Some effects of post-harvest treatments of abscisic acid (ABA) and kinetin on the maintenance of quality and consumer appeal were studied on young lettuce plants. The treatments employed two concentrations of abscisic acid (1 and 5 ppm), one concentration of kinetin (20 ppm) and a combination of 5 ppm abscisic acid and 20 ppm kinetin. The plants were sprayed to the run-off point and placed in a storage chamber at 3±1°C with relative humidity close to 100%. After 6 weeks of storage all lettuce including untreated controls were in good condition. The chemical treatments did not have any distinct effect on the quality of lettuce as evaluated by a panel of observers for visual quality rating. The 20 ppm kinetin retarded chlorophyll degradation when compared to the control or the ABA-only treatments. Considering chlorophylls A and B separately, the kinetin-treated plants showed a significantly higher chlorophyll A content than other treatments, including the control. The differences in chlorophyll B content followed the same trend but only approached the 5% level of significance. ABA in the 5 ppm + 20 ppm kinetin treatment had a mild antagonistic activity to kinetin, and hence reduced the effect of kinetin on both chlorophyll A and B. Measurement of chlorophyll contents and adjustment to the original fresh weight before the samples were put in storage, provided a common basis to make comparisons for the study of chlorophyll degradation as functions of storage time and chemical treatment. Means of chlorophyll contents reported on this basis showed a trend of degradation from the 5th week to the 7th week. Temperature at 3±1°C and high relative humidity in the storage appear to be favourable for keeping lettuce. Hygenic preparation of the storage chamber also resulted in disease-free product even at the end of 7 weeks in storage. / Land and Food Systems, Faculty of / Graduate

The moisture loss and changes in colour and firmness of tomatoes in storage were investigated using a 4x4x5 factorial experiment. The first factor selected involved four delay times after harvest, before cooling. After harvest, the tomatoes were left at room temperature for 0 hours, 10 hours, 20 hours and 30 hours, respectively, before being cooled. The second factor involved four pre-storage treatments to reduce moisture loss : (a) wrapping the individual tomatoes in polymeric film, (b) waxing the calyx or stem ends only, with a fruit wax, (c) applying wax to the whole surfaces of individual fruits, and (d) control, with no treatment. The third factor consisted of five controlled temperature and humidity storage environments : a) 10°C and 90% rh (relative humidity); b) 15°C and 88% rh; c)10°C and 60% rh; d)15°C and 50% rh; and e)18°C and 40% rh. An analysis of variance of the results showed that individually wrapping tomatoes in polymeric film resulted in the lowest rates of weight, loss during the steady state. Also the rate of weight loss from a tomato was found to be influenced by the storage condition (combination effect of temperature and humidity), and the air flow characteristics inside the storage chamber. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The prevention of storage disorders in sweet cherries resulting from mechanical damage was investigated. Pre- and post-harvest treatments were applied to modify fruit texture, fruit composition and fruit desiccation in storage. The effects of the treatments applied were related to fruit susceptibility to the incidence of fruit bruises, surface markings and surface pitting. The application of calcium in the form of pre-harvest sprays or post-harvest dips decreased mechanical damage expression. Warm fruit was less susceptible to mechanical injury than cold fruit early in the storage period but fruit temperature had little effect after 8 days of cold storage. Similarly, high storage temperatures enhanced pitting development early in the storage life but storage temperatures had negligible effect after 8 days. A delay in 0℃ storage prior to bruising greatly reduced the susceptibility of cherries to mechanical injury. Fruit was most resistant to mechanical damage after 8 days in 0°C. The development of fruit symptoms in response to impact was enhanced by rough surfaces. Slowly applied compressive forces resulted in low incidences of injury symptoms. Fruit firmness and bioyield values were increased with mesocarp calcium from preharvest sprays and post-harvest dips, but did not show consistent relationships to the susceptibility of fruit to mechanical damage. Weight loss enhanced by low relative humidity increased the rate of development of damage but did not influence the total damage incidence. Soaking fruit in water or fungicide solution increased damage expression in storage. Less mature and intermediate maturity fruit were more susceptible to mechanical injury than were the most mature fruit. Fruit with relatively high alcohol insoluble solids content associated with pre-harvest gibberellic acid sprays or advanced maturity fruit had reduced susceptibility to mechanical damage. Large fruit was less susceptible to mechanical damage and had higher alcohol insoluble solids content than did small fruit. High levels of fruit nitrogen were associated with high susceptibility to mechanical damage. A great many factors were found to modify fruit susceptibility to surface disorders resulting from mechanical damage. This provides a great flexibility to producers and marketing agents to minimize fruit losses due to the effects of rough handling. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.

No description available.

Graduation date: 1950

Thesis (Ph. D.)--University of Florida, 1982. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 140-143).

abstract: This thesis concerns the impact of energy storage on the power system. The rapidly increasing integration of renewable energy source into the grid is driving greater attention towards electrical energy storage systems which can serve many applications like economically meeting peak loads, providing spinning reserve. Economic dispatch is performed with bulk energy storage with wind energy penetration in power systems allocating the generation levels to the units in the mix, so that the system load is served and most economically. The results obtained in previous research to solve for economic dispatch uses a linear cost function for a Direct Current Optimal Power Flow (DCOPF). This thesis uses quadratic cost function for a DCOPF implementing quadratic programming (QP) to minimize the function. A Matlab program was created to simulate different test systems including an equivalent section of the WECC system, namely for Arizo-na, summer peak 2009. A mathematical formulation of a strategy of when to charge or discharge the storage is incorporated in the algorithm. In this thesis various test cases are shown in a small three bus test bed and also for the state of Arizona test bed. The main conclusions drawn from the two test beds is that the use of energy storage minimizes the generation dispatch cost of the system and benefits the power sys-tem by serving the peak partially from stored energy. It is also found that use of energy storage systems may alleviate the loading on transmission lines which can defer the upgrade and expansion of the transmission system. / Dissertation/Thesis / M.S. Electrical Engineering 2012

Thermal energy storage via the latent heat of suitable phase change materials has the advantages of higher energy storage density and relatively isothermal behaviour compared to sensible heat storage systems. Glauber's salt (Na₂S0₄∙10H₂0) is one of the most extensively studied phase change materials for solar energy systems because of its low price, suitable phase change temperature and high latent heat. However, segregation due to incongruent melting behaviour leading to loss in the heat storage efficiency upon repeated melting-freezing cycling is a serious problem which has severely limited application of Glauber's salt. In this study Glauber's salt was encapsulated in 25 mm diameter hollow spheres and agitated in different systems including a liquid fluidized bed, rotating drum and rotating tube to reduce or eliminate the Toss in its heat storage efficiency. The encapsulated mixture consisted of 96% Glauber's salt and 4% borax by weight with 5% by volume air space in the capsules. Some capsules containing 25%, 15% and 5% by weight excess sodium sulfate and 10% by weight excess water were also prepared, to test the effect of sodium sulfate concentration under different agitation conditions. The heat storage capacity of 5756 capsules, agitated by fluidizing with water in a pilot plant size (0.34 m diameter) column, showed a decrease over the first three cycles to about 60% of that theoretically possible, but there was no further decrease over the next 93 cycles under fluidization conditions. The heat storage efficiency was found to be improved by increasing the superficial water velocity and by decreasing the cooling rate. Heating rate had little or no effect. The fluidized capsules provide enhanced heat transfer rates to or from the heat storage medium, enabling the energy to be charged or discharged in about one hour with realistic inlet and outlet temperatures. The high heat transfer rates are an important advantage for the system and may open new areas of applications for thermal energy storage by encapsulated phase change material. Economic analysis of the liquid fluidized bed heat storage system shows that operating costs are almost negligible compared to fixed capital costs. The heat storage efficiency of capsules decreased to 38.4% of the theoretical capacity or 67% of the corresponding agitated (fluidized) system in only 7 cycles under fixed bed conditions, and the efficiency decreased with further cycling. 97.5% of the original heat storage-capacity was recovered within three cycles when these capsules were refluidized. Performances of the regular and different composition capsules were tested in the rotating tube, with rotation around a fixed horizontal axis passing through the capsules' centers, and in the rotating drum, with impact due to collisions in addition to rotation. The results showed that full rotation of a capsule around a horizontal axis improves the heat storage efficiency. However, full recovery of the theoretical capacity was not possible, even under vigorous mixing conditions. The efficiencies in the rotating tube were similar to those in the rotating drum for capsules subject to the same number of rotations around a horizontal axis. At high rotation speeds centrifugal force had a negative influence, especially in the rotating tube. On the basis of heat storage capacity per unit volume or weight of phase change material, 47% by weight sodium sulfate concentration was found to be optimal for the rotating drum and the rotating tube cases. Some small scale experiments were performed to determine the relative importance of different factors in the loss of heat storage capacity. Sodium sulfate concentration gradients in the capsules with different thermal cycling histories were found by thermogravimetric analysis. The results showed that bulk segregation of anhydrous sodium sulfate is not the only reason for the loss of heat storage capacity in systems using Glauber's salt. Microencapsulation of anhydrous sodium sulfate beneath a layer of Glauber's salt crystals is at least as important. Experiments to determine the degree of subcooling, believed to be another factor in the loss of heat storage capacity, showed that a mixture of 96% Glauber's salt and 4% borax by weight undergoes subcooling of about 5 K in gently agitated capsules. Nucleation and crystallization temperatures both increase with increased agitation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate