1. Calculation Scope & Governing Equations
This rating sheet provides sizing and thermal-hydraulic verification for gasketed plate and frame heat exchangers (GPHE) in accordance with API Standard 662 Part 1 / ISO 15547-1 and ASME Section VIII Division 1.
$$Q = \dot{m}_h C_{p,h} (T_{h,in} - T_{h,out}) = \dot{m}_c C_{p,c} (T_{c,out} - T_{c,in})$$
$$\text{LMTD} = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1 / \Delta T_2)}, \quad \Delta T_1 = T_{h,in} - T_{c,out}, \quad \Delta T_2 = T_{h,out} - T_{c,in}$$
$$A_{\text{req}} = \frac{Q}{U_{dirty} \cdot F_t \cdot \text{LMTD}}, \quad A_{\text{installed}} = (N_{plates} - 2) \cdot A_1$$
$$\frac{1}{U_{dirty}} = \frac{1}{h_{hot}} + R_{f,hot} + \frac{t_{plate}}{k_{plate}} + R_{f,cold} + \frac{1}{h_{cold}}$$
$$Nu = C_h \cdot Re^m \cdot Pr^{1/3} \cdot \left(\frac{\mu}{\mu_w}\right)^{0.14}, \quad h = \frac{Nu \cdot k_{fluid}}{D_h}, \quad D_h = \frac{2 b}{\phi}$$
$$\Delta P_{total} = 4 f \left(\frac{L_v}{D_h}\right)\left(\frac{\rho v_{ch}^2}{2}\right) N_{pass} + 1.3 \left(\frac{\rho v_{port}^2}{2}\right) N_{pass}$$
$$A_{nominal} = N_{plates} \times (t_{plate} + b)$$
2. Standard Parameters & API 662 Design Criteria
| Service / Fluid Type | Typical Overall U ($W/m^2\cdot K$) | Recommended Design Limits |
|---|---|---|
| Water to Water (District Cooling) | $3,000 - 6,500\text{ W/m}^2\cdot\text{K}$ | $v_{ch} = 0.3 - 0.8\text{ m/s}$; $v_{port} \le 4.5\text{ m/s}$; allowable $\Delta P \le 0.70\text{ bar}$. |
| Wort / Milk Pasteurizer (Food CIP) | $2,500 - 4,500\text{ W/m}^2\cdot\text{K}$ | $v_{ch} = 0.2 - 0.6\text{ m/s}$ (prevents shearing); allowable $\Delta P \le 0.80\text{ bar}$. |
| WFI Subcooler (Pharmaceutical) | $2,800 - 5,000\text{ W/m}^2\cdot\text{K}$ | $v_{ch} = 0.3 - 0.7\text{ m/s}$; PTFE/EPDM gaskets; allowable $\Delta P \le 0.50\text{ bar}$. |
| Viscous Oil Cooling (ISO VG 46) | $400 - 1,200\text{ W/m}^2\cdot\text{K}$ | $v_{ch} = 0.1 - 0.4\text{ m/s}$; $30^\circ$ Low-theta plate; allowable $\Delta P \le 1.20\text{ bar}$. |
| LMTD Correction Factor ($F_t$) | $\ge 0.95$ (Pure counterflow) | Allows close temperature approach down to $1.0^\circ\text{C}$ without temperature cross. |
3. Engineering Assumptions & Boundary Limits
- Fouling Resistances: Default calculations utilize modern PHE empirical fouling factors ($0.00003 - 0.00006\text{ m}^2\cdot\text{K/W}$), capitalizing on high shear stress scouring action.
- Port Velocity & Maldistribution: Port nozzle velocities are capped at $\le 4.5\text{ m/s}$ to eliminate flow maldistribution and nozzle erosion.
- Frame Tightening (A-Dimension): Sizing outputs enforce minimum and maximum tightening tolerances ($A_{min}$ to $A_{max}$) to prevent gasket crushing or fluid leakage.
- Self-Cleaning Scour: Channel wall shear stress ($\tau_w$) should exceed $\ge 30\text{ Pa}$ to inhibit particulate sedimentation and biological fouling.
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This specification sheet and its mathematical formulations adhere to internationally recognized process codes (API Standard 662 Part 1, ISO 15547-1, and ASME Section VIII Division 1). Sizing parameters and default design allowances are cross-referenced with empirical industry design practices.