Question 6.86: Reconsider Prob. 6–85. Using EES (or other) software, invest......
Reconsider Prob. 6-85. Using EES (or other) software, investigate the effect of the inlet temperature of cooling water on the mass flow rate of water. Let the inlet temperature vary from 10 to 40^{\circ} \mathrm{C}, and assume the exit temperature to remain constant. Plot the mass flow rate of water against the inlet temperature, and discuss the results.
Problem 6-85 is reconsidered. The effect of the inlet temperature of cooling water on the mass flow rate of water as the inlet temperature varies from 10^{\circ} \mathrm{C} to 40^{\circ} \mathrm{C} at constant exit temperature) is to be investigated. The mass flow rate of water is to be plotted against the inlet temperature.
Analysis The problem is solved using EES, and the solution is given below.
“Input Data”
{T_w[1]=20 [C]}
T_w[2]=55 [C] “w: water”
m_dot_eg=2 [kg/s] “eg: ethylene glycol”
T_eg[1]=80 [C]
T_eg[2]=40 [C]
C_p_w=4.18 [kJ/kg-K]
C_p_eg=2.56 [kJ/kg-K]
“Conservation of mass for the water: m_dot_w_in=m_dot_w_out=m_dot_w”
“Conservation of mass for the ethylene glycol: m_dot_eg_in=m_dot_eg_out=m_dot_eg”
“Conservation of Energy for steady-flow: neglect changes in KE and PE in each mass steam”
“We assume no heat transfer and no work occur across the control surface.”
E_dot_in – E_dot_out = DELTAE_dot_cv
DELTAE_dot_cv=0 “Steady-flow requirement”
E_dot_in=m_dot_w*h_w[1] + m_dot_eg*h_eg[1]
E_dot_out=m_dot_w*h_w[2] + m_dot_eg*h_eg[2]
Q_exchanged =m_dot_eg*h_eg[1] – m_dot_eg*h_eg[2]
“Property data are given by:”
h_w[1] =C_p_w*T_w[1] “liquid approximation applied for water and ethylene glycol”
h_w[2] =C_p_w*T_w[2]
h_eg[1] =C_p_eg*T_eg[1]
h_eg[2] =C_p_eg*T_eg[2]
