Influence of the wetting state of a heated surface on heat transfer and pressure loss in an evaporator tube

Technical Report · Mon Sep 01 04:00:00 EDT 1986

DOI:https://doi.org/10.2172/5236497· OSTI ID:5236497

Koehler, W; Hein, D

The influence of the wetting state of a heated surface on heat transfer and pressure loss in an evaporator tube was investigated for a parameter range occurring in fossil-fired steam generators. Included in the analysis are quantities which determine the wetting state in steady and transient flow. The experimental work consists of the following: Occurrence of critical heat flux (CHF) and post-CHF heat transfer in a vertical upflow evaporator tube; influence of pressure and enthalpy transients on heat transfer in the unwetted region; influence of pipe orientation on heat transfer; and two phase flow pressure loss in wetted and unwetted region. Based on these experiments a method of predicting CHF for a vertical upflow evaporator tube was developed. The heat transfer in the unwetted region was newly formulated taking into account thermal nonequilibrium between the water and steam phases. Wall temperature excursions during pressure and enthalpy transients are interpreted with the help of the boiling curve and the Leidenfrost phenomenon. A method is developed by means of which it is possible to determine the influence of the pipe orientation on the location of the boiling crisis as well as on the heat transfer in the unwetted region. The influence of the wetting state of the heated surface on the two phase flow pressure loss is interpreted as ''Wall effect'' and is calculated using a simplified computer model. 68 refs., 83 figs.

• Research Organization: Nuclear Regulatory Commission, Washington, DC (USA). Office of Nuclear Regulatory Research; Kraftwerk Union A.G., Erlangen (Germany, F.R.)
• OSTI ID: 5236497
• Report Number(s): NUREG/IA-0003; ON: TI87900030
• Country of Publication: United States
• Language: English

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BOILERS
BOILING
DRYOUT
ENERGY TRANSFER
ENTHALPY
EVAPORATORS
FILM BOILING
FLUID FLOW
FLUID MECHANICS
FOSSIL-FUEL POWER PLANTS
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PRESSURE EFFECTS
STEAM GENERATORS
STEAM QUALITY
TEMPERATURE EFFECTS
TEST FACILITIES
THERMAL POWER PLANTS
THERMODYNAMIC PROPERTIES
TRANSIENTS
TUBES
TWO-PHASE FLOW
VAPOR GENERATORS
VELOCITY
WETTABILITY