0.1.62 release

docs/tutorial.rst

@@ -856,7 +856,81 @@ V=3 m/s, Di=0.05, roughness 0.01 mm):
 >>> dP_from_K(K, rho=1000, V=3)
 37920.51140146369
 
-There are five entrance loss coefficient methods:
 
->>> entrance_sharp() # sharp entrances
-0.57
+Electric motor sizing
+---------------------
+Motors are available in standard sizes, mostly as designated by the
+National Electrical Manufacturers Association (NEMA). To easily determine what
+the power of a motor will actually be once purchased, motor_round_size implements
+rounding up of a motor power to the nearest size. NEMA standard motors are
+specified in terms of horsepower.
+
+>>> motor_round_size(1E5) # 100 kW motor
+111854.98073734052 # 11.8% larger than desired
+>>> from scipy.constants import hp
+>>> motor_round_size(1E5)/hp # convert to hp
+150.0
+
+Motors are designed to generate a certain amount of power, but they themselves are 
+not 100% efficient at doing this and require more power due to efficiency losses.
+Many minimum values for motor efficiency are standardized. The Canadian standard
+for this is implemented in fluids as CSA_motor_efficiency.
+
+>>> CSA_motor_efficiency(P=5*hp)
+0.855
+
+Most motors are not enclosed (the default assumption), but those that are closed
+are more efficient. 
+
+>>> CSA_motor_efficiency(P=5*hp, closed=True)
+0.875
+
+The number of poles in a motor also affects its efficiency:
+
+>>> CSA_motor_efficiency(P=5*hp, poles=6)
+0.875
+
+There is also a schedule of higher efficiency values standardized as well,
+normally available at somewhat higher cost:
+
+>>> CSA_motor_efficiency(P=5*hp, closed=True, poles=6, high_efficiency=True)
+0.895
+
+A motor will spin at more or less its design frequency, depending on its type.
+However, if it does not meet sufficient resistance, it will not be using its
+design power. This is good and bad - less power is used, but as a motor 
+drops under 50% of its design power, its efficiency becomes terrible. A function
+has been written based on generic performance curves to estimate the underloaded
+efficiency of a motor. Just how bad efficiency drops off depends on the design
+power of a motor - higher power motors do better operating at low loads than 
+small motors.
+
+>>> motor_efficiency_underloaded(P=1E3, load=.9)
+1
+>>> motor_efficiency_underloaded(P=1E3, load=.2)
+0.6639347559654663
+
+This needs to be applied on top of the normal motor efficiency; for example,
+that 1 kW motor at 20% load would have a net efficiency of:
+
+>>> motor_efficiency_underloaded(P=1E3, load=.2)*CSA_motor_efficiency(P=1E3)
+0.5329404286134798
+
+
+Many motors have Variable Frequency Drives (VFDs) which allow them to vary the
+speed of their rotation. The VFD is another source of inefficiency, but by allowing
+the pump or other piece of equipment to vary its speed, a system may be designed to
+be less energy intensive. For example, rather than running a pump at a certain
+high frequency and controlling the flow with a large control valve, the flow 
+rate can be controlled with the VFD directly.
+
+The efficiency of a VFD depends on the maximum power it needs to be able to
+generate, and the power it is actually generating at an instant (load).
+A table of typical modern VFD efficiencies is implemented in fluids as
+VFD_efficiency.
+
+>>> VFD_efficiency(1E5) # 100 kW
+0.97
+>>> VFD_efficiency(5E3, load=.2) # 5 kW, 20% load
+0.8562
+

fluids/__init__.py

@@ -93,4 +93,4 @@
 __all__.extend(separator.__all__)
 
 
-__version__ = '0.1.61'
+__version__ = '0.1.62'

fluids/fittings.py

@@ -120,7 +120,7 @@ def entrance_angled(angle):
     Parameters
     ----------
     angle : float
-        Angle of inclination, [degrees]
+        Angle of inclination (90=straight, 0=parallel to pipe wall) [degrees]
 
     Returns
     -------
@@ -130,7 +130,7 @@ def entrance_angled(angle):
     Notes
     -----
     Not reliable for angles under 20 degrees.
-    Loss coefficient is the same for a upward or downward angle.
+    Loss coefficient is the same for an upward or downward angled inlet.
 
     Examples
     --------
@@ -155,7 +155,7 @@ def entrance_rounded(Di, rc):
 
         \lambda = 1 + 0.622\left(1 - 0.30\sqrt{\frac{r}{d}}
         - 0.70\frac{r}{d}\right)^4
-
+        
     Parameters
     ----------
     Di : float
@@ -170,8 +170,8 @@ def entrance_rounded(Di, rc):
 
     Notes
     -----
-    Applies for r/D < 1.
-    For generously rounded entrances (r/D ~= 1):  K = 0.03
+    For generously rounded entrance (rc/Di >= 1), the loss coefficient converges
+    to 0.03.
 
     Examples
     --------
@@ -183,12 +183,14 @@ def entrance_rounded(Di, rc):
     .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
        and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.
     '''
-    lbd = 1 + 0.622*(1 - 0.30*(rc/Di)**0.5 - 0.70*(rc/Di))**4
-    return 0.0696*(1 - 0.569*rc/Di)*lbd**2 + (lbd-1)**2
+    if rc/Di > 1:
+        return 0.03
+    lbd = 1. + 0.622*(1. - 0.30*(rc/Di)**0.5 - 0.70*(rc/Di))**4
+    return 0.0696*(1. - 0.569*rc/Di)*lbd**2 + (lbd - 1.)**2
 
 
 def entrance_beveled(Di, l, angle):
-    r'''Returns loss coefficient for a beveled entrance to a pipe
+    r'''Returns loss coefficient for a beveled or chamfered entrance to a pipe
     flush with the wall of a reservoir, as shown in [1]_.
 
     .. math::
@@ -205,9 +207,9 @@ def entrance_beveled(Di, l, angle):
     Di : float
         Inside diameter of pipe, [m]
     l : float
-        Length of bevel, [m]
+        Length of bevel measured parallel to the pipe length, [m]
     angle : float
-        Angle of bevel, [degrees]
+        Angle of bevel with respect to the pipe length, [degrees]
 
     Returns
     -------
@@ -229,9 +231,9 @@ def entrance_beveled(Di, l, angle):
     .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
        and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.
     '''
-    Cb = (1-angle/90.)*(angle/90.)**(1./(1 +l/Di ))
-    lbd = 1 + 0.622*(1 - 1.5*Cb*(l/Di)**((1-(l/Di)**0.25)/2.))
-    return 0.0696*(1-Cb*l/Di)*lbd**2 + (lbd-1)**2
+    Cb = (1-angle/90.)*(angle/90.)**(1./(1 + l/Di ))
+    lbd = 1 + 0.622*(1 - 1.5*Cb*(l/Di)**((1 - (l/Di)**0.25)/2.))
+    return 0.0696*(1 - Cb*l/Di)*lbd**2 + (lbd - 1.)**2
 
 
 ### Exits

fluids/packed_tower.py

@@ -248,7 +248,7 @@ def separation_demister_ElDessouky(vs, voidage, d_wire, d_drop):
     was used in the conversion.
     
     In [1]_, V ranged from 0.98-7.5 m/s, rho from 80.317-208.16 kg/m^3, depth 
-    from 100 to 200 mm, wire diameter of 0.2mm to 0.32 mm, and particle 
+    from 100 to 200 mm, wire diameter of 0.2 mm to 0.32 mm, and particle 
     diameter from 1 to 5 mm.
     
     Examples
@@ -614,7 +614,7 @@ def to_zero(inputs):
 
 
 
-def Robbins(Fpd=24, L=None, G=None, rhol=None, rhog=None, mul=None, H=1, A=None):
+def Robbins(L, G, rhol, rhog, mul, H=1, A=None, Fpd=24):
     r'''Calculates pressure drop across a packed column, using the Robbins
     equation.
 

fluids/pump.py

@@ -168,13 +168,15 @@ def VFD_efficiency(P, load=1):
     Table extends down to 3 hp and up to 400 hp; values outside these limits
     are rounded to the nearest known value. Values between standardized sizes
     are interpolated linearly. Load values extend down to 0.016.
+    
+    The table used is for Pulse Width Modulation (PWM) VFDs.
 
     Examples
     --------
     >>> VFD_efficiency(10*hp)
     0.96
-    >>> VFD_efficiency(100*hp, load=0.5)
-    0.96
+    >>> VFD_efficiency(100*hp, load=0.2)
+    0.92
 
     References
     ----------
@@ -271,7 +273,6 @@ def motor_round_size(P):
 nema_min_full_closed_6p_i = interp1d(nema_min_P, nema_min_full_closed_6p)
 nema_min_full_closed_8p_i = interp1d(nema_min_P, nema_min_full_closed_8p)
 
-#print nema_min_full_closed_8p_i(345)
 
 def CSA_motor_efficiency(P, closed=False, poles=2, high_efficiency=False):
     r'''Returns the efficiency of a NEMA motor according to [1]_.

setup.py

@@ -57,8 +57,8 @@
   name = 'fluids',
   packages = ['fluids'],
   license='MIT',
-  version = '0.1.61',
-  download_url = 'https://github.com/CalebBell/fluids/tarball/0.1.61',
+  version = '0.1.62',
+  download_url = 'https://github.com/CalebBell/fluids/tarball/0.1.62',
   description = 'Fluid dynamics component of Chemical Engineering Design Library (ChEDL)',
   long_description=open('README.rst').read(),
   extras_require = {

tests/test_fittings.py

@@ -32,6 +32,7 @@ def test_fittings():
 
     K =  entrance_rounded(Di=0.1, rc=0.0235)
     assert_allclose(K, 0.09839534618360923)
+    assert_allclose(entrance_rounded(Di=0.1, rc=0.2), 0.03)
 
     K = entrance_beveled(Di=0.1, l=0.003, angle=45)
     assert_allclose(K, 0.45086864221916984)