Series Of Heat Transfer Tests Research Articles

Experimental Investigation on the Heat Transfer Characteristics in Upward Flow of Supercritical Carbon Dioxide

The SuperCritical Water-cooled Reactor (SCWR) is one of the candidates for the fourth-generation nuclear power plant, and it uses light water as a coolant. Heat transfer between a fuel assembly and water may degrade at certain conditions of supercritical pressure flows. Therefore, accurate and reliable estimation of heat transfer coefficients is necessary for the design of the fuel assembly and the reactor core. A series of heat transfer tests has been carried out at a test facility named SPHINX by using carbon dioxide as a stimulant of water. The tests produced heat transfer data of the supercritical pressure flows inside a circular tube of 4.4-mm inside diameter at varying operating pressures, mass fluxes, and wall heat fluxes. The test range of the mass flux was 400 to 1200 kg/m2 s, and the maximum heat flux was 150 kW/m2. The operating pressures were 7.75, 8.12, and 8.85 MPa in the tests. The test results were compared with estimations of the existing correlations for supercritical pressure flows. The comparison showed reasonable agreement between our data and the correlations. However, a rather large departure from the normal heat transfer correlations was observed near pseudocritical temperatures. Besides the comparison of the normal heat transfer coefficients, the onset of heat transfer deterioration was compared between the test cases and two existing criteria. One of the criteria was derived from experiments by using Freon but with a test section of identical geometry while the other criterion was for a flow of carbon dioxide in a larger bore channel than ours. Both criteria showed fair agreement with our experiment. Most test cases with noticeable heat transfer degradation were located in the region of deterioration predicted by the criteria.

Heat Transfer Testing of Thermal-Magnetic Circuit Breakers

Abstract The forensic engineering investigation of a fire will include the post-fire examination of electrical panelboards and circuit breakers if such equipment is available on the premises and survives the fire. Post-fire circuit breakers may be found in the on, off, tripped, or unknown position. It is sometimes assumed by investigators that a tripped circuit breaker is the result of an overcurrent condition either before or during the fire. Sometimes the tripped (or untripped) circuit breaker is used to prove or disprove theories about the cause of the fire. Since thermal-magnetic circuit breakers employ thermal sensors, it should be possible for the heat from a fire to be transferred by convection, conduction, and radiation into a circuit breaker and cause it to trip in the absence of an overcurrent condition. It should also be possible for the heat from a fire to shift the circuit breaker time-current characteristic curve and cause the circuit breaker to trip at reduced currents. The question then becomes, at what ambient temperature will the circuit breaker be expected to trip? Also, can the heat from a nearby fire be conducted by the metallic circuit conductors into a circuit breaker and cause, or assist it to trip? If so, what fire conditions are required to cause the circuit breaker to trip? This paper reviews the operating principle of thermal-magnetic circuit breakers, describes a series of heat transfer tests conducted on nine circuit breakers of various ratings and from various manufacturers, presents the results of the tests in graphical form, and discusses the potential impact of conduction and convection heat transfer on circuit breaker performance during fires.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.