Small Flow Rate Research Articles

Design and Analysis of a Thermal Flowmeter for Microfluidic Applications: A Study on Sensitivity at Low Flow Rates

To address the challenge of precise flow rate measurement in microchannels, this research details the conceptualization and comprehensive evaluation of a thermal flowmeter which works on the principle of calorimetry for measuring small flow rates between 0.1 and 180 mL/h. The thermal flowmeter is composed of a silicone pipe, a heater, three platinum thermal sensors (T1, T2, T3), and water as the working fluid. The flowmeter is strategically placed to monitor the complex thermodynamics between upstream and downstream flows. The analysis revealed a notable decay in the slope of the temperature differences beyond a flow rate of 40 mL/h, indicating the exceptional sensitivity of the device at lower flow rates and making it an ideal choice for medical applications. Parametric analysis was also carried out to place the sensors at optimized locations for better sensitivity.

Experimental study of CO2 jet field and CO2-MQL-assisted turning of Ti-6Al-4V based on mass flow rate and pressure

The effectiveness of jet cooling is significantly influenced by both mass flow rate and pressure, which are interrelated and exhibit a coupled relationship. This study examined the effects of mass flow rate and pressure from the perspectives of thermodynamic theory, jet field temperature, micromorphology, and the performance of CO2-MQL-assisted turning of Ti-6Al-4V alloys. Comparative experiments demonstrated that a small mass flow rate of CO2 (1.00 g/s) can achieve cooling and lubrication effects comparable to those of a larger mass flow rate (1.83 g/s) when applied at pressures of 7.38 and 6.00 MPa, respectively. For varying pressures, the maximum differences in improving the CO2-MQL on turning force, turning zone temperature, and surface roughness were 2.36%, 26.31%, and 39.63%, respectively. Conversely, the maximum differences for varying mass flow rates were 1.32%, 17.53%, and 19.66%. The results indicate that pressure has a more significant impact and that optimizing the combination of pressure and mass flow rate is substantial for cooling and lubrication. This study offers a reference for reducing CO2 consumption in CO2-MQL applications, thereby enhancing the alignment of CO2-MQL with sustainable manufacturing practices.

The Effect of Tailwater on the USBR Type III Stilling Basin Model

This study evaluates the impact of tailwater on the USBR Type III stilling pond model, which is often used to construct reservoirs with low hydrostatic pressure and small flow rates. The model includes channel blocks, barrier blocks, and end barriers to dampen energy, converting flow from supercritical to subcritical. Hydraulic characteristics, including potential jump types, pressure regimes, and forces on the barrier, are not considered. Any change in discharge during the test also changes the tailwater depth position. The purpose of this study was to determine the effects of tailwater conditions on water height (y1 and y2), pool length (Lj), Froude number (Fr), critical depth (yc), and energy dissipation effectiveness (ΔE). This study shows that the average energy dissipation ratio of USBR Type III Quiet Pool is 87.45% without the effect of Tailwater, with an efficiency rate of 12.55%. When exposed to Tailwater, the average energy dissipation ratio drops to 69.47%, resulting in an efficiency rate of 30.53%. The optimum stilling pond performance is affected by the presence of tailwater (Tw), which reduces the energy dissipation ratio. The depth of the tailwater aids in the dissipation that occurs. Technical abbreviations will be explained in the first use. The water level rise under tailwater conditions exceeds that without tailwater. This finding shows tail water's importance for height rise and flow conditions. Flow conditions with Froude Number (Fr2) values of 0.22 (<1) and Tw are classified as subcritical flow.

Research on positioning control strategy of hydraulic support pushing system based on multistage speed control valve

The precise position control of the hydraulic support pushing system in the coal mining face is a key technical support for intelligent coal mining. At present, the hydraulic support pushing system uses the electro-hydraulic directional valve as the control element. However, the electro-hydraulic directional valve has problems such as discrete input values, low switching frequency, delay, inability to adjust flow, and large flow fluctuations during the switching process, which results in relatively low positioning control accuracy of the hydraulic support pushing system. Therefore, this study introduces a multi-stage speed control valve that is suitable for underground coal mine conditions and can achieve flow regulation. At the same time, a segmented control strategy combining Bang-Bang control and online predictive control is proposed. Bang-bang control is used for fast propulsion with large flow rate, large range, and short time. Online predictive control method is used to achieve precise positioning control with small flow rate and small range, thereby solving the problem of low positioning control accuracy caused by the imperfect characteristics of electro-hydraulic directional valves. Finally, this study verified the effectiveness of the proposed scheme through simulation and experiments. The results showed that compared with existing logic positioning control methods based on electro-hydraulic directional valves, the proposed scheme can improve the accuracy of single cylinder positioning control from 62 mm to within 10 mm.

Design, construction and testing of the prototype cryogenic circulation centrifugal pump for the high energy photon source

A cryogenic circulation pump (CCP) with the small flow rate and low heat leakage, which is thekeyequipment of the cooling system for the cryogenic permanent magnet undulator (CPMU)and synchrotron monochromator in High Energy Photon Source(HEPS), is developed according to the design parameters and operation experiences. The mechanic structure of the CCP including a motor at room temperature, an impeller and a volute in the cryogenic environment is designed, and numerical simulation on the rotating shaft and internal flows are performed to predict the mechanical and hydrodynamic performances of the pump. Meanwhile, the experimental investigation of the CCP is carried out in the liquid nitrogen (LN2) cryogenic system, and the hydrodynamic performances of the CCP are verified experimentally. The results are shown that the calculated performances of the CCP are in reasonable agreement with the experimental results, which indicates that the numerical calculation model of the CCP is more effective. Moreover, the deviations of pressure drop and efficiency between the calculation and measurement are analyzed in this paper.

Investigations on cooling heat transfer of CO2-based mixtures in a novel airfoil fin mini-channel at supercritical pressure

Thermal-hydraulic characteristics of three supercritical CO2-based mixtures (CO2/H2S, CO2/Xe and CO2/propane) in an airfoil fin (AFF) mini-channel adopted in the printed circuit heat exchanger (PCHE) under cooling conditions are comprehensively investigated through numerical simulations. The results show that the CO2/H2S mixture, which has higher critical temperature and larger critical pressure than the pure CO2, exhibits the greatest heat transfer performance among three mixtures. This advantage is particularly pronounced at relatively large Reynolds number, with small mass fraction of the H2S and under near-critical conditions. The overall friction loss of mixtures with the additive mass fraction smaller than 0.3 is comparable to that of the pure CO2. The heat transfer coefficient of the mixtures presents fluctuations during the cooling processes, and this goes against the stable and safe operation of the PCHEs. These fluctuations could be mitigated at relatively small mass flow rate and with small mass fraction of the additive. Three widely-recognized buoyancy criteria are employed to predict the onset of the buoyancy effects in the AFF channel, and the superior heat transfer of the CO2/H2S mixture could be attributed to the fiercer buoyancy effects. Considering the buoyancy effects, modified correlations for the flow and heat transfer of pure CO2 and the CO2-based mixtures in the novel mini-channel are proposed. The maximum deviations of the modified Nusselt number and fanning friction factor correlations are ± 25 % and ± 20 %, respectively.

Robot-LDA Plane Measurements And Smoke Investigations On A 30° Inclined Flat Plate In An Open Wind Channel With And Without Plasma Actuation Effect

Active flow control is a relatively new approach to influence the velocity vector field for plane airfoils or process engineering applications with a plasma source. The goal is to positively effect the point of separation to increase the lift/drag ratio or increase separation efficiency and to reduce pressure drop. In the presented study two approaches, the Robot-LDA measurements and smoke investigations, are chosen to find out whether the plasma source has an effect on the velocity vector field on a 30°inclined flat plate and the separation point. A flow rate of 250 m³/h resulting in a Reynolds number of 100 000 is chosen, since this is typical for already presented results within the field of plasma source investigations. With Robot-LDA in total 825 measurements points of the axial wind channel velocity components are captured twice, with and without activated plasma source. The measurement plane was set 80 mm x 50 mm orthogonal to the flat plate in the middle of the wind channel axis. The plasma source was powered with 14 kVp−p and 5 kHz. Due to stability of the plasma actuator, the LDA measurements were subdivided into eight regions. For the same configurations smoke investigations are performed. A chromium-nickel wire with a diameter of 0.213 mm is heated by an electronic circuit including capacitor and power source to vaporize liquid paraffin. The flow field is captured by a highspeed camera. Robot-LDA measurement results show a free-stream axial wind channel velocity component of about 15 m/s. In the shadow region of the 30°inclined flat plate a recirculation zone is found due to negative velocity components. At a distance up to 12 mm close to the plat plate, wall reflections dominated and to find valid LDA measurement results were not possible. With and without activated plasma source velocity differences between -0.5 m/s and 0.5 m/s are found. The biggest velocity differences are in the region of 15 mm to 45 mm relative to the tip of the inclined flat plate. For post-processing purposes, the 3D wind channel geometry and the Robot-LDA measurement results are loaded in ParaView 5.10.1. Smoke investigations show that the plasma source minimally attach the flow to the flat plate. This effect is higher with smaller flow rates (50 m³/h) than with 250 m³/h. Robot-LDA and smoke measurement results are promising that flow influence due to plasma has potential in various applications in future.

Performance enhancement of a vortex ring thruster by adopting the Coanda effect

A vortex ring thruster (VRT) is a propulsion device in which a piston pushes fluid and thrusts it in reaction. As the fluid inside a VRT is moving, the boundary layer near the wall at the edge of the exit surface of a VRT separates and rolls up into a vortex ring. In this paper, we performed performance analysis on a regular VRT and a VRT enhanced by the Coanda effect (hereafter referred to as a CoVoRT) on axisymmetric geometry. A CoVoRT consists of two jets: a primary jet and a Coanda jet. The primary jet has a relatively large volume flow rate compared to the Coanda jet, and the Coanda jet attracts the surrounding fluid by flowing along the curved surface at a relatively small flow rate. The present study evaluates the propulsion performance in two ways using SNUFOAM. This software was developed based on OpenFOAM, which is an open-source computational fluid dynamics (CFD) toolkit and specialized for naval hydrodynamics. The first one quantifies the propulsion performance by calculating the ratio of energy input and energy output generated by two jets during a stroke of the piston motion. The second one is to observe the evolution and pinch-off process of a vortex ring with formation time, which is a non-dimensional time scale. The comparison of propulsion performance was conducted with changes in the curvature of the Coanda jet, changes in the length of the Coanda jet exit, and changes in the Coanda jet velocity and piston stroke ratio. For quantitative evaluation of propulsion performance, the propulsion performance evaluation index (PPEI) was introduced. The results showed that the PPEI of a CoVoRT was improved by about 50% compared to that of a VRT, and it was confirmed that the dynamic characteristics of a CoVoRT’s vortex ring were superior to those of a VRT in terms of propulsion performance.

Characterization of loss, temperature, and stress on partial admission axial impulse turbines with liquid jet impingement cooling

The turbines for underwater applications can use abundant water as the cooling medium. However, the use of liquid water is associated with the multi-phase and multi-physics problems and presents additional losses. This paper proposes a numerical coupling method and corresponding loss breakdown approach to analyze the performance of this particular turbine cooling problem at different water mass flow rates. The results show that the cooling water induces additional loss, while the influence of the resulted structural deformation on turbine efficiency is comparatively small. Through numerical loss breakdown, it is found that the exit kinetic energy loss is significantly decreased, but other losses are increased correspondingly due to the cooling water. By examining the turbine stress and temperature distribution, the small water mass flow rate of 0.02 kg/s is sufficient to avoid damage to the disc, however, additional cooling is necessary to minimize the plastic region at the turbine blades. The suitable loss model for the turbine with cooling water is established and a relative difference less than 3 % is attained by comparing mean-line and numerical results. This work provides new insight into the analysis method and characteristics of the partial admission axial turbine with cooling water.

Influence of Impeller Structure Parameters on the Hydraulic Performance and Casting Molding of Spiral Centrifugal Pumps

In order to study the influence of impeller structural parameters on the hydraulic performance and casting moulding of spiral centrifugal pumps, this paper selects a double vane spiral centrifugal pump with a specific rotation number of 170 as the research object. The Plackett–Burman experimental design is used to screen the influencing factors, and the results show that the vane thickness and the impeller outlet width are the significant influencing factors. Based on this result, five different scenarios were set for these two key parameters, numerical calculations were carried out using numerical simulation software for each of the five flow ratio cases, and casting simulations were carried out for the model of each scenario using AnyCasting6.0 to analyze the influence of these two factors on the hydraulic performance and casting forming of the spiral centrifugal pump. It was found that in terms of vane thickness, a moderate increase in vane thickness improved the hydraulic performance at small flow rates, but an excessive increase at large flow rates led to a decrease in efficiency and an increase in the probability of casting defects. In terms of impeller outlet width, increasing the outlet width caused the design point to be shifted, leading to a decrease in efficiency at small flow rates, but an increase in efficiency when the design flow rate was higher. At the same time, increasing the outlet width makes casting defects more likely to occur at the blade and back cover joint than on the blade surface. The study in this paper clarifies the significant effects of these two parameters on the performance and casting quality of spiral centrifugal pumps, and provides guidance for the optimal design of spiral centrifugal pumps.

Influence of offset blade on pressure fluctuation in a centrifugal pump under different conditions

Abstract In this paper, the pressure fluctuation under different working conditions of hydrofoil blade impeller (AF), offset blade impeller (SP) and offset winglet impeller (DAF) were measured and the influence of different structures on pressure fluctuation was analyzed. The results show that the discrete frequency caused by rotor-stator interaction (RSI) between impeller and tongue is the blade passing frequency (fBPF ) and its harmonic frequency. Pressure fluctuation amplitude of blade passing frequency is obviously suppressed by offset blade. The value of pressure fluctuation of DAF is small near the tongue under small flow rate, and the energy suppression effect is obvious. With the increase of flow rate, the fluctuation energy of DAF increases gradually, and that of SP decreases gradually.

The Study of Using the Inducer to Improve the Cavitation Performance of a Centrifugal Pump

Abstract To improve the cavitation performance of a single-stage, single-suction centrifugal pump, this study compared the effects of an equal-pitch inducer and a variable-pitch inducer. Experimental results revealed that the NPSH3 of the pump without an inducer is 4.6m for operation at Q=80m3/h, while with an equal-pitch inducer and a variable-pitch inducer are respectively 2.6m and 2.2m. Both two inducers significantly increase the shut-off heads, while the BEP shift towards smaller flow rates, with the maximum efficiency value reduced by about 3%. The CFD simulation analysis show that when the inlet total pressure is greater than 4m, the equal-pitch inducer has better anti-cavitation performance, while the variable-pitch angle inducer has a better inhibitory effect on cavitation development which the inlet total pressure is less than 4m. To further enhance the pump’s cavitation performance, filing blade inlet suction side of the variable-pitchinducer is necessary to reduce the NPSH3 from 2.2m to 1.7m, resulting in a 22% improvement in cavitation performance.

Elasto-inertial particle focusing in sinusoidal microfluidic channels.

Dean flow existing in sinusoidal channels could enhance the throughput and efficiency for elasto-inertial particle focusing. However, the fundamental mechanisms of elasto-inertial focusing in sinusoidal channels are still unclear. This work employs four microfluidic devices with symmetric and asymmetric sinusoidal channels to explore the elasto-inertial focusing mechanisms over a wide range of flow rates. The effects of rheological property, flow rate, sinusoidal channel curvature, particle size, and asymmetric geometry on particle focusing performance are investigated. It is intriguing to find that the Dean flow makes a substantial contribution to the particle elasto-inertial focusing. The results illustrate that a better particle focusing performance and a faster focusing process are obtained in the sinusoidal channel with a small curvature radius due to stronger Dean flow. In addition, the particle focusing performance is also related to particle diameter and rheological properties, the larger particles show a better focusing performance than smaller particles, and the smaller flow rate is required for particles to achieve stable focusing at the outlet in the higher concentration of polyvinylpyrrolidone solutions. Our work offers an increased knowledge of the mechanisms of elasto-inertial focusing in sinusoidal channels. Ultimately, these results provide supportive guidelines into the design and development of sinusoidal elasto-inertial microfluidic devices for high-performance focusing.

Research on the factors influencing the width of hydraulic fractures through layers

The method of segmented hydraulic fracturing in the coal seam roof has proven to be an efficient technique for coalbed methane exploitation. However, the behavior of hydraulic fractures in multilayer formations with significant differences in mechanical properties is still unclear. This paper studied the variation in hydraulic fracture width at the coal-rock interface by employing experimental method with a true triaxial hydraulic fracturing experimental system and numerical simulation method. Results revealed that the hydraulic fracture more likely to expanded along the coal-rock interface instead of break through it with the small horizontal stress difference and low flow rate injection condition. And improving the injection flow rate lager than a critical value, the hydraulic fracture tends to break through the coal-rock interface. Hydraulic fractures in both mudstone and coal beds exhibited a trend of increasing and then decreasing of fracture width at the interface. Since the strength of the coal seam was lower compared to that of the mudstone, maintaining high pressure was no longer necessary when the hydraulic fracture crossed the interface and entered the coal seam, leading to a reduction in fracture width within the mudstone. During the later stages of fracturing, the entry of proppant into the coal seam became challenging, resulting in a phenomenon characterized by excessive fluid but insufficient sand. The time required for the fracture width to traverse the proppant was found to be inversely proportional to the difference in horizontal ground stress and the flow rate of the fracturing fluid. And it was directly proportional to the modulus of elasticity, permeability of the coal seam, and interface strength. The interface strength has the greatest influence on the width of hydraulic fractures. In conclusion, this study provides valuable insights into the behavior of hydraulic fractures in multilayer formations with varying mechanical properties. The findings contribute to a better understanding of the factors affecting hydraulic fracture width within coal seams, which can ultimately enhance the efficiency of coalbed methane exploitation.

Effect of precooling the in-charged on the performance of hydrogen storage systems packed with typical kinds of adsorbents

Selecting suitable adsorbents and managing the thermal effect are two important aspects on the practical application of the hydrogen storage system by adsorption. In this research, three kinds of promising adsorbents, which include MOF-5, MIL-101(Cr) and activated carbon AX-21, were selected for evaluating the effect of pre-cooling of hydrogen in-charged into a 0.5 L cylindrical vessel experimentally and numerically as per the temperature fluctuation, heat generated, accumulated amount of the charge under the flow rate of hydrogen required by an on board 5 kW PEMFC power unit. The validation of the prediction accuracy of the model was performed by the experiments conducted respectively at 77.15 K and 298.15 K where the vessel was packed with MIL-101(Cr). Simulations were further performed to evaluate the performance of the vessel respectively packed with three kinds of adsorbents within the flow rate range 15–40 L min−1 and temperature range 77.15–298.15 K. Results show that precooling the hydrogen in-charged is conducive to weakening the temperature fluctuation of the storage system, and heat from adsorption is the main factor affecting the accumulated amount of charge and the temperature fluctuation within the hydrogen storage system. It suggests that MOF-5 is a more suitable hydrogen storage medium than MIL-101(Cr) and AX-21, and charging the system with hydrogen precooled at 77.15 K under a smaller flow rate is beneficial to improving the performance of the storage system.

Efficiency Improvement of Small Cryogenic Helium Turbo-expanders in TIPC

An experimental helium liquefier/refrigerator, using ultra high speed cryogenic turbo-expanders is designed and developed in Technical Institute of Physics and Chemistry (TIPC), and liquefaction rate of around 42 L/hr and refrigeration capacity of around 130 W @ 4.5 K is achieved. The turbo-expander constitutes the most critical component of a helium liquefier/refrigerator causing that the turbine efficiency has a great influence on the performance of the whole cryogenic process plant. Inlet Flow Radial (IFR) turbine design is dictated by criteria like velocity ratios. For small flow rate plants the size of the turbine impeller needs to be reduced. In order to reach a high efficiency, the rotational speed must be increased to complete a large specific enthalpy drop. The present article describes the latest technical developments at TIPC, including results obtained during field trials with the TIPC helium liquefier and refrigerator. The motivation of these developments is to improve the efficiency of the machines, and also to widen the range of operation.

Energy-efficient bubble aeration guided by bubble dynamics model: From bubble formation at submerged orifice to oxygen utilization during uprising

Bubble aeration is a significant consumer of energy in wastewater treatment processes. Optimizing oxygen transfer, from an energy usage perspective, is crucial in the development of clean production techniques and for the stimulation of the circular economy. Although large efforts have been made in enhancing this process, particularly in ameliorating bubble diffusers, a main problem lies in energy wastage due to over-pursuing ultra-fine bubble generation. In this study, a dynamic model, that integrated both bubble expansion and detachment at submerged orifices, and consequential oxygen utilization during the uprising, was developed in order to better facilitate energy savings during the control of bubble generation. We demonstrate through calibrated models that bubble formation is governed by many factors including gas flow rate, orifice radius, surface tension, liquid viscosity, and surface wettability. Small bubbles are more prone to form when subjected to conditions of high wettability, small orifice size and low flow rate, since the bubbles are easily detached by the increasing upward forces in these scenarios. The oxygen transfer during the rising process was calculated as a function of bubble size, gas type and water depth. Bubbles with a radius smaller than a threshold value can shrink and collapse while below the water surface and thus provide 100% oxygen utilization. The threshold values of bubble radius are determined to be 150 μm and 250 μm at 5 m and 15 m initial water depth, respectively. The parameter set for bubble generation in order to obtain the desired bubble size may then be inversely determined by our bubble formation model, and it's considered as optimal aeration strategy to realize precise aeration. With these results, our study highlights the viability of the approach employing the proposed model in order to direct energy-efficient bubble generation.

Low-order modelling of three-dimensional surface waves in liquid film flow on a rotating disk

Using low-dimensional numerical simulations, we investigate the characteristics of complex and three-dimensional surface waves in a liquid film flowing over a rotating disk, focusing on large flow rates from a nozzle. Existing integral boundary layer (IBL) models, which are based on spatially averaged variables along the direction normal to the disk surface, have primarily focused on the formation of axisymmetric waves under relatively small flow rates. In this study, an extended IBL model that accounts for both laminar and turbulent regimes is developed by considering the non-uniformity of the local flow rate in the spreading film flow and incorporating closure models dependent on the local Reynolds number. Our numerical results successfully capture the generation of concentric waves by an impinging circular liquid jet and their transition into three-dimensional solitary waves. These findings are in good agreement with visualization images and time-series data of free-surface fluctuations from a displacement sensor. The backscattering of small-scale three-dimensional turbulence into large-scale horizontal turbulence inside the film plays a critical role in determining the transition of wave modes and the nonlinear dynamics of the waves in the turbulent regime. Furthermore, the behaviour of three-dimensional waves in the downstream region, including frequent wave coalescence in the transition region and the breakup of small-scale solitons, is distinct from that of gravity-driven falling film flows. The amplitude of the three-dimensional waves is inversely related to the generalized Reynolds number defined for rotating films.

Подземные источники балки Пещерная озера Баскунчак: гидрохимические особенности и эмиссия парниковых газов

For the first time, full-scale measurements of methane and carbon dioxide emissions by the chamber method were carried out in summer for groundwater sources discharged in the valley of the Peshernaya Gulch creek, located in the north-west of Lake Baskunchak. pH values, concentrations of CH4, basic ions, gross Fe and Mn were determined in the water of the sources; concentrations of CH4, H2S, organic matter, Eh and pH values, density and humidity were determined in various layers of bottom sediments (up to 27 cm). A detailed description of the identified groundwater sources was carried out, their primary morphometric and morphological characteristics were measured, as well as the flow rate. It was found that more than 10 ascending karst sources of groundwater are discharged in the Peshchernaya beam, 5 of which were active during the research period and mainly confined to the left screw of the beam. The active sources of the left screw of the beam are characterized by a small flow rate and are sodium chloride brines with a mineralization of 93.9–107.1 g/l. The bottom sediments accumulating in the sinkholes of underground sources are characterized by a neutral acid-base environment and restorative conditions. The concentrations of CH4 and ∑H2S in the sediments of the sources varied, respectively, in the range of 0.08–0.77 µg/g vl.o. and 0.023–2.63 mg/g vl.o. with minimal values for both gases in the lower less reduced layer with a low content of Sorg. The concentration of methane in the water of active sources varied from 26.3 up to 38.4 µl/l and was on average 2 times higher than in the waters of a stream fed by them and an inactive source. The specific methane flux from the water surface of active sources varied in the range of 0.6–1.5 mg/(m2∙h), which is 2 orders of magnitude lower than the specific CO2 flux of 46.4–106.1 mg/(m2∙h). The isotopic composition of carbon (δ13C) CH4 and CO2 measured in gas bubbles rising from the bottom of one of the ascending sources indicates the modern biochemical genesis of these greenhouse gases.

CALCULATION OF CLOSED WET COOLING TOWERS USING MODIFIED Ε-NTU APPROACHES

Two modified ε-NTU approaches developed for air-to-air indirect contact evaporative coolers have been adapted for calculation of heat/mass transfer in the closed wet cooling towers. These approaches use the analogy between the heat and mass transfer and the linearization of the direct or inverse correlations of moist air enthalpy on the temperature of the wet bulb. The results of calculation based on the modified ε-NTU approaches were compared with the data obtained by the traditional method, using the average logarithmic temperature and concentration differences. The comparison was carried out in terms of heat transfer efficiency according to the temperature of the wet bulb, this temperature is the theoretical limit of the outlet water temperature for this type of heat and mass exchange equipment of the indirect evaporative type. Calculations showed that both ε-NTU approaches demonstrate almost identical results, the possible inconsistency between them may be related to the inaccuracy of linearization. These data agree well with the data of the calculations, which are based on application of the average logarithmic difference of the flow parameters and the empirical dependencies of the heat and mass transfer coefficients. A small discrepancy (up to 7%) occurs with a small flow rate of working water. Bibl. 15, Fig. 5