Search

We have designed an apparatus dedicated for measurement of heat transfer coeffcient during saturated nucleate pool boiling. After several performed measurements, we have applied three important modifications of the apparatus motivated by discrepancies between measured and correlated heat transfer coeffcients. Firstly, the cubic stainless-steel heated block of the apparatus no longer accommodates heating cartridges. It now stands on a copper carrier of the cartridges, which are vertically oriented. Secondly, we have insulated the heated block with plates made of cellular glass. Thirdly, thermocouples used for measurement of temperatures inside the block have been fixated with a special high-temperature adhesive. These modifications were applied in order to improve the temperature distribution inside the block and to eliminate the impact of surroundings on measured heat transfer coeffcients. This contribution presents and discusses experimental results obtained with these modifications.

We have designed a simple apparatus for measurement of heat transfer during pool boiling in order to find or create suitable correlations for heat-transfer coefficient, which could be used for various liquids and conditions. We have run several testing experiments with tap and deionized water. This contribution presents proceedings and the first results of these experiments as well as comparison of these results with some published and verified correlations.

Heat transfer coefficient (HTC) was experimentally measured for saturated and subcooled pool boiling of binary mixtures of water and glycerin. Saturated boiling was studied for mixtures with water mass fractions ω w from 100 % to 60 % on horizontal flat nickel-plated surfaces at heat fluxes from 50 to 650 k W m − 2 at atmospheric pressure. Subcooled boiling was investigated in the range of subcooling from 0 to 30 K at heat fluxes of approximately 250, 450 and 650 k W m − 2 . It was found that mixture effects have a significant impact on saturated boiling HTC even for mixtures with very low content of glycerin as significant drops of HTC were observed for subtle changes in composition for mixtures of high ω w . Measured HTC was successfully correlated with the combination of Yagov (1999) and Inoue and Monde (2009) correlations with a mean relative error of 12 %. A simple empirical HTC correlation is also proposed. For subcooled boiling, developed subcooled boiling regime was reached for all investigated heat fluxes. For this regime, correlations, which were able to predict HTC for saturated boiling, were employed to predict subcooled boiling HTCs for all investigated concentrations, heat fluxes and subcoolings. Effect of subcooling and effect of liquid composition on total HTC were of the same importance for mixtures with higher water content. With the increase in concentration of glycerin in the mixture, decrease in total HTC with increasing subcooling became more significant. [ABSTRACT FROM AUTHOR]

Pool boiling of cryogenic nitrogen and oxygen is important, as both substances represent more than 99 % of all particles in the atmosphere. Boiling of cryogens is commonly utilized in gas processing, air separation, cooling, or superconducting systems. The so-called chilldown is a characteristic process when handling cryogens, which occurs when a surface at ambient temperature gets into contact with a cold cryogenic liquid. The chilldown is accompanied by transient film boiling. Investigating critical heat fluxes and film boiling of cryogens is thus more important compared with non-cryogenic liquids. This contribution deals with heat transfer during pool boiling of cryogenic nitrogen, oxygen, and nitrogen-oxygen mixtures. Knowledge of heat transfer coefficients and of critical heat fluxes is crucial for qualified design of cryogenic apparatuses and for improved handling of cryogens. In this contribution, pool boiling performance of pure nitrogen, oxygen, and their mixtures is investigated and suitable predictive correlations for the heat transfer coefficient and critical heat flux are analyzed. It was found that variations of thermophysical properties with composition are quite weak and sufficiently linear for nitrogen-oxygen mixtures. The pure-fluid correlation of McNelly is shown to be suitable for HTC estimation during boiling of pure nitrogen and oxygen. The mixture correlation of Thome was found to be suitable for nitrogen-oxygen mixtures. [ABSTRACT FROM AUTHOR]