The design process can be broken into three major steps.

B. Build a model

Explanation:

1/ Identify the need: the need of potential customers are investigated.

Criteria and constraints are used to evaluate the quality of a design. Once criteria and constraints are identified, the design team generates ideas for designs. These ideas come from many different sources; these include existing products, BRAINSTORMING and other creative activities, and market and technical research. After potential designs are generated, they are explored to understand their characteristics and likely advantages and disadvantages.

2/ Create a concept (Select a design concept): Potential designs are evaluated relative to the constrains and criteria, and one or more is selected to be designed in detail and prototyped.

Then the selected  design is developed in more detail.

3/ Build a model : One or more prototypes are typically implemented to characterize various aspects of the design.

Then prototypes are tested to see whether the design meets all constraints and performs acceptably relative to the criteria.

oil flow is a highly convective flow compared to water flow at normal temperature and pressure.