Browsing by Subject "Frost"

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    Heat and mass transfer during the melting process of a porous frost layer on a vertical surface
    (2013-05) Mohs, William Francis
    An important problem in the refrigeration industry is the formation and removal of frost layers on sub-freezing air coolers. The frost layer, a porous structure of ice and air, directly diminishes the performance and efficiency of the entire cooling system by presenting resistances to air flow and heat transfer in the air cooler. To return the system to pre-frosted performance the layer must be removed through a defrost cycle. The most common defrost cycle uses heat applied at the heat exchanger surfaces to melt the frost. Current methods of defrosting are inherently inefficient, with the majority of the heat being lost to the surrounding environment. Most studies have concentrated on the formation of the frost layer, and not the melting phenomena during the defrost cycle. In this study, direct measurements and a fundamental model to describe the melting process of a frost layer on a vertical heated surface are presented. The experimental facility provides the first direct measurements of heat and mass transfer during defrost. The measurements confirmed the multistage nature of defrost. The multistage model characterized the different thermal and mass transport processes that dominate each stage. The first stage is dominated by sensible heating of the frost layer. Both the experiment and model showed that heat and mass transfer through sublimation during the initial stages are insignificant, accounting for less than 1% of the total energy transfer. The second stage of defrost is dominated by the melting of the frost layer. The melt rate model generally predicts the front velocity within 25% of the velocity determined using the digital image analysis technique. Higher heat transfer rates resulted in faster melt velocity, and thus shortened defrost times. Evaporation of the melt liquid from the surface dominates the final stage. The heat transfer model for this stage predicts the heat transfer coefficient within ±25% of the experiment. The overall defrost efficiency was found to be primarily dependent on the initial frost thickness, with thicker layer having less heat lost to the ambient space and a higher efficiency.
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    Re-defining rural community spatially separated neighborhoods.
    (2010-08) Schonborn, Bradley Michael
    Frost is small agricultural community in rural southern Minnesota that developed at the turn of the 20th century. In its prime it had a flourishing Main Street with all of the necessities that were required to sustain a small community. There were grocers, hardware stores, barbers, cafes, churches and schools. Today most of those things are gone. Buildings sit empty and lots sit vacant. There are communities like Frost all across the country who have been watching a slow and continuous migration take place over the last few decades. Young people have been leaving the country for opportunities in urban areas. Frost is important because it is emblematic of thousands of other small cities and towns suffering from the effects of this rural migration. The topic of “rural community” is generating a great deal of discussion today amongst policy makers, sociologists, planners and economists. The debate is focused around how rural communities are defined in terms of today’s changing social and economic pressures. Small towns that were once individual self sustaining communities today are reliant on larger cities within their surrounding area for the goods and services that are a part of daily life. Some people suggest that there is no role for a small town like Frost in this evolution. I believe there is and I believe there is a role that designers can play in the planning and design of a rural community. I am interested in this topic because this is a part of me; it is where I am from.