Performance of a liquid flow ultra-compact heat exchanger

A numerical analysis of the performance of compact pin-fin array heat exchangers was carried out using water and JP-4 fuel as the working fluids. Three different configurations were used with hydraulic diameters ranging from 0.137 to 0.777 mm, and volumetric area densities varying between 4.5 and 14.5 mm2/mm3. Numerical simulations were carried out to determine the performance of each heat exchanger over a series of Reynolds numbers in both the laminar and turbulent flow regimes. It was found that very large heat transfer coefficients (in the kW/m2K range) can be achieved compared to air for the same footprint. In addition, the simulations were used to predict the Reynolds number range for transition from laminar to turbulent flow which was found to vary depending on the compactness of the heat exchanger configuration. As a final point, this study also investigated the effects of boiling of the liquid within the heat exchanger on its performance. It was found that despite improved heat transfer rates due to latent heat removal, vapor formation and resulting fluid expansion effects could result in undesirable flow patterns at low Reynolds numbers. The results from this study would be useful in the design of micro-scale heat exchangers for applications in the micro-electronic and gas turbine industries.http://archive.org/details/performanceofliq109452701US Navy (USN) author.Approved for public release; distribution is unlimited

Honeybee Colony Vibrational Measurements to Highlight the Brood Cycle

Insect pollination is of great importance to crop production worldwide and honey bees are amongst its chief facilitators. Because of the decline of managed colonies, the use of sensor technology is growing in popularity and it is of interest to develop new methods which can more accurately and less invasively assess honey bee colony status. Our approach is to use accelerometers to measure vibrations in order to provide information on colony activity and development. The accelerometers provide amplitude and frequency information which is recorded every three minutes and analysed for night time only. Vibrational data were validated by comparison to visual inspection data, particularly the brood development. We show a strong correlation between vibrational amplitude data and the brood cycle in the vicinity of the sensor. We have further explored the minimum data that is required, when frequency information is also included, to accurately predict the current point in the brood cycle. Such a technique should enable beekeepers to reduce the frequency with which visual inspections are required, reducing the stress this places on the colony and saving the beekeeper time

Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?

The conservation of insect pollinators is drawing attention because of reported declines in bee species and the ‘ecosystem services’ they provide. This issue has been brought to a head by recent devastating losses of honey bees throughout North America (so called, ‘Colony Collapse Disorder’); yet, we still have little understanding of the cause(s) of bee declines. Wild bumble bees (Bombus spp.) have also suffered serious declines and circumstantial evidence suggests that pathogen ‘spillover’ from commercially reared bumble bees, which are used extensively to pollinate greenhouse crops, is a possible cause. We constructed a spatially explicit model of pathogen spillover in bumble bees and, using laboratory experiments and the literature, estimated parameter values for the spillover of Crithidia bombi, a destructive pathogen commonly found in commercial Bombus. We also monitored wild bumble bee populations near greenhouses for evidence of pathogen spillover, and compared the fit of our model to patterns of C. bombi infection observed in the field. Our model predicts that, during the first three months of spillover, transmission from commercial hives would infect up to 20% of wild bumble bees within 2 km of the greenhouse. However, a travelling wave of disease is predicted to form suddenly, infecting up to 35–100% of wild Bombus, and spread away from the greenhouse at a rate of 2 km/wk. In the field, although we did not observe a large epizootic wave of infection, the prevalences of C. bombi near greenhouses were consistent with our model. Indeed, we found that spillover has allowed C. bombi to invade several wild bumble bee species near greenhouses. Given the available evidence, it is likely that pathogen spillover from commercial bees is contributing to the ongoing decline of wild Bombus in North America. Improved management of domestic bees, for example by reducing their parasite loads and their overlap with wild congeners, could diminish or even eliminate pathogen spillover

Solstice: An Electronic Journal of Geography and Mathematics, Volume XXI, Number 2.

This document was delivered over the internet. Look for animations and .kmz files for Google Earth as attachments within the pdf version of this journal. These appear naturally within the online html version. See the full html files, also located at: http://www.imagenet.org/ The .zip file contains all static images, animated images, and some text files.The purpose of Solstice is to promote interaction between geography and mathematics. Articles in which elements of one discipline are used to shed light on the other are particularly sought. Also welcome, are original contributions that are purely geographical or purely mathematical. These may be prefaced (by editor or author) with commentary suggesting directions that might lead toward the desired interaction. Contributed articles will be refereed by geographers and/or mathematicians. Invited articles will be screened by suitable members of the editorial board. IMaGe is open to having authors suggest, and furnish material for, new regular features.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78440/1/Solstice2010Number2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/78440/3/SolsticeVol21No2.ziphttps://deepblue.lib.umich.edu/bitstream/2027.42/78440/5/SolsticeVolXXINo2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/78440/6/SolsticeVolXXINo2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/78440/8/SolsticeVolXXINo2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/78440/9/Solstice_VolXXINo2.pdfDescription of SolsticeVolXXINo2.pdf : Cover fileDescription of SolsticeVolXXINo2.pdf : Cover of JournalDescription of Solstice2010Number2.pdf : Full journal: Solstice, Volume XXI, Number 2.Description of SolsticeVol21No2.zip : All files including animated images.Description of SolsticeVolXXINo2.pdf : Cover of JournalDescription of Solstice_VolXXINo2.pdf : Solstice with attachments, VolXXI No