•No condensation occurs and feather-shaped frost crystals are formed directly on the surface.•Crystal growth processes in the initial stage of the frosting were observed.•The effect of cooling ...surface temperature on the frost mass was insignificant.•Increase of air velocity only increased the density of frost layer, not the frost thickness.
The purpose of this study is to understand the behavior of frost layer growth under conditions favorable for desublimation. The frosting experiments were conducted on a horizontal cooling surface. Condensation did not occur at the initial stage of frosting, and feather-shaped frost crystals were formed on the cooling surface. These frost crystals grew one-dimensionally while maintaining their shapes. In addition, the effects of operating conditions (air temperature, air velocity, air absolute humidity, cooling surface temperature) on frost layer growth under the conditions favorable for desublimation were investigated. As the cooling surface temperature decreased, the increase in the amount of frost was insignificant. Additionally, an increase in air velocity increased the frost density but not the thickness of the frost layer.
To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, ...waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm < 17.25 cm). The insulation effect of the airbag is positively correlated with its thickness and negatively correlated with the thermal conductivity of the filling gas. The insulation effect of CO
is better than that of air. The rubber airbag interlayered composite lining system provides a new scheme for freezing damage control in cold-region tunnels.
•Heat and mass transfer analogy was proposed under cryogenic conditions.•A dimensionless correlation was developed for the frost density.•The correlation for thermal conductivity was derived via ...regression analysis.
An experimental study on the phase change occurring on a cryogenic cooling surface was conducted under forced convection conditions. The mass and surface temperature of frost and the heat flux at the cooling surface were measured in the experiment. The heat and mass transfer analogy was investigated under cryogenic conditions. The mass estimated under various experimental conditions using the modified analogy differed by up to 8% from the experimentally measured mass. The density and thermal conductivity of frost at cryogenic temperatures were lower than those of general-low temperature frost; the dimensionless correlations of density and thermal conductivity of frost were derived via regression analysis. The calculated frost density and thermal conductivities were differed from the measured value by up to 9% and 11%, respectively. Therefore, a model was built to predict the heat and mass transfer and improve the thermal performance on the cooling surfaces of various cryogenic devices using the presented frost density and thermal conductivity correlations.
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•A method employing the electric heat tracing (EHT) in seasonal cold region tunnel was proposed.•The layout of the EHT-based freeze-proof system and installation procedures were ...introduced.•The EHT-based freeze-proof system is feasible and effective in tunnel frost damage prevention.
In recent decades, numerous tunnels have been built in the cold region of China. However, frost damage occurs frequently inside the tunnels; this damage threatens the stability of the tunnels. In order to prevent frost damage, a method employing electric heat tracing (EHT) was presented in this study. Moreover, the EHT-based freeze-proof system layout and installation procedures were also introduced. The tunnel liner EHT system is composed of four parts: heating cable, insulation layer, protective layer and fire protection layer. This EHT system was adopted in the Dongnanli highway tunnel (located in northeastern China) to verify its applicability. In-situ test results indicated that the temperature behind the liner begins to heat up after one hour of electrifying the system; next, the temperature becomes positive and remains stable after three hours of electrifying the system. The operation of the heating system is quite stable, and the insulation effect is significant. Through the assessments of the heating efficiency that is required to reach the target temperature and a constant temperature heating effect, it is suggested that the combination of thermal insulation and electric heat tracing is feasible and effective in preventing frost damage in tunnels. The research results provide references for the design and construction of frost prevention systems in tunnels in cold regions.
ABSTRACT
The aim of the study was to investigate the temporal and spatial variability of last spring and first autumn frost events as well as the length of the frost‐free season (FFS) in Central ...Europe in relation to atmospheric circulation. Studies were conducted for the period 1951–2010 using gridded, daily minimum air temperature data obtained from the E‐OBS dataset at 0.25° spatial resolution. To assess the possible impact of air temperature variability on plants, late spring frost events and severe frost events were also examined with respect to the beginning of the thermal growing season. The role of atmospheric circulation was described using Grosswetterlagen circulation types and NAO index, and finally estimated using empirical orthogonal function analysis (EOF). The results confirm a significant increase in the length of the FFS, up to 10 days per decade in the western parts of Europe. This is mostly a result of earlier occurrence of last spring frost in the west up to 5 days. The occurrence of first autumn frost shows no significant trend in most of the studied regions. The obtained spatial pattern of the trends reflects oceanic (west) and continental (east) climatic conditions of the study area. Detailed analysis of circulation types favouring the occurrence of frost in Central Europe indicates that anti‐cyclonic situations are mainly responsible. EOF analyses for the springtime confirm that the first mode, which accounts for 56% of total variance, is related to an extensive high pressure system over eastern Ukraine and Belarus, which brings an inflow of cold, continental air masses to Central Europe. The results provide a broaden information on the region climatologically important due to its transitional location, which may be relevant for investigating past and future trends in spring freeze risk for perennial crops, as changes in the frequency of these airflow patterns will result in changes in the risk of frost damage.
Fixed grid numerical modelling of frost growth and densification Bartrons, Eduard; Galione, Pedro Andrés; Pérez-Segarra, Carlos David
International journal of heat and mass transfer,
March 2019, 2019-03-00, 20190301, 2019-03, Letnik:
130
Journal Article, Publication
Recenzirano
Odprti dostop
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•A frost growth model based on a finite volume, fixed grid method for porous media is proposed.•A single set of equations is set for both free air and frost layer.•The proposed model ...is tested against 2D experimental results.•The effect of allowing humid air flow inside the frost layer is analysed.•The artificially enhanced μ seem to decrease when advection within the frost layer is accounted for.
A fixed-grid-porous-media method capable of simulating the growth and densification of frost sheets is here presented. A velocity field is calculated across the entire domain, in which a porous media treatment is given to the ice-containing cells. The transported temperature and vapour density are used to define the thermophysical state of each cell, which might enable phase change. As an improvement to Bartrons et al. (2017), the method hereby presented accounts for solidification and sublimation phase transitions. The explicit time step has also been increased by using a semi-implicit treatment of the energy equation. Furthermore, a special boundary condition for cold surfaces has been developed in order to overcome the averaging effect that prevents ice formation in the cells adjacent to the wall. The method is then tested with a study case of a duct flow with a non-homogeneously cooled lower boundary. Several numerical tests are carried out in order to understand the capabilities of the model. The influence of accounting for the convection, as well as the enhanced diffusion resistance factors within the frost layer, is studied by means of the calculated porosity and velocity fields throughout the domain.
Blockfields remain enigmatic regarding their origin, internal structure, surface processes, and glaciological implications. In Scandinavia, blockfields are found on high‐elevation, low‐relief ...mountains (plateaus) across the Arctic and Subarctic. In this study, we present a 1D numerical model that uses near‐surface temperatures measured between summer 2018 and summer 2020 to calculate frost‐cracking intensities (FCI) within the ground column in three different blockfields in Norway and Svalbard. Eighty‐nine miniature temperature loggers were distributed on Tron Mountain (1650 m a.s.l.) in Alvdal, Gamlemsveten (780 m a.s.l.) near Ålesund in southwestern Norway and on Platåberget (460 m a.s.l.) near Longyearbyen, Svalbard. We modelled FCI by scaling the time spent in the frost cracking window (between −3 and −8°C) with the temperature gradient and a penalty function for distance to available water. At Tron and Gamlemsveten, ground temperatures never reached the frost cracking window at one third of our sites due to insulation by a thick snow cover in depressions and on the lee sides of summits. The highest FCI (0.05–0.4 K m) are obtained where the subsurface consists of boulders and stones in a matrix of relatively fine sediment (sand, silt, gravel). In contrast, very low FCI (0.003–0.02 K m) were modelled for blocky layers with large air‐filled pores because of the low water availability. On Platåberget, all sensors reached the frost‐cracking window during the annual temperature cycle, but FCI are extremely low (0.0004–0.15 K m) as water availability is limited due to (i) permafrost and (ii) near‐surface temperatures remaining below the frost‐cracking window for 3/4 of the year. This indicates that boulder‐rich blockfields with air‐filled hollows are preserved in very cold climates, whereas warmer, maritime settings with higher availability of fine interstitial material place blockfields in the fast lane for frost weathering.
Our study focuses on frost‐cracking activity in blockfields in Scandinavia and Svalbard, using measured near‐surface temperatures to model first the subsurface thermal regime and then frost‐cracking intensities. The simulated frost‐cracking intensities provide insights into the processes governing weathering in blockfields and deliver constraints on the age and formation of the blockfield landform.
Tunnels located in cold regions are vulnerable to frost damage resulting from the special atmosphere, which directly threatens the safety of the tunnel structure and operation. Frost problems of ...tunnels in cold regions have not been fundamentally resolved. This paper reviews design theory and the frost mitigation techniques currently used in the design, construction and maintenance of cold region tunnels. The depths of freezing and thawing and frost heaving force are the key indexes of design theory. Insulation is the main design technology used to prevent frost heaving and thawing, and the active heating technology has also been applied in practice. In construction, reducing the heat of hydration and blasting by specific winter construction techniques can prevent tunnel freeze–thaw damages. In operation, the restoration of drainage systems, the reinforcement of structures and the reinstallation of freezing-prevention systems are effective measures to treat frost problems. Finally, some constructive suggestions and opinions are put forward to improve the service performance of tunnels.
Plant ecologists have long been concerned with a seemingly paradoxical scenario in the relationship between plant growth and climate change: warming may actually increase the risk of plant frost ...damage. The underlying hypothesis is that mild winters and warm, early springs, which are expected to occur as the climate warms, may induce premature plant development, resulting in exposure of vulnerable plant tissues and organs to subsequent late-season frosts. The 2007 spring freeze in the eastern United States provides an excellent opportunity to evaluate this hypothesis and assess its large-scale consequences. In this article, we contrast the rapid prefreeze phenological advancement caused by unusually warm conditions with the dramatic postfreeze setback, and report complicated patterns of freeze damage to plants. The widespread devastation of crops and natural vegetation occasioned by this event demonstrates the need to consider large fluctuations in spring temperatures a real threat to terrestrial ecosystem structure and functioning in a warming climate.
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