分析傳熱與保溫工程dissertation
分析傳熱與保溫工程dissertation
當兩個機構在不同的溫度下彼此放置接近或保持接觸,熱量從高溫度的機構流動到較低溫度的機構。傳遞從一個身體到另一個身體,或者從一個身體的一部分到另一部分,可以通過三種不同的傳導過程,對流和輻射發生。總熱量從一個身體到另一個身體的傳遞形式有一個或多個上述三種模式。熱或熱傳遞，從而發生通過：傳導過程中的能量轉移是由于溫度的差異，對流是上升和向下運動的氣體和液體，而在輻射過程中，能量直接從一個身體到另一個。熱傳導的過程中，在不同的溫度下的介質顆粒，存在在直接或間接的物理接觸。因此傳導是一個從熱端到冷端的熱傳遞過程，在介質中形成粒子。物體通過傳導傳遞熱量的速度稱為導熱系數。一個低傳導率的物體會比一個具有高導電率的物體傳導更慢。這就是為什么一些物質被用作絕緣體，而其他的則被用于應用中，如烹飪。在一般情況下，固體是更好的熱導體比液體和氣體。金屬是最好的熱導體，非金屬固體往往是不良導體。
在建筑機械（機械結構）中，熱傳導起著至關重要的作用。建筑物內的保溫是實現其居住者的熱舒適性的重要因素。保溫可以減少不必要的熱量損失與過量，減少加熱和冷卻系統的能量需求。絕緣可以指采用緩慢的熱損失的保溫材料如：纖維素，玻璃棉，巖棉，聚苯乙烯，聚氨酯泡沫，蛭石（化學絕緣型），與地球或土壤。但它也涉及到一系列的設計和技術，以解決的主要模式的熱傳導，輻射和對流材料。
Analysing Heat Transfer And Insulation Engineering Essay
When two bodies at different temperatures are placed near each other or they are kept in contact, heat flows from a body at a higher temperature to the body at lower temperature. The transfer of heat from one body to the other, or from one part of a body to the other part, can take place by three different processes conduction, convection and radiation.The total transfer of heat form one body to other can be by one or more than one of the above three modes.Thermal or heat transfer thus takes place through: conduction process of transfer of energy due to the differences in the temperature, convection is the up and down movement of gas and liquids, and radiation-a process by which energy directly passes from one body to another. Heat is transferred by the process of conduction when particles of the medium at different temperatures are in direct or indirect physical contact.Thus conduction is a process of transfer of heat from the hot end to the cold end, form particle to particle of the medium. The rate that an object transfers heat through conduction is called thermal conductivity. An object with low conductivity will transfer heat slower than an object with high conductivity. This is why some substances are used as insulators while others are used in applications such as cooking. In general, solids are better conductors of heat than are liquids and gases. Metals are the best thermal conductors while non-metal solids tend to be poor conductors.
In building mechanism (structure of machine), thermal conduction plays a vital role. Thermal insulation in buildings is an important factor to achieving thermal comfort for its occupants. Insulation reduces unwanted heat loss or gain and can decrease the energy demands of heating and cooling systems. Insulation can just refer to the insulation materials employed to slow heat loss, such as: cellulose, glass wool, rock wool, polystyrene, urethane foam, vermiculite (type of chemical insulation), and earth or soil. But it can also involve a range of designs and techniques to address the main modes of heat transfer conduction, radiation and convection materials.
There are various ways through which heat escapes our homes. As our houses are built on cold soil or rocks, heat directly flows down into the Earth by conduction. Heat travels by conduction through the solid walls and roof of our houses. On the outside, the outer walls and the roof tiles are hotter than the atmosphere around them, so the cold air near to them heats up and flows away by convection. Heaters use fuels and air conditioners uses lots of electricity, which is why insulation is used. Insulation makes the house comfortable and keeps the temperature of house cool in summers and warm in winters. It is very useful to keep the temperature of the house independent from outside temperature. How much insulation a house should have depends on building design, climate, energy costs, budget, and personal preference.
In cold regions, most houses use insulation. Most of the homes are fitted with cavity wall with two layers of brick or block between the inner rooms and the outer atmosphere and an air gap between the walls. The air gap reduces heat losses from the walls by both conduction and convection: conduction, because there's relatively little air between the walls and it's sealed in, so convection currents can't really circulate.
The best way to insulate is to fill the air gap with expanding foam or other insulators. Cavity walls are often filled with loosely packed, air-filled materials such as vermiculite, shredded recycled paper, or glass fibers, it traps the heat and prevents it from escaping.
Since warm air rises, plenty of heat escapes through the roof of the houses. Most people also have insulation inside the roof, also known as the loft area, of their homes. Loft insulation is generally made from the same materials as cavity-wall fillings-such things as rock wool and fiberglass.
Wall and roof insulation cuts down on heat losses by conduction. Double-glazed windows have two panes of glass separated by a sealed air gap. The air stops heat losses by conduction, while the extra pane of glass reflects more light and heat radiation back into home and reduces heat losses. If a thin reflective metallic coating or made from special thermal glazing (such as Pilkington-K, which traps heat a bit like a greenhouse) is added to the windows, the heat loss will reduce further.
Window insulation film can be applied to reduce heat gain in summer and heat loss in winter. Pipe insulation is also important in buildings for pipes that carry heated or cooled fluids.. In industry, energy has to be expended (extended) to raise, lower, or maintain the temperature of objects or process fluids. If these are not insulated, this increases the heat energy requirements of a process, and therefore the cost and environmental impact.
In hot regions, the greatest source of heat is the solar radiation, which enters the buildings through windows, heat the building shell and causing the heat transfer to increase through the building envelope. Solar gain can be reduced by adequate shading from the sun, light colored roofing, spectrally selective (heat-reflective) paints and coatings and various types of insulation for the rest of the envelope.
The graphs above represent a comparison study between the insulation capacity of Cellulose and Fiber glass.
Cellulose is basically glucose-tapped from recycled newspapers, magazines and cardboard which are treated with chemicals to produce an insulating material with varying properties. Fire resistant chemicals are added to cellulose to increase the efficacy*. Fiberglass is an artificial synthetic fiber that consists of calcium silicates, aluminum and other metals.
This essay is an example of a student's work
There are various benefits consumers receive with the use of conduction and/or insulation systems in their houses. Some of the benefits include:
It is energy-efficient
It is cost-effective, durable
Their uses doesn't cause any harm to the surrounding environment.
It provides more uniform temperatures throughout the space.
It has minimal recurring expense. Unlike heating and cooling equipment, insulation is permanent and does not require maintenance, upkeep, or adjustment.
It absorbs noise and vibrations coming form both the outside and from other rooms inside the house, thus producing a more comfortable occupant environment
Thermal insulation materials fixed on inside surface of the room walls prevent condensation on interior walls and ceiling.
There are also limitations to the use of insulation systems, like the use of cellulose for insulation attracted many rodents to the house. . The main technical limitations of fiberglass matting as insulation are poor structural strength, poor compression (to shorten) resistance, permeability to moisture and a tendency to settle after installation if not properly installed. There are many areas in insulated houses which lack of sufficient insulation, like the corners of buildings, and areas where insulation has been removed or displaced to make room for system infrastructure. During rainy seasons, most of paints used to absorb or emit heat are washed away or gets dull, even metals rusts.
Most of the above limitations are solved by science and technology. As the use of cellulose on wooden pipes and furniture attracts rodents, after many experiments they made cellulose which won't attract rodents. As paints gets dull or washed away with rain and metals rust, scientists have devised new un-washable paints and metals are coated with other substances that won't rust or wash away with rain water.
Environment- In countries which experiences extremely harsh winters and hot summers, cane reed offers better insulation than brick. This keeps heating and cooling costs down, which translates into energy savings as well as cost savings for the family. It also contributes towards a reduction in the dependency on foreign solid fuel sources and reduces pollution. The cane reed used in the house construction is a locally produced, renewable resource. Harvested (grown) annually, reeds sustain life in ponds and lakes; their roots also stabilize the surrounding earth, preventing soil erosion. The use of the reeds also reduces dependence on, and misuse of, forests. Other building materials used in the process are sourced locally, including the pipes used in the under-floor heating system, which are produced locally by a partner company. The use of insulation even reduces the use of heaters and air conditioners, in turn saving fuel and reducing pollution.#p#分頁標題#e#
Economic- Buildings made of cane reeds area helps the local economy by employing a community labor force to harvest the reeds which are woven into the timber frame, as well as gathering the clay, sand and mud used to fortify the reed. In some cases, residents have been able to obtain permanent employment as a result of the training received during the construction process. The cane reed technology increases affordability as it offers a 40 per cent reduction in housing cost compared with conventional brick housing. Plans are currently underway for the development of a Building and Training Centre where all construction materials to be used in Habitat homes will be produced, further decreasing the costs to participating families.
Social- As these buildings are easy to make every body in the family and community takes part in making it, they found a improved way of living as they are no longer required to gather firewood, wash dishes and clothes outside by hand and cook in a confined space. They have time and energy to pursue work outside the home, therefore helping to increase household income. The reduction in the use of solid fuels has also resulted in decreased levels of indoor air pollution and has consequently improved health, with a particular fall in respiratory illnesses.
Thus, an insulated home is comfortable as the temperature remains consistent over weather changes. It makes the house comfortable and keeps the temperature of house cool in summers and warm in winters. Effective use of insulation is necessary for each and every people who face harsh summers or winters. It helps them to stay warm and cozy in their homes, while contributing less to global warming and pollution. With the increase in the uses of insulation, the use of heater and air conditioning units will reduce. The use of fuels and other non-renewable sources will also be automatically reduced as this is a natural technique of absorbing or emitting heat. If the use of air conditioning units and heaters keeps on increasing, then there will be drastic effect on the climatic changes. To keep our surrounding safe as well as save natural resources for the upcoming generations, insulating our homes instead of using air conditioners, heaters, and other technologies which cause harm to the environment, is essential . Though insulation is expensive, its worth as it's durable and doesn't have a recurring cost unlike other means.
