Heat Exchange Devices Research Articles

Study of heat pipe in motor cooling: A review

The heat pipe as one of the most efficient heat exchanger device is used in many thermal engineering applications. Through sufficient literature research and summary, a comprehensive and systematic analysis of the application of heat pipe cooling technology in motor cooling is provided. The basic principles and key technologies of heat pipe cooling technology is introduced. What’s more, various factors affecting the cooling efficiency of heat pipes and two main types of heat pipe applications in motor cooling are discussed. Finally, the current status of research on heat pipe cooling motors at home and abroad are reviewed.

Conjugated heat transfer of power-law fluids in double-pass concentric circular heat exchangers with sinusoidal wall fluxes.

An analytical formulation, referred to as conjugated Graetz problems, is developed to predict the temperature distribution and Nusselt numbers for the power-law fluid flowing in a double-pass concentric circular heat exchanger under sinusoidal wall fluxes. A new design of inserting an impermeable sheet into a concentric tube, in parallel, to conduct recycling double-pass operations has been studied theoretically in the fully developed region, resulting in substantial improvements in the performance of heat exchanger device. The analytical solution was derived using the complex functions by transforming the boundary value problem into ordinary differential equations with the aid of the Frobenius method. The influences of power-law index and impermeable-sheet position on average Nusselt numbers with various designs and operating parameters are also delineated. The theoretical predictions show that the heat transfer efficiency is considerably improved through operating the double-pass device compared to via a single-pass circular heat exchanger (where an impermeable sheet is not inserted). The economic feasibility of operating double-pass concentric circular heat exchanger for power-law fluids is exemplified by the ratio of the heat-transfer efficiency enhancement and the increment in power consumption. The double-pass effect from increasing the convective heat-transfer coefficient can compensate for the rise in power consumption, which serves as important economic advantage of this design.

INTENSIFICATION OF HEAT EXCHANGE IN DIABATIC RECTIFICATION COLUMNS

The heat exchange in a diabatic column was investigated during the rectification of an ethanol-water mixture, in which partial condensation of rising vapors on the surface of vertical heat exchange tubes installed vertically along the height of the installation was carried out, as well as the evaporation of intermediate condensate on the surface of horizontal plates. Based on the review of diabatic columns, it is shown that they can reduce the cost of conducting the rectification process. Heat-exchange devices placed on trays of rectification units are considered and ways to intensify heat transfer in them are proposed. It has been established that the most efficient heat removal in heat exchangers of diabatic columns is achieved when using a film flow of a coolant on a heat transfer surface. Heat transfer in a diabatic column is investigated during gravitational flow of surfaces of heat exchange tubes, as well as when organizing an ascending and descending co-current film flow, both in the case of heating and boiling of the coolant. To intensify heat transfer in the coolant film, a helical artificial roughness was installed on the surface of the pipes, made in the form of a wire spiral tightly mounted on the heat transfer surface. The geometric parameters of the helical roughness, such as the distance between the turns of the spiral and the height of the wire, which have the greatest influence on the intensity of heat transfer, have been established. Dependences for determining the value of the heat transfer coefficient are presented and an estimate of the value of the specific heat flux in the diabatic column is given.

Обоснование расходных характеристик рекуператора для тепловой подготовки агрегатов машин и оборудования

Introduction. Machines and equipment in its composition may contain hydraulic systems to ensure the functioning of the main and auxiliary systems. It is known that a common disadvantage of hydraulic systems and drives is the dependence of the viscosity of the applied fluids on temperature. A noticeable part of technological machines and equipment is located in unheated or poorly heated industrial premises and a change in the viscosity of working fluids with a decrease in the ambient temperature can significantly affect the parameters of technological processes. An important factor in ensuring the stability of the technological processes parameters is the degree of preparation of machines and equipment for operation at low temperatures or in conditions of fluctuating temperature conditions. In this regard, the question arises of ensuring the required temperature of technical fluids before turning on machines and equipment, and maintaining the required thermal regime during the operation of its units and assemblies. One way to solve this problem is to use external heat sources. Various heat exchange devices can serve as such sources. In the heat exchange device, the heat carrier is heated, which is then fed into the heat exchange jacket of the machinery and equipment units. Both liquid and gaseous media are used to heat the coolant in the heat exchanger. In the latter case, the heat exchanger is called a recuperator. The efficiency of the recuperator is determined by its design and flow characteristics. There are methods for the analytical determination of both the design and flow characteristics of the recuperator, but these methods are quite laborious. The use of computer simulation of thermal processes makes it possible to successfully solve the calculation problem, and also significantly reduces the design time of heat exchangers. The aim of the work is to substantiate the flow characteristics of the recuperator for maintaining the thermal regime through computer simulation. The research method is computer simulation of thermal processes, which is implemented using the SolidWorks software package from Dassault Systems and its Flow Simulation application for simulating thermal processes in scientific research and engineering. Results and discussion. Simulation carried out in stationary and non-stationary modes made it possible to determine the effect of pump performance on the temperature of the coolant at the outlet of the recuperator. It is found that when the heat carrier flow rate is more than 20 l/h, its temperature does not reach the required values, despite the fact that the gases leaving the recuperator have a significant residual temperature. The efficiency of the recuperator is assessed by determining the exergy efficiency. Based on the data obtained, the most preferable are the pump productivity values lying in the range from 4 to 20 l/h.

Conjugate heat transfer study comprising the effect of thermal conductivity and irreversibility in a pipe filled with metallic foams

A parametric study is proposed in this paper to examine heat dissipation rate and entropy generation of a forced convection in a horizontal pipe which is filled with high porous metallic foams. The study quantifies the effect of thermal conductivity and pore density on entropy generation when the pipe is fully filled with copper, aluminium and nickel metallic foams of 0.6 m length in the fluid flow direction. To predict fluid flow and heat transfer features through these metallic foams the Darcy-extended Forchheimer (DEF) flow and the local thermal non-equilibrium (LTNE) models are employed. The characteristics of laminar, transition and turbulent in the non-foam region of the pipe are captured by considering the appropriate flow models. To affirm the methodology adopted in this work, the results of the present numerical solutions are validated with the available experimental results reported in the literature. Colburn j factor and thermal performance factor are the important factors that decide the performance and efficiency of any heat exchange device. Hence, these parameters are critically evaluated and are observed to increase with increasing pore densities of the metal foams and decrease with increasing flow rates of the fluid. Furthermore, the numerical analysis is extended to obtain the results of wall temperature, Nusselt number, heat transfer enhancement ratio, frictional irreversibility and Bejan number.

Thermodynamic Behaviors of Adsorbed Methane Storage Systems Based on Nanoporous Carbon Adsorbents Prepared from Coconut Shells.

The present work focused on the experimental study of the performance of a scaled system of adsorbed natural gas (ANG) storage and transportation based on carbon adsorbents. For this purpose, three different samples of activated carbons (AC) were prepared by varying the size of coconut shell char granules and steam activation conditions. The parameters of their porous structure, morphology, and chemical composition were determined from the nitrogen adsorption at 77 K, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM) measurements. The methane adsorption data measured within the temperature range from 178 to 360 K and at pressures up to 25 MPa enabled us to identify the most efficient adsorbent among the studied materials: AC-90S. The differential heats of methane adsorption on AC-90S were determined in order to simulate the gas charge/discharge processes in the ANG system using a mathematical model with consideration for thermal effects. The results of simulating the charge/discharge processes under two different conditions of heat exchange are consistent with the experimentally determined temperature distribution over a scaled ANG storage tank filled with the compacted AC-90S adsorbent and equipped with temperature sensors and heat-exchanger devices. The amounts of methane delivered from the ANG storage system employing AC-90S as an adsorbent differ from the model predictions by 4–6%. Both the experiments and mathematical modeling showed that the thermal regulation of the ANG storage tank ensured the higher rates of charge/discharge processes compared to the thermal insulation.

Exergy analysis and multi-objective optimisation for energy system: a case study of a separation process in ethylene manufacturing

In chemical industry, most processes face the challenge of high energy consumption. The approach presented in this study can reduce the energy footprint and increase efficiency. The energy system of a separation process in ethylene manufacturing is used to demonstrate the effectiveness of the approach. The chilling train system of the separation process in a typical ethylene plant consumes most cooling and provides appropriate feed for distillation columns. The steady state simulation of system was presented and the simulation results were proved accurate. The conventional exergy analysis identifies that Dephlegmator No.1 (a heat exchange and mass transfer device) has the highest exergy destruction (1401.28kW). Based on advanced exergy analysis, Dephlegmator No.1 has the highest rate of avoidable exergy destruction (89.04 %). Finally, a multi-objective optimisation aiming to maximise system exergy efficiency and to minimise operational cost was performed and the Pareto frontier was obtained. The multi-objective optimized exergy efficiency is 79.53 % (improved by 0.61 %) and the operational cost is 0.02031 yuan/kg (saved by 11.19 %). This study will guide future research to reduce energy consumption in process manufacturing.

THE WAYS OF RATIONAL USE OF COOLING TOWERS

In order to improve the economic performance of the company, the establishment of rational water use schemes and the reduction of the use of fresh water obtained from water supply systems or natural bodies of water can become an important factor. Water-cooling circulating systems, where cooling towers are used as cooling facilities, are the basis of rational water use systems. In water recycling systems that need stable water cooling at high specific hydraulic and thermal loads, cooling towers are used. By spraying water with nozzles or irrigation devices, the surface of water needed to cool it by contact with air is formed. A cooling tower is a heat exchange device for removing heat from various production processes to the environment by evaporating part of the water passing through it. The share of evaporated water usually does not exceed 1.5 %. Most of the cooling towers used were built 30 - 50 years ago. Almost all of these installations are morally and physically outdated. To consider the main criteria that should be guided with the choice of method for reconstruction of cooling towers to increase the efficiency and effectiveness of their operation.

Thermo-hydraulic performance of nanofluids in enhanced tubes - a review

Technological developments are continuously growing to improve the efficiency of thermal systems on the demand of present era. To get rid of the scientists and engineers from traditional heat transfer intensification methods and to miniaturize thermal transport devices, novel and innovative techniques are obligatory. In this whole drive, the effective tube geometries and efficient working fluids perform vital role in the betterment of heat exchange devices. Geometrical argumentations/surface modifications impose on smooth tubes are called as enhanced tubes. These tubes contribute towards high rate of heat transfer by reducing the formation of boundary layer near the wall surfaces of the tube. Also, nanofluids with superior thermo-physical properties compared to conventional fluids also assist the rate of heat exchange in various heat transfer applications. This article begins with the introduction of enhanced tubes and nanofluids and followed by overview of nanofluid synthesis and different tube geometries. An attempt has been made to summarize last decade research contributions in the field of forced convection heat transfer and flow characteristics (HTFC) with employing the combined effect of enhanced tubes and nanofluids. Additional heat transfer enhancement techniques (swirl flow devices, magnetic field, agitation, rotation and pulsation) brace with present ones, are also discreetly deliberated. Proposed correlations by authors are also represented which shows the good agreement with experimental data. Important findings and outcomes from reviewed studies are compiled in discussion section. A number of suggestions and guidelines are highlighted to intensify the heat transfer rate as well as to mitigate the effects of pressure losses in fluid flow pipes.

Structure, DFT calculations and heat transfer enhancement in [ZnO/PG + H2O]C hybrid nanofluid flow as a potential solar cell coolant application in a double-tube

This study concentrated on the deployment of PG + H2O (30:70) in a solar cell cooling system-based combination ZnO nanofluid. Zinc oxide nanoparticles [ZnO]NPs, with crystallite size of average 70 ± 1 nm, were synthesized by a sol–gel method. The results specifically demonstrate that, the optical energy band difference values decrease from 4.644 eV for [ZnO + PG]NPs to 4.615 eV for and [ZnO/PG + H2O]C using the Tauc’s equation. Propylene glycol (PG)/water blend was doped with [ZnO]NPs at various concentrations < 1.0 wt% to study the optical characteristics of these nanofluids. The goal of this analysis is to test the hydrothermal efficiency, thermal conductivity, and viscosity of a non-Newtonian hybrid nanofluid in double-channel heat exchange device. Different experimental characterization techniques for [ZnO/PG + H2O]C like UV–Vis, FT-IR, XRD, SEM, DFT calculations and optical characteristics have been used. The overall coefficient of heat transfer in the cell cooling system has been improved, with the rise of [ZnO]NPs (has achieved the most at 0.3 vol%) in ZnO–PG nanofluid. The coefficient of heat transfer has been enhanced 46% at the temperature from 40 to 60 °C with 0.2 vol% of [ZnO]NPs. The findings showed [ZnO/PG + H2O]C nanofluid is rapidly absorbing heat and solar radiation, compared with PG–H2O.

UPPER LAYER HEATING SYSTEM AT DUAL COMPLETION

At a late stage of oil field development under declining profitability of production, dual completion of layers, varying in geological and filtration characteristics, is particularly relevant. The paper considers ways to improve the efficiency of a single-lift dual completion installation for the operation of two layers with rod and electric centrifugal pumps. A variant of dual completion with the upper layer operated by a rod pump, includes the possibility of natural heating of the bottom-hole zone of the upper layer due to the thermal energy of the lower layer liquid. To increase the efficiency of heat exchange, an improved design of an installation with a heat exchange device in the upper productive layer interval is proposed. In order to study the optimal geometric and technological parameters of the heat exchanger in system well-heat exchanger-productive, the temperature field was simulated. It is theoretically proved that the use of a heat exchanger contributes to an increase in the intensity of heat transfer from the lower layer liquid passing through the heat exchanger to the upper layer liquid in the inter-tube space. The increase in heat transfer efficiency is due to an increase in the surface of the heat exchange device due to fins placed on the side surface of the heat exchanger housing. The optimal value of the height of the plates for which the maximum heating of the liquid in the inter-tube space in the upper layer interval is achieved is calculated. It is shown that a set of interrelated processes (acceleration of flow motion and increase in hydrodynamic friction due to a decrease in the diameter of the body relative to the diameter of the tubing, turbulence when passing through a swirler), provided by the heat exchanger device, contributes to increase the temperature of the liquid in the heat exchanger and increase its efficiency. The influence of the internal cross-section of the heat exchanger body on its surface temperature is studied. As a result of taking into account two factors that are opposite in efficiency: a positive one (an increase in the speed of the liquid in the heat exchanger and an increase in the temperature on the surface the heat exchanger housing when the housing diameter decreases) and negative (increase in hydraulic losses in the heat exchanger and the head of the electric centrifugal pump) the optimal diameter of the heat exchanger housing is selected.

Effect of selected geometric parameters on natural convection in concentric square annulus

ABSTRACT The research is focused on natural convection heat transfer in a concentric square annulus with tilted inner elliptic cylinder subjected to isothermal heating and cooling. Numerical method was adopted for the solution. The governing elliptic conservation equations were solved using Garlerkin Finite Element Method. Ranges of parameters considered for the study were orientation angle, aspect ratio and Rayleigh number. Physical model was generated using CorelDRAW 2019 version while meshing and simulation was done using COMSOL Multiphysics software. Results show that orientation angle had no significant effect on the average Nusselt number at low Rayleigh number. Beyond a critical Rayleigh number, average Nusselt number increases with an increase in orientation angle. Analyses of the results show that Rayleigh number, Nusselt number and orientation angle significantly influence the natural convection in concentric square annulus. The results presented in this study can be applied in heat exchanger devices, solar collectors, nuclear reactors and thermal storage systems.

Investigation on flow and heat transfer of compact brazed plate heat exchanger with lung pattern

This study relates to an evaluation of the thermo-hydraulic performance for a state-of-the-art compact brazer plate heat exchanger (PHE) in 3 kW for 3-plates. To improve heat transfer and pressure drop of the PHE, a lung pattern is designed at certain heights on the plate surface by using biomimetic approach in first time. It is known that human pulmonary system is one of the most effective heat exchanger devices in the nature. Its tree like structure provides good compactness, consequently better heat transfer rate per unit volume. By means of achievements in additive manufacturing technologies in recent years, a heat exchanger with any desired plate or fin geometry can be manufactured. In this study, plate surfaces have been designed as a 3D lung like structure in order to increase the heat transfer area. CFD simulations are then performed with Ansys-Fluent program in operating condition under supply temperatures of 90 °C and 40 °C with a mass flow rate of 0.05 kg/s for hot and cold sides, respectively. The simulation is validated by the numerical and experimental results of an existing Chevron type compact brazed PHE. The results show that there is a 71.30% increase in heat transfer and a 67.8% decrease in pressure drop for 6.66% less volume compared to the reference PHE. The effectiveness of the lung patterned PHE is found to be 0.350. Fluid velocity in plate cavities on lung pattern is quite irregular due to turbulence formation at almost constant Reynolds numbers. This increases its effectiveness. Finally, lung patterned plates designed with biomimetric method is a guideline study to improve the performance of PHEs.

Properties of the Iron Bacteria Biofouling on Ni–P–rGO Coating

Biofouling on heat exchange devices can decrease heat transfer efficiency, corrode materials, and even lead to safety accidents. Most heat exchange devices are made of carbon steel that efficiently produces biofouling. However, in this paper, a nickel–phosphorus–reduced graphene oxide (Ni–P–rGO) coating was prepared on carbon steel by electroless plating to investigate the properties of iron bacteria biofouling. The surface coating was analyzed via scanning electron microscopy and Raman spectroscopy. After the carbon steel and the Ni–P–rGO coating were immersed into an iron bacteria solution for 120 h, the weight of the iron bacteria biofouling on the Ni–P–rGO coating sharply decreased when compared with the carbon steel. We can conclude that the concentration of graphene can affect the weight of iron bacteria biofouling. We also found that the coating solution with 40 mg/L of graphene performed the best in inhibiting biofouling by decreasing the weight of the biofouling by 97.2% compared to carbon steel.

Calculation of heat transfer from a continuous fin of a heat exchanger under conditions of unequal temperatures of gas flows and the base of the ribs

The solution of the problem of heat flux from a fin surface washed by gaseous media with different temperatures at asymmetric temperatures of the solid rib bases and unequal values of the heat transfer coefficients is obtained. The solution of the problem of heat transfer through a flat rib of constant cross section at different temperatures of the end sources, unequal media temperatures and different heat transfer coefficients on the surfaces of the rib is presented. The calculated dependencies can be used for designing heat-exchange devices in power plants, agricultural technological equipment systems, air conditioning, ventilation and heat supply systems.

Properties of Iron Bacteria Biofouling on Ni-P-rGO Coating under Flowing Conditions.

Biofouling on heat exchange devices can decrease heat transfer efficiency, corrode materials, and even lead safety accidents. Most heat exchange devices are made of carbon steel, which produces biofouling easily. In this paper, nickel-phosphorus-reduced graphene oxide (Ni-P-rGO) coating was prepared on carbon steel by electroless plating as a kind of advanced material to study the properties of iron bacteria biofouling under flowing conditions. The coating was analyzed via scanning electron microscopy and Raman spectroscopy. The properties of iron bacteria biofouling on carbon steel and Ni-P-rGO coating were then compared under flowing conditions. Compared with carbon steel, the asymptotic value of fouling resistance on the Ni-P-rGO coating significantly decreased. Additionally, the induction period and the time of reaching the asymptotic value greatly increased. The inhibition properties of biofouling of advanced materials Ni-P-rGO coating under different temperatures, flow velocities, and initial concentrations was also studied.

Signal processing method based on energy ratio for detecting leakage of SG using EVFM

In the sodium-cooled fast reactor, the steam generator is a heat exchange device between sodium and water, which may cause leakage, resulting in a sodium-water reaction accident, which in turn affects the safe operation of the entire nuclear reactor. To this end, the electromagnetic vortex flowmeter is used to detect leakage of the steam generator and its signal processing method is studied in this paper. The hydraulic experiment was carried out by using water instead of liquid sodium, and the sensor output signal of the electromagnetic vortex flowmeter under different gas injection volumes was collected. The bubble noise signal is reflected by the base line of the sensor output signal. According to the relationship between the proportion of the bubble noise signal in the sensor output signal and the gas injection volume, a signal processing method based on the energy ratio calculation is proposed to detect whether the water contains bubbles. The gas injection experiment of liquid sodium was conducted to verify the effectiveness of the signal processing method in the detection of bubbles in sodium, and the minimum detectable leak rate of water in the steam generator was detected to be 0.2 g/s.

MEMANFAATKAN CONDENSATE HYDROCARBON NATURAL GAS SEBAGAI FUEL GAS DENGAN PENGATURAN KONDISI OPERASI ALAT HEAT EXCHANGER

One of the problems faced in operating the fuel gas system is the loss due to wasting condensate hydrocarbons from the fuel gas system surge drum. The purpose of the study was to determine the factors that cause natural gas condensation problems in the fuel drum supply surge gas and provide an overview of how to overcome the problem with the heat exchanger tool operation method. The method used in the research is the research method used with a case study approach to handling wasted condensate hydrocarbon problems and how to overcome them by maximizing the operation of heat exchanger devices. The expected results from this study are that the removal of hydrocarbon condensate can be prevented and utilized as fuel gas. With the results of this study, it is expected to be an innovation in order to adding value to value creation for the company.

Passive intensifiers in heat exchange devices

Passive intensifiers in heat exchange devices

On the Problem of Rejection of Low-Potential Heat from High-Power Space Systems

Consideration has been given to the problems of organization of the operating process in spacecraft heat-exchange devices for rejecting low-potential heat to outer space. It has been shown that as far as the heat-rejection efficiency and weight-size characteristics are concerned, droplet radiant coolers outperform all the existing designs of heat exchangers. The use of droplet radiant coolers at heat-rejection powers exceeding 100 kW, i.e., at megawatt powers, is particularly efficient. A description of individual elements has been given, and results of investigations of the processes of generation of flows of monodisperse droplets and their collection under ground conditions and under microgravity and high-vacuum conditions have been presented. The latter were investigated from the results obtained in experiments on spacecraft.