Forced Convection Of Water Research Articles

Dynamics of ternary-hybrid nanofluids due to dual stretching on wedge surfaces when volume of nanoparticles is small and large: forced convection of water at different temperatures

Management of heat energy and control of temperature distribution are major problems in the industry. With emphasis on the heat and mass transfer when the volume of nanoparticles is small and large, nothing is known on forced convection flow of water at different temperatures conveying platelet aluminum nanoparticles, cylindrical magnesium oxide nanoparticles, and titanium dioxide nanoparticles due to dual stretching on wedge surfaces. The mathematical model for the problem mentioned above is presented in this report, transformed using similarity variables, and solved numerically using the approach of shooting technique together with fourth order Runge-Kutta integration scheme. The analysis of results, justification, and discussion of results was established after the positive outcome of the reliability and validity. It is worth concluding that as time goes on in all the four cases of water at different temperature as in the case of four ternary-hybrid nanofluid flows, the local skin friction coefficients increases at the rate of 0.07 when the volume of nanoparticles is small and at a most minimum rate of 0.008 when the volume of nanoparticles is large. At 80°C temperature of water-based ternary hybrid nanofluid, as time grows large, the heat transfer decreases at the optimal rate of −0.354681119 when the volume of nanoparticles is small but the same heat transfer increases at the minima rate of 0.159722534 when the volume of nanoparticles is large.

Flow pattern transition during condensation of R134a and R1234ze(E) in microchannel arrays

Two-phase flow pattern transition during the condensation of R134a and R1234ze(E) was experimentally investigated in a microchannel array made of borosilicate glass cooled symmetrically on the top and bottom by forced convection of water. The microchannel array consisted of 50 channels with the aspect ratio of 2.46, the hydraulic diameter of 301.6μm and the length of 50mm. Saturation temperatures are 20–25°C with mass fluxes varying from 6 to 50kg/m2/s. Observed patterns are annular flow, steady injection flow, quasi-symmetric wave flow and slug/bubbly flow. In addition, three flow pattern transition modes including steady injection, wave-coalescence injection, and liquid bridging were observed and mapped in terms of liquid Webb number versus condensation number. The steady injection transition was more studied in detail by measuring the bubble length variation and the moving velocity of bubbles and slugs with different mass fluxes of R134a and R1234ze(E). The transition mechanism of injection flow was identified by analyzing the force balance based on the experimental results. The flow pattern transition locations and frequencies were measured and compared with the prediction correlations in the previous investigations.

Thermal and hydraulic characteristics of discretely rough tubes at transient flow regimes

Results are presented from an experimental study of heat transfer and hydraulic friction in tubes with discrete roughness in the form of annular protrusions and systems of spherical protrusions in forced convection of water. The thermohydraulic efficiency of these tubes is estimated.

Transition from annular flow to plug/slug flow in condensation of steam in microchannels

A visualization study has been conducted to investigate the transition from annular flow to plug/slug flow in the condensation of steam in two different sets of parallel microchannels, having hydraulic diameters of 90 μm and 136 μm, respectively. The steam in the parallel microchannels was cooled on the bottom by forced convection of water and by natural convection of air from the top. It is found that the location, where the transition from annular flow to plug/slug flow takes place, depends on mass flux and cooling rate of steam. The effects of mass flux and cooling rate on the occurrence frequency of the injection flow in a single microchannel, having a hydraulic diameter of 120 μm and 128 μm, respectively, are investigated. It is found that two different shapes of injection flow occur in the smooth annular flow in microchannels: injection flow with unsteady vapor ligament occurring at low mass flux (or high cooling rate) and injection flow with steady vapor ligament occurring at high mass flux (or low cooling rate). It is also found that increase of steam mass flux, decrease of cooling rate, or decrease of the microchannel diameter tends to enhance instability of the condensate film on the wall, resulting in occurrence of the injection flow further toward the outlet with an increase in occurrence frequency.

A study in forced convection of water in a single uneven planar rock fracture for geothermal application

For geothermal applications, a study in forced convection of water in a single uneven planar rock fracture is conducted in the laboratory, using actual rock samples that have been artificially fractured. The results show that, over tha range of experimental data collected, the heat transfer correlation may be described by the Nusselt number being a simple power function of the Peclet number.

Forced convection of water in rod-bundles

Heat transfer of water in rod-bundles is of particular importance in many engineering applications. Although numerous experimental studies have been conducted to develop heat transfer correlations for forced convection in rod-bundles, with either a square or a triangular lattice, most data was taken at high Reynolds numbers (Re > 6,000); only a few data points had been reported at lower Reynolds number [1-5]. Recently, El Genk and co-workers have performed a series of heat transfer experiments of forced convection of water at the low and high Reynolds numbers as well as of natural and combined convection in uniformly heated, triangularly and square arrayed rod-bundles with P/D = 1.25, 1.38, and 1.5 [6-10]. Like all other investigators, they correlated the heat transfer data for square lattice and triangular lattice separately, with P/D as a parameter. This paper shows that forced convection data for both square and triangularly arrayed rod-bundles, when expressed in terms of the bundle porosity, can be represented by a single correlation, one each for forced turbulent convection land forced laminar convection. Also, the experimental values of the Reynolds number at the transition between these two convection regimes is expressed in terms of the bundle porosity, regardless of themore » lattice type and rod diameter. This approach reduces the number and simplifies the form of the forced convection correlations, making them easy to use in potential engineering applications. Although the effect of the rod diameter and the type of lattice in the bundles is implicit in the expressions of the bundle porosity, it is explicit in the definition of the heated equivalent diameter in both Re and Nu, and hence will influence the heat transfer coefficient.« less

The Influence of Twisted Tapes in Subcritical, Once-Through Vapor Generators in Counter flow

The swirl flow of Freon 12 in a tubular heat exchanger, indirectly heated by forced convection of water in an annular gap, is studied. Two identical situations are compared, with and without a twisted tape, to deduce the influence of the swirl flow in the particularly interesting boundary condition of indirect heating by another fluid (and not simply of uniform Joule heating). The heat transfer is greatly increased by the swirl flow, up to a factor of two at the burnout or dryout point.