Thermal power is a subject involving power, boiler, blast furnace,heat engineAll mechanical and thermal systems related to thermal energy are the objects of thermal power professional research.The major of thermal power in most colleges and universities has a beautiful nameThermal energy and power engineering。It changed from only studying heat engine（Steam turbine）Our subject has expanded to refrigeration, blast furnace and other fields.Moreover, students in this major are still in demand nationwide, mainly because the south is dominated by light industry, electronic industry and agriculture.The college students in this major are mainly for power plants.
From the perspective of energy statistics, heat refers to hot water, superheated or saturated steam that can provide heat sources;includeindustrial boiler The hot water and steam produced by public thermal power stations and enterprise owned power stations, and the hot water and steam produced by users.
Thermal calculation
Announce
edit
The force calculation of steam and hot water is related to the temperature and pressure of steam and hot water at the boiler outlet. The calculation method is as follows:
Step 1: Determine the temperature and pressure of steam and hot water at the boiler outlet, and find out the corresponding enthalpy per kilogram of steam and hot water in the enthalpy entropy diagram (table) according to the temperature and pressure values;
Step 2: determine the temperature and pressure of boiler feed water (or return water), and find out the corresponding enthalpy per kilogram of feed water (or return water) in the enthalpy entropy diagram (table) according to the temperature and pressure values;
Step 3: calculate the difference between the enthalpy found in step 1 and step 2, and then multiply it by the quantity of steam or hot water (calculated according to the reading of the flowmeter). The value obtained is the quantity of heat.
thermal state
Announce
edit
The state may be balanced or unbalanced (see thermodynamic equilibrium).Classical thermodynamicsThe research usually focuses on the thermodynamic equilibrium state and the process composed of the equilibrium state.The physical quantity used to describe the state of the thermodynamic system is calledThermal state parameters, or simply state parameters, such as pressure, temperature and specific volume.The value of the state parameter only depends on the state of the thermodynamic system, andThermodynamic processirrelevant.Therefore, a given state has a definite value of the state parameter.In other words, when the value of a state parameter changes,thermodynamic system The state of.Critical stateIt is a specific case of thermal state.
Thermodynamic circulation
Announce
edit
It is formed due to uneven cooling and heating of the groundAir circulation, called thermal circulation.It isAtmospheric motionThe simplest form of.
The uneven heating of the air near the ground causes the rise of the air flow
Or sinking movement, the difference of air pressure on the same level and atmosphericHorizontal movementWill affect the change of thermal circulation.
Thermodynamic circulation is the simplest form of atmospheric movement, which is formed due to uneven heat and cold on the groundAir circulation。The formation process is as follows: the atmosphere in the heated area expands and rises, forming near the groundLow atmospheric pressure, while high altitude formationHigh barometric pressure；On the contrary, the cold area forms a pressure difference on the level near the ground and in the upper air, which promotes the horizontal movement of the atmosphere and forms a thermal circulation at high and low levels.The air in the hot place expands and rises when heated, and the cold place shrinks and sinks.So at the same altitude above, the unit area of hot placesAir columnWhen the weight (i.e. air pressure) is high, the air pressure in cold places is low, and hot cold air flow forms in high places.After the air flow in the hot part is lost, the whole air column is reduced, and the ground forms a low pressure, while the cold part forms a high pressure, and a cold hot air flow is formed near the ground
Judgment of atmospheric pressure value in thermodynamic circulation
。Plus riseDowndraft, forming the thermal circulation.
Thermal circulation exists widely in real life, such asValley breeze、Sea land breeze, urban wind, etc. are the concrete embodiment of thermal circulation.
Thermal circulation and urban planning.Due to human activities, a large amount of waste heat is discharged inside the city, which is more than that in the suburbs“heat island effect”。City and Suburb
Thermal circulation will be formed occasionally to protect the cityatmospheric environment In urban planning, the sinking distance of urban wind should be studied.On the one handair pollutionseriousIndustrial layoutBeyond the sinking distance of urban wind, in order to prevent the pollution discharged by factories from flowing into the urban area;On the other hand, industrial satellite cities should be built in the urban stylecirculationTo avoid mutual pollution.
About sea and land breeze: sea breeze blows in the daytime, and land breeze blows at night.The main reason is waterSpecific heat capacityLarge.The specific heat capacity of water is 4.2 * 10 ^ 3jouleDegrees Celsius per kilogram.
application
Announce
edit
edit
Kongming latern、Hot Air BalloonThe principle of thermal circulation is used for heating;The radiator and electric oil heater use the principle of thermal circulation to raise the room temperature.
In a transparent glass box sealed with plastic wrap, place it on one sideice blockPut sand at the same time. When you put a lighted incense on the side of the ice, you can clearly see the smoke circulating in the box.(It is better to dry the sand in the sun for some time in advance, so that the effect is more obvious.)
0, about 40 cm high)PlywoodOr plastic film, a basin of hot water, a basin of ice, a bunch of incense, matches, etc.
Experiment steps: ① Transfer a basin of hot water
And a basin of ice blocks are respectively placed at both ends of the glass jar;
② Cover the upper opening of the glass cylinder tightly with flat plywood or plastic film;
③ Make a small hole on one side of the plywood or plastic film (above the ice basin);
④ Light a bunch of incense and put it into the small hole.
Students observe how the smoke moves in the glass jar. Can you find any rules?What conclusions can be drawn from the experiment?
Method 2: Close the doors and windows of the classroom and try to keep the air flow in the classroom stable.Light two thick incense sticks. The distance between the two sticks is about 30-40 cm. Place a 1000 watt electric stove next to one stick and a large ice cube next to the other stick. After the electric stove is powered on for 5 minutes, let the students observe the moving direction of the sanitary cigarette.Switch the electric furnace and ice block, and observe the moving direction of smoke.
In this experiment, the air above the electric furnace is heated and the air pressure is reduced;The air above the ice is cooled and the pressure rises.The fragrant smoke always floats above the electric furnace, indicating that hot places produce near the groundLow atmospheric pressureAir flows from cold places to hot places, while high air flows from hot places to cold places.
Thermodynamic process
Announce
edit
Thermal process,thermodynamic system The characteristics of thermodynamic process are reflected in the process of state change driven by certain factorsequationThe process equation describes theThermalBetween state parametersfunctionRelationship, from which the state before and after the system changes can be obtainedParameter relation。
Introduction Edit
Announce
edit
Constant volume process
Thermal process with constant volume V, also called constant volume process, such as closedcontainerHeating orcoolingProcess.The process equation is: V=constant, so according to the state equation, p1, p2, T1, T2 are the pressure and temperature of the initial and final states of the system respectively.The constant volume process is represented by the vertical line 1-2 on the p-V diagram.It indicates that the system does not work externally, and all the heat Q input to the system is converted into the increase of the internal energy U of the system, that is, m is the mass of the system, and cv is the constant volumespecific heatCapacity[1]。
Constant pressure process
The thermodynamic process in which the pressure p remains constant is also called isobaric process.For example, under atmospheric pressure, the gas in the cylinder expands when heated.The process equation is: p=constant, so V1/V2=T1/T2.It is represented by horizontal lines 3-4 on the p-V diagram.At this time, the work done by the system
W=p(V2－V1)=m﹙R÷M﹚(T2－T1)=nR(T2-T1)
Heat input from outside to the system
Q=H2－H1=mcp(T2－T1)
Where R is general for ideal gasGasConstant, cp is constant pressureSpecific heat capacity；H is the enthalpy of the system.
Constant temperature process
The process of keeping the temperature T constant, also calledIsothermal process。E.g. slow compression at room temperatureGasProcess.The process equation is: T=constant, so p1V1=p2V2. It is represented by an equilateral hyperbola 5-6 on the p-V diagramquantity of heatIt is equal to the work done by the system to the outside world. In the formula, ln isNatural logarithm。
Complex process/thermodynamic process editing
Announce
edit
Adiabatic process
A thermodynamic process in which there is no heat exchange between the system and the outside world.For example, gasCylinderAdiabatic expansion inside.The reversible adiabatic process is also called entropy fixing process because its entropy does not change during the process.The process equation is: pV=constant, so there are: in the formula, calledAdiabatic indexOr specific heat capacity ratio, where cv isSpecific heat capacity at constant volume。The adiabatic process is shown as
High order hyperbola 7-8 is the work done by the system to the outside world.
Polytropic process
It conforms to the process equation pV=constant, in which the polytropic exponent n remains unchanged in the process.The parameter relationship is the work done by the system to the outside world by the heat input to the system during the process. When the polytropic exponent n values are 0, 1, γ, ± ∞, the polytropic process will correspondingly become the constant pressureConstant temperature, adiabatic and constant volume processes.
