Showing papers on "Critical heat flux published in 1982"

Heat-Transfer Augmentation in Rod Bundles Near Grid Spacers

Abstract: Heat-transfer augmentation by straight grid spacers in rod bundles is studied for single-phase flow and for post-critical heat flux dispersed flow. The heat transfer effect of swirling grid spacers in single-phase flow is also examined. Governing heat-transfer mechanisms are analyzed, and predictive formulations are established. For single-phase flow, the local heat transfer at a straight spacer and at its upstream or downstream locations are treated separately. The effect of local velocity increasing near swirling spacer is considered. For post critical heat flux (CHF) dispersed flow, the heat transfer by thermal radiation, fin cooling, and vapor convection near the spacer are calculated. The predictions are compared with experimental data with satisfactory agreement.

Heat Transfer Experiments and Flow Visualization for Arrays of Short Pin Fins

Abstract: Results from several sets of experiments are presented to illustrate the character of streamwise heat transfer development in large aspect ratio ducts filled with uniform staggered arrays of circular pins. The short (height-to-diameter ratio 1.0) pins span the full height of the duct and are packed in moderately dense arrays (pitch-to-diameter ratios 1.32 to 2.5) typical of internal cooling applications in gas turbine airfoils. Heat transfer experiments have been performed on two separate test sections utilizing (i) highly conducting, fin effectiveness unity pins, and (ii) low conductivity, fin effectiveness near zero pins. In both cases the streamwise development of heat transfer, averaged across the duct width, is resolved to a single pin row spacing. Additional information on the flowfield and local heat transfer is provided from a large scale test rig where kerosene-lamp black flow visualization and small heat flux gages were utilized.Copyright © 1982 by ASME

Critical Heat Flux During Natural Convective Boiling in Vertical Rectangular Channels Submerged in Saturated Liquid

Abstract: An experimental study of the critical heat flux has been carried out for natural convective boiling at atmospheric pressure in vertical rectangular channels. Experiments in four kinds of test liquids (water, ethanol, freon 113, and benzene) have been made for the ratio l/s less than 120, in which l is the length of the heated surface and s is the width of the channels. A generalized correlation for the critical heat-flux data in the four test liquids is evolved.

Physical principles of heat pipes

Abstract: Heat pipes are used whenever high rates of heat transfer or the control or conversion of heat flows are required. This book covers the physical principles of operation of heat pipes and choice of working fluid related to temperature range. The authors demonstrate how performance is limited by capillary pumping action in the wick together with impedance to liquid and vapor flow between the evaporator and condenser, sonic conditions, entrainment, evaporation and condensation rates.

Three phase absorption systems and methods for refrigeration and heat pump cycles

Abstract: A three phase absorption system containing two or more reactor systems for binding refrigerant in a thermally reversible chemical reaction to absorbent materials within the reactor systems, means for supplying heat to, and removing heat from the reactor systems, means for recovery of at least part of the sensible heat energy from reactors in each of the reactor systems, and means for conveying, expanding, evaporating and condensing refrigerant gas from the reactor systems. A method for providing continuous cooling and/or refrigeration which includes the steps of desorbing refrigerant in a gas phase from an absorbent in a first reactor using a low temperature heat source, transferring the desorbed refrigerant gas to a condensor, expanding the condensed refrigerant to a lower temperature and pressure liquid, evaporating the low temperature liquid with the heat from the cooling and/or refrigerant load, absorbing vapor from the evaporated refrigerant with an absorbent in a second reactor which is being cooled by a cooler, concurrently preparing two other absorption reactors for the same absorbing and desorbing steps by transferring heat between the two other reactors, and heating one and cooling the other of the two reactors at constant volume thereby pressurizing one and depressurizing the other of the two reactors, and cyclically repeating the steps by alternating the desorbing and absorbing steps between the four reactors. A method for providing continuous heating using a heat pump effect to recover heat energy at a low temperature and deliver heat energy to a heat sink at a higher temperature with such heating method comprising the same steps as used in the above cooling method but with the condensing and evaporating steps occurring at relatively lower temperature and with the condensor and cooler providing the heat energy to the heat sink and the evaporator recovering heat energy from a low temperature heat source to accomplish the heat pump effect.

Passive heat transfer means for nuclear reactors

Abstract: An improved passive cooling arrangement is disclosed for maintaining adjacent or related components of a nuclear reactor within specified temperature differences. Specifically, heat pipes are operatively interposed between the components, with the vaporizing section of the heat pipe proximate the hot component operable to cool it and the primary condensing section of the heat pipe proximate the other and cooler component operable to heat it. Each heat pipe further has a secondary condensing section that is located outwardly beyond the reactor confinement and in a secondary heat sink, such as air ambient the containment, that is cooler than the other reactor component. Means such as shrouding normally isolated the secondary condensing section from effective heat transfer with the heat sink, but a sensor responds to overheat conditions of the reactor to open the shrouding, which thereby increases the cooling capacity of the heat pipe. By having many such heat pipes, an emergency passive cooling system is defined that is operative without electrical power.

Thermal Loading of the Cylinder Head of a Spark-Ignition Engine

Abstract: The effects of operating parameters on the steady-state heat flux and surface temperature at several locations on the cylinder head of a single-cylinder spark-ignition engine were investigated. The local heat flux was found to be strongly affected by engine speed and volumetric efficiency. Air-fuel ratio and spark timing had comparatively smaller effects. Coolant temperature, in the range of this study (300-380 K), had no effect on the average heat flux. Both the heat flux and the surface temperature varied considerably with the location of measurement. Except at very rich mixtures, the average heat flux was found to vary as the 0.65 power of the rate of fuel consumption.

Observations on the characteristics of a fluidized bed for the thermal shock testing of brittle ceramics

Abstract: The heat transfer characteristics of a fluidized bed used as a quenching medium for the thermal stress testing of brittle ceramics, were determined by measurements of the thermal shock behaviour of rods of a soda-lime—silica glass. The heat transfer coefficient was found to be strongly dependent on the mean particle size of the powder and air flow rate, and was relatively independent of the position within the bed. The results indicate that the heat transfer coefficient during thermal shock fracture may have a value lower than that obtained under heat transfer conditions which more closely resemble steady state. The heat transfer data inferred from the quenching experiments with the glass gave excellent agreement between calculated and measured values for the thermal shock behaviour for rods of a polycrystalline aluminium oxide. It is concluded that fluidized beds are excellent inert quenching media with variable heat transfer coefficient controlled by particle size and flow rate.