Implemented surface tension for R1234ze(Z) and bib entry

CoolPropBibTeXLibrary.bib

@@ -1037,6 +1037,19 @@
   Timestamp                = {2013.08.05}
 }
 
+@Article{Kondou-IJR-2015,
+  Title                    = {{Surface tension of low GWP refrigerants R1243zf, R1234ze(Z), and R1233zd(E)}},
+  Author                   = {Chieko Kondou and Ryuichi Nagata and Noriko Nii and Shigeru Koyama and Yukihiro Higashi},
+  Journal                  = {Int. J. Refrig.},
+  Year                     = {2015},
+  Pages                    = {80-89},
+  Volume                   = {53},
+
+  Doi                      = {10.1016/j.ijrefrig.2015.01.005},
+  Owner                    = {Belli},
+  Timestamp                = {2015.07.20}
+}
+
 @InProceedings{Kretzschmar-PWS-1990,
   Title                    = {{An Alternative Method for the Numerical Calculation of the Maxwell Criterion in Vapour Pressure Computations}},
   Author                   = {H.-J. Kretzschmar and T. Zschunke and J. Klinger and A. Dittman},

dev/fluids/R1234ze(Z).json

@@ -168,6 +168,17 @@
       "max_abs_error": 1.0220801074081636, 
       "max_abs_error_units": "J/mol/K", 
       "type": "rational_polynomial"
+    }, 
+    "surface_tension": {
+      "BibTeX": "Kondou-IJR-2015", 
+      "Tc": 423.27, 
+      "a": [
+        0.05657
+      ], 
+      "description": "sigma = sum(a_i*(1-T/Tc)^n_i)", 
+      "n": [
+        1.220
+      ]
     }
   }, 
   "CAS": "29118-25-0",