Přechodné stavy přestupu tepla na skrápěném trubkovém svazku

Influence of Underpressure on Heat Transfer And Temperature Field at Sprinkled Tube Bundle

článek v časopise - ostatní, Jost

en

Sprinkled tube bundles with a thin liquid film flowing over them are used in various technology processes where it is necessary to separate the vapour and liquid phases quickly and efficiently at low temperatures with a corresponding decrease of pressure around the tube bundle. In ideal conditions water boils at the whole surface of an exchanger, but in practice it must be considered that in original spots of contact between water and the exchanger wall the water will not boil at the tubes' surface but the cooling liquid will merely be heated-up. The article focuses on these processes. Experiments have been carried out at a tube bundle consisting of copper tubes of 12 mm diameter placed horizontally one above another that have been heated by water of an average input temperature approx. 40 °C. This bundle has been sprinkled by cool water at temperature of 15 °C and pressure has been gradually decreased using an exhauster at constant flow rates of heating and falling film liquid inside an experimental device's chamber. Was tested flow of sprinkled liquid in the range of 4-9 liters per minute, which corresponds to the range of Reynolds numbers of about 300 to 600 [-]. The result of these experiments is a studied heat transfer coefficient at the surface of a sprinkled tube bundle during heating of the cooling liquid with a transition into boiling of the liquid at the bundle. At a flow of 8 liters per minute were acquired sequence thermal camera FLIR SC 660. After evaluation of the sequences were generated maps of the temperature field according to decreasing the pressure and its standard deviation. From the contour graphs can evaluate the thermal stability of the liquid film on the spray tube bundle.

Skrápěné trubkové svazky, po kterých proudí tenký kapalný film, se používají v různých technologických procesů, kde je to nezbytné pro oddělení fází parami a kapalinou rychle a efektivně při nízkých teplotách s odpovídajícím poklesem tlaku kolem trubkového svazku. V ideálních podmínkách voda vaří na celém povrchu výměníku, ale v praxi je třeba považovat to v původní místa kontakt mezi vodou a stěny výměníku voda nebude vařit na povrchu trubek, ale chladicí kapaliny bude pouze vyhřívané up. Článek se zaměřuje na tyto procesy. Experimenty byly provedeny na trubní svazek skládající se z měděné trubky o průměru 12 mm umístěné vodorovně nad sebou, které byly vytápěny vody vstupní teplotou cca 40 ° C. Tento svazek byl pokropil chladnou vodou při teplotě 15 ° c a tlak byl postupně snižovaly pomocí výfuk při konstantní průtok topení a pádu filmu kapalina uvnitř komory experimentální zařízení. Byl testován tok kapaliny, sypané v rozmezí 4-9 litrů za minutu, což odpovídá rozsahu Reynoldsových čísel asi 300 až 600 [-]. Výsledkem těchto experimentů je koeficient prostupu studovaných tepla na povrchu sypané trubkového svazku během vytápění chladicí kapaliny s přechodem do varu kapaliny na svazku. Při průtoku 8 litrů za minutu bylo získané sekvence termální kamery FLIR SC 660. Po vyhodnocení sekvence byly generované mapy teplotní pole podle klesající tlak a jeho směrodatnou odchylku. Od obrysy grafů může vyhodnotit tepelná stabilita kapalina film na sprej trubkového svazku.

Sprinkled tube bundles with a thin liquid film flowing over them are used in various technology processes where it is necessary to separate the vapour and liquid phases quickly and efficiently at low temperatures with a corresponding decrease of pressure around the tube bundle. In ideal conditions water boils at the whole surface of an exchanger, but in practice it must be considered that in original spots of contact between water and the exchanger wall the water will not boil at the tubes' surface but the cooling liquid will merely be heated-up. The article focuses on these processes. Experiments have been carried out at a tube bundle consisting of copper tubes of 12 mm diameter placed horizontally one above another that have been heated by water of an average input temperature approx. 40 °C. This bundle has been sprinkled by cool water at temperature of 15 °C and pressure has been gradually decreased using an exhauster at constant flow rates of heating and falling film liquid inside an experimental device's chamber. Was tested flow of sprinkled liquid in the range of 4-9 liters per minute, which corresponds to the range of Reynolds numbers of about 300 to 600 [-]. The result of these experiments is a studied heat transfer coefficient at the surface of a sprinkled tube bundle during heating of the cooling liquid with a transition into boiling of the liquid at the bundle. At a flow of 8 liters per minute were acquired sequence thermal camera FLIR SC 660. After evaluation of the sequences were generated maps of the temperature field according to decreasing the pressure and its standard deviation. From the contour graphs can evaluate the thermal stability of the liquid film on the spray tube bundle.

skrápění, přenos tepla, bez varu, trubkový svazek, podtlak

sprinkled, heat transfer, non-boiling, tube bundle, under pressure

01.04.2016

Trans Tech Publications

Switzerland

1662-7482

832

200–206

7