The heat transfer rate Q is commonly expressed in which unit in heat exchanger calculations?

The heat transfer rate Q is commonly expressed in which unit in heat exchanger calculations?

• A. BTU/hr
• B. kW
• C. J/s
• D. Calories per second

Answer: (A)

The main idea is that Q represents energy transfer per unit time, i.e., power. In heat exchanger calculations, using BTU per hour is the most common convention in many traditional US engineering contexts because many data and tables are built around BTU and pound mass. If you’re working with typical fluid properties, you often have mass flow in pounds per hour and enthalpy changes in BTU per pound, so multiplying gives Q directly in BTU/h without extra unit juggling. This makes the numbers, ratings, and performance data (like UA, LMTD, and capacity) fit together smoothly on familiar scales. While kilowatts (and thus joules per second) are perfectly valid power units and are used in SI-based analyses, the question’s context reflects the traditional practice of expressing heat transfer rate in BTU/h. Calories per second isn’t a standard engineering unit for these calculations, as it doesn’t line up with common property data and equipment ratings.

The main idea is that Q represents energy transfer per unit time, i.e., power. In heat exchanger calculations, using BTU per hour is the most common convention in many traditional US engineering contexts because many data and tables are built around BTU and pound mass. If you’re working with typical fluid properties, you often have mass flow in pounds per hour and enthalpy changes in BTU per pound, so multiplying gives Q directly in BTU/h without extra unit juggling. This makes the numbers, ratings, and performance data (like UA, LMTD, and capacity) fit together smoothly on familiar scales.

While kilowatts (and thus joules per second) are perfectly valid power units and are used in SI-based analyses, the question’s context reflects the traditional practice of expressing heat transfer rate in BTU/h. Calories per second isn’t a standard engineering unit for these calculations, as it doesn’t line up with common property data and equipment ratings.