scispace - formally typeset
Search or ask a question
Author

Balazs Toth

Bio: Balazs Toth is an academic researcher from European Space Agency. The author has contributed to research in topics: Flame spread & Spacecraft. The author has an hindex of 4, co-authored 15 publications receiving 82 citations. Previous affiliations of Balazs Toth include European Space Research and Technology Centre.

Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, a large-scale flame spread experiment was conducted inside an orbiting spacecraft to study the effects of microgravity and scale and to address the uncertainty regarding how flames spread when there is no gravity and if the sample size and the experimental duration are, respectively, large enough and long enough to allow for unrestricted growth.

59 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present the approach of the European Space Agency to promote research in weightlessness and in particular onboard the International Space Station, focusing on two-phase (liquid-gas phase change) heat transfer related experiments.
Abstract: The article presents the approach of the European Space Agency to promote research in weightlessness and in particular onboard the International Space Station. In order to maximize the return on investments, a strong international scientific collaboration is encouraged. These Science Teams support the preparation and utilisation of the flight hardware and exploit the measurement data. In the domain of physical sciences the topics dealt with at the time of writing the present paper cover fundamental physics, fluid physics, material sciences research and specific preparatory studies in anticipation of space exploration missions. The present article focuses on two-phase (liquid-gas phase change) heat transfer related experiments. These activities cover evaporation driven thermocapillary convection, pool- and flow boiling, evaporation and condensation of films together with wettability realted issues on both reference and structured surfaces, and heat pipe systems. Some hardware are in an advanced state of development, the feasibility of some was studied or is under definition at the time of the preparation of this paper. The objectives of the experiments are described together with their expected capabilities. Beyond the understanding of mostly fundamental physical processes, the data of all the described experiments are intended to be used to validate theoretical approaches and numerical tools, which are often developed by the Science Teams in parallel with the the flight hardware design activities of space industry.

17 citations

Journal ArticleDOI
01 Jan 2021
TL;DR: In this article, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed.
Abstract: Novel, high-fidelity results related to soot from microgravity flames were obtained by an international topical team on fire safety in space. More specifically, embedded optical techniques for evaluation of the soot-related radiative feedback to the base material from a spreading non-premixed flame in microgravity were developed. The configuration used a non-buoyant axisymmetric flame propagating in an opposed laminar stream over a Low Density PolyEthylene coating of an electrical wire. Within this context, both the standard Broadband Two Color Pyrometry (B2CP) and its recent extension Broadband Modulated Absorption/Emission (BMAE) technique can be deployed to measure the spatial distribution of soot temperature and volume fraction within the flame. Both fields are then processed to establish the field of local radiative balance attributed to soot within the flame, and ultimately the soot contribution to the radiative flux to the wire. The present study first assesses the consistency of the methodology contrasting an experimental frame and a synthetic one, the latter being produced by a signal modeling that processes fields delivered by a numerical simulation of the configuration as inputs. Using the synthetic signals obtained, the fields of local radiative balance within the flame are then computed and significant discrepancies were disclosed locally between the fields originating from the synthetic BMAE and B2CP inputs. Nevertheless, the subsequent evaluation of the soot-related radiative heat feedback to the wire shows that a weak deviation among the techniques implemented is expected. This finding is corroborated by similar evaluations conducted with experimental BMAE and B2CP measurements obtained in parabolic flights. As BMAE is implemented in an ISS configuration within the SCEM rig, BMAE and B2CP will soon provide long-duration soot observations in microgravity. In order to contrast the upcoming results, this current study quantifies discrepancies originating from the post-processing regarding soot temperature and volume fraction, and shows that the radiative feedback evaluation from both methods should be consistent.

13 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report preliminary results on experimental investigations on condensation in the framework of the European Space Agency funded programme Enhanced Condensers in Microgravity (ENCOM-2) which aims at better understanding underlying phenomena during condensation.
Abstract: We report preliminary results on experimental investigations on condensation in the framework of the European Space Agency funded programme Enhanced Condensers in Microgravity (ENCOM-2) which aims at better understanding underlying phenomena during condensation. The first experiment is a study on condensation of HFE on external curvilinear surface of 15 mm height during reduced gravity experiments. It is found that the local minimum of the film thickness exists at the conjugation area of condensed film and the meniscus at the bottom of the fin; this leads to the local maximum of the heat transfer coefficient, which we also found moves towards the fin tip. The second experiment is a study of falling films hydrodynamics inside a vertical long pipe. In particular, characteristics of wavy falling films produced employing intermittent liquid feed are examined in order to assess wave effects on film condensation. Preliminary results suggest that intermittent feed simply divides the film in two autonomous regions with the wave feature of each one depending only on its flow rate. The processing of registered film thickness data can lead to the estimation of the transverse velocity profile in the film, which is mainly responsible for heat transfer during condensation. The third experiment looks at in-tube convective condensation at low mass fluxes (typical of Loop Heat Pipes and Capillary Pumped Loops) of n-pentane inside a 0.56 mm diameter channel. The results show that the mean heat transfer in the annular zone when it is elongated may be less than the mean heat transfer when it is shorter, due to the interface deformation involved by surface tension effect. When the length of this annular zone reaches a critical value, the interface becomes unstable, and a liquid bridge forms, involving the release of a bubble. The heat transfer due to the phase-change in this isolated bubble zone appears to be very small compared to the sensible heat transfer: the bubbles evolve and collapse in a highly subcooled liquid. The last experiment concerns in-tube condensation of R134a inside a square channel of 1.23 mm hydraulic diameter at mass fluxes of 135 kg m−2 s−1 and 390 kg m−2 s−1 for three different configurations: horizontal, vertical downflow and vertical upflow. For the calculated heat transfer coefficient it is found that gravity has no effect on condensation in downflow configurations at 390 kg m−2 s−1 and in upflow conditions at both values of mass velocity. The effect of gravity on the condensation heat transfer coefficient becomes noteworthy in downflow at mass velocity G = 135 kg m−2 s−1 and vapour quality lower than 0.6.

12 citations

Journal ArticleDOI
TL;DR: In this article, the authors used PMMA (polymethylmethacrylate) samples that were 50mm wide and 290mm long with two variations, one sample was a 10mm thick flat slab, while the other sample had a 4mm thick grooved center section.
Abstract: Spacecraft fire safety is an important consideration when designing future exploration missions. Concurrent flow flame spread experiments were carried out aboard the Cygnus spacecraft while in orbit to address current knowledge gaps related to solid fuel combustion in microgravity. The experiments used PMMA (polymethylmethacrylate) samples that were 50 mm wide and 290 mm long with two variations—one sample was a 10 mm thick flat slab, while the other was a 10 mm thick flat sample that had a 4 mm thick grooved center section. The thickness variation had a major impact on the flame shape, and the grooved sample developed a deep inverted-V shaped notch as the thin center section burned through. This notch enhanced heat transfer from the flame to the solid through an effectively wider flame base, which is the part of the flame with the highest temperature. Unlike in normal gravity (and also likely in partial gravity), where buoyant flow promotes acceleratory upward flame growth, the microgravity flames reached a steady size (limiting length) for a fixed forced convective flow in agreement with theory (i.e. there is a zero net heat flux at the flame tip). The limiting length implies that the spread rate of the flame will be controlled by the regression rate (burnout rate) of the material because the flames remains anchored to the upstream end of the fuel samples. This is a significant finding for spacecraft fire safety, and makes the probability of flashover in a spacecraft unlikely as the flame size will be small for low convective ventilation flow environments typical in spacecraft. On the other hand, long-burning flames in small vehicles will generate significant quantities of fuel vapor that may reach the lean flammability limit and cause a backdraft. The rapid extinction of the flame when the flow was turned off also supports the existing fire mitigation strategy on the ISS to deactivate the ventilation system in the event of fire alarm. These findings can be applied to improve the safety of future space exploration missions.

6 citations


Cited by
More filters
01 Jan 2016
TL;DR: The principles of enhanced heat transfer is universally compatible with any devices to read and is available in the book collection an online access to it is set as public so you can get it instantly.
Abstract: Thank you very much for reading principles of enhanced heat transfer. As you may know, people have look numerous times for their chosen books like this principles of enhanced heat transfer, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they are facing with some infectious bugs inside their desktop computer. principles of enhanced heat transfer is available in our book collection an online access to it is set as public so you can get it instantly. Our books collection spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the principles of enhanced heat transfer is universally compatible with any devices to read.

553 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation of convective processes within horizontal evaporating liquid layer under shear-stress of inert gas flow is presented, where the average evaporation flow rate has a local maximum.

49 citations

Journal ArticleDOI
TL;DR: In this article, the authors revisited the problem of opposed fire spread under limited and excessive oxygen supply and reviewed various near-limit fire phenomena, as recently observed in flaming, smoldering, and glowing spread under various environment and fuel configurations.

40 citations

Journal ArticleDOI
TL;DR: The theoretical foundations for mathematical modeling of the convective flows with evaporation are presented, and the topical research areas are given as discussed by the authors, with special attention paid to models constructed within continuum mechanics, to comparison of the different formulations of corresponding problems including formulations of boundary conditions at the interfaces.
Abstract: The theoretical foundations for mathematical modeling of the convective flows with evaporation are presented, and the topical research areas are given. The special attention is payed to models constructed within continuum mechanics, to comparison of the different formulations of corresponding problems including formulations of boundary conditions at the interfaces. Alternative analytical approaches and experimental studies are briefly discussed in the context of thermal convection accompanied by evaporation (or condensation) in the systems with thin liquid layers which are mostly sensitive to the phenomena of interphase exchange.

32 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of pressure and microgravity on upward/concurrent flame spread over 10 mm thick polymethyl methacrylate (PMMA) slabs was investigated and correlated in terms of a non-dimensional mixed convection analysis that describes the convective heat transferred from the flame to the solid.

30 citations