PartagerICR2011 highlights: micro-refrigeration development
Micro-refrigeration development was one of the important themes of the IIR Congress in Prague.
Micro-refrigeration development was one of the important themes of ICR2011. It has been underway for a few decades, and is strongly associated with a progress in such technologies as autonomous power supply, integrated micro transportation and enhanced heat transfer techniques and the 21st century brought new possibilities thanks to micro-electric and mechanical systems (MEMS) technology.
Kosoy (1) suggests a microfluidic refrigeration platform approach, as a combinable set of refrigerant handling steps together with a suitable micro-fabrication technology which could be selected by identifying imperative requirements of specific applications e.g. portability, low power consumption, high coefficients of performance, etc. Examples of such devices can be found in microelectronics, nuclear technology, aerospace, bioengineering, etc.
Ebel et al.(2) focused on miniature vapour-compression technology and its achievable cooling-output-to-system-mass ratio. However, their paper also gave a comparison of a variety of cooling approaches that could be used in autonomous (and mostly man-mounted) systems for cooling vests. These included the evaporative type, the most commonly encountered, mainly for reasons of simplicity and low cost. However this approach requires the removal of outer clothing as it depends on evaporation. Phase-change materials (PCM) are also used in PCM vests in the U.S Navy since 1991, a system which implies relatively high mass and some of the systems are hand-carried. Other cooling systems for individuals are based on expansion of compressed air with cooling thanks to the Joule Thomson effect or the Ranque-Hilsch effect; their efficiency is known to be relatively low but they are robust, due to the small number of moving parts. The Peltier effect may be used in such systems but its requirements in terms of heat rejection must be taken into account and theses systems come at a relatively high cost.
The approach chosen in the study was a direct-expansion system which requires a completely different evaporator design from those using vapour-compression technology to chill a secondary fluid such as water or glycol, circulated through loops inside the cooling vests. In this case, the pressurized primary refrigerant circulates directly through the cooling loops, thanks to tubing materials which combine suitable pressure resistance with a certain degree of flexibility so as not to hinder the user’s movements. With a system cooling output per unit mass ratio of 26 W kg-1 (including power source) at 35°C ambient temperature, it is claimed to be “one of the most compact and light weight systems ever reported in the open literature.”
(1) Microfluidic refrigeration platforms: strengths and limitations, B.V. Kosoy
(2) Development and analysis of miniature vapour compression cooling technology, S. Elbel et al.
Kosoy (1) suggests a microfluidic refrigeration platform approach, as a combinable set of refrigerant handling steps together with a suitable micro-fabrication technology which could be selected by identifying imperative requirements of specific applications e.g. portability, low power consumption, high coefficients of performance, etc. Examples of such devices can be found in microelectronics, nuclear technology, aerospace, bioengineering, etc.
Ebel et al.(2) focused on miniature vapour-compression technology and its achievable cooling-output-to-system-mass ratio. However, their paper also gave a comparison of a variety of cooling approaches that could be used in autonomous (and mostly man-mounted) systems for cooling vests. These included the evaporative type, the most commonly encountered, mainly for reasons of simplicity and low cost. However this approach requires the removal of outer clothing as it depends on evaporation. Phase-change materials (PCM) are also used in PCM vests in the U.S Navy since 1991, a system which implies relatively high mass and some of the systems are hand-carried. Other cooling systems for individuals are based on expansion of compressed air with cooling thanks to the Joule Thomson effect or the Ranque-Hilsch effect; their efficiency is known to be relatively low but they are robust, due to the small number of moving parts. The Peltier effect may be used in such systems but its requirements in terms of heat rejection must be taken into account and theses systems come at a relatively high cost.
The approach chosen in the study was a direct-expansion system which requires a completely different evaporator design from those using vapour-compression technology to chill a secondary fluid such as water or glycol, circulated through loops inside the cooling vests. In this case, the pressurized primary refrigerant circulates directly through the cooling loops, thanks to tubing materials which combine suitable pressure resistance with a certain degree of flexibility so as not to hinder the user’s movements. With a system cooling output per unit mass ratio of 26 W kg-1 (including power source) at 35°C ambient temperature, it is claimed to be “one of the most compact and light weight systems ever reported in the open literature.”
(1) Microfluidic refrigeration platforms: strengths and limitations, B.V. Kosoy
(2) Development and analysis of miniature vapour compression cooling technology, S. Elbel et al.