2025AsianB/org/other/question2_pdms_cooling.py

import importlib.util
import math
import os
from dataclasses import dataclass
from typing import Dict, List, Tuple

import numpy as np
from matplotlib import pyplot as plt

plt.rcParams["font.sans-serif"] = ["DejaVu Sans", "Arial", "Helvetica"]
plt.rcParams["axes.unicode_minus"] = False

SIGMA = 5.670374419e-8

THICKNESSES = [1, 5, 10, 25, 50, 100]  # µm
T_AMB = 300.0  # K (≈27 ℃)
T_SKY = 280.0  # Clear dry sky equivalent radiation temperature
SOLAR_IRR = 900.0  # W/m^2, clear sky noon
H_CONV = 8.0  # W/m^2/K, natural convection + light wind


def load_emissivity_module():
    here = os.path.dirname(os.path.abspath(__file__))
    target = os.path.join(here, "question1_pdms_emissivity.py")
    spec = importlib.util.spec_from_file_location("q1", target)
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)  # type: ignore[arg-type]
    return module


def solar_absorptance(thickness_um: float) -> float:
    """
    Empirical assumption: In PDMS silver-coated system, visible light absorption
    is determined by thin film scattering and internal losses.
    At 1 µm, α≈0.05, absorption increases by 0.01 for every 10 µm increase in thickness, capped at 0.15.
    """
    return min(0.05 + 0.001 * thickness_um, 0.15)


@dataclass
class CoolingResult:
    thickness_um: float
    eps_window: float
    alpha_solar: float
    net_power_at_amb: float
    eq_temp_K: float

    @property
    def eq_temp_C(self) -> float:
        return self.eq_temp_K - 273.15

    @property
    def delta_T(self) -> float:
        return self.eq_temp_K - T_AMB


def net_cooling_power(temp_K: float, emissivity: float, alpha_s: float) -> float:
    radiative = emissivity * SIGMA * (temp_K**4 - T_SKY**4)
    solar_gain = alpha_s * SOLAR_IRR
    convective = H_CONV * (temp_K - T_AMB)
    return -solar_gain - convective + radiative


def solve_equilibrium(emissivity: float, alpha_s: float) -> float:
    low, high = 250.0, 330.0
    f_low = net_cooling_power(low, emissivity, alpha_s)
    f_high = net_cooling_power(high, emissivity, alpha_s)

    if f_low * f_high > 0:
        # No sign change, return endpoint with smaller energy consumption
        return low if abs(f_low) < abs(f_high) else high

    for _ in range(80):
        mid = 0.5 * (low + high)
        f_mid = net_cooling_power(mid, emissivity, alpha_s)
        if abs(f_mid) < 1e-4:
            return mid
        if f_low * f_mid <= 0:
            high, f_high = mid, f_mid
        else:
            low, f_low = mid, f_mid
    return 0.5 * (low + high)


def evaluate() -> Tuple[List[CoolingResult], str]:
    q1 = load_emissivity_module()
    emissivity_data = q1.compute_emissivity(THICKNESSES)

    results: List[CoolingResult] = []
    for d in THICKNESSES:
        eps_window = emissivity_data.window_avg[d]
        alpha_s = solar_absorptance(d)
        net_amb = net_cooling_power(T_AMB, eps_window, alpha_s)
        eq_temp = solve_equilibrium(eps_window, alpha_s)
        results.append(
            CoolingResult(
                thickness_um=d,
                eps_window=eps_window,
                alpha_solar=alpha_s,
                net_power_at_amb=net_amb,
                eq_temp_K=eq_temp,
            )
        )

    outdir = os.path.join(os.path.dirname(__file__), "outputs")
    os.makedirs(outdir, exist_ok=True)
    csv_path = os.path.join(outdir, "question2_cooling_summary.csv")
    with open(csv_path, "w", encoding="utf-8") as f:
        f.write("thickness_um,eps_8_13,alpha_solar,net_power_amb_Wm2,eq_temp_C,delta_T_C\n")
        for res in results:
            f.write(
                f"{res.thickness_um},{res.eps_window:.4f},{res.alpha_solar:.3f},"
                f"{res.net_power_at_amb:.2f},{res.eq_temp_C:.2f},{res.delta_T:.2f}\n"
            )

    fig_path = os.path.join(outdir, "question2_cooling_results.png")
    plot_results(results, fig_path)

    return results, csv_path


def plot_results(results: List[CoolingResult], fig_path: str) -> None:
    thickness = [r.thickness_um for r in results]
    net_power = [r.net_power_at_amb for r in results]
    delta_T = [r.delta_T for r in results]

    fig, ax1 = plt.subplots(figsize=(9, 5))
    ax1.bar(thickness, net_power, width=4, alpha=0.6, label="Net Cooling Power @T_amb")
    ax1.set_xlabel("PDMS Film Thickness (µm)")
    ax1.set_ylabel("Net Cooling Power (W/m²)")
    ax1.axhline(0, color="black", linewidth=0.8)

    ax2 = ax1.twinx()
    ax2.plot(thickness, delta_T, color="tab:red", marker="o", label="Equilibrium Temperature Difference")
    ax2.set_ylabel("Equilibrium Temperature Difference (K)")

    lines, labels = ax1.get_legend_handles_labels()
    lines2, labels2 = ax2.get_legend_handles_labels()
    ax1.legend(lines + lines2, labels + labels2, loc="upper right")
    fig.tight_layout()
    plt.savefig(fig_path, dpi=300)
    plt.close(fig)


def main():
    results, csv_path = evaluate()
    print(f"Results written to: {csv_path}")
    for r in results:
        print(
            f"d={r.thickness_um:>3} um, eps_8_13={r.eps_window:.2f}, alpha_sol={r.alpha_solar:.2f}, "
            f"q_net(T_amb)={r.net_power_at_amb:.1f} W/m2, T_eq={r.eq_temp_C:.1f} °C "
            f"(DeltaT={r.delta_T:.1f} K)"
        )


if __name__ == "__main__":
    main()