A chemical combination of two or more substances in variable proportions is called
a. a mixture.
b. a compound.
c. an ion.
d. a molecule.
b
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A blood warmer is often used in certain clinical transfusion procedures. While safely storing and preserving blood requires refrigeration, cold blood when used in rapid transfusion procedures could cause clinically dangerous hypothermia in a patient. A new compact and miniature heat exchanger has been proposed that is used “inline” with the transfusion delivery system. It consists of a multi-tube bundle of 5-mm diameter tubes arranged in an equilateral-triangular array with tube centers 7.5 mm apart. Blood flows inside the tubes and is warmed by a heated airstream that is in external cross flow such that the tube surface is maintained at 40°C. The inlet air flow to the tube array is at 70°C with a free stream velocity of 2 m/s, and there are five lateral or transverse rows in the
bundle. Determine the average heat transfer coefficient and pressure drop in the airstream. Also, what is the change in both of these quantities if the tube center-to-center pitch is reduced to 6.0 mm? GIVEN Heated air flowing over an equilateral staggered tube bank Air temperatures Tair,in = 70°C Number of tube rows (N) = 5 Tube diameter (D) = 5 mm= 0.005 m Center to center pitch(S) = 7.5 mm=0.0075 m Free stream velocity (Ua) = 2 m/s Tube surface temperature (Tt) = 40°C FIND The average heat transfer coefficient ( h c) and pressure drop in airstream. Change in average heat transfer coefficient and pressure drop when center to center pitch is reduced to 6 mm. ASSUMPTIONS Steady state The correlation of Equation 6.38 can be applied to a pitch-to-diameter ratio of 1.5 Tube wall temperature is uniform and constant
A current in a long, straight wire produces a magnetic field. The magnetic field lines:
a. go out from the wire to infinity. b. come in from infinity to the wire. c. form circles that pass through the wire. d. form circles that go around the wire.
Two flat rectangular mirrors are set edge to edge and placed perpendicular to a flat nonreflecting surface. The edges of the two mirrors meet at a 30° angle. A light ray that approaches mirror 1 is parallel to mirror 2 . The angle of reflection of that ray from mirror 1 is
a. 0°. b. 30°. c. 60°. d. 90°. e. 120°.
A 4 kilogram block of ice is removed from a freezer where its temperature was maintained at –20 degrees Celsius. How much heat does the ice absorb as it is warmed to –10 degrees? (The specific heat capacity of ice is 2,000 joules per kilogram degree Celsius.)