Flow resistance characteristics of water in narrow annulus during heat exchange

Considering the special resistance characteristics of fluids flowing through ducts with small gaps, experiments are performed to investigate the resistance characteristics of single-phase water, which is forced to flow through ver tical annuli. The gap sizes are 0.9, 1.4 and 2.4mm, respectively. The experiments are conducted under condition of 1atm. The water in the annuli is heated by high temperature water reversely flowing through the inner tube and the outer annulus. The results show that the flow pattern begin to change from laminar to turbulent before Reynolds number approaches 2000, the flow resistance in annulus has little relations with the temperature difference and ways of being heated, but mainly depends on the ratio of mass flux to the width of annulus.

CFD Study on Local Fluid-to-Wall Heat Transfer in Packed Beds and Field Synergy Analysis

To reach the target of smaller pressure drop and better heat transfer performance, packed beds with small tube-to-particle diameter ratio(D/dp<10) have now been considered in many areas. Fluid-to-wall heat transfer coefficient is an important factor determining the performance of this type of beds. In this work, local fluid-to-wall heat transfer characteristic in packed beds was studied by Computational Fluid Dynamics(CFD) at different Reynolds number for D/dp=1.5, 3.0 and 5.6. The results show that the fluid-to-wall heat transfer coefficient is oscillating along the bed with small tube-to-particle diameter ratio. Moreover, this phenomenon was explained by field synergy principle in detail. Two arrangement structures of particles in packed beds were recommended based on the synergy characteristic between flow and temperature fields. This study provides a new local understanding of fluid-to-wall heat transfer in packed beds with small tube-to-particle diameter ratio.

A Least-Squares Solution to Nonlinear Steady-State Multi-Dimensional IHCP

In this paper,the least-squares method is used to solve the Inverse Heat Conduction Problem(IHCP)to determine the space-wise variation of the unknown boundary condition on the inner surface of a helically coiled tube with fluid flow inside,electrical heating and insulation outside.The sensitivity coefficient is analyzed to give a rational distribution of the thermocouples. The results demonstrate that the method effectively extracts information about the unknown boundary condition for the heat conduction problem from the experimental measurements. The results also show that the least-squares method converges very quickly.

Thermal Performance of a Single-row Fin-and-tube Heat Exchanger

Experiments were carried out to study the heat transfer characteristics of a single-row aluminum fin-and-tube crossflow heat exchanger with an emphasis in the regime of low flow rate of the in-tube fluid. The Chilton-Colburn analogy, in conjunction with the least-squares power-law technique, was used to correlate experimental data. Both air- and water-side heat transfer correlations were developed in the form of the Nusselt numbers as a function of Reynolds and Prandtl numbers. The experimental observations are quantitatively compared to the predictions of correlations available in the published literature. Different transfer mechanisms were found to be operative in the ranges of water-side Reynolds numbers based on the hydraulic diameter. In a range of Reynolds number from 1,200 to 6,000, the water-side thermal resistance accounts for less than ten percent of the overall thermal resistance. The dominant thermal resistance is always on the air-side. On the other hand, the thermal resistance of water-side is nearly equal to that of air-side in a Reynolds number range from 500 to 1,200.