Number Of Transfer Units Research Articles

A dynamic method to optimize cascaded latent heat storage systems with a genetic algorithm: A case study of cylindrical concentric heat exchanger

The flow of heat to and from Phase Change Materials (PCMs) is governed by the temperature differences. One of the most viable passive strategy to enhance temperature differences is by using cascaded PCMs. Based on a dynamic heat transfer model coupled with a genetic algorithm, a method for optimizing the performance of cascaded latent heat storage systems is proposed. In this method, the optimization variables and thermal performance based on different objective functions and boundary conditions are investigated. The results show that the mass of the PCM and the number of transfer units (NTU) in each cascaded stage should not always be the same under different objective functions and boundary conditions, unlike in the literature. Additionally, the objective function based on charged exergy is better than that based on charged energy or entransy. Increasing the charging time would increase the charged energy, exergy and entransy, but it will result in a decrease in the efficiencies. As the heat transfer fluid (HTF) has a flow rate greater than 0.2 kg/s, the energy, exergy and entransy efficiencies drop sharply, but have no significant influence on the charged energy, exergy and entransy. For a steady state HTF, an increase of inlet temperature, causes the charged energy, exergy and entransy to increase linearly. However, in this case the rate of temperature increase of the PCMs increase as expected, but the efficiencies decrease slightly. For an unsteady HTF, as the fluctuation in the temperature increases, the charged energy, exergy, entransy along with the efficiencies decrease linearly. In addition, the latent heat capacity of PCMs in different stages will have a significant influence on the optimization variables and thermal performance. In the model in this study, the recommended charging time and HTF flow rate are 3000 s and 0.2 kg/s, respectively.

Thermal entropy and exergy efficiency analyses of nanodiamond/water nanofluid flow in a plate heat exchanger

The study is aimed to understand the heat transfer coefficient and thermal entropy generation analyses of plate heat exchanger by using water-based nanodiamond nanofluids. The experiments were conducted in the volume concentration range: 0 ≤ ϕ ≤ 1.0%, the Reynolds number range: 140 ≤ Re ≤ 610, the mass flow rate range: 0.05≤ṁ≤0.183kg/s, and the Peclet number range from 895.78 ≤ Pe ≤ 3882.72, respectively. The effect of Reynolds number, Peclet number and particle volume loadings of nanodiamond nanofluids on heat transfer characteristics and entropy generation has been investigated. Water and nanodiamond nanofluids were considered as hot and cold medium in the plate heat exchanger, respectively, for the experimental study. The study reveals considerable augmentation in heat transfer coefficient and Nusselt number with an increase of nanofluid particle loadings. The study showed 32.50%, 55.47%, 35.11%, 22.80%, and 18.93% enhancements in overall heat transfer coefficient, heat transfer coefficient, Nusselt number, pressure drop and pumping power compared to base fluid at a Reynolds number of 526.37 at ϕ = 1.0%. Improved effectiveness, number of transfer units and exergy efficiency of 14.41%, 32.81% and 19.72% was observed at ϕ = 1.0% and at a Reynolds number of 526.37 against base fluid data. The thermal entropy and friction entropy generation was showed decreasing and increasing trends respectively, in the measured particle volume loadings. The Bejan number and entropy generation number demonstrated the roles of heat transfer and friction factor in the entropy generation. From the experimental results a new Nusselt number and friction factor correlations were proposed.

Joule–Thomson effect investigations on a cryogenic three‐fluid–three thermal communication heat exchanger

AbstractThe present study investigates the Joule–Thomson (JT) effect due to pressure drop on three‐fluid heat exchangers (HXs) with three thermal communications. The increased miniaturization of cryogenic HXs has led to the introduction of the JT effect. The present study investigates JT effects on a three‐fluid HX with three communications presenting different JT effects, which leads to a rise or drop in effectiveness values. The study is carried out using finite element analysis and MATLAB, considering seven nondimensional parameters of which one is JT pressure drop. The highest effectiveness is achieved for the positive JT effect at the hot stream. This improved effectiveness at hot fluid is achieved by maintaining the size (number of transfer units) of the HX more than 3.1, along with the ratio of the cold fluid heat capacity to the hot fluid heat capacity above 0.8 and the intermediate fluid temperature above 0.7.

Technological design elements for pulsed extraction columns with sieve trays

Solvent extraction process is frequently used to obtain chemical compounds used in the nuclear field. In order to make nuclear energy a safe, clean and cheap energy source, one has resorted to the identification of new, innovative methods in the immediate transfer of the laboratory results to an industrial scale. A method is described for the design of liquid extraction columns by scaling up from the results of small scale plant tests. Such a method was applied for scaling up a pulsed column with sieve trays using the dimensions of an experimental model column. The scale-up method is based on the assumption that the height of the column is independent of column diameter, and that increased backmixing accounts entirely for differences in performance on small and large scales. This paper uses the results obtained on an experimental model column for the purpose of designing a high capacity column. The final result consists in determining the diameter and height of a scaled up column by using like parameter the number of transfer units corresponding to a compartment, a value that will stay the same for the laboratory-scale column and for the large-scale (pilot or industrial) column.

Thermal-hydraulic performance of a nanofluid in a shell-and-tube heat exchanger equipped with new trapezoidal inclined baffles: Nanoparticle shape effect

The influences of diverse shapes of nanoparticles on thermal-hydraulic efficacy of a nanofluid having boehmite nanoparticles in a shell and tube heat exchanger (STHE) are analyzed. The shell-side of the STHE is equipped with novel trapezoidal inclined baffles to develop torsional flows. The nanofluid with five different particle shapes is selected as the hot liquid in the tube-side, whereas the pure water is adopted as the cold liquid in the shell-side. When enhancing the cold fluid's Reynolds number, the pressure loss, overall heat transfer cofficient, heat transfer rate, effectiveness, and Number of Transfer Units (NTU) increase, while the performance index decreases. The nanofluid with platelet particles causes the greatest overall heat transfer cofficient, while that with the Os nanoparticles presents the smallest pressure loss. Additionally, the nanofluid with the Os nanoparticles presents the greatest effectiveness, pursued by the nanoparticle suspensions with the brick-, blade-, cylinder-, and platelet-shaped particles, respectively.

Experimental investigation on the performance of hybrid Fe3O4 coated MWCNT/Water nanofluid as a coolant of a Plate heat exchanger

The performance of MWCNT + Fe3O4/water hybrid nanofluids as the coolant of a plate heat exchanger is experimentally investigated for particle concentrations in the range from 0.05 to 0.3 vol % and for coolant flow rate from 3 to 7 lit/min. The hybrid MWCNT + Fe3O4 nanoparticles were prepared by the chemical precipitation method and characterized with XRD, SEM, Raman, and VSM techniques. The thermal conductivity, viscosity, density and specific heat of MWCNT + Fe3O4 hybrid nanofluid was measured experimentally and compared with the literature values. The results show that the exergy efficiency of the hybrid nanofluid is 10.5% higher than that of de-ionized water at flow rate of 7 lit/min and particles concentration of 0.3 vol %. Thermal performance factor is found to be greater than 1 for the hybrid nanofluids (0.05–0.3 vol %), with its maximal value of 1.12 occurs at 0.3 vol % and flow rate of 7 lit/min. The effectiveness of 0.3 vol % nanofluid is higher than the de-ionized water by 11.65% at the flow rate of 3 lit/min and by 13.21% at 7 lit/min. The number of transfer units of 0.3 vol % hybrid nanofluid is higher than that of de-ionized water by 20.88% and 24.29% at flow rates of 3 and 7 lit/min, respectively. A tradeoff between the first and operating costs suggest that operating at a coolant flow rate of 5 lpm will yield the lowest cost. Therefore, benefits of reducing the size and enhancing heat transfer of the PHE via the use of MWCNT + Fe3O4/water hybrid nanofluid outweigh the additional power requirement.

Performance of Pure Crossflow Heat Exchanger in Sensible Heat Transfer Application

All process industries involve the usage of heat exchanger equipment and understanding its performance during the design phase is very essential. The present research work specifies the performance of a pure cross flow heat exchanger in terms of dimensionless factors such as number of transfer units, capacity rate ratio, and heat exchanger effectiveness. Steady state sensible heat transfer was considered in the analysis. The matrix approach that was established in the earlier work was used in the study. The results were depicted in the form of charts, tables, and performance equations. It was observed that indeterminately increasing the number of transfer units past a threshold limit provided very marginal improvement in the performance of a pure cross flow heat exchanger. Likewise, flow pattern in a heat exchanger is usually assumed either as mixed or unmixed. However, due to various operating conditions, partially mixed conditions do exist. This work considers partially mixed conditions in the tube side of the heat exchanger. The correction factor for heat exchanger effectiveness was developed to accommodate partially mixed flow conditions in the pure cross flow heat exchanger.

Analisis Pengaruh Modifikasi Penukar Panas Terhadap Efisiensi Pendinginan Oli Gearbox Separator pada Pabrik Semen

Inside the cement factory, there is a finish mill which functions for the mixing process between clinker and gypsum to be used as cement. In that section there is a separator that functions to separate the finished cement and cement that still requires a re-milling process. In the separator there is a separator rotor which has a role to separate cement according to the size of the granulation so that those with standard sizes can be easily pushed by the circulating air fan and brought to the cement silo. The separator rotor is rotated by a motor which is passed by the gearbox as the transmission system. In order for the gearbox to work optimally, oil with certain temperature conditions is needed. Over time, the oil will become hot and cannot work effectively, so an oil cooling system is installed in this system. The oil cooler is a heat exchanger with water cooling fluid. This study aims to apply the NTU (Number of Transfer Units) method, in order to obtain an efficient and suitable heat exchanger working system as an oil cooler. The results obtained are an increase in efficiency of 2.74% from 35% to 37.74%.

Effect of Flow Rate and Concentration of Water / TiO2 Nanofluid on the Performance of Heat Exchanger

Nowadays, nanofluids are plays a prominent role in enhancing the mechanism of the heat transfer. However, some nanofluids could have adverse impact on environment. The main objective of this work is to experimentally investigate the improvement of mixing nanoparticle (Titanium Oxide in this case) with the conventional fluid (water) on the heat exchanger performance. Various concertation of the nanoparticle and different flow rates of nanofluid are tested to observe the variation of the Number of Transfer Unit (NTU) as well as the exchanger effectiveness. Exchanger/Environment interaction is also of interest in the study. The heat transfer between the exchanger and the atmosphere is quantified at different flowrates. Results shows that presence of nanoparticle does improve the exchanger performance and such enhancement is augmented with the increase in the flowrate of the nanofluid. Mixing more particles of TiO2 ameliorates the energy interaction of the hot/cold fluids. Nevertheless, the loss of heat to the atmosphere is shown to increase.

Optimization of NTUm allocation between dehumidifier and regenerator in liquid-desiccant air-conditioning system

Abstract Heat and mass transfer capacities of dehumidifier and regenerator significantly affect the performance of a heat pump driven liquid desiccant air-conditioning (HPLDAC) system. When the dehumidifier and regenerator have the same air flow rates, an equal allocation of the total usable number of mass transfer units (NTUm) between the dehumidifier and regenerator is an intuitive choice. However, whether the equal allocation can result in the optimal system performance is still a pending question. Thus, the optimization principle of NTUm allocation between dehumidifier and regenerator in the HPLDAC system is theoretically deduced and illustrated in this study. The results reveal the equal allocation is recommended when the nonlinearity of the isoφ line is insignificant, whereas allocating more NTUm to the dehumidifier than regenerator is recommended when the nonlinearity of the isoφ line is significant. When the NTUm values of the dehumidifier and regenerator are large enough, further increases of the NTUm values show limited effect on performance improvements of the dehumidifier and regenerator. Only when the total NTUm is below 10, does the NTUm allocation optimization play an important role in the system performance improvement, and is a pre-estimation necessary for achieving the optimal system performance.

Thermodynamic study on charge-discharge processes and cycle of cascaded latent heat storage in heating system

Thermodynamic analysis can guide the application of the cascaded latent heat storage system (CLHSS) for space heating. However, in previous studies, the CLHSS charge–discharge process and the cycle are not distinguished, and the applicability of the corresponding models is not analyzed. In addition, the technical advantages of CLHSS in heat utilization are still unclear. This paper solved the above three problems to provide theoretical guidance of the CLHSS integrated into heating systems. First, the CLHSS charge–discharge cycle is the special charge–discharge processes in which the initial and final states of each PCM are consistent. The CLHSS charge–discharge processes and cycle models are established and optimized. Second, the optimization results of charge–discharge processes model cannot ensure the same initial and final states of each PCM, which leads to unstable operation and performance degradation of the CLHSS. Thus, the CLHSS charge–discharge cycle model is recommended. Third, when the total number of heat transfer unit (NTU) of CLHSS is less than that of single-stage latent heat storage system (SLHSS), the thermal performance of CLHSS may be worse than that of SLHSS. Besides, the use of CLHSS instead of SLHSS is suitable for scenes with large temperature differences between heating equipment and heating terminals. Finally, parameters effects on optimization results are analyzed. From the perspective of improving entransy efficiency, it is recommended that the total NTU of CLHSS during charge process and discharge process are between 4.5 and 6, and as close as possible.

A study on vapor transport characteristics in hollow-fiber membrane humidifier with empirical mass transfer coefficient

Proton exchange membrane fuel cells are used in vehicles as a power source that generates electrical energy from hydrogen fuel and oxygen. Proton diffusion through the membrane module requires a certain level of water content in the supply air to maintain its performance. Therefore, water management plays an essential role in fuel cell operation. For large cells, external humidifiers are commonly installed to deliver the desired amount of water to the reactant gasses. This study investigated the performance of a hollow-fiber membrane humidifier through water transport in the membrane module using a mass exchanger model and various operating variables. In the humidifier, water particles from the high-concentration side, or wet air flow, transfer through the membrane to the dry air flow, which has a lower concentration rate. The vapor transport depends on the membrane's physical characteristics and the flow properties on both sides. These influences are represented by a parameter called the overall mass transfer coefficient, which is estimated by experiments. Then, the effectiveness–NTU (number of transfer units) approach is employed to analyze the mass transfer in the humidifier as a mass exchanger model. The analogy between heat transfer and mass transfer helps in applying the traditional effectiveness–NTU method from heat transfer analysis to a mass transfer analysis with additional information from experiments. In this study, a best fit equation is generated from experimental data and employed mass transfer calculations at varying temperatures, humidities, and flow rates. The results suggest that the wet air's relative humidity is the most crucial operating parameter that influences the dry air humidity. The dry air flow rate has more significant effects on the humidification process than the wet flow. In the case of geometric parameters, the length, number of membranes, and type of arrangement are discussed.

Thermal performance, embodied energy and environmental CO2 emissions analyses for double pipe U-bend heat exchanger working with MWCNT/water nanofluid

The thermal performance, embodied energy, and environmental CO2 emissions are evaluated experimentally for MWCNT/water nanofluid flow in a double pipe U-bend heat exchanger. The experiments were conducted at different Reynolds number (3500–12000) and particle volume concentrations (0.05%–0.3%). The thermal conductivity and viscosity are augmented by 15.27% and 9.15% at a temperature of 70 °C with respect to water data. The Nusselt number, heat transfer coefficient, thermal performance factor are enhanced by 31.3%, 44.17%, and 25.5% at a particle concentration of 0.3% and a Reynolds number of 10,005 over water data. The pressure drop, pumping power, friction factor penalty are 17.05%, 15.96%, and 14.29%, at 0.3% particle concentration and a Reynolds number of 10,005, compared to water. The effectiveness and number of transfer units are increased by 2.49% and 2.75% at 0.3% particle concentration and a Reynolds number of 10,005 compared to water data. The cost, weight, embodied energy, and CO2 emissions are analyzed based on the enhanced effectiveness of the heat exchanger. The total embodied energy from the heat exchanger using water is 403.7 MJ and it reduced to 393.1 MJ with 0.3% nanoparticle concentration. The heat exchanger cost is reduced to 61.46$ using 0.3 vol % of nanofluid whereas it is 63$ using water. The environmental CO2 emissions released from the heat exchanger are reduced to 81 kg of CO2 using 0.3 vol % of nanofluid, whereas it is 83.3 kg of CO2 using water.

Advancing Water Conservation in Cooling Towers through Energy-Water Nexus

Life without water is not possible on the earth, while modern humans need water not only for drinking, sanitization, and agriculture but also for industrial activities including electricity and cooling generations. Hence, emphasis on water sustainability through different sectors including thermoelectric and cooling plants is an intelligent strategy while the tight connections of water and energy guide study towards energy-water nexus investigations. Cooling towers are equipment for dissipating the excess heat by water evaporation or they hidden gates for wasting water. The objective of the present study is to elaborate on the role of cooling towers in improving environment sustainability by presenting various methods of energy and water modeling, categorizing various methods for modifying water and energy consumptions through past studies and mapping future studies. regarding cooling towers. Presenting a history of energy-water modeling methods of cooling towers, the Markel, the Poppe, and the effectiveness– Number of Transfer Unit (NTU) models, has followed by assessing the environmental impact of cooling towers in the form of excess water consumption, plume, and energy usage. Summarizing and organizing the past efforts for upgrading water management in cooling towers have been in two directions either providing more water supply, or modifications of the cooling tower to use less water. Then the different methodologies for each direction are introduced for further elaborations. This study’s practical outcome is proposing the methods of improving water sustainability for any cooling towers from past studies to assist engineers in the industry in modifying cooling towers water consumption. Showing the roadmap for the planning future investigations on the cooling towers based on the past efforts is another outcome of the present study to provide an insight for academia with research interest on cooling towers.

Effects of water-aluminum oxide nanofluid on double pipe heat exchanger with gear disc turbulators: A numerical investigation

The effects of adding the aluminum oxide to water in the water to water double pipe heat exchanger with six gear disc turbulators are numerically investigated; in which the nanoparticle with a concentration of 1%, 4%, and 6% is added to the hot fluid and streaming inside a tube with the Reynolds range from 3000 to 13000. Water as the cold fluid goes through the shell in Reynolds of 500, and six gear disc turbulators are located at the shell. The results indicate that turbulators enhance thermal effects. The collision of fluid with the surface of the turbulator and breaking of the boundary layer increase the heat transfer and local Nusselt number about 70%. Also, adding nanoparticles in the heat exchanger with turbulators increases the average Nusselt number, the effectiveness, and the number of transfer units. They increase by increasing the concentration of nanofluid. So that at the maximum state, adding nanofluid in the heat exchanger with turbulators increases these parameters by 1.21, 1.19, and 1.20 times compared to the heat exchanger with turbulators and pure water, respectively. Furthermore, from the contour of the number of transfer units is pointed out more useful of the nanofluid at the higher Re number.

Heat Exchanger Performance in Pilot Plant Testing of Piperazine with the Advanced Stripper™

The performance of four key heat exchangers at the National Carbon Capture Center (NCCC) during 4000 hours of operation is analyzed in this paper. A 0.5 MW integrated absorption-stripping pilot plant using Piperazine with the Advanced StripperTM (PZASTM) was used, with 5 m piperazine (PZ) as the capture solvent. Data from the coal and Natural Gas Combined Cycle (NGCC) campaigns were used, with flue gas compositions of 12% and 4% CO2. For the steam heater, data from multiple campaigns at the Separations Research Program (SRP) at the University of Texas J. J. Pickle Research Campus were used. All the exchangers were simulated in Aspen Plus®, and the IndependenceTM model was used to estimate properties not measured on-site. The performance metric used was the number of transfer units (NTU) for the cold, hot, and CO2 exchangers, and the overall heat transfer coefficient for the steam heater. The cold and hot exchangers exhibited similar performance throughout both campaigns, averaging a lean side NTU of 13.4 and 4, respectively. The pressure drop on both sides of both exchangers was correlated with the operating variables, with an added term to represent the flashing of the rich stream in the hot exchanger. Model deviations were under ± 25% for both units. The steam heater at NCCC underperformed in relation to design expectations. When compared to the performance of the steam heater at SRP, the low fluid velocities measured at NCCC suggest pool boiling operation, which is characterized by low thermal performance. The CO2 exchanger performed better than expected, with average NTU of 3.7 and 5.4 on the CO2 and rich sides. The cold, hot, and CO2 exchangers were analyzed for performance loss during the NCCC campaigns. The cold and CO2 exchangers did not show any statistically significant loss of performance during the campaigns, but the performance of the hot exchanger degraded slightly over time, suggesting the presence of fouling or leaking due to corrosion of the SS316L plates by the flashing rich stream.

A CFD study on thermohydraulic characteristics of a nanofluid in a shell-and-tube heat exchanger fitted with new unilateral ladder type helical baffles

The present study aims to research the thermohydraulic characteristics and performance index for flow of the nanofluids containing varied particle shapes including cylinder, blade, brick, platelet, and Oblate Spheroid (OS) in a shell and tube heat exchanger (STHX). The STHX is equipped with new unilateral ladder-type helical baffles to develop spiral stream inside the shell side. The nanofluid is assumed as the hot fluid that passes inside the tube side. Water is selected for the cold fluid that flows within the shell side with Reynolds numbers of 5000 to 20,000. The flow pattern developed by the baffles has noticeable impacts on the STHX performance. By the rise in the Reynolds number of the shell side, the heat transfer rate, overall heat transfer coefficient, effectiveness, Number of Transfer Unit (NTU), and pressure drop increase, whereas the performance index decreases. Moreover, the highest heat transfer rate, overall coefficient, and pressure loss belong to the nanofluid containing the platelet additives, while the greatest effectiveness, NTU, and performance index happen for the nanofluid with the OS additives. The severe cross and secondary flows are completely obvious in the shell side due to the existence of the new baffles, specially at high Reynolds numbers.

Usefulness of adding magnetic nano-powders to water: Introducing novel criteria for assessing heat transfer applications

In this study, the usefulness of adding Fe3O4 nanoparticles to water was considered, taking into account the energy demand management. Based on experimental measurements, an increase of 90% and 130% in thermal conductivity and viscosity has been experienced owing to loading Fe3O4. The nanofluid advantage over base fluid is assessed by evaluating the figure of merit (FOM) proposed by various researchers. Taking into account the Prasher, Garj, Lee and Timofeeva criterion, the use of Fe3O4/water nanofluid is acceptable. According to Tesfai criterion, up to 1 vol%, utilizing Fe3O4/water nanofluid has priority over the base fluid. A novel criterion was derived for assessing the heat transfer potential in a smooth tube subjected to constant surface temperature. It was found that the heat transfer potential depends on the number of transfer units (NTU). For NTU > 5, loading nanoparticles decreased the heat transfer potential up to 11% owing to a decrease in specific heat.

Effect of curved segmental baffle on a shell and tube heat exchanger thermohydraulic performance: Numerical investigation

In this paper a numerical investigation on shell-and-tube heat exchanger (STHE) with three configurations of novel segmental curved baffles (convex core baffles/convex peripheral baffles (CB1), convex peripheral baffles/convex core baffles (CB2), and convex peripheral baffles/concave core baffles (CB3)) for thermohydralic performance analysis and enhancement is presented. STHE with conventional straight baffles (SB) is also numerically studied for comparison. Each baffle configuration was tested under different Reynolds number in shell side (Rec) (17693–30331) based on the overall heat transfer coefficient (U), effectiveness (ε), and number of transfer unit (NTU). Also, pressure loss across the shell side is calculated to estimate the energy loss from the system due to the suggested design. In addition, the influence the inlet cold fluid temperature, baffle cutting ratio, and baffle spacing are tested, analyzed and discussed. The results showed that CB3 configuration results in a significant augmentation of the heat exchanger performance compared with the others two configurations for all investigated cases. The enhancements in U, ε, NTU by using CB3 configuration compared to SB are 48.98%−51.31% and 22.92%–23.62% and 48.98%–51.31% respectively, with decreasing in pressure loss by 12.40%–11.22%.

Performance Assessment of Double Corrugated Tubes in a Tube-In-Shell Heat Exchanger

In this article, the performance of double corrugated tubes applied in a tube-in-shell heat exchanger is analysed and compared to the performance of a heat exchanger equipped with straight tubes. The CFD (computational fluid dynamics) analysis was performed considering a turbulent flow regime at several mass flow rates. It is observed that the double corrugated geometry does not have a significant impact on the pressure drop inside the analysed heat exchanger, while it has the potential to increase its thermal performance by up to 25%. The ε–NTU (effectiveness–number of transfer units) relation also demonstrates the advantage of using double corrugated tubes in tube-in-shell heat exchangers over straight tubes.