131,253 research outputs found
Study of the Effects of Microgroove Geometry on Frost Structure
No full textThe variation in the frost structure on a number of microgrooved brass surfaces is examined through an experimental study. The microgrooved samples are 45 mm x 45 mm in dimension with a broad range of groove dimensions. Frost is grown on these microgrooved surfaces under natural convection for a range of plate temperature (-8 to -18o C) and relative humidity (30-70%) conditions. The frost structure on the microgrooved surfaces, especially at the early stages of frost formation, is found to be significantly affected by the groove geometry (i.e. groove depth and pillar width). Coalescence of the condensed and hence frozen droplets, covering multiple pillars and grooves, is found to occur more frequently on the surfaces with shallow grooves and/or narrow pillars. For surfaces with intermediate groove depth and pillar width, a regular (brick-wall-like) frost pattern on the pillar surface is observed. Thickness and density of frost layer on the microgrooved surfaces are also found to vary with the dimension of the grooves in frost cycles up to 4 hours long. The relationships between frost structure, frost properties, and frost melt-water drainage is discussed, emphasizing the importance of these morphological features
Frost Formation on Fan-Supplied Tube-Fin Evaporators: A Visual and Numerical Analysis
No full textThis paper presents an experimental and numerical study to evaluate the thermal-hydraulic performance of light commercial capacity evaporators operating under frosting conditions. A tube-fin heat exchanger was tested on a closed-loop wind-tunnel considering the fan performance. A visual analysis of the frost formation processes was carried out to compare the frost layer morphology in different conditions. A mathematical model was developed and the numerical results were compared with the experimental accumulated mass of frost, air flow rate and cooling capacity, with all the predictions falling within the experimental band of uncertainties. Based on this comparison, a frost density correlation was proposed for a typical range of light commercial refrigeration applications. The results show evaporator cooling capacity reductions up to 40% due to frost formation process. Moreover, the effects of air flow reduction and low conductivity frost layer on the overall thermal resistance were analyzed, when it was found that the former is the main cause of the cooling capacity reduction under frosting conditions
Avaliação de métodos para quantificar geada em evaporadores de refrigeradores frost-free
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2015.Em evaporadores no-frost o acúmulo de geada é inevitável. Por degenerar a capacidade de refrigeração do sistema, degelos periódicos são necessários. Esse processo normalmente ocorre através do acionamento de um resistor elétrico e tem impacto negativo para o sistema, pois aumenta a carga térmica e causa variação da temperatura no refrigerador. Portanto, em um refrigerador é normalmente desejada a ocorrência de degelo somente quando necessário, para manter a eficiência do sistema de refrigeração. Entretanto, o atual controle desse processo permite que degelos desnecessários ocorram, não atuando de forma inteligente. Em vista disso, este trabalho tem por objetivo estudar possibilidades de identificação da quantidade de geada presente nos evaporadores para que o degelo possa ser controlado pela demanda. Para isso, investigaram-se experimentalmente diversas possibilidades. Deu-se enfoque às possibilidades que não exigem inserção e utilização de mais transdutores nos refrigeradores. Para os ensaios, construiu-se bancada própria e um refrigerador de modelo comum foi adaptado permitindo a visualização do processo. Testaram-se soluções baseadas na perda de carga do escoamento de ar sobre o evaporador, na eficiência da troca térmica do evaporador e também na evolução das temperaturas do evaporador e suas consequências, tais como a variação de resistência elétrica do resistor de degelo e a do enrolamento do motor do ventilador. Alguns transdutores capacitivos, indutivos e ópticos também foram avaliados. Os melhores resultados foram obtidos nas soluções baseadas na evolução de temperaturas. Um transdutor de fluxo de calor instalado permitiu analisar a influência da geada. Os resultados mostraram a degradação do coeficiente de transferência de calor devido à presença da geada, porém de maneira insuficiente para indicar a quantidade de geada. A possibilidade baseada na análise da dinâmica de variação das temperaturas frente à perturbação do sistema foi validada. Porém, o conceito encontrou obstáculo para diferenciar quantidades menores de geada depositada. Ao final deste trabalho não foi possível encontrar um método eficiente para o presente problema.Abstract : In no-frost evaporator, frost accumulation is unavoidable. Since this accretion depletes the cooling capacity of the refrigeration system, defrosts must be periodically carried out. This process is usually made by electrical heaters but it has a negative impact for the system because it increases the thermal load, and also causes temperature variation in the refrigerator. For this reason, in a refrigerator, it is normally desirable to defrost only as necessary to maintain an efficient cooling system. However, the current control of this process allows unnecessary defrosts, and not intelligent actions. Therefore, the present work aims to study possibilities to identify amount of frost accumulated in evaporators, so that process of melting can be controlled by demand. Because of this, some solutions were experimentally investigated. The main focus were the possibilities that do not require insertion and use of more transducers in refrigerators. In order to test, an experimental apparatus was assembled; a common model of refrigerator was adapted allowing the visualization of the process. Solutions based on the pressure loss of the airflow over the evaporator, the heat exchange efficiency of the evaporator; and the evolution of evaporator temperatures and its consequences, such as the variation of the electrical resistance of the heater and the fan motor winding, were tested. Some sensors, based in capacitive, inductive and optical principle, were also evaluated. The best results were obtained in solutions based on the temperature development. A heat flow transducer installed in coil allowed analysis of the frost. The results showed the degradation of heat transfer coefficient due to the presence of frost, but insufficiently to indicate the amount of frost. The option based on the analysis of the dynamics of temperatures variation by a system disturb was validated. However, the concept encountered an obstacle in real operation condition of refrigerator. At the end of this work was not possible to find an efficient method to this problem
Calculating maximum frost depths at Mn/ROAD : winters 1993-94, 1994-95 and 1995-96
No full text75209This effort involved calculating maximum frost penetration depths for each of the 40 test cells at Mn/ROAD, the Minnesota Department of Transportation's pavement testing facility, for the 1993-94, 1994-95, and 1995-96 winters. The report compares results with measured maximum frost penetration depths for the same three winters. Generally, calculated depths were within plus or minus 15% of measured depths, but differences were much greater for the four test cells underlain by the granular subgrade. Researchers conducted sensitivity tests to determine the influence of the n-factor, soil moisture content, material density, layer thickness, thermal conductivity, mean annual soil temperature, and volumetric latent heat of fusion. Conclusions included the following: (1) Small variation in layer thickness will have a very minor effect on computed frost depths; (2) Reasonable variations in moisture content and density of the various base course, subbase course, and subgrade layers will have a minor effect on calculated frost penetration depths; (3) Large n-factors caused deeper calculated frost penetration depths, and the use of n-factors of .90 and .95, respectively, for flexible and rigid pavements provided the most reasonable estimates of frost depths; (4) Increasing the thermal conductivity of the materials by 25% resulted in closer calculated agreement with measured frost depths; and (5) Using a mean annual soil temperature of 9.4 deg C rather than 11.1 deg C resulted in better agreement between calculated and measured data. Tables, figures. 1879k, 70p
Frost and minimum temperature probabilities
No full textFROST is one of the climatic hazards with which primary producers must contend.
Three distinct types of tables have been produced for each station :
(i) First and last frost occurrence
(ii) Minimum temperature probabilities
(iii) Frost occurrence and duration percentage probabilities
The locations for which these data are available to date arc Charleville, Dalby, Emerald, Goondiwindi and Roma
No. 83, Arthur Frost, interview by Robert Miller
No full textTranscript (31 pages) of interview by Robert Miller with Arthur A. Frost, former chemistry professor at Northwestern University, on March 12, 1985. This interview is no. 83 in the Everett L. Cooley Oral History Project, and tape no. U-262Frost, professor of chemistry at North Western recalls Henry Eyring\u27s contributions to the field of chemistry. Interviewer: Robert Mille
Frost rings frequency as indicator of increased frost susceptibility under current warming
No full textClimate change is observed and predicted to have a profound impact on forest ecosystems. Warmer conditions are one of the main drivers of recent increases in productivity and changes in structure and function observed in forests growing in temperature-limited environments. However, the extent of these changes is not homogeneous. With growing seasons lengthening but temperature variability increasing plants remains at risk of frost damage that could negatively affect plant growth.
This research aims to investigate the timing and occurrence of frost rings in tree species to get insight on how current warming impacts cold adaptation strategies in trees.
In this study, we investigate the sensitivity to frost events in three high altitude tree species Larix decidua Mill., Picea abies L., and Pinus cembra L. We analysed ring width time series of X individuals collected in from two sites in the Eastern Alps (Croda da Lago (BL) and Latemar (BZ) and identified frost rings. By considering daily temperature records, we were able to determine the day in which these frost rings had been formed.
Results show that for all the species at both sites, there is a trend of earlier frost ring formation over the last century and a half, shifting from late June in the mid-1800s to mid-May. This shift could confirm the earlier onset and lengthening of cambial activity, increasing the susceptibility time window of trees to frost damage. These findings provide valuable insights into cambial phenology, offering a deeper understanding of how shifting climate patterns influence the timing and activity of tree growth
Frost, M L, NX10701
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/386443Surname: FROST. Given Name(s) or Initials: M L. Military Service Number or Last Known Location: NX10701. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 36016.208213
Item: [2016.0049.18736] "Frost, M L, NX10701
Frost, D L, 403918
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/386432Surname: FROST. Given Name(s) or Initials: D L. Military Service Number or Last Known Location: 403918. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 48316.208202
Item: [2016.0049.18725] "Frost, D L, 403918
Modelagem semi-empírica de um refrigerador frost-free sujeito à abertura de portas
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.O projeto de refrigeradores domésticos é focado não somente na redução do consumo de energia em condições normalizadas, mas também em condições reais de operação, quando as portas dos compartimentos refrigerados são abertas periodicamente. Nesse caso, há transporte de umidade para os compartimentos refrigerados com consequente formação de geada sobre o evaporador, redução da vazão de ar e elevação no tempo de funcionamento do compressor. O efeito de tais fenômenos deve ser considerado para o adequado projeto dos componentes assim como para a definição de estratégias de controle do produto. A robustez do produto à formação de geada é geralmente estudada através de ensaios experimentais complexos, demorados e dispendiosos. Tal cenário favorece o uso de modelos matemáticos, embora nenhum dos modelos disponíveis na literatura seja capaz de simular o comportamento de um refrigerador doméstico submetido a ciclos de aberturas de portas e a consequente formação de geada sobre as superfícies do evaporador. Para eliminar essa lacuna, desenvolveu-se um modelo matemático para simular o comportamento transiente de um refrigerador doméstico sujeito a condições típicas de um teste de robustez à formação de geada. Para tanto, adotou-se uma abordagem semi-empírica, onde os componentes do refrigerador foram modelados com base em trabalhos disponíveis na literatura. Alguns dos parâmetros empíricos associados aos modelos desses componentes foram derivados de resultados experimentais obtidos com o próprio refrigerador. As estimativas do modelo foram devidamente validadas contra dados experimentais. O desvio máximo observado na previsão da evolução temporal da vazão mássica de refrigerante, da potência consumida e das pressões de evaporação e condensação foi de ±10%, da perda de carga no evaporador de ±20%, da massa de geada acumulado no evaporador de ±30% e das temperaturas dos compartimentos refrigerados de ±2ºC. Além disso, o modelo foi utilizado para estimar o comportamento de variáveis não facilmente mensuráveis tais como a evolução temporal da posição da fronteira entre as regiões bifásica e superaquecida no evaporador, da densidade e espessura da camada de geada e da distribuição da massa de geada e da perda de carga em cada fileira do evaporador.Abstract : Modern refrigerator design is aimed not only at energy savings but also at product robustness to evaporator frosting. Whilst the former is evaluated by means of standardized test procedures, the latter is assessed by testing the refrigerator under real usage conditions, when the doors are opened in a regular basis, allowing moisture to enter the refrigerated compartment and, consequently, frost to accumulate on the evaporator surface. As the frost layer grows, the air-side pressure drop rises, reducing the air flow rate and, therefore, the evaporator capacity. As a consequence, the compressor is driven to run longer cycles, thus increasing the energy consumption. The laboratory procedures required for product assessment and development rely on costly and time consuming experiments. Albeit it has been advocated that the adoption of simulation models may aid the product development process, there is no model available in the open literature which is capable of simulating the refrigerator performance under door-opening and frost build-up conditions. Therefore, a mathematical model for simulating the transient behavior of a domestic refrigerator in such conditions has been advanced in this work. A first-principles simulation model was put forward for the refrigeration loop, whereas a semi-empirical approach was adopted for the refrigerated compartment, in such a way that the key empirical parameters were obtained by testing the refrigerator in an environmental chamber. The model was validated against experimental data, when it was found that its predictions for power consumption and refrigerant mass flow rate fell within a ±10% error band, its predictions for accumulated frost mass were within a ±20% error band, and its predictions for compartment air temperatures were within a ±2K error band. The model is also capable of predicting the behavior of some non-measurable variables, such as the time evolution of the liquid-vapor to vapor transition point of the refrigerant in the evaporator, the density and thickness of the frost layer over the different rows of the evaporator and also the contribution of each of these rows on the air side pressure drop on the evaporator
- …
