Problem 58P

Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the pressure in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapor at the compressor inlet, and the isentropic efficiency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.11 kg/s, determine (a) the mass flow rate of the refrigerant through the upper cycle, (b) the rate of heat removal from the refrigerated space, and (c) the COP of this refrigerator.

Spencer Kociba CHEM 101 Lecture 11/15/16 THERMOCHEMISTRY ● Enthalpy ○ Represented as ΔH ○ Internal energy + pressure*volume ■ We will mostly be concerned with constant pressure. This is where the formula ΔH = ΔE + PΔV comes from ○ ΔH = q (enthalpy=heat gained or lost in the system) ● Properties of Enthalpy (ΔH ) ○ ΔH is directly proportional to mass ○ ΔH for a reverse reaction is equal in magnitude (quantity) but opposite in sign for the forwards reaction ○ Hess’s Law: ΔH is independent of the number of steps involved ■ If Reaction(1) + Reaction(2)=Reaction(3), then ΔH =3ΔH + 1H 2 ● Endothermic reactions ○ Gains heat from sur