Cold Link Africa January/February 2018 | Page 11

INTERNATIONAL NEWS
INCORPORATING COLD CHAIN
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REFRIGERANTS AND HEAT PUMPS FOR EFFICIENT USE OF LOW-GRADE THERMAL EFFICIENCY
Thanks to heat pumps , low-grade thermal
energy , such as solar energy , waste heat from industries , and geothermal energy , can be upgraded into high-temperature heat for central heating or industrial manufacturing processes .
The selection of suitable cycles and refrigerants is important for getting good performance of heat pumps . In their paper presented at the 5th IIR Conference on Thermodynamic Properties and Transfer Processes of Refrigerants , R . Z . Wang et al . analysed the performance of typical refrigerants — such as R152a , R1233zd ( E ), R1234yf , R1234ze , R134a , R245fa , R717 , R718 , and R744 — and various thermodynamic cycles for vapour compression , absorption , solid sorption and chemical HPs . A broad-spectrum diagram of HP applications is provided for different working modes .
system and component design is helping to reduce charge sizes by more than 70 % when compared with pumped circulation . Developments in evaporator technology and the use of variable speed drive technology are ensuring that reduction in charge doesn ’ t come at the expense of efficiency . The introduction of packaged systems enables refrigeration plants to be located adjacent or close to evaporators , reducing pipework length and sizing .
• R . Lamb . Low charge packaged ammonia refrigeration systems .
ADVANCEMENT IN INTEGRATED CO 2
SYSTEMS
This was also widely discussed at the IIR Ohrid
Conference . A . Hafner highlighted that integrated CO 2 systems can simultaneously provide refrigeration capacities at various temperature levels as low as -50 ° C , air conditioning ( AC ), heating , and even sanitary hot water at adequate temperature levels . A further integration of advanced thermal storage devices will enable these systems to become a valuable element within smart ( thermal ) grids .
to their fast recovery times , low jitter , and low dark count rates .
SNSPDs operate at extremely low temperatures , only a few degrees above absolute zero ( -273.15 ° C ). Until now , that level of cooling was achieved with liquid-helium systems , which present a few disadvantages : they are large , expensive , complicated , and demand considerable expertise to operate safely .
NIST recently found an alternative and created a very small prototype , adapted to the size of SNSPDs since it measures 0.31m high and 0.61m long . Its power demand is about 250W , whereas the previous best alternative drew 1.5kW of power . The prototype device relies on a hybrid cooling system comprised of a Joule-Thomson cryocooler and a pulse-tube refrigerator that can reach
temperatures as low as 10K . It precools the cryocooler that can reach below 2K , which is an almost adequate temperature for SNSPDs operating at temperatures between 1K and 2K .
The NSA supported the initial planning and asked NIST to write a paper . The project is currently receiving funding under a cooperative research and development agreement .
• Kotsubo V . et al . Compact 2.2K cooling system for superconducting nanowire single photon detectors .
GEOTHERMAL ENERGY TO POWER A COLD STORAGE FACILITY
In Fiji , two remote villages located on the
tiny island of Vanua Levu do not have
• R . Z . Wang et al . Refrigerants and heat pumps for efficient use of low grade thermal efficiency .
REFRIGERANT CHARGE REDUCTION OF AMMONIA REFRIGERATING SYSTEMS
This was a subject of extensive debate during the 7th IIR Ohrid Conference on Ammonia and CO 2 Refrigeration Technologies that took place last year .
In his paper , P . Hrnjak presented recent developments in charge reduction of ammonia systems : both new unitary systems for cooling air or secondary fluid and also conventional ammonia chillers . The paper also presents a case for a small , low-charge , air-cooled ammonia chiller using microchannel air-cooled condensers and hermetic compressors as an extremely strong option for the replacement of current chillers based on positive displacement compressors .
• P . Hrnjak . Efficient very low charged ammonia systems .
R . Lamb stressed that phasing down of HFCs and regulatory requirements associated with large ammonia charges are driving the development of lowcharge ammonia systems . Innovation in
• A . Hafner . Integrated CO 2 system for refrigeration , air conditioning and sanitary hot water .
K . H . Kvalsvik et al . presented an integrated refrigeration and AC system with CO 2 as the only working fluid for use in very hot climates (+ 45 ° C ). Based on the simulation results , its feasibility is proven . The use of ejectors is essential for the system performance at these extreme ambient temperatures , and enables , until now , an impossible application for CO 2 . The system achieves a similar performance compared to existing solutions applying high-GWP synthetic refrigerants .
• K . H . Kvalsvik et al . Integrated CO 2 refrigeration and AC unit for hot climates .
COOLING SYSTEM FOR SUPERCONDUCTING NANOWIRE SINGLE-PHOTON DETECTORS
Single-photon detectors have many applications , such as optical quantum computing or ultra-secure quantum communications , among others . Superconducting nanowire single-photon detectors ( SNSPDs ) are very efficient in detecting photons in the near-infrared due priyainfiji . blogspot . co . za NIST
In Fiji , on the tiny island of Vanua Levu , two remote villages are piping hot water from its hot springs ( which is coming out of the ground at 70 ° C ) to power an absorption chilling facility in Natewa Bay .
Sae Woo Nam ( left ) and Vincent Kotsubo examine the prototype for their new cryocooler .
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