W1D1 - First Half

Formula for BTUs Calculation

To calculate the BTUs required, use the following formula:
BTUs=CFM×0.68×(T<em>out−T</em>in)BTUs = CFM \times 0.68 \times (T<em>{out} - T</em>{in})
For example, for 1600 CFM and a temperature difference from 78 to 60, it results in 19,584 BTUs per hour.

Measuring Tools

For measuring heat-related variables, avoid complex tools like psychrometers. Instead, simpler tools such as thermometers or measuring buckets should be used based on the change in state or weight of the substance involved.

Heat Change Types

  1. Sensible Heat: Involves temperature changes without a change in moisture content.

  2. Latent Heat: Occurs with a change in state but no temperature change.

  3. Total Heat: Combines both sensible and latent heat changes, represented by CFM×4.5×ΔhCFM \times 4.5 \times \Delta h.

Calculation of Total Heat Example

Using a total heat formula example:
BTUs=CFM×4.5×ΔhBTUs = CFM \times 4.5 \times \Delta h
For (1600×4.5×8(1600 \times 4.5 \times 8 gives 57,600 BTUs per hour.

Sensible Heat Ratio Calculations

Used to determine the efficiency of the heating process.
Specific heat formula:
BTU=weight×specific heat×(T<em>final−T</em>initial)BTU = weight \times specific\ heat \times (T<em>{final} - T</em>{initial}).

Conversion Between Fahrenheit and Celsius

  • To convert from Celsius to Fahrenheit:
    F=(C×1.8)+32F = (C \times 1.8) + 32

  • To convert from Fahrenheit to Celsius:
    C=(F−32)/1.8C = (F - 32) / 1.8

Heating Specific Calculations

For specific materials, use their specific heats (e.g., alcohol: 0.6 BTUs/lb/°F). The heat required for heating or evaporating substances is calculated based on their specific heat and weight, without time being a factor.

Example Scenarios

  • When heating alcohol from 62°F to 113°F for 12.6 pounds, apply the specific heat formula to find total BTUs required.

  • For a heating coil in air, determine total heat using specific heat and temperature differences to calculate the effect on air temperature.

Pressures and Temperature Charts

To find absolute pressure:
Absolute Pressure=Gauge Pressure+Atmospheric PressureAbsolute\ Pressure = Gauge\ Pressure + Atmospheric\ Pressure
Use temperature-pressure charts to find the boiling point and heat requirements for processes such as evaporation under varying pressures.

  • For sodium chloride solutions, use specific heat values for calculations, ensuring to interpolate the required temperature based on gauge and absolute pressures.