If the saturation pressure of water is increased, the relative values shown on the illustrated graph will change. According to pertinent information found in the steam tables of SG-0004, this will result in __________. See illustration SG-0001. See illustration SG-0004.
• Line 4 on SG-0001 represents the latent heat of vaporization at the saturation temperature (horizontal line at constant temperature). • From steam tables (SG-0004), as saturation pressure increases, the saturation temperature rises but the latent heat (h_fg) changes in a specific way. • On this T–BTU/lb diagram, the length of a horizontal line shows a change in heat content, while its height shows the associated change in temperature.
• When you look up higher saturation pressures in the steam tables, what happens to the numerical value of latent heat of vaporization h_fg compared with atmospheric pressure? • On the diagram, does line 4 show any temperature change during vaporization, or only a heat-input change at constant temperature? How does that affect its height when pressure changes? • If the saturation temperature shifts upward on the graph, does that alter the vertical size of line 4 itself, or only its position on the temperature axis?
• Verify in SG-0004 how h_fg (latent heat) changes as pressure increases (compare a low pressure and a higher pressure). • Confirm from the diagram that line 4 is drawn at constant temperature, meaning its inherent temperature difference is zero. • Make sure you distinguish between a line’s length (BTU per lb change) and its height (temperature change); the question is about how each of these properties changes, not where the line is located on the graph.
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