EFFECT OF RED MUD AS A NANOFLUID ON COOLING PERFORMANCE

Fluids such as water, oil, glycerin and ethylene glycol are conventional heat transfer fluids that are used in heat exchangers. Improving heat transfer and effectiveness of heat exchangers by means of fluids is one of the principle topics. A type of improvement works is adding solid materials that have high thermal capacity and conductivity into the fluid. Al2O3, CuO, TiO2, SiC, TiC, Ag, Au2, Cu2 and Fe are the most common materials as solid particles that are used for enhancing heat transfer of fluids. Early on, macro scaled additives were tried; however desired outcomes couldn’t be obtained due to fouling, blockage and sedimentation. Recently, studies on ability to be enhanced and improved in terms of heat transfer and hence heat exchangers with high effectiveness by the addition of nano-particles to fluid have become intensive. It is known that precious elements such as Al2O3, SiO2, Fe2O3, TiO2, Na2O, CaO, P2O5 are contained in the body of red mud that is a disposal material coming from the process of producing aluminum from bauxite. Thermal capacity and thermal conductivity of these matters are very high. Effects of nano scale red mud added into heat transfer fluid on the cooling performance are investigated in this work

Numerical assessment of heat sink for pressure sensor connections

Pressure sensors, converting pressure force to electrical outputs such as 4-20 mA or 0-10 V, are used in a vast variety of areas while being facing numerous challenging thermal conditions. A common way is to design a heat sink for establishing natural convection cooling to protect the sensor. This work assesses a heat sink design and conveys its performance as a heat sink for an application interval. Special orientation as well as design geometry is introduced. Computational fluid dynamics were utilized for evaluation and assessment. A core region of heat transfer was identified. Natural convection wake boundaries were detected. It is concluded that the design can successfully protect the pressure sensor at the pressure tap. Future projections and aspects are also described in the paper

Steady and transient flow structure in a rotameter with a ball float

Dimensions and material specifications of a commercial rotameter were used for investigating steady and transient flow structure in a rotameter with a ball float. Since drag coefficient of sphere versus Reynolds number is well known and the range of the commercial rotameter is given, the investigation relies on strong validation data. An axially symmetric geometric model is used for steady analysis of the system as the initial step of the investigation. Assessing the proper mesh structure and turbulence model is aimed for this step. Then full three dimensional solid model is put into transient analysis with RANS and LES models. Vortex shedding frequency, Strouhal number and drag coefficient values are evaluated. Vortex induced vibrations are assessed according to transient results. The work is a preliminary study for future investigation on rotameter floats. The framework of future studies is also presented

Heating and cooling vehicle seat via air conditioner coils

A real vehicle seat was modified in order to locate evaporator coils extended from a vehicle air conditioner system just beneath the back and cushion surfaces. The seat back and cushion surface temperatures were measured by several thermocouples. Air conditioner system was operated in heat pump and cooling modes for different compressor speeds. After steady operation of the air conditioner was attained, a live manikin sat to the seat and remained in sitting position for five minutes. The temperatures were recorded during the existence of the manikin and they were recorded for an additional five minutes after the manikin left the seat. The coils embedded under the seat surfaces were made of flexible hoses for the sake of usage due to the shape changing seat surfaces under the load of the manikin weight. Coils were in parallel configuration by the help of a distributer and collector. The temperatures of the seat surfaces were evaluated in respect of the thermal comfort and feasibility of the application. Air conditioner system was also monitored in respect of the COP and energy consumption values. At the instance of sitting, the transient response of the system is very significant due to the weight of the live manikin. However it settles quickly. Cooling was observed to be more realizable while heating seat surfaces had problems due to flow blockage. There were no significant discomfort issues due to the seat surface temperatures and the existence of the coils. The surface temperatures of the seat back exhibited differences from the seat cushion although the formations were same. The orientation of the coils and the weight of the passenger were concluded to be the reason for that. COP was found to be changing between 3 and 3.56 for cooling mode while the highest amount was found for 600 rev/min compressor speed in cooling operation. Heat pump operation had relatively higher COP values ranging between 3.31-3.64. 700 rev/min compressor speed gave the 3.64 COP value for heat pump operation. The difference between COP values of the working modes was concluded to be due to the seat coils and their effect on the additional pumping work. The potential of the application and possible field of studies were evaluated according to the conducted tests and the survey about the topic

Conjugate heat transfer for turbulent flow in a thick walled plain pipe

Laminar and turbulent flow have their own characteristics in respect of heat transfer in pipes. While conjugate heat transfer is a major concern for a thick walled pipe with laminar flow inside it, there are limited studies about a turbulent flow in a thick walled plain pipe considering the conjugate heat transfer. In order to conduct such a work by means of in-house developed code, it was desired to make a preliminary investigation with commercially available CFD codes. ANSYS CFD was selected as the tool since it has a positive reputation in the literature for reliability. Defined heat transfer problem was solved with SIMPLE and Coupled Schemes for pressure velocity coupling and results are presented accordingly

Conjugate heat transfer for turbulent flow in a thick walled plain pipe

Laminar and turbulent flow have their own characteristics in respect of heat transfer in pipes. While conjugate heat transfer is a major concern for a thick walled pipe with laminar flow inside it, there are limited studies about a turbulent flow in a thick walled plain pipe considering the conjugate heat transfer. In order to conduct such a work by means of in-house developed code, it was desired to make a preliminary investigation with commercially available CFD codes. ANSYS CFD was selected as the tool since it has a positive reputation in the literature for reliability. Defined heat transfer problem was solved with SIMPLE and Coupled Schemes for pressure velocity coupling and results are presented accordingly

Comparison of turbulence models and CFD solution options for a plain pipe

Present paper is partly a declaration of state of a currently ongoing PhD work about turbulent flow in a thick walled pipe in order to analyze conjugate heat transfer. An ongoing effort on CFD investigation of this problem using cylindrical coordinates and dimensionless governing equations is identified alongside a literature review. The mentioned PhD work will be conducted using an in-house developed code. However it needs preliminary evaluation by means of commercial codes available in the field. Accordingly ANSYS CFD was utilized in order to evaluate mesh structure needs and asses the turbulence models and solution options in terms of computational power versus difference signification. Present work contains a literature survey, an arrangement of governing equations of the PhD work, CFD essentials of the preliminary analysis and findings about the mesh structure and solution options. Mesh element number was changed between 5,000 and 320,000. k-ϵ, k-ω, Spalart-Allmaras and Viscous-Laminar models were compared. Reynolds number was changed between 1,000 and 50,000. As it may be expected due to the literature, k-ϵ yields more favorable results near the pipe axis and k-ωyields more convenient results near the wall. However k-ϵ is found sufficient to give turbulent structures for a conjugate heat transfer problem in a thick walled plain pipe

Comparison of turbulence models and CFD solution options for a plain pipe

Present paper is partly a declaration of state of a currently ongoing PhD work about turbulent flow in a thick walled pipe in order to analyze conjugate heat transfer. An ongoing effort on CFD investigation of this problem using cylindrical coordinates and dimensionless governing equations is identified alongside a literature review. The mentioned PhD work will be conducted using an in-house developed code. However it needs preliminary evaluation by means of commercial codes available in the field. Accordingly ANSYS CFD was utilized in order to evaluate mesh structure needs and asses the turbulence models and solution options in terms of computational power versus difference signification. Present work contains a literature survey, an arrangement of governing equations of the PhD work, CFD essentials of the preliminary analysis and findings about the mesh structure and solution options. Mesh element number was changed between 5,000 and 320,000. k-ϵ, k-ω, Spalart-Allmaras and Viscous-Laminar models were compared. Reynolds number was changed between 1,000 and 50,000. As it may be expected due to the literature, k-ϵ yields more favorable results near the pipe axis and k-ωyields more convenient results near the wall. However k-ϵ is found sufficient to give turbulent structures for a conjugate heat transfer problem in a thick walled plain pipe

Experimental and Numerical Investigation of Flow Structures around Cylindrical Bluff Bodies

The understanding and quantitative prediction of velocity and pressure fluctuations in turbulent flows around such bluff bodies have been evolving over the years. The main aim of the present work is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed horizontally perpendicular to the uniform flow. The experimental studies were performed by Particle Image Velocimetry (PIV) method in an open water channel at Reynolds numbers 5000 and 10000 defined according to the characteristic lengths of the cylinders in the facilities of Selcuk University of Advanced Technology Research and Application Center in Turkey. The experimental results are compared to the numerical results obtained by means of transient simulation with LES turbulence model of ANSYS-Fluent Software. It is shown that the numerical and experimental results have a good agreement in respect of the instantaneous and time-averaged flow field patterns of vorticity, velocity component streamwise direction and streamline topology. In addition, drag coefficient of the geometries were also numerically calculated. For all geometries the wake length in x and y directions and size of the foci of the streamlines are decreasing by increasing Reynolds numbers in time-averaged results. The time-averaged flow patterns of both experimental and numerical results have considerable symmetry with respect to the centerline of each cylinder. Contours of the time-averaged stream wise velocity for Re=10000 demonstrate that the stagnation point around the symmetry plane moves further upstream for all cylinders in accordance with Re=5000. The maximum drag coefficient value was yielded for the square cross-section cylinder as 1.78 due to the sharp-edged geometry

Experimental and Numerical Investigation of Flow Structures around Cylindrical Bluff Bodies

The understanding and quantitative prediction of velocity and pressure fluctuations in turbulent flows around such bluff bodies have been evolving over the years. The main aim of the present work is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed horizontally perpendicular to the uniform flow. The experimental studies were performed by Particle Image Velocimetry (PIV) method in an open water channel at Reynolds numbers 5000 and 10000 defined according to the characteristic lengths of the cylinders in the facilities of Selcuk University of Advanced Technology Research and Application Center in Turkey. The experimental results are compared to the numerical results obtained by means of transient simulation with LES turbulence model of ANSYS-Fluent Software. It is shown that the numerical and experimental results have a good agreement in respect of the instantaneous and time-averaged flow field patterns of vorticity, velocity component streamwise direction and streamline topology. In addition, drag coefficient of the geometries were also numerically calculated. For all geometries the wake length in x and y directions and size of the foci of the streamlines are decreasing by increasing Reynolds numbers in time-averaged results. The time-averaged flow patterns of both experimental and numerical results have considerable symmetry with respect to the centerline of each cylinder. Contours of the time-averaged stream wise velocity for Re=10000 demonstrate that the stagnation point around the symmetry plane moves further upstream for all cylinders in accordance with Re=5000. The maximum drag coefficient value was yielded for the square cross-section cylinder as 1.78 due to the sharp-edged geometry