Edney III type shock-shock interaction over a hemisphere cylinder

Numerical study of hydrodynamics with surface heat transfer in a bubbling fluidized-bed reactor applied to fast pyrolysis of rice husk

Unsteady surface pressure and heat transfer have been measured on a blade of a linear turbine cascade exposed to unsteady oncoming wakes generated by moving cylinders on a squirrel cage device. The Reynolds number and the Strouhal number corresponded to the values in a real turbomachine. The periodic components of pressure and heat transfer showed clear response to the unsteady wakes. However, the distribution along the blade surface of both pressure and heat transfer coefficient changed very little from phase to phase. The heat transfer results have shown that the boundary layer on the pressure side remained laminar for all cases, but that the boundary layers on the suction side became transitional under the wake disturbance. With increasing wake-passing frequency, the start of the transition moved forward. Increasing the wake-passing frequency resulted in a significant increase in heat transfer along the whole blade surface including the portions where the boundary layers were nominally laminar.

Transient MHD stagnation flow of a non-Newtonian fluid due to impulsive motion from rest

Assessment on thermal behavior of municipal sewage sludge thin-layer during hot air forced convective drying

A new simplified model to calculate surface temperature and heat transfer of radiant floor heating and cooling systems

Pool boiling heat transfer experiments were performed for small heat transfer surfaces at 0.101 MPa by using ethanol as test fluid. The test heat transfer surfaces were made of copper. The diameters of the heat transfer surfaces were 1.0, 2.0, 3.0, 5.0, 7.0 10.0 and 20.0 mm. When the heat flux was low, small isolated bubbles left from the heat transfer surface irrespective of size of the heat transfer surface. As the heat flux was increased, coalescent large bubbles were formed on the heat transfer surface in the case that the surface diameter was larger than 5.0 mm. Large bubbles left from place to place of the coalescent large bubbles on the heat transfer surface. In the case that the surface diameter was smaller than 3.0 mm, a single bubble stayed on the heat transfer surface and a single bubble periodically left form the bubble when the heat flux was increased to the middle and high heat flux region. As the diameter of the boiling surface became smaller, the boiling heat transfer was enhanced and the critical heat flux increased. The dependency of the critical heat flux on the heat transfer surface size was well correlated with the Ded and Lienhard relation developed for spheres.

Comparisons with experimental heat transfer and surface pressures were made for seven turbine vane and blade geometries using a quasi-three-dimensional thin-layer Navier–Stokes analysis. Comparisons are made for cases with both separated and unseparated flow over a range of Reynolds numbers and free-stream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity model. Modifications were made to account for the effects of: (1) free-stream turbulence on both transition and leading edge heat transfer; (2) strong favorable pressure gradients on relaminarizations; and (3) variable turbulent Prandtl number on heat transfer. In addition, the effect on heat transfer of the near-wall model of Deissler is compared with the Van Driest model.

Through an experiment of nucleate boiling under free convection in subcooled water, we came to the following conclusions : (1) The effective stirring length of bubbles in surface boiling is reasonably estimated to be one-third of their condensing height which is decided identically with the degree of subcooling of bulk water. (2) Correlation of heat transfer in surface boiling by using Δθs instead of Δθ corresponds to the replacing of He by Hes, where Δθs=temperature difference between heating surface and saturated liquid, Δθ=temperature difference between heating surface and bulk liquid, He=effective stirring length of bubbles in saturated boiling, Hes=effective stirring length of bubbles in surface boiling. From these conclusions, we derived an extention of author's correlating equation of nucleate boiling transfer, and confirmed that it fairly agreed with the experimental results in surface boiling.

To evaluate the system pressure response of a water wall type containment cooling system, which is one of the passive safety systems, the evaporation and condensation behaviors in a suppression chamber have been experimentally examined. In the system, the suppression pool water evaporates from the pool surface, passing into the wetwell due to pool temperature rise, while steam in the wetwell condenses on the steel containment vessel wall due to the heat release through the wall. The wetwell is a gas phase region in the suppression chamber and its pressure, which is expressed as the sum of the noncondensable gas pressure and saturated steam pressure, is strongly affected by the evaporation heat transfer from the suppression pool surface and condensation heat transfer on the containment vessel wall. Based on the measured temperature profiles near the heat transfer surface and the wetwell pressure using two apparatuses, evaporation and condensation heat transfer coefficients were evaluated. The following results were obtained. (1) Both heat transfer coefficients increased as the ratio of the steam partial pressure to the total pressure increased. (2) Comparison of the results from two types of test apparatuses confirmed that the size of the heat transfer surface did not affect the heat transfer characteristics within these tests. (3) The heat transfer coefficients were expressed by the ratio of the steam to noncondensable gas logarithmic mean concentration, which considered the steam and gas concentration gradient from the heat transfer surface to the wetwell bulk.

Effect of mass flow ratios on the conjugate heat transfer of a metal turbine vane at medium temperature

Heat and mass transfer rates from complex surfaces to a turbulent channel flow were measured using an infrared imaging system and the naphthalene sublimation technique, respectively. The surfaces are composed of spherical particles embedded either in a layer of thermally conducting, nonevaporating liquid or in an isothermal layer of subliming naphthalene. The experimental results indicate that, in general, the surface heat and mass transfer coefficients vary as the surface roughness increases, whereas the surface heat transfer coefficient changes as the solid-to-liquid thermal conductivity ratio is varied. Mass transfer rates exhibit less sensitivity to variations in the naphthalene height for surfaces composed of smaller particles, and heat transfer rates from surfaces of smaller particles remain fairly constant as the liquid level and thermal conductivity ratios are varied. The results are discussed relative to drying of partially wetted surfaces with surface complexity induced by the presence of droplets upon an impermeable substrate or a receding moisture front in a bed of granular material.

Computation of airflow effects on heat and mass transfer in a microwave oven

The inherent low thermal conductivity of working fluids used in transferring heat from energy system makes the performance of the system less efficient. The introduction of nanoparticles into the working fluid enhances the thermal conductivity of the fluid, thereby improving the overall performance of the energy system. Deposition of nanoparticles on the heat transfer surface of the heat exchanger occurs and this affects the mechanism of bubble formation, wettability, surface roughness of the heating surface and the overall heat transfer coefficient. In this review, the use of nanofluid showed improvement in the critical heat transfer flux (CHF) of the heat transfer fluid while the deposition of nanoparticles on the heater surface enhanced the wettability for pool boiling but caused deterioration in the heat transfer. The influence of nanoparticles deposition on surface characteristics and heat transfer coefficient during single and two phase flows in flow boiling needs to be further investigated.

With the CFD calculation software FLUENT, numerical simulation has been conducted to study the surface flow and heat transfer in inclined wave fin-and-tube heat exchanger, including uniform angle wave fin and inclined increase-angle wave fin. Velocity field, pressure field and the distribution of temperature field on the air side of fin surface were obtained. Heat transfer performance of the two kinds of fin were discussed and the curve of both heat exchange and pressure drop related to the inlet velocity were analyzed. The results indicates that in the same conditions, heat transfer effect is better than uniform angle wave fin. When the inlet velocity is 4 m/s ,the heat transfer of inclined increase-angle wave fin is about 1.1 times higher than that of uniform angle wave fin meanwhile the pressure resistance is as much as around 1.2 times, which provides a theoretical basis on heat transfer enhancement of wave finned tube.

Numerical simulation of motion characteristics and heat transfer enhancement of free particles in boiling heat transfer