Engineering English
Reynolds Number
Chemical Engineering · Aerospace Engineering · Mechanical Engineering · Last updated: July 30, 2026 · How this entry was written
Definition: The Reynolds number is a dimensionless quantity that characterizes the flow regime, predicting whether flow will be laminar or turbulent. It is defined as the ratio of inertial forces to viscous forces.
Example in context
“We calculated the Reynolds number for the pipe flow to determine if the regime is turbulent.”
“Boru akışı için Reynolds sayısını hesaplayarak rejimin türbülanslı olup olmadığını belirledik.”
Where engineers use it
The Reynolds number is essential in fluid flow analysis to predict flow patterns, friction factors, and heat transfer coefficients. Engineers use it to design piping systems and optimize process equipment.
Synonyms: Re number
In Aerospace Engineering
Reynolds number is a dimensionless quantity that compares inertial forces to viscous forces in a fluid flow. It is used to predict flow regimes, such as laminar or turbulent.
“The aerodynamic engineer computed the Reynolds number to assess whether the flow over the airfoil would remain laminar or transition to turbulent at cruising speed.”
In Mechanical Engineering
A dimensionless group formed from density, velocity, characteristic length, and viscosity that expresses the ratio of inertial to viscous forces in a flow. Its value indicates whether the regime is laminar, transitional, or turbulent.
“Calculating the Reynolds number for the duct showed a value near four thousand, placing the airflow in the transitional range.”
Practice: can you use “Reynolds Number” at work?
You are designing a cooling water pipe for a reactor. The velocity and pipe diameter are known. Calculate the Reynolds number to decide if the flow will be laminar or turbulent.
Show a model answer
“To check the flow regime, you must first calculate the Reynolds number.”
“Reynolds Number” in 21 languages
| English | Reynolds Number |
|---|---|
| Turkish | Reynolds sayısı |
| French | nombre de Reynolds |
| German | Reynolds-Zahl |
| Spanish | número de Reynolds |
| Chinese | 雷诺数 |
| Arabic | عدد رينولدز |
| Portuguese | número de Reynolds |
| Russian | число Рейнольдса |
| Japanese | レイノルズ数 |
| Italian | numero di Reynolds |
| Vietnamese | số Reynolds |
| Hindi | रेनॉल्ड्स संख्या |
| Thai | เลขเรย์โนลด์ส |
| Indonesian | bilangan Reynolds |
| Korean | 레이놀즈 수 |
| Bengali | রেনল্ডস সংখ্যা |
| Dutch | Reynoldsgetal |
| Swedish | Reynoldstal |
| Finnish | Reynoldsin luku |
| Ukrainian | число Рейнольдса |
Frequently asked questions
What does Reynolds Number mean in engineering?
The Reynolds number is a dimensionless quantity that characterizes the flow regime, predicting whether flow will be laminar or turbulent. It is defined as the ratio of inertial forces to viscous forces. In Chemical Engineering, the term carries a usage-frequency rating of 10/10 in the Engineering English library.
How do you pronounce Reynolds Number?
Reynolds Number is pronounced /ˈrɛnəldz ˈnʌmbər/ (IPA). The Engineering English app plays audio for the term and checks your pronunciation with speech recognition.
How is Reynolds Number used in a sentence?
Example from an engineering context: “We calculated the Reynolds number for the pipe flow to determine if the regime is turbulent.”
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