Arrhythmias during halothane anaesthesia II: the influence of atropine

The effect of i.v. atropine premedication on cardiac rhythm was studied in healthy adult patients during thiopental-N2O/O2-halothane anesthesia without intubation. A higher incidnece of arrhythmias was seen in younger patients in close relation to administration of atropine, but the overall incidence during anesthesia was identical in atropine groups and the control groups. The most common arrhythmias were supraventricular ectopies. None of the ECG irregularities led to serious arrhythmias. No consistent changes in blood pressure were observed as the result of arrhythmias or changes in heart rate. It is concluded that atropine should be reserved for situations where severe bradycardia and hypotension occur, or can be expected to occur, and not given automatically, since cardioacceleration which is inherent in its action may be injurious to patients with limited cardiac reserve.     

A NEW TOOL FOR NUCLEATE BOILING RESEARCH

A new tool for the study of nucleate boiling heat transfer has been developed. Photographic etching was shown to be effective in the manufacture of copper lest surfaces containing precise arrays of artificial pits, with densities as high as 2742 pits/cm².

The pits were shallow segments of spheres, with depth: diameter ratios on the order of 0.1. Pit diameters were on the order of 0.003 cm. Data showed that the pits significantly affected the characteristic boiling curves and critical fluxes for the surfaces studied while boiling Freon 113 at one atmosphere pressure.

Photoetching can be used in the future to produce a wide variety of test surface textures or site arrays. Careful control of such surface conditions may well lead to a better understanding of the nucleate boiling phenomena.     

EFFECT OF CONTAMINANTS ON CRITICAL HEAT FLUX AT LOW PRESSURES

Critical heat flux (CHF) tests were performed to evaluate the effect of dissolved, nonreactive contaminants on low-pressure industrial boilers. These tests were conducted on a 2.38-inch (60.5 mm) I.D. vertical smooth bore tube with nonuniform circumferential heating at pressures between 100 and 500 psia (0.69 and 3.45 MPa). Tests were performed under two water chemistry conditions: clean (less than 1.6 ppm total dissolved solids) and contaminated (greater than 2000 ppm TDS). With all other operating parameters held constant, the following effects of contamination on the steam quality (X) at CHF were determined at the pressures indicated:

At 100 psia (0.69 MPa) X_clean < X_cont

At 300 psia (2.1 MPa) X_clean?X_cont

At 500 psia (3.5 MPa) X_clean > X_cont

The effect of contamination on CHF was found to be a function of pressure, initial contaminant concentration, and the relative steam quality at which CHF conditions occur. These results are compared to data available in the open literature where X_clean is always greater than X_cont. A method for correlating these data is also illustrated.     

A GENERALIZED BLASIUS EQUATION FOR POWER LAW FLUIDS

Making use of a generalized turbulent velocity distribution for power law fluids, a Blasius type equation was derived which explicitly relates the friction factor to a generalized Reynolds number in fully developed pipe flow. Comparison of the equation with experimental data shows an agreement of approximately ± 8% A modification of the equation to account for geometry appears to allow its application to non-circular duct flow.