Exogenous application of molybdenum affects the expression of CBF14 and the development of frost tolerance in wheat.

Wheat is able to cold acclimate in response to low temperatures and thereby increase its frost tolerance and the extent of this acclimation is greater in winter genotypes compared to spring genotypes. Such up-regulation of frost tolerance is controlled by Cbf transcription factors. Molybdenum (Mo) application has been shown to enhance frost tolerance of wheat and this study aimed to investigate the effect of Mo on the development of frost tolerance in winter and spring wheat. Results showed that Mo treatment increased the expression of Cbf14 in wheat under non-acclimating condition but did not alter frost tolerance. However, when Mo was applied in conjunction with exposure of plants to low temperature, Mo increased the expression of Cbf14 and enhanced frost tolerance in both spring and winter genotypes but the effect was more pronounced in the winter genotype. It was concluded that the application of Mo could be useful in situations where enhanced frost resistance is required. Further studies are proposed to elucidate the effect of exogenous of applications of Mo on frost resistance in spring and winter wheat at different growth stages

Device for determining frost depth and density

A hand held device having a forward open window portion adapted to be pushed downwardly into the frost on a surface, and a rear container portion adapted to receive the frost removed from the window area are described. A graph on a side of the container enables an observer to determine the density of the frost from certain measurements noted. The depth of the frost is noted from calibrated lines on the sides of the open window portion

Frost as an insulator

Insulating qualities of frost and mechanisms for using frost in specific applications in controlled experiments are discussed. With available supply of moist air, frost possesses inherent advantage of easy insulation of cryogenic lines and improvement of overall system efficiency

The control of carbon dioxide cryodeposits

An experimental study has been conducted to investigate the parameters affecting the cryodeposition of carbon dioxide frost. In the investigation carbon dioxide frost was cryodeposited from a helium-carbon dioxide mixture into a layer of fibrous insulation surrounding a cylindrical cryogenic tank. Results of the study indicated that not only did deposition occur on the frost surface but also within the frost layer. Over the range of variables investigated both the frost density and the mass of frost deposited were most sensitive to the time of deposition, the percent of carbon dioxide in the purge-gas mixture, and the thickness of the insulation. Frost density and mass of frost deposition were found to increase with time and percent carbon dioxide, and to decrease with increasing insulation thickness

The effect of favourable and unfavourable frost on air cooling coil performance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology, at Massey University

The most common type of air cooling coil used in the refrigeration industry is the finned tube heat exchanger. The performance of such coils can be greatly hindered by frost formation, which will occur when the coil surface temperature is both below the dewpoint of the air passing over it, and below 0°C. Frost reduces performance, both through the increased thermal resistance of the frost layer, and by reduction of the air flow through the coil. Whilst frosting on coils is influential on performance, there is comparatively little information available on the performance of finned tube heat exchangers under frosting conditions. Smith (1989) has proposed an "unfavourable" frost formation theory. The theory states that unfavourable frost formation occurs when the line representing the temperature and humidity of the air passing through the coil, crosses the saturation line of the psychrometric chart. This criteria is more likely to occur under conditions of high relative humidity, low sensible heat ratio (SHR), and/or high refrigerant-to-air temperature difference (TD). Under unfavourable conditions it is suggested that the frost will be of particularly low density, which would cause coil performance to decline to a much greater extent for the same total frost accumulation, than under "favourable" frosting conditions. The objectives of this study were to measure the change in performance of a cooling coil under frosting conditions, and to assess the validity of the unfavourable frost formation theory. A calorimeter style coil test facility was used, that allowed coil performance to be measured as frost accumulated in a manner consistent with coil operation in industrial practice (i.e. declining air flowrate and a wide range of SHR's). The data collected supported the concept of unfavourable frost formation with a more rapid decline in performance for operation with low SHR, than that at high SHR, for the same total frost accumulation. Some recovery of coil performance was observed when operation at low SHR (with rapid performance deterioration) was followed by a period of high SHR operation. Equations were developed that allowed the theoretical conditions for the formation from favourable to unfavourable frosting to be quantified. The measured change in the rate of coil performance deterioration with frost buildup was dependent on air and coil conditions, in a manner consistent with these equations. The transition between favourable and unfavourable frost formation appeared to be related to the lowest temperature on the coil surface rather than the mean surface temperature. Satisfactory predictions of frost formation types were obtained by using the refrigerant evaporation temperature as an approximation to the lowest coil surface temperature

Simulating the Performance of a Heat Exchanger During Frosting

Factors affecting frost distribution are explored using a finite element model, developed and validated using a full-scale 8-row heat exchanger in a wind tunnel. The heat exchanger is typical of the type used in supermarket display cases; so face velocities and air inlet temperatures were varied from 0.5-2.3 m/s and 0 to -20 ??C, respectively, and inlet humidities from 70-90%. In order to focus on frost distribution, the prototype was designed to have a simple geometry and single-phase refrigerant to provide maximum certainty on parameters not directly related to frost. Measured and predicted total and sensible heat transfer agreed within RMS 6% and 8%, respectively, over the range of operating conditions. For latent heat, there was more scatter due to frost nonuniformities induced by the experimental apparatus. The simulation model was used to illustrate how the point of maximum frost thickness moved from the front to the rear of the heat exchanger, depending on face velocity, inlet humidity and fin surface temperature. Heat transfer and pressure drop were calculated from standard correlations, with fin thickness and tube diameter increasing as a function of frost thickness. The model was further extended to simulate the performance of the heat exchanger under the effect of a fan curve. A comparison is made between DX and indirect refrigeration system performance with respect to capacity, pressure drop and air flow variations under frosting conditions.Air Conditioning and Refrigeration Project 10

Concrete Pavement Mixture Design and Analysis (MDA): Assessment of Air Void System Requirements for Durable Concrete, TPF-5(205), 2012

Concrete will suffer frost damage when saturated and subjected to freezing temperatures. Frost-durable concrete can be produced if a specialized surfactant, also known as an air-entraining admixture (AEA), is added during mixing to stabilize microscopic air voids. Small and well-dispersed air voids are critical to produce frost-resistant concrete. Work completed by Klieger in 1952 found the minimum volume of air required to consistently ensure frost durability in a concrete mixture subjected to rapid freezing and thawing cycles. He suggested that frost durability was provided if 18 percent air was created in the paste. This is the basis of current practice despite the tests being conducted on materials that are no longer available using tests that are different from those in use today. Based on the data presented, it was found that a minimum air content of 3.5 percent in the concrete and 11.0 percent in the paste should yield concrete durable in the ASTM C 666 with modern AEAs and low or no lignosulfonate water reducers (WRs). Limited data suggests that mixtures with a higher dosage of lignosulfonate will need about 1 percent more air in the concrete or 3 percent more air in the paste for the materials and procedures used. A spacing factor of 0.008 in. was still found to be necessary to provide frost durability for the mixtures investigated