Question

I need help with 84 and 87

84. Water at 29°C flows through the inner pipe of a counterflow double-pipe heat exchangers shown in the figure. Hot oil at 204°C enters the annular space between the inner and outer pipes at a flow rate of 2.25 kg/s. The following physical data are known: Property Specific heat, kJ/(kg-K) Viscosity, kg/(ms) Density, kg/m3 Water 4.186 5.06 x 10 4 986.7 Oil 3.5 6.3 x 10-3 815.3 H20 OUT 79°C OIL IN 204°C H2O IN 29°C OIL OUT 79°C The mass flow rate of the water (kg/s) is most nearly OOOO 2.25 4.70 6.58 19.7 in op 8 = 9867 kg/m Q- mc 4T

Answer 1

Sol (84) x Tc2= 79°C Th790 Specific heat of water co= 4.186 KI/kg k Specific heat of oil co = 3.5 kJ/kg.k - mass flow rate of oil (mg) = 2.25 kg/ mass flow rate of water (rw) = ? for the given heat exchanges applying Energy Balance mox cox (Thy. The) = miw XC w x (Tcz-TC) 2.258 3.5 (204-79) = mw x 4.106 99-29 1 984 375 = wiw X 209.3 mw = 4.70317 kg/s Hence Option (B)- 4.70 is correct which is the mass flow rate of water in kyls.