2. A cylinder/piston arrangement contains water at 105ºC, 85% quality, with a volume of 1 L. The system is heated, causing the piston to rise and encounter a linear spring. At this point the volume is 1.5 L, the piston diameter is 150 mm, and the spring constant is 100 N/mm. The heating continues, so the piston compresses the spring. What is the cylinder temperature when the pressure reaches 200 kPa?

Respuesta :

Explanation:

The given data is as follows.

      [tex]T_{1} = 105^{o}C[/tex],     x = 0.85

       [tex]V_{1}[/tex] = 1 L = 0.001 [tex]m^{3}[/tex]   (as 1 L = 0.1 [tex]m^{3}[/tex])  

      [tex]V_{2}[/tex] = 1.5 L = 0.0015 [tex]m^{3}[/tex],

      [tex]d_{p}[/tex] = 150 mm = 0.15 m,     K = 100 N/mm = 100 kN/m

      [tex]P_{3}[/tex] = 200 kPa

According to the table,

     [tex]P_{1}[/tex] = 120.8 kPa,    [tex]v_{f}[/tex] = 0.001047 m/kg

    [tex]v_{fg} = 1.41831 [tex]m^{3}/kg[/tex]

So, we have

         [tex]v_{1} = v_{f} + xv_{fg}[/tex]

                    = 0.001047 + 0.85 \times (1.41831 m^{3}/kg)[/tex]    

                    = 1.2066 [tex]m^{3}/kg[/tex]

Now, we will calculate [tex]m_{1}[/tex] as follows.

        [tex]m_{1} = \frac{V_{1}}{v_{1}}[/tex]

                   = [tex]\frac{0.001}{1.2066}[/tex]

                   = 0.000828 kg

Now,  Area = [tex]\frac{\pi}{4} dp^{2}[/tex]

                   = [tex]\frac{\pi}{4} (0.15)^{2}[/tex]

                   = 0.0176 [tex]m^{2}[/tex]

As we have,

            [tex]v_{2} = v_{1} \times (\frac{V_{2}}{v_{1}})[/tex]

                       = [tex]1.2066 \times \frac{0.0015}{0.001}[/tex]

                       = 1.8099 [tex]m^{3}/kg[/tex]

From table, [tex]T_{2} = 203.5^{o}C[/tex] for [tex]P_{2}[/tex] = 120.8 kPa and [tex]v_{2} = 1.8099 m^{3}/kg[/tex].

       [tex]P_{3} = P_{2} + (\frac{K}{A^{2}})m (v_{3} - v_{2})[/tex]

    200 = [tex]120.8 + (\frac{100}{(0.0176)^{2}})(0.000828)(v_{3} - 1.8099)[/tex]

       [tex]v_{3} = 2.106 m^{3}/kg[/tex]

Therefore, from the table

               T = [tex]600^{o}C[/tex],      v = 2.01297 [tex]m^{3}/kg[/tex]

               T = [tex]700^{o}C[/tex],     v = 2.2443[tex]m^{3}/kg[/tex]

     [tex]T_{3} = 600 + \frac{2.106 - 2.01297}{2.2443 - 2.01297} (700 - 600)[/tex]

                = [tex]640.2^{o}C[/tex]

Thus, we can conclude that the cylinder temperature when the pressure reaches 200 kPa is [tex]640.2^{o}C[/tex].