Testing and Analysis of an Exergetically Efficient 4 K to 2 K Helium Heat Exchanger

Modern experimental nuclear physics programs that utilize advanced superconducting devices require refrigeration below the lambda temperature of helium (2.1768 K) and involve sub-atmospheric helium at some point in the process. They typically operate between 1.8 and 2.1 K (16 to 40 mbar) and can require refrigeration ranging from tens to thousands of watts. These processes are very energy intensive, requiring roughly 850 W/W even for large and well-designed refrigerators, though they can easily require much more. Adiabatic expansion of sub-cooled liquid helium to these sub-atmospheric pressures will result in a two-phase mixture with a large liquid to vapor density ratio. Since there are no practical expanders to handle this condition, a counter flow heat exchanger is used to cool the super-critical helium supply using the returning sub-atmospheric helium. Typically, the super-critical helium exiting this 4.5 K to 2-K counter flow heat exchanger is throttled across an expansion valve to a sub-atmospheric pressure. This is a substantial irreversibility, typically 13 percent of the enthalpy difference between the load supply and return. A significant process improvement is theoretically obtainable by handling the exergy loss across the expansion valve supplying the flow to the load in a simple but different manner. The exergy loss can be minimized by allowing the supply flow pressure to decrease to a sub-atmospheric pressure concurrent with heat exchange with the sub-atmospheric flow from the load. This dissertation work encompasses testing of a practical implementation using a Collin’s type heat exchanger to investigate the overall performance, as well as, the optimum selections of independent process parameters and how this affects the heat exchanger size distribution. The thermodynamics of heat exchange with a significant pressure drop for a non-ideal fluid are investigated, in regards to an equivalent expansion efficiency pseudo-property, a practical process expansion efficiency equivalence and an overall 2-K system performance improvement expectation. Theoretically predicted optimum independent process parameters are compared to those measured

Process Study for the Design of Small-Scale 2 Kelvin Refrigeration Systems

Helium refrigeration at temperatures below 4.5-Kelvin (K), but greater than 0.8-K typically employ a sub-atmospheric process utilizing a vacuum pumping system. These types of helium refrigerators are of keen interest to present and future particle physics programs utilizing super-conducting magnet or radio-frequency technology. As such, there is a need for small scale 2-K helium refrigeration systems (i.e., those that operated below the lambda temperature) in small laboratories and test facilities at this time. This study establishes the key process parameter choices of flow ratio, heat-exchanger size, and supply pressure, and how they influence the overall system performance for various process configurations that do not utilize rotating machinery within the cold box (i.e., turbo-machinery for either cryogenic vacuum pumping or expansion) but do utilize a separate commercially available 4.5-K helium liquefier system. Three 2-K process configurations are studied to determine the key process parameter values that yield the best performance. These process configurations are compared to the commonly employed (but inefficient) direct vacuum pumping process, which typically uses a dewar as the 4.5-K liquid helium supply source. It is found that the performance of these configurations is similar and substantially superior to direct vacuum pumping, providing an inverse coefficient of performance of around 1800 W/W

Design and Use of a Large-Scale Liquid Helium Conversion System

A large-scale liquid helium (LHe) to high-pressure (HP) gas conversion system has been implemented at the John F. Kennedy Space Center (KSC). Helium is used by the Space Shuttle, Titan, Atlas, and Delta programs for prelaunch processing, during launch count-down, and for postlaunch securing. The first phase of modifications to the Compressor Converter Facility (CCF), operational in April 1998, allowed the facility to accept bulk liquid helium from tanker containers and to off-load the helium at super-critical pressures. The second phase of modifications, planned to be operational by January 2001, will implement a 227-cubic-meter (m(sup 3)) on-site liquid helium storage system. This paper describes the design and operation of the current system and discusses the design and implementation for the second phase system

The fear of bad smell: Health risk awareness related to using waste in agricultural production in Vietnam

Waste watersWater reuseAgricultural productionFish farmingIrrigation waterPublic healthRisksSkin diseasesOrganic fertilizersWomen

Perceived indoor environment in social housing with different ventilation principles

The need for renovation and energy retrofitting of Danish social housing from the 1960s and 1970s is substantial. Such energy retrofits often include the installation of mechanical ventilation systems with heat recovery to fulfil the current standards for energy efficiency. These systems typically ensure a more constant and higher ventilation rate than previous systems. Therefore, there is potential for residents to perceive a higher air quality and a reduction in problems due to condensation on cold surfaces and mould growth after retrofits. The purpose of the present study was to evaluate if this potential is realised for residents in social housing complexes. A questionnaire survey was performed among residents in dwellings with ventilation categorised within one of the five ventilation principles: natural ventilation, bathroom fan, exhaust fans in the kitchen and bath, decentralized balanced mechanical ventilation and centralized balanced mechanical ventilation. Compared with residents without balanced mechanical ventilation, residents having such systems perceived less often problems with unpleasant odour from their own apartment and less visible mould, but more often perceived the air as dry. Residents with decentralized mechanical ventilation tended to experience more often problems with noise from their ventilation system. However, results show that nuisance are avoidable with correctly designed decentralized ventilation.publishedVersio

Experience with CO2 capture from coal flue gas in pilot-scale: Testing of different amine solvents

AbstractAs part of the EU project CASTOR, a 1 t/h CO2 absorption pilot plant has been erected at Esbjergværket (Esbjerg power station) in Denmark. The main purpose of the pilot plant is to demonstrate the post combustion capture technology in conjunction with a coal-fired power station. Additionally, the pilot plant has been used to test the performance of new energy efficient solvents and to validate modelling work. The pilot plant operates on a slipstream of flue gas from the power plant without any further pre- treatment. During the CASTOR project, four 1000-hours test campaigns have been conducted at the facility using conventional solvent, 30%-weight MEA as well as two novel amine-based solvents, CASTOR 1 and CASTOR 2. Among others, the test campaigns consisted of parameter variation tests and longer periods of continuous operation. This paper summarises the operation experience and some of the results obtained during the CASTOR project