Let's break down the problem shown in the image: --- ### **Problem Statement** > Saturated moist air enters a heating coil at temperature 40°F and exits the coil at 110°F. The amount of moist air entering the heating coil is 25,000 CFM. Find the amount of heat addition in Btu/min. ### **Given Data** - **Inlet temperature (T₁):** 40°F - **Outlet temperature (T₂):** 110°F - **Airflow rate (Q):** 25,000 CFM - **Units for answer:** Btu/min --- ### **General Formula** The heat added to air (\(Q_h\)) is calculated as: \[ Q_h = \dot{V} \cdot \rho \cdot c_p \cdot (T_2 - T_1) \] Where: - \( \dot{V} \) = volumetric flow rate (ft³/min) - \( \rho \) = density of air (lb/ft³) - \( c_p \) = specific heat (Btu/lb·°F) - \( (T_2 - T_1) \) = temperature rise (°F) For standard air: - \( \rho \approx .075 \) lb/ft³ - \( c_p \approx .24 \) Btu/lb·°F --- ### **Calculation** 1. **Temperature Difference:** \[ \Delta T = 110^\circ F - 40^\circ F = 70^\circ F \] 2. **Plug in the values:** \[ Q_h = 25,000 \times .075 \times .24 \times 70 \] 3. **Step-by-step Calculation:** - \( 25,000 \times .075 = 1,875 \) - \( 1,875 \times .24 = 450 \) - \( 450 \times 70 = 31,500 \) So, \[ Q_h = 31,500 \text{ Btu/min} \] --- ### **Matching to Options** - The closest option to **31,500 Btu/min** is **32,465 Btu/min**. --- ## **Final Answer** > **The correct option is:** > > **32,465 Btu/min** (last option) --- Let me know if you need a detailed explanation or further breakdown!