Hot and cold fluids enter a parallel flow double tube heat exchanger at 100°C and 15°C, respectively. The heat capacity rates of hot and cold fluids are Ch = 2000 W/K and Cc = 1200 W/K, respectively. If the outlet temperature of the cold fluid is 45°C, the log mean temperature difference (LMTD) of the heat exchanger is ________ K (round off to two decimal places).

Answer :

57.71

C_h = 2000 W/K

C_c = 1200 W/K

By energy equation, C_h (ΔT_h ) = C_c (ΔT_c )

                                        2000 (100 – T_ho) = 1200 (30)

                                                                T_ho = 82°C

                                                                LMTD = {(100 - 15) - (82 - 45)}/ ln{(100-15)/(82-45)} = 57.71°C

                                                         Since LMTD is temperature difference so the answer will be 57.71 K