This question relates to thermodynamics. I have asked this question already toda

Question

This question relates to thermodynamics.

I have asked this question already today, however I did not understand they reply when thay answered the question.

My question is as follows.

When calculating the evaporation rate of water at atmospheric pressure 101.42 kPa. Do I use the value for Ufg or Hfg? I am having trouble understanding when to use Ufg compared to Hfg. Could you pleaseclarify this for me.

TABLE A-4 Saturated water-Temperature table Specific volume, m3/kg Internal energy kJ/kg Enthalpy kJ/kg Entropy kJ/kg Sat Sat. Sat. Sat. liquid, Evap, vapor, iquid, Evap vapor, iquid, Evap., vapor, Sat. Sat. Sat. vapor Temp., press. liquid, Sfg 0.000 2374.9 2374.9 0.001 2500.9 2500.9 0.0000 9.1556 9.1556 21.019 2360.8 2381.8 21.020 2489.1 2510.1 0.0763 8.9487 9.0249 42.020 2346.6 2388.7 42.022 2477.2 2519.2 0.1511 8.7488 8.8999 62.980 2332.5 2395.5 62.982 2465.4 2528.3 0.2245 8.5559 8.7803 83.913 2318.4 2402.3 83.915 2453.5 2537.4 0.2965 8.3696 8.6661 0.01 0.6117 0.001000 206.00 10 15 20 0.8725 0.001000 147.03 1.2281 0.001000 106.32 1.7057 0.001001 77.885 2.3392 0.001002 57.762 25 30 35 40 45 3.1698 0.001003 43.340 104.83 2304.3 2409.1 104.83 2441.7 2546.5 0.3672 8.1895 8.5567 4.2469 0.001004 32.879 125.73 2290.2 2415.9 125.74 2429.8 2555.6 0.4368 8.0152 8.4520 5.6291 0.001006 25.205 146.63 2276.0 2422.7 146.64 2417.9 2564.6 0.5051 7.8466 8.3517 167.53 2261.9 2429.4 167.53 2406.0 2573.5 0.5724 7.6832 8.2556 9.5953 0.001010 15.251 188.43 2247.7 2436.1 188.44 2394.0 2582.4 0.6386 7.5247 8.1633 7.3851 0.001008 19.515 12.352 0.001012 12.026 209.33 2233.4 2442.7 209.34 2382.0 2591.3 0.7038 7.3710 8.0748 15.763 0.001015 9.5639 230.24 2219.1 2449.3 230.26 2369.8 2600.1 0.7680 7.2218 7.9898 19.947 0.001017 7.6670 251.16 2204.7 2455.9 251.18 2357.7 2608.8 0.8313 7.0769 7.9082 25.043 0.001020 6.1935 272.09 2190.3 2462.4 272.12 2345.4 2617.5 0.8937 6.9360 7.8296 31.202 0.001023 5.0396 293.04 2175.8 2468.9 293.07 2333.0 2626.1 0.9551 6.7989 7.7540 50 60 65 70 38.597 0.001026 4.129 313.99 2161.3 2475.3 314.03 2320.6 2634.6 1.0158 6.6655 7.6812 47.416 0.001029 3.4053 334.97 2146.6 2481.6 335.02 2308.0 2643.0 1.0756 6.5355 7.6111 57.868 0.001032 2.8261 355.96 2131.9 2487.8 356.02 2295.3 2651.4 1.1346 6.4089 7.5435 70.183 0.001036 2.3593 376.97 2117.0 2494.0 377.04 2282.5 2659.6 1.1929 6.2853 7.4782 84.609 0.001040 1.9808 398.00 2102.0 2500.1 398.09 2269.6 2667.6 1.2504 6.1647 7.4151 75 85 90 95 100 101.42 0.001043 1.6720 419.06 2087.0 2506.0 419.17 2256.4 2675.6 1.3072 6.0470 7.3542 105 120.90 0.001047 1.4186 440.15 2071.8 2511.9 440.28 2243.1 2683.4 1.3634 5.9319 7.2952 110 143.38 0.001052 2094 461.27 2056.4 2517.7 461.422229.7 2691. 1.4188 5.8193 7.2382 115 169.18 0.001056 .0360 482.42 2040.9 2523.3 482.59 2216.0 2698.6 1.4737 5.7092 7.1829 120 198.67 0.001060 0.89133 503.60 2025.3 2528.9 503.8 2202.1 2706.0 1.5279 5.6013 7.1292 125 232.23 0.001065 0.77012 524.83 2009.5 2534.3 525.07 2188.1 2713.1 1.5816 5.4956 7.0771 130 270.28 0.001070 0.66808 546.10 1993.4 2539.5 546.38 2173.7 2720.1 1.6346 5.3919 7.0265 135 313.22 0.001075 0.58179 567.4 1977.3 2544.7 567.75 2159.1 2726.9 1.6872 5.2901 6.9773 140 361.53 0.001080 0.50850 588.77 1960.9 2549.6 589.16 2144.3 2733.5 1.7392 5.1901 6.9294 145 415.68 0.001085 0.44600 610.19 1944.2 2554.4 610.64 2129.2 2739.8 1.7908 5.0919 6.8827 150 476.16 0.00109 0.39248 631.66 1927.4 25591 632.18 2113.8 2745.9 1.8418 4.9953 6.8371 155 543.49 0.001096 0.34648 653.19 1910.3 2563.5 653.79 2098.0 2751.8 1.8924 4.9002 6.7927 160 618.23 0.001102 0.30680 674.79 1893.0 2567.8 675.47 2082.0 2757.5 1.9426 4.8066 6.7492 165 700.93 0.001108 0.27244 696.46 1875.4 2571.9 697.24 2065.6 2762.8 1.9923 4.7143 6.7067 170 792.18 0.001114 0.24260 718.20 1857.5 2575.7 719.08 2048.8 2767.9 2.0417 4.6233 6.6650 180 1002.8 185 1123.5 190 1255.2 195 1398.8 200 1554.9 175 892.60 0.001121 0.21659 740.02 1839.4 2579.4 741.02 2031.7 2772.7 2.0906 4.5335 6.6242 0.001127 0.19384 761.92 1820.9 2582.8 763.05 2014.2 2777.2 2.1392 4.4448 6.5841 0.001134 0.17390 783.91 1802.1 2586.0 785.19 1996.2 2781.4 2.1875 4.3572 6.5447 0.001141 0.15636 806.00 1783.0 2589.0 807.43 1977.9 2785.3 2.2355 4.2705 6.5059 0.001149 0.14089 828.18 1763.6 2591.7 829.78 1959.0 2788.8 2.283 4.1847 6.4678 0.001157 0.12721 850.46 1743.7 2594.2 852.26 1939.8 2792.0 2.3305 4.0997 6.4302

Explanation / Answer

Enthalpy refers to the sum of internal energy and the product of its pressure volume that is the work done on it to change its state (pressure and volume). since evaporation involves both the change in internal energy and change of state you should use the values enthalpy (Hfg).

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