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HVAC system design and optimization of the ventilation and air-conditioning of indoor environments are crucial for human comfort. Especially in recent years, due to the Covid pandemic, the importance of this hot topic is noticed. This study aims to focus on the HVAC performance of a dorm compartment onboard a naval surface ship since the ship environment is a good example of indoor air ventilation problem. The HVAC performance was investigated using a RANS solver. The numerical analyses were conducted for different scenarios and the results were finally discussed in terms of HVAC system location, air temperature, air intake and outlet conditions. As a conclusion, the current HVAC system design was found insufficient and alternative solutions were proposed in order to improve indoor air quality and thermal comfort.

Enerji verimliliği günümüzde giderek önem kazanmaktadır. Enerji verimliliğinin arttırılması ile yakıt tüketimi ve çevreye zararlı olan etkileri azaltmak mümkün olmaktadır. Ayrıca yakıt fiyatlarının önümüzdeki yıllarda artan trend göstermesi öngörülmektedir. Gemilerde uygulanan enerji verimliliği uygulamalarında enerji kaybının yaklaşık %25'ini oluşturan eksoz gazından enerji kazanım yöntemleri öne çıkmaktadır. Gemilerde atık egzoz baca gazı enerjisini geri kazanmak için ekonomizör kullanılmaktadır. Bu çalışmanın amacı, ekonomizer ana kazanın ön ısıtıcısı olarak çalışırken, kızgın yağ sisteminin performans, maliyet ve çevresel etki analizlerini gerçekleştirmektir. Bu kapsamda ana makinesi 4350 kW, kazanı 1500 kW ve ekonomizeri 340 kW olan bir gemi ele alınmıştır. Sonuç olarak gemilerde ekonomizer gibi atık ısı dönüştürücülerinin kullanılması ile hem tasarruf sağlanmış hem de emisyonlarda azalmalar görülmüştür.

The increasing of fuel prices and global energy demand and enactment of new restrictive emissions regulations require more efficient and environmentally friendly engines to be designed. In this context, conversion of waste heat to useful energy is necessary to design more energy efficient vessel including using more efficient main engines and auxiliary engines. The aim of this study, thermodynamic characteristic of recovery of a ship's main engine waste heat is determined parametrically for waste heat recovery system (WHRS). Naturally, heat exchangers are used for waste heat recovery. Because of that reason, firstly shell–and–tube heat exchanger will be investigated parametrically. In order to make a more accurate calculation, it is important to reflect the pressure and enthalpy variations in the heat exchanger to the heat transfer calculations. After that the Transcritical Organic Rankine Cycle (TORC), which is recommended by many authors for the recovery of waste heat sources at low and medium temperatures, will be examined parametrically. The results show that increasing the number of pipes in the heat exchanger at a certain value may result in a decrease in system performance parameters that is The Net Power and Thermal Efficiency due to decreasing velocity of the mass flow in tubes. Moreover, The Net Power and Thermal Efficiency curves behaved differently with variable mass flow rate. Therefore, we will define performance parameter being important for WHRS.

Increasing oil prices, the growing demand for energy, the adoption of new regulations for greenhouse gases and other harmful particulate emissions, as well as political instabilities and crises have necessitated the design of more efficient and environmentally-friendly plants. This paper presents a useful combination of mean cycle irreversibility (MCI) for thermodynamically optimizing the Rankine cycle using the MCI as the currently proposed criterion. The thermal irreversibilities and physical size of a system are evaluated together using the criterion that aims to minimize the ratio of the thermal irreversibilities or exergy destruction to a specified size that is characterized as the difference between the maximum and the minimum specific volumes of the cycle. The analyses consider the effects of different boiler-outlet or turbine-inlet pressures and temperatures, different condenser pressures, and different isentropic efficiencies on cycle performance. The results show that increasing the inlet temperature for a constant turbine-inlet pressure increases the MCI and increasing the turbine-inlet pressure at a constant inlet temperature decreases the MCI. With boiler pressure at 500 kPa, the boiler temperature increases from 500K to 600K, the MCI value increases nearly seven-fold, and thermal efficiency increases from 14% to nearly 16%. Also, the results show that the criterion gives more beneficial information to designers and engineers in terms of exergy destruction for designing more environmentally friendly and smaller thermal systems.

Ekonomiden siyasete, tarımsal üretim tekniklerinden endüstriyel teknolojiye, sosyal düşünceden bilimsel düşünceye kadar birçok alanda büyük değişimlerin yaşandığı ve bir o kadarına da gebe kalınan bir dönemde yani 17. ve 18. yüzyıllarda Avrupa kıtası, kullanışlı veya kullanışsız, bilimsel veya bilimsel olmayan muazzam bir bilgi üretimine sahne olmuştur. Kilise kurumunun, bilginin üretilmesinden bilginin onaylanmasına kadar birçok alandaki tekelinin ya da otoritesinin zayıflamaya başladığı bu dönemde gerek bireysel gerekse kurumlar bünyesinde üretilen farklı türlerdeki bilgilerin değer kazanabilmesi ve uygulamaya koyulup onaylanabilmesi için ilgili kitlelere doğru ve hızlı bir şekilde sunulması yani bilginin üretilmesinden bilginin pazarlanmasına ve onaylanmasına kadar geçirdiği her aşama oldukça önemlidir. Bu çalışmada günümüzde özellikle gemi inşaatı ve denizcilik alanlarında otorite olmuş bir kurum olan İngiliz Loydu’nun (Lloyd’s Register) bir kafeden klaslama kuruluşuna dönüşümü bilgi ile olan ilişkisi üzerinden ele alınmış ve önemli hususlar paylaşılmıştır.

The use of efficient refrigerator/freezers helps considerably to reduce the amount of the emitted greenhouse gas. A two-circuit refrigerator-freezer cycle (RF) reveals a higher energy saving potential than a conventional cycle with a single loop of serial evaporators, owing to pressure drop in each evaporator during refrigeration operation and low compression ratio. Therefore, several industrial applications and fish storage systems have been utilized by using multipurpose refrigeration cycle. That is why a theoretical performance analysis based on the exergetic performance coefficient, coefficient of performance (COP), exergy efficiency and exergy destruction ratio criteria, has been carried out for a multipurpose refrigeration system by using different refrigerants in serial and parallel operation conditions. The exergetic performance coefficient criterion is defined as the ratio of exergy output to the total exergy destruction rate (or loss rate of availability). According to the results of the study, the refrigerant R32 shows the best performance in terms of exergetic performance coefficient, COP, exergy efficiency, and exergy destruction ratio from among the other refrigerants (R1234yf, R1234ze, R404A, R407C, R410A, R143A and R502). The effects of the condenser, freezer-evaporator and refrigerator-evaporator temperatures on the exergetic performance coefficient, COP, exergy efficiency and exergy destruction ratios have been fully analyzed for the refrigerant R32.

The supercritical CO2 (s-CO2) power cycle has been taking into account as one of the most effective alternatives for energy conversion because of its higher efficiency and smaller compressor and turbine sizes for many years. A plenty number of parametric and experimental studies for the different type of s-CO2 cycles have been accomplished in the literature. In this paper, a performance analysis based on a power density criterion has been carried out for a simple s-CO2 Brayton power cycle. The parameters which are obtained from analyzes were compared with those of a power performance criterion that is shown that design parameters at maximum power density give a chance to smaller cycle components and more efficient s-CO2 Brayton power cycle. Due to loses in the cycle, the power and thermal efficiency will reduce by a certain amount, however, the maximum power density conditions will still give a better performance than at the maximum power output conditions. The analysis exemplified in this paper may provide a reference for the finding of optimal operating conditions and the design parameters for real s-CO2 Brayton power cycles.

A theoretical performance analysis based on the exergetic performance coefficient (EPC) criterion has been carried out for a cascade refrigeration system for different refrigerant couples. The EPC criterion is defined as the ratio of exergy output to the total exergy destruction rate (or loss rate of availability). According to the results of the study, the refrigerant couples R23-R717 show the best performance in terms of EPC and coefficient of performance from among the other refrigerant couples (R23-R290, R23-R404A, R23-R507A and R23-R717). In the analysis, R23 was used for the lower temperature cycle and the other refrigerants are used for the higher temperature cycle. The effects of the temperature difference in the cascade condenser and the evaporator and condenser temperature on the EPC, coefficient of performance and exergy destructions have been thoroughly investigated for the refrigerant couple R23-R717.

Refrigeration systems are one of the most common and the oldest thermodynamic system that almost equal to human history. Exergetic and economic effects of subcooling & superheating on vapor compression refrigeration system are analyzed and examined in terms of different refrigerants, working conditions (temperature and pressures), condenser and evaporator effectiveness and temperatures and isentropic efficiency of compressor behalf of coefficient of performance, exergetic efficiency, exergetic performance coefficient and ecological coefficient of performance. The results show that variations of the condenser and evaporator temperatures, pressure losses in heat exchangers and isentropic efficiency of compressor are highly related to performance and economic parameters such as heat exchange areas and power consumption for subcooling & superheating refrigeration system (SSRS).

Within the scope of developing a new method to optimise the use of economic and ecological thermal systems, a comparative study was conducted by means of different compression ratios and temperature ratios according to mean cycle pressure (MCP) criterion for the simple Joule-Brayton cycle. The results, when compared with the other performance criteria's results in the literature, show that the thermal efficiency and network at maximum MCP condition are approximately 1–2% more and 12–13% times less than other criteria, respectively. Moreover, the thermal efficiency that corresponds to the maximum MCP condition is nearly 15% more than the maximum network condition, and the network at the maximum MCP and maximum thermal efficiency conditions are equal. Thus, MCP criterion will give more useful and realistic information in terms of designing more efficient and smaller thermal systems.

Power consumption highly increases which is related with the growing of the industrial plants and daily using. Increasing power demand can be supplied with building up more efficient plants or optimized old power plants. One of the most important items of a power plant is steam turbine which is designed according to defined parameters (inlet pressure and temperature, flow rates, outlet pressure and power) which also effect the dimensions and performance of the turbine. Turbine loses and irreversibilities are minimum and so efficiencies and power generation are maximum at design conditions. However, power plants always have to operate at off-design or part-load conditions because of the changing of power demands and drop outs of the turbines and other items of the plants. In this study, it is aimed to analyses the isentropic efficiency of a high pressure steam turbine and thermal efficiency of power plant at different load conditions. Analyses showed that both steam turbines and power plant performance were reduced when the power plant operates at partial load conditions.