WO2021112780A1

WO2021112780A1 - A preservative containing phase-changing materials for thermal protection of citrus trees

Info

Publication number: WO2021112780A1
Application number: PCT/TR2019/051148
Authority: WO
Inventors: Yalcin YALAKI; Halime OMUR PAKSOY
Original assignee: Cukurova Universitesi Rektorlugu
Priority date: 2019-12-02
Filing date: 2019-12-20
Publication date: 2021-06-10

Abstract

The invention relates to the thermal protection and prevention of damage of the body parts of citrus plants by thermal energy storage method by using Phase-Change Materials during a frost event.

Description

A PRESERVATIVE CONTAINING PHASE-CHANGING MATERIALS FOR THERMAL PROTECTION OF CITRUS TREES TECHNICAL FIELD OF THE INVENTION

The invention relates to the thermal protection and prevention of damage to the body parts of citrus plants during a frost event.

PRIOR ART Various methods developed to protect plants from frost damage are available in the literature. These methods are classified as passive and active methods which are briefly summarized below.

Passive methods include location selection, which is the method of avoiding agricultural activity in frost-risk areas; plant management, which is the method of taking measures such as fertilizing and strengthening the plants to increase their resistance to frost; plant selection and production, which is the method of preferring the planting of frost-resistant plants.

Active methods include stopping radiation to the atmosphere with artificial fog, which is the method of stopping heat loss by radiation with artificial fog created by spraying water into the air; heat insulation, which is the method of preventing heat loss by coating plants with non-toxic protein foams; air-mixing, which is the method of mixing the air cooled by contact with the ground with the warmer air 150 m above the ground with the help of fans and thus raising the air temperature around the plant by a few degrees. Other active methods include direct air and plant heating, which is a method of directly heating the plant environment by using fuels and equipment such as coal, diesel oils, etc.; forced harvest, which is a method of harvesting mature products urgently in the case of an imminent frost; soil cultivation and management, which is a method of cleaning and pressing the soil and keeping it moist and thus providing more heat storage.

Another active method is the application based on covering the surfaces of plants with water droplets by irrigation with sprinkling from the top and protecting the plant with the generated heat resulting from freezing of water at low temperature. In this application, the plant temperature is tried to be kept from falling below zero degrees thanks to the ice covering the plant surface.

Still another active method is delaying flowering, which is the method of putting snow or ice in a diameter of 1 m around the root of the plant and keeping the plant cold in order to delay the flowering of fruit trees where frost events are frequent.

LIST OF FIGURES

Figure 1. Schematic representation of the PCM package model Figure 2. Thermal protection performance of the developed PCM packages Figure 3. Application of the developed PCM packages to the tree trunk

Figure 3.1. Application of the developed PCM packages to the tree trunk

MEANINGS OF NUMBERS SHOWN IN THE FIGURES

1. Sapling 2. Insulation material

3. Packet with PCM solution

4. Stabilizer

BRIEF DESCRIPTION OF THE INVENTION Within the scope of our present invention, it is aimed to protect citrus saplings from frost damage with the thermal energy storage (TES) method, which is different from the methods specified in the previous techniques and potentially more useful, cheaper and more effective.

TES is classified as latent, sensible, and chemical storage. The amount of energy stored is determined by the heat of phase change in latent heat storage systems, specific heat and temperature difference of the storage material in sensible heat storage systems, and the reaction enthalpy in chemical storage. Chemical storage is a newer area and its commercial applications are limited. Latent and sensible heat storage systems are more commonly used and have commercial applications. The advantage of latent heat storage among these methods is that it allows higher density energy storage in small temperature changes. Latent heat storage uses Phase-Changing Materials (PCM). PCMs are classified as solid-liquid, liquid-gas, solid-gas and solid-solid based on the type of phase change. Those containing the gas phase are impractical because they require large volume changes and do not have commercial applications. Solid-solid phase changes are related to the transition from one crystal type to another crystal type and their use is limited because the phase change heat is generally low. Among PCMs, the most used types are those that include solid-liquid phase changes. PCMs act as thermal regulators thanks to the heat they receive from or release to the environment in proportion to their mass during phase changes and they limit the temperature change in their environment. Because of this advantage, among TES systems, latent heat storage was used in this study. With this method, the aim was to store enough thermal energy with PCM placed in a limited volume to provide protection in a narrow temperature range for sufficient time.

DETAILED DESCRIPTION OF THE INVENTION

Increased extreme temperature events due to global climate change cause damage to plants, reduced production in agriculture and material losses. One of the extreme temperatures that adversely affect agriculture is frost. The frost event is a meteorological phenomenon that occurs especially at night when the temperature drops below 0°C. Damage to citrus plants due to frost in winter is a problem that has been known for a long time. Frost events are classified as mild, moderate and severe based on the level of damage endured by the plants. This classification is summarized in Table 1.

Chart 1. Classification of the frost event

Among citrus plants, lemon begins to be damaged at -3.5°C and orange at -5°C during frost events. Frost damage affects the leaves, flowers, fruits and trunks of citrus trees, but the damage to the trunk makes it much harder for the plant to recover than the damage to the leaves, flowers and fruit.

Small-molecule alcohol solutions were used as PCMs to thermally protect the body parts of citrus plants during frost events and to prevent damage. Solutions of ethanol (E), one of the most used alcohols in the industry, ethylene glycol (EG) and propylene glycol (PG), which are frequently used as antifreeze in the industry, were prepared and used as PCM. The advantages of these alcohols are that they are not corrosive, they completely mix with water, they are chemically stable and the freezing points of their aqueous solutions are below zero. The phase change heat of the prepared PCM solutions were intended to keep the plant temperature in the range of -2/-4 °C, thus protecting the plants from excessive frost damage. For this purpose, the phase change temperatures (freezing points) of the PCM solutions must be within this range. Freezing points of the alcohol solutions selected as PCMs at a concentration of 10% by volume are shown in Table 2. Accordingly, concentrations of E and EG solutions have been prepared slightly lower to obtain freezing points around -2/-3 °C, which is a slightly safer level (Table 2).

Chart 2. Concentrations and methods of preparation of alcohol solutions prepared as PCM

Different amounts of solutions were prepared using the ratios given in Table 2. A nucleating agent was used to solve the supercooling problem in the prepared PCM solutions. Supercooling occurs when a liquid does not freeze at temperatures below its freezing point. Nucleating agents are substances that facilitate crystal formation in supercooled liquids. The crystal structure of silver iodine (Agl) is similar to that of ice and is one of the best nucleating agents for water. Because of this feature, 1 % of Agl by mass was used as the nucleating agent in this study to trigger phase change (freezing) of PCM solutions, which contain mostly water.

Plastic produced from polyethylene with additives has been used for the packaging of prepared PCM solutions, but PVC (polyvinyl chloride) material that is more durable can also be used for the same purpose. Packages (3) containing PCM solutions with appropriate sizes to fit 250m L of the solutions were prepared with a plastic sealing machine as models for use in experimental measurements. A 5 mm (millimeter) thick polyethylene foam material with 100kg/m³ density (2) was added to one surface of the packages (3) containing PCM solutions as insulation layer. Packages (3) containing PCM solution combined with insulation material (2) were wrapped around a citrus sapling sample (1 ) and fixed with the plastic clamp stabilizers (4) and experimental measurements were taken. Figure 1 shows the schematic representation of the prepared model.

In order to determine the thermal protection performance of the packages (3) containing the developed PCM solutions, each PCM package (3) was respectively wrapped on a sapling body sample and temperature changes were measured with thermocouple sensors placed on the sapling sample which was placed in an incubator device set to an ambient temperature of -7.5 °C to simulate a severe frost event. These measurements were obtained using packages (3) containing PCM solutions together with the insulation material (2) and also a package prepared with only the insulation material (2) without the PCM for comparison. The results obtained are provided in Figure 2.

When Figure 2 is examined, it is seen that the packages (3) containing all three PCM solutions provided very successful results compared to the insulation-only package (2) which did not contain PCM. Among the packages containing the prepared PCM solutions (3), in the package containing the E solution, the temperature increased to -2,5 °C, in the packages containing the EG and PG solutions, the temperature increased to -3 °C and -3,5 °C respectively due to the heat of freezing and all packages provided thermal protection. The temperature of the sapling sample was kept between -2 °C and -4 °C, i.e. above the extremely hazardous -4.4°C for 7 hours by the PCM package containing the E solution, 6.6 hours by the PCM package containing the EG solution, and 5.5 hours by the PCM package containing the PG solution. For the package containing only insulation, this time was around 20 minutes. According to these results, it was observed that the thermal protection performance of the PCM package containing the E solution was the highest, the performance of the package containing EG was slightly lower and the performance of the package containing PG was lowest. All three packages could be used for thermal protection of citrus trees.

PCM packages (3) containing E, EG and PG solutions developed in this study were determined to provide adequate thermal protection for citrus trees against severe frost in laboratory measurements. The dimensions of these packages (3) and the amount of PCM solution they contain can be adjusted based on the size of trees desired to be thermally protected, accordingly packages (3) containing larger amounts of PCM solutions can be prepared. Within the framework of the method developed in this study, the concentration and amount of the PCM solution, the type of alcohol used in the preparation of the solution, the type of material used as a nucleating agent, the type of plastic used in packaging, the type of insulation material (2) and the dimensions of the package prepared may vary when preparing PCM packages (3). Packages (3) containing prepared PCM solutions can be wrapped around the trees by means of plastic clamps or Velcro stabilizers (4) and these packages can be used repeatedly. Figure 3 schematically shows the application of the developed PCM solution containing packages (3) to the trees together with the insulation material (2).

Claims

1. A package (3) containing phase-changing-material for thermal protection of citrus frees characterized by comprising 1% Agl (silver iodide) by mass as the nucleating agent in order to trigger phase change (freezing) of one of the solutions prepared by 6-7-10% mL of pure ethanol, ethylene glycol or propylene glycol added to 90-93-94% mL of water In volume in at least one of the polyethylene or PVC plastic packages which are coated with a 5 mm thick, 1QGkg/m³ density polyethylene foam layer insulation material on one surface of the packages (2),