College

A window air conditioner uses 1074 W of electricity and has a coefficient of performance of 3.49. Assume that all of the electrical energy is transformed into work done by the air conditioner to cool a room with dimensions of 7 m × 7 m × 3 m. The air inside this room initially has the same temperature as the air outside (316 K), and the air conditioner will attempt to cool the room to 295 K. For estimation purposes, assume that the air in this room will be cooled at constant volume, the specific heat of air at constant volume is 720 J/kg-K, and the density of air is 1.2 kg/m³.

1. How much energy must be transferred out of this room to decrease the temperature of the air from 316 K to 295 K? ___________

2. How much work will be done by the air conditioner during the process of cooling the room? ___________

3. How much time in minutes will it take for the room to cool using this air conditioner? ___________

4. How much time in minutes would the cooling process take if we used an air conditioner that uses a Carnot cycle operating between 316 K and 295 K? ___________

Answer :

The Energy to be transferred out is given as 2,676,096 J

How to solve

Volume of room = 7m * 7m * 3m = 147m³

Mass of air = 147m³ * 1.2kg/m³ = 176.4kg

Energy = mass * specific heat * temperature change = 176.4kg * 720J/(kg*K) * (316K - 295K) = 2,676,096 J

Work done by the air conditioner:

Work = Energy / Coefficient of Performance = 2,676,096J / 3.49 = 767,207 J

Time for the air conditioner:

Power = Work / Time

Time = Work / Power = 767,207J / 1,074W = 715 seconds or 11.9 minutes

Time using Carnot cycle air conditioner:

Carnot efficiency = 1 - (295K/316K) = 0.0664

Work = 2,676,096J / 0.0664 = 40,305,542 J

Time = 40,305,542J / 1,074W = 37,528 seconds or 625.5 minutes

Read more about Energy here:

https://brainly.com/question/8101588

#SPJ4