工学建筑环境学chapterthermalcomfortablePPT课件

1、 this chapter describes: 2.1 Nature of heat, its measurement and its effect 热的性质、量度和作用热的性质、量度和作用 2.2 Heat transfer 热传递 2.3 Gases and vapours, and their effects 气体和水蒸气，及其作用气体和水蒸气，及其作用 2.4 Refrigerators and heat pumps 制冷机及热泵制冷机及热泵 2.1 Nature of heat 热的性质热的性质 2.1.1 Heat energy 热能热能 Heat (H or Q) is a f

2、orm of energy 热是能量的一种形式热是能量的一种形式 The joule is the standard SI unit of energy used for measuring any other form of energy. Other units of energy still found in use include the following units. Unit: calorie, where 1 cal 4.187 J kilowatt hour, where 1kwh=3.6MJ British Thermal Unit, where 1BTU=1.055kJ

3、英制热量单位英制热量单位 Heat energy 热能热能is an internal molecular property of a material. Other forms of energy ？ mechanical energy机械能机械能, electrical energy电能电能 and chemical energy化学能化学能 Can you give some examples ? Combustion of fuels 燃料的燃烧燃料的燃烧 Thermal energy Power is a measure of the rate at which work is do

4、ne, or at which energy is converted from one form to another. Unit : watt (W) By definition, 1watt = 1 joule / second. it is useful to remember that it already contains information about time and there is no need to divided by seconds. (t) time H) (energy Heat (P)Power 2.1.2 Power 功率功率 能力能力, , 力量力量,

5、 , 动力动力, , 权力权力 Temperature is not the same thing as heat. A red-hot spark 火花火花and a pot of boiling water 一盆开水一盆开水? much higher temperature ？ much higher heat “content” ？ more damaging？ Unit: kelvin (K) 2.1.3 Temperature 温度 Heat flows from objects at high temperature to objects at low temperature. W

6、hen there is no net heat transfer between two objects they are at the same temperature. The brain tends to judge temperature by the rate of heat flow in or out of the skin. Some material change in a regular manner with changes in temperature. Mercury水银水银 ; alcohol酒精酒精; electric resistance 电阻电阻； A th

7、ermometers is an instrument that measures temperature by making use of such property 温度计 Some of the more common types of thermometers are described below: Mercury-in-glass thermometer 玻璃水银温度计玻璃水银温度计 Alcohol-in-glass thermometer玻璃酒精温度计玻璃酒精温度计 Thermoelectric thermometer 热电温度计热电温度计 Resistance thermome

8、ter 电阻温度计电阻温度计 Optical pyrometer 光学高温计光学高温计 Thermoelectric thermometer 热电温度计热电温度计 Use the electric current generated in a thermocouple,热电偶热电偶which is made by joining two different metals such as iron and constantan alloy铁铁-康铜合金康铜合金. The current quickly varies with temperature and can be incorporated

9、 in remote or automatic control systems 热电偶：用于准确测量温度的热电子元件，由两种连在一起的不同金属组成，这样连结点间热电偶：用于准确测量温度的热电子元件，由两种连在一起的不同金属组成，这样连结点间 产生的电压变化就是两点间温度差异的量度产生的电压变化就是两点间温度差异的量度 Resistance thermometer 电阻温度计电阻温度计 Use the change in electrical resistance which occurs when a metal changes temperature. Pure platinum is co

10、mmonly used and the changes in its resistance can be measured very accurately by including the thermometer in an electrical circuit 电路电路 Optical pyrometer 光学高温计光学高温计 Measure high temperature by examining the brightness and colour of the light emitted from objects at high temperatures. The light vari

11、es with temperature and is compared with a light from a filament 灯丝灯丝 at a known temperature. 1) Celsius scale 摄氏温标摄氏温标 Unit : degree Celsius () 温标温标 This is a proper noun. Notice that the first letter must be capitalized 2) Thermodynamic scale T 热力学温标热力学温标 Unit : degree kelvin (K) melting point of

12、ice 冰的熔点冰的熔点, boiling point of water 水的沸点水的沸点 absolute zero 分子停止运动时的温度绝对零度分子停止运动时的温度绝对零度, triple point of water水的三相点为水的三相点为273.15K The same mass of different materials hold the same quantities of heat? Different quantities of heat ? To produce the same rise in temperature , water and oil, which one

13、should be supplied more heat ? Water has a greater heat capacity than oil. 热容热容 The SPECIFIC HEAT CAPACITY (C) 比热比热of a material is the quantity of heat energy required to raise the temperature of 1 kg of that material by 1 degree kelvin ( or 1 degree Celsius) Unit: J/ kg. K (or J/kg) Table 1.1 give

14、s values for a variety of materials What does 4190 J/ kg. K mean? Water is a good medium for storing heat. How to use the high heat capacity of water? Unit: kilogram per cubic metre ( kg/m3) Heavyweight masonry materials石材石材, such as brick, concrete 混凝混凝 土土and stone, have high densities. (V) Volume

15、m) ( Mass )(Density 2.1 Nature of heat, its measurement and its effect 热的性质、量度和作用热的性质、量度和作用 Heat energy Power Temperature Thermometers Temperature scale Heat capacity density The state of a substance depends on the conditions of temperature and pressure which act on the substance. three possible sta

16、tes are interchangeable相互转换相互转换 There are three possible states of matter Solid state Liquid state Gas state with absorption of heat 吸热吸热 Solid liquid gas With release of heat 放热放热 Gas liquid solid 显热显热 is the heat energy absorbed or released from a substance during a change in temperature. 潜热潜热 is

17、the heat energy absorbed or released from a substance during a change of state, with no change in temperature. 显热和潜热显热和潜热 A liquid may change to a gas with heating being supplied. without heating being supplied, A liquid may change to a gas ? 蒸发蒸发 The latent heat required for this change is taken fr

18、om the surroundings and produces an important 制冷制冷 效果效果 Enthalpy can be described an the total heat content of a sample, with reference to 0. 焓是物质相对于0所包含的总热能。 figure 2.1 the steam at 100 has a much higher total heat content than liquid water at 100 . Steam at high temperature and pressure has a very

19、 high enthalpy transferring large amounts of energy such as from a boiler to a turbine. This steam is also very dangerous if it escapes. 焓焓 注册设备师考试题 某理想气体经历了一个内能不变的热力过程，则该过程中工质的焓变为某理想气体经历了一个内能不变的热力过程，则该过程中工质的焓变为 （ ） A 大于零大于零 B 等于零等于零 C 小于零小于零 D 不确定不确定 Sensible heat : When a substance changes tempera

20、ture the amount of sensible heat absorbed or released is given by the following formula. 热量计算热量计算 mcH Worked example 1.1 Latent heat mlH Worked example 1.2 J/kg Specific latent heat of ice=335kJ/kg Specific latent heat of steam=2260kJ/kg Most substances expand on heating and contract on cooling. Dif

21、ferent substances expand by different amounts How to measure the relative change of length? The coefficient of linear thermal expansion 线性热膨胀系数线性热膨胀系数 物体物体在在温度温度上升上升11时所增加的长度和原来长度之比。时所增加的长度和原来长度之比。 The coefficient of linear thermal expansion 线性热膨胀系数线性热膨胀系数 The coefficient of Superficial (area) expan

22、sion 表面膨胀（系数）表面膨胀（系数） The coefficient of Cubical (volumetric) expansion 体积膨胀（系数）体积膨胀（系数） Can be predicted推导推导 from the linear expansion The coefficient of linear expansion for steel is about 12x10-6/ . What does this mean? It means that a steel bar increases its length by 12/1000,000 for each degree

23、 of temperature rise. Concrete expands at a similar rate to steel The expansion of aluminium steel The expansion of plastic steel question: Expansion is troublesome or useful? Allowance 补偿补偿must be made in construction for the effects of expansion. Particularly for concrete, metals and plastics. Som

24、etimes we can use the expansion of solid Bimetallic strip 双金属片双金属片 A bimetallic coil 双金属线圈双金属线圈 from a thermometer reacts to the heat from a lighter, by uncoiling and then coiling back up when the lighter is removed. figure 2.2 simple thermostat 简易式温度调节器 Liquids tend to expand more than solids, same

25、 temperature rise. The expansion rates of different liquids vary The expansion of alcohol water. Most liquids contract on cooling but water is unusual in that its volume increases as it cools from 4 to 0 Use the expansion of liquids thermometers Avoid the expansion of liquids. expansion water tank 膨

26、胀水箱 The expansion of gases is the liquids . Gas expand under constant pressure, the coefficient of volumetric expansion is 1/273 per degree, stating at 0 At -273 the volume of the gas would therefore be zero, and matter would have Disappeared. 绝对零度绝对零度 Summary 2.1 Nature of heat 热的性质热的性质 2.1.1 Heat

27、energy 热能热能 2.1.2 Power 功率功率 2.1.3 Temperature 温度温度 2.1.4 Thermometers 温度计温度计 2.1.5 Temperature scales 温标温标 2.1.6 Heat capacity 热容：热容： 2.1.7 Density 密度密度 2.1.8 Change of state 相态变化相态变化 2.1.9 Sensible and latent heat显热和潜热显热和潜热 2.1.10 Enthalpy 焓焓 2.1.11 Calculation of heat quantities 热量计算热量计算 2.1.12 E

28、xpansion 膨胀膨胀: gas; liquid; soild Heat capacity; specific heat capacity Latent heat; specific latent heat mcHmlH Difficulties : Definition formula symbolUnit and Alternative units Calculate formulation Thermal energy H or QJoule Calorie; kWh; BTU Power P= H / tPWatt temperatureTDegree Kelvin(K) ther

29、mometersTypes: Temperature scales Celsius thermodynamic T Heat capacity c Density = m/vKg/m3 Change of stateSolid liquidgasinterchangeable Sensible heat Latent heat expansion Now lets move on to the second topic 2.2 Heat transfer 传热 Heat energy always tends to high temperature low temperature region

30、s. three different modes of heat transfer. 1 Conduction 导热导热 2 Convection 对流对流 3 Radiation 辐射辐射 Conduction 导热导热 is the transfer of heat energy through a material without the molecules of the material changing their basic positions. 物体各部分无相对位移或不同物体直接接触时依靠分子、原子及自由电子等微观物体各部分无相对位移或不同物体直接接触时依靠分子、原子及自由电子等

31、微观 粒子热运动而进行的热量传递现象粒子热运动而进行的热量传递现象 in theory , can occur in solids, liquids and gases in fact， dense solids. Different materials conduct heat at different rates 导热率导热率 best conductors are Metals Poor conductors are called 隔热体隔热体 A very famous Law? Fouriers Law 各向同性材料的导热问题 注册设备师考题 单纯的导热发生在（单纯的导热发生在（ ）

32、 A A 气体中气体中 B B 液体液体 C C固体固体 D D以上三种物体以上三种物体 稳态导热是指（稳态导热是指（ ） A A温度不随时间变化温度不随时间变化 B B温度不随空间位置变化温度不随空间位置变化 C C温度在各点的值相等温度在各点的值相等 D D温度不随时间和空间位置变化温度不随时间和空间位置变化 : (a) Natural / Free Convection (b) Forced Convection uses a mechanical pump to achieve a faster flow of fluid. Convection 对流 is the transfer

33、of heat energy through a material by the bodily movement of particles can occur in fluids ( liquids and gases) ,but never in solids. 注册设备师考题： 对流换热以（ ）作为基本计算式 A 傅里叶定律 B 牛顿冷却定律 C 普朗克定律 D 热力学第一定律 Stack effect 烟囱效应烟囱效应 主要作用是拔火拔烟，排走烟气，改善主要作用是拔火拔烟，排走烟气，改善 燃烧条件。燃烧条件。 natural convection can occur in buildin

34、gs ？ Useful？ Destructive? Hot air rises, and cold air sinks reverses in summer There are some pictures showing the damage of stack effect during a fire The three features of Radiation heat transfer Can travel through a vaccum, conduction and convection cannot Can not only cause heat transfer , but a

35、lso accompany with conversion of different forms of energy. All bodies of matter, regardless of its temperature ,can emit radiation Radiation 辐射 is the transfer of heat energy by electromagnetic waves. Can radiation occur in gases? 分子结构不对称得双原子气体、单原子气体具有辐射性质分子结构不对称得双原子气体、单原子气体具有辐射性质 Dull black surfac

36、es阴暗的黑色表面阴暗的黑色表面 have the highest absorption and emission of radiation heat. Shiny silver surfaces光亮的银色表面光亮的银色表面 have the lowest absorption and emission of radiation heat. 有人认为由于白色外墙与黑色外墙相比能有效地养减少其吸收的太阳辐射量，那么白色内墙与黑色内墙相比其吸收的辐有人认为由于白色外墙与黑色外墙相比能有效地养减少其吸收的太阳辐射量，那么白色内墙与黑色内墙相比其吸收的辐 射量是否也会小？射量是否也会小？ 人环题人环题

37、20082008 注册设备师考试题 若粗糙红砖、空气、表面氧化的铜管、磨光的铝表面的发射率若粗糙红砖、空气、表面氧化的铜管、磨光的铝表面的发射率 大小排序大小排序 粗糙红砖：粗糙红砖：0.9 空气：空气：0 表面氧化的铜管表面氧化的铜管 0.65 磨光的铝的表面磨光的铝的表面 0.05 Example: How much does the human body radiate? - Body temperature = 37 C = 37 +273 = 310 K, Estimate surface area A = 1.5 m2 e = 0.70 H = esA T4 = (0.70)(5.

38、67 x 10-8)(1.5 m2)(310)4 = 550 watts (5 light bulbs) - The rate at which a body emits heat increases with the temperature of the body. 以下不是辐射气体的是（ ） A 氧气 B甲烷 C水蒸气 D二氧化碳 2.2.4 The greenhouse effect 温室效应 Sun: short wavelength radiation from sun is transmitted through glass Objects at normal temperatur

39、e: long wavelength radiation is trapped inside glass Absorption + reflection + A modern Greenhouse in RHS Wisely Royal Horticultural Society 英皇家园艺学会 After 2.2 heat transfer, we will talk about 2.3 Gases and vapours Gas:气体、煤气气体、煤气 Vapour: 蒸气蒸气 Steam: 水蒸气、蒸汽水蒸气、蒸汽 moist:湿的湿的 Vapor is a gas - there is

40、no significant physical or chemical difference between a vapor and a gas. a vapor is a substance in a gaseous state - at a condition where it is ordinarily liquid or solid Our most common example of a vapor is steam - water vaporized during boiling or evaporation. The water vapor surrounding us in t

41、he atmosphere is invisible and is often called moist. Knowledge about moist in air is important in air-condition applications like HVAC systems and dryers. The collisions of many molecules acting on a particular area will be detected as pressure. (A) Area F) ( Force )( Pressurep 2.3.1 Gases unit: pa

42、scal (Pa) By definition: 1 pascal = 1newton/ metre2 (1N/m2) 压强的国际单位是？ Other units which may be found in use include : millibars (mb) , where 1 mb = 101 Pa mm of mercury , where 1mm = 133Pa Boyles Law 波义耳定律 Charles Law 查理定律 Pressure Law 压力定律 General Gas Law 气体普遍定律 tons tanc T pV 2 22 1 11 T Vp T Vp t

43、onspVtanc TtonstancV const,tm const,pm const,VmTtonstancp 2.3.2 Gas laws 气体定律 注册设备师考试题注册设备师考试题 容器内盛有一定量的理想气体，如果将气体放出一部分后达到容器内盛有一定量的理想气体，如果将气体放出一部分后达到 新的平衡状态，问放气前后两个平衡状态之间的参数能否按状新的平衡状态，问放气前后两个平衡状态之间的参数能否按状 态方程表示为下列形式？态方程表示为下列形式？ 2 22 1 11 T Vp T Vp Daltons Law of Partial Pressures 道尔顿分压定律 mixture gas

44、es 混合气体混合气体 each gas exerts an individual partial pressure分压分压 and has the following features. 1) The partial pressure exerted by each gas is independent of the pressure of the other gases 2) The total pressure总压总压 of the mixture equals the sum of the partial pressures. 注册设备师考试题 道尔顿分压定律适用于（道尔顿分压定律适用

45、于（ ） A 理想气体理想气体 B 非理想气体非理想气体 C 所有气体所有气体 D 实际气体实际气体 Standard Temperature and pressure, STP 标准温度和压力 Standard temperature =0=273K Standard pressure = 101.3kPa = 760 mm of mercury The critical temperature 临界临界 温度温度of a substance is the temperature above which a vapour is not able to exit. 2.3.3 Vapours

46、蒸气 不同温度下对气体加压时，其压力和体积的变化情况不同温度下对气体加压时，其压力和体积的变化情况 A vapour is a material in the gas state which can be liquefied by compression, without change in temperature. So it is seen that steam is a vapour at 100 but a gas at 500 Table 2.2 critical temperatures air is a mixture of gases has the following per

47、centage composition when its clean and dry Nitrogen(N2) 78% Oxygen (O2) 21% Carbon dioxide (CO2) 1% 2.3.4 The atmosphere 大气 Other gases : water vapour, local pollution products. Mercury barometer 水银气压计水银气压计 Aneroid barometer 无液气压计无液气压计 2.4 Refrigerators & Heat Pump 制冷机和热泵制冷机和热泵 Refrigeration: 制冷制冷Th

48、e transfer of heat from lower temperature regions to higher temperature is called refrigeration. Refrigerator: 制冷机制冷机Devices that produces refrigeration are called refrigerators. Refrigerant:制冷剂制冷剂 The working fluid used in refrigerators are called refrigerant. Heat Pump:热泵热泵 Refrigerator used for t

49、he purpose of heating a space by transferring heat from a cooler medium are called heat pump. Can be divided into: 2.4.1 The refrigeration cycle 制冷循环 Four main components： Compressor 压缩机压缩机 Condenser 冷凝器冷凝器 Expansion valve 膨胀阀膨胀阀 Evaporator 蒸发器蒸发器 Four main components of a kitchen refrigerator. Not

50、every gas behaves in a way that is suitable for the cycle of vapour-liquid-vapour changes used in refrigeration. A refrigerant must be below its critical temperature, or it will not liquefy, and it must be above its melting point, or else it will solidify. in general a useful refrigerant should poss

51、ess the following properties: Low boiling point 低沸点低沸点 High latent heat of vaporisation 高的气化潜热高的气化潜热 Easy liquefaction by compression 压缩后容易液化压缩后容易液化 Stable, non-toxic and non-corrosive 稳定、无毒无腐蚀稳定、无毒无腐蚀 Environmental safety 对环境无害对环境无害 2.4.2 Refrigerants :制冷剂 Chlorofluorocarbon (CFC) is a mixture of o

52、rganic compounds contain carbon碳碳, chlorine氯氯, and fluorine 氟氟 freon 氟利昂氟利昂 . It is now accepted that CFCs help cause a reduction of the ozone layer臭氧层 in the upper atmosphere of the earth and contribute to global warming of the Worlds weather systems. CFCs ) 氟氯碳化物类 CFC replacements 氟利昂替代物 Ammonia 氨

53、氨is an efficient refrigerant but its toxicity and flammability requires special safety measures. Carbon dioxide 二氧化碳二氧化碳is used in some large refrigeration plants and requires high operating pressures. Compression refrigeration cycle 压缩式制冷循环 Absorption refrigeration cycle 吸收式制冷循环 2.4.3 refrigerators

54、 制冷机 A heat pump is a device which extracts heat from a low temperature source and upgrades it to a higher temperature. For a heat pump, The condenser coils are used to heat air or other medium 2.4.4 Heat pumps 热泵 The coefficient of performance (COPH) of a heat pump 热泵的性能系数热泵的性能系数 is the ratio of he

55、at output to the energy needed to operate the pump 21 1 H inputenergy Pump output energy Heat COP TT T Heat pump efficiency 一热泵功率为一热泵功率为10kW10kW，从温度为，从温度为-13-13的周围环境向用户供的周围环境向用户供 热，用户要求供热温度为热，用户要求供热温度为95 95 。如果热泵按逆卡诺循环。如果热泵按逆卡诺循环 工作，求供热量。工作，求供热量。 解：设热泵按逆卡诺循环运行，根据题意，解：设热泵按逆卡诺循环运行，根据题意，t1= 95 t1= 95 ，

56、 t2= -13t2= -13 41.3 inputenergy Pump output energy Heat COP 21 1 H TT T pump energy input :10kWpump energy input :10kW heat energy output: 34.1kW heat energy output: 34.1kW 热泵从环境中取得的热量热泵从环境中取得的热量24.1kW24.1kW 供热量中供热量中24.1/34.1=70.7% 24.1/34.1=70.7% 是热泵从周围环境中提取的是热泵从周围环境中提取的 注册设备师考试题 冬季冬季 利用热泵为房屋供暖，使室

57、内温度保持在利用热泵为房屋供暖，使室内温度保持在2020，需要向室内供，需要向室内供 热热3000W3000W，室外环境温度为，室外环境温度为-5-5，试求该热泵的热泵性能系数（供热，试求该热泵的热泵性能系数（供热 系数）？系数）？ 带动该热泵工作所需要的最小功耗是多少？带动该热泵工作所需要的最小功耗是多少？ 254.2W254.2W Heat sources for heat pumps Air Earth Water Exhaust heat A geothermal heat pump system. Summary of chapter 2 2.1 Nature of heat, it

58、s measurement and its effect 热的性质、量度和作用热的性质、量度和作用 2.2 Heat transfer 热传递 2.3 Gases and vapours, and their effects 气体和蒸气，及其作用气体和蒸气，及其作用 2.4 Refrigerators and heat pumps 制冷机及热泵制冷机及热泵 useful sentence patterns： XX is the standard SI unit of YY 焦耳是国际单位制中能量的单位 开尔文是国际单位制中温度的单位 Table XX gives YY values for a

59、 variety of materials 表（1.1）给出了不同材料的（比容）值 xx will be discussed in later chapter. 这些问题在以后的章节中会讲到。 物质/体：matter material substance They have the basic characteristics given below. 它们具有以下特性 XX is given by the following formula. (潜热）可用下式计算 (显热）可用下式计算 XX is about YY times that of ZZ 铝的膨胀系数是钢的2倍 塑料的膨胀系数是钢的

60、10倍 酒精的膨胀系数是水的5倍 Expand on heating and contract on cooling 受热膨胀冷却收缩 For each degree of temperature rise 温度每降低1 xx is inversely proportional to yy 体积与压力成反比 xx is directly proportional to yy 体积与热力学温度成正比 压力与热力学温度成正比 Temperature must always be in xx 温度应采用开氏温度 温度可采用摄氏温度 The sum of xx 各分压力之和 Have already