Question

N a counterflow heat exchanger, hot fluid enters at 60c and cold fluid leaves at 30c. Mass flow rate of the hot fluid is 1 kg/s and that of the cold fluid is 2 kg/s. Specific heat of the hot fluid is 10kj/kgk and that of the cold fluid is 5 kj /kgk. The log mean temperature difference (lmtd) for the heat exchanger in c is

Answer 1

Mass flow rate, m˙H=1kgs, and,  m˙c=2kgs

Specific heat, CH = 10 kJ/kgK, and, Cc = 5 kJ/kgK

Heat capacity of hot fluid =m˙H˙cH=1×10=10kJk−s

Heat capacity of cold fluid =m˙c˙cc=5×2=10kJk−s

Since heat capacity is same so LMTD is difference of temperature of fluid at either ends.

LMTD = 60° - 30° = 30°C

Answer 2

Answer:

Liquid water has one of the highest specific heats among common substances, about 4182 J/(K kg) at 20 °C; but that of ice just below 0 °C is only 2093 J/(K kg).