Three Dimensional CFD Simulation of Condensation Inside Inclined Tubes

2017 ◽  
Author(s):  
Amirhosein Moonesi Shabestary ◽  
Eckhard Krepper ◽  
Dirk Lucas ◽  
Thomas Höhne
Keyword(s):  
Heat Transfer ◽  
Annular Flow ◽  
Cfd Simulation ◽  
Cooling System ◽  
Heat Removal ◽  
Normal Operation ◽  
Cooling Systems ◽  
Horizontal Pipes ◽  
Subcooled Water ◽  
Operation Conditions

The current paper comprises CFD-modelling and simulation of condensation and heat transfer inside horizontal pipes. Designs of future nuclear boiling water reactor concepts are equipped with emergency cooling systems which are passive systems for heat removal. The emergency cooling system consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser occurs. In the case of an accident the water level in the core is decreasing, steam comes in the emergency pipes and due to the subcooled water around the pipe, this steam will condense. The emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core when any accident happens. The actual project is defined in order to model all these processes which happen in the emergency cooling systems. The most focus of the project is on detection of different morphologies such as annular flow, stratified flow, slug flow and plug flow. The first step is the investigation of condensation inside a horizontal tube by considering the direct contact condensation (DCC). Therefore, at the inlet of the pipe an annular flow is assumed. In this step, the Algebraic Interfacial Area Density (AIAD) model is used in order to simulate the interface. The second step is the extension of the model to consider wall condensation effect as well which is closer to the reality. In this step, the inlet is pure steam and due to the wall condensation, a liquid film occurs near the wall which leads to annular flow. The last step will be modelling of different morphologies which are occurring inside the tube during the condensation via using the Generalized Two-Phase Flow (GENTOP) model extended by heat and mass transfer. By using GENTOP the dispersed phase is able to be considered and simulated. Finally, the results of the simulations will be validated by experimental data which will be available in HZDR. In this paper the results of the first part has been presented.

scholarly journals Improving the cooling system of ship equipment

2020 ◽  
Author(s):  
А.В. Фомин ◽  
Е.В. Фомин
Keyword(s):  
Power Plants ◽  
High Efficiency ◽  
Cooling System ◽  
Heat Removal ◽  
Normal Operation ◽  
Water Cooling ◽  
Cooling Systems ◽  
Start Up ◽  
Membrane Type ◽  
Water Cooling System

В статье представлены результаты исследования эффективности работы системы охлаждения корабельного оборудования и предложены конструктивные решения, позволяющие модернизировать данную систему. В настоящее время, для обеспечения нормальной работы корабельного оборудования, применяются системы охлаждения. В корабельных энергетических установках распространены системы водяного охлаждения из-за целого ряда преимуществ. К ним относится и высокая эффективность теплоотвода, и меньшее влияние внешней среды, а также более надежный пуск и возможность использования энергии отводимого тепла для других нужд. Одним из основных элементов в таких системах является расширительный бак гравитационного типа, обеспечивающий правильную циркуляцию дистиллированной воды во внутреннем контуре и расположенный в верхней точке системы. Однако практика испытаний и эксплуатации показала, что есть и серьезный недостаток в таком расположении бака – в случаи его перелива или разрыва может пострадать дорогостоящее оборудование, расположенное ниже. В связи с этим, определены направления по совершенствованию системы водяного охлаждения корабельного оборудования, которые связаны с применением расширительного бака мембранного типа и использования воздухоудаляющих клапанов. The article presents the results of a study of the efficiency of the cooling system of ship equipment and offers design solutions that allow to modernize this system. Currently, to ensure the normal operation of ship's equipment, cooling systems are used. Water cooling systems are common in ship power plants due to a number of advantages. These include high efficiency of heat removal, less influence of the external environment, as well as more reliable start-up and the ability to use the energy of the heat being withdrawn for other needs. One of the main elements in such systems is a gravity-type expansion tank that ensures proper circulation of distilled water in the internal circuit and is located at the top of the system. However, the practice of testing and operation has shown that there is a serious drawback in this arrangement of the tank – in cases of overflow or rupture, expensive equipment located below may suffer. In this regard, the directions for improving the water cooling system of ship equipment, which are associated with the use of an expansion tank of the membrane type and the use of air-removing valves, have been identified.

scholarly journals Analysis of Wetting Characteristics on Microstructured Hydrophobic Surfaces for the Passive Containment Cooling System

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Wei Zhao ◽  
Xiang Zhang ◽  
Chunlai Tian ◽  
Zhan Gao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Heat Removal ◽  
Interface State ◽  
Transfer Performance ◽  
Hydrophobic Property ◽  
High Mechanical Strength ◽  
Feasible Solutions ◽  
Baxter Model

As the heat transfer surface in the passive containment cooling system, the anticorrosion coating (AC) of steel containment vessel (CV) must meet the requirements on heat transfer performance. One of the wall surface ACs with simple structure, high mechanical strength, and well hydrophobic characteristics, which is conductive to form dropwise condensation, is significant for the heat removal of the CV. In this paper, the grooved structures on silicon wafers by lithographic methods are systematically prepared to investigate the effects of microstructures on the hydrophobic property of the surfaces. The results show that the hydrophobicity is dramatically improved in comparison with the conventional Wenzel and Cassie-Baxter model. In addition, the experimental results are successfully explained by the interface state effect. As a consequence, it is indicated that favorable hydrophobicity can be obtained even if the surface is with lower roughness and without any chemical modifications, which provides feasible solutions for improving the heat transfer performance of CV.

Network modelling of dry-type transformer cooling systems

2018 ◽  
Vol 37 (3) ◽  
pp. 1039-1053 ◽  
Author(s):  
Andrea Cremasco ◽  
Wei Wu ◽  
Andreas Blaszczyk ◽  
Bogdan Cranganu-Cretu
Keyword(s):  
Network Model ◽  
Thermal Model ◽  
Cfd Simulation ◽  
Cooling System ◽  
Cfd Simulations ◽  
Network Modelling ◽  
Cooling Systems ◽  
Content Type ◽  
System Configurations ◽  
Dielectric Insulation

Purpose The application of dry-type transformers is growing in the market because the technology is non-flammable, safer and environmentally friendly. However, the unit dimensions are normally larger and material costs become higher, as no oil is present for dielectric insulation or cooling. At designing stage, a transformer thermal model used for predicting temperature rise is fundamental and the modelling of cooling system is particularly important. This paper aims to describe a thermal model used to compute dry transformers with different cooling system configurations. Design/methodology/approach The paper introduces a fast-calculating thermal and pressure network model for dry-transformer cooling systems, preliminarily verified by analytical methods and advanced CFD simulations, and finally validated with experimental results. Findings This paper provides an overview of the network model of dry-transformer cooling system, describing its topology and its main variants including natural or forced ventilation, with or without cooling duct in the core, enclosure with roof and floor ventilation openings and air barriers. Finally, it presents a formulation for the new heat exchanger element. Originality/value The network approach presented in this paper allows to model efficiently the cooling system of dry-type transformers. This model is based on physical principles rather than empirical assessments that are valid only for specific transformer technologies. In comparison with CFD simulation approach, the network model runs much faster and the accuracies still fall in acceptable range; therefore, one is able to utilize this method in optimization procedures included in transformer design systems.

A Compact Nanostructure Integrated Pool Boiler for Microscale Cooling Applications

2009 ◽  
Author(s):  
Muhsincan S¸es¸en ◽  
Cem Baha Akkartal ◽  
Wisam Khudhayer ◽  
Tansel Karabacak ◽  
Ali Kos¸ar
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
High Efficiency ◽  
Cooling System ◽  
Bubble Formation ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
External Energy ◽  
Excessive Heat ◽  
Aluminum Base

An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.

Cooling Thin Parts of Pressure Casting Moulds by Means of Liquid CO2

2015 ◽  
Vol 669 ◽  
pp. 71-78
Author(s):  
Iva Nováková ◽  
Martin Seidl ◽  
Pavel Brdlík ◽  
Jan Štverák ◽  
Jaromír Moravec
Keyword(s):  
Cooling System ◽  
Heat Removal ◽  
Pressure Casting ◽  
Optimal Temperature ◽  
Heat Transfer Medium ◽  
Cooling Systems ◽  
Start Up ◽  
Casting Cycle ◽  
Heat Processes ◽  
Heat Amount

To ensure optimal temperature conditions during casting cycle the pressure casting moulds are equipped with cooling systems. These days the cooling systems used in the most of Czech foundry plants enable pre-heating of pressure casting moulds to the working temperature before start-up of production and during casting operation to keep optimal temperature balance among the casting and the mould. Pressure casting mould temperature balance is provided by system of mutually connected channels which are mostly parallel with parting line and inside those the heat transfer medium flows. However such a system allows removal only limited heat amount from the most overheated places of the casting mould and does not allow heat removal from cores of small diameters. This inhomogeneous heat removal causes porosity of the casting in certain areas and also lifetime of the pressure casting mould is dramatically reduced. Cooling by means of liquid CO2 was developed as one of the new cooling possibilities for such places in the pressure casting mould where the heat is concentrated and for standard cooling systems it is too complicated to fully control the heat processes there. The paper deals with the behaviour monitoring of the new cooling system utilizing the potential of liquid CO2. This system was applied into pressure casting mould core and its final impact on the casting quality in the close surrounding was observed.

Design of the Controller Cooling System of an Electric Vehicle

2014 ◽  
Vol 663 ◽  
pp. 213-217 ◽  
Author(s):  
M.M. Rahman ◽  
T.J. Hua ◽  
H.Y. Rahman
Keyword(s):  
Heat Transfer ◽  
Electric Vehicle ◽  
Cooling System ◽  
Removal Rate ◽  
Heat Removal ◽  
Developed Countries ◽  
Internal Resistance ◽  
Heat Transfer Fluids ◽  
Computational Fluid Dynamics Cfd ◽  
Forced Air

As an effort in reducing the dependency on fossil fuel, efforts have been gathered to develop electric vehicle (EV) for the past decades. Technology of electric vehicles (EV) has been initialized in developed countries. However, the latter have different geographical and environmental conditions. Therefore, the system of EV cannot be utilized directly in this country. The controller of an EV functions by utilizing a potentiometer; supplying a certain amount of voltage from the batteries to the motor by driver’s force applied to the acceleration pedal. This action generates a huge amount of heat due to the internal resistance of the controller (e.g. potentiometer). In order for an EV to operate at optimum condition, temperature of the controller has to be maintained at a certain limit. Hence an effective cooling system is required to be designed to fulfill the above condition. The objective of this paper is to present the design of the cooling system for the controller of an electric vehicle (EV). Two types of cooling system namely liquid cooled plate heat exchanger and forced air cooled finned structure are designed and evaluated to assess the behavior of heat transfer as well as effects of heat transfer fluids and cooling system material towards the heat removal rate. Simulation using Computational Fluid Dynamics (CFD) for both cooling systems has been carried out to have better understanding. CFD results are compared with some of the analytical results. The findings revealed that both systems are suitable to be implemented as EV controller cooling system in Malaysian Environment.

On Development of a Semi-Mechanistic Wall Boiling Model

2013 ◽  
Author(s):  
Saurish Das ◽  
Hemant Punekar
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Stresses ◽  
Cooling System ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Wall Heat Transfer ◽  
Cooling Systems ◽  
Transfer Phenomenon

In modern cooling systems the requirement of higher performance demands highest possible heat transfer rates, which can be achieved by controlled nucleate boiling. Boiling based cooling systems are gaining attention in several engineering applications as a potential replacement of conventional single-phase cooling system. Although the controlled nucleate boiling enhances the heat transfer, uncontrolled boiling may lead to Dry Out situation, adversely affecting the cooling performance and may also cause mechanical damage due to high thermal stresses. Designing boiling based cooling systems requires a modeling approach based on detailed fundamental understanding of this complex two-phase heat and mass transfer phenomenon. Such models can help analyze different cooling systems, detect potential design flaws and carry out design optimization. In the present work a new semi-mechanistic wall boiling model is developed within commercial CFD solver ANSYS FLUENT. A phase change mechanism and wall heat transfer augmentation due to nucleate boiling are implemented in mixture multiphase flow framework. The phase change phenomenon is modeled using mechanistic evaporation-condensation model. Enhancement of wall heat transfer due to nucleate boiling is captured using 1D empirical correlation, modified for 3D CFD environment. A new method is proposed to calculate the local suppression of nucleate boiling based on the flow velocity, and hence this model can be applied to any complex shaped coolant passage. For different wall superheat, the wall heat fluxes predicted by the present model are validated against experimental data, in which 50-50 volume mixture of aqueous ethylene glycol (a typical anti-freeze coolant mixture) is used as working fluid. The validation study is performed in ducts of different sizes and shapes with different inlet velocities, inlet sub-cooling and operating pressures. The results are in good agreement with the experiments. This model is applied to a typical automobile Exhaust Gas Recirculation (EGR) system to study boiling heat transfer phenomenon and the results are presented.

CFD Simulation of a Coolant Flow and a Heat Transfer in a Pebble Bed Reactor

2008 ◽  
Author(s):  
Wang-Kee In ◽  
Won-Jae Lee ◽  
Yassin A. Hassan
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Reverse Flow ◽  
Temperature Drop ◽  
Coolant Flow ◽  
Normal Operation ◽  
Fuel Temperature ◽  
Pebble Bed Reactor ◽  
Detailed Simulation

This CFD study is to simulate a coolant (gas) flow and heat transfer in a PBR core during a normal operation. This study used a pebble array with direct area contacts among the pebbles which is one of the pebbles arrangements for a detailed simulation of PBR core CFD studies. A CFD model is developed to more adequately represent the pebbles randomly stacked in the PBR core. The CFD predictions showed a large variation of the temperature on the pebble surface as well as in the pebble core. The temperature drop in the outer graphite layer is smaller than that in the pebble-core region. This is because the thermal conductivity of graphite is higher than the fuel (UO2 mixture) conductivity in the pebble core. Higher pebble surface temperature is predicted downstream of the pebble contact due to a reverse flow. Multiple vortices are predicted to occur downstream of the spherical pebbles due to a flow separation. The coolant flow structure and fuel temperature in the PBR core appears to largely depend on the in-core distribution of the pebbles.

scholarly journals Experimental Investigation on Condensation of Vapor in the Presence of Non-Condensable Gas on a Vertical Tube

2018 ◽  
Author(s):  
Shengjun Zhang ◽  
Feng Shen ◽  
Xu Cheng ◽  
Xianke Meng ◽  
Dandan He
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Total Pressure ◽  
Mass Fraction ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Transfer Model ◽  
Operation Conditions ◽  
The Heat Transfer Coefficient

According to the operation conditions of time unlimited passive containment heat removal system (TUPAC), a separate effect experiment facility was established to investigate the heat transfer performance of steam condensation in presence of non-condensable gas. The effect of wall subcooling temperature, total pressure and mass fraction of the air on heat transfer process was analyzed. The heat transfer model was also developed. The results showed that the heat transfer coefficient decreased with the rising of subcooling temperature, the decreasing of the total pressure and air mass fraction. It was revealed that Dehbi’s correlation predicted the heat transfer coefficient conservatively, especially in the low pressure and low temperature region. The novel correlation was fitted by the data obtained in the following range: 0.20~0.45 MPa in pressure, 20% ~ 80% in mass fraction, 15°C ~ 45°C in temperature. The discrepancy of the correlation and experiment data was with ±20%.

scholarly journals Perfection of cooling systems of overhead tuyeres heads of 250-t BOFs

2019 ◽  
Vol 75 (3) ◽  
pp. 327-336
Author(s):  
S. P. Panteikov ◽  
L. M. Uchitel’ ◽  
V. V. Ivko ◽  
Yu. I. Kharchenko ◽  
Yu. P. Makhlai ◽  
...  
Keyword(s):  
Cooling System ◽  
Heat Removal ◽  
Internal Surface ◽  
Side Surface ◽  
Operating Characteristics ◽  
Blow Down ◽  
Cooling Systems ◽  
Nozzle Block ◽  
Heat Removal Efficiency ◽  
Positive Effect

Deterioration of tips cooling as a result of number of nuzzles increase in tuyere heads does not allow to use multinozzle (six and more) overhead tuyeres for increasing of steel melting technical and economical indices and operating characteristics of technological equipment. The main reason of it is as follows: deterioration ofcooling results in over-heating and burnt-outof tips material in the farthest nozzle zone following the overhead tuyeres breakage. To avoid the water stagnant areas in the farthestnozzle zones of the heads cooling route and therefore to increase the overheads oxygen tuyeres of 250-t BOF operation life, a new design of the six-nozzle tuyere head with asymmetric cooling of tips farthest zones elaborated, manufactures and tested. The perfection of the six-nozzle heads cooling system included asymmetric (relating the side surface of the nozzle block) installation behind every nozzle (in the water direction) a guidingblade of special design. It enabled to increase to a maximum degree the heat removal efficiency from the internal surface in the tip farthest zones and had a positive effect on the overhead tuyeres heads resistance. The workability of the proposed design of the six-nozzle tuyere head with asymmetric cooling of farthest zones was confirmed during test-industrial heats at 250-t BOFs of OJSC “Dneprovskysteel-works”. The heats were carried out with oxygen consumption of 800–1200 m 3/min and regime of partial afterburning ofexit gases. The water consumption for tuyeres cooling decrease from 320–340 m 3 /h, at that the  water temperature difference at the tuyere entry and exit varied in the range of 11–16 °C depending on blow-down duration. Application of the new design of the six-nozzle tuyere head with asymmetric farthest zones cooling enabled to increase the sixnozzle heads resistance by a factor 1.287 comparing with six-nozzle heads without farthest zones cooling and by a factor of 3.327 comparing with regular five-nozzle tuyere heads. The effect reached thanks to more rational cooler distribution and increase ofits velocity. The metal pick up of shafts of the six-nozzle tuyere head with asymmetric farthest zones cooling: while the five-nozzle tuyeres were taken off for salamander cutting off after 1–5 heats, the six-nozzle tuyeres were taken off for the salamander cutting off after 79–81 heats. It indicated a higher efficiency of heat running blow-down and slag regimes with application of proposed design of the six-nozzle tuyere head with asymmetric farthest zones cooling.

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