Experimental investigation of heat transfer characteristics of distilled water and ethanol in electrospray surface cooling

Experimental investigation of heat transfer characteristics of water in a vertically–upward tube under ultra-supercritical pressure and ultrahigh-temperature conditions

This study focuses on the heat transfer characteristic of a horizontal subsea Xmas tree assembly at a high spatial resolution. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) in combination with Low Reynolds number modelling (LRNM) is adopted for heat transfer analysis, which has been validated against a full scale underwater gate valve heat transfer experiment with good agreements. The characteristics of cold sea water flowing through the subsea tree, and of convection heat transfer between the subsea tree and ambient cold water are obtained. The typical “hot spots,” which have high Convection heat transfer coefficient (CHTC) and create great large amounts of heat loss, are numerically determined. Under the designed water depth, the effects of installation orientation, sea water velocity, and inner oil temperature on convection heat transfer are investigated as well. Such work is significant for thermal design of the subsea tree to increase structural reliability and flow assurance level.

A combined experimental and numerical investigation of the heat transfer characteristics within an array of impinging jets has been conducted. The experiments were carried out in a perspex model using a transient liquid crystal method. Local jet temperatures were measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. The effects of the variation in different impingement patterns, jet-to-plate spacing, crossflow schemes, and jet Reynolds number on the distribution of the local Nusselt number and the related pressure loss were investigated experimentally. In addition to the measurements, a numerical investigation was conducted. The motivation was to evaluate whether computational fluid dynamics (CFD) can be used as an engineering design tool in the optimization of multijet impingement configurations. This required, as a first step, a validation of the numerical results. For the present configuration, this was achieved assessing the degree of accuracy to which the measured heat transfer rates could be computed. The overall agreement was very good and even local heat transfer coefficients were predicted at high accuracy. The numerical investigation showed that state-of-the-art CFD codes can be used as suitable means in the thermal design process of such configurations.

This paper reports an experimental investigation of heat transfer characteristics during water jet impingement cooling of a moving heated steel plate. The research examines boiling regimes under the effect of several process parameters including jet Reynolds number, plate velocity, and initial plate temperature. Parametric studies are undertaken systematically to examine the effect on different heat transfer regimes. The findings indicate that transition and nucleate boiling predominate due to elevated surface temperatures, achieving a maximum heat flux (HF) of 17 MW m2 at a surface temperature of 310 °C during transition boiling, with maximum cooling rates reaching 82.68 °C s−1. Surface motion is observed to significantly affect cooling performance, with optimal heat transfer occurring at an intermediate plate speed of 0.4 m s−1. Critical HF increases by 26% when initial plate temperature increases from 560 °C to 760 °C, and by 30% when Reynolds number increases from 35000 to 60000. An experimental correlation is developed for predicting peak HFs as a function of the key process parameters, demonstrating 85% accuracy. The study provides fundamental insights and useful information for optimizing thermal management strategies in industrial cooling processes.

Experimental investigations of heat transfer characteristics of MPCM during charging

Investigation of heat transfer characteristics on various kinds of fin-and-tube heat exchangers with interrupted surfaces

Heat transfer characteristics of a gas-to-gas parallel flow microchannel heat exchanger have been experimen- tally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger are measured to obtain heat transfer rates and pressure drops. The heat transfer and pressure drop characteristics are discussed. The results show that experimental pressure drop is approximately ten times as large as theoretically estimated pressure drop. Geometric con- figuration of the heat exchanger dominates pressure drop characteristics. The conventional log-mean temperature differ- ence method and the constant wall temperature model proposed in our earlier work are applied to predict heat transfer rate of the parallel flow microchannel heat exchanger. Prediction accuracy of the log-mean temperature difference method is superior to that of the constant wall temperature model. Applicability of the log-mean temperature difference method de- pends on direction of fluid flow.

The thermal performance of shell and tube heat exchangers has been enhanced with the use of different techniques. Air bubble injection is one such promising and inexpensive technique that enhances the heat transfer characteristics inside shell and tube heat exchanger by creating turbulence in the flowing fluid. In this paper, experimental study on heat transfer characteristics of shell and tube heat exchanger was done with the injection of air bubbles at the tube inlet and throughout the tube with water based Al2O3 nanofluids i.e. (0.1%v/v and 0.2%v/v). The outcomes obtained for both the concentrations at two distinct injection points were compared with the case when air bubbles were not injected. The outcomes revealed that the heat transfer characteristics enhanced with nanoparticles volumetric concentration and the air bubble injection. The case where air bubbles were injected throughout the tube gave maximum enhancement followed by the cases of injection of air bubbles at the tube inlet and no air bubble injection. Besides this, water based Al2O3 nanofluid with 0.2%v/v of Al2O3 nanoparticles gave more enhancement than Al2O3nanofluid with 0.1%v/v of Al2O3 nanoparticles as the enhancement in the heat transfer characteristics is directly proportional to the volumetric concentration of nanoparticles in the base fluid. The heat transfer rate showed an enhancement of about 25-40% and dimensionless exergy loss showed an enhancement of about 33-43% when air bubbles were injected throughout the tube. Moreover, increment in the heat transfer characteristics was also found due to increase in the temperature of the hot fluid keeping the flow rate of both the heat transfer fluids constant.

Nanofluids are emerging two-phase thermal fluids that play a vital part in heat exchangers owing to its heat transfer features. Ceramic nanoparticles aluminium oxide (Al2O3) and silicon dioxide (SiO2) were produced by the sol-gel technique. Characterizations have been done through powder X-ray diffraction spectrum and scanning electron microscopy analysis. Subsequently, few volume concentrations (0.0125–0.1%) of hybrid Al2O3–SiO2 nanofluids were formulated via dispersing both ceramic nanoparticles considered at 50:50 ratio into base fluid combination of 60% distilled water (W) with 40% ethylene glycol (EG) using an ultrasonic-assisted two-step method. Thermal resistance besides heat transfer coefficient have been examined with cylindrical mesh heat pipe reveals that the rise of power input decreases the thermal resistance and inversely increases heat transfer coefficient about 5.54% and 43.16% respectively. Response surface methodology (RSM) has been employed for the investigation of heat pipe experimental data. The significant factors on the various convective heat transfer mechanisms have been identified using the analysis of variance (ANOVA) tool. Finally, the empirical models were developed to forecast the heat transfer mechanisms by regression analysis and validated with experimental data which exposed the models have the best agreement with experimental results.

Experimental and numerical investigations of heat transfer characteristics of vertical falling film heat exchanger in data center cabinets

Numerical Investigation of Heat Transfer Characteristics of Pin-Fins with Roughed Endwalls in Gas Turbine Blade Internal Cooling Channels

The heat transfer performance of a tube heat exchanger has great significance for the metal smelting, catalytic cracking and combustion performance in the fluidized bed reactor. In this paper, a three dimensional Eulerian–Eulerian simulation for the vertical heater tube to bed heat transfer within a baffle type internal circulating fluidized bed (ICFB) was conducted numerically and the results were compared to experimental ones. Gidaspow’s drag correlation was adopted to describe the interaction between the gas and solid phases in the ICFB. Temperature and heat transfer coefficient were numerically analyzed under different operating conditions as same as the experimental setup. The effects on the heat transfer characteristic of input heat flux, air inlet velocity, and initial solid packing height were investigated as the average temperature was compared with the experimental data in the literature. The simulation results showed that along the height of the bed, the velocity of the solid particles increases, lateral movement of the particles from the low-speed area to the high-speed area can be observed at the bottom of the acceleration area. The convective heat transfer coefficient of solid particles is the main component of heat transfer in the dense phase zone, with the increase of the initial solid packing height, the average convection heat transfer coefficient between the fluid and the heated surface is shown an upward trend. By comparing the experimental datas, it can be concluded that the numerical simulation of the flow and heat transfer process of the inner circulating fluidized bed by the Eulerian-Eulerian method is in good agreement with the experimental results.

A comparative study on heat transfer characteristics of the whole turbine vane surface without films and another one with two rows of film holes was conducted through tests and numerical calculations. The results show that the heat transfer of the vane surface is influenced greatly by the cascade passage structure. Heat transfer is strong at the stagnation point of the vane leading edge and the mainstream severely accelerated position. The generations of channel vortices enhance the heat transfer at the vane end wall and compress the mainstream towards the middle of the vane. Film holes can enhance local convection heat transfer of the vane surface, but do not change the trend of the whole vane surface heat transfer.

Convective Heat Transfer through Thick-Walled Pipe

Oblique ribs are widely applied to the internal cooling of turbine blades to promote the heat transfer between blade wall and coolant. In this study, the effect of several new types of truncated ribs on the heat transfer characteristics in 45° oblique rib channels is investigated experimentally and numerically. The numerical results obtained by the SST k-ω turbulence model agree well with the experimental data for the Reynolds number ranging from 10000 to 60000. The results indicate a significant entrance effect on the heat transfer in truncated rib channels. The numerical results show that ribs continuously truncated at 3.8 mm gives the best heat transfer performance among the newly truncated ribs. Compared with the original structure, the Nusselt number and heat transfer enhancement factor of newly truncated ribs increased by 24.6 % and 17.8 %, respectively. Concurrently, the friction factor is reduced by 5.1 %.