Heat Transfer Characteristics In Channel Research Articles

Development of a new criterion for predicting critical heat flux in rod bundles with supercritical water flowing upward

Investigations of heat transfer characteristics in channels with supercritical fluids are crucial for power cycle applications, such as supercritical water-cooled reactors. To ensure the safety of the system, heat transfer deterioration (HTD) should be avoided. The criteria to identify the onset of HTD in heated rod bundles are still not determined. This study summarizes indicators for the onset of HTD in a rod bundle with supercritical water flowing upward based on observations from experimental data. Existing criteria for the tube flow are assessed by comparing predicted critical heat flux (CHF) values with experimentally identified values. Considering effects of different operating parameters, a new criterion for predicting HTD behavior in rod bundles is developed. The results indicate that the new criterion has a better performance than all existing criteria, with a mean average relative deviation of 0.26 %. Predicted CHF values are within ± 20 % of the respective experimentally identified CHF values.

Heat transfer characteristics in channel with square rib at different Mach numbers

The detailed flow structures and closely-related heat transfer characteristics were investigated along the wall of a cooling channel with rib tabulator by computation. The two-dimensional Navier-Stokes equations were solved using the density-based algorithm and strongly-coupled with the heat-transfer equation. Three typical Reynolds numbers defined by rib height and Mach numbers were set at 500, 750, 1000 and at 0.2, 0.3, 0.4, respectively. Results show that, As the Mach numbers changing from 0.2 to 0.4, the local Nusselt numbers increase and the average heat transfer effects are enhanced. Based on the instantaneous field of vortices evolvement, the vortexes are first generated near the top surface of the rib by the strong shear effects. Then the vortexes are shed and intensified gradually downstream. Particularly, an important phenomenon is, for the first time, discovered that the high Nusselt number has a consistent correlation with the positive and negative sign alteration of the shear layer on the wall, which satisfactorily explains the mechanisms of heat transfer enhancement due to the flow.

Flow and Heat Transfer Characteristics in Channels With Groove–Protrusions and Combination Effect With Ribs

Passive flow control and heat transfer enhancement technique has become an attractive method for device internal cooling with low resistance penalty. In the present paper, the flow and heat transfer characteristics in the small scale rectangular channel with different groove–protrusions are investigated numerically. Furthermore, the combination effect with ribs is studied. The numerical results show that on the groove side, the flow separation mainly occurs at the leading edge, and the reattachment mainly occurs at the trailing edge in accordance with the local Nusselt number distribution. On the protrusion side, the separation mainly occurs at the protrusion back porch and enhances the heat transfer at the leading edge of the downstream adjacent groove. The rectangle case provides the highest dimensionless heat transfer enhancement coefficient Nu/Nu0, dimensionless resistance coefficient f/f0, and thermal performance (TP) with the highest sensitivity of Re. When ribs are employed, the separation bubble sizes prominently decrease, especially inside the second and third grooves. The Nu/Nu0 values significantly increase when ribs are arranged, and the one-row case provides the highest heat transfer enhancement by ribs. Besides, the two-row case provides the highest Nu/Nu0 value without ribs, and the three-row case shows the lowest Nu/Nu0 value whether ribs are arranged or not.

An Experimental and Numerical Study of Flow and Heat Transfer in Channels With Pin Fin-Dimple Combined Arrays of Different Configurations

An experimental and numerical study was conducted to investigate the flow and heat transfer characteristics in channels with pin fin-dimple combined arrays of different configurations, where dimples are located transversely or both transversely and streamwisely between the pin fins. The flow structure, friction factor, and heat transfer characteristics of the pin fin-dimple channels of different configurations have been obtained and compared with each other for the Reynolds number range of 8200–50,500. The experimental study showed that, compared to the pin fin channel, depending on the configurations of the pin fin-dimple combined arrays the pin fin-dimple channel can have distinctively further improved convective heat transfer performance by 8.0%–20.0%, whereas lower or slightly higher friction factors over the studied Reynolds number range. Furthermore, three-dimensional and steady-state conjugate computations have been carried out for similar experimental conditions. The numerical computations showed detailed characteristics of the distribution of the velocity and turbulence level in the flow, which revealed the underlying mechanisms for the pressure loss and heat transfer characteristics in the pin fin-dimple channels of different configurations.

Spatially-resolved heat transfer characteristics in channels with pin fin and pin fin-dimple arrays

A comparative study has been conducted to investigate the spatially-resolved heat transfer characteristics of air turbulent flow in rectangular channels with pin fin and pin fin-dimple arrays. A combined method of experiments and numerical computation was adopted to obtain the spatially-resolved Nusselt numbers on the endwall surface of the pin fin and pin fin-dimple channels. Compared with the pin fin channel, the pin fin-dimple channel shows distinctive local heat transfer characteristics on the endwall beneath the main flow and the wake flow region. Due to the presence of the dimples in the pin fin arrays, extra strong vortex flows are generated near the wall beneath the main flow region downstream the dimples, which distinctively increase the turbulent mixing there and enhance the heat transfer rates; however the turbulent mixing in the wake of the pin fins is reduced appreciably, which leads to decreased heat transfer rates in the wake especially at relatively low Reynolds number. Overall, the dimples in the pin fin arrays increase not only the averaged heat transfer coefficient, but also the heat transfer area on the endwall.

Numerical simulation of fluid flow and heat transfer characteristics in channel with V corrugated plates

A detailed numerical study is carried out to investigate fluid flow and heat transfer characteristics in a channel with heated V corrugated upper and lower plates. The parameters studied include the Reynolds number (Re = 2,000–5,500), angles of V corrugated plates (θ = 20°, 40°, 60°), and constant heat fluxs (q″ = 580, 830, 1,090 W/m2). Numerical results have been validated using the experimented data reported by Naphon, and a good agreement has been found. The angles of V corrugated plates (θ) and the Reynolds number are demonstrated to significantly affect the fluid flow and the heat transfer rate. Increasing the angles of V corrugated plates can make the heat transfer performance become better. The increasing Reynolds number leads to a more complex fluid flow and heat transfer rate. The numerical calculations with a non-equilibrium wall function have a better accuracy than with a standard wall function for solving high Reynolds numbers or complex flow problems.

A Numerical Study of Fluid Flow and Heat Transfer Characteristics in Channels with Staggered Wavy Walls

A two-dimensional steady developing fluid flow and heat transfer through a periodic wavy channel with staggered walls is studied numerically for a fluid with a Prandlt number of 0.7 and compared to flow through the corresponding wavy channel with nonstaggered walls. The lower wall is displaced relative to the upper wall by one-fourth, one-half, and three-fourths of the total one-module length. Sinusoidal and arc-shaped configurations are studied for a fixed set of geometric parameters. Periodically fully developed flow is attained downstream of the first module of the 10 modules considered in this study. Sinusoidal channels with one-half displacement provide lower normalized pressure drop values when compared to all other channels (staggered and nonstaggered) considered in this study. The module average Nusselt number increases monotonically with Reynolds number. Moreover, the heat transfer enhancement ratio for arc-shaped channels with three-fourths displacement is as high as 5.7%.

Heat Transfer Characteristics in Sharply Turned Serpentine Channels with Inclined partition Wall.

Experimental study was conducted on heat transfer characteristics in rectangular cross-sectioned two-pass serpentine channels with an inclined partition wall. The cross section of the channel at the entrance was 50 mm×25 mm, and the inclination angle of the partition (inner) wall was changed from -6° (convergent channel) to +6° (divergent channel) for three turn clearances of 30 mm, 50 mm, and 70 mm. Distributions of local heat (mass) transfer rates on the long-side wall were measured by the naphthalene sublimation method under a single Reynolds number of 3.5×104. In this paper, influences of the inclination angle of the partition wall and of the turn clearance on heat transfer characteristics in the channels are discussed in detail. Then, the optimum combination of the inclination angle and the turn clearance is examined from viewpoints of the trade-off between the mean heat transfer rate and pressure loss, and of the improvement of uniformity in the distribution of local heat transfer rates.