has been proposed. In this in-transit power-feeding system, it is necessary to consider transient phenomena when the EV to be fed deviates from the feeding lane. Therefore, we propose a new repeater coil configuration on the transmission side that assumes a no-load condition. In this study, a new repeater coil system combining rectangular coils and orthogonal coils is proposed, which enables stable feeding of power to EVs by rectangular coils and response to transient phenomena. A comparison was also made with the single coil method that has been studied previously.

Impurities removal from acidic solution of nickel cobalt complex hydroxide using pulsed disc and doughnut column

In this work, a 30 mm diameter pulsed disc and doughnut solvent extraction column was used for impurities removal from nickel cobalt complex hydroxide acid solution by solvent extraction. The effects of dispersed phase velocity, continuous phase velocity and pulse intensity on drop diameter, dispersed phase holdup and mass transfer were investigated. The results show that the drop size decreases gradually, and the dispersed phase holdup decreased initially and then increased with the increase of pulse intensity. The dispersed phase holdup increases with the increase of dispersed phase velocity but is independent of the continuous phase velocity. The experimental data of this study are predicted by correlations with regressed parameters. The average absolute relative error of drop size and dispersed phase holdup were 10.07 % and 18.28 %. With the increase of pulse intensity, the extraction efficiency of impurities decreased firstly and then increased. The number of mass transfer units and the height of mass transfer unit were calculated. The trend of number of mass transfer units of impurities are similar to extraction efficiency. Mass transfer results indicate that pulsed disc and doughnut column can be applied to the nickel cobalt complex hydroxide acid solution-P204/kerosene system.

ANALYSIS OF THE SINGLE-BLOW TRANSIENT TESTING TECHNIQUE FOR NONMETALLIC HEAT EXCHANGERS

For measuring the efficiency of nonmetallic heat exchangers, a mathematical model was established based on the principle of the single-blow testing technique, in which the conductive thermal resistance across nonmetallic plates of the exchangers was taken into account. The analytical solution was obtained by means of the Laplace transformation and numerical inverse transform method. The accuracy of the model was verified by comparing it with the literature. The effect of the plate Bi number on the evaluated number of transfer units (NTU) was analyzed. Based on the single-blow transient testing technique and the present model, the heat transfer performance and frictional pressure drop of four types of nonmetallic plates with different structural parameters were experimentally studied. The correlations for heat transfer and frictional pressure drop of nonmetallic heat exchange structures are established.

Experimental investigation on cooling tower performance with Al<sub>2</sub>O<sub>3</sub>, ZnO and Ti<sub>2</sub>O<sub>3</sub> based nanofluids

<p>This study deals with an experimental investigation of the thermal performance of a prototype mechanical wet cooling tower with a counter flow arrangement. Different volume concentrations ranging from 0.18 to 0.50 vol.% of stable Al oxide (Al<sub>2</sub>O<sub>3</sub>), Zn oxide (ZnO), and Ti oxide (Ti<sub>2</sub>O<sub>3</sub>) nanoparticles of 80, 35, and 70 nm diameter were considered. Water was taken as a base fluid, and the experiment was carried out at 60, 70, and 80 ℃, respectively, in laboratory conditions. The study revealed that an increase in the volume concentration of the nanofluids increased the cooling range, cooling efficiency, convective heat transfer coefficient, tower characteristic called number of transfer unit (NTU), and effectiveness of the cooling tower compared with water at the same mass flow rate and inlet temperature. However, increasing the volume concentration increased the viscosity of the nanofluids, leading to an increase in friction factor. For instance, for 0.18% volume concentration of ZnO, at an inlet water temperature of 66.4 ℃ and water/air (L/G) flow ratio of 1.93, the cooling range increased by 3.62%, cooling efficiency increased by 33.3%, and NTU increased by 50.5% compared with fresh water (FW).</p>

Effectiveness and number of transfer units of plate heat exchanger with Fe3O4–SiO2/Water hybrid nanofluids: Experimental and artificial neural network predictions

This paper analyses the effectiveness and number of transfer units of water dispersed Fe3O4–SiO2 hybrid fluids passing via plate heat exchanger experimentally. The flow of Fe3O4–SiO2/water hybrid nanofluids in plate heat exchanger remains the laminar flow conditions. The experimental studies were carried out with particle loadings ranging from 0.2 % to 1.0 % and flow rates ranging from 0.05 kg/s to 0.1166 kg/s. The obtained results of effectiveness and number of transfer units from these experiments were predicted with artificial neural network based scaled conjugate gradient (SCG) method. Based on the chemical reaction and in-situ growth methods, the Fe3O4–SiO2 nanoparticles were prepared and then characterized using x-ray diffraction (XRD) and vibrating sample magnetometer (VSM) equipment. Water diluted hybrid nanofluids were developed and used for the experimental studies. Results from the XRD indicates that, the particle size of synthesized Fe3O4–SiO2 nanoparticles were found to be 47 nm and the results from VSM shows, the final Fe3O4–SiO2 sample contains 67.8 % of SiO2 and 32.2 % of Fe3O4. Results also indicates with an increase of volume loadings and Reynolds number, the effectiveness and number of transfer units were enhanced. The effectiveness and number of transfer units were increased by 13.23 % and 24.51 % at 1.0 % vol. of hybrid nanofluid and at a Reynolds number of 571.89, over water data. Through the SCG method, the correlation coefficient R2 for effectiveness is 0.99040, and the R2 for number of transfer units is 0.98771, respectively. New generalized equation was proposed for the evaluation of effectiveness and number of transfer units.

Optimizing the effect of micro-surface on the thermal hydraulic performance of plate heat exchanger

This research used electrochemical etching as a new method for generating micro surfaces in an effort to improve the thermal–hydraulic performance of a plate heat exchanger (PHE). This technique has significant advantages in terms of producing evenly structured surfaces and enabling exact size control compared to other techniques such as sandblasting and electroplating. Thus, it has great potential to be a pioneer in the industrial implementation of micro surface on heat exchangers. This work is the first to examine the impact of optimum roughness on both the Nusselt number (Nu) and the Performance of Evaluation Criterion (PEC) of PHE using a multi-objective genetic algorithm. In order to do this, several microstructure surfaces were generated on the PHEs, with average roughness values ranging from 0.65 to 1.51 μm. The impact of these microstructure surfaces on heat transfer and pressure drop was experimentally investigated through heat transfer experiments conducted at Reynolds numbers (Re) ranging from 3,000 to 12,500. The findings reveal that the introduction of microstructure surfaces leads to a noteworthy enhancement of 10 % to 18 % in the overall heat transfer coefficient (OHTC) across all experimental scenarios. Conversely, the friction factor experienced an increase of 28 % to 53 % compared to a smooth surface. PEC values ranged from 1.05 to 1.21, showing a superior heat transfer performance over a marginal pressure drop increase. Furthermore, the microstructure surfaces demonstrated significantly improved values of 0.23 to 0.32 for the Number of Transfer Units (NTU) and 0.18 to 0.26 for effectiveness, in comparison to the smooth surface. This corresponds to an enhancement of 9.7 % to 18.5 % and 7.2 % to 16.4 %, respectively. In addition, a multi-objective genetic algorithm determined that an optimal roughness value of Ra = 1.1 μm achieves a balance between maximizing Nu and PEC.

Prediction of the discharging time of a latent heat thermal energy storage system with a UA approach

Designing latent heat thermal energy storage systems is a cumbersome task and the estimation of the performance of such a storage system normally involves experiments and detailed numerical simulations. Analytical, empirical and simplified numerical models are much faster but subject to large uncertainties. Even the prediction of the performance of an existing latent heat thermal energy storage system under different boundary conditions is often not possible in an easy way. Therefore, we present an analytical method – the UA approach – to predict the discharging (solidification) time of a flat plate latent heat thermal energy storage system. A special feature of the UA approach is that one can incorporate experimental or numerical results to improve the prediction of the performance under a variety of boundary conditions or material properties. The UA approach was tested for a variation of the Stefan number (Ste), the Biot number (Bi), the number of transfer units (NTU) and the heat transfer fluid and was compared to the results of a validated numerical model. The results are promising, especially for small Ste. In addition, the prediction of performance for a high thermal heat conductivity of the phase change material based on a numerical reference solution with a low thermal conductivity worked remarkable well.

A general effectiveness-NTU modeling framework for membrane dehumidification systems

Selective membrane dehumidification is a promising technology for energy efficient air dehumidification in buildings and has been ranked as a top alternative technology by the Department of Energy. One critical area that needs to be addressed is system modeling that incorporates device mass transfer characteristics and sizing. This work develops, validates, and applies a simple effectiveness-number of transfer units (ε-NTU) modeling framework for dehumidification technologies that can be used to predict performance and determine required membrane area for a wide range of technologies, including energy recovery ventilators, vacuum membrane dehumidification, and desiccant dehumidifiers. Although the ε-NTU method is a well-established framework for sizing and modeling heat exchangers, past attempts to create εL-NTUL(meaning ε-NTU for latent loads) models for dehumidification (referred to as latent cooling): (1) don’t agree on the definition of NTUL, (2) are not fully analogous to the heat transfer definition of NTU, (3) cannot be easily applied across all technologies, (4) use humidity ratio, not vapor pressure, as the driving force, and (5) are often complex or lack a fundamental basis. In this work, we develop an effectiveness-NTU model for membrane humidity exchangers that is based on vapor pressure differences, employs a novel definition of the latent number of transfer units for dehumidification applications (NTUL) and is fully analogous to the heat transfer effectiveness-NTU models employed for sensible heat exchangers. The resulting εL-NTUL relationships are validated against experimental data with a maximum error of 1.2%. The overall methodology is applied in case studies for vacuum membrane dehumidification system sizing showing that the ratio of required membrane area per building floor area ranges between 0.1 and 3.5 depending on the building type and operating conditions. Finally, the framework is further generalized for applicability to any gas separation application.

An optimization of a pre-cooling system for batch processes: A case study of the tubular ice production process

Mathematical models for predicting the thermal behavior of feed water precooling systems for tubular ice makers were developed. A commercial water chiller and plate type heat exchanger were used as the cooling source and heat exchanging device. The simulation results suggest that the system, in which the feed water is circulated through the heat exchanger, provides a higher effectiveness (ε) with a lower heat capacity rate ratio of the feed water to the chilled water (wr) for a certain number of transfer units (NTU). In the range of the ice maker capacities popularly used, at a NTU of unity, the optimum heat capacity rate ratio of the feed water to the chilled water (wr) could be estimated to be 0.48. The water chillers would operate in the range of their minimum specific power consumptions when the feed water temperature was higher than 11 °C. The system has the potential to reduce the energy consumption about 6.7–11.6%. In addition, it can improve the productivity. The system was tested with a conventional ice maker. The energy consumption can be reduced as predicted by the model. The results could be also applied to a precooling or preheating of any production process.

Sensible heat recovery systems for batch processes with waste heat fluid drained at the end of the process

Mathematical models for modelling the behaviors of heat recovery systems of batch processes with waste heat fluid drained at the end of the process were developed. The results show that the optimum heat capacity rate ratio of the feed to the drain fluids might be estimated to be unity. For the drained fluid circulated (Dc), and flowing through heat exchanger (Dt) systems, the optimum number of transfer units might be estimated to be 1 and 4, and the effectiveness increases as the heat capacity rate ratio of the feed water to the drain water decreases and increases, respectively. The drained fluid circulated with the feed flowing through the heat exchanger system provides not only the highest effectiveness but also the lowest number of transfer units. A prototype of energy recovery system for the drained water from a 30 ton/day conventional tubular ice maker was developed according to the obtained result. It shows that the system is able to increase the productivity about 1600 kg/day and decrease the energy consumption by 5%. This concept has never been found. It may be applied to recover energy from batch processes having high or low temperature fluid drain after the end of the process.

Enhancement of heat transfer in a vertical shell and tube heat exchanger using air injection and new baffles: Experimental and numerical approach

Vertical shell and tube heat exchangers play a critical role in many industrial processes, and their importance lies in their high heat transfer efficiency, versatility, compact size, easy maintenance, and longevity. To improve the hydrothermal performance, this research investigates the influences of air bubbles injection inside the shell with disc and ring baffles with circular holes, which is the first time to be addressed. The experiments used a fixed oil mass flow rate with 0.23 kg/s inside the tube sides and various cold water flow rates on the shell side within the 0.15–0.23 kg/s range. Three baffles’ configurations, such as single segmental (SSB), disc and ring (DRB), and disc and ring with circular holes (DRCHB), were investigated with different volume flow rates of air bubbles injection in the shell experimentally. A numerical model is performed and validated for the three baffles shapes. The performance parameters such as number of transfer units, effectiveness, heat transfer coefficient, pressure drop, and performance evaluation criterion are studied. The experimental findings showed that efficacy improved with the increase of the cold-water mass flow rates, whereas the DRCHB baffle shape with air injection)10 × 10−5 m3/s(achieved the highest effectiveness with an enhancement rate of 202% to 231%. The DRCHB configuration with maximum air injection has the highest values of the number of transfer units, heat transfer coefficient, and performance evaluation criterion compared to the other baffles configurations moreover, the pressure drop is the smallest in this case DRCHB without air injection. The numerical results showed that both novel configurations (DRB and DRCHB) have more uniform velocity and temperature distributions compared to the segmental baffles, which may effectively increase the hydrothermal performance.

Theoretical and experimental studies for a transcritical CO2 heat pump with spirally fluted tube gas cooler

Transcritical CO2 system has been widely used in many fields to provide heating and cooling capabilities, and optimizing the structure of the gas cooler is an effective way to improve its performance. This paper presents a theoretical and experimental study of a spirally fluted tube-in-tube heat exchanger used as a gas cooler in a transcritical CO2 heat pump. The theoretical research uses numerical simulations to investigate the flow and heat transfer characteristics. The effect of the different CO2 mass flow rates, inlet pressure, and temperature on the performance of the spirally fluted gas cooler is evaluated and analyzed. The simulation results show that the spirally fluted structure can significantly improve the heat transfer performance of the CO2 side compared to the flat tube, which indicates that the spirally fluted gas cooler could be an effective way to enhance the operating performance of the transcritical CO2 system. Then experimental research is conducted in a transcritical CO2 heat pump prototype to validate the functional performance of the spirally fluted gas cooler. The effect of the different CO2 mass flow rates, inlet pressure and temperature, and the different water inlet and outlet temperatures on the performance of the spirally fluted gas cooler in the prototype are tested. The heat exchanger efficiency - number of transfer units (ε-NTU) method is employed to analyze the operating performance based on the experimental data. In addition, the exergy loss method is used to quantitatively evaluate the side-effect of the large pressure drop by the spirally fluted structure. Both the theoretical and experimental results show that the spirally fluted tube gas cooler can significantly improve the performance of the transcritical CO2 system. Besides, a heat transfer and friction coefficient correlation are established based on the experimental data for future research guidance.

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.

A proposed method of bubble absorption-based deep dehumidification using the ionic liquid for low-humidity industrial environments with experimental performance

Liquid desiccant deep dehumidification (LDDD) is an excellent way to achieve low-carbon transformation of low-humidity industrial buildings. Currently, it is essential to improve its ability to produce lower humidity air (i.e., with a dew point below −10 °C). Functional ionic liquids (ILs) with extremely low vapor pressure, non-crystallization, and non-corrosion are ideal substitutes for high mass fraction aqueous inorganic solutions (e.g., LiCl, LiBr) in traditional liquid desiccant deep dehumidification. Meanwhile, the bubble absorption mode allows water vapor to condense on the huge contact surface between the bubbles and desiccant. Accordingly, it is expected to solve the low wettability and transfer unit number (NTUm) in falling-film absorption mode caused by the high viscosity of ILs. Thus, a new method of bubble absorption-based deep dehumidification using the IL is proposed. To validate it, the bubble absorption-based deep dehumidifier using a novel ionic liquid (BADD-IL) is developed and tested under different operating conditions. Besides, its moisture effectiveness is compared with those of falling film absorption-based dehumidifiers. The results show that increasing the liquid height, superficial velocity, as well as lowering the solution temperature, can strengthen the deep dehumidification performance, effectiveness and cooling ability to varying degrees. The increase of liquid height and superficial velocity promotes the gas-liquid interfacial area from different aspects, thus enhancing the transfer efficiency. Notably, the insufficient interfacial areas caused by low solution temperature cannot prevent better transfer efficiency dominated by high potential difference. Moreover, the NTUm of BADD-IL has a wide adjustment range (0.1–1.7), and the minimum supply air humidity ratio and maximum moisture effectiveness can reach 1.1 g/kgda and 81%, respectively. In overall, this study aims to further explore the deep dehumidification potential of ILs, and inform ideas for the LDDD development.

Performance characteristics of shell and helically coiled tube heat exchanger under different tube cross-sections, inclination angles and nanofluids

The current research deals with an experimental and numerical inspection of the shell and helically coiled tube heat exchanger (SHCTHE) under various circular, elliptic, and square tube cross-sections. The research study strives to ameliorate the thermal-hydraulic performance with single nanofluids of Al2O3/H2O, MgO/H2O, and TiO2/H2O. Various factors were inspected to consider the heat exchanger performance under parameters, SHCTHE inclination angle, HCT diameter ratio, flow direction, the cross-section geometry shape, nanomaterials type, and nanomaterials concentration. The modeling engaging a numerical code tool of ANSYS-FLUENT 19 was accomplished with a 3D (RNG)/k–ϵ model. The mass flow rate and working fluid temperatures through the coil and shell sides were (0.05:0.2 kg/s at 80 °C and 0.05–0.2 kg/s at 10 °C, respectively. One of the most important results was that the SHCTHE with a circular tube cross-section gave the highest Nusselt number with an approximate percentage of 62.5%. The SHCTHE effectiveness and the number of transfer units were enhanced by around 19.35% and 30.78%, respectively, by the greater HCT diameter ratio and Al2O3 nanomaterials. Nusselt number, friction factor, and SHCTHE effectiveness were correlated through equations (52:55) with dimensionless factors and their limitations.