Use of compositions comprising 1,1,1,2,3-pentafluoropropane and optionally Z-1,1,1,4,4,4-hexafluoro-2-butene in power cycles

1. A method for converting heat from a heat source to mechanical energy, comprising:

heating a working fluid comprising from about 41 to 50 weight percent Z-HFO-1336mzz and from about 59 to 50 weight percent HFC-245eb using heat supplied from the heat source; and

expanding the heated working fluid to lower the pressure of the working fluid and generate mechanical energy as the pressure of the working fluid is lowered.

2. The method of claim 1 , wherein the working fluid is compressed prior to heating; and the expanded working fluid is cooled and compressed for repeated cycles.

3. The method of claim 2 wherein heat from a heat source is converted to mechanical energy using a sub-critical cycle comprising:

(a) compressing a liquid working fluid to a pressure below its critical pressure;

(b) heating the compressed liquid working fluid from (a) using heat supplied by the heat source to form vapor working fluid;

(c) expanding the vapor working fluid from (b) to lower the pressure of the working fluid and generate mechanical energy;

(d) cooling the expanded working fluid from (c) to form a cooled liquid working fluid; and

(e) cycling the cooled liquid working fluid from (d) to (a) for compression.

4. The method of claim 2 wherein heat from a heat source is converted to mechanical energy using a trans-critical cycle comprising:

(a) compressing a liquid working fluid above said working fluid's critical pressure;

(b) heating the compressed working fluid from (a) using heat supplied by the heat source;

(c) expanding the heated working fluid from (b) to lower the pressure of the working fluid below its critical pressure and generate mechanical energy;

(d) cooling the expanded working fluid from (c) to form a cooled liquid working fluid; and

(e) cycling the cooled liquid working fluid from (d) to (a) for compression.

5. The method of claim 2 wherein heat from a heat source is converted to mechanical energy using a super-critical cycle comprising:

(a) compressing a working fluid from a pressure above its critical pressure to a higher pressure;

(b) heating the compressed working fluid from (a) using heat supplied by the heat source;

(c) expanding the heated working fluid from (b) to lower the pressure of the working fluid to a pressure above its critical pressure and generate mechanical energy;

(d) cooling the expanded working fluid from (c) to form a cooled working fluid above its critical pressure; and

(e) cycling the cooled liquid working fluid from (d) to (a) for compression.

6. The method of claim 1 wherein the working fluid is a non-flammable composition consisting essentially of HFC-245eb and Z-HFO-1336mzz.

7. A power cycle apparatus containing a working fluid to convert heat to mechanical energy, characterized by:

said apparatus containing a working fluid comprising from about 41 to 50 weight percent Z-HFO-1336mzz and from about 59 to 50 weight percent HFC-245eb.

8. The power cycle apparatus of claim 7 comprising (a) a heat exchange unit; (b) an expander in fluid communication with the heat exchange unit; (c) a working fluid cooling unit in fluid communication with the expander; and (d) a compressor in fluid communication with the working fluid cooling unit, the compressor further being in fluid communication with the heat exchange unit such that the working fluid then repeats flow through components (a), (b), (c) and (d) in a repeating cycle.

9. A working fluid comprising from about 41 to 50 weight percent Z-HFO-1336mzz and from about 59 to 50 weight percent HFC-245eb, which, optionally (i) further comprises E-HFO-1336mzz, or (ii) has a temperature above its critical temperature, or both (i) and (ii).

10. The working fluid of claim 9 consisting essentially of HFC-245eb and Z-HFO-1336mzz above its critical temperature and pressure.

11. A composition suitable for use in organic Rankine apparatus, comprising a working fluid of claim 9 and a lubricant.

12. The composition of claim 11 wherein the working fluid component of the composition consists essentially of HFC-245eb and Z-HFO-1336mzz.

13. The composition of claim 11 wherein the composition has a temperature above the critical temperature of the working fluid and the lubricant is suitable for use at said temperature.

14. A method for raising the maximum feasible evaporating temperature of an existing Rankine cycle system containing a first working fluid comprising:

replacing the first working fluid with a second working fluid comprising from about 41 to 50 weight percent Z-HFO-1336mzz and from about 59 to 50 weight percent HFC-245eb.