# What is Hydraulic Resisting Force – Definition

Hydraulic Resisting Force. Natural circulation flow rate, V, is determined from the balance between the driving head and the resisting forces. Thermal Engineering

## Hydraulic Resisting Force As was written, natural circulation flow rate, V, in the loop, under steady state condition is determined from the balance between the driving head and the resisting forces. Like pipe friction, the overall pressure losses are proportional to the square of the flow rate and therefore they can be easily integrated into the Darcy-Weisbach equation. Engineers often use the pressure loss coefficient, PLC. It is noted K or ξ (pronounced “xi”). This coefficient characterizes pressure loss of a certain hydraulic system or of a part of a hydraulic system. It can be easily measured in hydraulic loops. The pressure loss coefficient can be defined or measured for both straight pipes and especially for local (minor) losses. Since the Darcy friction factor is a function of velocity (in Reynolds number), then the calculation of the pressure loss coefficient is an iterative process.

## Natural Circulation – Flow Rate

Natural circulation flow rate in the loop, under steady state condition is determined from the balance between the driving and the resisting forces. Driving force results from density difference between hot leg and cold leg of the loop. The head required to compensate for the head losses is created by density gradients and elevation changes.

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