14,064 research outputs found

    An Experimental Investigation of the Air-Side Convective Heat Transfer Coefficient on Wire and Tube Refrigerator Condenser Coils

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    This thesis presents the results of an experimental investigation of the convective airside heat transfer from wire and tube condensers. The ftrst law of thermodynamics is applied to the "refrigerant", water in this investigation, flowing through the tubes in order to determine the total heat loss from the condenser. The test section is 910 mm (36 in) wide by 300 mm (12 in) tall; thus the coil is tested in an essentially inftnite stream. During the course of the experiments, the influence of the free stream air velocity ranging from 0.15 rn/s to 2.0 rn/s (0.49 ftls to 6.56 ftls) is established. The angle of attack, n, was varied from - 40 degrees to 40 degrees with the air flow always normal to the tubes ('11= 1t/2) and varied from -20 degrees to 20 degrees with the air flow normal to the wires ('II = 0). A method for , calculating view factors and the radiation heat transfer for wire and tube condensers is derived. The effect of the length of the coil is measered at 0 and -5??angle of attack. In addition, the influence of the ftn efftciency on the heat transfer is investigated and accounted for in the deftnition of the heat transfer coefftcient. The heat transfer data in the inertia dominated regime (Richardson number less than 0.0013) are correlated assuming NUcoil = t(Re, n, 'II)' g( S: ) with the Reynolds number based on the wire diameter. The range of Reynolds numbers covered is 15.7 < Rew < 207.5. The ranges of coil geometric parameters (nondimensionlized by dividing by the wire diameter) covered in this study are: 3.022 < nondimensional tube diameter < 5.134, 18.84 < nondimensional tube spacing < 40.94,2.819 < nondimensional wire spacing < 4.427,53.80 < nondimensional tube length< 143.6, and 207.2 < nondimensional wire length < 500.2. The function is represented by tl(a)??Reh (a) for 'II = 0 and h(a).Rei4 (a) for'll=1t/2. Approximately 1700 tests were performed in this investigation using seven different coils. The ftnal correlation is capable of predicting the data with 2cr equal to 16.7% for Ri < 0.0013. A limited natural convection study is also presented.Air Conditioning and Refrigeration Center Project 4

    Allozyme and mitochondrial DNA variability within the New Zealand damselfly genera Xanthocnemis, Austrolestes, and Ischnura (Odonata)

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    We collected larval damselflies from 17 sites in the North, South and Chatham Islands, and tested the hypotheses that: (1) genetic markers (e.g., allozymes, mtDNA) would successfully ¬discriminate taxa; and (2) the dispersal capabilities of adult damselflies would limit differentiation among locations. Four species from three genera were identified based on available taxonomic keys. Using 11 allozyme loci and the mitochondrial cytochrome c-oxidase subunit I (COI) gene, we confirmed that all taxa were clearly discernible. We found evidence for low to moderate differentiation among locations based on allozyme (mean FST = 0.09) and sequence (COI) divergence (<0.034). No obvious patterns with respect to geographic location were detected, although slight differences were found between New Zealand’s main islands (North Island, South Island) and the Chatham Islands for A. colensonis (sequence divergence 0.030–0.034). We also found limited intraspecific genetic variability based on allozyme data (Hexp < 0.06 in all cases). We conclude that levels of gene flow/dispersal on the main islands may have been sufficient to maintain the observed homogeneous population structure, and that genetic techniques, particularly the COI gene locus, will be a useful aid in future identifications

    Scotland as an Optimal Currency Area

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    Since the Scottish independence movement has reached the point that there will be a referendum on Scottish independence this September, the issue of whether the Scotland is optimal currency areas is very topical.In this paper we review the microeconomic foundations of an optimal currency area. We test these microeconomic foundations. We find that the UK, Scotland and the UK without Scotland meet the microeconomic criteria for a common currency area. While adopting a common currency is ultimately a political decision, these results imply that the broadest of these areas, the UK, is the optimal currency area in the sense of minimizing transactions costs.We do find differences in the UK less Scotland and Scotland economies in loan data. We further find that neither the euro bloc nor the euro bloc including Scotland meet the microeconomic criteria for a common currency area. In the event of a “yes” vote for Scottish independence, the immediate problem facing the Scottish government is to decide on an exchange rate regime that is seen as credible by the financial markets to avoid a flight of capital. How policymakers chooses between alternative exchange rate regimes is currently a topic for hot debate in central banking circles and the process of a monetary union breaking up is a fascinating area worthy of future research

    At the Collision Between

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    Grace

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