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发表于 2004-10-20 16:57:40
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热工测量（thermal meter ）[/COLOR]
What is a thermocouple?
A thermocouple is a sensor for measuring temperature. It consists of two dissimilar metals, joined together at one end, which produce a small unique voltage at a given temperature. This voltage is measured and interpreted by a thermocouple thermometer.
Thermocouples
A thermocouple is a device primarily used for the measurement of temperature. It is based upon the findings of Seebeck (1821) who showed that a small electric current will flow in a circuit composed of two dissimilar conductors when their junctions are kept at different temperatures. The electromotive force (emf) produced under these conditions is known as the "Seebeck emf". The pair of conductors that constitute the thermoelectric circuit is called thermocouple.
What are the different thermocouple types?
Thermocouples are available in different combinations of metals or calibrations.' The four most common calibrations are J, K, T and E. Each calibration has a different temperature range and environment, although the maximum temperature varies with the diameter of the wire used in the thermocouple.
How do I choose a thermocouple type?
Because thermocouples measure in wide temperature ranges and can be relatively rugged, they are very often used in industry. The following criteria are used in selecting a thermocouple:
Temperature range
Chemical resistance of the thermocouple or sheath material
Abrasion and vibration resistance
Installation requirements (may need to be compatible with existing equipment; existing holes may determine probe diameter.
评?refrigeration)[/COLOR]
Refrigeration is the withdrawal of heat from a substance or space so that temperature lower than that of the natural surroundings is achieved.
Refrigeration may be produced by
? thermoelectric means
? vapor compression systems
? expansion of compressed gases
? throttling or unrestrained expansion of gases.
the most important diagram
(循环图)
Vapor compression systems are employed in most refrigeration systems. Here, cooling is accomplished by evaporation of a liquid refrigerant under reduced pressure and temperature. The fluid enters the compressors at state 1 where the temperature is elevated by mechanical compression (state 2). The vapor condenses at this pressure, and the resultant heat is dissipated to the surrounding. The high pressure liquid (state 3) then passes through an expansion valve through which the fluid pressure is lowered. The low-pressure fluid enters the evaporator at state 4 where it evaporates by absorbing heat from the refrigerated space, and reenters the compressor. The whole cycle is repeated.
COMPONENTS
? Compressor
? Condenser
? Expansion valve
? Evaporator
PERFORMANCE EVALUATION
COEFFICIENT OF PERFORMANCE :
cop=refrigeration effect/net work
thermodynamics(热力学)+heat power plant (热电站)[/COLOR] （图略）
Power plants generate electrical power by using fuels like coal, oil or natural gas. A simple power plant consists of a boiler, turbine, condenser and a pump. Fuel, burned in the boiler and superheater, heats the water to generate steam. The steam is then heated to a superheated state in the superheater. This steam is used to rotate the turbine which powers the generator. Electrical energy is generated when the generator windings rotate in a strong magnetic field. After the steam leaves the turbine it is cooled to its liquid state in the condenser. The liquid is pressurized by the pump prior to going back to the boiler A simple power plant is described by a Rankine Cycle.
RANKINE CYCLE（图略）
Saturated or superheated steam enters the turbine at state 1, where it expands isentropically to the exit pressure at state 2. The steam is then condensed at constant pressure and temperature to a saturated liquid, state 3. The heat removed from the steam in the condenser is typically transferred to the cooling water. The saturated liquid then flows through the pump which increases the pressure to the boiler pressure (state 4), where the water is first heated to the saturation temperature, boiled and typically superheated to state 1. Then the whole cycle is repeated.
REHEAT（图略）
When steam leaves the turbine, it is typically wet. The presense of water causes erosion of the turbine blades. To prevent this, steam is extracted from high pressure turbine (state 2), and then it is reheated in the boiler (state 2') and sent back to the low pressure turbine.
REGENERATION（图略）
Regeneration helps improve the Rankine cycle efficiency by preheating the feedwater into the boiler. Regeneration can be achieved by open feedwater heaters or closed feedwater heaters. In open feedwater heaters, a fraction of the steam exiting a high pressure turbine is mixed with the feedwater at the same pressure. In closed system, the steam bled from the turbine is not directly mixed with the feedwater, and therefore, the two streams can be at different pressures.
COMPONENTS
Boiler/Superheater
Condenser
Turbine
Pump
thermal efficiency=net power out /heat in
heat exchanger(换热器)[/COLOR]
Introduction
Exchange systems are widely used both in living organisms and industrial applications. An exchange process, whether it involves heat, gases, solutes, or water, is an important feature in many different physiological processes. Knowledge of these exchange principles is important for the understanding of many physiological principles like respiration, thermoregulation, osmoregulation, water balance,etc. One of the most effective exchange principles is the counter-current principle.
We can use the exchanger for transferring heat, gases, or water between two media separated by a thin membrane that has good thermal conductance or a high conductance for different gases, solutes or water. Depending on the flow arrangements, we can classify an exchanger as counter-exchanger, con-exchanger or cross-counter exchanger. A fourth type is the mixing-heat-exchangers, where we mix the two in the exchanger, such as the nasal passages in some animals and some human applications. The efficiency of the exchanger is dependent on a number of factors, such as the flow direction of the media, the flow rate of the media and diffusion distance, or conductance of the exchanger material.
Heat exchanger is a heat exchanging set.
Heat exchanger can be classified: recuperative exchanger, mixed exchanger, accumulated heat exchanger, intermediated heat-carrier exchanger.
Heat transfer equation: Q=kF△tm
Q=heat load
K=heat transfer coefficient
△ tm=average temperature difference of two kinds of flows（两种流体的平均温差）
There are three kinds of average temperature:
logarithmic average temperature difference: △tm=(△tmax-△tmin)/ln△tmax/△tmin
arithmetic average temperature difference: △tm=(△tmax+△tmin)/2
integrating average temperature difference
Boiler（锅炉）[/COLOR]
Boiler surface may be defined as those parts of tubes, drums and shells which are part of the boiler circulatory system and which are in contact with the hot gases on one side and water or a mixture of water and steam on the other side.
Coal contains: Carbon, Hydrogen, oxygen, Nitrogen, Sulfur, ash, moisture.
Calorific capacity(heat output): Heat emits when every unit coal burned completely.煤的发热量：煤单位质量燃烧所放出的热量。
High calorific power(高位发热量)：Add the latent heat of steam after burning completely.
Low calorific power: Not add the latent heat of steam after burning.
Coal can be classified: anthracite(无烟煤), poor coal, bituminous coal( 烟煤), lignite coal(褐煤)。
Ash-fusion point(灰熔点)：Deformation temperature, soften temperature, Fluid temperature.
Theoretical air capacity(理论空气量): Under the ideal condition that every kilogram combustible matter burned completely and running out of Oxygen, it requires capacity of air.
Productions of completely burning: carbon dioxide, sulfur dioxide, steam, nitrogen gas, oxygen.
Not completely burning: Add carbon monoxide, methane(CH4), Hydrogen
Excess air coefficient: The ratio of real air capacity and ideal air capacity.
Heat of fuel: BQar,net,p
BQyx=Heat of effectively absorbed by boiler
BQgt=loss of solid not completely burned
BQqt=loss of gas not completely burned
BQpy=exhaust smoke carrying
BQlq=loss of outside of boiler cooled
BQhz=physical loss of breeze(灰渣)
Generally, there are two ways of combustion: stoke(层燃),suspension combustion(悬浮燃)
Stoker: fuel is solid; suspension: fuel is gas or fluid
There are two methods of combustion of coal gas: premixing type combustion and diffuser type combustion.( 预混型和扩散型)
Engle viscosity: Under experiment temperature, the ratio of the time that 200millilitre experiment oil flows from Engle viscosimeter and 20 centigrade 200 millilitre distilled water flows from it.
Boiler circulation: Natural circulation and forced circulation.
The force of gravity available to produce flow in natural circulation comes from the difference between the densities of the fluids in the downcomer and riser portions of the circuit. This difference in density establishes the force available for circulation.
Selection of coal-burning equipment
1. (磨煤系统)
The function of a Pulverized-coal system is to pulverize the coal, deliver it to fuel-burning equipment, and accomplish complete combustion in the furnace with a minimum of excess air.
2.Tow principal systems(仓储式): the bin system and the direct firing system have been used for processing, distributing and burning pulverized coal.
安装工程经济与管理
the ecomomy and administration of installation project management[/COLOR]
the main content of this course is about when we receive an installation project, how to complete it by ecomomic reasonable methods.
For example,shen we receive a project ,there are three steps to do:
First, plan and decision, if we receive a project ,we should push it toward the society.from the society,we will receive many plans about it,then we decide which is the best.
Second, organization and derection.after decision,we should to organize various work. Such as buy equipment and material, organize work labor and so on.
Third, control and regulate. Then put the plan in operation. during the operation,we should keep control constantly.last, in order to find the errors and correct or regulate,it should keep the project complete economy and reasonable.
建筑概论
architecture introduction[/COLOR]
this course mainly introduces some brief ideas of architecture.
For example,buildings:it divided into three general classifications according to its using conditions.it include:
the civil building ,
industrias building
agricultural building.
According to its floors ,buildings is divided into three classifications:
The low floors building
The multipoe floors
The high floors
Buildings is divided into four classifications according to the material of building:
Brick and wood structure building
Brick and concrete structure building
Steel and concrete structure and steel structure
能耗测定[/COLOR] the measurement of energy consume
in the practice,we went to the boiler room of our college and measure the exit temperature of flue gas and the pressure of the out water and use the heat balance equation.
mechanical drawing（机械制图）[/COLOR]
The purpose of a mechanical drawing is to show the design intent pictorially. One way to do this is to choose certain views of your subject that show interesting features. The simplest of these views can normally be labeled front, back, top, bottom, left and right.
还有很多就不贴了，以上资料得到我的两位mm同学的帮助，谢谢你们~~~~，希望可以能为以后本专业的或近专业的有所帮助 |
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发表于 2004-10-20 16:57:02
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