Numerical and Experimental Analysis of Fire Resistance for Steel Structures of Ships and Offshore Platforms

The requirements for the fire resistance of steel structures of oil and gas facilities for transportation and production of hydrocarbons are considered (structures of tankers and offshore platforms). It is found that the requirements for the values of fire resistance of structures under hydrocarbon rather than standard fire conditions are given only for offshore stationary platforms. Experimental studies on the loss of integrity (E) and thermal insulating capacity (I) of steel bulkheads and deck with mineral wool under standard and hydrocarbon fire regimes are presented. Simulation of structure heating was performed, which showed a good correlation with the experimental results (convective heat transfer coefficients for bulkheads of class H: 50 W/m2·K; for bulkheads of class A: 25 W/m2·K). The consumption of mineral slabs and endothermic mat for the H-0 bulkhead is predicted. It is calculated that under a standard fire regime, mineral wool with a density of 80–100 kg/m2 and a thickness of 40 to 85 mm should be used; under a hydrocarbon fire regime, mineral wool with a density above 100 kg/m2 and a thickness of 60–150 mm is required. It is shown that to protect the structures of decks and bulkheads in a hydrocarbon fire regime, it is necessary to use 30–40% more thermal insulation and apply the highest density of fire-retardant material compared to the standard fire regime. Parameters of thermal conductivity and heat capacity of the applied flame retardant in the temperature range from 0 to 1000 °C were clarified.

PARAMETRIC IDENTIFICATION OF THE DIFFERENTIAL MODEL OF HEAT EXCHANGE IN A GASIFIER

На основе одномерной дифференциальной модели теплообмена в газификаторе закрытого типа сформулирована задача параметрической идентификации модели на основе измерений на штатном оборудовании промышленной газификационной установки. Модель включает в себя дополнительное интегральное условие и самосогласованно определяемую подвижную границу, отделяющую зону обледенения трубки испарителя. С применением метода сглаживания особенности разработан алгоритм итерационного решения уравнений модели, использующий метод сквозного счета для решения уравнения переноса на одной итерации. Для параметрической идентификации модели использована смешанная стратегия. Часть идентифицируемых параметров (теплоемкость испарителя, мощность нагревателя, массовая производительность насоса, коэффициент теплоотдачи в окружающую среду) определялась на основе специально организованных измерений: нагрева испарителя без прокачки сверхкритического флюида, газификации в условиях теплоизолированности корпуса испарителя, газификации в стационарном режиме работы. Остальные параметры (коэффициенты теплоотдачи в теплоноситель и сверхкритический флюид) идентифицировались в пассивных измерениях с различными производительностями насоса. Отмечено, что ввиду плохой обусловленности задачи и ограниченности вариаций коэффициентов применение регрессионных методов в данной модели неэффективно. На основе метода стрельбы разработан способ идентификации, заключающийся в определении параметров по измерениям с предельными производительностями с построением функциональной связи между идентифицируемыми параметрами, с последующей верификацией на промежуточных измерениях. Метод апробирован на примере штатной газификационной установки СГУ-7КМ-У We formulated the problem of parametric identification of the model based on measurements on the standard equipment of an industrial gasification plant on the basis of a one-dimensional differential model of heat transfer in a closed-type gasifier. The model includes an additional integral condition and a self-consistently defined movable boundary separating the icing zone of the evaporator tube. Using the method of smoothing the singularity, we developed an algorithm for iterative solution of the model equations, using the end-to-end counting method to solve the transfer equation in one iteration. We used a mixed strategy for parametric identification of the model. We determined some of the identified parameters (evaporator heat capacity, heater power, mass pump capacity, heat transfer coefficient to the environment) on the basis of specially organized measurements: heating of the evaporator without pumping supercritical fluid, gasification under conditions of thermal insulation of the evaporator body, gasification in stationary operation. We identified the remaining parameters (heat transfer coefficients to the coolant and supercritical fluid) in passive measurements with different pump capacities. We noted that due to the poor conditionality of the problem and the limited variation of coefficients, the use of regression methods in this model is ineffective. Based on the ballistic method, we developed an identification method, which consists in determining parameters by measurements with marginal performance with the construction of a functional relationship between the identified parameters, followed by verification on intermediate measurements. We tested the method on the example of a standard gasification plant SGU-7KM-U

Numerical Study on the Thermal Field and Heat Transfer Characteristics of a Hexagonal-Close-Packed Pebble Bed

Fuel elements in a high-temperature gas-cooled reactor (HTGR) core may be stacked with a hexagonal close-packed (HCP) structure; therefore, analyzing the temperature distribution and heat transfer efficiency in the HCP pebble bed is of great significance to the design and safety of HTGR cores. In this study, the heat transfer characteristics of an HCP pebble bed are studied using CFD. The thermal fields and convective heat transfer coefficients under different coolant inlet velocities are obtained, and the velocity fields in the gap areas are also analyzed in different planes. It is found that the strongest heat transfer is shown near the right vertices of the top and bottom spheres, while the weakest heat transfer takes place in areas near the contact points where no fluid flows over; in addition, the correlation of the overall heat transfer coefficient with the Reynolds number is proposed as havg = 0.1545(k/L)Re0.8 (Pr = 0.712, 1.6 × 104 ≤ Re ≤ 4 × 104). It is also found that the heat transfer intensity of the HCP structure is weaker than that of the face-centered-cubic structure. These findings provide a reference for reactor designers and will contribute to the development of safer pebble-bed cores.

The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications

This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces.

Experimental validation of a quasi-transient coupling approach for the modeling of heat transfer in autoclave processing

Structural aerospace composite parts are commonly cured through autoclave processing. To optimize the autoclave process, manufacturing process simulations have been increasingly used to investigate the thermal behavior of the cure assembly. Performing such a simulation, computational fluid dynamics (CFD) coupled with finite element method (FEM) model can be used to deal with the conjugate heat transfer problem between the airflow and solid regions inside the autoclave. A transient CFD simulation requires intensive computing resources. To avoid a long computing time, a quasi-transient coupling approach is adopted to allow a significant acceleration of the simulation process. This approach has been validated for a simple geometry in a previous study. This paper provides an experimental and numerical study on heat transfer in a medium-sized autoclave for a more complicated loading condition and a composite structure, a curved shell with three stringers, that mocks the fuselage structure of an aircraft. Two lumped mass calorimeters are used for the measurement of the heat transfer coefficients (HTCs) during the predefined curing cycle. Owing to some uncertainty in the inlet flow velocity, a correction parameter and calibration method are proposed to reduce the numerical error. The simulation results are compared to the experimental results, which consist of thermal measurements and temperature distributions of the composite shell, to validate the simulation model. This study shows the capability and potential of the quasi-transient coupling approach for the modeling of heat transfer in autoclave processing with reduced computational cost and high correlation between the experimental and numerical results.

Numerical Study on Water Sealing Effect of Freeze-Sealing Pipe-Roof Method Applied in Underwater Shallow-Buried Tunnel

The freezing-sealing pipe-roof method is a new presupporting technique, which fully combines the advantages of pipe-roof method and artificial ground-freezing method, and can adapt to the construction needs of underground projects in complex and sensitive strata. After the Gongbei Tunnel of Hong Kong–Zhuhai–Macao Bridge, this method will be applied for the first time in an underwater shallow-buried railroad tunnel, and there are still many urgent problems to be solved. In this article, based on the field situation and the preliminary design scheme, a convective heat transfer model under complex boundary conditions was first established. Then, the development of frozen wall thickness during the active freezing period was solved by numerical simulation for three different pipe filling modes, and the cloud map of temperature distribution in the whole section is analyzed. After that, the moving state of river water was characterized by different heat transfer coefficients, and the weakening effect of flow velocity on the top freezing wall was studied. Finally, six critical water sealing paths were selected, and the temperature differences of the frozen curtain were calculated. The results show that the mode with interval concrete filling can form a reliable frozen curtain within the scheduled time, whereas the nonfilling mode cannot achieve the water sealing requirement. River water has a large effect on the temperature at the boundary of jacking pipe and almost no effect on the center of the jacked pipe. It takes approximately 15 days from the frozen soil covering the pipe wall to reach the designed thickness, and the freezing effect of empty pipe lags approximately 28 days compared with that of solid pipe, which requires targeted enhancement measures in field projects.

Analysis Effects of Average Value of Convective and Evaporative Heat Transfer Coefficient on Solar Cabinet Dryer for Reduction of Mass of Papad

In this research paper, the behavior of heat and mass transfer phenomenon during greenhouse papad drying under forced convection mode has been investigated. Various experiments were performed during the month of April 2020 at SRCEM Banmore, morena (26o 34’13” N 78o 10’48” E). Experimental data obtained for forced convection greenhouse drying of papad were used to determine the constants in the Nusselt number expression by using the simple linear regression analysis and, consequently, the values of convective and evaporative heat transfer coefficients were evaluated. The average values of experimental constants C and n were determined as 0.9714 and 0.0129 respectively. The average values of convective and evaporative heat transfer coefficients were determined as 0.0886 W/m2 oC and 6.7583 W/m2 oC respectively. The experimental error in terms of percentage uncertainty was also evaluated. Keywords: Papad, Papad drying, Heat transfer coefficient, Convective, Evaporative, Forced convection greenhouse

A Study to Explore the Dew Condensation Potential of Cars

The metal surfaces of a car exhibit favorable properties for the passive condensation of atmospheric water. Under certain nocturnal climatic conditions (high relative humidity, weak windspeed, and total nebulosity), dew is often observed on cars, and it is appropriate to ask the question of using a vehicle as a standard condenser for estimating the dew yield. In order to see whether cars can be used as reference dew condensers, we report a detailed study of radiative cooling and dew formation on cars in the presence of radiating obstacles and for various windspeeds. Measurements of temperature and condensed dew mass on different car parts (rooftop, front and back hoods, windshield, lateral and back windows, inside and outside air) are compared with the same data obtained on a horizontal, thermally isolated planar film. The paper concludes that heat transfer coefficients, evaluated from temperature and dew yield measurements, are found nearly independent of windspeed and tilt angles. Moreover, this work describes the relation between cooling and dew condensation with the presence or not of thermal isolation. This dependence varies with the surface tilt angle according to the angular dependence of the atmosphere radiation. This work also confirms that cars can be used to estimate the dew yields in a given site. A visual observation scale h = Kn, with h the dew yield (mm) and n = 0, 1 2, 3 an index, which depends whether dew forms or not on rooftop, windshield, and lateral windows, is successfully tested with 8 different cars in 5 sites with three different climates, using K = (0.067 ± 0.0036) mm.day−1.