Yazar "Guruf, Gursah" seçeneğine göre listele

Listeleniyor 1 - 4 / 4
  • Küçük Resim Yok
    Öğe
    ANALYSIS OF LOCAL THERMAL EQUILIBRIUM ASSUMPTION IN TRANSIENT FORCED CONVECTION IN A GRAPHITE FOAM CHANNEL
    (Yildiz Technical Univ, 2020) Guruf, Gursah; Solmaz, Ismail; Bayer, Ozgur
    In this study, the validity of Local Thermal Equilibrium (LTE) assumption in the transient forced convection of a rectangular channel filled with a block of graphite foam is examined numerically. The governing macroscopic energy conservation equations for solid and gas phases are derived by taking the average of the microscopic one over the averaging volume. Initially, LTE is in existence between the phases and then, the fluid temperature at the channel inlet is suddenly raised. Besides, an appropriate insulation is provided for the wall of the channel. Hence, a transient one-dimensional Local Thermal Non-Equilibrium (LTNE) model is considered in the numerical investigation. Thermo-physical properties of the solid and fluid phases are presumed to be constant. The graphite foam porosity is spatially uniform and constant. The impact of two dimensionless variables such as fluid to solid Nusselt number (Nu(fs)) and Reynolds number (Re) on the LTE assumption is extensively investigated. . It was found that the dimensionless time required to attain LTE between the phases (tau(LTE)) increases with the increasing value of Reynolds number. However, the real-time (sigma(LTE)) corresponding to tau(LTE) was found to be nearly 4 sec over the range of Re numbers studied. Additionally, an increase in the Nu(fs), resulted in a decrease in TLTE for a constant value of Re number and sigma(LTE) varied from 1.5 to 5 sec. As a result, the obtained findings showed that it is reasonable to assume the LTE between the phases under the investigated conditions.
  • Küçük Resim Yok
    Öğe
    Exergy, exergoeconomic, enviroeconomic, and sustainability index analysis of diesel engine fueled by binary combinations of diesel/waste animal fat biodiesel
    (Springer, 2023) Simsek, Suleyman; Guruf, Gursah; Uslu, Samet; Simsek, Hatice
    In this study, the exergy, exergoeconomic, enviroeconomic, and sustainability index analyzes of blends of biodiesel and diesel obtained from waste animal fats were examined. Within the scope of this study, the engine used in the experimental study has the features of a 3000-rpm fixed-speed four-stroke, single-cylinder, and air-cooled compression ignition engine. In addition, seven different fuels (D100 (0% Biodiesel + 100% Diesel), D90B10 (90% Diesel + 10% Animal Biodiesel), D80B20 (80% Diesel + 20% Animal Biodiesel), D70B30 (70% Diesel + 30% Animal Biodiesel), D50B50 (50% Diesel + 50% Animal Biodiesel), D25B75 (25% Diesel + 75% Animal Biodiesel), B100 (0% Diesel + 100% Animal Biodiesel)) were used in this study. The experiments were performed by loading the engine at 500 W intervals between 500 and 3000 W. As a result, the highest exergy efficiency was 24.86%, and obtained in D90B10 fuel at a 3000 W engine load. The lowest relative cost difference was 2.04, and obtained in D90B10 fuel at 3000 W engine load. The maximum sustainability index value was 1.98, and obtained in D90B10 fuel at a 3000 W engine load. In terms of enviroeconomics, while the cost of annual CO2 emission of all fuels is low at low engine loads, it increases as engine load increases. It is seen that D90B10 fuel is closest to D100 fuel at low engine loads. Their values are respectively 42.55 USD year(-1) and 43.22 USD year(-1).
  • Küçük Resim Yok
    Öğe
    Experimental based numerical approach for determination of volumetric heat transfer coefficients of modified graphite foams
    (Pergamon-Elsevier Science Ltd, 2020) Guruf, Gursah; Solmus, Ismail; Bilen, Kadir; Bayer, Ozgur
    Graphite-based porous materials are emerging as attractive alternatives to metals for use as heat dissipation elements in thermal management applications. While having several desirable features such as high thermal conductivity and low density, graphite foam heat sinks also tend to have low permeability that can limit transport of working fluid within the component and result in inefficient heat transfer. In order to improve their heat dissipation performance, graphite foams can be modified by channels drilled in various arrangements. However, the heat transfer characteristics of such modified graphite foams are not well characterized. In order to address this problem, we report novel empirical correlations for graphite foams modified in a specific configuration where circular channels with 2 mm diameter are drilled in graphite foam along the flow direction in a staggered arrangement. Then, volumetric heat transfer coefficients between the modified graphite foam and a stream of air are obtained by using transient single-blow technique (TSBT). The transient one-dimensional local thermal nonequilibrium (LTNE) model is employed for determination of the volumetric heat transfer coefficient from experimentally obtained data. Nine different modified graphite foam samples of various L/H ratios are studied in experiments and an empirical correlation of the form Nu(v) = CRea for each sample is derived. Empirical correlations for three different sample lengths (L = 27 mm, 52 mm, 76 mm) at a fixed height are also developed in the form of Nu(v) = CRea(L/H)(b). The novel empirical correlations in question are valid for the Reynolds (Re) number varying from approximately 1000 to 10000. Results show that Nuv generally increases with the increasing value of Re and L at a fixed value of H and the uncertainties associated with Re and Nu(v) are evaluated to be less than 1.3% and 3.6%, respectively. Consequently, we anticipate that the proposed correlations will be useful in reliable design of a new generation of electronic devices.
  • Küçük Resim Yok
    Öğe
    An experimental study on a novel defrosting method for cold room
    (Pergamon-Elsevier Science Ltd, 2021) Abdulla, Mahade Omran Ali; Deniz, Emrah; Karagoz, Mustafa; Guruf, Gursah
    Refrigeration systems can be blocked by frost accumulating on the evaporator, when they operate at a temperature below the dew point of air and the freezing point of water. Therefore, a defrost process that consumes extra energy needs to be started from time to time. Conventional defrosting methods require energy and time to complete, which reduce the refrigeration efficiency and cause a temperature fluctuation in the storage room during the defrosting process. In this study, a new type of defrosting is used in order to reduce the energy needed for defrosting, improve refrigeration efficiency and decrease temperature fluctuations, which utilize the heat from the liquid refrigerant to defrost the evaporator using two evaporators and a four-way valve. When one of the evaporators cools the room, the other is used for sub-cooling the refrigerant before entering the cooler evaporator. The sub-cooling process provides defrosting of the second evaporator. When the cooler evaporator requires defrosting, the four-way valve reverses the cycle, and the second evaporator becomes cooler. The first evaporator then becomes the sub-cooler to be defrosted. A cold room with this concept was built and tested experimentally together with a conventional cooling system. Energy, exergy, economic and environmental (4E) analyses of both systems were made and the results were compared. The results show that the new method can perform the defrosting process using the energy dissipated from the sub-cooling refrigerant without using any external power source and improve refrigeration efficiency by 12%. Moreover, this new system does not interrupt the cooling process during defrosting process as the conventional systems do. Temperature fluctuations also decrease by about 60% following this method.