Search

To enhance the liquid nitrogen freezing efficiency and improve the quality of frozen prepared Monopterus albus, the effect of variable temperature liquid nitrogen quick-freezing combined with composite cryoprotectant treatment on the quality of prepared M. albus was investigated. Deep-fried cured M. albus was treated with a novel composite cryoprotectant consisting of 4% xylooligosaccharides, 4% sorbitol and 0.3% sodium bicarbonate before precooling followed by liquid nitrogen freezing at variable temperatures (from -80 to -50 ℃). Internal temperature, moisture content, thawing loss, centrifugal loss, moisture state, thiobarbituric reactive substances (TBARS) value, acid value (AV), fluorescent compound content, and total volatile basic nitrogen (TVB-N) content were measured, and ice crystal morphology and microstructure were observed. The results indicated significantly lower thawing loss (3.80%), centrifugal loss (11.6%) and free water percentage (24.4%) under variable temperature liquid nitrogen quick-freezing compared with freezer freezing (P 0.05). These findings suggested that pre-cooling followed by variable temperature liquid nitrogen quick-freezing combined with the novel composite cryoprotectant could enhance the quality of prepared M. albus during frozen storage, which will offer theoretical support for the development of highly efficient freezing and preservation technology for prepared M. albus products.

Abstract To further raise the gas extraction efficiency of the tight sandstone, the liquid nitrogen (LN2) freezing-thawing cycles method can be employed to improve the permeability of the low-permeability reservoirs. Permeability is generally regarded as a macroscopic description of the pore structure and usually has functional relationship to pore structure properties. The permeability of the rock is closely related to the change of microscopic pore structure. The permeability of rock depends on how the subzero temperatures changed the microscopic pore structure of rock, but it has not yet been confirmed obviously. In this study, the nuclear magnetic resonance (NMR) technique was adopted to investigate the pore structure evolution law and permeability of the tight sandstone with different LN2 freezing-thawing cycles. The results demonstrate that the LN2 freezing-thawing cycles promotes pore development and micro-fracture connection, and enhances the pore connectivity. The proportion of meso-pores, macro-pores and micro-fractures in the sandstone samples increases significantly, which provides a channel for the sandstone gas flow and extraction. Total porosity and effective porosity of the samples present a trend of rapid increase as the number of LN2 freezing-thawing cycles increasing, while the residual porosity decreases as the number of LN2 freezing-thawing cycles increasing. Coates model, SDR model (mean T2 model) and PP model were used to calculate and evaluate the permeability of the samples subjected to different LN2 freezing-thawing cycles. Furthermore, PP model can provide a better permeability estimate than the classical Coates and SDR model.

To investigate the impact of liquid nitrogen quick freezing on the quality of prepared chicken chops during frozen storage, this study compared −18 ℃ air freezing with −80 ℃ and −100 ℃ liquid nitrogen quick freezing. Then the frozen samples were stored in a −18 ℃ refrigerator for 0~180 days. The evaluation criteria included sensory scores, color, water holding capacity, texture characteristics, electronic nose analysis, pH, oxidation indicators, and total bacterial count. The results revealed a significant decrease in sensory scores for all groups with the extension of frozen time (P0.05), and the count remained below 5 lg (CFU/g) during frozen storage. Measurement of relevant oxidation indicators revealed that liquid nitrogen quick freezing effectively delayed protein and lipid oxidation. On the 180th day of frozen storage, the malondialdehyde (MDA) content in the −18 ℃ air freezing group was 21.95% and 37.43% higher than that in the −80 ℃ and −100 ℃ liquid nitrogen quick freezing groups, respectively. The total sulfhydryl group (-SH) content was reduced by 26.58% and 44.09% compared to the other two groups, respectively. In summary, the prepared chicken chops by all three freezing methods remained safe for consumption after being frozen at −18 ℃ for 180 days. But the quality characteristics of the prepared chicken chops treated with liquid nitrogen quick freezing were significantly improved during frozen storage.

In order to study the influence of liquid nitrogen leaching treatment on the mechanical properties and failure modes of coal samples under uniaxial and triaxial loading, uniaxial and triaxial tests were carried out on coal samples with different liquid nitrogen leaching time by triaxial test device. The results show that whether liquid nitrogen leaching treatment is carried out has no obvious influence on the evolution trend of mechanical properties of coal samples during uniaxial loading and triaxial loading; with the increase of axial strain, the axial stress increases slowly at first, then increases linearly, and decreases rapidly after reaching the limit of coal samples. The peak axial stress of coal samples under uniaxial loading at different time of liquid nitrogen leaching is 4.28 MPa, 7.21 MPa, 2.32 MPa and 2.34 MPa respectively, and the peak axial stress under triaxial loading is 44.31 MPa, 25.73 MPa, 37.74 MPa and 39.78 MPa respectively. With the increase of liquid nitrogen leaching time, the peak axial stress of coal samples under uniaxial loading shows a trend of increasing first and then decreasing, and the peak axial stress under triaxial loading shows a trend of decreasing first and then increasing. The liquid nitrogen leaching coal sample is partially broken more thoroughly after uniaxial loading and triaxial loading, but the longer the liquid nitrogen leaching time is, the more the number and volume of large coal generated after the coal sample is broken.

Phyllostachys praecox shoots were frozen using liquid nitrogen at –60, –90 or –120 ℃ to an internal temperature of –18 ℃, or frozen at –90 ℃ to an internal temperature of –6, –12 or –18 ℃, vacuum-packed and stored in a freezer at –18 ℃ for 24 weeks. In order to analyze the effect of liquid nitrogen freezing on physiological and biochemical characteristics of P. praecox shoots during frozen storage, L-phenylalanine ammonialyase (PAL) and peroxidase (POD) activities, total phenolic content, relative electrical conductivity, and water state were measured and ice crystal structure and cell morphology were observed. The results showed that with increasing freezing time, the PAL and POD activities, total phenolic content, and peak area of free water in all six groups decreased significantly (P 0.05). The PAL and POD activities and relative conductivity of P. praecox shoots frozen at –6 ℃ were higher than those frozen at –12 and –18 ℃, and the size of ice crystals was smaller and the degree of cell damage was greater in P. praecox shoots frozen at –6 ℃ than at –12 and –18 ℃. The difference between P. praecox shoots frozen at –12 and –18 ℃ was not significant (P > 0.05). Collectively, these findings indicated that the most suitable liquid nitrogen freezing conditions of P. praecox shoots are –90 and –12 ℃ for freezing and internal temperature, respectively.

In order to study the effect of liquid nitrogen injection cooling on spontaneous combustion of coal, coal samples from the second and third panel areas of Tingnan Coal Mine were selected for thermal and physical property experiments. First, the coal sample was pretreated by LFA457 laser flash analyzer, and then the thermophysical property parameters of the coal sample were measured in the range of 30-300 ℃, and the change law of the thermophysical property parameters of the coal sample with temperature was obtained after liquid nitrogen injection and cooling, and the factors affecting the thermophysical properties of the coal sample were compared and analyzed. The results show that the thermal diffusivity decreases with the increase of temperature, and the specific heat capacity and thermal conductivity increase with the increase of temperature; in the range of 30-200 ℃, the average change rate of thermal property parameters of coal samples after liquid nitrogen injection treatment is higher than that of raw coal samples, indicating that liquid nitrogen injection treatment will increase the sensitivity of coal samples to temperature; in addition, at the same temperature, the thermal physical property parameters of coal samples after liquid nitrogen injection treatment increased to different degrees compared with the original coal samples, and the average growth rate of thermal diffusion coefficient was the highest, indicating that the thermal diffusion ability of coal samples after liquid nitrogen injection treatment was enhanced during the oxidation and heating process.

Liquid nitrogen freezing has a certain promoting effect on improving the permeability of coal samples. In order to study the quantitative changes in the pore structure and permeability of coal samples after liquid nitrogen freezing, this paper carried out a three-dimensional reconstruction of the pore space structure of coal samples based on CT scanning experiments, and based on this, the porosity, connected pore volume, the equivalent pore radius, pore coordination number and permeability were studied based on the reconstruction model. The results show that the porosity of the coal samples in group B is 42.02% higher than that in group A after freezing with liquid nitrogen, the average value of the total connected pore volume, pore equivalent radius and coordination number of coal samples in group B are greater than those in group A, and they have increased by 16.5%, 2.95% and 14.8% respectively; the permeability in group B is 26.86% higher than that of group A, indicating that the pore connectivity and permeability of the coal samples in the liquid nitrogen freezing group have been significantly improved. [ABSTRACT FROM AUTHOR]

In this manuscript, we report on the synthesis of a polynitrogen material from a potassium azide precursor using nanosecond-pulsed spark discharge plasma in liquid nitrogen. The polynitrogen material was characterized using Raman and Fourier transform infrared (FTIR) spectroscopy and identified as K2N6, with planar N6 rings and K- ions that have P6/mmm symmetry. An analysis of the mechanism behind such a transformation shows the importance of direct plasma–chemical effects in polymerization, while the crystal structure changes are believed to be due to plasma-emitted radiation in the ultraviolet range. [ABSTRACT FROM AUTHOR]

Background: Actinic keratoses (AK) may progress into squamous cell carcinoma. Many combination therapies were used to improve the clearance rate. However, there are limited studies on the efficacy and safety of lesion-directed Liquid nitrogen cryotherapy combined with field-directed photodynamic therapy (PDT). Objective: This study is aimed to determine the efficacy and safety of Liquid nitrogen cryotherapy combined with PDT in Chinese patients with actinic keratosis. Methods: A total of 61 patients with AK were selected at the Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College between August 2018 and August 2023. They were randomly divided into PDT plus Liquid nitrogen cryotherapy group (LN-PDT) and control PDT group (C-PDT) with 30 patients and 31 patients, respectively. 27 patients in the LN-PDT group and 28 patients in the C-PDT group completed the clinical sessions. Efficacy, adverse effects, and cosmetic outcomes were recorded and compared between the two groups. Results: 3 months after the final treatment, the clearance rates for total AK lesions were 97.4 % (449/461) in the LN-PDT group and 93.4 % (456/488) in the C-PDT group (P < 0.05). For grade I AK lesions, the clearance rates were 99.2 % (234/237) for the LN-PDT group and 98.3 % (237/241) for the C-PDT group (P >0.05). For grade II lesions, the clearance rates were 97.5 % (156/160) for the LN-PDT group and 91.9 % (172/186) for the CPDT group (P < 0.05). For grade III lesions, the clearance rates of the LN-PDT and C-PDT groups were 87.5 % (58/64) and 78.7 % (47/61), respectively (P < 0.05). The two groups had no significant differences in pain, erythema, edema, hyperpigmentation and scarring. Cosmetic outcomes mainly were excellent or good in both groups with no significant difference. Conclusion: Liquid nitrogen cryotherapy combined with PDT showed higher efficacy on grade II and grade III AK lesions than PDT alone. The two groups have similar adverse effects and cosmetic outcomes.

The gold standard treatment for primary bone sarcomas has been surgical resection with wide margins. However, there is no consensus regarding an optimal method for limb salvage reconstruction. In 2005, a technique for recycling resected bone after intraoperative treatment with liquid nitrogen was described. This technique has been reported to have a spectrum of advantages; nonetheless, acceptance for routine use has been limited, primarily for fear of local recurrence. A systematic search of the literature using PubMed and Google Scholar was performed. Full-text articles published between 2008 and 2023 were included if the study presented sufficient information regarding patients with a diagnosis of a primary bone sarcoma of the limbs or pelvis who had undergone reconstruction with liquid nitrogen recycled autografts. Sixteen studies that included 286 patients met criteria for analyses. Local recurrence occurred in 25 patients (8.7 %) during the first 4 years following limb salvage reconstruction using recycled autografts for treatment of primary bone sarcomas, which compares favorably to the 15–30 % local recurrence rates reported for patients undergoing limb salvage reconstruction using artificial implants. Systematic synthesis of the current evidence regarding local recurrence rates following use of the liquid nitrogen recycled autograft technique for limb salvage reconstruction after bone sarcoma resection suggests a favorable comparison to other limb salvage reconstruction options. As such, this technique warrants further consideration as a viable option for indicated patients based on relative advantages regarding costs, availability, and biologic and surgical reconstruction benefits.

Due to the significant pollution caused by the current extraction technology for deep coalbed methane (CBM), we propose the application of anhydrous cracking technology—liquid nitrogen cyclic freeze–thaw technology—to crack deep coal seams to achieve the release and extraction of coal bed methane. The self-made system for applying confining pressure is employed to simulate the deep coal seam in coal sample testing. Subsequently, the effect of joint structure with different angles of coal surface and bedding on the liquid nitrogen cyclic freeze–thaw process is evaluated. The investigation study identifies the damage patterns of the coal sample against the sole factor and coupling effect of confining pressure and joint angle. The findings reveal a clear impact of the cyclic freeze–thaw of liquid nitrogen on the expansion of deep coal seams. The application of appropriate inclined joints, combined with confining pressure, significantly minimizes the crushing time of coal samples, with the maximum expansion rate occurring at joints with a bedding angle of 45°±5°. This study provides vital theoretical support for the green and efficient exploitation of deep CBM. Practical Applications: The results of this study indicate that the waterless hydraulic fracturing technology—liquid nitrogen cyclic freeze–thaw technology—is highly suitable for coalbed methane extraction in deep, low-permeability coal seams, leading to increased gas recovery. The deeper the coal seam, the more pronounced the effects. Moreover, this technology does not cause environmental pollution. It specifically targets the pores, fractures, and joint structures within the coal, preserving the overall framework of the coal and preventing tunnel instability, thereby enhancing coal mining safety. Additionally, under the influence of liquid nitrogen cyclic freeze–thaw, joints at different angles exhibit varying rates of expansion. Joints extending at a 45° angle to the coal's bedding planes show the most rapid expansion, indicating that this orientation stores the maximum amount of coalbed methane postliquid nitrogen freeze–thaw. This pattern can be scientifically applied in the actual engineering design of extraction wells. The experimental results can provide a theoretical basis for guiding the on-site application of deep coal seam permeability enhancement and green coalbed methane extraction technology, thereby reducing environmental pollution. [ABSTRACT FROM AUTHOR]

This study presents research on the stress distribution characteristics of rock in the bottomhole and the influence laws of various parameters under the impact of liquid nitrogen jet. A multi-field coupled numerical model considering transient flow field, conjugate heat transfer, and nonlinear solid deformation was established to investigate the damage-induced fracturing mechanism of rock under liquid nitrogen jet. The study compares the impact effects of liquid nitrogen jet and water jet on rock and analyzes the variations in the stress field under different parameters. Due to its extremely low temperature, the liquid nitrogen jet creates a strong thermal stress gradient in a short time, significantly increasing the maximum principal stress and Mises stress in the rock compared to a water jet. Solid parameters, particularly the confining pressure and elastic modulus of the rock, have a more significant impact on stress distribution, while fluid parameters such as outlet pressure and fluid temperature have a smaller and more volatile effect. An increase in confining pressure inhibits tensile failure in the rock, while a higher elastic modulus enhances both tensile and shear failure. The initial rock temperature significantly affects the stress distribution, with optimal tensile failure observed at intermediate temperatures. The liquid nitrogen jet achieves a higher maximum velocity and overflow velocity than the water jet, contributing to more effective rock fracturing. The results provide a theoretical basis for the optimization of liquid nitrogen jet drilling parameters, which can help improve drilling efficiency. [ABSTRACT FROM AUTHOR]

Abstract The methane in the coal seams of abandoned mines is a valuable natural gas resource. However, the ultra-low permeability of coal seams restricts the extraction of coalbed methane. The liquid nitrogen fracturing technology is a novel approach suitable for enhancing the permeability of coal seams in abandoned mines. The ultra-low temperature could potentially facilitate the growth and propagation of pores and fractures in coal seams. In this study, we observed inconsistent alterations in coal properties measured by multiple instruments at different scales, whether in dry or wet coal specimens. This suggests that the mechanisms influencing the pore structure due to LN2 treatment differ across various scales in dry and wet coal specimens. For dry specimens, heterogeneous thermal deformation and freezing shrinkage exhibited opposing effects during LN2 treatment. Thermal stress-induced micro-fractures might counteract the freezing contraction of micropores in coal matrices, preventing a significant decrease in coal macropores and fractures. In wet specimens, the effects of LN2 treatment on wet coal specimens were predominantly controlled by frost heaving. However, due to low water saturation, LN2 treatment had negligible effects on coal micropores, even in the presence of local frost heaving. In field applications, water migration from smaller to larger pores could further diminish the impact of LN2 treatment on micropores.

Osteosarcoma treatment with limb-sparing surgery using liquid nitrogen can be applied to canine patients experiencing diminished quality of life after leg amputation. In particular, forelimb amputation may affect gait more than hindlimb amputation. In this study, limb-sparing surgery using liquid nitrogen was applied to primary osteosarcomas arising in the proximal scapula of a Welsh Corgi, the proximal humerus of a Golden Retriever, and the distal radius of a Great Pyrenees, according to the protocol of Tsuchiya et al. In all cases, postoperative radiographic examination revealed bone union between the treated and matrix bones. All patients recovered their gait postoperatively. These results suggest that limb-sparing surgery using liquid nitrogentreated autologous bone is an effective option for patients with osteosarcoma. [ABSTRACT FROM AUTHOR]

Biomass, as a renewable energy source, features wide availability, multiple functions, and carbon neutralization. The high-value resource utilization of biomass is conducive to reducing reliance on high-carbon fossil energy, ensuring national energy security, and curbing environmental pollution, aligning with the needs of China's "dual carbon" national strategy. Pyrolysis, as the foundation of biomass thermochemical conversion, is one of the best technologies to achieve a high-value utilization of biomass energy. However, it has some core issues such as low bio-oil yield and poor quality. To overcome these problems, a cryogenic technology was innovatively applied to the field of biomass pyrolysis, and a new biomass oil production method of "cryogenic + fast pyrolysis" was proposed to increase the yield and quality of pyrolytic bio-oil. Taking two types of crop straw as experimental research objects, the rapid freezing pretreatment method with liquid nitrogen was adopted to study the evolution mechanism of the product distribution and composition of biomass pyrolysis under cryogenic pretreatment. The experiments show that compared with conventional pyrolysis, the increase in the bio-oil yield after cryogenic pretreatment of biomass pyrolysis can reach 14.16% to 23.73%, and the cryogenic pretreatment temperature has a positive correlation with the bio-oil yield, and the maximum bio-oil yield (22.3% to 26.3%) is reached at −90 ℃, exceeding the bio-oil yield of the aluminum method by 8.50% to 22.71%. The cryogenic pretreatment has a significant transformation effect on the composition of the bio-oil, and the content of benzene series (BTEX) and phenolic substances in the bio-oil composition increases significantly, with the maximum increase of 43.61% and 12.45%, respectively. The cryogenic pretreatment of liquid nitrogen inhibited the release of CO2 and CO in biomass pyrolysis gas, and the proportion of components decreased by 7.2%−29.7%. In addition, the inhibition of the release of CO2 and CO in the biomass pyrolysis gas and the increase of CH4 and H2 by cryogenic pretreatment increase by 0.2% to 14.7%. Moreover, the increase in C content and the decrease in O content in the solid product under cryogenic pretreatment are conducive to improving the combustibility of biochar and reducing its risk of spontaneous combustion.

In order to study the influence of low temperature liquid nitrogen immersion treatment on the pore structure and fractal characteristics of middle grade coal in Huainan Mining Area, coal samples were treated with different liquid nitrogen immersion time, and the pore structure of coal was measured by mercury injection and liquid nitrogen adsorption method. The fractal theory was combined to analyze the development law and scale characteristics of coal pores under different immersion time from multiple angles. The results show that with the increase of liquid nitrogen immersion time, the total pore volume of coal increases from 198.089×10−3 cm3/g to 371.553×10−3 cm3/g, while the total specific surface area decreases from 4.984 m2/g to 4.496 m2/g, and the effect is significant. The adsorption pore decreases, the seepage pore increases, and the pore connectivity of the adsorption pore increases to form a larger level of pore, which gradually changes to the seepage pore. There was a negative linear correlation between D1 (fractal dimension of seepage pore) and D2 (fractal dimension of adsorption pore) and the immersion time of liquid nitrogen, and the influence of liquid nitrogen immersion on D1 was more significant than that of D2. D1 and D2 decreased gradually with the increase of liquid nitrogen immersion time, indicating that the structural complexity of internal pores decreased with the increase of liquid nitrogen immersion time, and the porosity and permeability of coal increased. Dc (comprehensive fractal dimension) decreases with the increase of average pore diameter and total pore volume of coal body, and increases with the increase of total specific surface area. With the increase of liquid nitrogen immersion time, the comprehensive fractal dimension of coal body decreases, the adsorption capacity of coal body is weakened, and the seepage capacity is enhanced, which is helpful to improve the coal-bed methane extraction effect of low permeability coal seam in Huainan Mining Area.

To design the two-dimensional structural parameters of the core throttling component, i.e., the perforated plate for a liquid nitrogen (LN2) balanced flowmeter, this paper presented an orthogonal experiment scheme with three parameters, three factors, and three interactions, combined with the three-dimensional CFD numerical simulation. The constructed mixture multi-phase flow numerical model considers the complex cavitation effect of LN2 with a thermal effect. A DN40 balanced flowmeter and an LN2 flowrate test setup based on a standard flowmeter were constructed, and the measured flowrate data were used to evaluate the CFD model. Based on the optimized two-dimensional structure and the validated numerical model, the influence of the three-dimensional thickness of the perforated plate on the flow and pressure drop coefficient was investigated. It was found that there are two throttling forms as the thickness increases, resulting in two pressure-changing characteristics. The formation mechanism was explained by analyzing the turbulence intensity distribution. Finally, the final flow coefficient, pressure drop coefficient, and upper limit of measurement due to the cavitation were analyzed and obtained. The results provide a feasible parameter design method for the cryogenic balanced flow meters. [ABSTRACT FROM AUTHOR]

A clean and effective unconventional fossil fuel is coalbed methane (CBM). The development of CBM is essential to reducing the lack of oil and gas resources, preventing coal mine gas mishaps, and safeguarding the atmosphere. After the coal samples prepared in this study were frozen and thawed by liquid nitrogen, the change rules of coal surface and internal pores were investigated by metallurgical microscopy and carbon dioxide adsorption. The results showed that: 1) The values of specific surface area, characteristic adsorption energy, and total SF microvolume of coal samples increased after freeze-thawing of liquid nitrogen, but the CO2 adsorption experiments showed that the pore width decreased, which indicated that the mechanism of freeze-thawing fracture effect coal by liquid nitrogen mainly increased the number of micropores in coal. 2) The water saturation of coal samples rose with the degree of surface cracking, but when the water content reached a specific level, the rise in surface porosity of coal reduced with the water saturation. 3) The increase in the number of cycles has a greater effect on the extent of expansion of pores on the coal surface than on the expansion of pores in the coal. [ABSTRACT FROM AUTHOR]

Copyright of Revista de la Asociación Colombiana de Dermatología y Cirugía Dermatológica is the property of Asociacion Colombiana de Dermatologia y Cirugia Dermatologica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research has dealt with the simulation of liquid nitrogen cavitation inside a convergent nozzle. This is important in cryogenic industrial applications. So in this study, computational fluid dynamics methods have been used for simulating the cavitation phenomenon. The Two-phase model in this research has been a hybrid/mixed model. Also, k- ε turbulence model has been employed in realizable state. For meshing the nozzle geometry, Gambit software has been used, while for numerical simulation, Ansys Fluent software has been employed. For simulation of cavitation, Schnerr and Sauer cavitation model has been utilized. This research has also examined the effect of changing the nozzle outlet diameter and the impact of changing the pressure difference in the inlet and outlet of the nozzle on the cavitation. As a novelty and unlike what would have been expected based on the Bernoulli effect, the results obtained from the simulation showed that the increase/decrease in the nozzle's outlet diameter resulted in an enhanced/diminished extent of cavitation in the nozzle's outlet region. Also, the increase/decrease of the pressure difference in the input and output of the nozzle would lead to a higher/lower extent of cavitation. This research also found that the effect of altering the nozzle's outlet diameter on the extent of cavitation has been far higher than the effect of changing pressure difference in its inlet and outlet. The results also indicated that upon reduction of the nozzle's outlet diameter from the base state (1.02 mm) by 10, 20, 30, 40, and 50 %, the volume fraction of the vapor diminished by 22.23, 43.029, 60.66, 74.73, and 87.16 % respectively. Finally, with the increase in the nozzle's outlet diameter from the base state (1.02 mm) by 10, 20, 30, 40, and 50 %, the volume fraction of the vapor increased by 26.83, 55.27, 84.47, 117.12, and 149.31 % respectively.

The glass transition temperature Tg’ of ‘Northcountry’ blueberries was determined according to its state diagram. Using Tg’ as the freezing end point, blueberries were frozen at −80 ℃ using an ultra-low temperature freezer (RF−80 ℃), or at −80, −100 or −120 ℃ by direct immersion in liquid nitrogen (LN−80 ℃, LN−100 ℃, and LN−120 ℃, respectively). Freezing curves, juice loss, hardness, nutrient contents, cell membrane integrity, enzyme activities and microstructure were measured to investigate the effects of liquid nitrogen quick freezing combined with Tg’ on the quality characteristics of blueberries. The results showed that the Tg’ of blueberries was −52.55 ℃; compared with RF-80 ℃, the quality of liquid nitrogen frozen blueberries was better maintained. The freezing time of liquid nitrogen quick freezing was significantly shortened, the frozen fruit lost less juice after thawing, and the hardness was better maintained. The contents of soluble solids, titratable acid, ascorbic acid and anthocyanin were closer to those of fresh fruit, the relative conductivity and malondialdehyde (MDA) content were lower, the integrity of the cell membrane was less broken, the activities of peroxidase (POD) and polyphenol oxidase (PPO) were lower, and the microstructural compactness and integrity were stronger. The lower the ambient temperature of liquid nitrogen quick freezing, the better the freezing effect, and LN-120 ℃ minimized the quality deterioration of frozen blueberries. In conclusion, liquid nitrogen quick freezing significantly increased the freezing rate, and its combined with Tg’ helped to maintain good quality of frozen blueberries. The results of this study can provide a theoretical basis for the selection of blueberry freezing conditions.

The pore structure measurement in coal is commonly analyzed by mercury intrusion method, low temperature liquid nitrogen method and nuclear magnetic resonance method. Due to the different test methods, the results cannot be used uniformly, and the matrix compression effect in mercury intrusion method will cause large errors. In order to solve this problem, three high-rank coal samples from Jincheng and Changzhi Mining Areas in Qinshui Basin were taken as examples, and used mercury injection, low-temperature liquid nitrogen adsorption and nuclear magnetic resonance relaxation methods to test the pore structure of coal samples respectively. Through the compressibility correction of mercury injection data and splicing with low-temperature liquid nitrogen data at the connection aperture, the pore structure of coal was characterized by joint characterization, and the pore size distribution characteristics of coal were compared and analyzed in combination with nuclear magnetic resonance. The results show that the pore volume corrected by mercury intrusion data is closer to that of low temperature liquid nitrogen, and the deviation value is 22.40%-38.51%; the pore structure of different coal samples is analyzed by the joint pore method, and the position of the joint pore is between 75-89 nm; the results show that the pore volume of coal samples is 0.001 36-0.004 58 cm3/g, and the pore volume ratio of different pore sizes is transition pore>macropore>mesopore>micropore; compared with the single test method, the pore size distribution of the combined pore method and the nuclear magnetic resonance method is closer, but there are also differences. The average distribution ratios of micropores, transition pores, mesopores and macropores characterized by the combined pore method are 8.68%, 45.58%, 20.54% and 25.20%, respectively. The average distribution ratios of micropores, transition pores, mesopores and macropores characterized by the nuclear magnetic resonance method are 10.64%, 64.21%, 14.23% and 10.92%, respectively. The reason for the difference may be mainly related to the pore structure of coal changed by mercury intrusion method and low temperature liquid nitrogen method; through the comparison of NMR results, it is found that the combined corrected mercury injection and low temperature liquid nitrogen data can improve the accuracy of the pore size distribution test results in coal.

Liquid nitrogen is a widely utilized effective low-temperature cooling medium, also employed in the ATR-GG (Gas Generator cycle Air Turbo rocket) engine to cool high-temperature components. Due to the high-temperature work environment and the ease with which liquid nitrogen evaporates and boils, liquid nitrogen would experience a flash boiling process. In order to study the influence of flash boiling on spray characteristics, experiments and simulations were conducted with two types of hollow-cone nozzles and two types of solid-cone nozzles under subcooled water at normal temperature which is not affect by flash boiling and superheat liquid nitrogen inflow conditions. The research found that flashing already begins inside the nozzle, significantly reducing the discharge coefficient of the solid-cone nozzle. The nitrogen gas-liquid mixture fills the air core of the hollow-cone spray, resulting in a comparatively smaller impact on the discharge coefficient. The liquid nitrogen spray exhibit spray collapse, unable to achieve the spray cone angels as the water spray. The major reason is that during the flashing process, nitrogen vapor expansion enhances the axial velocity, reducing the spray cone angle. The study recommends using hollow-cone nozzles to mitigate the impact of flash boiling on the spray characteristics. [ABSTRACT FROM AUTHOR]

AbstractLiquid nitrogen spray cooling is crucial in cryogenic wind tunnels, while the understanding of its basic phenomenon, liquid nitrogen droplet impact, remains elusive. In this study, a numerical model of a liquid nitrogen droplet impacting on a liquid nitrogen film is established, and the impact mechanisms and influencing factors are analyzed. The dynamic behavior of the liquid nitrogen droplets reveals that as the dimensionless liquid film thickness varies from 0.1 to 0.8, the droplet impact behavior changes from deposition, and crown formation to splash with the Weber number increasing from 0 to 1000. The variation of the dimensionless crown diameter with the dimensionless time solely negatively correlated with liquid film thickness. The maximum dimensionless crown height increases approximately linearly with the Weber number. The splash characteristics indicate that the lower surface tension and viscosity of liquid nitrogen make the droplet easier to exhibit splash as compared with water droplets. As the dimensionless liquid film thickness increases from 0.1 to 0.4, the critical Weber number enabling splash to occur increases from 170 to 375, indicating that a thick liquid film suppresses the splash. [ABSTRACT FROM AUTHOR]