Experimental investigation of water vapor condensation from hot humidified air in serpentine heat exchanger

Data availability: Data will be made available on request.Copyright © 2023 The Authors. Condensing economizers are used in industry and power plants for waste heat recovery. Despite widespread use, their thermal design is still not optimized due to the complexity of the condensation process especially when non-condensing gasses are prevalent. This paper presents an experimental study of water vapor condensation on the vertical tubes of a serpentine bundle in a humidified air crossflow at water vapor mass fractions of 10% and 20%. The analysis showed a clear dependence of the efficiency of the condensation process on the humidified air inlet temperature and Reynolds number, and the efficiency increases as these parameters decrease. Condensation efficiency also depends highly on flow humidity especially in the region of higher Reynolds numbers. A comparison of the average Nusselt number in the case of dry air with the experimentally determined average Nusselt number is also presented, and showed a uniform increase in the Nusselt number as the inlet temperature of the humidified air decreased.This work was partly funded by the European Union H2020 program project iWAYS under grant agreement number 958274

Modelling of the fire impact on CONSTOR RBMK-1500 cask thermal behavior in the open interim storage site

Copyright © 2023 Korean Nuclear Society, Spent nuclear fuel and long-lived radioactive waste must be carefully handled before disposing them off to a geological repository. After the pre-storage period in water pools, spent nuclear fuel is stored in casks, which are widely used for interim storage. Interim storage in casks is very important part in the whole cycle of nuclear energy generation. This paper presents the results of the numerical study that was performed to evaluate the thermal behavior of a metal-concrete CONSTOR RBMK–1500 cask loaded with spent nuclear fuel and placed in an open type interim storage facility which is under fire conditions (steady-state, fire, post-fire). The modelling was performed using the ANSYS Fluent code. Also, a local sensitivity analysis of thermal parameters on temperature variation was performed. The analysis demonstrated that the maximum increase in the fuel load temperatures is about 10 °C and 8 °C for 30 min 800 °C and 60 min 600 °C fires respectively. Therefore, during the fire and the post-fire periods, the fuel load temperatures did not exceed the 300°C limiting temperature set for an RBMK SNF cladding for long-term storage. This ensures that fire accident does not cause overheating of fuel rods in a cask

Modelling of decay heat removal from CONSTOR RBMK-1500 casks during long-term storage of spent nuclear fuel

Management of spent nuclear fuel is a very important part in the whole cycle of nuclear energy generation. Ignalina nuclear power plant operated two RBMK-1500 reactors that are now being decommissioned. After careful consideration “dry” storage technology in casks was selected for the interim storage of spent nuclear fuel (SNF) for up to 50 years. SNF after pre-storage time in water pools for not less than 5 years is loaded into cast-iron or metal-concrete casks. In this paper decay heat removal was modeled from specific GNB (Gesellschaft für Nuklear Behälter GmbH) metalconcrete (CONSTOR RBMK-1500) casks for the long-term storage period up to 300 years. The ALGOR code was used for the numerical modeling of the distribution of the heat fluxes and temperatures in a loaded cask placed in an open type storage facility in both summer and winter taking into account local environmental conditions. A local sensitivity analysis of the impact of fuel parameter uncertainties is also performed

An experimental investigation of water vapor condensation from biofuel flue gas in a model of condenser, (2) local heat transfer in a calorimetric tube with water injection

Data Availability Statement: Not applicable.Copyright © 2021 by the authors. In order for the operation of the condensing heat exchanger to be efficient, the flue gas temperature at the inlet to the heat exchanger should be reduced so that condensation can start from the very beginning of the exchanger. A possible way to reduce the flue gas temperature is the injection of water into the flue gas flow. Injected water additionally moistens the flue gas and increases its level of humidity. Therefore, more favorable conditions are created for condensation and heat transfer. The results presented in the second paper of the series on condensation heat transfer indicate that water injection into the flue gas flow drastically changes the distribution of temperatures along the heat exchanger and enhances local total heat transfer. The injected water causes an increase in the local total heat transfer by at least two times in comparison with the case when no water is injected. Different temperatures of injected water mainly have a major impact on the local total heat transfer until almost the middle of the model of the condensing heat exchanger. From the middle part until the end, the heat transfer is almost the same at different injected water temperatures.Research Council of Lithuania (LMTLT), grant number S-MIP-20-30

Flue Gas Condensation in a Model of the Heat Exchanger: The Effect of the Cooling Water Flow Rate and Its Temperature on Local Heat Transfer

In boiler houses, the biggest heat energy losses are caused by flue gas being released into the atmosphere. Installation of condensing heat exchangers allows reducing the temperature of the flue gas being released, condensation of water vapor, and, thus, efficient use of the waste heat. There are many investigations of average heat transfer in different types of condensing heat exchangers. They indicate also that the cooling water flow rate and its temperature are important parameters defining water vapor condensation efficiency. Investigations of local condensation heat transfer in condensing heat exchangers are very limited. Only recently experimental investigations of the flue gas temperature and Re number effect on local condensation heat transfer in the model of the condensing heat exchanger at a constant cooling water flow rate and its temperature have started being published. In this paper, for the first time, detailed experimental investigations of the cooling water flow rate and its temperature effect on local condensation heat transfer of the water vapor from the flue gas in the model of the condensing heat exchanger (long vertical tube) are presented. The results revealed that at higher flue gas Rein, the effect of the cooling water flow rate and its temperature has a stronger impact on local heat transfer distribution along the test section.Research Council of Lithuania (LMTLT), grant number S-MIP-20-30

Investigation of complex mass and heat transfer transitional processes of dispersed water droplets in wet gas flow in the framework of heat utilization technologies for biofuel combustion and flue gas removal Energy

In this paper, complex processes of water droplet heat and mass transfer are analyzed in a cycle of condensing, transitional evaporation and equilibrium evaporation regimes during phase change which occurs on a droplet’s surface. The dynamics of a heated droplet’s surface temperature is directly related to the change in the regimes. The definition of the dynamics is based on a numerical iterative scheme which depends on the balance of a droplet surface’s heat flux. In this scheme, the energy of phase change and external heat transfer are combined as well as the internal heat transfer occurring in droplets. The numerical investigation results of the water droplets’ phase change were used as a basis while defining the inputs provided by the droplet slipping and the radiation absorbed in the flue gas within the interactions between the processes of complex transitional transfers. For this investigation, the conditions have been set to be typical for heat utilization technologies and biofuel furnaces used in flue gas removal

Biofuel production using thermochemical conversion of heavy metal-contaminated biomass (HMCB) harvested from phytoextraction process

Over the past few decades, bioenergy production from heavy metal-contaminated biomasses (HMCBs) has been drawing increasing attention from scientists in diverse disciplines and countries owing to their potential roles in addressing both energy crisis and environmental challenges. In this review, bioenergy recovery from HMCBs, i.e. contaminated plants and energy crops, using thermochemical processes (pyrolysis, gasification, combustion, and liquefaction) has been scrutinized. Furthermore, the necessity of the implementation of practical strategies towards sustainable phytoextraction and metal-free biofuels production has been critically discussed. To meet this aim, the paper firstly delivers the fundamental concepts regarding the remediation of the brownfields using phytoremediation approach, and then, reviews recent literature on sustainable phytoextraction of heavy metals from polluted soils. Thereafter, to find out the possibility of the cost-efficient production of metal-free biofuels from HMCBs using thermochemical methods, the impacts of various influential factors, such as the type of feedstock and metals contents, the reactor type and operating conditions, and the role of probable pre-/post-treatment on the fate of heavy metals and the quality of products, have also been discussed. Finally, based on relevant empirical results and techno-economic assessment (TEA) studies, the present paper sheds light on pyrolysis as the most promising thermochemical technique for large-scale electricity and heat recovery from HMCBs

An Experimental Investigation of Water Vapor Condensation from Biofuel Flue Gas in a Model of Condenser, (1) Base Case: Local Heat Transfer without Water Injection

Waste heat recovery from flue gas based on water vapor condensation is an important issue as the waste heat recovery significantly increases the efficiency of the thermal power units. General principles for designing of this type of heat exchangers are known rather well; however, investigations of the local characteristics necessary for the optimization of those heat exchangers are very limited. Investigations of water vapor condensation from biofuel flue gas in the model of a vertical condensing heat exchanger were performed without and with water injection into a calorimetric tube. During the base-case investigations, no water was injected into the calorimetric tube. The results showed that the humidity and the temperature of inlet flue gas have a significant effect on the local and average heat transfer. For some regimes, the initial part of the condensing heat exchanger was not effective in terms of heat transfer because there the flue gas was cooled by convection until its temperature reached the dew point temperature. The results also showed that, at higher Reynolds numbers, there was an increase in the length of the convection prevailing region. After that region, a sudden increase was observed in heat transfer due to water vapor condensation

Experimental investigation of water vapor condensation from flue gas in different rows of a heat exchanger model

Data availability: Data will be made available on request.Condensing heat exchangers (HE) are used in many applications because of their usability with different fluids and a wide operating range in terms of pressure, temperature and power. Despite that, the thermal design of condensing heat exchangers is still not optimized, due to the complexity of the condensation process and lack of related research. This paper presents results of experimental investigations of biofuel flue gas water vapor condensation on vertical tubes in different rows of a tube bundle in a crossflow. The effects of water vapor mass fraction, inlet flue gas temperature and the Reynolds number on heat transfer when the inlet cooling water temperature and flow rate are constant were analyzed. The results obtained showed that the main parameters which had the most influence on the condensation process were the water vapor mass fraction in the flue gas and its temperature at the inlet to the test section. In the range of inlet flue gas Reynolds numbers investigated, the Re effect on heat transfer was not as significant as the effect of the parameters indicated above. However, the Re number had some influence on the heat transfer variation along the inline tube bundle. A comparison of the average Nu number in the case of dry air with the experimentally determined average Nu number, even with low condensable gas mass fraction (6 %), showed that it increased considerably. A correlation was proposed, which helps to determine the average Nu number for the heat exchanger in the range of experiments performed.partly funded from the European Union’s H2020 programme iWAYS project under grant agreement number 958274