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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Relação da tolerância ao frio de espécies do gênero Eucalyptus e Pinus com a presença de carboidratos totais em sementes e mudas / Relationship of cold tolerance of species of the genus Eucalyptus and Pinus in the presence of total carbohydrates in seeds

Schneider, Priscilla Félix 27 February 2014 (has links)
Made available in DSpace on 2016-12-08T16:44:46Z (GMT). No. of bitstreams: 1 PGPV14MA133.pdf: 884014 bytes, checksum: b440026c6c3ad9eccfc95b8c3d78bfa9 (MD5) Previous issue date: 2014-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Aimed to evaluate the concentration of soluble carbohydrates in different species of Eucalyptus and Pinus taeda L and its relationship with cold tolerance, and determine the best method to defrost in seeds of Eucalyptus. Pure seeds from three clones of the species were used: Eucalyptus dunnii Maiden, Maiden et Cambage benthamii E. grandis Hill ex Maiden and E. saligna. Was used seedlings E. benthamii and E. dunnii, two clones each. Seeds and seedlings were subjected to hardening into three periods at temperatures of 5 ° C and 1 ° C, photoperiod and thermoperiod 12 hours. At the end of each level of hardening, the seeds were subjected to four gradients (-2 , -4 , -6 and -8 ° C) , with an exposure of three hours. Before hardening, and photoperiod were maintained in controlled thermoperiod 20 º C and 12 º C and a treatment for three days and the other for six days. The temperature was changed to 15 º C and 9 º C. Then reduced to 10 ºC and 5 º C. Determined the concentration of sugars and survival after hardening. Seeds were subjected to two methods of thawing water bath and environment. Data were subjected to analysis of variance and mean comparison test (Tukey p < 0.05). The results indicated that the sugar concentration does not influence cold tolerance at - 8 ° C and the best method is to thaw at room temperature / Objetivou-se avaliar a concentração de carboidratos solúveis totais em diferentes espécies de Eucalyptus e Pinus taeda Le sua relação com a tolerância ao frio, além de determinar o melhor método de descongelamento em sementes de Eucalyptus. Foram utilizadas sementes puras de três clones das espécies: Eucalyptus dunii Maiden, E. benthamii Maiden et Cambage E. grandis Hill ex Maiden e E. saligna Smith. Utilizou-semudas de E. benthamii e E. dunnii, de dois clones cada. As sementes e as mudas, foram submetidas à rustificação em três períodos a temperaturas de 5 ºC e de 1 ºC. Ao final de cada nível de rustificação, as sementes foram submetidas a quatro gradientes (-2, -4, -6 e -8 ºC), com exposição de três horas. A temperatura foi alterada para 15 ºC e 9 ºC. Determinou-se a concentração de açúcares e a sobrevivência das após a rustificação. As sementes foram submetidas a dois métodos de descongelamento, banho maria e ambiente. O experimento foi realizado com quatro repetições. Os dados obtidos foram submetidos à análise da variância e teste de comparação de médias (Tukey a p<0,05). Os resultados indicaram que a concentração de açúcares não influencia a tolerância ao frio em - 8ºC e, o melhor método de descongelamento é em temperatura ambiente
2

Modeling and Numerical Investigation of Hot Gas Defrost on a Finned Tube Evaporator Using Computational Fluid Dynamics

Ha, Oai The 01 November 2010 (has links) (PDF)
Defrosting in the refrigeration industry is used to remove the frost layer accumulated on the evaporators after a period of running time. It is one way to improve the energy efficiency of refrigeration systems. There are many studies about the defrosting process but none of them use computational fluid dynamics (CFD) simulation. The purpose of this thesis is (1) to develop a defrost model using the commercial CFD solver FLUENT to simulate numerically the melting of frost coupled with the heat and mass transfer taking place during defrosting, and (2) to investigate the thermal response of the evaporator and the defrost time for different hot gas temperatures and frost densities. A 3D geometry of a finned tube evaporator is developed and meshed using Gambit 2.4.6, while numerical computations were conducted using FLUENT 12.1. The solidification and melting model is used to simulate the melting of frost and the Volume of Fluid (VOF) model is used to render the surface between the frost and melted frost during defrosting. A user-defined-function in C programming language was written to model the frost evaporation and sublimation taking place on the free surface between frost and air. The model was run under different hot gas temperatures and frost densities and the results were analyzed to show the effects of these parameters on defrosting time, input energy and stored energy in the metal mass of the evaporator. The analyses demonstrate that an optimal hot gas temperature can be identified so that the defrosting process takes place at the shortest possible melting time and with the lowest possible input energy.

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