Effect of temperature difference

Figure 9.53. Effect of temperature difference on heat flux and heat transfer coefficient to water boiling at...

Figure 9.54. Effect of temperature difference on the heat transfer coefficient for boiling liquids (Cryder and...

Figure 6.8 illustrates nondimensional solutions for a fixed Reynolds number of Re = 100, but for varying values of AT, temperature difference between the inlet and the stagnation surface. The solutions depend on the temperature difference, but the dependence is relatively weak considering large temperature differences of up to 900 K. The temperature-difference influence is principally through the convective terms, which involve p and u. Thus as the Reynolds number increases, the effect of temperature difference will increase. 

The effect of temperature difference on the segregation coefficient was determined experimentally. Although the segregation coefficient data vary with concentration, the effect is small in this type of system and was considered to have no significance in the economic study. Tubes ranging in size from 7/16 to 1 inch containing salt water were immersed in a constant temperature bath and the segregation coefficient was determined. 

Hence, the Prandtl number is a measure of the ratio of the rate of spread of die effects of momentum changes in the flow to the rate of spread of the effects of temperature differences, i.e., of die effects of heat transfer in the flow. 

The effect of temperature differences is illustrated in Figure 4 on a soy oil sample. There was no measurable change for any sample run between ambient and 100 C temperatures. However, above 100 C some reactions began to occur. For the majority of samples, 100 C was sufficient to prevent any carryover. For samples containing large amounts of volatile components that might have carryover at 100 C, higher temperatures can be used for rapid cleanup. 

To further investigate the catalyst s potential for multiple applications and the effect of temperature, different runs with the cat./oil ratios shown in Figure 1 were performed at one temperature, followed by the same set of experiments at a different temperature. This is illustrated by the three catalysts studied in Figure 2. No activation decay was observed for MCM-41 and the equilibrium catalyst, which was confirmed by a control experiment at cat./oil ratio 3 and 482 °C after 16 runs. 

Operating Pressure and Temperature. Fluidized beds generally operate more smoothly with increasing absolute pressure, so that elevated pressures do not present a problem from a fluidization point of view. Many fluidized bed reactors also operate at high temperatures. The effects of temperature differ from system to system, probably because temperature affects particle properties (e.g., surface hardness and stickiness) in addition to causing well-characterized changes in gas properties. The effects of pressure and temperature have been reviewed by Yates. 

Figure 2.2 Effects of temperature differences between the object to be weighed and the balance in (a) the object is at a higher temperature than its surroundings within the balance, and the resulting convection currents of air circulate so as to exert an upward force on the object, i.e., lead to a mass reading that is too low in (b) the object is at a lower temperature resulting in the opposite effect.

FIGURE 3.45 Effect of temperature differences between the ground and the air on the propagation of sound. (Source Davis, D. and Davis, C. 1987. Sound System Engineering, 2nd ed., p. 151. Howard Sams.)... 

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