Question

Fluid milk is being heated from 60C to 115C at a rate of 500 kg/hr using 120C steam as a heating medium. The heat exchanger being utilized has an efficiency of 85% and the steam quality will be 90%. The system is designed to allow condensate to be released at 115C. What is the required mass flow rate of the steam?

Table A.4.2 (Continued Specific volume (m/kg) Enthalpy (kJ/kg) Entropy (kJfIkg C]) Vapor Saturated vapor Temperature pressure Saturated Liquid Saturated Liquid 0.0010146 0.0010172 0 0010199 0.0010228 0.0010259 0.0010291 0.0010325 0.0010360 0.0010397 0.0010435 00010475 00010516 0.0010559 0.0010603 0.0010649 0.3010697 0.0010746 0.0010797 0.0010850 0.0010905 0.0010961 0.001 1020 0.001 1080 0.0011143 0.0011207 0.0011274 vapor u: 9.568 230.23 0.7679 60 2618.3 7.8310 7.7553 0.8935 70 2626.8 0.9549 313.93 334.91 355.90 376.92 30 1.0753 76122 90 1.1925 7.4791 7.4159 7.3549 7.2958 7.2387 7.1833 2691.5 198.53 232.1 7.0775 7.0269 6.9777 2720.5 1 6870 0.5089 610.63 2740.3 2746.5 2752.4 2758.1 2763.5 2768.7 1 7907 6.8833 6.8379 653.84 675.55 1.9427 6.7078 0 2428 2.0419 6.6256 0.19405 763.22 6.5857 0.15654 2786.4 2 2359 0.0011565 0.0011992 00012512 0.0013168 0.0010436 200 852.45 2.5639 2803.3 2801.5 2785.0 2749.0 1085.36 6.0730 0.05013 0.03279 0.02167 1210.07 3.0208 300 3.2534

Answer 1

Given Data Inlet temperature of the milk, T_m_1 = 60 degree C Exit temperature of milk, T_m_2 = 115 degree C Mass flow rate milk, m^dot_m = 500 kg/hr Efficiency of heat exchange, eta = 85% Quality of sream, x = 90% steam temperature, T_c_1 = 120 degree C Tempetature for condensate release, T_c_2 = 115 degree C Specific heat of water, C_p = 4.187 kJ/kg . K Specific heat of milk, C^1_p = kJ/kg . K convert the mass flow rate of milk into kg/s m^dot_m = (500 kg/hr) [1 hr/3600 s] = 0.139kg/s Write the expression for specific enthalpy of steam at inlet h_c_1 = h_1 + x(h_1 + h_2) Substitute the given values from the table for 120 degree C h_c_1 = 5.3071 + 0.90(2706.3-503.71) = 2486.04kJ/kg Write the amount of heat transfer by steam q_s = (h_c_1 - h_1) + C_p(T_c_1 - T_c_2) Substitute the given values in the above expression q_s = (2486.04 - 503.71) + 4