To achieve cooling to a lower temperature on an industrial scale, a cascade refrigeration system like the one shown below employs two vapor-compression refrigeration cycles. The low- temperature cycle (B) uses ammonia to remove heat from a cold space at a rate of 0.5 kg/s. Saturated vapor enters the compressor at -40 °C, and exits the condenser as a saturated liquid at 0.5 MPa. Condenser Compressar A Valve Heat Exchanger Valve Compressar Evaperator Heat is released from the low-temperature cycle to the high-temperature cycle using an interconnected heat exchanger. The high-temperature cycle (A) uses refrigerant 134a, with saturated vapor entering its compressor at 0.24 MPa and exiting the condenser as a saturated liquid at 1 MPa. The isentropic efficiency of each compressor is 0.78. Determine the mass flow rate of the refrigerant 134a, and the overall coefficient of performance of the cycle.

A heat pump is required for a single-family 2-story, 3-person, 30 ft x 30 ft x 18 ft (L x W x H), energy- efficient residential house in Philadelphia, PA, for a typical winter season. Assuming a comfortable indoor temperature is 70 °F and on a cold winter day the outdoor temperature is 10 °F. Exercise #1: Calculate total heat loss from a house in Philadelphia on a cold winter day. Assume 40% of the wall area is windows with U-value of 0.81 BTU/hr-ft²-°F. The remaining 60% of the walls has a U-value of 0.2 BTU/hr-ft²-°F. The roof has a U value of 0.05 BTU/hr-ft?-°F and the floor U-value is 0.41 BTU/hr-ft²-°F. For simplicity assume that the ground temperature is the same as the air temperature. [However, in your project design calculations you should refine this assumption.] Assume 0.5 air changes per hour (ACH) due to natural ventilation, such as leakage through windows, etc. Neglect any radiative heat loss/grain from the house. Exercise #2: Determine the watts of electricity needed by…

a cylinder-plunger contains 2.4x10 ^ -2 kg of air that is subjected to a cycle: Process 1-2: Isochoric process (0.02m ^ 3) from .1MPa to 0.42MPa Process 2-3: isobaric cooling Process 3-1: Isothermal heating Calculate Q and W for each stage

2 A wire of diameter D = 2 mm and uniform temperature T has an electrical resistance of 0.01 N/m and a current flow of 20 A. (a) What is the rate at which heat is dissipated per unit length of wire? What is the heat dissipation per unit volume within the wire? (b) If the wire is not insulated and is in ambient air and large surroundings for which T = Tsur = 20°C, what is the temperature T of the wire? The wire has an emissivity of 0.3, and the coefficient associated with heat transfer by natural convection may be approximated by an expression of the form, h = C[(T-T)/D]¹/4, where C = 1.25 W/m7/4.K5/4 (c) If the wire is coated with plastic insulation of 2-mm thickness and a thermal conductivity of 0.25 W/m.K, what are the inner and outer surface temperatures of the insulation? The insulation has an emissivity of 0.9, and the convection coefficient is given by the expression of part (b). Explore the effect of the insu- lation thickness on the surface temperatures. Note: 1. The metal wire…