Question

4. Refrigeration and air conditioning is quite useful, but it is, in effect, a way to move heat from a low temperature to a high temperature. Is this possible, given the second law? Answer the following questions below, for R-134a (a common refrigerant), and then state whether you believe refrigeration violates the second law, and why (or why not) a. R-134a arrives to the inside of the refrigerator that you are trying to keep cooled to T- 4°C. The air and food inside the refrigerator is gaining heat from the outside room temperature at a rate ofdin-40 k/s. The refrigerant is at Ti = 4°C with a specific volume of v0.02581when it enters. If it has a mass flow rate of - 0.342 9 what is the temperature, T2. of the R-134a at the exit? Will the inside of the refrigerator kg still be able to be kept at 4°C, or will it heat up (much)? Remember that heat will always go from a hot temperature to a cold temperature After the exit conditions from part (a) (you may need to solve for more properties) the R- 134a is compressed to Ps 12 bar (1.2 MPa) and T3 60°C. How much power is required for this process? Now that the temperature of the refrigerant is warmer than the room temperature (a common room temperature is 20 °C), the refrigerant will be able to reject heat to the air If it experiences isothermal condensation until it's a saturated liquid (state 4), what is the rate of heat rejection? Given the conditions at the end of the condensation process, the fluid finally undergoes a throttling process to arive at the initial conditions. Is this refrigeration cycle possible? How does the refrigerant temperature change from the high temperature to the low temperature? Does violate the first or second laws of thermodynamics at any point in time? b. c. d. Given that the coefficient of performance (COP) of desired output required input Wnetin e. refrigeration cycle is COP = u, where Q is the rate of heat removed from the low temperature side of the cycle, and Wnetin is the power supplied to the refrigerator, what is the COP for this refrigerator?

Answer 1

4.

Yes, it is possible by second law of thermodynamics. Because second law of thermodynamics given by clausius states that heat can be removed from a low temperature body to a high temperature body by doing external work. Compressors generally provide such work.

a)

At T= 4 C

and specific volume v= 0.02581 cubic meter.

ち S 、 Past ) 12.box-t ㄧ , z 3 60 QIVEN 4 1: に and Specific volume匕 :0.02581 k3go using R-134a, Table fpaspexties ( ) Tabie A-I ゾ ニ0.0 6 0 328. We knou Spea ic Velume using 0.02581:0.0007723 +JL (0,060338-o-oo7-22) Agaism Fsom sasme table h4g Thus entholpy at exit 57.2S+ 0.421 95.1) 139.36 K/

Re at Conatant temperature rattot is to be maimtaumed Thuus teat gaim fsom Outside goum fs ニ. Heat Removed by Repgeuarych exato し10: O.342/h1-139.36) Now latent Reot is semoved dweim this stag e "repea ex atat uilt also scmmim semo

b) Agam Using table R134a Subes heat losk done by Compsexos -0342(290-256. 223) c) low Givem thet Conditiong axe sother mal aiul it us a saturated iquid stute [in blot) satucated iguid AgcunFsom Ate.am oble m (h-h - (.342) (290 -139.36