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分析传热与保温工程论文

时间:2015-10-22 15:39来源:www.ukthesis.org 作者:英国论文网 点击联系客服: 客服:Damien

分析传热与保温工程论文

当两个机构在不同的温度下彼此放置接近或保持接触,热量从高温度的机构流动到较低温度的机构。传递从一个身体到另一个身体,或者从一个身体的一部分到另一部分,可以通过三种不同的传导过程,对流和辐射发生。总热量从一个身体到另一个身体的传递形式有一个或多个上述三种模式。热或热传递,从而发生通过:传导过程中的能量转移是由于温度的差异,对流是上升和向下运动的气体和液体,而在辐射过程中,能量直接从一个身体到另一个。热传导的过程中,在不同的温度下的介质颗粒,存在在直接或间接的物理接触。因此传导是一个从热端到冷端的热传递过程,在介质中形成粒子。物体通过传导传递热量的速度称为导热系数。一个低传导率的物体会比一个具有高导电率的物体传导更慢。这就是为什么一些物质被用作绝缘体,而其他的则被用于应用中,如烹饪。在一般情况下,固体是更好的热导体比液体和气体。金属是最好的热导体,非金属固体往往是不良导体。

在建筑机械(机械结构)中,热传导起着至关重要的作用。建筑物内的保温是实现其居住者的热舒适性的重要因素。保温可以减少不必要的热量损失与过量,减少加热和冷却系统的能量需求。绝缘可以指采用缓慢的热损失的保温材料如:纤维素,玻璃棉,岩棉,聚苯乙烯,聚氨酯泡沫,蛭石(化学绝缘型),与地球或土壤。但它也涉及到一系列的设计和技术,以解决的主要模式的热传导,辐射和对流材料。

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.(责任编辑:charlie)



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