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The widespread deployment of microwaves in domestic, commercial and industrial food processing operations, necessitates quality assurance. This review critically assesses key microwaved-food quality assurance issues such as process lethality, product degradation mechanisms, non-uniform heating and volumetric temperature sensing. Non-uniform heating, the root-cause of quality assurance problems, is shown to have negative consequences on process energy consumption, and linked to the poor controllability of conventional microwave power sources, magnetrons. A case is therefore made for the use of solid-state generators as alternative power sources by a cost-benefit analysis, which includes energy and reliability aspects. The feasibility of a paradigm shift to solid-state power delivery in the development of smart processing systems, is shown, and potential commercialisation opportunities, identified. [ABSTRACT FROM AUTHOR]

As a natural working fluid, CO 2 has been widely applied in refrigeration systems where heat is conventionally released to ambient through external airflow. Owing to its extraordinary thermophysical properties, especially a low critical temperature, the CO 2 heat release through a high-pressure side heat exchanger will inevitably undergo either supercritical or subcritical processes, depending on ambient air temperatures and head pressure controls. Correspondingly, the heat exchanger will act intermittently as either a gas cooler or condenser within the system during an annual operation. Such evidence should therefore be taken into account for an optimal design of the heat exchanger and head pressure controls in order to significantly enhance the performance of both components and the associated system. To achieve these targets, two CO 2 finned-tube gas coolers/condensers with different structural designs and controls have been purposely built, instrumented and connected with an existing test rig of a CO 2 booster refrigeration system. Consequently, the performance of the CO 2 gas coolers/condensers with different structure designs, controls and system integration at different operating conditions can be thoroughly investigated through experimentation. In the meantime, models of the finned-tube CO 2 gas coolers/condensers have been developed using both the distributed (detailed model) and lumped (simple model) methods. The former is employed to give a detailed prediction of the working fluid temperature profiles, localised heat transfer rates and effects of pipe circuitry arrangements, while the latter is suitable for the simulation and optimisation of system integration with less computation time. Both models have been validated with measurements, and moreover the simple model has been integrated with other component models so as to create a system model. The effects of the CO 2 gas cooler/condenser sizes and controls on the system performance can thus be compared and analysed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Application of supermarket energy control system model. [•] Heat recovery from CO2 refrigeration system in supermarket space conditioning. [•] Effect of pressure controls of CO2 refrigeration system on heat recovery potentials. [•] Control optimization of CO2 refrigeration system for heat recovery in supermarket. [Copyright &y& Elsevier]

There is increasing interest in using phase change materials (PCMs) to store energy within refrigeration equipment. The main purpose is to increase the thermal capacity of the equipment and maintain product temperature within safe limits during frequent door openings, on–off cycling of the compressor and mains power failure. This paper considers candidate phase change materials for application in chilled food refrigeration cabinets for product temperature range between 0°C and +5°C. The results showed that paraffin products exhibited negligible supercooling but have low latent heat compared to water based products which have higher latent heat but exhibit a greater degree of supercooling. The addition of appropriate quantities of nucleate agent (AgI) can reduce supercooling significantly, making water based products suitable for use as PCMs for cold storage in chilled food cabinets. [ABSTRACT FROM AUTHOR]

Abstract: A modern supermarket energy control system has a concurrent need for electricity, space heating or cooling, and food refrigeration. The power supply to the supermarket is primarily from the national grid, where losses in efficiency are due to the processes of energy conversion and transmission. Combined heat and power (CHP) offers the potential to locally produce electrical power and heating which could save energy and reduce CO2 emissions in the long run. During the summer months, as the space heating requirement in a supermarket is relatively small, the energy efficiency of a CHP installation can be improved by using excess thermal energy to drive a sorption refrigeration system to provide space cooling or refrigeration. This process is also known as tri-generation. In recent years, the use of CO2 as a refrigerant in supermarkets has received considerable attention due to its negligible contribution to direct greenhouse gas emissions and excellent thermophysical and heat transfer properties. Consequently, the application of a tri-generation system in a supermarket with CO2 refrigeration merits further investigation. In this paper, to evaluate the performance of a tri-generation system in the supermarket, a previously tested 80kWe microturbine device was applied into an operational supermarket to generate power and provide space heating and cooling through exhaust heat. The performance evaluation and comparison for this tri-generation application is based on the prediction from an integrated model of supermarket energy control, cascade CO2 refrigeration and tri-generation systems. The results from this simulation demonstrate the feasibility of a tri-generation system in the supermarket and pave the way for further consideration towards designs in future. [Copyright &y& Elsevier]

Abstract: Continuous frying systems are very energy intensive. They also involve the interaction of many variables and complex heat and mass transfer processes. Better control of these processes can lead not only to improved product quality but also energy reduction. This paper presents a model that can simulate the dynamic behaviour of a continuous frying system in sufficient detail that enables the influence of controls on the important product attributes of moisture and oil content to be investigated. A conjugate 2-D transient model of the fryer was used to develop correlations for the oil and moisture content based on the important fryer control variables, namely supply oil temperature, potato mass throughput, fryer paddle velocity and crisp takeout velocity. The correlations were validated against data for an industrial continuous fryer system and used within the overall frying system model which was implemented in MATLAB. Proportional Integral (PI) controls implemented within the MATLAB/Simulink environment have shown that closer control of the important parameters can lead to 10% energy savings compared to the actual industrial frying system. The modelling approaches developed can also be used to investigate further improvements in the design and control of continuous frying systems. [Copyright &y& Elsevier]

Abstract: This paper reports on the development, experimental validation and application of a semi-empirical model for the simulation of the phase change process in phase change materials (PCM). PCMs are now increasingly being used in various building materials such as plasterboard, concrete or panels to improve thermal control in buildings and accurate modelling of their behaviour is important to effectively capture the effects of storage on indoor thermal conditions. Unlike many commercial simulation packages that assume very similar melting and freezing behaviour for the PCM and no hysteresis, the methodology employed treats the melting and freezing processes separately and this allows the inclusion of the effect of hysteresis in the modelling. As demonstrated by the results in this paper, this approach provides a more accurate prediction of the temperature and heat flow in the material, which is of particular importance in providing accurate representation of indoor thermal conditions during thermal cycling. The difference in the prediction accuracy of the two methods is a function of the properties of the PCM. The smaller the hysteresis of the PCM, the lower will be the prediction error of the conventional approach, and solution time will become the determining factor in selecting the simulation approach in practical applications. [Copyright &y& Elsevier]

Abstract: Phase change materials (PCMs) are increasingly being used for thermal energy storage in buildings and industry to produce energy savings and reduce carbon dioxide emissions. PCM slurries are also being investigated for active thermal energy storage or as alternatives to conventional single phase fluids because they are pumpable and have advanced heat transport performance with phase change. The present study investigates several types of phase change materials for the preparation of PCM slurries which have potential for cooling applications. The thermophysical properties of paraffin in water emulsions, such as latent heat of fusion, melting and freezing temperature ranges, viscosity and the effect of surfactants, have been tested using appropriate experimental techniques. It has been identified that the use of small quantities of higher melting temperature paraffin and surfactants in the emulsion can reduce the effect of supercooling and increase the useful heat of fusion. However there are negative impacts on viscosity which should be considered in heat transport applications. [Copyright &y& Elsevier]

Abstract: The environmental impact of supermarkets is significant not only because of the indirect effect from CO2 emissions at the power stations but also due to the direct effect arising from refrigerant leakage to the atmosphere. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of CO2 refrigeration and trigeneration systems where the refrigeration generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. This paper reports on experimental and theoretical investigations of such a system and its potential application in a supermarket. The results show that the system can offer energy savings of 30%, greenhouse gas emission savings of 43% and a payback period of just over 3 years compared to conventional systems. [Copyright &y& Elsevier]

Abstract: The CO2 refrigerant is widely applied in retail refrigeration systems to replace HFC fluids such as R404A, but its system performance requires further improvement. One feasible method would be to pinpoint the matching components of the system, in particular its evaporator coils. This paper focuses on the potential optimization of the CO2 evaporator design in an existing multi-deck medium temperature display cabinet charged previously with R404A refrigerant. To achieve this target, a display cabinet model with an integrated CFD and detailed evaporator sub models was utilized. This model could readily imitate the actual cabinet performance under varied operating conditions and component designs. Various design options of the CO2 cabinet evaporator were considered and their impacts on the cabinet performances were predicted by the integrated model. Ultimately, the optimized designs of CO2 cabinet evaporator coil geometries and refrigerant side operating parameters have been attained. [Copyright &y& Elsevier]

Abstract: Due to less environmental impact, the CO2 booster refrigeration system has been widely applied in the modern supermarket as a substitute for the conventional R404A multiplex system. However, the performance efficiency of the CO2 system still requires further improvement in order to save energy; thus, one of the most efficient techniques would be to investigate and employ the optimal controls for refrigerant high side pressures at various operating states. In this paper, the possible parameters affecting system efficiency of the CO2 system in the transcritical cycle at a higher ambient air temperature are identified through thermodynamic analysis, but cannot be quantified mathematically because of the high non-linearity involved. Instead, sensitive analyses of the system by means of the thermodynamic model is used to examine the effects of parameters including high side refrigerant pressure, ambient air temperature, refrigerant intermediate pressure, and medium and low evaporating temperatures, superheating, effectiveness of suction line heat exchanger, and compressor efficiency on system performance. Consequently, the optimal high side pressure in the transcritical cycle is established and derived as a function of three important parameters consisting of ambient air temperature, the effectiveness of suction line heat exchanger and compressor efficiency. In addition, optimal operating parameters such as the intermediate pressure are also proposed to improve the system performance. [ABSTRACT FROM AUTHOR]

Abstract: Conventional supermarket refrigeration systems are responsible for considerable CO2 emissions due to high energy consumption and large quantities of refrigerant leakage. In the effort to conserve energy and reduce environmental impacts, an efficient design tool for the analysis, evaluation and comparison of the performance of alternative system designs and controls is required. This paper provides a description of the modelling procedure employed in the supermarket simulation model ‘SuperSim’ for the simulation of the performance of centralised vapour compression refrigeration systems and their interaction with the building envelope and HVAC systems. The model which has been validated against data from a supermarket has been used for the comparison of R404A and CO2 refrigeration systems and the optimisation of the performance of transcritical CO2 systems. These results are presented in Part II of the paper. [Copyright &y& Elsevier]

Abstract: As described in Part I, the supermarket simulation software “SuperSim” with its integrated refrigeration, building and HVAC system models, can be used to evaluate, compare and optimize alternative supermarket refrigeration systems. In Part II the model was used to evaluate and compare the performance of a CO2 booster refrigeration system with that of a conventional R404A multiplex system in a supermarket application. Floating head pressure control was implemented for both systems when they were in subcritical cycles. For the CO2 system, when the system was in transcritical cycle due to higher ambient air temperature, the head pressure was optimized through extensive thermodynamic cycle analysis as a function of ambient air temperature. The performance of the CO2 booster system in the supermarket was then simulated during a one year period and compared with that of the R404A system. As a result, the system performance will benefit from a lower ambient temperature and a sizeable heat recovery for the CO2 system. [Copyright &y& Elsevier]

Abstract: In this paper, the model for the multi-deck medium temperature display cabinets is developed with the integration of CFD and cooling coil sub-models. The distributed method is used to develop the cooling coil model with the airside inputs from the outputs of the CFD model. Inversely, the airside outputs from the cooling coil model are used to update the boundary conditions of the CFD model. To validate this cabinet model, a multi-deck medium temperature display cabinet refrigerated with a secondary refrigerant cooling coil was selected as a prototype and mounted in an air conditioned chamber. Extensive tests were conducted at constant space air temperature and varied relative humilities. The cabinet model has been validated by comparing with the test results for the parameters of air at different locations of the flow path, and temperatures of refrigerant and food product, etc. The validated model is therefore used to explore and analyse the cabinet performance and control strategies at various operating and design conditions. [Copyright &y& Elsevier]

Abstract: A test rig for a tri-generation system was set up in the laboratory to investigate the system performance and application feasibility. The rig was composed of three modules, a power component containing a microturbine, a refrigeration unit consisting of an absorption chiller with gas pipe connection, and a supermarket section containing a display cabinet. This system was supposed to be effectively applied into a supermarket energy control system where cooling, heating and electricity power are simultaneously required and subsequently, valuable test results have been produced. In the mean time, a simulation model for the particular tri-generation system has been established by integrating the component models of the system in accordance with the components’ actual flow paths and energy streams. These component models, which include a compressor, recuperator, combustion chamber, gas turbine, electric generator, gas pipes, generator (desorber), rectifier, absorbers, condenser and evaporator etc., were developed based upon the balance of heat and mass. The calculations of heat transfer and phase equilibrium were included in the component models and chemical reaction balances were considered in the model of the combustion chamber. The system model has been validated with the test results and has consequently been used to predict the system performance at different operating and design conditions, such as varied ambient temperature, fuel flow rate and pressure ratio etc. The ultimate results of the performance analysis formulated by the system model can contribute significantly to the optimal component and system designs in various practical applications. [Copyright &y& Elsevier]

Abstract: This paper describes a detailed procedure into the investigation of optimised control strategies for CO2 cycles in medium temperature retail food refrigeration systems. To achieve this objective, an integrated model was developed composing of a detailed condenser/gas cooler model, a simplified compressor model, an isenthalpic expansion process and constant evaporating temperature and superheating. The CO2 system can operate subcritically or transcritically depending on the ambient temperature. For a transcritical operation, a prediction can be made for optimised refrigerant discharge pressures from thermodynamic cycle calculations. When the system operates in the subcritical cycle, a floating discharge pressure control strategy is employed and the effect of different transitional ambient temperatures separating subcritical and transcritical cycles on system performance is investigated. The control strategy assumes variable compressor speed and adjustable air flow for the gas cooler/condenser to be modulated to achieve the constant cooling load requirement at different ambient conditions. [Copyright &y& Elsevier]

A detailed energy and exergy analysis of the low global warming potential refrigerants R744 and R290 was preformed and compared against the commercial refrigerant R404A in a single-stage vapour compression cycle and R744 in a two-stage vapour compression cycle with an internal heat exchanger. [ABSTRACT FROM AUTHOR]

This paper presents the simulation of a low-temperature gas-fired ammonia–water absorption chiller for refrigeration applications. The model was developed as part of a research effort to investigate microturbine-based tri-generation systems for application in the food retail industry. The absorption chiller model was developed in the TRNSYS environment by integrating the main component models in the system and will form part of an overall TRNSYS-based supermarket model. The chiller model was validated against experimental results obtained on a 12 kW absorption chiller in the laboratory. The model was subsequently used to investigate the influence of important design and operating parameters on the performance of the chiller. [ABSTRACT FROM AUTHOR]

Abstract: An analytical model is developed to characterize the radiative transport process in highly porous, open-celled metal foams having idealized cellular morphologies in terms of fundamental radiative parameters such as emissivity, reflectivity and configuration factors. In comparison with the conventional two-flux approach or the diffusion approximation utilizing the Rosseland mean coefficient, the present model is explicit and yet relatively simple. Overall, the predicted effective radiative conductivity as a function of pore size and relative density (defined as the ratio of foam density to solid density) agrees well with that measured using a guarded-hot-plate apparatus for steel alloy foams. A systematic parametric study is subsequently carried out. The contribution of reflectance to thermal radiation is found to be significant, up to 50%, but the effect of temperature gradient is relatively small. The equivalent radiative conductivity increases linearly with increasing cell size for a fixed relative density, whilst for a given cell size the variation of relative density only has a small effect on radiation due to the mixed effects of increased emission and extinction. [Copyright &y& Elsevier]

Abstract: The food industry, both food manufacturing and retailing has a need for heating and electrical power as well as refrigeration. Invariably, plant is installed, which consists of heating systems employing low pressure hot water, high pressure hot water or steam, vapour compression refrigeration systems and an electrical power supply derived from the National Grid. The overall utilisation efficiency of these processes is low, because of the relatively low electricity generation efficiency in power stations and distribution losses in the grid. A way of increasing the energy utilisation efficiency of food manufacturing and retail facilities is through tri-generation. This paper considers tri-generation technology and the feasibility of its application to the food retail industry and examines the economics and environmental impacts of the technology compared to conventional systems. The results indicate that the economic viability of these systems is dependent on the relative cost of natural gas and grid electricity. The system investigated can provide payback periods of less than 4.0 years when the relative cost of gas to electricity is below 0.3. [Copyright &y& Elsevier]

Abstract: The environmental impact of refrigeration systems can be reduced by operation at higher efficiency and reduction of refrigerant leakage. Refrigerant loss contributes both directly and indirectly to global warming through inefficient system operation, increased power consumption and greenhouse gas emissions and higher maintenance costs. Existing sensor-based leak detection methods are limited by the inability to detect gradual leakage and the need for careful sensor location. There is a requirement for a real-time performance monitoring approach to leak detection and fault diagnosis which overcomes these disadvantages. This paper reports on the development of a fault diagnosis and refrigerant leak detection system based on artificial intelligence and real-time performance monitoring. The system has been used successfully to distinguish between faulty and fault free operation, steady-state and transient operation, leakage and over charge conditions. Work currently underway is aimed at testing additional fault conditions and establishing further rules to distinguish between these patterns. [Copyright &y& Elsevier]

Abstract: This paper provides an overview of existing ice slurry cooling applications, and highlights areas of research and development that could lead to future applications. The material presented is a compilation of information published in the open literature by designers, consultants, manufacturers and users of the technology. In many applications significant operating savings have been realised. With further research and development, the number of applications is likely to increase and the capital cost of equipment reduced. This is expected to increase the attractiveness of the technology to potential users. [Copyright &y& Elsevier]

The objective of this paper is to examine solar cooling and low energy cooling technologies. A brief review of various cooling systems is presented, including solar sorption cooling, solar-mechanical systems, solar related air conditioning, and other low energy cooling technologies. The relative efficiencies and applications of the various technologies are presented. These technologies can be utilized to reduce both the energy consumption and environmental impact of mechanical cooling systems. [Copyright &y& Elsevier]

This study uses the TRNSYS computer program, for the modelling and simulation of the energy flows of modern houses, to examine measures to reduce the thermal load. For the calculations, a typical meteorological year (TMY) and a typical model house are used. The measures examined are natural and controlled ventilation, solar shading, various types of glazing, orientation, shape of buildings, and thermal mass. In summer, ventilation leads to a maximum reduction of annual cooling load of 7.7% for maintaining the house at 25 °C. The effect depends on the construction type, with the better-insulated house saving a higher percentage. Window gains are an important factor and significant savings can result when extra measures are taken. The saving in annual cooling load, for a well-insulated house, may be as much as 24% when low-emissivity double glazing windows are used, which are recommended since the payback period is short (3.8 years). Overhangs may have a length over windows of 1.5 m. In this way, about 7% of the annual cooling load can be saved for a house constructed from single walls with no roof insulation. These savings are about 19% for a house constructed from walls and roof with 50 mm insulation. The shape of the building affects the thermal load. The results show that the elongated shape shows an increase in the annual heating load, which is between 8.2 and 26.7% depending on the construction type, compared with a square-shaped house. Referring to orientation, the best position for a symmetrical house is to face the four cardinal points and for an elongated house to have its long side facing south. In respect to thermal mass, the analysis shows that increasing the wall and roof masses and utilizing night ventilation is not enough to lower the house temperature to acceptable limits during summer. Also, the analysis shows that the roof is the most important structural element of the buildings in a hot environment. The roof must offer a discharge time of 6 h or more and have a thermal conductivity of less than 0.48 W/mK. The life-cycle cost analysis has shown that measures that increase the roof insulation, pay back in a short period of time, between 3.5 and 5 years. However, measures taken to increase wall insulation pay back in a long period of time, of about 10 years. [Copyright &y& Elsevier]

• Design of CO 2 -enriched greenhouses using captured CO 2 from a biogas to biomethane upgrading unit. • Economic and environmental assessment of the proposed CO 2 Utilization route. • Comparison with CO 2 geologically stored plant configurations. • CO 2 utilization route exhibits better economic performance than the CO 2 storage case. • Net greenhouse gas emission savings for the Utilization case are strongly dependent on system/boundary assumptions. Anaerobic digestion plants enable the production of power, heat and fuel. Biogas can be upgraded to biomethane fulfilling grid injection requirements by separating CH 4 from CO 2. By- product CO 2 could be geologically stored or utilized as a feedstock to produce valuable goods, enabling in both cases negative climate change impact fuel production. CO 2 utilization could as well improve plant economics, as a consequence of the profits related to the commercialization of the final products whilst allowing further emission reductions. In this paper, a techno-economic assessment of the use of the CO 2 by-product in CO 2 -enriched agricultural greenhouses for tomato production is discussed. The results of the research show that, depending on the operating mode and the design approach, the use of a greenhouse enables the recovery of 14–67% of the by-product CO 2 when the internal CO 2 concentration is kept at 1000 ppm. In addition, it is estimated that the associated heat and power demand ranges from 0.097 to 0.138 kWh th /kg of used CO 2 and 0.04–0.05 kW e /kg of used CO 2 , respectively. Revenues related to the tomato production are partially offset by the greenhouse capital investment and operating costs; however, a net profit between 16 and 19 p/kg of used CO 2 was calculated, leading to a net profit of 1.3–1.6 p/kWh of injected biomethane. These results show that CO 2 utilization is technically feasible and economically more convenient than CO 2 storage. While both geological storage and CO 2 utilization would allow negative climate change impact fuel production, the net greenhouse emission savings for the utilization configuration were found to be strongly dependent on the assumptions regarding fuel substitution for the produced biomethane. [ABSTRACT FROM AUTHOR]

Employing phase change materials (PCMs) for latent heat storage (LHS) application has a great potential to improve a solar thermal system performance. Despite this fact, the use of PCM in this area is quite limited due to the poor thermal conductivity of available PCMs. Therefore, heat transfer enhancement is one of the essential strategies that can overcome this obstacle. In this paper and related project, a PCM heat exchanger (HX) is purposely designed with spiral-wired tubes and integrated in an indirect solar assisted heat pump test system. Although the spiral-wired tube has not been applied in a PCM HX, it is expected to enhance significantly the PCM heat transfer and heat storage performance. To verify this and understand the PCM heat storage and releasement processes, a detailed 3D CFD model has been developed for the PCM HX and validated with measurements. The temperature variations and visualizations of the PCM during charging and discharging processes are therefore simulated and presented temporally. Furthermore, the effects of different inlet heat transfer fluid flow rates and temperatures on the PCM melting/solidification time are demonstrated in this study. Some significant simulation results have been obtained which can instruct efficiently the operation of the heat exchanger and its integration with the solar system. [ABSTRACT FROM AUTHOR]

Refrigeration systems are crucial in retail food stores to ensure appropriate merchandising of food products. This paper compares four different CO 2 refrigeration system configurations in terms of cooling performance, environmental impact, power consumption and annual running costs. The systems studied were the conventional booster refrigeration system with gas bypass (reference system), the all CO 2 cascade system with gas bypass, a booster system with a gas bypass compressor, and integrated cascade all CO 2 system with gas bypass compressor. The weather conditions of London, UK, and Athens, Greece, were used for the modelling of energy consumption and environmental impacts to represent moderate and warm climatic conditions respectively. The control strategies for the refrigeration systems were derived from experimental tests in the laboratory on a conventional booster refrigeration system. The results from the analysis showed that the CO 2 booster system with gas bypass compressor can provide best performance with 5.0% energy savings for the warm climate and 3.65% for the moderate climate, followed by the integrated cascade all CO 2 system with gas bypass compressor, with 3.6% and 2.1% savings over the reference system for the warm and moderate climates respectively. [ABSTRACT FROM AUTHOR]

Solar assisted heat pump systems have been widely applied in domestic hot water productions due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Accordingly, a test rig of a new indirect solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The IDX-SAHP system consists of three operational loops: solar thermal, solar assisted heat pump and load profile. A PCM heat exchanger tank was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. In addition, an air cooling heat exchanger was also installed in the solar thermal loop to absorb heat from the ambient air for the heat pump. A detailed control strategy has been designed and implemented for the system for efficient operation in different modes and maintain constant load supply water temperature during an operational day. In different weather conditions of sunny and overcast, comprehensive measurements were carried out on the test rig and system structures with and without the PCM tank. Test results showed that the system could efficiently meet the daily domestic hot water demand and the PCM heat exchanger integration exerted a significant effect on system stability and performance efficiency. Quantitatively, the average COP of the IDX-SHAP system with a PCM tank could increase 6.1% and 14.0% on sunny and cloudy days respectively compared to systems without PCM tank integration. [ABSTRACT FROM AUTHOR]

In this work the application of macroencapsulated Phase Change Materials (PCM) on the envelope of a typical dwelling in the Mediterranean region is evaluated. This is the first time PCMs are evaluated for application under the specific climatic conditions of Cyprus. The simulation process is carried out using Transient Systems Simulation software (TRNSYS). Two types of simulations have been carried out: the energy rate control test and the temperature level control test. The energy savings achieved by the addition of the PCM layer on the envelope of the test cubicle compared to the base case (no insulation) ranged between 21.7 and 28.6%. The optimum PCM case was also combined with a common thermal insulation topology in Cyprus. The results showed that the maximum energy savings per year was achieved by the combined case (66.2%). In the temperature level control test the constructions containing PCM performed better during summer. The results of the optimum PCM case and the combined case were economically evaluated using Life Cycle Cost (LCC). The results of this analysis showed that the PCM case has a very long payback period (14 ½ years) while this is changing when it is combined with insulation where the payback period is reduced to 7 ½ years. [ABSTRACT FROM AUTHOR]

In this paper, 2D CFD models have been developed for a prototype refrigerated open type multi-deck display cabinet with and without integrated phase change material (PCM). The models can predict the effect of adding a PCM container on cabinet efficiencies, air temperature distributions, product temperatures and air flow patterns inside the cabinet at a range of operating conditions including space air temperatures and evaporator air velocities. To validate the cabinet models, the prototype cabinet was mounted in an air conditioned chamber and extensive experiments were conducted at constant space air temperature and relative humidity. The cabinet models have therefore been validated through comparison with experiment results for air temperatures at different locations of the airflow path and of food products. Simulation results show that significant energy can be saved through the installation of a PCM container. Further benefits include greater stabilization of product temperatures during defrost periods for the modified display cabinet. Consequently, the validated models can be used to explore and analyse the cabinet performance and control strategies at various operating and design conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the thermal and optical characterisation of PCM (phase change material) RT27 using the T-history method and spectrophotometry principles, respectively, and the experimental and numerical performance evaluation of a PCM-glazed unit. Various relationships describing the variations in the extinction, scattering and absorption coefficients within the phase change region were developed, and were validated in a numerical CFD model. The results show that: (i) during rapid phase changes, the transmittance spectra from the PCM are unstable, while under stable conditions visible transmittance values of 90% and 40% are obtained for the liquid and phases, respectively; (ii) the radiation scattering effects are dominant in the solid phase of the PCM, while radiation absorption dominates in the liquid phase; (iii) the optical/radiation performance of PCM can be successfully modelled using the liquid fraction term as the main variable; (iv) the addition of PCM improves the thermal mass of the unit during phase change, but risks of overheating may be a significant factor after the PCM has melted; (v) although the day-lighting aspects of PCM-glazed units are favourable, the change in appearance as the PCM changes phase may be a limiting factor in PCM-glazed units. [Copyright &y& Elsevier]

Abstract: Food frying is very energy intensive and in industrial potato crisp production lines frying is responsible for more than 90% of the total energy consumption of the process. This paper considers the energy flows in crisp frying using a First Law of Thermodynamics modelling approach which was verified against data from a potato crisp production line. The results indicate that for the frying process considered, most of the energy used is associated with the evaporation of water present in the potato and on the surface of potato slices. The remainder is from evaporation of frying oil and air of the ventilation system and heat losses from the fryer wall surfaces by convection and radiation. The frying oil is heated by an industrial gas furnace and the efficiency of this process was calculated to be 84%. The efficiency of the overall frying process which was found to be of the order of 70% can be improved by employing exhaust heat recovery and optimising other operating and control parameters such as exhaust gas recirculation. [Copyright &y& Elsevier]

Abstract: The forced convection heat transfer characteristics in high porosity open-cell metal-foam filled tube heat exchangers are analysed in this paper. The Brinkman-extended Darcy momentum model and two-equation heat transfer model for porous media are employed for the analysis of the heat transfer performance. The morphological effects of metal foams on overall heat transfer are examined. The optimal foam-area ratio for a metal-foam filled counter-flow tube-in-tube heat exchanger is predicted. The study shows that the thermal performance of a metal-foam heat exchanger can be superior to that of conventional finned tube heat exchangers. [Copyright &y& Elsevier]

Abstract: This paper presents an analytical study of the forced convection heat transfer characteristics in high porosity open-cell metal-foam filled pipes. The Brinkman-extended Darcy momentum model and two-equation heat transfer model for porous media were employed. Based on the analytical solutions, the velocity and temperature distributions in metal-foam filled pipes were obtained. The effects of the microstructure of metal foams on overall heat transfer were examined. The results show that the pore size and porosity of metal-foams play important roles on overall heat transfer performance. The use of metal-foam can dramatically enhance the heat transfer but at the expense of higher pressure drop. [Copyright &y& Elsevier]

The objective of this paper is to present a method to evaluate the characteristics and performance of a single stage lithium bromide (LiBr)–water absorption machine. The necessary heat and mass transfer equations and appropriate equations describing the properties of the working fluids are specified. These equations are employed in a computer program, and a sensitivity analysis is performed. The difference between the absorber LiBr inlet and outlet percentage ratio, the coefficient of performance of the unit in relation to the generator temperature, the efficiency of the unit in relation to the solution heat exchanger area and the solution strength effectiveness in relation to the absorber solution outlet temperature are examined. Information on designing the heat exchangers of the LiBr–water absorption unit are also presented. Single pass, vertical tube heat exchangers have been used for the absorber and for the evaporator. The solution heat exchanger was designed as a single pass annular heat exchanger. The condenser and the generator were designed using horizontal tube heat exchangers. The calculated theoretical values are compared to experimental results derived for a small unit with a nominal capacity of 1 kW. Finally, a cost analysis for a domestic size absorber cooler is presented. [Copyright &y& Elsevier]

Presents a modeling and simulation of an absorption solar cooling system in countries with high solar availability. Significance of the transient simulation program and the meteorological year file containing the weather parameters of Nicosia, Cyprus to the study; Details of the system optimization; Discussion of the system's long term performance; Analysis of the economic aspect of the complete system.

Highlights • Experiment in a power generation system with CO 2 transcritical power cycles (T-CO 2 ). • Preliminary test results from the T-CO 2 power generation system. • Model development and validation of the tested T-CO 2 power generation system. • Some important operating parameters on system performance are identified. • The research outcomes can be used to instruct the system control and operation. Abstract Globally, there are vast amounts of low-grade heat sources from industrial waste and renewables that can be converted into electricity through advanced thermodynamic power cycles and appropriate working fluids. In terms of the working fluid’s environmental impact, temperature match of cycle heat processes and system compactness, CO 2 transcritical power cycles (T-CO 2 ) were deemed more applicable for low-grade heat to power conversion. However, the system thermal efficiency of a T-CO 2 requires further improvement. Subsequently, a test rig of the small-scale power generation system with T-CO 2 power cycles was developed with essential connected components. These include a plate thermal coil CO 2 supercritical heater, a CO 2 transcritical turbine, a plate recuperator, an air-cooled finned-tube CO 2 condenser and a CO 2 liquid pump. Various preliminary test results from the system measurements are demonstrated in this paper. Meanwhile, the system model has been developed and applied to predict system performance at different operating conditions. The simulation results can therefore instruct further design and optimisation of system and components. [ABSTRACT FROM AUTHOR]

Natural refrigerants are recognised as the most promising working fluids to replace conventional HFCs in food refrigeration systems. Due to its negligible GWP, zero ODP and attractive thermo-physical properties, the CO 2 working fluid has grown in popularity over the last decade, especially in supermarket refrigeration systems. These systems can be classified into three main categories: indirect, cascade and all CO 2 transcritical booster structures. However, the appropriate control and design optimisation of such systems require further investigation. This paper presents an experimental investigation into the performance of CO 2 finned-tube gas coolers/condensers with different designs in a CO 2 booster system. The heat exchangers were mounted in a specially designed test facility that allowed the control of different test conditions and parameters, including air on temperatures and flow rates, approach temperatures and CO 2 operation pressures. The integrated refrigeration system can provide specified CO 2 fluid parameters at the heat exchanger inlet, through which the system efficiency can be calculated. Subsequently, extensive measurements were recorded from this test rig, with insightful indications into system performance and the most influential parameters for system optimisation. These include heat exchanger designs, air on temperatures and flow rates, supercritical and subcritical pressure controls and cooling capacity controls, which are described in the paper. [ABSTRACT FROM AUTHOR]