Yeni bir güneş enerjili hava ısıtıcı üzerinde deneysel çalışma
Experimental study on a novel solar air heater
Yazar: RÜZGAR ÖZKAN BİLDİK
Danışman: PROF. DR. HASAN SAYGIN ; DR. ÖĞR. ÜYESİ RAHELEH NOWZARI
İstanbul Aydın Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Makine Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Enerji = Energy

Özet:
Yenilenebilir ve sürekli bir enerji kaynağı olan güneş enerjisi, ülkemizin de içinde bulunduğu güneş enerji açısından şanslı ülkeler için bir kaynak oluşturmaktadır. Bunun yanı sıra; ucuz, temiz ve çevre dostu olması en önemli özelliklerindendir. Türkiye güneş enerjisini kullanarak çeşitli alanlarda fayda sağlayabileceği ülkeler arasındadır. Ne yazıkki günümüzde güneş enerjisi teknolojisini ya su ısıtmada yada düşük verimli elektrik üretiminde kullanmaktayız. Güneş enerjisi potansiyelin artırılabilmesi düşük sıcaklıklarda da yenilikçi sistemlerin kullanılmasıyla mümkün olacaktır.
Ülkemiz, güneş enerjisini ortam havalandırma, ortam ısıtma ve endüstriyel ısıtmalarda kullanarak enerji tasarufu yapılabilmektedir. Yalnız bu sistemlerin kurulum ve yapısal mağliyeleri de yüksek olmaktadır. Bu tezde güneş ışınımlarını absorbe eden yutucu denilen tel örgü kullanarak analizlerini yapmaktır. Bu tel ile absorbe malzemesinin mağliyetini düşürmek ve sistemde ufak eklemeler ile ısıl verimi yükseltebilmektir. 
Deneysel çalışma 2018 tarihinin Eylül ve Ekim aylarında gerçekleştirilmiştir. Her deney sabah saat 09:00'da başlamış olup 16:00'da bitmiştir. Analiz için veriler her saat başı alınmış olup değerlendirmelere katılmıştır. 
Deneysel çalışmada güneş kollektörünün tabanından başlayarak üst üste 16 adet tel örgü malzeme dizilmiştir. Daha sonra tel örgülerden 3 cm mesafeden sonra delikli pleksiglas malzeme eklenmiştir. Her bir delik çapı 3 mm ve iki delik arası mesafe 3 cm olarak hizalanmıştır. Bu malzeme bize sistemin fazla ısı kaybını önlemede büyük performans kazandıracaktır. Deneysel olarak yaptığımız bu çalışmada ısı kayıplarını belirleyebilmek için pleksiglas malzemenin üst ve alt kısımlarına delikler açılmış, orta kısmında işlem yapılmamıştır. T tipi termokopl ile üst deliklerden, alt deliklerden ve orta kısımdan sıcaklık ölçümü alınarak kayıt altına alınmıştır. Double sistemimizde ilave olarak pleksiglas malzemeden sonra normal cam yüzey eklenmiştir. Bu cam yüzey sadece pleksiglas malzemede delik bulunan bölümlerin üzerinde yer almaktadır. Bu cam yüzeyler verimi ve performansı arttırmak için bize ön ısıtma görevi görmektedir. Deney esnasında güneşten gelen verileri bir pirnometre ile ölçerek kayıt altına alınmıştır. Santüfrüj fan hızını kontrol etmek için hız kontrol cihzı, sistemin giriş basıncını ölçmek için manometre ve orifismetre kullanılmıştır. Tüm veriler data loger ile kayıt altına alındıktan sonra sistemin verimlerini hesaplayarak en son kendi çalışmamızı diğer benzer çalışmalar ile kıyaslayarak analizlerimizi bitirmiş olmaktayız. Deneyimiz hem single hemde double sistemimizde 3 ayrı havanın kütlesel akış hızı (0,011, 0,035 ve 0,045 Kg/s) test edilmiştir. Delikli pleksiglas, kapaktan atmosfere olan ısı kayıplarını azaltmak ve verimi arttırmak için kullanılmıştır. Elde edilen sonuçlar, hangi kolektör tipinin daha yüksek bir termal performans gösterdiğini görmek için analiz edilmiştir.

Anahtar Kelimeler: Güneş Enerjisi, Hava Isıtmalı Güneş Kollektörü, Hava Isıtmalı Güneş Enerji Sistemleri, Güneş Kollektör Çeşitleri, Yenilenebilir Enerji

Abstract:
Solar energy is considered as one the most common sources of renewable energy sources. It is free, environmentally friendly and almost available everywhere. Due to its geographical location, Turkey can vastly benefit from this source of energy but unfortunately, the areas in which solar energy technologies are being used are mainly limited to water heating applications and low-efficiency electricity generation fields. By designing and introducing innovative systems, the possibility to use this source of energy will be increased specially at places with low temperatures.  
The importance of solar energy systems is increasing day by day all around the world. Turkey is also showing interest in such systems nowadays. While Turkey is taking major steps in the energy sector, infrastructure is being prepared for investments in solar energy systems. Due to the fact that Turkey's location on the earth is so good in case of solar radiation gain throughout the year specially at its south side, by making great investments in such technologies a great deal of demanded energy can be produced here. According to the regions, Southeastern Anatolia is the region that receives the most sunshine on an annual basis, followed by the Mediterranean region. 
Turkey can save energy and pay less for fuels by using solar energy more in areas like ventilation, air-heating applications and also in industrial heating. As the installation and structural expenses of these systems are a bit high, the aim of this research is to introduce a novel solar air heater which can be made with low cost and has high performance compared with conventional solar air heaters.
Flat plate collectors generally consist of a transparent cover, an energy-collecting surface, heat-carrying pipes, insulating material and a case for holding each part. Some of the solar energy coming on the transparent cover is reflected and goes to the environment while the other part comes onto the absorber surface. A large part of the radiation emitted onto the absorber surface is absorbed by the absorber surface and some of it is reflected to the transparent cover as long wavelength radiation. A part of this radiation reflected on the transparent cover is reflected on the absorber surface and a part passes through the transparent cover to the environment. The heated absorber transmits most of the surface energy to the carrier fluid. Some of them are spread from the casing and the cover to the environment via transmission and transport. In order to improve the performance of these systems, the amount of heat loss should be reduced.
An experimental work was carried out on single and double pass solar air heaters which included wire layers instead of an absorber plate and a perforated cover instead of a normal glazing. The experiments were conducted in Istanbul Aydin University located on the European side of Istanbul, Turkey. Tests and readings started at 9:00 am and continued until 04:00 pm on each day of the experiment. At each day of experiment, the outlet and inlet (ambient) air temperatures and also glazing temperature were recorded hourly. In addition, solar radiation was also recorded. Wind speed and humidity values were read every hour from the official Turkish Meteorological Service website. The air mass flow rate and pressure drop inside the collector were measured with a 15° inclined tube manometer. Using a speed controller, different air mass flow rates could be obtained. The speed controller was connected to the fan to allow the user to set the speed to the desired value. In addition each system was tested with three different air mass flow rates (0.011, 0.035 and 0.045 kg/s).
16 wire mesh layers are located inside the collector. The plexiglas cover is placed at the distance of 3 cm from the bottom of collector on top of the mesh layers. The diameter of the holes drilled in the plexiglas cover is 3 mm and the center to center distance between the holes is 3 cm. The perforated cover improves the performance of the solar air heater as it reduces the heat loss from the collector to the environment. 
The holes are made on the top and bottom sides of the plexiglas cover. They are arranged in line format. T-type thermocouples are used in these experiment. The thermocouples are located at various places at the iner side of the cover. The first thermocouple is placed at the middle of the holes at the top side of the cover, the second one is placed exactly at the middle of the plexiglas cover and the third one is located at the middle of the holes at the bottom side of the cover. 
In order to convert the system to double pass collector, a normal glass cover is placed on top of the plexiglas cover.  The air enters into the collector through an openinig at the middle of this glass cover. The length and width of the opening is 100 cm and  3 cm ,respectively. The aim of putting the second cover was to preheat the air before it eneters to the first channel of the collector and to increase the thermal performance of the solar air collector. The hourly solar radiation is measured using a Pyranometer and data loggers. The air is circulated through the system by a centrifugal fan. The fan speed was controlled by a speed controller. The air mass flow rate inside the collector is controlled and measured using an orifice meter and a manometer. The data loggers are used to record the data hourly. The obtained results are analysed and compared woth other similar studies. 
The data obtained from the experiments were analyzed and the following results were achieved. In case of the single pass collector, mostly there was a sudden reduction in air outlet temperature and thermal efficiency of the system at around 02:00 pm. The reason for these changes was due to the sky condition, as the experiments were carried out in September and October and most of the time the sky was cloudy and there was no direct solar radiation on the collector surface. It is found that using small depth channel reduces pumping power. However, on the other hand, the porous medium increases the pressure drop, which is important at high volume flows of air. 
In this experimental study, the highest measured thermal efficiency of the single pass solar air heater is calculated to be 52% at the mass flow rate of 0.045 kg/s. The measured highest performance is obtained at the average outdoor conditions of 18 ˚C inlet air temperature, 14 m/s wind speed and 79% humidity.
The maximum amount of thermal efficiency was achieved with the double pass solar air heater. At the mass flow rate of 0.045 kg/s, and the average outdoor conditions of 19˚C inlet air temperature, 27 m/s wind speed and 60% humidity, the maximum thermal efficiency of the system was about 83%. 
By considering all the obtained results it is found that the collector efficiency increases as the air mass flow rate increases. But ΔT decreases as air mass flow rate increases. In case of pressure drop, in both single and double pass solar collectors by increasing the mass flow rate of air the pressure drop increases as well. But generally the pressure loss is more in double pass solar collector.  
The obtained results from this study are compared with the results of other published works in order to analyze the performance of different systems with each other and to see which factors affect the overall efficiency more. 
The main goal of this research was to reduce the amount of heat loss from the cover by the help of perforated cover. The measured temperatures on the perforated cover showed that the parts of the cover with holes are cooler than the middle part without the holes and this proves that our model improves the collector performance by reducing the cover temperature which leads to less heat loss through the glazing. It has to be mention that the proposed model has less construction cost compared with the conventional models and this is beneficial from the economical point of view.
 Although similar studies exist in the literature, there is no other study that analyzes a collector with stainless steel wire mesh layers and the air passage through the holes on the top and bottom of the cover. In future works, new designs have to be proposed in a way that they enhance the performance of the solar collectors in a most economical and efficient way.

Keywords: Solar air collector; Solar energy; Perforated cover; Solar air heater systems; Renewable energies.