Cooling effects study on ventilated embankments under the influence of the temperature differences between the sunny slopes and the shady slopes

Based on theories of heat and mass transfer, three-dimensional theoretical and numerical models were presented to analyze the temperature characteristics of embankments in permafrost regions. Conditions of air convective within crushed rock layer and the background of the climate warming in the future were considered. In addition, temperature differences between the sunny and shady slopes of embankments, as well as the uneven distribution of air temperatures inside the ventilated duct were also considered in the models. Cooling effects and temperature field characteristics of three kinds of embankments were analyzed and compared. Results of traditional embankment indicated that there were significant differences in permafrost tables between the sunny and shady slopes, and the underlying permafrost was in serious degradation. A large asymmetric 0 °C melting bulb was formed in and beneath the embankment over winter time. The analysis indicated that the duct-ventilated embankment could lower the temperature of underlying permafrost, and elevate the permafrost table under the embankment. The duct-ventilated embankment could also adjust the differences of permafrost tables, and improve the asymmetry of the temperature fields between the sunny and shady slopes. Due to climate warming, however, a 0 °C melting bulb still developed at the sunny slope foot of the duct-ventilated embankment. To prevent the 0 °C melting bulb from occurring, a closed crushed rock revetment was applied on the sunny slope, and the results indicated that the cooling effect of duct-ventilated embankment with the closed crushed rock revetment was better than that without the closed crushed rock revetment. Soils in and beneath the duct-ventilated embankment with closed crushed rock revetment could refreeze completely over winter time and this kind of embankment could also effectively adjust the differences of permafrost tables between the sunny and shady slopes.     

Study on design optimization of a crushed stone layer with shading board placed on a railway embankment on warm permafrost

Under the impact of potential climate warming and human engineering activities, the Embankment with Crushed Stone Slope Protection (ECSSP) needs further countermeasures to protect the underlying permafrost along the Qinghai–Tibet railway in warm (− 1 to 0 °C) permafrost regions according to the observed in situ data. In this paper, a new strengthening countermeasure, the Embankment with Shading Board and Crushed Stone Slope Protection (ESBCSSP), is proposed to cool the foundation soil and to protect the warm permafrost. The crushed stone layers placed on the side slopes of the embankment have an apparent “thermal semi-conductor” effect by intensive natural convection of pore air in the winter and a “heat shield” effect in the summer. The shading boards erected on crushed stone slope protection can shade the ground surface from the sun to lower its surface temperature, and can keep snow from covering the crushed stone layer in the winter, which can enhance the cooling effect of the crushed stone layer. Based on the processes of natural convective and conductive heat transfer in porous media, systemic numerical tests were performed to study the cooling effect of the ESBCSSP, and to propose the reasonable range in thickness, height and grain size of the crushed stone slope protection.     

Characteristics and mechanisms of embankment deformation along the Qinghai-Tibet Railway in permafrost regions

Based on field monitoring datasets, characteristics of embankment deformation were summarized along the Qinghai-Tibet Railway in four permafrost regions with different mean annual ground temperatures (MAGTs). Then, further analyses were carried out at some typical monitoring profiles to discuss mechanisms of these embankment deformations with consideration of detailed information of thermal and subsurface conditions. The results indicated that in regions with MAGT <− 1.5 °C, embankments only experienced seasonal frost heaves, and of which the magnitudes were not significant. So, the embankments in the regions performed satisfactorily. Whereas in regions with MAGT ≥− 1.5 °C, both traditional embankment and crushed rock embankment experienced settlements, but characteristics and mechanisms of the settlements were different for the two kinds of embankment. For crushed rock embankment, the magnitudes of settlement and differential settlement between right and left embankment shoulders were not significant and increased slowly. In respect that upwards movements of permafrost tables and better thermal stability of permafrost beneath embankment, mechanism of settlements on the embankment was inferred as creep of warm and ice-rich layer often present near permafrost table. While for traditional embankment, particularly in warm and ice-rich permafrost regions, the magnitudes of settlement and differential settlement between right and left embankment shoulders were significant and still increased quickly. Considering underneath permafrost table movements and permafrost temperature rises, mechanisms of settlements on the embankment included not only creep but also thawing consolidation of underlying permafrost. Therefore, some strengthened measures were needed to ensure long-term stability of these traditional embankments, and special attention should be paid on temperature, ice content and applied load within the layer immediately beneath permafrost table since warming and thawing of the layer could give rise to considerable settlement.     

Comparative analysis of the natural convection process between hollow concrete brick layer and crushed rock layer

On the basis of cooling mechanisms and its factors of crushed rock layer widely used in the Qinghai–Tibet railway, a new hollow concrete brick layer is proposed for the Qinghai–Tibet freeway. A high-precision macro wind velocity detector was employed to study the natural convective characteristics of both types of rock layers and their differences. The natural convection velocity in both types of rock layers resulting from the temperature difference was investigated for the first time through modeling experiment. Natural convection velocity in the hollow concrete brick layer with weak convection resistance was higher than that in the crushed rock layer. Their maximum velocities were 0.10 m/s and 0.08 m/s, respectively. The different heat transfer processes and their intensities resulting from the boundary temperature fluctuations were the primary reasons for inner asymmetric temperature fluctuation and decline. The cooling process closely related to convection time and convection velocity. The temperature difference was the key factor in the occurrence of convection and its intensity change, although the air temperature changes also had an effect on the airflow process. The occurrence of natural convection required a start-up temperature difference. Moreover, a linear relationship was observed between natural convection velocity and temperature difference.     

Using perforated ventilation ducts to enhance the cooling effect of crushed-rock interlayer on embankments in permafrost regions

A previous laboratory test carried out by the authors proved that the addition of ventilation ducts can efficiently enhance the cooling effect of crushed-rock interlayer. The mechanism revealed by the laboratory test was that, the ventilation ducts intensified natural convection and thus enhanced cooling effect of the crushed-rock interlayer by decreasing its upper boundary temperature. In this study, to further enhance the cooling effect of the crushed-rock interlayer, the ventilation ducts were perforated and then positioned at the upper boundary of the crushed-rock interlayer. Two crushed-rock interlayer embankments with perforated and imperforated (ordinary) ventilation ducts were tested under the same test conditions. The analysis of the temperature characteristics of the two test crushed-rock interlayer embankments with perforated and imperforated ventilation ducts showed that the crushed-rock interlayer embankment performed a more efficient cooling effect when the ventilation ducts were perforated. The effect was straightforward: the addition of the perforation on the ventilation duct wall let the air that was flowing through ventilation ducts partially penetrated into the crushed-rock interlayer. The result was that, during negative air temperature period, the upper boundary temperature of crushed-rock interlayer was decreased to a great extent, and consequently natural convection in the crushed-rock interlayer was intensified. The cooling effect during negative air temperature was efficient enough to restrict the heat injected into the embankment during positive air temperature period. On the whole, the crushed-rock interlayer embankment with perforated ventilation ducts has a good cooling effect to the underlying permafrost. Based on these, the new type of embankment is recommended in the construction of large-width highways in permafrost regions in the future.     

Low temperature exothermic effects on cooling of homoionic clays

Results of differential scanning calorimetry (DSC) experiments on homoionic montmorillonites (Ca²⁺, Mg²⁺, Na⁺, K⁺) and Na-kaolinite are reported. The low temperature exothermic peaks were observed on cooling down to − 90 °C after the initial peak corresponding to the breakdown of supercooling of water in macro- and mezopores. In some experiments, the samples were then warmed to − 10 °C or − 5 °C and cooled again to − 90 °C. According to expectations, the non-equilibrium exothermic peaks were absent in this case, being replaced by a wide peak analogical to that obtained on warming. However, the low temperature exothermic peaks were still observed, but their fields were characteristically cut, proportionally to the extent of the previous warming. The stochastic deconvolution applied to the endothermic peaks obtained on warming allowed to compare the thermal effects corresponding to the cooling and warming. The results gave evidence that the portion of water, solidification of which can be attributed to the low temperature exothermic peaks, on warming melts in a wide temperature range and a separated melting point does not exist.     

Impacts of diurnal temperature cycles on the geothermal regime on Qinghai-Tibet Plateau

This study investigates whether the diurnal temperature cycle affects the geothermal regime on the Qinghai-Tibet Plateau. To separately characterize this effect, the impact of climatic warming on the ground's thermal regime is eliminated by setting the global warming rate to 0 °C/year. The diurnal temperature cycle at the natural ground surface is denoted as sinusoidal functions with amplitudes of 0, 5, 8, and 12 °C, respectively. A one-dimensional heat conduction model was utilized to compute the geo-temperature under the natural ground surface, eliminating the effect of geometric boundaries, such as the roadway's embankment, on the geothermal regime. The results show that the diurnal temperature cycle does affect the geothermal regime as (1) under the same mean annual ground temperature, the higher diurnal temperature fluctuation amplitude (DTFA) on the ground surface, the thinner the active layer; (2) the higher the DTFA, the colder the underlying soil. An analysis of the heat flow at the ground surface showed that the diurnal temperature cycle resulted in a net negative heat balance at the earth's surface. This heat loss induced by the diurnal temperature cycle cools the underlying soil. The results and analysis suggest that, currently, the documented numerical model which ignores the diurnal temperature cycle overestimates the warming of the underlying soil. This overestimation, if the DTFA at ground surface is 12 °C, would be up to 0.4 °C. Considering that pavement surface usually undergoes high diurnal temperature cycles, the impact of the DTFA on pavement subgrade's frost conditions and on the pavement deformation is simply discussed.     

Compression temperature and binder ratio on a process for fabrication of open-celled porous Ti

This study was performed to investigate the fabrication of open-celled porous Ti by space holder using spherical polymer balls, and to evaluate the effect of temperature and binder ratio in the compression process. In compression condition of 80 °C, the open cellular structure consisted of continuously connected Ti struts with pore fraction above 85% and with the pores distributed homogeneously with nominal diameters between 200 μm and 400 μm. The large stress of 700 MPa applied to the acryl balls, containing the Ti feedstock, were not crushed, because the uniaxal stress applied to the acryl balls was transferred into the pseudo-hydrostatic stress state. A compression temperature of 90 °C caused the agglomeration of Ti feedstock and penetration of Ti powders into the inner part of acryl balls by softening. The thinner struts were gradually developed with increase of binder ratio due to increase of deformation.     

Development of double-stage ADR for future space missions

We report a development of a portable dewar with a double-stage ADR in it, and its cooling test results. The purpose of this system is to establish a cooling cycle of double-stage adiabatic demagnetization from 4.2 K to 50 mK, which is strongly desired for future space science missions. In our test dewar, two units of ADR are installed in parallel at the bottom of a liquid He tank. We used 600 g of GGG (Gadolinium Gallium Garnet) for the higher temperature stage (4 Tesla) and ∼90 g of CPA (Chromic Potassium Alum) for the lower temperature stage (3 Tesla). A passive gas-gap heat switch (PGGHS) is used between these two stages, while a mechanical heat switch between the He tank and the GGG stage. Using this system, 50 mK was achieved, and various kinds of cooling cycles with different operating temperatures and different sequences of magnetization were tested. We also evaluated the performance of the PGGHS, and interference of the magnetic field with each other during a stable temperature control.     

湖北就业大厦空调通风设计

分别从设计参数、空调负荷、风系统、冷冻水系统、通风与防排烟系统、冷热源等方面介绍湖北就业大厦空调通风设计，并结合工程实际情况，对今后此类设计提出了建议和看法。     

Temperature conditions of rock excavation

Heat exchange is considered between ventilating air and mining rocks in the case of variable air temperature at the rock excavation entrance. Formulas are given for the temperature of the ventilating air according to the extent of exploitation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 2, pp. 339–346, August, 1976.     

The thermal effect of differential solar exposure on embankments along the Qinghai-Tibet Railway

The difference in solar radiation produces a predictable thermal effect on the sunny and shaded slopes of embankments constructed in permafrost regions of the Qinghai-Tibet Highway and Railway, which results in differences in soil temperatures and the permafrost table under the shoulder. From the period 2005 to 2008, a systemic network of 42 sites was established along the Qinghai-Tibet Railway to monitor permafrost conditions and embankment performance. Soil temperatures up to 20 m in depth under the embankment were continuously measured hourly. In this article, we investigate daily mean soil temperatures under embankments for 25 observed sites and the temperature difference under the shoulder for both the sunny and shaded slopes of the embankments. We found significant differences in the thermal effect from the sunny and shaded slopes of the embankments along the Qinghai-Tibet Railway. On the sunny slope of the embankment the cooling process of soils under the shoulder is shorter and the thawing process is longer by 15-30 days than on the shaded slope. The multiyear average temperatures under the shoulder for the sunny slope are higher—0.23-1.58 °C with an average of 0.86 °C—than those for the shaded slope. The temperature differences in winter (DJF) are much larger than those in summer (JJA). The multiyear mean permafrost table under the shoulder for the sunny slope of the embankment is larger than for the shaded slope, ranging from 0.1 to 3 m, with an average of 1.13 m. However, engineering measures can effectively reduce the thermal effect between the sunny and shaded slopes of embankments, resulting in a decreasing temperature difference that ranges from 0.46 to 0.71 °C, with an average of 0.58 °C.     

Ablation behavior and mechanism of 3D C/ZrC composite in oxyacetylene torch environment

Ablation property of three dimensional carbon fiber reinforced zirconium carbide composite (3D C/ZrC composite) was determined using oxyacetylene torch test with a heat flux of 4187 kW/m² and flame temperature of over 3000 °C. C/ZrC composite exhibited an excellent configurational stability with a surface temperature of over 2000 °C during 60-300 s period, while 3D C/SiC composite was perforated at 55 s. After ablation for 300 s, the composite showed a mass loss rate of 0.006 g/s and a linear recession rate of 0.004 mm/s. The formation of zirconia melt on the surface of the C/ZrC composite contributed mainly the ablation property improvement. The C/ZrC composite after ablation showed four different layers due to the temperature and pressure gradients: the melting layer, the loose tree-coral-like ZrO₂ layer, the undersurface oxidation layer, and the composite layer.     

直接蒸发冷却空调在我国非干燥地区应用分析--大空间厂房、高温车间的通风降温应用

介绍了蒸发冷却空调在非干燥地区的应用分析。以东莞市为例,直接蒸发冷却空调被用于大空间厂房、高温车间的通风和降温,虽然处理后的空气湿度高达80％。作者讨论了空气湿度对温差的影响,并分析了蒸发冷却空调的通风降温效果。     

Cathodoluminescence of TiO2 nanotubes prepared by low-temperature anodization of Ti foils

We show that anodization of Ti sheets in an ethylene glycol and HF containing electrolyte at temperatures under 0 °C results in the formation of a self-arranged ordered porous structure at the top surface of the sample. This perforated surface structure initiates the growth of an ordered array of titania nanotubes. The inner diameter of nanotubes can be modified in a controlled fashion in the range from 10 nm to more than 250 nm through the change of the electrolyte temperature from −20 °C to + 50 °C. The spectral distribution of cathodoluminescence from a cluster of nanotubes clearly demonstrates the formation of resonator modes which are separated from each other by around 200 meV.     

A very light and thin liquid hydrogen/deuterium heat pipe target for COSY experiments

A liquid hydrogen/deuterium heat pipe (HP) target is used at the COSY external experiments TOF, GEM and MOMO. The target liquid is produced at a cooled condenser and guided through a central tube assisted by gravitation into the target cell. An aluminum condenser is used instead of copper, which requires less material, improves conductivities and provides shorter cooling down time. Residual condenser temperature fluctuations in the order of ≈0.4 K are reduced by using thermal resistances between the cooling machine and the condenser of the heat pipe combined with a controlled heating power. A new design with only a 7-mm-diameter HP has been developed. The diameter of the condenser part remains at 16 mm to provide enough condensation area. The small amount of material ensures short cooling down times. A cold gas deuterium HP target has been designed and developed which allows protons with energy ?1 MeV to be measured. A 7-mm-diameter HP is used to fill a cooling jacket around the D₂ gas cell with LH₂. The D₂ gas is stabilized at 200 mbar to allow for thin windows. Its density is increased by factor 15 compared to room temperature.     

Cooling mechanism of a solar assisted air conditioner: An investigation based on pressure–enthalpy chart

This paper reports a theoretical study of a conventional vapor compression air conditioner combined with a solar energy source. This system comprises two parts: the cooling mechanism and the solar heat source to operate it. Only the cooling machine part will be considered here, in which the refrigerant temperature leaving the immersed coil inside the storage tank can be calculated directly from the pressure–enthalpy diagram of the operating refrigerant. The investigation has been made using a new low global warming potential refrigerant that belongs to HFO family as an alternative to two high global warming potential refrigerants that belong to HFC family. These are R-1234ze(E) as an alternative to R-134a and R-410A. Comparisons between the classical vapor compression air conditioner and the solar assisted air conditioner and also between the selected refrigerants are investigated. The effects of the refrigerant temperature leaving the storage tank on the main performance parameters such as the coefficient of performance, the gain based on compression work, and the required condenser surface area are discussed.     

In-situ test study on the cooling effect of two-phase closed thermosyphon in marshy permafrost regions along the Chaidaer-Muli Railway, Qinghai Province, China

More than half of the recently built 142-km long Chaidaer-Muli Railway (CMR) in northern Qinghai Province, China travels across warm (≥−1 °C), ice-rich permafrost in wetlands on the southern flank of the Qilian Mountains. In comparison with the Qinghai-Tibet Railway from Golmud to Lhasa, the CMR traverses mostly across wetlands underlain by more ice-rich permafrost. Warm and ice-rich permafrost is sensitive to human activities and environmental changes, which can result in changes in the active layer thickness and permafrost temperatures, inducing instability and failure of infrastructures in permafrost regions. Thermosyphons were adopted in a quarter of the whole CMR route. For studying the cooling effect of the thermosyphon technique, two monitoring sites with different mean annual ground temperatures were installed since 2007. According to analysis of the ground temperature monitoring results from 2007 to 2010, the thermosyphon technique cooled the underlying permafrost and raised the permafrost table. The CMR has been put in operation since February 2010. The deformation monitoring data from 2008 to 2010 showed that the maximum accumulated settlement was 0.08 m and the minimum was 0.01 m. The settlements mainly happened in the initial months after the embankment construction was finished. In-situ monitoring results indicate that the thermosyphon technique has effect on cooling down the underlying permafrost and keeping the thermal stability of embankment in the unstable, marshy and ice-rich cold regions.     

Investigation of the effects of three key parameters on the heat transfer capability of a CLHP

A cryogenic loop heat pipe (CLHP) has been developed for future aerospace applications at the TIPC (Technical Institute of Physics and Chemistry). The device has been tested in different situations with constant heat sink temperature of about 78 K. The effects of the reservoir volume and the pore size of the primary wick on the performance of CLHP were investigated. With a wick pore size of 2 μm, the CLHP can transfer a heat load of 26 W under horizontal orientation no matter what size of the reservoir volume being used. On the contrary, when the pore size was large (10 μm), the heat transfer capability of the CLHP can be up to 26 W only when a smaller reservoir (60 cc) was used, and its ability to operate against gravity was greatly weakened. Moreover, when the working fluid was oxygen instead of nitrogen, the heat transfer capability can be up to 50 W under horizontal orientation with the other experimental conditions remaining the same.     

Porous alumina/zirconia layered composites with unidirectional pore channels processed using a tertiary-butyl alcohol-based freeze casting

Symmetric three-layer porous alumina/zirconia composites with controlled “designer” pore structure have been prepared by a tertiary-butyl alcohol-based freeze casting and sintering at 1400–1500 °C in air. Unidirectional aligned macropore channels were developed over a long range by controlling the solidification direction of tertiary-butyl alcohol solvent; in this case, they were surrounded by more dense structured walls. In layered composite, the bottom layer consisted of small sized pore channels (∼11 μm in diameter) compared with the middle and the top layer, due to the comparatively rapid velocity of the TBA crystal growth during solidification. The compressive strength (63–376 MPa) of the sintered porous layered composite remarkably increased as the porosity decreased (64–32%).