Ultra-low Temperature Freezer Research Articles

Experimental study on Joule-Thomson refrigeration system with R1150/R290/R601a for ultra-low temperature medical freezer

Since the global outbreak of the COVID-19, the requirement for ultra-low temperature medical freezers has increased rapidly. Joule-Thomson refrigeration systems, known for their simple structure and low cost, are an excellent choice for ultra-low temperature medical freezers. To further improve the performance of Joule-Thomson system for large-capacity ultra-low temperature freezer, this study conducted a series of experiments on the performance of a ternary hydrocarbon mixture R1150/R290/R601a. The impacts of refrigerant charge, capillary tube size, compressor speed, and environmental temperature on the steady-state and dynamic performance were investigated in detail. The results showed that under a fixed system configuration and charge, the freezer can achieve an ultra-low temperature of −82.2 °C and a COP of 0.256 at an environmental temperature of 25 °C, while maintaining a low compressor pressure ratio not exceeding 12. Furthermore, the matching relationship between capillary size and charge was emphatically studied, and it was found that the optimal refrigerant charge increased as the inside diameter of the capillary tube decreased or its length increased. The inside diameter had a more significant effect on system performance than the length. The suitable charge was 225–275 g for capillary tubes with an inside diameter of 1.4 mm, and increased to 400–450 g for an inside diameter of 0.7 mm. In addition, the experiments with various compressor speeds indicated that, before the cabinet temperature dropped to −40 °C, the variation of compressor speed had little effect on the pull-down rate. However, the higher the compressor speed, the lower the cabinet temperature that can be achieved. When the speed was 3500 rpm, the system achieved its lowest daily energy consumption, which was 8.42 kW·h/24 h.

Labelled dataset for Ultra-Low Temperature Freezer to aid dynamic modelling & fault detection and diagnostics

Ultra-low temperature (ULT) freezers are used to store perishable biological contents and are among the most energy-intensive equipment in laboratory buildings, biobanks, and similar settings. To ensure reliable and efficient operation, it is essential to implement data-driven fault detection and diagnostic algorithms, along with energy optimization techniques. This study presents labelled and long-term ULT-freezer performance dataset, the first of its kind, derived from 53 ULT freezers featuring two different control strategies. The dataset comprises high-resolution historical operation data spanning up to 10 years. More than 10 attributes are recorded from the freezing chamber and critical locations in the refrigeration systems. The dataset is labelled with regular events, such as door openings, as well as fault events obtained from 46 service reports. A scalable data pipeline, consisting of extraction, transformation, and loading processes, is developed to convert the raw data into a format ready for analysis. The dataset can be utilized to support the development of data-driven models and algorithms that advance the intelligent digital operation of ULT freezers.

PSVII-17 Differential Freeze/Thaw Rates Affect Water-Holding Capacity and Lipid Oxidation in Beef Rib Primal Cuts

Abstract Fresh meat is vulnerable to microbial contamination and loss of quality. Hence, freezing is used to mitigate these issues during transport and storage. However, freezing may negatively impact the same quality characteristics it was meant to preserve, resulting in products that are dissatisfying to the consumer. During the freezing process of meat, water forms ice crystals of various shapes and sizes. The degree of ice crystal growth, mainly due to the freezing rate, has been shown to affect several meat quality characteristics, including tenderness, juiciness, and color. Previous research has primarily evaluated the effect of freezing/thawing on the quality of beef retail cuts. To the best of our knowledge, however, minimal research has been devoted to examining the impact of freezing/thawing on the quality of beef primal and sub-primal cuts. Therefore, this study aimed to gain deeper insight into the histological, ultrastructural, and physiochemical changes occurring in whole beef ribs in response to different freezing/thawing treatments. To achieve our objective, we purchased 32 choice beef rib primals from a local harvest facility 24 h postmortem. Ribs were vacuum packaged and randomly divided into four groups (8 ribs/group). The first group was frozen in a −20 °C freezer (slow freezing), stored in the same freezer for 12 weeks, and thawed at 4 °C for 24 h (slow thawing). The second group was frozen in an ultralow temperature freezer (−80 °C; fast freezing), stored in the same freezer for 12 weeks, and thawed at 4 °C for 48 h. The third and fourth groups were frozen and stored in the same manner as groups one and two, respectively, but were thawed in a water bath (10 °C) for 8 h (fast thawing). Two 2.5-cm-steaks from the middle and each end were collected to represent the entire rib. One steak from each of the three areas was used for color, cook loss, and tenderness evaluation, while the other three supplied tissue for drip loss and lipid oxidation analysis. Data were analyzed using the mixed model of SAS with P ≤ 0.05 considered significant. No differences were observed in color or tenderness between the treatments (P > 0.05). However, slow thawing increased drip loss, regardless of the freezing rate (P < 0.05). Greater cook loss was observed in the fast frozen-slow thawed samples compared with fast frozen-fast thawed samples (P < 0.05). The slow frozen-fast thawed steaks had greater lipid oxidation than the slow frozen-slow thawed treatment (P < 0.05). In general, our data show that subjecting whole beef rib sections to fast freezing may reduce water loss at the expense of increased lipid oxidation. This demonstrates that additional research is needed to further optimize beef primal cut storage.

Experimental study on a -86°C cascade refrigeration unit with environmental-friendly refrigerants R290-R170.

Ultralow-temperature refrigeration faces significant issues linked to the security of the cold chain for the production, storage, transportation, and distribution of COVID-19 vaccines. The use of environmentally friendly refrigerants in cascade refrigeration systems (CRS) to provide low-temperature range is motivated by the high demand for ultralow-temperature refrigeration units. In the current study, a CRS is built to generate a low temperature of -86°C for the storage of COVID-19 vaccines. In the CRS, the natural refrigerant combination R290-R170 is used as high-temperature and low-temperature fluids. The pull-down performance of the -86°C freezer is explored experimentally, and the stable operating performance is determined at two different dry bulb and wet bulb temperatures. Various status monitors are set up to analyze the CRS's operation features, and several temperature monitors are put in the freezer to analyze temperature variations. The power consumption of the CRS is examinedand evaluated. Finally, several key findings are summarized. The current work is the first to involve experimental measurements on -86°C temperature generated by a CRS, which can substantially enhance experiment data in ultralow-temperature refrigeration and contribute to a more in-depth understanding of the operation performance of a -86°C ultralow-temperature freezer.

Linc01614 Regulates the Proliferation, Apoptosis, and Chemotherapy Resistance in Esophageal Squamous Cell Carcinoma by Targeting Mir-4775.

Esophageal squamous cell carcinoma (ESCC), a widely known esophageal disease, severely affects people's health. Numerous investigations demonstrated that long non-coding RNAs (lncRNAs) performed key jobs inside a wide scope of organic cycles and stand out in malignant growth. Our study planned to investigate the roles and mechanisms of linc01614 in ESCC. A Total of 60 ESCC tissue samples including 30 patients with cisplatin sensitivity and 30 patients with cisplatin resistance, who received DDP-based treatment, were obtained from Zhuhai People's Hospital, Zhuhai City during 2021. These tissues were frozen and saved in a -80 °C ultra-low temperature freezer. We performed CCK-8, clone formation, flow cytometry assays to determine the effect of linc01614 on ESCC progression, and explored the specific mechanism of linc01614 in ESCC cell proliferation, apoptosis, and chemotherapy resistance. linc01614 expression was upregulated in ESCC tissues and cells compared with non-tumor tissues and human normal esophageal epithelial cells (Het-1A). Knockdown of linc01614 repressed cell expansion, chemotherapy opposition, and advanced cell apoptosis in ESCC. Besides, linc01614 regulated the expression of miR-4775 as a competitive endogenous RNA (ceRNA). The linc01614/miR-4775 axis played an important role in ESCC progression and drug resistance, revealing that linc01614 is a promising target in ESCC treatment.

A Situational Based Reliability Indices Estimation of ULT Freezer using Preventive Maintenance under Fuzzy Environment

Reliability of high demand machines is quite necessary and it can be maintained through proper and timely maintenance, Ultra-low temperature (ULT) freezer is one of those kinds of machines which are in high demand during covid-19 pandemic for the storage of vaccine. The rapid production of vaccines for the prevention of coronavirus disease 2019 (COVID-19) is a worldwide requirement. Now the next challenge is to store the vaccine in a ULT freezer. It’s become really a big problem to store the vaccine which creates the demand of ULT freezer. The present paper investigates a situational based performance of the ULT freezer with the aim to predict the impact of different component failures as well as human errors on the final performance of the same. For the study, it is not possible to extract the parameters (failure rate and repair time) of the components that never failed before. Thus, to overcome this difficulty, here authors use the possibility theory. Authors present the available data in Right triangular fuzzy number with some tolerance as suggested by system analyst. The lambda-tau methodology and arithmetic operations on right triangular generalized fuzzy numbers (RTrFN) are used to find the various performance parameters namely MTTF, MTTR, MTBF, reliability, availability, maintainability (RAM) and ENOF, under fuzzy environment. The proposed model has been studied using possibility theory under working conditions, preventive maintenance as well as under the rest of conditions. This study reveals the most and least critical component of the ULT freezer which helps maintenance department to plan the maintenance strategy accordingly.

Operation performance of an ultralow-temperature cascade refrigeration freezer with environmentally friendly refrigerants R290-R170.

In the present study, the operation performance of an ultralow-temperature cascade refrigeration freezer is experimentally researched. The natural refrigerants R290-R170 are adopted as high-temperature and low-temperature fluids. The experimental test is conducted in a type laboratory with a dry bulb temperature of 32.0°C and awet bulb temperature of 26.5°C. Different state monitors are set to display the system operation performance, and several temperature monitors are arranged to study the pull-down performance and temperature variations in the freezer. Based on the established experimental rig, three freezing temperatures, including - 40°C, - 80°C, and - 86°C, are measured and compared. The results show that it takes about 240min for the freezer to be pulled down to - 80°C. During the pull-down period, different monitors all experience rapid temperature drop, and the power consumption reduces from 1461.4W to 997.5W. Once the target temperature is achieved, the freezer comes into periodic start-stop operation. With the set temperature ranging from -40°C to -86°C, the inlet temperature of two compressors gradually decreases, while the discharge temperature has an increase trend. The cooling effect of the pre-cooled condenser reduces with the freezing temperature, while the long connection pipe has opposite variation profile. Moreover, it is observed that for different freezing temperatures, most of the space in the freezer can be cooled down to the target temperature. It is confirmed that the present ultralow-temperature freezer can be used for the storage and transportation of COVID-19 vaccines. However, it is also found that the cascade refrigeration system is not suitable for high freezing temperature, due to high power consumption and extensive start-stop switch of refrigeration system.

Experimental test on the performance of a −80 °C cascade refrigeration unit using refrigerants R290-R170 for COVID-19 vaccines storage

With the urgent demand for ultralow-temperature refrigerators worldwide, the operation reliability and stability of the refrigeration system becomes greatly crucial. In this study, a -80 oC ultralow-temperature cascade refrigeration system (CRS) is developed. From aspects of global warming potential (GWP) and ozone depletion potential (ODP), the environmentally friendly refrigerants R290 and R170 are utilized in the high-temperature cycle and low-temperature cycle of CRS. The experimental measurement is conducted in a Type-laboratory with a dry bulb temperature of 25.0 °C and a wet bulb temperature of 20.2 °C. The pull-down and stable operation performance of the CRS freezer are experimentally investigated. Both the inlet and outlet temperature and pressure of two compressors are monitored, and the operation characteristic of the CRS is analyzed. With some temperature test points arranged in the freezer, the temperature drop and temperature fluctuation variation of air are assessed. The operation power consumption of the CRS is also measured during the whole process. It shows that the −80 °C temperature can be generated and realized by the developed ultralow-temperature freezer.

Thermodynamic performance optimization and analysis of an auto-cascade refrigeration cycle with vapor injection for ultra-low temperature freezer

To improve the performance of the conventional auto-cascade refrigeration cycle, a modified auto-cascade refrigeration cycle with vapor injection is proposed for the application of a -80 ℃ freezer in this study. The particle swarm optimization algorithm is used to obtain the cycle performance at different operation conditions. The mixture concentration, compression ratio and condenser outlet quality are optimized globally. The binary mixture selection is carried out among the R1150/R290, R150/R600 and R1150/R600a. The results indicate that R1150/R600 is proposed as the alternative refrigerant. The performance comparisons between conventional and vapor injection auto-cascade refrigeration cycles show that the vapor injection technique efficiently improves system performance, especially at high condensation and low evaporation temperatures. Compared with the conventional auto-cascade refrigeration cycle, the optimal COP in the modified auto-cascade refrigeration cycles show a 9.3∼53.8% improvement in COP and the maximum improvement in the volumetric refrigeration capacity reaches 58.2% at low evaporation temperature. The statistical results of the optimal concentration of the mixture R1150/R600 at the selected operating conditions show that 88% of the optimal R600 concentration in the VARC cycle is in the range of 0.657∼0.699. The optimal concentration of R600 in the CARC cycle varies in a wide range of 0.57∼0.75. The optimal intermediate pressure is 38.1∼13.4% lower than the geometric mean of discharge pressure and evaporation pressure. The exergetic analyses illustrate that the largest exergy destruction of the VARC cycle occurs in the recuperator-2 instead of the compressor in CARC, contributing to 22.6∼23.5% of the total exergy destruction.

Long-term cryopreservation of Lentinus crinitus strains by wheat grain technique

Lentinus crinitus (Basidiomycota: Polyporales) is a saprophytic fungus with biotechnological importance described more than 20 years ago. However, there are few studies on the long-term preservation of this basidiomycete. Cryopreservation is a long-term storage technique that reduces the metabolic activity of microorganisms, but its success depends on the adjustment of the freezing process, the cryoprotectants, and the protective substrates for each species. This study aimed to assess the mycelial viability and genetic stability of L. crinitus strains cryopreserved at −86 °C for two years by the wheat grain technique using different cryoprotectants and freezing methods. Three strains of L. crinitus (U9–1, U13–5, and U15–12) were subjected to different concentrations and types of cryoprotectants (dimethyl sulfoxide, glycerol, glucose, and sucrose), freezing methods such as immediate freezing from 25 to −86 °C and progressing freezing from 25 to −86 °C in a freezing container with isopropyl alcohol to control the rate of cell freezing at −1 °C min−1, protective substrate (wheat grain and 2% malt extract agar), and cryopreservation period (1, 6, 12, and 24 months). After thawing, samples were evaluated for mycelial viability, time to mycelial recovery, mycelial stability, and genetic stability of the fungus. All techniques achieved effective cryopreservation at −86 °C, mainly with the wheat grain technique. All cryoprotectants (3.5% glycerol, 1.5% dimethyl sulfoxide, 25% sucrose, and 5% glucose), freezing methods (immediate and gradual), and protective substrate (wheat grain and malt extract agar) were effective for cryopreservation of the three L.crinitus strains in an ultra-low temperature freezer for two years. Mycelial viability, mycelial stability, and genetic stability of the fungus were not affected after two-year cryopreservation, evidencing the robustness of the long-term cryopreservation technique and the fungus.

Influence of internal heat exchanger position on the performance of ejector-enhanced auto-cascade refrigeration cycle for the low-temperature freezer

This paper presents a thermodynamic investigation on the configuration optimization of the ejector-enhanced auto-cascade refrigeration cycles for −80 °C freezers. The performance comparisons based on the genetic algorithm are carried out among four different modified cycles with differently positioned IHX. The natural binary mixture R1150/R600a is used as the working fluid. The simulation results illustrate that adding IHX could improve the overall system performance, and adopting IHX at the evaporator outlet is more effective for performance enhancement than that at the condenser outlet. The most significant performance improvements are obtained in the optimized cycle, which simultaneously adopts the dual-IHX at the condenser and evaporator outlets. Compared to the cycle withnot IHX, the average COP and exergy efficiency improvements reach up to 55.2%, and the compressor displacement and system initial capital cost are reduced by 52.9% and 17.5%, respectively. The pressure lift ratio increases, and the entrainment ratio declines due to the application of the IHX at the condenser outlet. Theoretical results provide a guide for improving the ejector-enhanced ultra-low temperature freezer in the applications of the −80 °C freezing.

Strategies used to meet the challenges of mass COVID-19 vaccination by the pharmacy department in a large academic medical center.

DisclaimerIn an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.PurposeHighly effective coronavirus disease 2019 (COVID-19) vaccines have brought hope for ending the pandemic. Unprecedented mass vaccination started first among healthcare workers. The aim of this report is to describe key strategies undertaken by a large hospital pharmacy department to meet the challenges of preparing a large quantity of COVID-19 vaccine doses in a short period of time.SummaryMedStar Washington Hospital Center (MWHC) was in the first group of hospitals in Washington, DC, to receive Pfizer-BioNTech vaccine in December 2020. The pharmacy department faced challenges including stringent vaccine storage requirements, a need for specific equipment and workflow, limited funding, and staffing constraints. The pharmacy department’s senior leaders defined pharmacy responsibilities, budgeted for equipment, participated in vaccination center design, and instructed pharmacy informatics personnel. The vaccine coordinators were appointed to oversee all vaccination-related operations. An ultra–low temperature freezer was installed 2 weeks before arrival of the first shipment of vaccine. All pharmacy order entry tools and operating procedures were standardized, and staff training and schedules were finalized by December 15. The first dose of the vaccine was administered on December 16 at the vaccination center. Pharmacy staff members dispensed the vaccine doses and monitored patients. By January 6, 2021, MWHC had vaccinated 3,812 employees with their first vaccine dose, with an average of 228 doses administered daily.ConclusionKey strategies such as systemic coordination, early preparation, detailed planning, operating procedure development, and staff education and engagement proved successful in facilitating preparation of thousands of COVID-19 vaccine doses for hospital employees within a short period of time.

초저온 냉동고용 스터링 냉동기 개발

초저온 냉동고용 스터링 냉동기 개발

Freezing methods affect the characteristics of large yellow croaker (Pseudosciaena crocea): use of cryogenic freezing for long-term storage

Large yellow croaker (Pseudosciaena crocea) is the main coastal economic fish in China. After harvesting, the fish is rarely traded as the fresh product, but usually held in cold storage. Therefore, it is important to understand the quality changes occurring during preservation. In this study, freshly collected fishes were frozen by cryogenic (cabinet liquid nitrogen freezer at -40, -60 and -80 °C) and forced convection (ultra-low temperature freezer at -40 °C) freezing and stored at -18 °C for 6 months. Drip loss, relative moisture loss (RML), water holding capacity (WHC), color and texture of frozen fish were evaluated. The results showed that forced convection freezing had significantly higher drip loss and RML values compared to cryogenic freezing. WHC decreased dramatically irrespective of freezing methods employed. Cryogenic freezing at -60 and -80 °C had the highest yellowness values during storage; but the highest springiness, gumminess and shear force values were obtained only at -60 °C. We conclude that cryogenic freezing at -60 °C is appropriate for long-term storage of large yellow croaker.

Principal effective factors on the dynamic pull-down performance of a zeotropic mixture based ultra-low temperature freezer

Cascade technology with less than −80 ℃ has risen sharply with the development of the biomedical industry. Although appropriate refrigerant-couples and corresponding improving-approaches have been presented, dynamic parameters of operating stability and security rather than COP are more important to evaluate an ultra-low temperature freezer. Refrigerant-couple R404A/R508A with pentane as oil carrier in the low stage is employed to be working fluids in this study, and the main dynamic parameters during the pull-down process are clearly discussed experimentally, especially the laws of highest discharge temperatures in both subsystems. Results demonstrate that the highest discharge temperature is generally appeared in the first half of the cooling-process, which should be the key-point of the discharge temperature protection. Additionally, the operating stability and security would be highly strengthened with decreasing charging amount, increasing zeotropic component fraction, and declining heat collector opening, however, corresponding negative effects will be definitely caused to a great extent.

First report of basal rot of dragon fruit caused by Fusarium oxysporum in Bangladesh.

Dragon fruit (Hylocereus polyrhizus) is a high value newly introduced fruit crop in Bangladesh. It has drawn considerable public attention due to its appealing flesh color, sweet taste and fruit qualities. Recently, basal rot of dragon fruit plants was observed in several farmer's fields, nurseries and in the research field of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) where about 10-15% of plants were infected in each location. Initially, the symptoms appeared in the basal part near the soil as brown lesions which gradually extended to the upper stem and finally becoming soft and watery (Figure 1a). Infected plants were collected from Kapasia of Gazipur district (Latitude 24.266 and Longitude 90.633) to isolate the causal organism. Isolations were carried out following the procedure reported by Briste et al. (2019). Briefly, infected plant parts were surface sterilized in 2% NaOCl for 1 min followed by 70% ethanol for 5 min and rinsed 3 times with sterile double distilled water. A large piece of a surface sterilized plant was cut into small pieces (2 mm × 2 mm) from the margin of the necrotic lesion and placed on half strength potato dextrose agar (PDA) and incubated for 7 days at 25 °C. The BTFD1 and BTFD4 isolates were purified from single spores resulting in white colonies with a growth rate of 1cm/day on PDA (Figure 1b). Colonies produced single celled microconidia from unbranched, short monophialidic conidiophores and septate macroconidia as well as chlamydospores in PDA which is consistent with Fusarium oxysporum (Figure 1c). To confirm the identity of the isolates, the internal transcribed spacer (ITS1, 5.8S rRNA and ITS2) and translation elongation factor-1alpha (EF-1α) were amplified using primers ITS-1/ ITS-4 and EF1-728F/ EF1-986R, respectively (Surovy et al. 2018). The ITS sequences of the isolates BTFD1 and BTFD4 (GenBank accession # MN727096 and MN727095, respectively) showed 100% similarity with the sequence from F. oxysporum strain JJF2 (MN626452). Sequence identity for EF-1α (GenBank accession # MN752123 and MN752124, respectively) was 100% with the sequence from F. oxysporum strain CAV041_EO (MK783088). The isolates (BTFD1 and BTFD4) were identified as F. oxysporum based on the aligned sequences of ITS and EF-1α, molecular phylogenetic analyses by maximum likelihood tree (Figure 2a) and maximum parsimony tree methods (Figure 2b). The isolates were stored at 4°C on dried filter paper as well as in an ultra-low temperature freezer (-80°C) at IBGE, BSMRAU, Bangladesh and are available on request. To ensure pathogenicity, isolate BTFD1 was grown on PDA, incubated at 25°C for 7 days and 250 ml conidial suspension (with 1 × 105 conidia/ml) was prepared. Twelve,three-month-old healthy dragon fruit plants were inoculated. Pathogenicity tests were carried out in two sets using three replications in each set. In one set, only the basal part of the plants was dipped into the conidial suspension and in another set the whole plant was dipped into the conidial suspension for two hours. Sterile distilled water was also used in another set of plants as a control. The inoculated plants were placed on wet tissue in a plastic box (31cm × 24cm × 8cm) covered and incubated at 25°C. After 10 days, all inoculated plants in both sets developed rot symptoms similar to those observed in the field, while the control plants remained healthy (Figure 1d). The pathogen was successfully re-isolated from the inoculated symptomatic parts on half strength PDA medium and had morphology as characterized before, thus fulfilling Koch's postulates. This disease has been reported in Argentina and Malaysia (Wright et al. 2007; Hafifi et al. 2019). To the bet of our knowledge, this is the first report of Fusarium basal rot of dragon fruit in Bangladesh caused by F. oxysporum.

Experimental investigation on the pull-down performance of a -80°C ultra-low temperature freezer

Abstract This paper presents an experimental investigation on the pull-down performance of a -80°C ultra-low temperature freezer. Experiments were conducted in a two-stage cascade refrigeration system with an inner recuperative heat exchanger in low temperature cycle (LTC). In addition, the pull-down performances of the freezer were discussed on different startup temperatures ranging from -20°C to 24°C when the ambient temperature was fixed at 26°C. In this paper, the cooling process was divided into early start-up phase, rapid cooling phase and stable cooling phase, and it was found that thermal parameters changed obviously with the startup temperatures, especially in the rapid cooling phase. The experimental results showed that there were maximum discharge temperatures of LTC compressor during pull-down process, and the maximum values increased with the rise of startup temperatures. When the startup temperature was -20°C, the maximum discharge temperature of LTC compressor was 8.1% (11.6°C) lower than that when the startup temperature was 24°C. As two factors affecting the discharge temperature of LTC significantly, the superheating degree was the main influencing factor in rapid cooling phase, while the decrease of the evaporation and condensation pressures had a more significant effect in the stable cooling phase. Besides, the volumetric efficiency of high temperature cycle (HTC) compressor deteriorated more obviously during the pull-down process, and had higher potential for performance improvement compared with that of LTC.

Experimental research of low-temperature throttling refrigerator for cryoconservation of medical and biological objects

Results of experimental research of low-temperature multicomponent mixed-refrigerant throttling refrigerator are given. Appliance of refrigerator in new domestic-made ultralow-temperature freezer for cryoconservation and long-term storage of medical and biological objects at temperature minus 150°C is described. Within experimental research, test bench with development prototype of ultralow-temperature medical freezer is made. Experimental and theoretical studies are compared. Availability and amount of local composition shift is defined. Ways to improve simulation model and increase energy efficiency of cryostatting systems are determined.

Long-term follow-up of cryopreservation with glycerol of autologous bone flaps for cranioplasty after decompressive craniectomy.

Autologous bone flaps adequately preserved can be used successfully for repair of cranial bone defects with biological and economic advantages. However, the effect or advantages of cryopreservation of autologous bone flaps using cryoprotectant solutions have not been investigated. The aim of this study was to investigate the utility of autologous bone flaps frozen with glycerol in cranioplasty after decompressive craniectomy. We evaluated postoperative complications and clinical and aesthetic results in 40 consecutive patients who underwent delayed cranioplasty using autologous bone flaps frozen with glycerol following decompressive craniectomy between 2001 and 2010. Bone flaps removed at the time of external decompression were dipped in 20 % glycerol solution with a sterilized plastic vessel and stored at -84 °C in an ultra-low temperature freezer. The bone flaps were thawed in the vessel at room temperature for 12 h. The bone flaps were taken out of melting glycerol, replaced in their original positions, and fixed with silk sutures or titanium plates. Follow-up periods ranged from 35 to 3745 days (median, 558 days). Mild resorption of the bone flap occurred in one case. However, there were no cases with local infection and no cases requiring reoperation for complications during the follow-up period. Cryopreservation with glycerol is a simple and safe method for preservation of autologous bone grafts. The clinical and aesthetic results of delayed cranioplasty using autologous bone flaps frozen with glycerol solution were satisfactory.

Cryopreservation of embryogenic tissues from mature holm oak trees

The development of a vitrification method for cryopreservation of embryogenic lines from mature holm oak (Quercus ilex L.) trees is reported. Globular embryogenic clusters of three embryogenic lines grown on gelled medium, and embryogenic clumps of one line collected from liquid cultures, were used as samples. The effect of both high-sucrose preculture and dehydration by incubation in the PVS2 solution for 30–90min, on both survival and maintenance of the differentiation ability was evaluated in somatic embryo explants with and without immersion into liquid nitrogen. Growth recovery of the treated samples and ability to differentiate cotyledonary embryos largely depended on genotype. Overall, high growth recovery frequencies on gelled medium and increase of fresh weight in liquid medium were obtained in all the tested lines, also after freezing. However, the differentiation ability of the embryogenic lines was severely hampered following immersion into LN. Two of the embryogenic lines from gelled medium were able to recover the differentiation ability, one not. In the lines with reduced or no differentiation ability, variation in the microsatellite markers was observed when comparing samples taken prior to and after cryopreservation. The best results were achieved in the genotype Q8 in which 80% of explants grown on gelled medium differentiated into cotyledonary embryos following cryopreservation when they were precultured on medium with 0.3M sucrose and then incubated for 30min in the PVS2 solution. Explants of the same genotype from liquid medium were unable to recover the differentiation ability. A 4-weeks storage period both in liquid nitrogen and in an ultra-low temperature freezer at −80°C was also evaluated with four embryogenic lines from gelled medium using the best vitrification treatment. Growth recovery frequencies of all lines from the two storage systems were very high, but their differentiation ability was completely lost.