Buharlaşma ve süblimleşme yoluyla gerçekleşen kütle kayıplarının meteorolojik değişkenlerle olan ilişkisinin araştırılması
Investigation of the relationship between atmospherical variables and mass loss by evaporation and sublimaton
Yazar: MEHMET AFİF
Danışman: PROF. DR. KASIM KOÇAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Meteoroloji Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Meteoroloji = Meteorology ; İstatistik = Statistics

Özet:
Küresel iklim değişikliğine bağlı olarak gerçekleşen hava sıcaklıklarındaki artış kullanılabilir su kaynaklarının hızla azalmasına neden olmaktadır. Serbest su yüzeylerinden olan buharlaşma sonucunda önemli miktarda su kayıpları gerçekleşmektedir. Bu kayıplarının doğru bir şekilde ölçülebilmesi ülkelerin sürdürülebilir su politikaları hazırlayabilmelerinde büyük önem arz eder.Günümüzde serbest su yüzeylerinden olan buharlaşmanın belirlenmesinde literatürdeki hesaplama yöntemleri ve ölçüm sistemleri arasında en doğru sonuçlara buharlaşma havuzları ile ulaşılmaktadır. Fakat bu sistem yapısal özellikleri dolayısıyla birçok yerde kullanılamamaktadır. Bu durum yeni bir ölçüm sisteminin gerekliliğini ortaya koymaktadır.Yapılan çalışmada, süblimleşebilen maddelerle bazı atmosferik değişkenlerin (sıcaklık, bağıl nem, rüzgâr hızı, güneş radyasyonu) buharlaşmayı açıklamadaki rolleri araştırılmıştır. Bu amaçla İstanbul Teknik Üniversitesi Meteoroloji Gözlem Parkı'nda 2011 yılı Haziran, Temmuz ve Ağustos aylarında süblimleşme ve buharlaşma ölçümleri yapılmıştır. Sıcaklık, bağıl nem, rüzgâr hızı, güneş radyasyonu değerleri yine meteoroloji parkındaki otomatik istasyondan elde edilmiştir. Süblimleşme ölçümleri için naftalin, kâfur ve mentol maddeleri kullanılmıştır.Buharlaşma ölçümleri Class A Pan tipinde buharlaşma havuzundan yapılmıştır. Süblimleşme ölçümlerinde kullanılacak maddeler küçük silindirik kaplara dökülmüştür. Böylelikle madde kabın şeklini almış ve süblimleşme sadece yüzeyden gerçekleşmiştir. Sonrasında kabı buharlaşma havuzunun yüzeyiyle yakın yükseklikte tutacak bir düzenek hazırlanmıştır.Ölçüm süresi boyunca yapılan naftalin süblimleşmesi ölçümlerine aralıksız devam edilmiştir. Mentol maddesiyle yapılan ölçümlere maddenin sıcak aylarda erimeye başlaması dolayısıyla son verilmiştir. Sonra mentol yerine kâfur maddesi ile ölçümlere başlanmıştır. Kâfur maddesi ile ölçümler genel ölçümlerin bitiş tarihine kadar yapılmıştır.Değişkenler arasındaki ilişkiyi belirlemede regresyon analizi yöntemi kullanılmıştır. Buharlaşma ile naftalin süblimleşmesi verileri arasında yapılan analiz sonucunda determinasyon katsayısı r2 = 0.778 olarak hesaplanmıştır. Bu da buharlaşma ile naftalin süblimleşmesi arasında güçlü doğrusal bir ilişki olduğunu göstermiştir. Atmosferik değişkenlerin de analize katılmasıyla determinasyon katsayısı artmıştır. Buradan buharlaşmanın naftalin süblimleşmesiyle birlikte sıcaklık, bağıl nem, rüzgâr hızı ve güneş radyasyonu gibi atmosferik değişkenlerle açıklanabileceği sonucuna ulaşılmıştır.Çalışmada kâfur ve mentol verileri için yapılan analizler sonucunda determinasyon katsayıları sırayla r2 = 0.184 ve r2 = 0.148 olarak bulunmuştur. Buradan kâfur ve mentolün buharlaşmayı açıklamada yeterli olmadıkları sonucuna ulaşılmıştır. Buna rağmen ölçümlerle ilgili sorunlar giderildikten sonra kâfur maddesin buharlaşmayı açıklamada daha yüksek koralasyon değerlerine ulaşması beklenmektedir. Mentol maddesinin ise, soğuk aylarda yapılacak ölçümler için daha ideal olduğu görülmüştür.

Abstract:
Major part of the Earth Surface is covered with water. Although there are large amount of water on the earth, very small part of earth water supplies are available for human use. Increase in air temperature depending on global climate change resulted in the reduction of available water resources. As a result of the evaporation on free water surface, significant amount of water loss occurs. Accurate measurement of these losses is crucial for countries to manage their sustainable water policies.Evaporation occurs from liquid surfaces. It is a phase transition from liquid to gas. In nature, evaporation generally happens from free water surfaces, soil and plant surfaces. When evaporation occurs on soil and plant surfaces, it takes the name of evapotranspiration. Heat is essential for evaporation. Heat increases the molecular kinetic energy thus surface tension decreases and molecule escapes from the surface accelerate. Additionally when air is saturated, water contend of air is the top of limit. Evaporation in this condition stops. Also vapour pressure deficit is important for evaporation. Vapour pressure deficit states difference between surface vapour pressure and air vapour pressure. If surface vapour pressure is bigger than air vapour pressure, vapour pressure deficit increase and evaporation accelerate. There are some other factors effecting evaporation such as, heating, wind speed, shape of evaporation surface, surface albedo, depth ect. Evaporation is generally measured from evaporation pans. Evaporation pan is an kind of cylindrical container that is filled with water and difference of water level is measured in a time interval. Alternately atmometers are also used to measure evaporation. An atmometer is a meteorological instrument which measure water loss from moist and porous surface. By the way lysimeters are mostly used to measure evapotranspiration. Lysimeter is a kind of tank which settles in underground and filled with soil correspond to horizons of ground and planted vegetations around it. Then water budged components take into account for calculating evapotranspiration.Today, more accurate evaporation measurements can be obtained by the evaporation pans than other calculation methods and measurements systems in the literature. Change of water level is measured from evaporation pans. Thus evaporation loss can be determined in a period of time. However evaporation pans are useless in frost seasons. By reason of water in evaporation pans freeze, they are removed in frost seasons. Also some structural features of this system limit its usage in many environments. This situation requires the need for a new measurement system.Sublimation is a thermodynamic process. As a result of sublimation, substances in solid phase turn into gas phase without passing through liquid phase. Also mass transfer occurs from solid matter?s surface. Mass transfer of a sublimable matter can be measured by two different ways. First way is weighing the sample of mass in aperiod of time. Second way is measuring the sublimation depth of sublimable matter via special deep measurement systems. In this system, change of surface elevation between two measurements is determined. These measurement systems are mostly used in heat transfer experiments to estimate local and average transfer coefficients.Mechanism of sublimation and evaporation seems like each other. Mass transfer from sublimation surfaces and evaporation surfaces to atmosphere exists in either thermodynamic process. Hereby, these thermodynamic processes can be associated with each other via mass transfer laws.In this study, the roles of some sublimable matters (naphthalene, camphor and menthol) and atmospheric variables (temperature, relative humidity, wind speed, solar radiation) explaining the evaporation were investigated. For this purpose, sublimation and evaporation measurements were performed at Meteorological Station of Istanbul Technical University in June, July and August in 2011. Temperature, relative humidity, wind speed, solar radiation values were obtained from automated weather observing system (AWOS) at the meteorological station. Naphthalene, camphor and menthol substances were used for sublimation measurements. Evaporation measurements were made with Class A Evaporation Pan. Hook-gauge and Stillwell instruments were used to measure evaporation sensitively. Substances used in the measurement of sublimation were filled in small cylindrical containers. Thus, sublimable material took the shape of the container and sublimation only occurred from the substance?s surface. As naphthalene and menthol substances could be melted in low temperature, camphor couldn?t be melted because of its chemical properties. Camphor were solved in aseton and filled to containers for this reason. Then, a measurement system was designed to keep container?s height close to the evaporation pan?s surface.Naphthalene measurements were continued uninterrupted during the period of measurements. Decreasing naphthalene containers were changed 3 times with new ones in the course of the measurement time. Due to melting of menthol substance in the warmer months, menthol measurements were terminated. Then, it was replaced by camphor container. Camphor measurements were made until the last date of the general measurements and containers were changed 2 times.Before the statistical analysis measurement data were arranged. First of all data which was measured in rainy days were removed. Mass of sublimation containers expect to decrease from one measurement to another. When mass of sublimation containers were weighed in rainy days, measured value was bigger than previous measurement value. Then, average values of temperature, relative humidity and wind speed were calculated between 10:00 - 20:00 time interval and total values of global radiation, naphthalene sublimation and evaporation were calculated at same time interval.Regression analysis method was used to determine the relationship between the variables. Evaporation is selected as depended variable in calculations and other variables (naphthalene sublimation, temperature, relative humidity, wind speed, global radiation) used for explaining evaporation. Firstly analysis was made between evaporation and naphthalene sublimation data. Then calculations were made that increasing the number of independent variables one by one. In final, all independent variables were added to calculations. As a result of the analysis, coefficient of determination between evaporation and naphthalene sublimation was found r2 = 0.778. This shows a strong linear relationship between naphthalene sublimation and evaporation. Coefficient of determination increased after adding atmospheric variables to the analysis. In final, coefficient of determination rose to 0.882. This shows the evaporation can be explained via naphthalene sublimation and atmospheric variables such as temperature, relative humidity, wind speed and global radiation.As a result of the regression analysis, naphthalene and global radiation seemed to be better group to explain evaporation than other variables. Also the group of naphthalene and temperature in analyses made less contribution to explain evaporation than other variables.Water vapour rate in air is bigger than naphthalene vapour rate in air. In theoretical meaning atmospheric variables except relative humidity of air are expected to have the same effect on naphthalene sublimation and evaporation. Then, sublimation and relative humidity must be the best variables together in order to explain evaporation. As a result of the regression analysis with evaporation, naphthalene sublimation and relative humidity data, coefficient of determination was found r2 = 0.786. This result showed naphthalene sublimation and relative humidity are not the best group in order to explain evaporation.During the period of measurements, naphthalene containers were replaced with new containers 3 times. After changing containers, deviations were seemed on the new data measured from naphthalene containers. Changing the containers affected analysis results in the other words. Regression analysis being done with whole data measured from start to end shows an average relationship between naphthalene sublimation and evaporation. On the contrary, a strong relationship was found as a result of analysis being done with measured data which was measured until removal date of first naphthalene container. Best solution is using identical and bigger size containers here. That can solve the problems from different sublimation surface. Also this solution can help to overcome sublimation problems that occur from melting substances at different times.In the course of measurements some days were rainy. These rainy days caused to data loss. This problem can not be solved along measurements. Besides this issue can be overcome settling a glass on the sublimation container which has high transmission rate.As a result of the analysis with camphor and menthol data coefficients of determination calculated as r2 = 0.184 for camphor and r2 = 0.148 for menthol. This shows, camphor and menthol are not sufficient for explaining the evaporation in this study. However, after the removal of issues related to the camphor measurements, is expected to reach a higher correlation value of evaporation. Besides, menthol measurements are not applicable for summer months and are expected to reach better results if measurements are made in cold months. Camphor and menthol are better alternative substances than naphthalene. Naphthalene has a lot of unhealthy effects on humans, and environment. Especially cancer risk can be seemed when high rate naphthalene vapour is exposed.