Presentation on theme: "2006.06.121/14 Term project 2006 Definition of Urban Heat Island and it’s mechanism Department of Civil and Environmental System Engineering University."— Presentation transcript:
/14 Term project 2006 Definition of Urban Heat Island and it’s mechanism Department of Civil and Environmental System Engineering University of Incheon, South Korea Chi-Man, Park Term project 2006
/14 Term project 2006 Contents Introduction - What is Urban Heat Island? Main subject - Black Body Theory - Albedo - A result of U.H.I. Conclusion - Relationship between albedo, black body theory and U.H.I.
/14 Term project 2006 Urban Heat Island? Densely populated urban area. Land is covered by concrete and bituminous structure like building and road. Restriction of wind flow by high rise buildings Figure: Urban heat island
/14 Term project 2006 Urban Heat Island? (Continue) Urban Heat Island? (Continue) Building, road and concrete absorbs or store more sun light than earth. A tropical night is also one of Urban heat island phenomenon. The phenomenon of higher temperature in urban area than other area is called Urban Heat Island Figure: Variation of heat level
/14 Term project 2006 Black Body Theory Blackbody theoy radiation Heat radiates from the stove Radiation is the emission of energy by hot object Without medium, energy of one reach other by radiation system black body Black Body absorbs light of all wavelength and then radiate That is, it absorb all light
/14 Term project 2006 Black Body Theory (continue) Black body doesn’t exist for real Ideal black body σ = x 10-8 Watt/m 2 k 4 Stefan-Boltzmann Law E= σAT 4 → Black body give off radiation as a rate proportional to the 4 th power of the temperature σ=Stefan-Boltzmann’s constant A= Surface area of object T= Temperature in Kelvin
/14 Term project 2006 Black Body Theory (Continue) Stefan- Boltzman n Law As temperature is high, Black body emits much energy. That is, black body give off radiation at a rate proportional to the 4 th power of the temperature. Wine Law Wien's Displacement Law states that the wavelength distribution peaks at a value that is inversely proportional to the temperature.
/14 Term project 2006 Albedo Heat balance Maintaining the proper balance between absorbed solar energy and emitted earth radiation energy. → ragular average temperature of the earth.
/14 Term project 2006 Albedo Albedo? The percentage of the incident sunlight that is reflected 30% of solar radiation energy which enters the earth are reflected by a cloud or surface Therefore an albedo of the earth is 30% SurfaceAlbedo(%) SurfaceAlbedo(%) Concrete17~27Sand (White)30~60 Crops (Green)5~25Snow (Fresh)80~90 Forest (Green)5~10Snow (old)7~45 Grassy plain (Green) 5~25Soil (Dark)5~15 Farm land14~17Soil (Bright)25~30 Road (Black)5~10Water8
/14 Term project 2006 Temperature inversion (continued) Because of Urban heat island, warm air of the urban rise on the city. Cold air of suburbs come to the urban. Urban heat island’s problem?
/14 Term project 2006 Temperature inversion As cool air from suburban with much dust and pollutants enter to the urban, pollutants is collected in urban, without diffusion of pollutants. Dust and pollutants cover the skies of city - it is called dust roof. That is, urban heat island is related to photochemical smog.
/14 Term project 2006 Relationship between albedo, black body theory and U.H.I Asphalt road Solar radiation energy(100) Albedo(5~10) ▣ Asphalt roads and concrete structures absorb 90~95 of solar radiation energy. When reaching an absolute temperature, these make radiation energy. It is principle of Urban heat island
/14 Term project 2006 Amount of radiation energy ▣ E= σAT 4 σ = 5.67x10 -8 w/ ㎡ k ⁴ ▣ Calculation of asphalt road’s radiation (Dimensions:1 m 2, Temperature: ( )K ← In summer solar constant: 2cal/cm 2 · min) E = 5.67x10-8 w/ ㎡ k ⁴ⅹ 1 m 2 ⅹ ( ) 4 K = w 1m T=( )K E= w 1400W/m 2 ·min Stefan-Boltzmann’s constant
/14 Term project 2006 Conclusion Absorbs many energy if Albedo is low When temperature rises, radiation energy also increase As Construction, such as asphalt, has lower albedo than soil, it absorbs more energy and emits radiation energy Urban heat Island is generated by this radiation energy.