Search

To assess the impact of cold and heat conditions on manual performance during maneuverability exercises in powerchair football players. Ten volunteers with heterogeneous pathologies engaged in FIPFA competitions participated in the study. The assessments consisted of answering a survey, carrying out a computer maneuverability path before and after immersion of upper limb in cold water (8 °C); before and after exposure to heat (hair-dryer). The skin temperature (hand and forearm) perceptive scales (thermal sensation and comfort, effort, pain) were also measured. Conditions did not significantly impact mean test result (Heat = +5.3 boxes; Cold = −6.3 boxes; NS) but some subject were highly impacted with cold condition. A slight downward trend was observed for the cold and a slight upward for the heat. The cold and heat influenced the both hand and forearm skin temperature, the thermal sensation and the thermal comfort of the players in contrast to the perception of effort and pain (hand after Heat = +5.9°3.9 °C, hand after Cold = −11°1.4 °C; forearm after Heat = +1.9°1.0 °C, forearm after Cold = −0.6°0.7 °C; P < 0.05). The results suggest that individually, cold condition might affect negatively manual dexterity and performance of some powerchair football players. To put athletes in best playing environment conditions, the instance of powerchair football need to legislate for a minimal ambient temperature. [ABSTRACT FROM AUTHOR]

• A dynamic performance model is developed and experimentally investigated for a domestic freezer under varying conditions. • Numerous heat and mass transfer parameters are investigated through repeated multiple experiments. • A semi-empirical door opening scheme is considered in the present dynamic model. • A close agreement is obtained between the model predictions and experimental measurements for temperature, pressure, humidity, power and energy consumption. This paper performs a comprehensive experimental and modelling study to examine the dynamic behaviour of an upright freezer with adjustable shelving under periodic door opening conditions with different temperature, pressure and relative humidity values. An uncertainty analysis is carried out for the experimentally measured data. Additionally, the dynamic model is developed with crucial sub-components, such as discretized upright cabinet, frosted evaporator and semi-empirical door opening mechanism using an object-orientated programming language called Modelica. The present model is the validated with experimental data employing the values of the airflow from ambient into the cabinet along with the average cabinet air flowrate and back wall temperatures, transient evaporation and condensation pressures, cabinet average relative humidity change, compressor operation time and power consumption, and finally total energy consumption of refrigerator for both 85%RH and 65% RH conditions at 32 °C ambient. The results show that the model predictions have a similar trendline with the experimental findings within ±3 K error bands regarding average cabinet air and back wall temperature. In contrast, the dynamic cyclic trend before and after door opening is closer to the experiments within ±1 K. The current model predictions for the low and high pressures are found to be within ±3% and ±5% error bands, respectively, whereas the average relative humidity level of the cabinet is captured within ±10% deviation. Furthermore, transient compressor power is well predicted with deviations, but not exceeding 4.5%, and the total energy consumption level is compatible with 6% error bands during the entire experimental period. [ABSTRACT FROM AUTHOR]

• A novel R744 multi-temperature unit for refrigerated road transport is presented. • An ejector is used to replace the low-temperature compressor. • Experimental tests on the ejector operating in LT suction conditions are performed. • The pressure lift requirement significantly influences the ejector performance. • The unit operating conditions choice should consider both cooling effect and COP. A novel vapor-compression system concept employing carbon dioxide as the refrigerant is proposed to serve the needs of a typical medium-size refrigerated truck used for multi-temperature (MT and LT) goods delivery. The system design is based on the implementation of an ejector as the only component increasing the refrigerant pressure from the LT evaporation pressure to the MT evaporation pressure, thus providing cooling effect at two different temperature levels with only one stage of compression. The ejector was experimentally tested and its ability to effectively entrain mass flow rate from low pressure suction conditions (corresponding to a LT evaporation temperature of −25 °C) was assessed. Lower external ambient temperatures and consequent lower expansion energy available at the ejector motive nozzle leads to a reduction of the maximum achievable pressure lift. Moreover, a significant degradation of the ejector performance towards the highest pressure lifts is experienced. Based on the ejector experimental data, a numerical evaluation of the proposed cooling unit performance has been performed, highlighting that in design conditions (LT evaporation at −25 °C) the cooling unit provides a LT freezing power ranging between 1.1 kW and 2.3 kW and a corresponding minimum MT cooling power ranging between 5.1 kW and 3.8 kW, depending on the chosen ejector lift. The MT cooling power can be further increased by increasing the compressor mass flow rate. The system COP is maximized at the maximum available lift provided by the ejector. [ABSTRACT FROM AUTHOR]

• A novel study on pressure exchanger for use in commercial refrigeration. • CFD based thermodynamic investigation. • Pressure lift correlation developed for thermodynamic study. • Performance superiority over ejector system analysed. • Significant energy savings over parallel compression system. This manuscript presents a method to thermodynamically model a pressure exchanger device. CFD-based model of a rotary energy recovery device used in desalination process is developed and validated with published experimental data with a maximum deviation of 5.19%. The dimensionality of the validated model was reduced to investigate the potential of the pressure exchanger device operating with CO 2 as the working fluid. Based on the data obtained from several numerical experiments, two correlations were developed, by means of non-linear regression analysis, for estimating the pressure lift generated by the device as a function of inlet velocity of high pressure fluid (0.5 – 3 m/s), rotor speed (500 – 3000 rpm), receiver pressure (25 – 40 bar) and gas-cooler pressure (90 – 120 bar). The correlations were found to be within acceptable error margin. The pressure lift generated by the pressure exchanger was found to be directly proportional to the inlet velocity of the high pressure fluid and inverse proportionality to the rotor speed. The developed correlations are used to evaluate the thermodynamic performance of a multi evaporator supermarket refrigeration system integrated with pressure exchanger to a conventional parallel compression system and a published multi-ejector system in the ambient temperature range of 30 to 40 °C. The pressure exchanger based system was found to outperform the parallel compression as well as the multi-ejector system and demonstrate significant energy savings. [ABSTRACT FROM AUTHOR]

• Expander-compressor boosted subcooling refrigeration system is proposed. • For different refrigerants optimum increment in COP with respect to conventional system is determined. • Heat transfer surface area of the subcooler is calculated. Many applications have made extensive use of refrigeration systems, which have a high energy requirement. Any improvement on the refrigeration systems can reduce the need for energy demand. A common method to improve the system performance is to subcool the condenser exit temperature and known as subcooling. An expander-compressor booster enhanced subcooling vapor compression cycle is proposed as an addition to the subcooling systems described in the literature. The refrigerant is split into two parts at the condenser exit: one portion expands in the expansion device to reach the necessary subcooling temperature, while the other part goes straight into a separate heat exchanger. Later, this additional refrigerant flows into the other expansion valve, the evaporator, and a booster expander-compressor to increase inlet pressure of compressor. As working fluids, six distinct refrigerants including low global warming potential (GWP) are used (namely R134a, R1234yf, R32, R290, R1270, and R600a) in simulations. The coefficient of performance (COP) and increment in COP values for each refrigerant are computed and graphically displayed for various evaporation temperatures between -10 °C and 5 °C. Furthermore, the heat exchanger analysis of subcooling heat exchanger is performed to compare heat transfer surface area and pressure drop for each refrigerant. Results indicate that R1234yf achieves the greatest performance with an increase in COP by 16.7, 19.1 and 21.8% depending on the mechanical efficiencies of the expander and compressors and as well as isentropic efficiency of the expander. By utilizing an expander-compressor with higher or lower mechanical and isentropic efficiencies, these enhancements can be raised or lowered. Heat exchanger analyses show that the pressure drop in the exchanger does not significantly affect the performance of the system. [ABSTRACT FROM AUTHOR]

Cold storage is one of the main ways to coordinate harvesting and packinghouse operations for extending the marketing period. In Morocco, for the new citrus varieties, limited research has been undertaken on the evolution of the fruit quality during cold storage. In this paper, we present results of a cold storage trial of ‘Nadorcott’ mandarin fruits. Fruits were harvested from a rootstock trial carried out in SEBNAK orchard and stored in Mazaria packinghouse facilities in North-West of the Morocco. The objective of the study is to assess the effects of the harvest dates, the storage duration and three citrus rootstocks: ‘Carrizo’ citrange (CC), C-35 citrange (C35) and Citrus macrophylla L (M) on the internal quality and weight loss of the ‘Nadorcott’ mandarin fruits stored at 6 °C and 80% ±5 % humidity. Fruits were harvested at three dates and the quality parameters (juice content, titratable acidity, total soluble solids and weight loss) were evaluated after 0, 20, 40 and 60 cold-storage days. Fruit quality characteristics varied according to the rootstock type, storage duration and harvesting dates. At harvest, juice content was affected by different rootstocks: C-35 and CC showed the highest values, with about 50 % compared to that of M with only 44%. In addition, fruits harvested in March (D3) were less juicy than those harvested in January (D1) and early February (D2). The juice content falls more or less rapidly during the cold storage depending on the rootstocks and harvest dates. For the three harvest dates (D1, D2 and D3) and 60 days storage, the ‘Nadorcott’ mandarin fruits on M recorded the lowest juice percentage with values of 31, 38 and 30% respectively. At late period (D3), the acidity in fruit juice dropped to the lowest levels reaching a rate of 0.68 % for CC and M and 0.77 % for C-35. With regards to TSS, CC and C-35 had higher TSS (total soluble solids) percentage compared with fruits from trees on M. Date of harvest and cold-storage period have no significant effect on this parameter. Similarly, the weight loss of ‘Nadorcott’ fruit was not affected by the rootstock.

The combination of an ORC (Organic Rankine Cycle) with a VCC (Vapor Compression Cycle) is studied analytically. In this work, the two cycles use the same fluid and operate with a common condenser. Elementary transformations of the fluid between two consecutive points of the system are calculated using a one-dimensional thermodynamic approach considering real fluid properties, the pressure losses and irreversibilities present in the compressor, in the expander and in the pump. The performances and the recommended inlet and outlet diameters of the expander and the compressor are established for various operating conditions and 12 fluids. The system can produce a typical useful cooling capacity of 0.60 kW at 5.5 °C when using a 2 kW heating source at 65 °C and when the condenser temperature is 30 °C. The cooling capacity reaches 1.0 kW if the cold source temperature is 15.5 °C. Results show the required diameters ratios at inputs and outputs of the compressor and the expander. They indicate the situations for which the compressor is smaller than the expander and vice versa. They identify the particular cases in which the compressor and the expander have exactly the same inlet and outlet diameters. This particular case allows using two identical compressors, one working as a compressor, the second as an expander. [ABSTRACT FROM AUTHOR]

• Silica gel–water adsorption heat pump with adsorbent microchannels developed. • Microchannels minimize heat and mass transfer resistances. • Single microchannel governs process performance, enabling scalability. • COP of 0.22, SCC of 177 W kg−1 without heat recovery achieved. • Near-continuous cooling with single adsorbent bed. Adsorbent-coated microchannels are used for the design of adsorption heat pumps, based on component-level fluid flow, heat and mass transfer modeling of a representative proof-of-concept unit with a cooling capacity of 300 W at 5 °C. Optimum channel geometry is determined using parametric studies. The use of adsorbent-coated microchannels results in operation with the heating time less than 10% of the total cycle time, opening the possibility for near continuous operation of the heat pump. Cyclic operation of the subject heat pump concept is simulated for the operating conditions used for silica gel-water chillers in the literature, and the results are used to document its benefits over those of existing designs. For a source temperature of 90 °C, cooling temperature of 35 °C, condenser inlet temperature of 42 °C, and evaporator outlet temperature of 5 °C, a Coefficient of Performance (COP) of 0.22 is attainable with a specific cooing capacity (SCC) of 177 W kg−1 without recovering any heat from the heating stage. COP > 0.55 and SCC ~1134 W kg−1 can be achieved for less severe operating conditions typically used in the literature. [ABSTRACT FROM AUTHOR]

• Modeled hydrogen liquefication from 80 to 20 K in a multi-stage AMR system using permanent magnets with 1-Tesla field. • Achieved over 60% of Carnot COP with the multistage design with optimized operation conditions. • Compared two types of 1D AMR models: steady state and time-dependent models. Hydrogen (H 2) is promising alternative to replace fossil fuels, but its transport and storage has been challenging. As H 2 fuel cell vehicles are gaining traction, the infrastructure for storing large amounts of liquid H 2 is needed. However, liquid H 2 would suffer from boil-off loss, and traditional vapor compression refrigeration systems would not be able to economically recover the lost H 2 due to the low efficiencies at cryogenic temperature. Magnetocaloric (MC) refrigeration systems could possess much higher coefficient of performance (COP) at cryogenic temperature compared to the vapor compression ones. Previous work on cryogenic MC systems, however, have only focused on large scale applications which use superconducting magnets to provide a large magnetic field but are prohibitively expensive to operate for small scale applications, such as that of a H 2 refilling station. In this work, we model the performance of a MC refrigeration cycle using 1-Tesla permanent magnets for H 2 liquefaction, with the objective of cooling H 2 from 80 K (using liquid nitrogen as the heat sink) to 20 K (boiling point of hydrogen). We evaluate main performance metrics including the total work input to the refrigeration system, COP, total MCM mass in the system, and total volume of the permanent magnets, etc. Our modeling results indicate that such a permanent magnet-based MC cooling system is feasible for small-scale H 2 liquefaction, with projected COP values significantly higher than those of vapor compression systems. This work provides design guidelines for future experimental efforts on permanent magnet MC cooling systems for cryogenic cooling. [ABSTRACT FROM AUTHOR]

• Temperatures in frozen display cabinets in retail stores were monitored. • Spatial and temporal temperature variations in and between cabinets were identified. • Temperatures were more uniform in doored vs combined door/open well cabinets. • Heated defrosts caused substantial temperature increases in product temperatures. Specially designed refrigerated retail display cabinets are used in shops throughout the world to display frozen foods. In order to maintain the quality of the frozen food in these cabinets' temperatures must be tightly controlled. Considering their importance, it is surprising that there is very little published data on how well frozen retail cabinets do this in practice. This study monitored temperatures in frozen retail display cabinets in four branches of a major UK supermarket chain, ranging from a medium size outlet to a large hypermarket. Two types of cabinet were monitored (1) combined frozen top doored and open bottom (well) cabinets (ISO classification RYF3) and (2) vertical frozen glass doored cabinets (ISO classification RVF4). The results showed that while cabinets may run at the required overall temperature(s), some frozen products in those cabinets can spend a substantial amount of time, up to 45%, above -12°C, at sub-optimal temperatures. While this will have no effect on the safety of the food, it is likely to have a detrimental impact on quality and shelf-life. Overall temperature control was far better in the vertical frozen glass doored cabinet. [ABSTRACT FROM AUTHOR]

• Beta Stirling machine for refrigeration application. • Experimental results. • Heat lift and Coefficient of Performance. • Torque and velocity measurements. As the concern for CO 2 emissions and global warming raises, the Stirling machine appears as a candidate alternative technology to vapor compression cycles that use refrigerant fluids. In this paper, we present the design, manufacturing and testing of a Beta Stirling machine for refrigeration applications. The first part of the paper presents the principle of the Stirling cycle, the mechanical configuration of the designed machine, and the key design parameters. The second part describes the experimental test bench and instrumentation of the Stirling machine. The last part of the paper presents experimental results. The prototype typical performance is a 450 W heat lift at 4°C and a COP of 0.9 when Nitrogen is used as the working gas. Cold end temperature variation as a function of heat lifts and charge pressure are presented. Coefficient of Performance is also discussed. Mechanical power, instantaneous torque and velocities curves are reported. [ABSTRACT FROM AUTHOR]

• This study focuses on a food plant of puff pastry. • A thermal and energy modelling approach was developed. • Industrial own-check data were mainly used. • The thermostat setting temperature can be raised in this application. This study focuses on the experimental and numerical characterization of the food temperature and energy consumption of cold facilities in a food processing plant. An event based framework was used to model the main components of the production line (kneader, conveyor, cooling spiral and cold room). Plant self-control data obtained by measurement in plant were used to inform and validate the model. Different scenarios were tested to evaluate the impact of modified operating conditions (thermostat setting temperature and duration) and refrigerating equipment outages on energy consumption and food temperatures. Up to 18% of energy savings could be achieved by increasing thermostat setting temperature of the process room and the storage room with a limited impact on the product temperature. This methodology can help manufacturers in decision making to optimize operating conditions and reduce energy consumption with a limited impact on food waste and safety. [ABSTRACT FROM AUTHOR]

• Single-effect absorption refrigeration system is simulated using aspen HYSYS. • Commercial butane as refrigerant and commercial hydrocarbons as absorbents are used. • Optimal working fluid is found to be butane/heavy naphtha. • Performance changes marginally with butane recovery unlike reboiler temperature. • Butane/heavy naphtha system competes effectively with current commercial chillers. A heat-powered single-effect absorption refrigeration system operating with commercial n-butane as a refrigerant and six commercial hydrocarbons (stabilized condensate, light naphtha, heavy naphtha, reformate, light reformate and heavy reformate) as absorbents was studied. The main target of the study was actuating these systems to the available waste heat. Simulation models were created using Aspen HYSYS process simulator. The main parameters of an absorption refrigeration system, using the proposed working fluids, were compared at different evaporator, condenser and absorber temperatures to select the best working fluid. Moreover, a focused interpretation was given to the behavior of the best system at different operating conditions. Furthermore, the effect of both butane recovery and purity, in the generator, on the performance of the best system was investigated. Results revealed that, among the proposed working fluids, the best performance was achieved by butane/heavy naphtha. It could achieve a Coefficient of Performance (COP) of 0.78 at evaporator temperature of 20 °C and both condenser and absorber temperatures of 30 °C. The COP passed through a different maximum value at certain recovery for each evaporator temperature and condenser and absorber temperatures and similar behavior was observed for purity. Low reboiler temperatures were feasible at low butane recoveries with almost the same COP of the high butane recoveries. Generally, Butane/heavy naphtha system could compete effectively with the commercial absorption refrigeration systems, within their range of operating conditions, without experiencing their limitations. [ABSTRACT FROM AUTHOR]

• Lubricating oil was found attenuating the pressure pulsation energy above the 1st order of pumping frequency. • The amplitude reduction of pressure pulsation depended on oil injection locations and distribution obviously. • The final compression pressure inside screw lobe cavity was found much lower than the expected value based on built-in radial VI. • The refrigerant pressure inside the last lobe cavity continued increasing until the axial port opening around 5.45°. • Several suggestions about design for lower pressure pulsation were recommended. An experimental investigation on pressure pulsations of twin-screw refrigeration compressor was conducted. The pressure pulsation energy at different radial locations on the screw housing, inside the discharge chamber, and the energy transmitting to downstream components during the working process were all tested. Various oil parameters have been investigated to disclose its influence on the pressure pulsation energy of twin-screw refrigeration compressors. With the total oil flow rate increasing, pressure pulsation was found attenuating above the 1st order of pumping frequency, while the amplitude reduction was found depended on the oil injection locations and oil distributions obviously. The final compression pressure inside the screw lobe cavity before the internal discharge port opening was found to be much lower than the expected value based on the built-in radial Vi, and the pressure continued increasing until the axial port opening around 5.45°. Several suggestions about design for lower pressure pulsations were recommended based on test findings. [ABSTRACT FROM AUTHOR]

• A new CSP-geothermal based integrated system with an ejector-absorption cooling cycle is developed. • Parametric energy and exergy analyses are conducted. • Both energetic and exergetic efficiencies and COP values are studied. • Exergy destruction rates are calculated for comparative evaluation. • Optimum operation of the proposed system is identified. A concentrated solar-geothermal integrated system with a combined ejector-absorption refrigeration cycle is proposed and analyzed thermodynamically for a small community application. A detailed thermodynamic model is established for analysis and performance evaluation. A case of a small community in the Yukon Territory is chosen and the system provides all the necessary demands of electric power, space heating and cooling and domestic hot water at high performance. The overall energetic and exergetic efficiencies are 53.33% and 37.07%, respectively, while the COP en and COP ex of the combined cooling cycle are 1.033 and 0.1131, respectively. In addition, numerous parametric studies are presented to illustrate the effects of several energy sources parameters on the overall performance of the integrated system and the combined cooling cycle. Furthermore, ejector parameters are controlled to get the highest COP en value of 1.164. Lastly, the integrated system is optimized exergetically to reach a value of 55.98%, while the overall energetic efficiency becomes 63.60%. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ammonia/water absorption–resorption refrigeration systems are an interesting technological alternative to conventional absorption systems thanks to their additional degree of freedom, which makes operation more flexible and can significantly reduce the typically high working pressure, so cheaper assembly materials can be used. This paper aims to review the theoretical and experimental works carried out so far on these systems, paying special attention to the experimental plants currently operating and recent progress in improving system control. This paper reports how to determine the operational pressure range when the temperatures of the main components of the ammonia/water single-stage cycle are fixed and how the pressure range changes when these working temperatures are varied. As a result of the theoretical study of the base case selected, the cycle performance was evaluated without rectification after the generator in order to reduce the size and cost of the system without reducing the performance. Finally, it should be pointed out that the effectiveness of the resorption solution heat exchanger plays an important role in the performance and operating conditions of the cycle because the cycle cannot work below certain values of effectiveness. [ABSTRACT FROM AUTHOR]

Power Regeneration Technique in Vapour Compression Refrigeration Plants is presented for the purpose of upgrading already existing plants, each characterized by Main Compressor, Evaporator, Condenser and Main Expansion Valve. The Power Regeneration Concept is illustrated and theoretical results deeply discussed in relation to the upgrading of Refrigeration Plants whose Cooling Power being given or whose Main Compressor remain unchanged. Changes in performance and internal variables are deeply analysed for various arrangement options. Experimental results are also given providing the performance improvement of the Refrigeration Plants equipped with Power Regeneration Systems. Cooling Power and COP improvements up to 100% and 80% respectively are expected for a given Main Screw Compressor; while COP increasing up to 70% and Main Compressor Delivery reduced to 50% are evidenced for constant Cooling Power Plants. [ABSTRACT FROM AUTHOR]

Highlights • Conceptual and operating performances analysis of a solar absorption refrigeration cycle. • Quasi-real irreversible cycle operating in transient regime. • Application of the first and the second laws of thermodynamic. • Total entropy generation is acquired and the performances are examined at various operating conditions. • The stagnation temperature of the solar collector is needed to approach the real operations. Abstract The performances of a solar absorption refrigerator cycle are investigated. The cycle is considered as a real irreversible plant operating in transient regime. The total entropy generation is acquired applying the two laws of thermodynamic and the performances are examined at various operating conditions. The results show that high efficiency value is obtained at high control temperature. The increase of this temperature allows reaching the minimum time to reach a prescribed cooled-space temperature. Greatest and optimal values of the stagnation temperature of the solar collector are needed to approach the real operations. The minimum time and the dimensionless size of the solar collector are significantly affected by both the cold thermal load and the thermal conductance of the walls. [ABSTRACT FROM AUTHOR]

Highlights • A novel LiBr/H 2 O absorption cooling and desalination system with three pressure levels. • Information was generated on the operational behavior of the proposed new technology. • The proposed technology has 19.5% more efficiency than a conventional single-effect absorption cooling system. • The system has a cooling capacity of 23 kW and produced 838 L/day of freshwater, with a FR of 0.08 and R of 1.84. • Increasing the pressure in the absorber, the cooling effect was enhanced. Abstract This paper presents a novel LiBr/H 2 O absorption cooling and desalination system with three pressure levels which uses seawater as a cooling medium and is activated by solar thermal energy. This system helps counteract coastal populations' thermal conditioning and water supply problems. In order to show technical feasibility, Aspen Plus was used to simulate the system with the following parameters: a 23 kW cooling capacity; different seawater temperatures; and, a concentration of 35,000 ppm. It was found that the proposed technology has 19.4% more efficiency than a conventional single-effect absorption cooling system, with an FR of 0.08 and an R of 1.84, and produces 838 additional L/day of water, enough to satisfy the requirements of a household for up to 7 people. With the configuration of the proposed technology, which manages three levels of pressure, and using seawater as a cooling medium, the simultaneous production of cooling and desalination is benefited. [ABSTRACT FROM AUTHOR]

Highlights • Development of a dynamic model to study the thermal response of the insulated box. • Evaluation of the dynamic behavior of the insulated box during a typical mission. • Thermal capacity and thermal resistance cannot be derived from stratigraphy. • Numerical model was able to well predict the evolution of the internal temperature. • Mission was designed to reproduce a long-distance delivery. • Simulation model allowed to identify dynamic load and cooling power demand of the truck. Abstract The average cooling demand of a refrigerated vehicle depends on the external conditions and on the journey's profile, such as ambient temperature, air velocity, vehicle speed etc. In order to understand the dynamic heat load on the system and predict the peak of cooling demand, a fully dynamic model of the insulated box of a refrigerated vehicle was developed and experimentally validated. Experimental data was collected during test of a vehicle following the International Agreement for the Transport of Perishable (ATP) test. The model validation demonstrates the capability of the model to correctly predict the evolution of the internal box air temperature in both transient and steady-state conditions. The trend of dynamic load, peak of cooling demand, influence of the solar absorption coefficient and influence of the walls thermal mass on the cooling energy demand during a typical mission are also simulated. [ABSTRACT FROM AUTHOR]

Highlights • Experimental investigation was performed in a model trailer filled with 215 carcasses. • Convective heat transfer coefficients were measured on 18 half-carcasses. • Convective heat transfer coefficients were measured on 6 parts of the carcasses. • Differences were observed between the rind and the muscle sides for all positions. • Correlation between measured coefficients and measured air velocity is proposed. Abstract Measurements of convective heat transfer coefficients on reduced-scale replicates of half pork carcasses were conducted. Measurements were performed on both the muscle and rind sides at three positions: ham, loin and shoulder. The carcasses were placed in the symmetry plane and near the wall of a reduced-scale refrigerated trailer with or without air distribution ducts. The convective heat transfer coefficient values varied significantly along the trailer in both configurations (with or without air duct). Differences were observed between the rind and muscle sides for all positions. The heat transfer coefficients of the ham part were higher than those of the loin and shoulder parts. An analysis was conducted by correlating the measured convective heat transfer coefficients with the air velocity fields measured by Laser Doppler Velocimetry presented in a previous study. [ABSTRACT FROM AUTHOR]

Highlights • 2D numerical model of a device with an active electrocaloric regenerator is presented. • Material hysteresis greatly impacts the efficiency of the cooling device. • A system for energy recovery can increase the device efficiency by ten times. • The electrocaloric cooling device has a maximum specific cooling power of 16 W kg−1. Abstract This paper reports on the research and development of a cooling device with an active electrocaloric regenerator (AER) based on the bulk ceramic material (1-x)Pb(Mg 1/3 Nb 2/3)O 3 –xPbTiO 3 (PMN-100xPT). For the purposes of the study a 2D transient numerical model of the AER was developed. This model makes it possible to investigate the cooling characteristics of a device with an AER while considering the effect of the hysteresis of the electrocaloric material and the effect of the electric-energy recovery related to the polarization/depolarization process. The results of the numerical analyses show that the degree of electric energy recovery has a major impact on the efficiency of the device. By considering an idealised system for electric-energy recovery the energy efficiency (expressed by the coefficient of performance) of the device could be increased by up to ten times. A validation of the numerical model was performed through the design, construction and experiments on an improved AER cooling device. The results revealed a maximum specific cooling power of 16 W kg−1 and a maximum temperature span of 3.1 K for the new device. [ABSTRACT FROM AUTHOR]

Highlights • Thermodynamic performance of a FTVI refrigeration cycle was investigated. • Binary mixtures of hydrocarbon refrigerants were used in simulations of a FTVI cycle. • Mixed refrigerants allow a better thermodynamic performance than pure fluids. • Mixed refrigerant R290/R600 60/40 wt% presented the greatest COP. • R170/R290 and R290/R600 presented the best temperature glide matching in the evaporator. Abstract Refrigeration systems are major consumers of electrical energy in many process industries. Hydrocarbons have regained interest as refrigerants because of the increasing restrictions applied to halogenated fluids. In this work, the use of hydrocarbons mixed refrigerants and an alternative flash tank with vapor injection (FTVI) refrigeration cycle were combined. Five different binary mixed refrigerants involving R170 (ethane), R290 (propane), R600 (n-butane) and R600a (isobutane) were studied. Using different refrigerant compositions, the cycle was simulated and optimized for maximum COP, considering a fixed refrigeration capacity in the evaporator to reduce the temperature of a secondary thermal fluid from 281.55 K to 269.15 K. Parameters analyzed were: coefficient of performance, temperature glide in the evaporator and refrigerant mass flow rate. The use of a FTVI led to a COP improvement from 4% to 36% when compared to the traditional vapor compression cycle (VCC). The pair R290/R600 with 60/40 wt% presented the maximum COP of 4.88. [ABSTRACT FROM AUTHOR]

Highlights • A hybrid system including high-temperature fuel cell and absorption chiller is developed. • Nanofluids are employed as absorbent for increasing of COP in the refrigeration system. • Exergy analysis has been conducted for the hybrid fuel cell refrigeration system. • Sensitivity analysis is employed for assessing of main parameters on the system performance. Abstract A hybrid system including high-temperature polymer fuel cell with capacity of 5 kW along with fuel processing unit for producing rich hydrogen from natural gas integrated by a 3 kW absorption chiller has been developed. The waste heat of flue gas from the burners is utilized in the ammonia-water absorption chiller for refrigerating purposes. The hybrid refrigeration system is simulated by Aspen HYSYS software in a steady state condition. After defining the properties of nanoparticles in HYSYS software, the water-based nanofluids are employed as absorbent liquid for increasing of COP in the refrigeration system, and their effects have been evaluated on overall system performance. The electrochemical model of the fuel cell as well as the main parameters of refrigeration system have been validated with experimental results and similar works. Electrical efficiency and overall efficiency of the hybrid system are equal to 36% and 77.3%, respectively. The overall efficiency in the presence of silver nanofluid can be increased up to 81%. Exergy analysis has been conducted for the hybrid system, and the obtained exergy efficiency of the system is equal to 29%. Sensitivity analysis has been employed for evaluating of significant parameters on the hybrid system performance. [ABSTRACT FROM AUTHOR]

Highlights • Investigation of the needed improvement in the properties of magnetocaloric materials. • The requirements for non-magnetic properties are also discussed. • Comparison between the existing refrigerators and simulated magnetic ones. • For demanding conditions and compact designs better materials are needed. Abstract A primary motivation underlying the research on room-temperature magnetic refrigeration is reaching energy efficiency levels beyond what is achievable with vapor-compression technology. However, the goal of building commercially viable magnetic refrigeration systems with high performance and competitive price has not been achieved yet. One of the obstacles to reach this goal is the inadequate properties of the currently existing magnetocaloric materials. In this article, the needed improvements in the properties of the magnetocaloric materials are investigated. Two existing vapor-compression refrigerators are used as reference for the required performance, and magnetic refrigerators are simulated using a numerical model. Apart from the requirements such as uniformity of transition temperature for each layer, small increment in transition temperature in adjacent layers, and mechanical strength of the materials, the study shows that for the investigated cases materials with adiabatic entropy change 2.35 times larger than the existing materials are needed to outperform vapor-compression systems. [ABSTRACT FROM AUTHOR]

Highlights • ANFIS is developed applying different evolutionary algorithms to predict pool boiling heat transfer. • A number of 405 empirical data were obtained from literature to train and test the models. • This model is an easy-to-use tool to estimate nucleate pool boiling heat transfer properties of refrigerant-oil mixtures with nanoparticles. Abstract Performance and improvements of refrigeration systems are greatly related to the nucleate pool boiling heat transfer of refrigerant-oil mixtures containing nanoparticles (h). Empirical correlations have been used previously in order to estimate this parameter. Improved Adaptive Neuro-Fuzzy Inference System (ANFIS) is developed in this research applying different evolutionary algorithms to predict pool boiling heat transfer. To that end, 405 data samples were collected to construct the model and evaluate its performance based on each evolutionary algorithm. PSO-ANFIS model has the most accurate structure compared to other algorithms with R 2= 0.998 and RMSE = 0.031 for all the 405 data samples. Moreover, the applicable domain of developed models was investigated and the dubious samples in the databank were indicated by using a technique based on Leverage algorithm. [ABSTRACT FROM AUTHOR]

Highlights • There are sorbents being thermodynamically more suitable for low driving temperatures. • Specialized zeotypes may have a strongly restricted operation field. • Liquid sorbents and Silica gel are quite flexible for what concerns operation conditions. • Ionic liquids may work at lower driving temperatures than inorganic salts. • Crystallization curves for lithium bromide are given. Abstract Thermally driven cooling machines allow for reduction of CO 2 emissions when using waste heat from industrial processes or cogeneration, or when using solar heat. The lower the necessary driving temperature level is the more heat sources are available to be used, or the more thermal power can be drawn from a heat source, or the smaller and cheaper the heat exchanger for a given power can be. There have been debates for decades whether adsorption chillers can be driven by heat sources at lower temperatures than absorption chillers. The paper at hand intends to continue this debate on a rather fundamental level. The inorganic salt lithium bromide which is the most common absorbent and the common adsorbent RD-Silica gel are compared to organic salts (ionic liquids) as designable absorbents on the one hand, and adsorbents designed for use at low driving temperatures, on the other hand. For that purpose, functions for the vapor pressure depression of the discussed sorbents are required. Simple correlations for the absorbents are derived in this paper, whereas the correlations for the adsorbents are taken from literature. The crystallization lines of lithium bromide derived from experimental data from two different sources are also discussed shortly. From these correlations, the minimum desorption temperature at various boundary conditions is derived for five sorbents and the influence of the desorption temperature on the change of composition in the sorbents is shown. The latter is traced back to the shape of the sorption isotherms. At small temperature lifts the zeotypes and the ionic liquid [mmim][DMP] can be operated with lowest driving temperatures, but at higher temperature lifts the zeotypes are inoperable. Finally, it is concluded that the possibility to tailoring sorbents according to the customer's needs prevails for both liquid and solid sorption as a pre-requisite to operate with very low driving temperatures. [ABSTRACT FROM AUTHOR]

Highlights • An experimental investigation has been conducted on an adjustable TADTAR. • This new design allows for an adjustment of the TADTAR resonator length. • Matching between frequency output of TAE and frequency required by TAR is achieved. • The length adjustment of the resonator alters the performance of the TADTAR. • Through the resonator adjustment, a single device could have different operating points. Abstract An experimental investigation is conducted on a new adjustable thermoacoustically-driven thermoacoustic refrigerator (TADTAR). This refrigerator comprises of a thermoacoustic engine which drives a thermoacoustic refrigerator. This study aims to demonstrate the possibility to alter the TADTAR performance through the adjustment of specific design parameters. An adjustable resonator, which consisted of stacks, spacing couplings and shell-tube heat exchangers was designed and built. Six different honeycomb ceramic stacks were investigated. For each system, three different stack configurations were studied. Measurements of temperature difference across the refrigerator stack and sound pressure levels at steady states were used to determine the performance of the device. Through the adjustment of the length and the insertion of the heat exchanger, the performance of the device with a longer resonator was relatively higher. This study shows that an adjustable resonator successfully alters the frequency output of the thermoacoustic engine to match the frequency required by the thermoacoustic refrigerator and achieve resonance. In addition, this study demonstrates the possibility to change the geometrical configuration of the device and ultimately alter the performance of the TADTAR. Through the adjustment of the length of the resonator, this study shows that a single device could have different operating points. This creates new possibilities to introduce control system able to adjust the geometry of thermoacoustic system while in operation. [ABSTRACT FROM AUTHOR]

Highlights • A thermal transient model (Modelica language) is developed for a display cabinet. • Comparison between experimental and numerical results is presented. • Numerical case studies (load configurations, demand response) are considered. Abstract Open display cabinets are widely used in supermarkets and represent an important contribution to their energy consumption. The present study is related to modeling and experimental characterizations of an open display cabinet in a transient state. The model is based on a simplified zonal approach to determine heat transfer by conduction, radiation and convection within the display cabinet using experimental evaporator outlet temperature as input data. It is used to simulate a fully loaded display case with 5 shelves. The model can be used to predict the dynamic behavior during the on-off process, defrost operations and power failure. The comparison with experimental data obtained on an open display shows a good agreement with simulating results and allows the model to be validated. [ABSTRACT FROM AUTHOR]

This article presents an analysis of the feasibility of R454C and R455A, two new low global warming potential (GWP of 148) refrigerants, in vapor compression refrigeration systems as alternatives to R404A for warm countries. R454C and R455A can be the most viable low GWP options to perform a direct replacement of R404A because of the similar characteristics. They only present meaningful differences in flammability, critical temperature, temperature glide and vapor density. The analysis is based on an experimental comparison of R404A with R454C and R455A, using a fully instrumented experimental setup equipped with Internal Heat Exchanger (IHX) at condensation temperatures that represent operating conditions of warm countries. The experimental results show that cooling capacity of the replacements is slightly lower than R404A, being the Coefficient of Performance (COP) of the new mixtures 10–15% higher than that of R404A, especially at higher condensation temperatures. The results also show that the adoption of an IHX is not recommended with the alternatives due to the discharge temperature increase and the low energy performance benefit. [ABSTRACT FROM AUTHOR]

With the arrival of electrified vehicles, the air-conditioning system has to be reconsidered. Battery cooling management system and high level of comfort for passengers make the single evaporator air-conditioning system a multi-evaporator one. In a multi-evaporator air-conditioning system, evaporating pressures are equal in each evaporator so that evaporators are coupled dynamically. However, the demand in cooling capacity and temperature target can vary from each other. For an operating point with a first evaporator working at high load and a second at low partial load, thermal interaction can occur from the superheated refrigerant coming from a first evaporator to the outlet of a second evaporator. This phenomenon makes the second evaporator sleeping since its expansion valve bulb misreads the superheat and closes. Furthermore, sleeping evaporator looks like an extreme case of refrigerant maldistribution in the evaporator. Refrigerant maldistribution is then investigated to show some drawbacks and advantages multi-evaporator air-conditioning systems (MEAC) have to face or can benefit by comparing two types of expansion valve: thermostatic and electronic ones. In this paper, sleeping evaporator and refrigerant maldistribution phenomena are experimentally investigated in order to propose in the future a robust control of an automotive MEAC. A test bench was built to compare two types of expansion valves (thermostatic/electronic) and study their behaviours in steady and transient state to tackle sleeping evaporators and benefit from refrigerant maldistribution. [ABSTRACT FROM AUTHOR]

The influence of downward vapor stream on the falling film evaporation with nucleate boiling outside a horizontal enhanced tube bundle arrayed in a vertical column is experimentally investigated. The variations in local and bundle averaged heat transfer coefficients with vapor velocity are presented. To simulate the practical condition in a falling film evaporator, the flow passages of the liquid/vapor are constructed using two quartz glass sheets and two columns of dummy half tubes. The test ranges are saturation temperature of 6 °C, film flow rate of 0.035–0.1 kgm –1 s –1 , heat flux of 20, 30, 40 kWm –2 . It is found that (1) the downward vapor effects are either positive or negative depending on the tube position, film flow rate, heat flux and vapor velocity; (2) the bundle effect becomes stronger under the effect of downward vapor stream; (3) the downward vapor has a significant effect on the heat transfer of the lower tubes than the upper tubes; and (4) the vapor stream effect on the bundle averaged heat transfer coefficient varies with the levels of film flow rate and heat flux. The experimental results provide significant guidance in the design of the vapor escape channel in a falling film evaporator. [ABSTRACT FROM AUTHOR]

Heat-powered thermochemical sorption refrigeration is a promising technology due to its distinct advantage of energy-saving and the close coincidence of cooling demands with the available solar thermal energy. In this paper, an advanced heat-powered thermochemical sorption refrigeration prototype using SrCl 2 /NH 3 working pair is developed for air-conditioning and deep-freezing process with the utilization of low-grade heat. Expanded graphite (EG) is used as porous matrix to enhance the heat and mass transfer of strontium chloride by preparing EG/SrCl 2 composite sorbent. Experimental results showed that the proposed refrigeration prototype can produce the cooling capacity with a refrigeration temperature from 5 to −15 °C by effectively utilizing thermal energy with a temperature below 100 °C. The system COP varies between 0.13 and 0.22 and the SCP ranges from 115 to 185 W kg −1 at the heat sink temperature of 25 °C and the global conversion reaches about 0.42. At the constant heat source temperature, the lower heat sink temperature contributes to the higher global conversion of reactive salt. The sorption reaction platforms of SrCl 2 /NH 3 working pair corresponding to different evaporation temperatures are analyzed during the adsorption–evaporation phase. Potential development is analyzed and proposed for further improving system COP by reducing the mass ratio of metal and reactive salt in the solid–gas reactor and enhancing the global conversion of reactive salt as much as possible with the optimization construction of the reactor and better performance of heat and mass transfer of composite sorbent. [ABSTRACT FROM AUTHOR]

Air flow distribution in chilled food facilities plays a critical role not only in maintaining the required food products temperature but also because of its impact on the facility energy consumption and CO 2 emissions. This paper presents an investigation of the thermal environment in existing food manufacturing facilities, with different air distribution systems including supply/return diffusers and fabric ducts, by means of both in-situ measurements and 3D CFD simulations. Measurements and CFD simulations showed that the fabric duct provides a better environment in the processing area in terms of even and low air flow if compared to that with the diffusers. Moreover, temperature stratification was identified as a key factor to be improved to reduce the energy use for the space cooling. Further modelling proved that air temperature stratification improves by relocating the fabric ducts at a medium level. This resulted in a temperature gradient increase up to 4.1 °C in the unoccupied zone. [ABSTRACT FROM AUTHOR]

Machine 2R is necessary in order to avoid the release of refrigerant during the repair of an air conditioning machine. The main goals of this paper are to determine the rate of exergy transfer, the rate of exergy destruction and the rate of exergy change in the compressor, condenser, oil separator and 2R machine. This study also determines the performance of the 2R machine. Pressure, temperature and mass of the refrigerant were measured every 0.5 minutes for 10 minutes. In conclusion, the results of this analysis show that the rate of destruction exergy in the compressor is 59.98%, and 25.37% in the condenser. The value of the Residual Trapped Refrigerant (RTR) of recycling and recovery machine meets the AHRI standard, that is, 34 grams, and the value of the Refrigerant Loss (RL) complies with the AHRI standard, which is 10 grams, while its performance is 91.2%. [ABSTRACT FROM AUTHOR]

A cooling experiment using flake ice was carried out on a stack of fish and a PVC plate in an expanded polystyrene box. The experiment on fish makes it possible to determine the cooling kinetics of the product according to its position and to validate the models which predict the product temperature changes with time. The first model is based on 2D Computational Fluid Dynamics and the second one is a 1D analytical model. To take into account the imperfect contact between the product and the flake ice due to the presence of air, an additional heat-resistant layer with an equivalent thickness between the fish and the flake ice was identified. This thickness depends on the size of the flakes and the air spaces between the flakes. Simple correlations to predict the cooling times of fish located at the bottom of the stack, where the cooling rate is the slowest, were proposed as a function of the stack thickness. [ABSTRACT FROM AUTHOR]

In this study an experimental analysis was carried out about a counter flow Ranque–Hilsch vortex tube with different nozzle materials. In order to observe the influences of working fluids on vortex tube, thermal performance oxygen and air were used as working fluids for different inlet pressure. Fiberglass, aluminum and steel were used as nozzle materials. The main object of this study is to investigate thermal effect of nozzle materials and working fluids on thermal performance of the vortex tube. Experimental studies were made by using three different nozzle materials (fiberglass, aluminum and steel) with inlet pressure between 150 kPa to 700 kPa with arrange of 50 kPa increment. The fraction of cold mass was kept at 0.36 and the ratio of vortex tube (L/D) was taken 10. Also an exergy analysis was carried out for each case. This study revealed that steel as a nozzle material has the highest value of temperature gradient for air as a working fluid. [ABSTRACT FROM AUTHOR]

Intermittent gas flow generates pressure oscillations in the twin-screw refrigeration compressor that cause serious problems such as structural vibration and noise. In order to reduce the amplitude of this pressure pulsation, a pressure pulsation dampener (PPD) applied in the discharge chamber of a twin screw refrigeration compressor was proposed based on the theory of Helmholtz resonator. A mathematical model was developed to design an optimal PPD by incorporating the R134-oil mixture sound speed model and the pressure pulsation simulation model. A comprehensive experimental study was then performed to validate the model and evaluate the effect of key parameters such as oil flow rate and cavity volume on attenuation performance of the PPD. Vibrational characteristics of the compressor equipped with and without the PPD were also measured and compared. Under the design frequency of 250 Hz, the vibrational acceleration of compressor under-chassis reduced by 36.2% to 41.1% when the compressor was fitted with the proposed PPD. [ABSTRACT FROM AUTHOR]

A numerical study of conjugated heat transfer in ceiling-slot refrigerated containers is carried out to analyze the temperature distribution effectiveness and to determine the ventilation characteristics. The effect of slot size on thermal characteristics is studied by considering half-span and full-span injection. The container walls are defined as conductive opaque and are interacting with outside environment. The outer surface heat transfer coefficients of conductive walls are computed by studying the flow around the refrigerated truck. The Reynolds number at the slot exit varied between 2 × 10 4  ≤ Re ≤ 2 × 10 5 . The gravity effect is taken into account, and the coupled mass, momentum, and energy equations are discretized in finite volumes. The heat transfer coefficients of inner flow are presented as plots of the mean Nusselt number versus the modified Reynolds number. The maximum dispersion in the numerical data being at 14.54-percent, the mean Nusselt number, the modified Reynolds number, and the aspect ratio of the container are correlated. [ABSTRACT FROM AUTHOR]

Kigali's amendment on Montreal Protocol has recognized the great impact of hydrofluorocarbons (HFCs) on climate change. In the European Union, the Regulation (EU) No. 517/2014 (F-gas Regulation) controls the use of HFCs in several applications. This paper reviews the recent investigations performed because of F-gas Regulation, with focus on lower global warming potential (GWP) synthetic alternatives. The GWP limit and the date of prohibition have an influence on the studies found for each application. The major relevance of the studies has been observed on mobile air conditioners for pure hydrofluoroolefins (HFOs), possibly caused by the earlier control. Additionally, a great number of studies have been found for stationary refrigeration systems using several mixtures and residential air conditioners using R32. An important number of articles investigate synthetic alternatives for domestic refrigerators given the flammability barriers for hydrocarbons in some countries. Despite higher GWP allowance on cascade supermarket systems, few articles are available on this topic. Given the extent of the current studies and the rate of new refrigerant developments, an increase in studies using the new synthetic mixture is expected in the coming years. [ABSTRACT FROM AUTHOR]

In the present study, tests were performed to investigate the direct expansion evaporation characteristics of ammonia on shell side of triangular pitch plain tube bundle at saturation temperature of −1.7 °C and −20 °C, with heat flux ranging from 5 to 45 kW m −2 , and inlet quality from 0 to 30% with exit degree of superheat ranging from 2 to 10 °C. The results suggest that heat transfer coefficient increases with both saturation temperature and heat flux and decreases with degree of exit superheat. The inlet quality effects were more significant at higher saturation temperature than at lower saturation temperature. A correlation was developed for outside boiling of ammonia on plain tube bundle in direct expansion mode with inlet vapor quality and compared with previous pool boiling and bundle correlations with ammonia as a refrigerant. [ABSTRACT FROM AUTHOR]

This work analyses experimentally the possibility of using the reduced GWP refrigerant R-407H (HFC family, GWP = 1378) as drop-in substitute of R-404A (HFC family, GWP = 3945) in low temperature centralized direct expansion refrigeration system. The experimental plant and the test methodology are described. It covered top up or partial drop-in and energy consumption tests at −20 °C of product temperature and 25, 35 and 45 °C of condensing temperature using a small-scale supermarket under laboratory conditions. It has been measured that the use of R-407H instead of R-404A is favourable from the point of view of energy efficiency. Reductions in the energy consumption of up to 7.7% (compressor) and 4.0% (whole system) have been measured. However, there is an increment in the compressor's discharge temperature of up to 13.8 K. In addition, the operation of the system with both refrigerants was correct. [ABSTRACT FROM AUTHOR]

The lowest attainable refrigeration temperature of a nitrogen based Joule–Thomson refrigerator is generally limited to 77 K since the compressor suction pressure is usually higher than atmospheric pressure. The Joule–Thomson process with an ejector is proposed to achieve a refrigeration temperature as low as 68 K by adjusting the evaporation pressure down to 28 kPa and boosting the return stream pressure up to 147 kPa. A one-dimensional numerical model is developed to predict the performance of the ejector at cryogenic temperature, and its accuracy is compared with experimental data. The analysis results show that the addition of the ejector in the Joule–Thomson refrigeration cycle increases up to 5 times the overall efficiency, where the maximum achievable COP and exergy efficiency are 0.0195 and 6.65%, respectively. Other featured advantages of the proposed Joule–Thomson refrigeration cycle with ejector are the simplicity of cycle, minimization of mechanical moving components, cost effectiveness, and high reliability compared to other cryogenic refrigeration methods using pumps or cold compressors in Joule–Thomson cycles. [ABSTRACT FROM AUTHOR]

This paper proposes a system design of an Adaptive Food Preservation System (AFPS). It is motivated by the fact that constant storage condition in today's refrigerators has deficiency. Customized storage with fast freezing capability can better manage food quality and energy efficiency. Key components include AFPS packages and vortex tubes. Superior fast freezing capability is demonstrated by comparisons with benchmarks from refrigerator tests and regulatory standards, and experimentation with a simulated test setup at various settings of input. Theoretical and analytical models are proposed to predict package inlet and exit temperatures, freezing capacities, and freezing efficiencies. At 7 bar inlet pressure, the maximum available freezing efficiency, mean efficiencies with vacuum insulation and with ABS insulation of the AFPS Package and Vortex Tube Assembly are 6%, 4.66%, and 2.80%, respectively. AFPS technology consumes 0.18% in time and 45% in energy during fast freezing comparing with what a typical household freezer does. [ABSTRACT FROM AUTHOR]

There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature range −1.7 to −20 °C, heat flux range 5 to 45 kW m −2 and exit superheat range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in heat transfer coefficient was observed with saturation temperature and heat flux. The effect of exit super heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Plant Science is the property of Canadian Science Publishing 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.)

The high operating pressure of a twin-screw compressor employed in high temperature heat pump or NH 3 /CO 2 cascade refrigeration systems often leads to extremely large axial force on the compressor rotors. Accurate calculation of this axial force is very important in selection of bearing and design of balancing pistons. In this paper, an experimental study of the axial force on the twin-screw compressor rotors was conducted. The variations of the axial force under different operating conditions were investigated. Furthermore, the axial force was also calculated by employing the mean pressure model and sector pressure model, and was compared with that of the experimental results. It was concluded that the sector pressure model is more accurate in predicting the axial force on the rotors in comparison with that of the mean pressure model. However, the mean pressure model was more accurate under operating conditions with large built-in volume ratio. Moreover, the axial force on the rotor end face was found to have larger influence than that on the rotor helical surface. [ABSTRACT FROM AUTHOR]