Cold Accumulator Research Articles

Human Immunodeficiency Virus Treatment Roll-Up: Challenges for Military Health Facilities in Cameroon in Sample Collection for Viral Load Testing and Early Infant Diagnosis

HIV viral load testing is an important element in the HIV elimination process, as it enables the efficacy of treatment to be assessed and, consequently, the patient’s viral suppression process to be monitored. A number of factors can affect the results of viral load tests, distorting patient outcomes and affecting follow-up. In developing countries, these challenges, linked to the technical platform, are much more likely to be encountered in the health facilities responsible for the pre-analytical phase, and can therefore compromise sample integrity. The aim of the study was to assess the challenges faced by Cameroon’s military health facilities in collecting samples for viral load and early infant diagnosis. A survey was carried out to 22 military health facilities to supervise sample collection activities using a specific grid. Data were recorded into the Google forms interface and followed by analysis using Microsoft office Excel 2013. 95% of facilities had a long working experience of over two (02) years for each type of handling. Only 27% of facilities used blood sampling protocols to the vacuum system in the HIV-VL test. During the survey, 18% of sites did not have a centrifuge and used decantation at room temperature. Additionally, 64% of health facilities did not fill in temperature control sheets properly, 23% jeopardize the cold chain due to insufficient cold accumulators or poorly maintained coolers. Only eight (08) health facilities did a HIV early infant diagnosis testing. The required technical platform was not present in all health facilities, and staff technical skills in charge of the pre-analytical stages were still not as high as expected. This is a call to strengthen the capacity of sample collection sites to achieve the WHO’s goal of eliminating HIV transmission by 2030.

A novel approach combining thermosiphon and phase change materials (PCM) for cold energy storage in cooling systems: A proof of concept

A novel approach combining thermal energy storage (TES) and a thermosiphon was investigated for cold storage. The use of TES units for cooling systems has been studied for many years, as they are well suited for short-term energy storage. A cold latent heat accumulator was designed to replace the function of any vapour compression cycle in the event of electrical failure without using any electrical device but rather the thermosiphon principle. A laboratory prototype of a thermosiphon combined with the cold accumulator was developed using a paraffin mixture as a phase change material (PCM). The accumulator was connected to the vapour compression system of a closed display cabinet. An experimental study was carried out by simulating 1.5 h compressor shutdowns with and without the accumulator. The thermosiphon loop effectively transferred 97 % of the stored energy to the display cabinet. The air and product temperatures in the cabinet, the behaviour of the compressor during restart, and the charging and discharging processes of the accumulator were analysed. The results showed that shutting down the compressor with the cold accumulator significantly reduces the increase of air and product temperatures compared to shutting down without the accumulator. The air temperature in the rear duct was maintained within the acceptable temperature range for 72 min with the accumulator, compared to 3 min without. A default in the design of the accumulator was observed during the charging phase, as some areas of the accumulator never reached 80 % of charge. This new approach extends demand-side management and renewable energies to all end users of vapour compression machines.

Optimisation of the Technological Parameters of the Ecological Milk Cooling Plant

The aim of this paper is to optimize the technological parameters of the ecological milk cooling plant with the application of natural cold, which ensures a significant increase in energy efficiency at collection points in the Republic of Moldova. The proposed plant captures the natural cold and stores it in the insulated cold accumulator without the use of freons, which is then used for cooling milk. In order to achieve the goal, the mathematical model of the intermediate refrigerant cooling process using renewable energy was developed in the paper. Based on the requirements imposed on the technological process as well as the developed mathematical model, it was determined that for cooling the intermediate refrigerant from the initial temperature of +140C to +40C, at the ambient temperature of +20C, 34.25 times more equivalent volume of air is required.

Cold accumulators using binary ice in air conditioning systems

Cold accumulators using binary ice in air conditioning systems

Оптимизации режимов работы судовой холодильной установки с аккумулятором искусственного холода

The ways of optimizing the operation of a refrigeration unit for fishing and refrigerated vessels with the additional inclusion of artificial cold storage devices are investigated. For this purpose, a new technology of cold storage has been developed on the basis of a refrigerating machine with direct contact between media and ice production. The refrigerant RC318 was taken as freon which does not form crystalline hydrates. Based on this, the optimization of the operation of a single-stage refrigeration machine was carried out using the Lagrange multiplier method for the target function of energy consumption, calculated by reducing the exergy flow in the system. The data obtained show the relevance and prospects of using cold accumulation on ships to reduce energy costs for the operation of refrigeration equipment and increase the autonomy of fishing vessels. Optimization according to the given method leads to two modes of operation of the refrigerating machine, as the most optimally beneficial in terms of operating conditions during the generation of cold. Optimization was carried out for two schemes for including a cold accumulator in the cold supply system. The proposed optimization methods make it possible to reduce the energy consumption of refrigeration units to the level of design loads, and to compensate for peak loads with the help of cold from batteries. Further research in this matter is aimed at reducing the size of the battery, increasing its energy efficiency and developing recommendations for inclusion in the general schemes of ship refrigeration plants based on mathematical optimization models and field experiments. It also plans to further improve the methods of cold accumulation based on ice generation with direct contact of media inside refrigeration units.

Analysis of the possibilities of increasing the energy efficiency of absorption refrigeration appliances through the use of refrigerating accumulators

One of the most important tasks of modern society is the solution of environmental and energy problems in power engineering and, in particular, refrigeration technology. At the same time, in the field of artificial cooling systems, it is necessary to solve the problems of reducing the impact on both the ozone layer and the greenhouse effect. An effective approach here can be absorption refrigeration systems with a natural working fluid (water-ammonia solution), which does not adversely affect the environment. For the effective use of absorption refrigeration systems, it is necessary to solve the problems of increasing their energy efficiency, in particular, through the use of cold accumulators. Thus, the object of research is absorption-type cooling systems with cold accumulators.
 The paper analyzes cold accumulators with different physical nature. It is shown that melting substances can be the most effective for solving problems of low-temperature cooling. An analysis of the thermal scheme of an absorption freezer of the «chest» type, which is the most problematic in terms of providing cooling modes at a level of (–18)–(–24) °С, was carried out. Optimization thermal calculations for typical absorption freezers up to 200 dm3 have been performed. It is shown that when the chamber is initially loaded with a product at an ambient temperature, the cooling capacity of the installed absorption refrigeration units is not enough – no more than 50 % of the required one. For an absorption freezer of the «chest» type, the most suitable cold-storage materials are a eutectic aqueous solution of sodium chloride or propylene glycol, since these solutions have the desired melting point of the order of –18 °C and a fairly high melting heat. The result of optimizing the weight and size characteristics of the internal volume of the absorption freezer is the following recommendations:
 – the optimal size of wire baskets for placing products is 315´370´240 mm;
 – the gaps between the basket and the cabinet wall, as well as between the baskets themselves, should be 10 mm to ensure normal convection conditions;
 – it is not advisable to place fans inside the volume of the freezer at this stage, since the freezing time is reduced by a maximum of 30 %, but this results in additional heat generation, energy consumption and increases the shrinkage of the products stored in the chamber.

Investigation of heat transfer processes at a full-scale object in a fruit and vegetable storage with a natural cold ground accumulator

This article studies the heat exchange processes between the natural cold of outdoor air and the soil battery in an experimental setup. In addition, the temperature field temperature between the surface of a reinforced concrete pipe with a diameter of d = 300 mm and the soil mass, the heat transfer coefficient, and the Fourier number were calculated and graphs were obtained. The accepted theoretical dependences for describing the processes of conductive heat transfer of a ground cold accumulator differ by 10-15% from the experimental data obtained on a physical model for various Fourier numbers.

Insulated box and refrigerated equipment with PCM for food preservation: State of the art

The use of Phase Change Material (PCM) as a cold accumulator in refrigeration contexts leads to better food safety, food security and energy management. However, applying PCM in real usage still depends on the user's experience or a trial-and-error basis. Studies carried out on insulated boxes and in refrigerated equipment (refrigerated trucks, cold storage facilities, display cabinets and domestic refrigerators) were reported. The influence of the studied conditions such as PCM melting point, position, mass of PCM and load, insulation material, external temperature on air/product temperatures and energy consumption was analyzed. Important parameters enabling the application of PCM in boxes and refrigerated equipment are the wall insulation and PCM configuration cited previously. Because of the complex interactions between these parameters, they need to be considered together with the usage conditions. The relationships between heat exchange and airflow inside the equipment should be further studied notably in function to the PCM position. • PCM enhances quality preservation and energy management in food cold chains. • PCM efficiency is related to the insulation of the system and PCM configuration. • Current studies have shown the most efficient design for specific conditions only. • A numerical study may be useful for box design and use conditions.

Methicillin Resistant <i>Staphylococcus aureus</i> in Pigs and Pig Breeders in Three Regions of Cameroon

The spread of antibiotic resistance, whether in the community or in the hospital, has recently become a major public health problem. Moreover, livestock seems to be a reservoir of resistant microorganisms such as porcine methicillin resistant Staphylococcus aureus (P-MRSA) whose carriage and transmission was mainly demonstrated in persons with occupational exposure to pigs. Much uncertainty remains about the public health implications of P-MRSA. To address concerns that exist regarding the zoonotic risk that pig carriers pose to breeders, the prevalence of P-MRSA in pigs and pig breeders was determined among 152 pig breeders in three regions of Cameroon. Materials and Method: Participants in this study came from Adamawa, Far North and Littoral regions of Cameroon. A total of 152 pig breeders or farm workers participated in this study. After having collected some social and cultural data with the aid of a questionnaire, nasal swabs were collected from pigs (n = 275) and their breeders using the standard collection procedures and placed in cooler containing cold accumulators. For each sample, microbiological assays were done as well as antibiotic susceptibility tests. Results: MRSA was isolated from 25 out of 275 pigs sampled (9.09%) and from 32 out of 152 (21.05%) pig breeders sampled; 33 breeders (21.71%) were carriers of S. aureus including 32 MRSA and one MSSA. The prevalence of MRSA nasal carriage was 21.05% ± 6.48. A significant negative association between body protection and nasal carriage of MRSA (OR = 0.29, 95% CI [0.093; 0.93]; p = 0.04) was observed. In each region, similar strains of MRSA were isolated both in pigs and their breeders with the same antibiotic resistant profile. Conclusion: The prevalence of MRSA though not high compared to European countries warrants further research as data on this zoonosis is scarce in our context. As such, transmission of MRSA from pigs to pig breeders or vice-versa constitutes a real danger, and this relationship may be a starting point for MRSA contamination in the community. Moreover, proper use of body protections and antibiotic medications as recommended will be a better protective measure against nasal MRSA carriage.

Developing a Cold Accumulator with a Capsule Bed Containing Water as a Phase-Change Material

The paper presents the investigation of a prototype cold accumulator using water–ice latent heat for the cold storage process. The concept of the cold accumulator was based on a 200-L-capacity cylindrical storage tank in which spherical capsules filled with water were placed. Beds of polypropylene capsules with diameters of 80 mm, 70 mm, and 60 mm were used in the tests. The cold accumulator operated with a water–air heat pump. Based on the test results, the following parameters were calculated: the cooling capacity, cooling power, energy efficiency of the cold storage, and energy efficiency ratio (EER) of the accumulator. The obtained measurement results were described with mathematical relationships (allowing for measurement error) using criterial numbers and the developed “Research Stand Factor Number” (RSFN) index. It has been found that, for the prototype cold accumulator under investigation, the maximum values of the cooling capacity (17 kWh or 85.3 kWh per cubic meter of the accumulator), energy efficiency (0.99), and EER (4.8) occur for an RSFN of 144·10−4. The optimal conditions for the operation of the prototype cold accumulator were the closest to laboratory tests conducted for a bed with capsules with a diameter of 70 mm and a mass flow of the water–glycol mixture flowing between the accumulator and the heat pump of 0.084 kg/s. During the tests, no significant problems with the operation of the prototype cold accumulator were found.

Actual approaches to the transportation of biological samples at low temperatures.

Taking into account the impact of shipment method of biosamples is necessary for obtaining high-quality biological samples in biobanking and laboratory research. The impact of liquid nitrogen, dry ice and cold accumulators on the quality of biological markers was considered, as well as recommendations to reduce the impact of these methods of shipment. The liquid nitrogen provides the best preservation of samples, however, dry ice is used much more often during their transportation. When transporting certain types of cells using dry ice, there is the way to use CryoStor CS1 and Cell Banker 1 cryoprotectors. The dry ice has a significant effect on both the pH of liquid biological samples and the coagulological parameters of plasma samples. The penetration of CO2 into the sample leads to changes in the parameters of PTT and APPT, as well as to decrease the protein C and fibrinogen level under certain conditions. Serum and plasma samples exposed to dry ice for more than 16 hours should be thawed open at room temperature, or instead of it should be kept at -80 °C for 24 hours to avoid changes in coagulation parameters, The use of cold accumulators is unacceptable for long-term shipment of serum and plasma containing unstable biomarkers because of insufficiently low temperature (increase over time to -25 °C and above). Besides, metal pellets can be used as cold storage batteries at low temperatures (up to -80 ° C), but they are not as effective as dry ice, since it is able to hold the required temperature for much longer.

ВИКОРИСТАННЯ НАДЛИШКУ ХОЛОДОПРОДУКТИВНОСТІ ХОЛОДИЛЬНИХ МАШИН ПРИ ОХОЛОДЖЕННІ ПОВІТРЯ НА ВХОДІ ГТУ

The processes of the gas turbine inlet air cooling by exhaust heat conversion chillers, which utilizing the gas turbine exhaust gas heat, converting it into cold were analyzed. The use of two-stage air cooling has been investigated: to a temperature of 15°C – in an absorption lithium-bromide chiller and below to a temperature of 10°C – in an ejector chiller as stages of a two-stage absorption-ejector chiller. To simulate air cooling processes, the program "Guentner Product Calculator", one of the leading manufacturers of heat exchangers "Guentner", was used. The possibility of using the accumulated excess refrigeration capacity of a combined absorption-ejector chiller, which is formed at reduced current heat loads on air coolers at the gas turbine inlet, to cover the refrigeration capacity deficit arising at increased heat loads due to high ambient air temperatures has been investigated. The refrigeration capacity required to the gas turbine inlet air cooling was compared to an excess refrigeration capacity which excess of the current heat load. The considered air cooling system provides pre-cooling of air at the gas turbine inlet by using the excess refrigeration capacity of the absorption-ejector chiller, accumulated in the cold accumulator, to provide the required refrigeration capacity of the air pre-cooling booster stage. The simulation results proved the expediency of the gas turbine inlet air cooling using the accumulated excess refrigeration capacity of the combined absorption-ejector chiller. The proposed solution reduces by about 50% the design refrigeration capacity and, accordingly, the cost of the installed absorption lithium-bromide chiller, which acts as a high-temperature stage for cooling the ambient air at the gas turbine inlet.

ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ ОХОЛОДЖЕННЯ ПОВІТРЯ НА ВХОДІ ГТД ХОЛОДИЛЬНИМИ МАШИНАМИ ШЛЯХОМ АКУМУЛЯЦІЇ ХОЛОДУ

The efficiency of air cooling at the inlet of gas turbine engines by exhaust heat conversion chiller, which transforms the GTE exhaust gases heat into cold, under variable climatic operating conditions, has been investigated. Considered is the use of a combined absorption-ejector exhaust heat conversion chiller with a step-by-step principle of air cooling at the gas turbine engines inlet: preliminary down to 15°C – by an absorption lithium-bromide chiller (ACh), which is used as a high-temperature air cooling stage, and further cooling down to 10°C – by a refrigerant ejector chiller (ECh) as a low-temperature cooling stage. Reserves have been identified for reducing the design (installed) refrigeration capacity of chillers by accumulating excess cold at reduced current heat loads with its use at increased heat loads. In this case, the design (installed) refrigeration capacity of chillers was determined by two methods: the first – based on the close to the maximum reduction in annual fuel consumption, the second – according to the maximum rate of increase in the reduction in annual fuel consumption. A scheme of the air cooling system at the gas turbine engines inlet using the refrigeration capacity reserve of the ACh, which provides preliminary cooling of the ambient air at the gas turbine engines inlet, in the booster stage, using the ACh accumulated excess refrigeration capacity has been proposed. The ACh excess refrigerating capacity, which is formed at decreased heat loads on the air coolers at the gas turbine engines inlet, is accumulated in the cold accumulator and is used at increased heat loads. The simulation results show the advisability of using the air cooling system at the gas turbine engine inlet with using the ACh accumulated excess refrigeration capacity, which allows reducing the ACh design (installed) refrigeration capacity by approximately 40%.

Ionic clathrate hydrates loaded into a cryogel – halloysite clay composite for cold storage

Mixed type phase change material (PCM) based on the tetra-n-butylammonium bromide (TBAB) hydrate loaded in a composite matrix included poly(vinyl alcohol) (PVA) and natural halloysite clay nanotubes can be used for the cold storage. Poly(vinyl alcohol) provides the formation of a cryogel, while the clay nanotubes promote the hydrate nucleation reducing the supercooling of the formed hydrate. At the same time, the cryogel formation ensures the sedimentation stability of halloysite inside the dispersion. The relationship between the concentration of the target compound in the initial solution, the presence/absence of halloysite, and specific enthalpy of the phase transition made it possible to optimize the properties of this material for cold storage. The formation of two hydrates in the systems under study with different water content as well as the possibility of recrystallization of the low content water hydrate into the high content water one and during the melting of ice was experimentally revealed. The obtained PCM melted at a temperature of 9–13 °C and had a melting enthalpy up to 196 J/g. It was shown that the halloysite is a nucleator for TBAB hydrates. Adding 1 mass% of halloysite to the composite increases the temperature of hydrate onset by 2 °C. The best thermal stability in an open system was shown for the 1:50 M ratio. The energy capacity of such material does not decrease during 50 cycles of the reversible melting-crystallization phase transition, which indicates the stability of the TBAB-PVA-halloysite system. As both halloysite clay nanotubes and poly(vinyl alcohol) cryogel are biocompatible, encapsulation of tetra-n-butylammonium bromide hydrate in such material will protect the environment from harmful effects of a quaternary ammonium salt and expand the scope of this cold accumulator. The halloysite as an additive for phase change composites is also low-cost, readily available from natural mineral deposits, and non-toxic.

On the issue of the usage of sealed containers for cooling the refrigerant in refrigerated trucks

The paper deals with the problem of using machine-free cooling in refrigerated trucks for intercity transportation in order to ensure environmental safety and to eliminate noise from a working refrigeration machine when unloading refrigerated products from refrigerated trucks to the distribution network. A machineless method for cooling the body of a refrigerator truck with cold accumulators without direct contact with a cooling medium due to the usage of frozen sealed containers is proposed. The accumulation of cold (AC) is carried out, as a rule, due to the heat of the phase transition at the melting point or crystallization of individual substances or there mixtures. The research of water-salt systems, which are widely used for temperature stabilization in refrigeration, for storage and transportation of medicines and food products, is presented. The results of the melting and freezing of three cold storage substances, which are H2O and water-salt solutions with NaCl concentrations of 8 and 13 % are presented. According to the results of studies, the usage of pressurized containers in refrigerated trucks with machine-free cooling is beneficial and opens up great opportunities for cooling the air in various destinations.

Modeling the crystallization process of an eutectic solution in cold accumulators of a refrigerated truck

The duration of crystallization process of an eutectic solution of an infinite plate may be presented as a sum of three components: duration of the cooling process of the eutectic solution of liquid phase τ1 from initial temperature tI to the crystallization beginning; duration of crystallization process τ2 and duration of the precooling process of solid phase τ3 to certain final temperature t f in the plate center.

Calculation of cold accumulators with phase change materials

The paper presents an improved technique (mathematical model) for numerical calculations of solid-liquid phase transitions based on a zero-dimensional solution of the Stefan problem for cases of placing phase change materials in ball-shaped or cylindrical capsules. According to the proposed model, numerical calculations of the liquid phase volume fraction in Scilab have good compliance with experimental data for n-octadecane, and the calculation time is reduced several hundred-fold in comparison with calculations in Fluent.

Microbiological Characterization of Grilled Meat “Tchatchanga” in Cotonou (Southern Benin): Enumeration, Isolation and Resistance Profile of Staphylococcus aureus and Escherichia coli

Collective food-borne diseases are the reason for a considerable number of deaths in developing countries. The contamination of meat is often noticed. The purpose of the present study was to enumerate, isolate and evaluate the resistance profile of Staphylococcus aureus and Escherichia coli in grilled meat consumed in Southern Benin. To achieve this goal, 30 thirty samples of grilled meat “Tchatchanga” were collected in three districts of the city of Cotonou. After collection, the samples were identified, stored in a cooler containing cold accumulator’s and sent to the laboratory for analysis. The resistance profile of the different isolated strains was then sought: 30% of the samples were contaminated with Escherichia coli and 100% with Staphylococci. In terms of hygienic quality, 70% of the samples were of unsatisfactory. Of the 30 staphylococcal strains, 11 were identified as Staphylococcus aureus. Regarding the strain resistance profile, 88.89% of the Escherichia coli strains were multi-resistant compared to 72.72% of Staphylococcus aureus. This study revealed the necessity of urgent actions to ensure food safety in Benin.

Experimental cycle air cooling system for gas microturbine unit

The article considers the Combustion Turbine Inlet Cooling (CTIC) system — an experimental system for cooling the cycle air entering the gas microturbine unit. This enables to save electrical power of the unit generated at the design level in the period of seasonal increase in air temperature. Cooling of the air at the inlet to the turbocharger of the unit occurs up to its design temperature (which is, according to the ISO standard, equal to 15˚С). The basis of the CTIC model is an industrial cooling system based on a vapor compression refrigeration unit with a cold accumulator. Water ice is used as a cold storage medium in the accumulator, while ice water is used as a medium cooling the cycle air (ice water is water at a temperature of 0.5˚С – 1˚С). The eff ect of cooling of cycle air is achieved by pumping ice water coming from the cold accumulator through an air-to-water heat exchanger installed at the inlet to the turbocharger. The purpose of the study was to determine the operating time of a cold accumulator, depending on the speed of the circulating water. The experiments were carried out on a model of a cooling system with a cold accumulator having a 200 kg ice storage and working with the Capstone C-30 microturbine. Maintaining the temperature of the cycle air at its design level is achieved using a frequency-controlled circulation pump and a digital measurement and control system with the LabVIEW software package. The results of the study show that the considered CTIC system, while discharging the cold accumulator, is able to maintain the required design temperature of the cycle air at 15°C for 6 hours, which is quite enough to cover the peak load of the working day. Technical and economic parameters of the plant are evaluated.

Cold accumulators in air conditioning systems

The appropriateness of using cold accumulators in air conditioning systems has been assessed. A cooling system with a storage tank is considered, in which ice is frozen on the outer surface of the evaporator heat exchange tubes. It is established that the accumulation of cold can lead to a significant reduction in cash costs. The analysis of the experience of using cold accumulators in air conditioning systems allows drawing the following conclusions: the most common solution for accumulating cold is the use of ice accumulators with ice freezing on the heat exchange surface of evaporators located in the storage tank; the melting mode of ice in ice accumulators with the chiller turned off is adopted in designing. The area of the heat exchange surface of the ice accumulator apparatus during cooling of ice water should be determined mainly depending on the conditions of ice melting; to freeze ice, it is necessary to increase the heat exchange surface area of the evaporator and lower the boiling point to minus 10...15 °C. Specific energy costs (kW of electricity per kW of cold) increase by 2 or more times, which reduces profit.