Method Of Heat Removal Research Articles

Methods of Emergency Heat Removal from Pools and Storages of Spent Fuel of Nuclear Power Plants

In the paper, consideration is given to possible methods of heat removal from water pools and storages of spent nuclear fuel of atomic power plants, which can be employed in an emergency due to failure of the regular cooling system of the pool. The authors present results of investigation of two passive methods of emergency cooling of spentfuel water pools: the first method is to use emergency accumulator reservoirs with a cooling-water supply, and the second, to use boiling channels whose action is based on the effect of creating driving head in the emergency system of natural circulation of the cooling pond of the coolant.

Comparison of three-phase transformers with rectangular and circular conversion of laminated magnetic cores (active power losses)

Purpose. In the mass production of low-power transformers, magnetic cores and windings are used with rectangular sections of rods and forming the contours of the coils turns. The contours of medium and high power transformers active elements are circles. The cross sections of the magnetic cores form rectangular steel packages of various widths with filling coefficients of circular circuits 0,786–0,925 at a power of 16–10000 kV·А. In recent decades, rectangular contour generators of planar electromagnetic systems have also been used in the transformers manufacture with a more than 250 kV·A capacity. The use of rectangular sections instead of rods circular cores changes the consumption of materials and active power losses. Therefore, it is of theoretical and practical interest an analytical substantiation of the expediency of such a replacement. Methodology. A comparative analysis of hree-phase transformer variants is performed by the method of generalized invariant structural-parametric synthesis. Target functions are used with a component of the source data and electromagnetic loads and dimensionless components. The dimensionless optimization components of mass and cost are functions of relative geometric controlled variables. The loss component additionally depends on the relative electromagnetic controlled variable. The values of optimization components are indicators of the objective function, and their minima represent the technical level indicators of transformer. Results. The indicators are determined with same source data and loads, which corresponds to electromagnetic power of the compared options identity. Calculations are performed in real range of electromagnetic controlled variable variation of dry and oil transformers. This eliminates the dependence of loss indicators on power, method of heat removal and other factors. Originality. It has been established that, in addition to improving the mass-carrying indices, a reduction in losses of three-phase transformers is achieved when replacing circular forming circuits to rectangular circuits. Practical value. The reduction of loss of transformers of voltage range 1–110 kV with rod laminated magnetic cores, copper and aluminum windings with rectangular generating circuits relative to analogs with circular circuits is 6,3–8,9 % and 2,64–3 % with the rods filling factor 0,786 and 0,925.

On the prediction of pressure drop in subcooled flow boiling of water

Subcooled flow boiling heat transfer is one of the most preferred heat removal methods, especially in areas where high heat fluxes are encountered. The design of heat sinks employing subcooled flow boiling involves prediction of pressure drop, in addition to heat transfer coefficient, as it exerts a huge influence on the local heat transfer, stability of the system and the critical heat flux. This paper provides a systematic review of the performance of the prior correlations and their applicability for different conditions based on a large experimental database compiled from 12 sources containing 1365 data points in total, focussing on water as the working fluid. The results of the assessment are used to identify the right correlation applicable for a specific operating range. New correlations are proposed for the cases and ranges for which the predictability of the prior correlations is unsatisfactory.

Laryngeal temperature simulations during carbon dioxide laser irradiation delivered by a scanning micromanipulator.

We use scatter-limited phototherapy techniques to calculate the time-dependent temperature profiles of incisions made with a commercial carbon dioxide laser being used to make a 1-mm incision under computer control using the Digital Acublade™ and with incisions made with the same laser under manual control. The goal is to understand the differences in the amount of lateral thermal damage that is likely from the computer-controlled incisions versus the manually controlled incisions. The temperature profiles are calculated from the absorption and scatter of light in a homogeneous material. The resulting temperature profiles are presented as videos showing how the tissue heats up and cools down with the incident laser pulses. The time-dependent thermal distributions indicate that the computer-controlled laser incision could show as little as 210μm of lateral thermal damage, whereas the manually controlled laser incisions could show as much as 375μm of lateral thermal damage. The computer-controlled laser incision is able to control laser pulses fast enough that subsequent pulses can ablate away tissue with a significant amount of residual heat from the previous laser pulse. Using the scatter-limited phototherapy techniques, we can see how a computer-controlled laser can make incisions with less thermal damage by ablating away tissue holding a significant amount of heat from the previous pulse before it has time to diffuse through the tissue. This method of heat removal from laser incisions has notbeen previously described or demonstrated.

General Concept of Thermal Vacuum Tests of Space-Appliance Elements at Helium Temperatures

Three main types of cryothermal vacuum units for testing spacecraft products at liquid-helium temperature are considered. Methods for heat removal from test objects depending on their geometric and thermophysical properties are presented. The designs of the different thermal vacuum chambers are discussed considering the thermophysical processes occurring in them. The operating efficiency of the thermal vacuum chambers and their advantages and disadvantages are estimated based on an analysis of heat-transfer processes.

Experimental investigation of heat transfer and pressure drop of alumina–water nano-fluid in a porous miniature heat sink

ABSTRACTThe thermal management of electronic devices has become of great concern in the last decade. Recent research has focused on heat transfer enhancement methods for heat removal from such devices. In this study, we investigated the convective heat transfer and pressure drop of alumina–water nano-fluids in a miniature heat sink occupied with a copper porous medium under a 62.5 heat flux. Nano-fluid volume fractions of 0.1, 0.3, and 0.5% were synthesized by a two-step method, and the thermal conductivity and kinematic viscosity of the nano-fluids were measured experimentally. Two copper metal foam heat sinks, with different pore densities of 15 pores per inch (PPI) and 30 PPI, were manufactured and inserted into a channel. The results indicated an enhancement in the convective heat transfer coefficients and Nusselt numbers with increase in the Reynolds number. The enhancement in the heat transfer coefficients using different nano-fluid volume fractions in higher- and lower-porosity media varied from 1 to 22% and 2.3 to 26.4%, respectively. An increment in the nano-fluid volume fraction, and pore density, led to a higher heat transfer rate. However, the higher pore density medium caused larger pressure drops. The thermal resistance of the samples was also studied. The results indicated an increase in Reynolds number, and volume fraction decreased the thermal resistance. According to the efficiency index, a lower pore density medium as well as higher nano-fluid volume fractions provided better performance in this porous heat sink.

Decreasing the Thermal Load on the Environment with the Help of Thermal Pumps in the Sewage Treatment System

We propose designs for practical use of residual heat of sewage by means of thermal-pump transformation of thermal energy in plants operating on inverse Rankine and Lorentz cycles, as well as a method for sewage heat removal in drainage canals of water removal systems based on the application of double-pipe heat exchangers known as Field tubes.

Quantification of the thermal resistance variation in evaporators surface due to ice formation

Refrigeration takes a very important role in society. Nowadays, a big portion of the refrigeration processes are taken into account in the food and drinks storage, and also in the cooling of closed spaces. The method of heat removal from the surrounding air through the evaporation of a fluid, being a process of continuous improving, has suffered many enhancements in order to obtain better energetic consumption levels. One of the main restrictions of the usual refrigeration mechanisms is the icing verified in the external surface of the evaporators, as a part of the refrigeration cycle. The present work discusses the mitigation process of ice formation through a proposed heat exchangers configuration. The experimental unit built for this purpose allows the ice layer formation over the heat exchangers surface for several values of air flow rate, temperature and relative humidity. The evaluation of the thermal resistance of the heat exchangers surface together with the condensates collected provides an insight of the consequences of the different air conditions and of the proposed configurations on the ice formation process.

Surviving the Heat Wave – A presentation on thermally induced failures and reliability risks created by advancements in electronics technologies

Abstract Since the advent of surface mount technology back in the 1970's we, as an industry, have continually worked to miniaturize our products. This evolution of product design has impacted us at the semiconductor, package, circuit board and system levels. So, the question is, Why do Electronics Fail Under Thermal Cycling? At the semiconductor level, you can have issues with delamination, IC complexity, degradation mechanisms, associated ceramic capacitor wearout, and electrical overstress (EOS). At the package level issues with bond wires and stacked die add to the reliability impact. At the printed circuit board level issues with solder wearout, solder phase coarsening, PWB laminates and glass materials, plated through hole (PTH) fatigue, and the impact of potting can also affect reliability while at the system level, heat sinks and other methods of heat removal can improve the situation. What drives these issues is that we use a variety of materials e.g. semiconductors, ceramics, metals and polymers. We then bond them together with other materials like solder and adhesives. Each of these materials has a Coefficient of Thermal Expansion (CTE) that is unique and therefore expands and contracts at different rates.

The Energy Multiplier Module (EM2): Status of Conceptual Design

The Energy Multiplier Module (EM2) is a helium-cooled fast reactor with a core outlet temperature of 850°C. It is designed as a modular, grid-capable power source with a net unit output of 265 MWe. The reactor employs a convert-and-burn core design that converts fertile isotopes to fissile and burns them in situ over a 30-year core life. The reactor is sited in a below-grade sealed containment. It uses passive safety methods for heat removal and reactivity control to protect the integrity of the fuel, reactor vessel, and containment. The plant also incorporates a below-grade, passively cooled spent fuel storage facility with capacity for 60 years of full-power operation. EM2 employs a direct closed-cycle gas turbine power conversion unit (PCU) with an organic Rankine bottoming cycle for 53% net power conversion efficiency assuming evaporative cooling. The high-power conversion efficiency and long-burn fuel cycle reduce the electricity cost by 35% when compared with the conventional light water reactor.The conceptual design has been conducted for the EM2 plant with focus on the reactor, fuel, and safety system designs. A detailed model of the passive direct reactor auxiliary cooling system was created to demonstrate functionality for selected design-basis accidents. The bench-scale fuel development campaign demonstrated high-quality uranium carbide pellet fabrication as well as β-SiC composite cladding and SiC-joining technologies. Irradiation tests of reactor materials are also being conducted. The PCU variable-speed generator mechanical design was validated with operational testing of its novel rotor at speeds >13 000 rpm. The design of the turbo-compressor with active magnetic bearings continues. A large cost database and financial model have been constructed for use as a key driver for the design to be economically competitive with competing generating technologies after 2030.

Heat transfer and flow characteristics of a cooling thimble in a molten salt reactor residual heat removal system

Abstract In the passive residual heat removal system of a molten salt reactor, one of the residual heat removal methods is to use the thimble-type heat transfer elements of the drain salt tank to remove the residual heat of fuel salts. An experimental loop is designed and built with a single heat transfer element to analyze the heat transfer and flow characteristics. In this research, the influence of the size of a three-layer thimble-type heat transfer element on the heat transfer rate is analyzed. Two methods are used to obtain the heat transfer rate, and a difference of results between methods is approximately 5%. The gas gap width between the thimble and the bayonet has a large effect on the heat transfer rate. As the gas gap width increases from 1.0 mm to 11.0 mm, the heat transfer rate decreases from 5.2 kW to 1.6 kW. In addition, a natural circulation startup process is described in this paper. Finally, flashing natural circulation instability has been observed in this thimble-type heat transfer element.

Analytical and numerical study on the fast refill of compressed natural gas with active heat removal

Heavy-duty vehicles powered by compressed natural gas (CNG) store the fuel in large onboard cylinders. Fast fill of depleted CNG cylinders is a common refueling method because it achieves refueling time comparable to liquid fuels. However, under-filling of CNG cylinders occurs during fast fill due to the recompression work of CNG in the cylinder that heats the fuel during the fill. The heated fuel has a lower density at the rated pressure, and thus less mass of CNG can be stored than if it was at ambient temperature. To increase the mass of dispensed CNG during fast fill, an active heat removal method is proposed. In this study, analytical and numerical models of the filling process of CNG into a Type-III cylinder with and without active heat removal are developed. In the analytical study, mass and energy conservation equations are coupled with an ideal-gas equation of state and orifice flow equations to predict the heat generation rates during fast fill. The influence of heat removal via a cooling coil inserted into the cylinder during fill on the dispensed mass and fill time is quantified. The analytical study is compared to numerical simulations employing a two-dimensional axisymmetric computational fluid dynamics (CFD) model for unsteady, compressible turbulent flow in a Type-III cylinder with and without active heat removal. Dynamic average temperature, pressure and mass curves as well as the local temperature distribution in the cylinder are obtained at different time instances during the fill. The effect of the location of the heat removal coils is also investigated. The results of the analytical/numerical study illustrate the benefit of heat removal from the cylinder as a means of improving fast-fill efficiency in natural gas fueled heavy-duty vehicles.

Pool Boiling Heat Transfer Characteristics of Inclined pHEMA-Coated Surfaces

New requirements for heat exchangers offered pool boiling heat transfer on structured and coated surfaces as one of the promising methods for effective heat removal. In this study, pool boiling experiments were conducted on polyhydroxyethylmethacrylate (pHEMA)-coated surfaces to investigate the effect of surface orientation on bubble dynamics and nucleate boiling heat transfer. pHEMA coatings with thicknesses of 50, 100, and 200 nm were deposited using the initiated chemical deposition (iCVD) method. De-ionized water was used as the working fluid. Experiments were performed on horizontal and inclined surfaces (inclination angles of 10 deg, 30 deg, 50 deg, and 70 deg) under the constant heat flux (ranging from 10 to 80 kW/m2) boundary condition. Obtained results were compared to their plain surface counterparts, and heat transfer enhancements were observed. Accordingly, it was observed that the bubble departure phenomenon was affected by heat flux and wall superheat on bare silicon surfaces, while the supply path of vapor altered the bubble departure process on pHEMA-coated surfaces. Furthermore, the surface orientation played a major role on bubble dynamics and could be considered as a mechanism for fast vapor removal from surfaces. Bubble coalescence and liquid replenishment on coated surfaces had a promising effect on heat transfer coefficient enhancement on coated surfaces. For horizontal surfaces, a maximum enhancement of 25% relative to the bare surface was achieved, while the maximum enhancement was 105% for the inclined coated surface under the optimum condition. iCVD was proven to be a practical method for coating surfaces for boiling heat transfer applications due to the obtained promising results.

3‐D numerical simulations for polycondensation of poly(p‐phenylene terephthalamide) in twin screw extruder

Poly(p‐phenylene terephthalamide) (PPTA) is a typical high‐performance fiber and usually synthesized by low temperature solution polycondensation in twin screw extruder. During the reactive extrusion, flow behavior, rheokinetics, and temperature are highly coupled, which makes it difficult to ensure the quality of product. In the present work, the rheokinetics of the PPTA solution is established by experiments and its reactive extrusion is investigated via 3‐D numerical simulation. The flow pattern, molecular weight distribution and temperature have been investigated for the extruders with three different elements, i.e., full flight screw (FF), kneading block (KB), and screw mixing element (SME). The results indicate that the unique flow characteristic of different screw elements affects mixing experience of the reactants and further the PPTA qualities. By numerical simulation, it shows the temperature increase within the tested extrusion stage is 7 K and reaction heat is found the main energy source for extrusion stage. Furthermore, heat removal method is verified with consideration of industrial production process. The numerical simulation work also discusses the reaction and mixing process in the extruders with three combined screws. The results show the introduction of more reverse FF and KB elements can lead to higher quality of PPTA. POLYM. ENG. SCI., 57:1252–1261, 2017. © 2017 Society of Plastics Engineers

CFD modeling of the gas–solid two-fluid flow in polyethylene FBRs: From traditional operation to super-condensed mode

A computational fluid dynamics (CFD) model based on the Eulerian–Eulerian approach, coupled with polymerization kinetics, has been implemented to describe the gas–solid flow behaviors in a gas phase polyethylene fluidized bed reactor (FBR). The model is firstly validated by the classic equations and reference data, and then extended to simulate the gas-phase polyethylene FBR under super-condensed mode for the first time. The influence of three important operating conditions (i.e., inlet gas velocity, inlet gas temperature, and condensable component isopentane concentration) on gas–solid flow hydrodynamics is investigated to give qualitative and quantitative insights on how these factors affecting FBR performances (like bed expansion, bed temperature and productivity) under super-condensed mode through CFD approach. The simulation results demonstrate that with the increase of inlet gas velocity, the bed expansion increases rapidly and the number of particles at the lower portion of the bed reduces while raises at the higher position. The rise of the bed temperature is mainly contributed by the increased exothermic reaction rate as the inlet gas temperature increasing, which is also influenced by the concentration of condensable component isopentane. The simulation results show that bed temperature decreases with the increase of condensable isopentane concentration in gas stream. It is found that the method of heat removal through the latent heat of vaporization is extremely significant and can effectively increases reactor productivity without enlarging the size of the reactor under super-condensed mode.

Urgent Problems in Thermal Physics of Design-Basis and Severe Accidents at Nuclear Power Plants

The paper considers thermal and physical aspects in dynamics of design-basis and severe accidents at water-cooled nuclear power reactors with nuclear fuel damage. The most promising concepts of the corium confinement in the damaged reactor were analyzed. The main objective was to define the main areas to search and implement methods of efficient and safe heat removal in progression of emergencies.

Optimization of circuits for pressure leaching of sulphide ores and concentrates

#$25.080 Pressure leaching is an option for copper recovery from chalcopyrite. Leaching takes place at high temperatures and pressures in the presence of an oxidizing agent. This work shows how the performance of pressure leaching circuits may be improved by optimizing the configuration of autoclaves and the heat removal method. The objective was achieved by creating an autoclave model that combines mass balances, energy balances, and population balances. A base case circuit consisting of a single autoclave was chosen, and this base case was compared with options for increasing capacity by adding more autoclaves to the circuit. These capacity increase options include circuits in which the additional autoclave is added in parallel, in series, and in series with thickening between the two autoclaves. The copper extraction, productivity, and cooling requirements for these options are compared. The series circuit with interstage thickening has the highest extraction and productivity; however, the cooling duty in the first autoclave is high. In addition to comparing circuit options, three options for heat removal were investigated: cooling coils, quench water, and flash recycling. The flash recycle option results in the highest copper extraction, and the quench water option the lowest copper extraction.

IEA EBC Annex 59 - Possibilities, Limitations and Capacities of Indoor Terminal Units

Indoor terminal units can be defined as the building elements that use different heat transfer mechanisms and media to emit and remove heat or moisture from indoor spaces (e.g. hydronic radiant heating and cooling systems, fan-coil units, active beams). Indoor temperature and humidity fields depend on the chosen terminal units.Terminal units differ in their capabilities of addressing sensible and latent loads, methods of heat emission or removal, maximum heating and cooling capacities, medium of energy distribution, and local or total volume conditioning.In the present study, operation characteristics, possibilities and limitations of different terminal units were specified. Considered terminal units were radiant heating and cooling systems, all-air systems (mixing, displacement, and personalized ventilation), passive and active beams. The results were summarized in a table, which aims at providing a reference for terminal unit selection during the design phases of HVAC systems.

Intensification and kinetics of methane hydrate formation under heat removal by phase change of n‐tetradecane

A method of direct heat removal resulting from the phase change of n‐tetradecane was used to intensify the heat transfer during hydrate formation. The growth rates of methane hydrate in aqueous slurries containing 25–45 wt % of solid n‐tetradecane were investigated at pressures between 4.70 and 6.46 MPa (gauge) and near the fusion point of solid n‐tetradecane. Methane hydrate growth started at a practically constant rate, which became variable after a sudden increase. Two rate laws were established to correlate with the experimental data for the constant and variable rate stages. The methane hydrate growth rates achieved with solid n‐tetradecane were significantly enhanced compared with those obtained under indirect heat removal. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3441–3450, 2015

A modified hydrodynamic model for pool boiling CHF considering the effects of heater size and nucleation site density

Boiling is commonly used in daily life and is an efficient heat removal method. During pool boiling, the critical heat flux (CHF) establishes the upper limit of efficient heat removal. Although, numerous studies have explored CHF, its exact mechanisms remain ambiguous. The hydrodynamic instability model is the most prominent CHF model, but it fails to explain the evident dependence of CHF on surface properties. The authors proposed modifying the hydrodynamic model to account for how nucleation site density and finite heater size affect the CHF. The experimental CHF values obtained from evaluating various types of surfaces qualitatively agreed with the predictions of the modified hydrodynamic model. This suggests that the CHFs on these surfaces were due to the hydrodynamic limit.