Impeller construction — A (radial) turbine impeller is typically built with flat blades having which configuration relative to the hub and disk?

Introduction:
Radial-flow turbine impellers, exemplified by the Rushton design, are common in gassed bioreactors. Their geometry influences shear, power number, and gas dispersion performance. This question asks for the classic construction detail of flat-blade turbines.

Given Data / Assumptions:

• Standard Rushton-type turbine design.
• Flat, rectangular blades arranged around a hub.
• Presence of a horizontal backing disk.

Concept / Approach:
A Rushton turbine consists of six (often) flat vertical blades welded to a horizontal disk attached to the shaft. This configuration throws fluid radially, enhancing mixing and gas breakup near the impeller. Pitched-blade turbines use angled blades (typically 30–45°) to impart axial components; they are a different impeller class.

Step-by-Step Solution:
Identify the hallmark: flat, vertical blades plus a horizontal disk.Associate with radial discharge and high shear zones.Select the option explicitly describing vertical pitch on a horizontal disk.

Verification / Alternative check:
Equipment catalogs and mixing texts depict Rushton turbines exactly as vertical flat blades mounted on a disk, confirming the answer.

Why Other Options Are Wrong:

• (a) and (b) omit the disk that characterizes the Rushton construction.
• (d) Describes pitched-blade turbines with axial discharge.
• (e) Refers to hydrofoils, not flat-blade turbines.

Common Pitfalls:
Conflating pitched-blade turbines (axial) with flat-blade radial turbines; overlooking the disk that helps define the Rushton geometry.

Final Answer:
A vertical pitch welded to a horizontal disk (e.g., Rushton turbine)