A review of emerging technologies for food refrigeration applications

TL;DR: In this paper, the authors provide a brief review of both current state of the art technologies and emerging refrigeration technologies that have the potential to reduce the environmental impacts of refrigeration in the food industry.

About: This article is published in Applied Thermal Engineering.The article was published on 2010-03-01 and is currently open access. It has received 200 citations till now. The article focuses on the topics: Food processing & Food industry.

Summary

1. INTRODUCTION

• In industrialised countries the food industry constitutes one of the largest industrial manufacturing groups and despite significant differences in per capita consumption of major food categories, there is a rising trend towards higher consumption of several food products with consequent increase in environmental impacts.
• Even though new refrigerants, namely HFCs, have been developed with zero ozone depletion potential, these refrigerants invariably have high ozone depletion potential (GWP) and make significant contributions to greenhouse gas emissions both directly through refrigerant leakage and indirectly through emissions from power stations that generate the electrical energy required to drive them.
• Reciprocating and screw compressors are predominantly used in ammonia refrigeration plants.
• New systems will invariably employ some form of capacity control to match the compressor capacity to the load and improve system efficiency.

Description of technology

• Magnetic refrigeration is based on the magnetocaloric effect (MCE), a basic property of magnetic solids characterized by a reversible temperature rise when a magnetic field is applied adiabatically.
• The MCE peaks around the magnetic ordering (or Curie) temperature [49].
• A heat exchange fluid, usually a water-based solution, is forced in alternate directions through the porous AMR bed in sequence with periodic application and removal of the magnetic field, as illustrated in Figure 9 [50].
• Net work input to the system is required to move the magnetic field relative to the magnetic material and for fluid pumping.
• Magnetization and demagnetization of the magnetic refrigerant can be likened to compression and expansion in a vapour compression cycle but, in contrast, the magnetic processes are virtually loss free.

State of development

• The magnetocaloric effect has been exploited for cooling to deep cryogenic temperatures (< 1 K) since the 1930s and is also used for gas liquefaction.
• Investigations in this area cover both conventional MCE materials, such as gadolinium, that undergo a second-order magnetic transition and advanced alloys that exhibit a giant MCE associated with a first-order magneticstructural transition [54,55].
• The more recent prototypes generally employ permanent magnet based field sources and the cooling capacities achieved are low.
• It was recently estimated that the introduction of this new technology will reach the commercialization stage around 2015 [53].
• It is evident that this technology has the potential for use across the food refrigeration temperature range, from near room temperature operation down to cryogenic temperatures.

Applications in the food sector

• Thermoelectric cooling has been extensively applied in numerous fields, handling cooling loads from milliwatts up to tens of kilowatts in systems using multiple modules in parallel, and temperature differences from almost zero to over 100 K with multistage modules [45].
• Thermoelectric cooling products available for the food sector include compact refrigerators (15-70 litre) for hotel rooms (mini-bar), mobile homes, trucks, recreational vehicles and cars; wine coolers; portable picnic coolers; beverage can coolers and drinking water coolers [46].
• Prototype domestic refrigerators of larger capacity (115 litre and 250 litre) have been built and tested, achieving COPs up to 1.2 [47].
• In addition, an overall COP of 0.44 was measured for a prototype 126 litre refrigeratorfreezer [48].

Barriers to uptake of the technology

• The main barriers to the uptake of magnetic refrigeration technology are: near room temperature refrigeration systems operating on the magnetocaloric effect are not yet commercially available.
• In their present state of development, the overall performance of prototype magnetic refrigerators does not match that of vapour compression systems, in terms of cooling power, temperature span and coefficient of performance.
• Albeit they have the potential to achieve higher energy efficiencies.

Research and development needs

• The requirement of prime importance is the identification and development of new magnetic refrigerant regenerator materials exhibiting strong MCEs.
• Candidate materials must also be evaluated against a number of other factors including problems of temperature hysteresis and adiabatic temperature rise time delay, large scale production and fabrication considerations (including associated costs), environmental concerns, friability and compatibility with heat exchange fluids.
• Further work is also needed on the development of permanent magnet arrays and magnetic field design to increase the applied magnetic field, minimize the amount of magnet material required and reduce the costs.
• Developments are also required in the design and operation of magnetic regenerators to improve heat transfer between the heat transfer fluid and the solid refrigerant, reduce pressure drops and minimize heat leakages, and to optimize the flow rate of the heat exchange fluid and the operating frequency.

Key drivers to encourage uptake

• The main drivers to encourage uptake of magnetic refrigeration technology in the food sector once it becomes commercially available are: environmental considerations and legislation that significantly limits or prohibits the use of HFCs in small capacity, self contained refrigeration equipment.
• Limits imposed on the amount of flammable refrigerant that can be used in self contained refrigerated cabinets.
• Environmentally safe and compact refrigeration systems that offer the prospect of significant efficiency, and cost advantages over vapour compression systems.

10. SUMMARY AND CONCLUSIONS

• The food industry relies heavily on the vapour compression refrigeration cycle for food preservation and processing.
• Magnetic refrigeration is also a candidate technology but its commercialisation is further downstream and placed approximately 10 years from now.
• CO2 based systems are also making inroads into the UK commercial refrigeration market and a number of different system configurations are currently being trialled.
• Ammonia vapour compression systems are dominant in food processing, also known as Food processing.
• Other possible approaches include the recovery and use of waste heat for refrigeration through sorption and ejector systems and for power generation (thermoelectric, Stirling, thermoacoustic, turbo-generators).

Figures

Figure 4. Schematic of a trigeneration system

Figure 5. Piston and displacer movements during a Stirling refrigeration cycle.

Figure 8. Travelling wave thermoacoustic device (Ben & Jerry ice-cream cabinet [48])

Figure 3. Air cycle with regenerative heat exchange and two-stage compression with

Figure 6. Thermoelectric cooling (or Peltier) couple

Figure 7. Sound wave thermoacoustic refrigerator

Figure 2. Schematic and T-s diagram of ejector refrigeration system

Figure 9. Active magnetic regeneration cycle (from Russek and Zimm [50])

Figure 9. Active magnetic regeneration cycle (from Russek and Zimm [50])

Table 1. Characteristics and applications of emerging refrigeration technologies

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "A review of emerging technologies for food refrigeration applications" ?

This paper provides a brief review of both current state of the art technologies and emerging refrigeration technologies that have the potential to reduce the environmental impacts of refrigeration in the food industry. The paper also highlights research and development needs to accelerate the development and adoption of these technologies by the food sector. 

Q2. What future works have the authors mentioned in the paper "A review of emerging technologies for food refrigeration applications" ?

Magnetic refrigeration also offers potential for the future. CO2 systems on their own or in a cascade arrangement with hydrocarbon ( HC ) or ammonia ( R717 ) systems are likely to become the dominant supermarket refrigeration technology in the future. There may also be possibilities for the use of biomass which may be a bioproduct of food processing for CHP and trigeneration. Large food storage facilities normally employ ammonia vapour compression plant and it is likely that this will continue in the future. 

Q3. What is the main driver to encourage uptake of adsorption refrigeration technology?

To increase the attractiveness and application of adsorption systems, research and development is required to:• increase efficiency and reduce size and cost of systems through heat and mass transfer enhancement. 

Q4. What are the main drivers to encourage uptake of air cycle technology in the food sector?

The main drivers to encourage uptake of the technology in the food sector are:• rising energy costs and requirement for faster food processing to increase throughput and reduce energy consumption. 

Q5. What is the main reason for the use of ammonia in food processing?

Since the early development of vapour compression refrigeration systems, ammonia has been used extensively in food processing and for cold storage due its low cost and high efficiency. 

Q6. What are the main drivers to encourage uptake of ejector refrigeration technology in the food?

• rising energy costs that could encourage the more effective utilisation of waste heat and better thermal integration of processes in food manufacturing. 

Q7. What is the role of the vapour compression refrigeration cycle in the food industry?

Since the emergence of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants in the 1930’s the vapour compression refrigeration cycle has gained dominance over alternative cooling technologies in all areas of food manufacturing, distribution and retail. 

Q8. What are the main drivers to encourage uptake of thermoelectric cooling technology in the food sector?

The main drivers to encourage uptake of thermoelectric cooling technology in the food sector are:• legislation that significantly limits or prohibits the use of HFCs in small capacity, self contained refrigeration equipment. 

Q9. What are the main drivers to encourage uptake of the Stirling cycle cooling technology in the food?

The main drivers to encourage uptake of the Stirling cycle cooling technology in the food sector are:• legislation that significantly limits or prohibits the use of HFCs in small capacity, self contained refrigeration equipment. 

Q10. How many kW of ejector refrigeration have been developed?

Systems have been developed with cooling capacities ranging from a few KW to 60,000 kW but despite extensive development effort the COP of the system, which can be defined as the ratio of the refrigeration effect to the heat input to the boiler, if one neglects the pump work which is relatively small, is still relatively low, less than 0.2. 

Q11. What are some other energy efficiency measures that are or can be applied?

Other energy efficiency measures that are or can be applied include head (condenser) pressure control in response to variation in ambient temperature with condenser fan on-off switching or variable speed fan control. 

Q12. What are the main technologies that are being trialled in the UK commercial refrigeration market?

CO2 based systems are also making inroads into the UK commercial refrigeration market and a number of different system configurations are currently being trialled. 

Q13. What are the main drivers to encourage uptake of thermoacoustic technology once they become?

The main drivers to encourage uptake of thermoacoustic technology once they become commercially available in the food sector are:• environmental considerations and legislation that significantly limits or prohibits the use of HFCs in small capacity, self contained refrigeration equipment. 

Q14. What are the main drivers to encourage uptake of the technology in the food sector?

The main drivers to encourage uptake of the technology in the food sector are:• legislation that limits or prohibits the use of HFCs. 

Q15. Why do food storage facilities offer potential for heat recovery?

Because of their location, normally in sparsely populated areas, food storage facilities offer potential for the use of biomass for combined heat and power or for trigeneration. 

Q16. What are the main drivers to encourage uptake of magnetic refrigeration technology in the food sector?

The main drivers to encourage uptake of magnetic refrigeration technology in the food sector once it becomes commercially available are:• environmental considerations and legislation that significantly limits or prohibits the use of HFCs in small capacity, self contained refrigeration equipment. 

Q17. What are the main barriers to uptake of trigeneration technology?

The main barriers to uptake of tri-generation technology are:• application range of off the shelf systems is currently limited to temperatures above 0oC, • insufficient experience and performance data from applications in retail food stores to provide confidence in the application of the technology, • economics are very sensitive to the relative difference between the price of grid electricity and fuel used by the trigeneration system. 

Q18. What is the main driver to encourage uptake of thermoelectric cooling in the food sector?

Increased application of thermoelectric cooling in the food sector will require a significant improvement of COP to make it competitive with vapour compression technology. 

Q19. What are the environmental impacts of supermarket refrigeration systems?

The environmental impacts of supermarket refrigeration systems can be reduced through the improvement of equipment efficiencies, reduction in the refrigerant charge and reduction or elimination of refrigerant leakage. 

Q20. What are the main barriers to the uptake of thermoacoustic technology?

The main barriers to the uptake of thermoacoustic technology are:• in their present state of development the efficiency of prototype therrmoacoustic refrigeration systems is lower than that of vapour compression systems. 

Q21. What applications can be found in food processing factories?

Such applications can be found in food processing factories where the ejector refrigeration system can be used for product and process cooling and transport refrigeration. 

Q22. What are the main drivers to encourage uptake of adsorption refrigeration technology in the food?

The main drivers to encourage uptake of the technology in the food sector are: • successful demonstration of the benefits of the technology in applications wherethere is sufficient waste heat or in tri-generation systems. 

Q23. What are the main drivers to encourage uptake of ejector refrigeration in the food sector?

The main drivers to encourage uptake of the technology in the food sector are:• successful demonstration of the benefits of the technology in applications where there is sufficient waste heat or in tri-generation systems.