91,493 research outputs found
Assessment of Factors Contributing to Refrigerator Cycling Losses
Thermal mass effects, refrigerant dynamics, and interchanger transients are three factors affecting the
transient and cycling performance of all refrigeration and air conditioning equipment. The effects of refrigerant
dynamics, including refrigerant/oil solubility, off-cycle migration, and charge redistribution, were found to be the
most important. These effects are quantified for a refrigerator instrumented with immersion thermocouples, pressure
transducers, and microphones. The analytical methods, however, are applicable to other types of refrigeration and air
conditioning systems, including those with capillary tube/suction line heat exchangers.Air Conditioning and Refrigeration Center Project 3
Performance characterisation of a new photo-microsensor based sensing head for displacement measurement
This paper presents a robust displacement sensor with nanometre-scale resolution over a micrometre range. It is composed of low cost commercially available slotted photo-microsensors (SPMs). The displacement sensor is designed with a particular arrangement of a compact array of SPMs with specially designed shutter assembly and signal processing to significantly reduce sensitivity to ambient light, input voltage variation, circuit electronics drift, etc. The sensor principle and the characterisation results are described in this paper. The proposed prototype sensor has a linear measurement range of 20 μm and resolution of 21 nm. This kind of sensor has several potential applications, including mechanical structural deformation monitoring system
Cloud condensation nuclei activity, closure, and droplet growth kinetics of Houston aerosol during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS)
In situ cloud condensation nuclei (CCN) measurements were obtained in the boundary layer over Houston, Texas, during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) campaign onboard the CIRPAS Twin Otter. Polluted air masses in and out of cloudy regions were sampled for a total of 22 flights, with CCN measurements obtained for 17 of these flights. In this paper, we focus on CCN closure during two flights, within and downwind of the Houston regional plume and over the Houston Ship Channel. During both flights, air was sampled with particle concentrations exceeding 25,000 cm^(−3) and CCN concentrations exceeding 10,000 cm^(−3). CCN closure is evaluated by comparing measured concentrations with those predicted on the basis of measured aerosol size distributions and aerosol mass spectrometer particle composition. Different assumptions concerning the internally mixed chemical composition result in average CCN overprediction ranging from 3% to 36% (based on a linear fit). It is hypothesized that the externally mixed fraction of the aerosol contributes much of the CCN closure scatter, while the internally mixed fraction largely controls the overprediction bias. On the basis of the droplet sizes of activated CCN, organics do not seem to impact, on average, the CCN activation kinetics
Optical power meter using radiation pressure measurement
This paper describes a radiation pressure meter based on a diamagnetic
spring. We take advantage of the diamagnetic property of pyrolytic carbon to
make an elementary levitated system. It is equivalent to a torsional
spring-mass-damper system consisting of a small pyrolytic carbon disc levitated
above a permanent magnet array. There are several possible measurement modes.
In this paper, only the angular response to an optical power single-step is
described. An optical detection composed of a laser diode, a mirror and a
position sensitive detector (PSD) allow measurement of the angular deflection
proportional to the voltage delivered by the PSD. Once the parameters of the
levitated system depending on its geometrical and physical characteristics have
been determined regardless of any optical power, by applying a simple physical
law, one can deduce the value of the optical power to be measured from the
measurement of the first maximum of the output voltage amplitude
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Experimental investigation on water injected twin screw compressor for fuel cell humidification
A water injection in Twin Screw compressors was examined in order to develop effective humidification and cooling schemes for fuel cell stacks as well as cooling for compressors. The temperature and the relative humidity of the air at suction and exhaust of the compressor were monitored under constant pressure and water injection rate and at variable compressor’s operating speeds. The experimental results showed that the relative humidity of the outlet air was increased by the water injection. The injection tends to have more effect on humidity at low operating speeds/ mass flow rates. Further humidification can be achieved at higher speeds as higher evaporation rate becomes available. It was also found that the rate of power produced by the fuel cell stack was higher than the rate used to run the compressor for the same amount of air supplied. The efficiency of the Balance-Of-Plant (BOP) was therefore higher when more air is delivered to the stack. However, this increase in the air supply needs additional subsystems for further humidification/ cooling of the BOP system
Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation
An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate 15 μW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the ν3 rotational-vibrational band of methane at 3.4 μm. To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of 12‰ is demonstrated for both δ13C and δD
Testing Lorentz and CPT symmetry with hydrogen masers
We present details from a recent test of Lorentz and CPT symmetry using
hydrogen masers. We have placed a new limit on Lorentz and CPT violation of the
proton in terms of a recent standard model extension by placing a bound on
sidereal variation of the F = 1 Zeeman frequency in hydrogen. Here, the
theoretical standard model extension is reviewed. The operating principles of
the maser and the double resonance technique used to measure the Zeeman
frequency are discussed. The characterization of systematic effects is
described, and the method of data analysis is presented. We compare our result
to other recent experiments, and discuss potential steps to improve our
measurement.Comment: 26 pages, 16 figure
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