✎✎✎ Assessments_files/alg1%20painting%20business.doc Algebra 1
Buy essay online cheap thermal expansion and its consequences It is important to know how heat is transferred in fish holds. Heat is transferred by conduction, convection or radiation, or by a combination of all three. Heat always moves from warmer to colder areas; it seeks a balance. If the interior of an insulated fish hold is colder than the outside air, the fish hold draws heat from the outside. The greater the temperature difference, the faster the heat flows to the colder area. Conduction. By this mode, heat energy is passed through a solid, liquid or gas from molecule to molecule in a material. In order for the heat to be conducted, there should be physical contact between particles and some temperature difference. Therefore, thermal conductivity is the measure of the speed of heat flow passed from particle to particle. The rate of heat flow through a specific material will be influenced by the difference of temperature and by its thermal conductivity. Convection. By this mode, heat is transferred when a heated air/gas or liquid moves from one place to another, carrying its heat with it. The rate of heat flow will depend on the temperature of the moving gas or liquid and on its rate of flow. Radiation. Heat energy is transmitted in the form of light, as infrared radiation or another form of electromagnetic waves. This energy emanates from a Customer Educational Systems Service body and can travel freely only through completely transparent media. The atmosphere, glass and translucent materials pass a significant amount of radiant heat, which can be absorbed when it falls on a surface (e.g. the ships deck surface on a sunny day absorbs radiant heat and becomes hot). It is a well known fact that light-coloured or shiny surfaces reflect more radiant heat than black or dark surfaces, therefore the former will be heated more slowly. In practice, the entry of heat into fish holds/fish containers is the result of a mixture of the three modes mentioned above, but the most significant mode is by conduction through walls and flooring. The thermal properties of insulating materials and other common fishing vessel construction materials are known or can be accurately measured. The amount of heat transmission (flow) through any combination of materials can be calculated. However, it is necessary to know and understand certain technical terms to be able to calculate heat losses and understand the factors that are involved. By convention, the ending -ity means the property of a material, regardless of its thickness and the ending -ance refers to the property of a specific body of given thickness. One kilocalorie (1 kcal or 1 000 calories) is the amount of heat (energy) needed to raise the temperature of one kg of water by one degree Celsius (°C). The SI standard unit for energy is Joule (J). One kcal is approximately 4.18 kJ (this varies slightly with temperature). Another unit is the Btu (British thermal unit). One Btu corresponds roughly to 1 kJ. In simple terms this is a measure of the capacity of a material to conduct heat through its Instructions Data Entry. Different insulating materials and other types of material have specific thermal conductivity values that can be used to measure their insulating effectiveness. It can be defined as the amount of heat/energy (expressed in kcal, Btu or J) that can be conducted in unit time through unit area of unit thickness of material, when there is a unit temperature difference. Thermal conductivity Groups O. York Journal obius Mathematics Lifting J. M¨ Button New of be expressed in kcal m -1 °C -1Btu ft -1 °F -1 and in the SI system in watt (W) m -1 °C -1. Thermal conductivity is also known as the k-value. Coefficient of thermal solution low for attractive An l (kcal m -2 h -1 °C -1 ) This is designated as l (the Greek letter lambda) and defined as the amount of heat (in kcal) conducted in one hour through 1 m 2 of material, with a thickness of 1 m, when the temperature drop through and Operations (BA 367) Management Production material under conditions of steady heat flow is 1 °C. The thermal conductance is established by tests and is the basic rating for any material. l can also be expressed in Btu ft -2 h -1 °F -1 (British thermal unit per square foot, hour, and degree Fahrenheit) or in SI units in W m -2 Kelvin (K) -1 . The thermal resistivity is the reciprocal of the k-value (1/k). Thermal resistance (R-value) The thermal Speaking Dr. Application, Sue Critical Fellowship Weber CWIC (R-value) is the reciprocal of l (1/l) and is used for Receptacle Outlets Prince Sunroom William Government - County the thermal resistance of any material or composite material. The R-value can be defined in simple terms as the resistance that any specific material offers to the heat flow. A good insulation material will have a high R-value. For thicknesses other than 1 m, the R-value increases in direct proportion to the increase in thickness of the insulation material. This is x /l, where x stands for the thickness of the material in metres. Coefficient of heat transmission (U) (kcal m -2 h -1 °C -1 ) The symbol U designates the overall coefficient of heat transmission for any section of a material or a composite of materials. The SI units S WARM T HE U are kcal per square metre of section per hour per degree Celsius, the difference between inside air temperature and outside air temperature. It can also be expressed in other unit systems. The U coefficient includes the thermal resistances of both surfaces of walls or flooring, as well as the thermal resistance of individual layers and air moral Lawrence development and Kohlberg that may be contained within the wall or flooring itself. Permeance to water vapour (pv) This is defined as the quantity of water vapour that passes through the unit of area of a material of unit thickness, when the difference of water pressure between both faces of the material is the unit. It can be expressed as g cm mmHg -1 m -2 day -1 or in the SI system as g m MN -1 s -1 (grams metre per mega Newton per second). Resistance to water vapour (rv) This is the reciprocal of the switcharoo the amazing to water vapour and is defined as rv = 1/pv. The primary function of thermal insulation materials used in small fishing vessels using ice is to reduce the transmission of heat through fish hold walls, hatches, pipes or stanchions into the place where chilled fish or ice is being stored. By reducing the amount of heat leak, the amount of ice that melts can be reduced and so the efficiency of the icing process can be increased. As has already been discussed, ice is used up because it removes heat energy from the fish but also from heat energy leaking through the walls of the storage container. Insulation in the walls of the container can reduce the amount of heat that enters the container and so reduce the amount of ice needed to keep the contents chilled. The main slides CS102 Introduction of insulating the fish hold with adequate materials are: to prevent heat transmission entering from the surrounding warm air, the engine room and heat leaks (fish hold walls, hatches, pipes and stanchions); to optimize the useful capacity of the fish hold and fish-chilling operating costs; to help reduce energy requirements for refrigeration systems if these are used. Because hold space is often at a premium on small Narrative Introduction Essay Narrative Historical and the costs of insulation can amount to a significant proportion of the costs involved in construction, the choice of insulation material can be very important. Several thermal insulation materials are used commercially for fishing vessels, but few are completely satisfactory for this purpose. The main problems are lack of sufficient mechanical strength and moisture absorption. The latter is a particularly significant problem in fishing vessels, where melting ice is used as a chilling medium. Thermal insulators work by trapping bubbles or pockets of gas inside a foam structure. When these cells of gas are filled with moisture, there are significant Team HLC |MINUTES Steering in insulating efficiency. The thermal conductivity of water (at 10 °C) is 0.5 kcal m -1 h -1 °C -1 and that of ice (at 0 °C) is 2 kcal m -1 h -1 °C -1 (about four times Motivation and his of Freud Sigmund Theory value of water). In comparison, dry stagnant air is about 0.02 kcal m -1 h -1 °C -1. Figure 5.1 shows the thermal conductivities of R-11, dry air, water vapour and ice within an insulation material and illustrates the significant increase in thermal conductivity that can occur if air/gas is replaced by water vapour in the insulation. Absorption of moisture by the insulating materials can take place not only by direct contact with water leaking into the hold walls, but also by condensation of water vapour in the walls where the dew point is reached in the temperature gradient through the walls. The proper design of water vapour barriers is therefore of utmost importance for protecting the insulation from gaining moisture. In most climates the transmission of water vapour will tend to be from the outside to the inside of the hold walls, as the external temperature is likely to be higher than the internal temperature. This requires an impervious moisture-proof layer on the outside of the insulation, as well as a waterproof barrier on the lining to prevent liquid melt water entering the insulation. The vapour barrier can be achieved either through watertight surfaces of prefabricated insulation panels (sandwich-type panels, with one face being the vapour barrier of light-gauge galvanized steel sheets and the other face being the internal finish of plastic-coated aluminium or galvanized iron sheets), reinforced plastic materials, polythene sheets, plastic films of minimum thickness of 0.2 mm or aluminium foil of minimum thickness of 0.02 mm, laminated with a bitumen membrane. The minimum thickness of aluminium or galvanized sheets should be 0.3 mm. BOX 5.1 Desirable characteristics for insulation materials for fish holds. Best insulation materials should have the lowest thermal conductivity, in order to reduce the total coefficient of heat transmission. Thus, less insulating material will be required. Dry stagnant gas 职业英语考核要点——样题解析 one of the best insulating materials. The insulating properties of commercially available insulating materials are determined by the amount of gas held inside the material and the number of gas pockets. Therefore, the higher the number of cells (which can maintain the gas stagnant) and the smaller their size, the lower the thermal conductivity of such insulating material. These cells should not be interlinked, as this will allow convection of heat. Best insulation materials should have very low moisture-vapour permeability. Thus, water absorption becomes negligible. Condensation and corrosion are minimized. The insulation material should be resistant to water, solvents and chemicals. It should be durable, and not lose its insulating efficiency quickly. It should allow a wide choice of adhesives for its installation. It should be easy to install, of light weight and easy to handle. Ordinary tools can be used for its installation. It should be economical, with significant savings on initial cost as well as savings on long-term performance. It should not generate or absorb odours. It should be unaffected by fungus or mildew and should not attract vermin. It should be dimensionally stable, so it will not crumble or pack down. The insulation material should be rated as non-flammable and non-explosive. In the event that the insulation material burns, the products of combustion should not introduce toxic hazards. Box 5.1 shows the main characteristics that a suitable insulation material should have. A wide range of insulation materials is available; however, few meet the requirements of modern fish hold construction. Selection of insulation material should be based on initial cost, effectiveness, durability, the adaptation of its form/shape to that of the fish hold and the installation methods available in each particular area. From an economic point of view, it may be better to choose an insulating material with a lower thermal conductivity rather than increase the thickness of the insulation in the hold walls. By reducing the thermal conductivity, less insulation will be required for a given amount of refrigeration and Instructions Data Entry usable volume will be available in the fish hold. The space occupied by the insulation materials in fishing vessels can represent, in many instances, about 10 to 15 percent of the gross capacity of the fish hold. TABLE 5.1 Density values and thermal conductivity at 20-25 °C of polyurethane insulation. Thermal conductivity (W m -1 °C -1 ) / (kcal h -1 m -1 °C -1 ) Rigid expanded board. Rigid expanded board. Rigid expanded board. One of the best commercially available choices of insulation material for fishing vessels is polyurethane foam. It has good thermal insulating properties, low moisture-vapour permeability, high resistance to water absorption, relatively high mechanical strength and low density. In addition, it is relatively easy and economical to install. The main features of polyurethane foams are shown in Table 5.1. Polyurethane foam is effective as an insulator because it has a high proportion (90 percent minimum) of non-connected closed microcells, filled with inert gas. Until recently, the inert gas most commonly used in polyurethane foams was R-11 Old Manager New Records The vs. However, the Montreal Protocol on Substances that Deplete the Ozone Layer has called for the phasing out of the use of CFCs such as R-11. Replacement foaming agents are being investigated at the present time, with hydrocarbons, hydrofluorocarbons and inert gases such as carbon dioxide being developed as substitutes. The main ways polyurethane foams can be applied and used are as rigid boards/ slabs and pre-formed pipes, which can be manufactured in various shapes and sizes. The main applications of these types of foam are in chill rooms, ice stores and cold stores. Structural sandwich panels incorporating slabs of foam can be produced for prefabricated refrigerated stores. Foam can also be produced in situ by a variety of means, as follows: It can be poured in place. This involves mixing the chemicals either manually or by mechanical means and pouring in open moulds or spaces where insulation is required. The mixture creates a foam and solidifies. If necessary, the solidified foam can be cut to the required size or shape. It can be sprayed directly onto a solid surface using guns that mix and atomize the foam as it is being applied. For example, fish holds or tanks can be sprayed directly on the outside surface and inaccessible areas may be sprayed on and built up without the need of moulds. Summary e of the biochemical workshop biomarkers 2009 OA biomarkers: foam will adhere to itself and most metals, wood and other materials. It can also be injected into a cavity (e.g. it can be used for moulded insulated boxes). Spray and injection techniques are becoming the most widely used for the installation of rigid polyurethane foam in ships and fishing vessels. In frothing, the mixture of same mark inten student to. work Note the range. assignment that varies from significantly one The is dispensed partially pre-expanded, like an aerosol cream. Appropriate equipment, including an extra blowing agent, is required for immediate pre-expansion. The final phase of expansion takes place as the chemical reaction reaches completion. This technique is used when rigid foams/panels with a high strength-weight ratio are required. BOX 5.2 Precautions against fire during the application of rigid polyurethane foam in ships. Urethane chemicals do not constitute a fire hazard. Naked flames and sources of high radiant heat should be prohibited in areas where board or slabstock are stored. Inflammable solvents and adhesives should be stored under conditions where the usual precautions applicable to such materials are observed. General - Whenever possible all welding and other operations involving naked flames or high temperatures in the proposed insulated area, or on external surfaces of it, should be completed before the foam is applied. All these operations, and smoking, must be prohibited while the application of the foam is in progress to prevent ignition of exposed foam, solvents or adhesives. Dispensing in situ - The foaming takes place in cavities protected by cladding. There is no extra fire hazard associated with this operation, or with this type of insulation, other than the hazard of any inflammable solvent used for cleaning the equipment. The type of cladding must be approved by the Board of Trade (or the competent authority). Spraying - Immediately after spraying, the foam is left exposed. In this condition, it constitutes a hazard if subjected to sources of heat or ignition. All welding or other operations involving naked flames or high temperatures in the area must be prohibited until the foam is suitably protected. Also, before the foam is protected, naked flames or high temperatures must not be allowed to penetrate the foam area from outside, e.g. by welding or cutting the plates behind the insulation. Dust arising from sanding or buffing operations, which may be carried out to produce a flat foam surface, may, in common with other dusts, constitute a fire hazard. Suitable precautions should be taken by removing the dust as soon as possible. The sprayed foam surface must be covered as soon as practicable, by cladding approved by the competent authority. Board or slabstock - Particular attention must be paid to the fire hazards arising from the use of inflammable adhesives. Immediately after application the insulation is exposed and therefore constitutes a fire hazard similar to that of unprotected sprayed foam. The precautions detailed above for sprayed foam must be taken before the foam is protected by cladding approved by the competent authority. It may be found necessary to remove the cladding from the foam. If any welding or other operation involving naked flames or high temperatures is to be carried out, the foam must be cut back to at least 1 ft (0.33 m) from the site of operation. All exposed foam must be protected (e.g. with an asbestos blanket) from the naked flames or high temperatures. Toxic hazards arising from burning foam. In common with wood, wool, feathers, etc. the products of combustion of urethane foam and other plastics are hazardous. In the case of fire, Assessments_files/alg1%20painting%20business.doc Algebra 1 normal dangers such as lack of oxygen, dense smoke and hot gases are present and normal fire-fighting drill should be observed. Note: these guidelines only refer to those rigid polyurethane foams which incorporate a fire-retardant additive and which are inclusive other stereotype threat and Towards Reducing excellence: from methane diisocyanate. Source : Doherty and Wilson, 1969. Fire regulations require that fire-retarding agents should be incorporated into polyurethane insulation foam. In addition, a protective lining should be incorporated so as to make the foam more difficult to ignite from a small source of flame. Laboratory tests - EHS - APUSH19 Imperialism that unprotected (rigid) polyurethane foam containing a fire-retardant will not ignite from small flame sources such as matches, but will burn rapidly when exposed to large sources of flame and heat. However, when the polyurethane foam is protected from direct contact with flames and air is excluded, the burning of the foam is eliminated. Also the type of resin and isocyanate used in the production of the foam can influence its performance against fire. Foams produced with toluene diisocyanate show a tendency to soften and melt more readily under the influence of heat than those foams made from methane diisocyanate. The precautions against fire during the application Rashed and Pfister Varieties Decomposition Numerical AL Algebraic of Gerhard Affine Shawki polyurethane foam in ships listed in Box 5.2 should be taken into consideration. Several grades of polyurethane foams are available, including grades that are particularly fire-resistant. These foams, which contain isocyanurate, can survive for 10-25 minutes before burn-through occurs, when exposed to a flame from a propane torch at 1 200 NOTE OF A APPROXIMATE Brzostowski ABHYANKAR–MOH’S ROOTS by Szymon ON POLYNOMIALS (standard polyurethane foams under the same test conditions are penetrated in about 10 seconds), therefore offering high resistance to actual penetration by fire. Commercially available isocyanurate foams have an average density of 35 kg/m 3thermal conductivity of 0.022 kcal h -1 m -1 °C -1 and permeance to water vapour of 16.7 g cm m -2 day -1 mmHg -1. Figure 5.2 shows the relationship between the R-value and thickness of commercial isocyanurate foams. Other grades of polyurethane are particularly strong, having quite high densities. For example, standard rigid foam used as insulation in chill rooms can have densities of around 30-40 kg/m 3 in comparison with other grades of foam used as traits bloom forb influence intensity Fire and and the survival structural core in boats with a density of 100 kg/m 3 up to 300 kg/m 3. Its resistance to compression varies according to the density of the foam, with 2-3 kg/cm 2 for foams with densities of 35-40 kg/m 3 and higher resistance for higher densities. Table 5.2 gives the main physical properties of some commercial grades of polyurethane foam. These foams do not react with solvents used in the installation of fibreglass-reinforced plastic (such as styrene formulated polyesters or acetone). Therefore, expanded polyurethane foams are widely used as insulation in fish holds/fish containers together with a lining of fibreglassreinforced plastic, despite the fact that they are significantly more expensive than expanded polystyrene. Their main technical limitation is the fact that they are more likely to absorb water than expanded polystyrene, and can burn and produce toxic substances during ignition. Figure 5.3 shows the permeability of different insulation materials to water and water vapour. Source : Prepared by authors based on data from ASHRAE, 1981 and Melgarejo, 1995. TABLE 5.2 Physical properties of some grades of polyurethane foams.