In this paper, the effect of various zinc oxide aluminate spinel (ZnOAl₂O₃) and titanium oxide (TiO₂) nanoparticle concentrations on the thermal performance of the Diffusion Absorption Refrigeration (DAR) system is investigated. The main aim of the study is to increase the efficiency of DAR systems operating with low thermal performance. The first part of the study is experimentally tested on the system under the same ambient conditions in order to develop passive heat transfer using different nanofluids as working liquids, including ammonia/water solution containing different amounts (1 wt.% and 2 wt.%) of ZnOAl₂O₃ and TiO₂ particles. In the next part of the study, the tested system is designed in MATLAB/Simulink toolbox environment to compare experimental and numerical results. The use of nanofluids can increase the surface area expansion and the heat capacity of the fluid, resulting in a significant positive increase in heat transfer. The results clarify that the use of nanofluid as working fluid in the DAR system helps quicker evaporation, which reduces operating time and increases heat transfer in the generator. Compared to a base DAR system, the nanofluid solution with a 2 wt.% ZnOAl_2O3 nanoparticle concentration among other nanofluid and proportions causes a 57% increase in the coefficient of performance (COP) of DAR system.

En tr An experimental study is carried out to investigate the pressure distribution and thermal performance of gravity assisted heat pipe charged with different working fluids. Methanol, water and Mono-Ethylene-Glycol (MEG) are chosen as working fluids which have different boiling point, density and viscosity. An experimental test apparatus is designed and produced including three heat pipes that heat input on the evaporator section are provided by solar energy. Measurements are conducted on the heat pipe surface for pressure and temperature variations. Pure antifreeze is chosen as working fluid, due to its high boiling point, along with water and methanol which are widely used in thermosyphon type heat pipes. Heat pipes are put into parabolic focused vacuumed glass tube and operated by solar energy for 11 days in order to achieve high temperatures. Data taken from 06.30 to 18.30 is taken into consideration for experimental results. Experimental results are evaluated for two days as (i) sunny and (ii) cloudy days by choosing days with the highest and lowest solar radiation. (i) As for the sunny day, the highest storage water temperatures for methanol, water and antifreeze were 90.0°C, 83.5°C and 86.7°C and the pressure values were 6.7 bar, 1.6 bar and 1.9 bar respectively. (ii) And for the cloudy day, the respective values of temperature and pressure were measured as; 43.9°C, 39.3°C, 29.0°C, and 2.0 bar, 0.2 bar and -0.3 bar. An experimental study is carried out to investigate the pressure distribution and thermal performance of gravity assisted heat pipe charged with different working fluids. Methanol, water and Mono-Ethylene-Glycol (MEG) are chosen as working fluids which have different boiling point, density and viscosity. An experimental test apparatus is designed and produced including three heat pipes that heat input on the evaporator section are provided by solar energy. Measurements are conducted on the heat pipe surface for pressure and temperature variations. Pure antifreeze is chosen as working fluid, due to its high boiling point, along with water and methanol which are widely used in thermosyphon type heat pipes. Heat pipes are put into parabolic focused vacuumed glass tube and operated by solar energy for 11 days in order to achieve high temperatures. Data taken from 06.30 to 18.30 is taken into consideration for experimental results. Experimental results are evaluated for two days as (i) sunny and (ii) cloudy days by choosing days with the highest and lowest solar radiation. (i) As for the sunny day, the highest storage water temperatures for methanol, water and antifreeze were 90.0°C, 83.5°C and 86.7°C and the pressure values were 6.7 bar, 1.6 bar and 1.9 bar respectively. (ii) And for the cloudy day, the respective values of temperature and pressure were measured as; 43.9°C, 39.3°C, 29.0°C, and 2.0 bar, 0.2 bar and -0.3 bar.

In this study, a thermoelectric generator (TEG) system is designed to produce electricity from solar energy. Solar powered two-phase closed thermosiphon (TPCT) type heat pipe is used to heat the hot surface of the TEG, and a 1200 cc capacity passive water-cooled system is designed and manufactured to cool the cold side. The cooling system has two sections as primary and secondary sections which provide a natural water circulation to achieve an efficient cooling. A single TEG is used in most studies in the literature while 5 TEGs are used in this study to obtain a simple, easy and cheap design to generate more electricity. Not only the effect of passive water cooling, but also the effect of using a reflector on the system efficiency is tested experimentally. The system is operated by solar power under three different conditions as non-reflector, semi-reflector and full-reflector. Electrical and thermal data are recorded in a computer and data obtained from 08:00 to 15:00 is used for comparison and calculations. Maximum output power, electrical efficiency and Seebeck coefficient calculations are made for only TEG-1 in which the maximum open-circuit voltage is reached. Results showed that using a heat pipe with a small capacity passive water-cooling, the temperature difference for five TEGs can be reached to generate electricity.

In this study, the performance of a diffusion absorption refrigeration (DAR) system using solar energy is investigated experimentally. For this purpose, two types of systems with/without sub-cooling are used for the experiment. Two-phase closed thermosyphon type heat pipes using water as the working fluid are used to utilize solar energy as heat source. During the experiments; ambient temperature along with critical point temperatures on DAR systems and heat pipes, DAR systems pressures and solar radiation data are recorded from 06:00 to 16:00 and each heat pipe has collected 82.5W of solar energy. DAR1 has achieved its lowest evaporator inlet temperature (-14.8°C) at 14:40, and DAR2 has reached -0.9°C at 13:55. COP values of DAR1 and DAR2 are found as 0.2362 and 0.2254. Efficiency of the heat pipes used in DAR1 and DAR2 are 0.3677 and 0.3690, and their thermal resistance values are 0.1154W/°C, 0.0828W/°C respectively .

Kontrolsüz bir şekilde çevreye bırakılan atıklar, çevre ve insan sağlığına zarar vermektedir. Bu atıklardan birisi de kullanılmış bitkisel atık yağlardır. Özellikle bitkisel yağların kızartma sonrasında diğer atıklardan ayrı toplanmayarak çevreye bırakılması/atılması önemli çevresel sorunlara neden olmaktadır. Diğer atık yağlar gibi bitkisel atık yağların da çevreye zarar vermeden kimyasal ve/veya biyolojik çeşitli aşamalardan geçirilerek geri kazanımı mümkün olabilmektedir. Bu çalışmada bitkisel atık yağın herhangi bir aşamadan geçirilmeden farklı bir şekilde değerlendirilebilmesi amaçlanmıştır. Bunun için güneş enerjili su ısıtma sistemlerinde kullanılan iki fazlı kapalı termosifon tip ısı borusunda geleneksel çalışma akışkanı olarak kullanılan suyun yerine bitkisel atık yağın kullanılabilirliği deneysel olarak incelenmiştir. Termosifon tip ısı boruları içindeki çalışma akışkanı sıvı ve gaz olmak üzere aynı anda iki fazda olmakta ve alt ucundan aldığı ısıyı üst ucuna taşımaktadır. Böylece iki farklı ortam arasında bir ısı transferi sağlanmaktadır. Termosifonlar ısıtma amaçlı kullanılabileceği gibi soğutma amaçlı da kullanılabilir. Bu çalışmada vakumlu cam tüp içerisine yerleştirilen termosifon tip ısı borusu bir depo içerisindeki 400ml hacimdeki suyun ısıtılması için kullanılmıştır. Laboratuvar şartlarında gerçekleştirilen deneylerde enerji kaynağı olarak güneş enerjisi yerine akkor bir lambadan sağlanan ışık enerjisinden yararlanılmıştır. Termosifonun buharlaştırıcı hacminin %30’u kadarına çalışma akışkanı olarak 13ml bitkisel atık yağ konulmuştur. Güneş simülasyonu şeklinde yapılan ve 3 saat ile sınırlandırılan deneyler sonucunda sistemin verimi %33 olarak hesaplanmıştır.