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

Comparative design study of a diesel exhaust gas heat exchanger for truck applications with conventional and state of the art heat transfer enhancements

The exhaust gas of heavy duty diesel engines can provide an important heat source that may be used in a number of ways to provide additional power and improve overall engine efficiency. The sizing of a heat exchanger that can manage the heat load and still be of reasonable size and weight without excessive pressure drop is of significant importance especially for truck applications. This is the subject of the present work. To approach the problem, a total of five different configurations are investigated and a comparison of conventional and state of the art heat transfer enhancement technologies is included. Two groups of configurations are examined: (a) a classical shell and tube heat exchanger using staggered cross-flow tube bundles with smooth circular tubes, finned tubes and tubes with dimpled surfaces and (b) a cross-flow plate heat exchanger, initially with finned surfaces on the exhaust gas side and then with 10 ppi and 40 ppi metal foam material substituting for the fins. Calculations were performed, using established heat exchanger design methodologies and recently published data from the literature to size the aforementioned configurations. The solutions provided reduce the overall heat exchanger size, with the plate and fin type consisting of plain fins presenting the minimum pressure drop (up to 98% reduction compared to the other configurations), and the 40 ppi metal foam being the most compact in terms of size and weight. Durability of the solutions is another issue which will be examined in a future investigation. However, coupling of the exhaust heat exchanger after a particulate trap appears to be the most promising solution to avoid clogging from soot accumulation

Sparsity-promoting dynamic mode decomposition

International audienceDynamic mode decomposition (DMD) represents an effective means for capturing the essential features of numerically or experimentally generated flow fields. In order to achieve a desirable tradeoff between the quality of approximation and the number of modes that are used to approximate the given fields, we develop a sparsity-promoting variant of the standard DMD algorithm. Sparsity is induced by regularizing the least-squares deviation between the matrix of snapshots and the linear combination of DMD modes with an additional term that penalizes the l(1)-norm of the vector of DMD amplitudes. The globally optimal solution of the resulting regularized convex optimization problem is computed using the alternating direction method of multipliers, an algorithm well-suited for large problems. Several examples of flow fields resulting from numerical simulations and physical experiments are used to illustrate the effectiveness of the developed method. (C) 2014 AIP Publishing LLC

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

A review on boiling heat transfer enhancement with nanofluids

There has been increasing interest of late in nanofluid boiling and its use in heat transfer enhancement. This article covers recent advances in the last decade by researchers in both pool boiling and convective boiling applications, with nanofluids as the working fluid. The available data in the literature is reviewed in terms of enhancements, and degradations in the nucleate boiling heat transfer and critical heat flux. Conflicting data have been presented in the literature on the effect that nanofluids have on the boiling heat-transfer coefficient; however, almost all researchers have noted an enhancement in the critical heat flux during nanofluid boiling. Several researchers have observed nanoparticle deposition at the heater surface, which they have related back to the critical heat flux enhancement