Issue36 coaxial pipes

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Current version
 
+### New features 
+
+* [Issue 36](https://github.com/MassimoCimmino/pygfunction/issues/36) - Added a `Coaxial` class to the `pipes` module to model boreholes with coaxial pipes.
+
 ### Enhancements
 
 * [Issue 118](https://github.com/MassimoCimmino/pygfunction/issues/118) - Refactored checks for stored `_BasePipe` and `Network` coefficicients to use `numpy.all()`. This decreases calculation time.

doc/source/examples/custom_borehole.rst

@@ -5,11 +5,11 @@ Definition and visualization of a borehole
 ******************************************
 
 This example demonstrates the use of the :doc:`borehole <../modules/boreholes>` module
-to define the positions of U-tube pipes inside a borehole and visualize the
+to define the positions of pipes inside a borehole and visualize the
 top view of a borehole.
 
-The following script generates a borehole with a single U-tube. The
-borehole cross-section is then plotted on a figure.
+The following script generates boreholes with a single U-tube, a double U-tube (in series and
+parallel configurations), and a coaxial borehole. The borehole cross-sections are then plotted.
 
 The script is located in: 
 `pygfunction/examples/custom_borehole.py`

pygfunction/examples/custom_borehole.py

@@ -3,71 +3,204 @@
     created and the borehole resistance is computed.
 
 """
+import numpy as np
+from scipy.constants import pi
+
 import pygfunction as gt
-from numpy import pi
 
 
 def main():
+    # -------------------------------------------------------------------------
+    # Simulation parameters
+    # -------------------------------------------------------------------------
+
     # Borehole dimensions
-    H = 400.        # Borehole length (m)
     D = 5.          # Borehole buried depth (m)
+    H = 400.        # Borehole length (m)
     r_b = 0.0875    # Borehole radius (m)
 
-    # Pipe dimensions
-    r_out = 0.0133      # Pipe outer radius (m)
-    r_in = 0.0108       # Pipe inner radius (m)
-    D_s = 0.029445      # Shank spacing (m)
+    # Pipe dimensions (all configurations)
     epsilon = 1.0e-6    # Pipe roughness (m)
 
-    # Pipe positions
-    # Single U-tube [(x_in, y_in), (x_out, y_out)]
-    pos = [(-D_s, 0.), (D_s, 0.)]
+    # Pipe dimensions (single U-tube and double U-tube)
+    r_out = 0.0211      # Pipe outer radius (m)
+    r_in = 0.0147       # Pipe inner radius (m)
+    D_s = 0.052         # Shank spacing (m)
 
-    # Define a borehole
-    borehole = gt.boreholes.Borehole(H, D, r_b, x=0., y=0.)
+    # Pipe dimensions (coaxial)
+    r_in_in = 0.0221    # Inside pipe inner radius (m)
+    r_in_out = 0.025    # Inside pipe outer radius (m)
+    r_out_in = 0.0487   # Outer pipe inside radius (m)
+    r_out_out = 0.055   # Outer pipe outside radius (m)
+    # Vectors of inner and outer pipe radii
+    # Note : The dimensions of the inlet pipe are the first elements of
+    #        the vectors. In this example, the inlet pipe is the inside pipe.
+    r_inner = np.array([r_in_in, r_out_in])     # Inner pipe radii (m)
+    r_outer = np.array([r_in_out, r_out_out])   # Outer pip radii (m)
+
+    # Ground properties
+    k_s = 2.0           # Ground thermal conductivity (W/m.K)
+
+    # Grout properties
+    k_g = 1.0           # Grout thermal conductivity (W/m.K)
 
-    k_p = 0.4     # Pipe thermal conductivity (W/m.K)
-    k_s = 2.0     # Ground thermal conductivity (W/m.K)
-    k_g = 1.0     # Grout thermal conductivity (W/m.K)
+    # Pipe properties
+    k_p = 0.4           # Pipe thermal conductivity (W/m.K)
 
     # Fluid properties
-    m_flow_borehole = 0.25  # Total fluid mass flow rate per borehole (kg/s)
-    cp_f = 3977.            # Fluid specific isobaric heat capacity (J/kg.K)
-    rho_f = 1015.           # Fluid density (kg/m3)
-    mu_f = 0.00203          # Fluid dynamic viscosity (kg/m.s)
-    k_f = 0.492             # Fluid thermal conductivity (W/m.K)
+    # Total fluid mass flow rate per borehole (kg/s)
+    m_flow_borehole = 1.0
+    # The fluid is propylene-glycol (20 %) at 20 degC
+    fluid = gt.media.Fluid('MPG', 20.)
+    cp_f = fluid.cp     # Fluid specific isobaric heat capacity (J/kg.K)
+    rho_f = fluid.rho   # Fluid density (kg/m3)
+    mu_f = fluid.mu     # Fluid dynamic viscosity (kg/m.s)
+    k_f = fluid.k       # Fluid thermal conductivity (W/m.K)
+
+    # -------------------------------------------------------------------------
+    # Initialize borehole model
+    # -------------------------------------------------------------------------
+
+    borehole = gt.boreholes.Borehole(H, D, r_b, x=0., y=0.)
+
+    # -------------------------------------------------------------------------
+    # Define a single U-tube borehole
+    # -------------------------------------------------------------------------
+
+    # Pipe positions
+    # Single U-tube [(x_in, y_in), (x_out, y_out)]
+    pos_single = [(-D_s, 0.), (D_s, 0.)]
 
     # Pipe thermal resistance
     R_p = gt.pipes.conduction_thermal_resistance_circular_pipe(
         r_in, r_out, k_p)
-    # Fluid to inner pipe wall thermal resistance (Single U-tube)
+
+    # Fluid to inner pipe wall thermal resistance
     m_flow_pipe = m_flow_borehole
     h_f = gt.pipes.convective_heat_transfer_coefficient_circular_pipe(
         m_flow_pipe, r_in, mu_f, rho_f, k_f, cp_f, epsilon)
     R_f = 1.0 / (h_f * 2 * pi * r_in)
 
+    # Single U-tube GHE in borehole
     SingleUTube = gt.pipes.SingleUTube(
-        pos, r_in, r_out, borehole, k_s, k_g, R_f + R_p)
-
-    R_b = gt.pipes.borehole_thermal_resistance(
-        SingleUTube, m_flow_borehole, cp_f)
-
-    print('Borehole thermal resistance: {0:.4f} m.K/W'.format(R_b))
+        pos_single, r_in, r_out, borehole, k_s, k_g, R_f + R_p)
 
     # Check the geometry to make sure it is physically possible
-    #
+
     # This class method is automatically called at the instanciation of the
     # pipe object and raises an error if the pipe geometry is invalid. It is
-    # manually called here for demosntration.
-    check = SingleUTube._check_geometry()
+    # manually called here for demonstration.
+    check_single = SingleUTube._check_geometry()
     print('The geometry of the borehole is valid (realistic/possible): '
-          + str(check))
+          + str(check_single))
+
+    # Evaluate and print the effective borehole thermal resistance
+    R_b = gt.pipes.borehole_thermal_resistance(
+        SingleUTube, m_flow_borehole, fluid.cp)
+    print('Single U-tube Borehole thermal resistance: '
+          '{0:.4f} m.K/W'.format(R_b))
+
+    # Visualize the borehole geometry and save the figure
+    fig_single = SingleUTube.visualize_pipes()
+    fig_single.savefig('single-u-tube-borehole.png')
+
+    # -------------------------------------------------------------------------
+    # Define a double U-tube borehole
+    # -------------------------------------------------------------------------
+
+    # Pipe positions
+    # Double U-tube [(x_in1, y_in1), (x_in2, y_in2),
+    #                (x_out1, y_out1), (x_out2, y_out2)]
+    # Note: in series configuration, fluid enters pipe (in,1), exits (out,1),
+    # then enters (in,2) and finally exits (out,2)
+    # (if you view visualize_pipe, series is 1->3->2->4)
+    pos_double = [(-D_s, 0.), (0., -D_s), (D_s, 0.), (0., D_s)]
+
+    # Pipe thermal resistance
+    R_p = gt.pipes.conduction_thermal_resistance_circular_pipe(
+            r_in, r_out, k_p)
+
+    # Fluid to inner pipe wall thermal resistance
+    # Double U-tube in series
+    m_flow_pipe_series = m_flow_borehole
+    h_f_series = gt.pipes.convective_heat_transfer_coefficient_circular_pipe(
+        m_flow_pipe_series, r_in, mu_f, rho_f, k_f, cp_f, epsilon)
+    R_f_series = 1.0 / (h_f_series * 2 * pi * r_in)
+    # Double U-tube in parallel
+    m_flow_pipe_parallel = m_flow_borehole / 2
+    h_f_parallel = gt.pipes.convective_heat_transfer_coefficient_circular_pipe(
+        m_flow_pipe_parallel, r_in, mu_f, rho_f, k_f, cp_f, epsilon)
+    R_f_parallel = 1.0 / (h_f_parallel * 2 * pi * r_in)
+
+    # Double U-tube GHE in borehole
+    # Double U-tube in series
+    DoubleUTube_series = gt.pipes.MultipleUTube(
+        pos_double, r_in, r_out, borehole, k_s, k_g, R_p + R_f_series, 2,
+        config='series')
+    # Double U-tube in parallel
+    DoubleUTube_parallel = gt.pipes.MultipleUTube(
+        pos_double, r_in, r_out, borehole, k_s, k_g, R_p + R_f_parallel, 2,
+        config='parallel')
+
+    # Evaluate and print the effective borehole thermal resistance
+    R_b_series = gt.pipes.borehole_thermal_resistance(
+        DoubleUTube_series, m_flow_borehole, cp_f)
+    print('Double U-tube (series) Borehole thermal resistance: {0:.4f} m.K/W'.
+          format(R_b_series))
+    R_b_parallel = gt.pipes.borehole_thermal_resistance(
+        DoubleUTube_parallel, m_flow_borehole, cp_f)
+    print('Double U-tube (parallel) Borehole thermal resistance: {0:.4f} m.K/W'.
+          format(R_b_parallel))
+
+    # Visualize the borehole geometry and save the figure
+    fig_double = DoubleUTube_series.visualize_pipes()
+    fig_double.savefig('double-u-tube-borehole.png')
+
+    # -------------------------------------------------------------------------
+    # Define a coaxial borehole
+    # -------------------------------------------------------------------------
 
-    # Create a borehole top view
-    fig = SingleUTube.visualize_pipes()
+    # Pipe positions
+    # Coaxial pipe (x, y)
+    pos = (0., 0.)
+
+    # Pipe thermal resistance
+    # (the two pipes have the same thermal conductivity, k_p)
+    # Inner pipe
+    R_p_in = gt.pipes.conduction_thermal_resistance_circular_pipe(
+        r_in_in, r_in_out, k_p)
+    # Outer pipe
+    R_p_out = gt.pipes.conduction_thermal_resistance_circular_pipe(
+        r_out_in, r_out_out, k_p)
+
+    # Fluid-to-fluid thermal resistance
+    # Inner pipe
+    h_f_in = gt.pipes.convective_heat_transfer_coefficient_circular_pipe(
+        m_flow_borehole, r_in_in, mu_f, rho_f, k_f, cp_f, epsilon)
+    R_f_in = 1.0 / (h_f_in * 2 * pi * r_in_in)
+    # Outer pipe
+    h_f_a_in, h_f_a_out = \
+        gt.pipes.convective_heat_transfer_coefficient_concentric_annulus(
+            m_flow_borehole, r_in_out, r_out_in, mu_f, rho_f, k_f, cp_f,
+            epsilon)
+    R_f_out_in = 1.0 / (h_f_a_in * 2 * pi * r_in_out)
+    R_ff = R_f_in + R_p_in + R_f_out_in
+
+    # Coaxial GHE in borehole
+    R_f_out_out = 1.0 / (h_f_a_out * 2 * pi * r_out_in)
+    R_fp = R_p_out + R_f_out_out
+    Coaxial = gt.pipes.Coaxial(
+        pos, r_inner, r_outer, borehole, k_s, k_g, R_ff, R_fp, J=2)
+
+    # Evaluate and print the effective borehole thermal resistance
+    R_b = gt.pipes.borehole_thermal_resistance(
+        Coaxial, m_flow_borehole, cp_f)
+    print('Coaxial tube Borehole thermal resistance: {0:.4f} m.K/W'.
+          format(R_b))
 
-    # Save the figure as a pdf
-    fig.savefig('borehole-top-view.pdf')
+    # Visualize the borehole geometry and save the figure
+    fig_coaxial = Coaxial.visualize_pipes()
+    fig_coaxial.savefig('coaxial-borehole.png')
 
 
 if __name__ == '__main__':