Intensification Of Heat Exchange Research Articles

The Thermohydraulic Characteristics Investigation of the Aluminum Alloy Monometallic Plate-finned Tube in Together with Numerical Simulation of Heat and Mass Transfer Processes

The article is devoted to the investigation of aluminium alloy plate-finned tube characteristics regarding to the heat exchange intensification. Outer thick finning, inner ribs quantity and rib shape allow to increase heat exchange efficiency. However, the most important task is finding an optimal combination of pipe geometry parameters. Seven different ribbed tube samples were investigated during the experiment. The samples differed by geometry, quality and quantity of ribbing, and consequently hydraulic and thermodynamic characteristics. The main criteria for an integrated assessment of pressure losses and energy indicators were the criteria of Kirpichev and Antufiev. The above evaluation criteria were intended for an overall assessment of sample effectiveness based on experimental data. In advance and parallel with a natural experiment, a numerical experiment was conducted. The purpose of the numerical experiment was obtaining an adequate model of the heat exchange section to be used in a full-sized oil cooler model in the future. Thus, the article discusses the results of comparing natural and numerical investigations and the prospect of using the best sample in the oil cooler composition. The ultimate goal is the development of an automatic air-cooling apparatus with a compact high-performance oil cooler.

ДОСЛІДЖЕННЯ МОЖЛИВОСТІ ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ ТЕПЛООБМІНУ В МОДИФІКОВАНИХ ТРАПЕЦІЄВИДНИМ ГВИНТОВИМ ПРОФІЛІМ ТРУБАХ МАЗУТОПІДІГРІВАЧА ПМ-40-15

Recently, a special direction in solving the problem of intensification of convection heat exchange, which is based on the idea of influencing the micro- and macrostructure of the flow of heat carriers by various swirls in the channels of their movement, has been widely developed in industrial heat engineering. Despite the huge number of publications on this topic, the issue of improving the effectiveness of heat exchangers remains far from its final solution. The research is aimed at studying the possibilities and limits of increasing the efficiency of heat transfer in the modified trapezoidal helical profile of the inner surface of the pipes of the fuel oil heater PM-40-15. To achieve this goal, the method of computer simulation using SolidWorks software was used. In this program, a geometric model of a fuel oil heater was created with both smooth standard pipes and modified pipes with trapezoidal profiles with a height of h = 2, 3 and 4 mm and relative steps of the screw profile S/D = 0.6, 0.8, 1.0, 1.2 and 1.5. The temperature of fuel oil M100 at the inlet of the fuel oil heater was taken to be 60°С, and the temperature of the walls of the pipes washed with superheated steam at a pressure of 1.0 MPa, 200°С. These parameters corresponded to the nominal mode of operation of the fuel oil heater PM-40-15. As a result of the research, it was found that the best efficiency indicators are achieved on pipes with a profile height h = 2 mm and a relative step S/D = 0.8.

Intensification of heat exchange by an ultrasound source for milk pasteurization.

The goal of this article is to investigate the effect of ultrasonic vibrations on the process of milk pasteurization. Ultrasound can potentially intensify heat transfer and reduce the formation of thermal sediment (soot deposit) on the walls of heat-exchange devices. The paper presents the results of experimental studies demonstrating the growth rate of thermal sediment on the wall of the heat-exchange apparatus and its amount in the volume of milk under the influence of ultrasonic vibrations and without it.

Analysis of increase in efficiency of air-cooled heat exchangers due to intensification of heat exchange

Currently, the issues of improving the heat transfer processes in air-cooled heat exchangers play a huge role in terms of increasing the cooling efficiency and thus reducing the size of heat exchangers. This significantly saves resources. There are several basic methods for increasing the heat transfer of fluids in air coolers, for example, such as: finning of tubes and heat exchange intensification with the help of tube inserts. The purpose of the study is to analyze the efficiency of different fin types and the use of tube inserts, as well as changes in the heat transfer coefficients of air and natural gas, depending on the changes in the types of fins and tube inserts, and their geometry. The application software is Xchanger Suite provided by the company HTRI to ITMO University. The result is the optimally selected geometry of the heat exchange intensifiers based on the analysis, what allows reducing the dimensions of the air- cooled heat exchangers, while providing the necessary heat load, the heat exchange surface reserve coefficient and the heat transfer coefficients.

Modern approaches to the intensification of heat and mass exchange in multi-temperature condensation filters

The article considers the problems and features of heat and mass exchange on developed surfaces in the conditions of both single-phase and vapour-liquid flow during its condensation. We give a brief analytical review of studies of hydrodynamics and heat exchange in such systems. We analyzed the efficiency of the working channel of the condensation filter and identified problematic points. We offer possible methods for intensifying heat and mass transfer on working surfaces.

Состояние разработок двухфазных систем терморегулирования космических аппаратов

The progress of space technology is leading to more and more energy-equipped spacecraft. The International Space Station already has the capacity of solar panels of more than 100 kW. Autonomous spacecrafts and satellites (including stationary ones) have the capacity of power units of kW, in the nearest future - more than 10 kW. Forced heat transfer using single-phase liquid coolants is still considered as the main method of thermal control on high-power spacecraft (SC). Single-phase mechanically pumped fluid loop is a fully proven means of thermal control of spacecraft with a moderate heat load. A significant disadvantage of such systems is that the coolant temperature varies significantly within the loop. The temperature difference can be reduced by increasing the coolant flow rate, but for this, it is necessary to increase the pump capacity, which inevitably leads to an increase in power consumption, pipeline diameters, and weight of the system as a whole. In the case of spacecraft with high power capacity (more than 5-10 kW) and large heat transfer distances (10 m and more), a two-phase mechanically pumped fluid loop for thermal control is more preferable in terms of weight, the accuracy of thermoregulation, power consumption (and other parameters). The use of a two-phase loop (2PMPL) as a spacecraft thermal control system allows to reduce significantly mass and power consumption for own needs in comparison with a single-phase thermal control system (TCS). The effect is achieved due to the accumulation of transferred heat in the form of latent heat of vaporization and intensification of heat exchange at boiling and condensation of coolant. The article provides a critical review of published works on 2PMPL for spacecraft with high power (more than 5...10 kW) and a large heat transfer distance (more than 10...100 meters) from 1980 up to nowadays. As a result, a list of the main problems on the way of practical implementation of two-phase loops is formed.

Gas–Liquid Two-Phase Flow and Heat Transfer without Phase Change in Microfluidic Heat Exchanger

This work presents an experimental study of the possibility of intensifying in microfluidic heat exchangers (MFHE) by creating a two-phase segmented flow (gas–liquid). Measurements of convective heat transfer were carried out using an MFHE, consisting of six channels 1 × 1 mm. Experimental studies have shown that segmented flow makes it possible to increase the Nusselt number of a laminar flow in MFHE up to 1.67 and reduce thermal resistance up to 1.7 times compared to single-phase flow. At the same time, it was found that the intensification of heat exchange by a two-phase flow is observed only for the range of the volume fraction of gas from 10 to 30%. In addition, the calculation of the thermal performance criterion, including both thermal and hydraulic parameters (friction factor), also confirmed the promise of using the Taylor segmented flow as a method for single-phase heat transfer intensifying in microchannels.

Computational parametric study on efficiency of low boiling point fluid plants under heat exchange process intensification

One of the main challenges for the energy industry is to improve the reliability and efficiency of heat exchange equipment in heating plants. Phase-change heat exchangers with low boiling point fluid (LBPF) are widely used in both conventional and renewable energy. The main objectives of increasing the efficiency of heat exchange equipment are to reduce the weight and dimensions, to increase the amount of heat transferred and to reduce the electricity consumption spent on pumping the heat transfer agent. These objectives are achieved by implementing various methods of heat exchange intensification in heat exchange equipment. A key aspect concerning application of various types of heat exchange intensifiers in heat exchange equipment is evaluation of possibility to increase their design efficiency. The paper presents the results of a computational parametric study of changes in efficiency of some LBPF-based plants when intensifying heat exchange processes by modifying functional surfaces of heat exchangers by laser ablation.

The influence of the supersonic nozzle length on the efficiency of energy separation of low-Prandtl gas flowing in the finned single Leontiev tube

The redistribution of the total temperature between the parts of the gas stream flowing through the Leontiev tube depends not only on the temperature recovery factor (Prandtl number) and the ratio of flows through the supersonic and subsonic channels of the tube (Mach numbers), but also on the thermal resistance of the separation wall. Earlier it has been shown that the reduction of thermal resistance due to the separation wall finning on the side of the subsonic flow leads to an increase in the efficiency of energy separation. It may be assumed that the intensification of heat exchange between channels, due to finning, reduces the length of the tube, which at the same intensity of heat exchange leads to a decrease in pressure losses and an additional increase in efficiency. This paper presents the results of numerical simulation of energy separation in Leontiev tubes with a finned separation wall and different lengths of supersonic nozzle. It is shown that the adiabatic efficiency of the energy separation in a short Leontiev tube with a finned wall increases when the outlet pressure decreases, while it does not change for smooth tubes.

Experimental comparative research of convective heat transfer enhancement in channels

This article presents the results of a comparative-experimental research of various methods to intensify heat transfer in the channel. Four different methods of heat exchange enhancement are considered: twisted tape, wire spiral, joint intensifier made of wire tape and twisted spiral, and acoustic method of intensification. The thermal and hydraulic characteristics of various methods of heat exchange intensification are experimentally investigated, and the efficiency of heat exchange intensification is determined. The thermal and hydraulic characteristics of a smooth channel without intensification obtained experimentally under the same conditions were used as a reference. In the course of the comparative analysis of the considered methods of intensification, the most effective ones are found in the range of changes in the Reynolds number from 10000 to 60000. The presented data can be used in the design of heat exchangers.

Diurnal variability of atmospheric cold pool events and associated air-sea interactions in the Bay of Bengal during the summer monsoon

Atmospheric cold pools generated from convective downdrafts can significantly modulate air-sea interaction processes, though the variability in cold pool events is not yet documented in the Bay of Bengal (BoB). In this study, the seasonal and diurnal variability of cold pool events (defined as a drop in air temperature greater than 1 °C within 30 min) in the BoB is examined using moored buoy measurements with 10-min temporal resolution at 8°N, 12°N, and 15°N along 90°E. The analysis shows that cold pools are plentiful and frequent during summer (May–September) and fall (October–November) compared to winter (December-February) and spring (March–April). Results also indicate a significant diurnal variability at 15°N and 12°N (but not at 8°N) during summer, with more frequent and intense cold pool events in the afternoon. Cold pools lead to an intensification of turbulent heat exchange between the ocean and atmosphere, with increased latent heat loss (~ 80 Wm−2) through both an increase in wind speed and reduction in air specific humidity and increased sensible heat loss (~ 40 Wm−2) due primarily to air temperature drops. There is also a significant diurnal variability in these air-sea exchanges during the summer, with a twofold enhancement in latent and sensible heat fluxes associated with afternoon vs nighttime cold pools events. Finally, we establish the connection between the enhancement of afternoon cold pool events and southeastward propagating synoptic-scale rainfall activity on diurnal time scales from the western BoB.

ИНТЕНСИФИКАЦИЯ ТЕПЛООБМЕНА В ТРУБКАХ С ПСЕВДООЖИЖЕННЫМ СЛОЕМ

It is shown that one of the promising methods of heat exchange intensification in the
 air-cooling unit is the organization of a fluidized layer.

3D Investigations of Heat Exchange and Hydrodynamics in Channels with Different Combinations of Ribs and Oval-Trench Dimples

As a result of 3D calculation in the ANSYS CFX software, combinations of ribs and oval trenches are revealed of the maximal thermal performance, intensification of heat exchange, and minimal drag coefficients.

Vortex intensification of heat exchange in rectangular section channel by the rotating disk on its wall

Vortex intensification of heat exchange in rectangular section channel by the rotating disk on its wall

Reduction thermal resistance methods in the thermal stabilizer

The thermal resistance of the composite thermal stabilizer and methods for its reduction are investigated. The thermal resistance of thermal stabilizer decreases due to the heat exchange intensification in evaporator by a layer of aluminum oxide nanoparticles. A method of producing aluminum oxide nanoparticles has been developed. The liquid capillary rise height is measured in the layer of nanoparticles. Estimate of the properties stability is obtained in the coating from aluminum oxide nanoparticles. The thermal resistance dependences are obtained on the transferred heat flux for models of thermal stabilizers from steel and aluminum

Thermal-Hydraulic Studies on the Shell-and-Tube Heat Exchanger with Minijets

In this paper a patented design of a heat exchanger with minijets, with a cylindrical construction is presented. It is followed by the results of its systematic experimental investigations in the single-phase convection heat transfer mode. Based on these results, validation of selected correlations (coming from the literature) describing the Nusselt number was carried out. An assessment of the heat exchange intensification level in the described heat exchanger was done through the comparison with a shell-and-tube exchanger of a classical design. The thermal-hydraulic characteristics of both units were the subjects of comparison. They were constructed for the identical thermal conditions, i.e., volumetric flow rates of the working media and the media temperatures at the inlets to the heat exchanger. The experimental studies of both heat exchangers were conducted on the same test facility. An increase in the heat transfer coefficients values for the minijets heat exchanger was observed in comparison with the reference one, whereas the generated minijets caused greater hydraulic resistance. Experimentally confirmed intensification of heat transfer on the air side, makes the proposed minijets heat exchanger application more attractive, for the waste heat utilization systems from gas sources.

ПІДВИЩЕННЯ ЕНЕРГОЕФЕКТИВНОСТІ ВОДОГРІЙНИХ КОТЛІВ ЗА ДОПОМОГОЮ ІНТЕНСИФІКАЦІЇ ТЕПЛООБМІНУ

In the work the research of the efficiency of the heat exchange intensification in the gas-tube heat exchanger of the water heating boiler was carried out, the analysis of the obtained results was carried out. It was noted that for heat pump gas boilers the problem of heat transfer intensification is especially important, since the coefficient of heat transfer from gases to the wall in the channels without intensification is rather small, and the temperature of the waste gases and the efficiency coefficient depend on the heat transfer intensity of the heat exchanger. The review of literary information, which showed that in modern water-heating boilers of small and medium power intensifiers are used: wired inserts of various configurations, ring grooves, spiral inserts, band swirls, screw turbulators, plates of different configurations, combined methods. As part of the course design, the design of a heat generator on wood chips with a rated power of 550 kW was developed. For this design, numerical studies of the influence of the installation of intensifiers on the performance of the boiler on the full and partial load are carried out. To study the boiler's energy characteristics, a mathematical model has been developed, which is supplemented with dependencies for the calculation of the intensified heat transfer in the boiler heat exchanger. Influence of installation of the intensifier on the temperature of flue gases at the output from the boiler and on the efficiency coefficient is investigated. It is shown that the greatest reduction of the temperature of the exhaust gases is observed for the intensifier in the form of a twisted tape, a combined method, an intensifier of the original construction and a bent plate with different geometric parameters. It is noted that when choosing a method for intensifying heat exchange in a boiler for solid fuels and parameters of intensifiers, it is necessary to carry out a detailed thermal and aerodynamic calculation when changing the boiler's thermal power and to estimate the ranges of rational work, which will exclude significant cooling of flue gases, and the effect of installing the intensifiers will exceed the cost of overcoming the additional hydraulic resistance in the heat exchanger.

About the intensification of convective heat transfer from combustion products to the walls of a cylindrical shaped pulsing combustion chamber

Franke’s critical dependence determines the theoretical relationship for the numbers Nu for pulsating and stationary flow regimes. It is based on the heat exchange intensification hypothesis due to the interaction of the pulsating velocity profile and the boundary layer near the heating surface. The article presents the results of studies to test the efficiency of the Franke’s ratio for a given range of pulsed combustion chamber diameters, as well as to determine the influence of the geometric parameters of the chamber on the convective heat transfer from the combustion products to the walls of the chamber

Hydraulic heat tests of the shell and tube heat exchanger using heated liquid of higher turbulization

A short characteristic of the heat power industry of the Russian Federation is analysed. Special attention is paid to the technological condition of the central thermal electric main lines and boiler equipment, thermal networks and heat consumption systems. Moreover, it is specified that the important heat supply equipment systems are shell and tube heat exchangers. The emphasis is that the use of shell and tube heat exchanger devices is based on reliable technical solution, financial viability, and convenience in its operation and repair. Based on the analysis of local and foreign scientists’ research, the classification of approaches of heat exchange intensification in shell and tube heat exchanger devices is propounded. The article presents the results of thermal and hydraulic tests of an intensive shell-and-tube heat exchanger with increased turbulization of the heated fluid. When carrying out tests, modern high-precision measuring devices are used. A test objective comparison of hydrodynamics (losses of pressure) and heat technical characteristics (heat transfer coefficient) of two heat exchangers has been conducted. These are serial (state standard No. 27590.) and intensive (RU 185391 patent) exchangers.

The heat exchange intensification under incomplete hydrophobization oil reservoirs

High-viscosity oil recovery often requires thermal methods of enhanced oil recovery combining surface acting agent (SAA) injection. Thermal treatment allows increasing hydrocarbon movability. Efficiency raisings’ limiting factor of this method includes injecting agent’s thermal loss (water and steam) as well as SAA molecules thermal destruction. This article assesses nanoparticles adding in SAA water solution’s influence. The authors consider a theoretic capability of increasing heat exchange’s inetnsity between oil reservoir and injected agents by means of adding nanoparticles as well as increase of the SAA thermostability’s capability under high temperatures influence. The results of the laboratory experiments on SAA’s adsorbed layer structure on the surface of solid state show the structure’s dependence on SAA concentration in the solution. According to the developed mathematic model, a periodic adsorbed field will lead to the increase of heat transfer coefficient by means of the Nusselt number increment. This will allow increasing efficiency of thermal methods EOR application.