The development of mathematical modeling for nanofluid as a porous media in heat transfer technology

Nanofluids as combinations of nanoparticles and base fluids are introduced to be used as working mediums in heat transfer and thermal fluid technologies. The solid parts or nanoparticles have high thermal conductivity property and can enhance overall heat transfer properties when they are mixed with the base fluids which have low thermal conductivity. In the nanofluid-flow field, the nanoparticles could be assumed to be distributed uniformly throughout the base fluid, this flow could also be presumed as the nanofluid flow through the uniform porous media (the solid parts) with nanofluid properties. The current work presented the developed mathematical model of the nanofluid flow; Al2O3 nanoparticles and water flow, as the steady fluid flow with the nanofluid properties through the porous medium with the Al2O3 properties. The simulated nanofluid flow was under fully developed laminar flow conditions through a rectangular pipe. The governing equations written in terms of the 3-D dimensionless variables were solved through the developed in-house program by using the finite volume method with the SIMPLE algorithm. Effects of the porous media characteristics; porosity, thermal conductivity and permeability, on accuracies of simulated results were investigated when the porosity value of 0.98 was considered to be equal to the nanofluid volume fraction of 0.02; as a synopsis relationship between the porosity and the volume fraction. The mixing thermal conductivity model; Yu and Choi model coupled with Maxwell model, was applied to be the thermal conductivity model of the porous media part. From the comparisons between the simulated and experimental results, the assumed relationships between the porosity and the volume fraction could be proved to be gratified and implied that the nanoparticles were distributed uniformly throughout the fluid and the nanofluid flow could be taken as the fluid with the nanofluid properties flowing through the porous media as well. The current developed model using the mixing thermal conductivity model with the porous media assumption could improve the model performance and supported its excellent potential in the nanofluid simulation as the fluid flow through the porous media.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

The study of the drying application distances from the condensing unit effecting on the air conditioning efficiency and drying rate

This work was focused on the study of the drying application distances, or the heated air-obstacle distance, from the condensing unit of the 24000 BTU/hr air conditioning systems (A/C) which effected on the A/C efficiency and the drying rate the application. The drying application utilized exhausted heat from the condensing unit and performed as the fabric dryer. The application or the experimental setup was investigated for the A/C efficiency and the drying rate in 4 different weather conditions; the normal and rainy daytime and nighttime. The fan, which was driven by electric from battery charged by a solar cell panel, was installed on the application to enhance heat convection inside the application. The application; which can be considered as an obstacle of exhausted air from the condensing unit, was placed behind the condensing unit at two different distances; 0.5 and 0.7 m, respectively, to investigate their effects on the A/C power consumption of the obstacle distances which directed the heated air into different heated-air-flow patterns. The velocities of inlet and outlet air through condensing unit, humidity ratios and temperatures of ambient air, sunlight intensity, fabric weights before and after drying and A/C power consumptions were measured. From the results, when the application was placed at 0.5 m behind the condensing unit, the A/C efficiency was better than it was at 0.7 m in all four weather conditions. Since the closer distance between the application and the condensing unit could enhance more convective and evaporative heat transfer of the heated-air flow behind the condensing unit, we found that the evaporative cooling and convective heat transfer played their important roles in the drying process of the application and in the heat rejection of the A/C system. We also confirmed that the A/C system cleanness plays an important role on the power consumption indicators.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Development in Rubber Preparation for Endoscopic Training Simulator

Endoscopy is one of the most important procedures in diagnosis and treatment of gastrointestinal tract problems. While endoscopic procedure has tremendous benefits, physicians require considerable practice and time to develop competency. Current endoscopic training process involves cognitive learning and hands-on training under the supervision of an expert gastroenterologist. Previous studies have shown that fellow involvement prolongs procedural time and incurs additional expenses to the institution. Moreover, the patient also experiences more discomfort and injury risk. Introduction of training simulator into the training process could reduce the involvement of the patients and thus reduce the risk. Porcine model is commonly used for training in endoscopy due to the similar tactile response to a human gastrointestinal tract. However, information on elastic behavior of pig or human gastrointestinal tract for the engineering purposes was limited. In this study, the modulus of elasticity and ultimate tensile stress data of the pig stomach and intestines, small and large intestines, were measured and compared with multiple rubber stomach and intestines models. Based on the experimental results and experienced gastroenterologists feedback, the proposed dipped rubber composition can provide a satisfactory tactile feedback and could be used to simulate a human gastrointestinal tract for an endoscopic simulation training model

Numerical Study of Mixing Thermal Conductivity Models for Nanofluid Heat Transfer Enhancement

Researchers have paid attention to nanofluid applications, since nanofluids have revealed their potentials as working fluids in many thermal systems. Numerical studies of convective heat transfer in nanofluids can be based on considering them as single- and two-phase fluids. This work is focused on improving the single-phase nanofluid model performance, since the employment of this model requires less calculation time and it is less complicated due to utilizing the mixing thermal conductivity model, which combines static and dynamic parts used in the simulation domain alternately. The in-house numerical program has been developed to analyze the effects of the grid nodes, effective viscosity model, boundary-layer thickness, and of the mixing thermal conductivity model on the nanofluid heat transfer enhancement. CuO–water, Al2O3–water, and Cu–water nanofluids are chosen, and their laminar fully developed flows through a rectangular channel are considered. The influence of the effective viscosity model on the nanofluid heat transfer enhancement is estimated through the average differences between the numerical and experimental results for the nanofluids mentioned. The nanofluid heat transfer enhancement results show that the mixing thermal conductivity model consisting of the Maxwell model as the static part and the Yu and Choi model as the dynamic part, being applied to all three nanofluids, brings the numerical results closer to the experimental ones. The average differences between those results for CuO–water, Al2O3–water, and CuO–water nanofluid flows are 3.25, 2.74, and 3.02%, respectively. The mixing thermal conductivity model has been proved to increase the accuracy of the single-phase nanofluid simulation and to reveal its potentials in the single-phase nanofluid numerical studies. © 2018, Springer Science+Business Media, LLC, part of Springer Nature