The applications and usage of surfactants in the field of nanofluids heat transfer and its stability were performed the present literature review. The usage of surfactants has been employed for the following areas of nanofluids study: nanofluid heat transfer, nanofluid agglomeration and nanofluid enhancement stability. Generally, a few interesting has been achieved to study the effects of using the surfactants on the nanofluids properties such as pH, thermal conductivity, specific heat, electrical conductivity, viscosity and stability mechanism of nanofluid. The using nanofluid in real applications is taken into consideration by two key issues emerge: erosion and settlement but there aare possible difficulties related to these issues that need to be studied and solved prior to the using of nanofluid in commercial applications. In addition, this paper summarizes the theoretical and experimental studies on the effects of applied various types of surfactants in nanofluids. This work can serve as a ready reference for application of surfactants in nanofluids.
The effects caused by convection and radiation heat transfer on the distribution of temperature, airflow and heat transfer in a greenhouse containing a heated solid block are studied numerically. Differential governing equations of the system are analyzed by utilized the finite volume method and the coupling of pressure-velocity is handled by the algorithm of SIMPLER. The systems algebraic equations are resolved by the conjugated of the gradient method. The greenhouse is supposed of an aspect ratio of A = 1.5, and the numerical results are presented in terms of streamlines, isotherms and Nusselt number for the range of Rayleigh numbers between 103 and 106. For the case of inlet airflow, the mixed convection of the airflow of in a greenhouse formed by two walls lateral and a roof with two symmetrical slopes were studied. The heating conditions of the walls for the greenhouse was taken as (Tc for the floor and Tf for the roof, with Tc> Tf), with openings of the cold air inlet is left-walled and the outlet is so the symmetry of right walls. The Prandtl number is set at 0.702 (for the case of air). Several situations have been considered for Rayleigh number and solid block height at fixed Reynolds number at Re = 100. The results showed that the Rayleigh number has important effect on the performance of the flow and thermal structure. Also, the isotherms and current lines is effected by varying the solid block height. In addition the local and medium Nusselt number along the hot wall increased with increasing the Rayleigh number and solid block height.
In this study, the natural and forced convection heat transfer in an enclosure with vertical heated block and baffles are experimentally and numerically investigated. The enclosure walls are kept as adiabatic, and the heating block contains extended baffles and receives heat flux. The effect of heat flux, Reynolds number and baffle configuration on the heat transfer characteristics and flow behaviour inside the enclosure is examined. The configuration parameter for natural and forced convection involves three heating block models, namely, block without baffle (plain), block with baffles and block with partially cut baffles. The widths of baffles are 2.5, 5 and 10 cm for the block with baffle case, and the width of partially cut baffle is 5 cm. The heat flux (q) ranges from 240 w/m 2 to 1425 w/m 2 for all the models. The Reynolds number (Re) ranges from 5650 to 15950 for forced convection heat transfer. In the numerical part, a finite volume method (via Ansys Fluent) is used to solve the governing equations. Result shows that the increase in baffle width has no remarkable effect on the heat transfer, and the partially cut baffles provide an enhancement of approximately 30% compared with the plain heating block. The baffle cases have an evident effect in reducing the block surface temperature by approximately 11% compared with the plain case at Re = 0 and q = 240 w/m 2 . Empirical correlations for the block with baffles are obtained for each heat flux to predict the average Nusselt number.
In this study the mixed convection heat transfer process in a square cross section cavity with a bottom groove heated from three side walls (left, right, and bottom) with vertically unheated baffle is investigated numerically and experimentally. In the numerical part the in-house CFD commercial code of ANSYS-FLUENT-V.16.0 based on finite volume method has been used to solve the 2D governing equations. The results are represented in terms of wall temperature profiles and Nusselt numbers of the heated wall. For the experimental work, a test rig were built to determine the effect of heater position, baffle height ratio (h/H), the baffle angle for the range of 300
Numerical modeling analysis of mixed convection heat transfer for air flow in a cavity with bottom local heat source and top inlet and outlet sections is studied. Also, the cavity equipped by vertical triangular obstacle on the top wall in order to enhancement the convection inside the cavity are researched. System of dimensionless stationary Navier-Stokes equations is solved numerically by discretizing the compositional domain into small grids. Mixed convection regimes are the viscous incompressible Newtonian fluid with Reynolds number range (800-1400) and the Grashof number ranged (105-108) and at fixed Prandtl number at (7.1). The pressure, temperature and velocity distributions characterizing the basic laws of viewed process. The results showed that the main circulating currents in different zones of the cavity is due to the effect of number of blocks and the presence vertical triangular obstacle on the top boundary of the cavity. The formation of thermal conditions in the region under study and the effect of low temperatures above the heated bottom wall on the circulation fluid flow in a cavity. Distribution pattern established velocity and temperature profile in centered sections depending on the height of vertical triangular obstacle. Also, the results showed that the Nusselt number increased by about 26% when increasing the height ratio of triangular obstacle to (h/H=0.5) with three blocks.
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