CERN Demineralised Water Distribution Network general data can be illustrated by a table like the following one. More detailled features here .pdf or here .pdf

CERN Water Distribution LHC Network	Data
	Label	Value	Unit
Absolute Nominal operating pressure	P.in, P.out	[1..16]	[bars]
Nominal designed available pressure drop @ equipement level	dP = P.in - P.out	3	[bars]
Maximum inlet temperature	T.in	27	[°C]
Maximum outlet temperature	T.out	37	[°C]
Nominal designed available dT @ equipement level	dT = T.out - T.in	TBD	[°C]
Conductivity	Cond.	0.5..1	[uS/cm]
Test Pressure Validation criteria	P.test @ 40°C	22	[bars] / 30min

LHC Water Layout Characteristics

• Solders are forbidden inside an electrical power module: water pipe must be made on one piece (water plate for example).
• Water flow is passively obtained with regards to the natural water pressure drop of the converter: no "active" device.

A major part of all design calculation described below are extracted from a document from Davide Tommasini (CERN).

Power Converter, and more specifically Rack and Power Module (s) distribution has to fit several general rules:

• In cases of Rack interal parallel paths, they must be individually controlled and interlocked.
• Rack Water distribution pressure drop must be kept as minimum as possible, with water pressure drop normally contained in Power Modules.This point is absolutely critical in case of a rack distribution filling two rack internal paths in parallel, to ensure a good water flow sharing. All Rack common path will then be designed adequately, since driving the full flow-rate, ant then leading naturally to worst conditions for pressure drop.
• Quick-Fit Coupling are a critical point regarding reliability. Water pressure drop of these devices are generally low. See example on 1/4" solution being measured .png.

Example of a Rack Internal distribution: 2 paths - 2 Modules in series .vsd

We generally use these conventions:

• Rack General Water Layout Input & Output: flexible hoses terminated by Female water Connector for both.
  Goal is to protect rack water connectors (transport), female connector assumed to be less fragile.
• Power Module Water Layout Input & Output: Male water Connectors for both.
  Male connectors on removable power module so that flexible hose attached to the rack are then also terminated by female connector.
  Coupling connexion is assumed to be more handy when plugging the female part in a "static" male part.
• Input Connector/Connexion = Blue
  Water leaving the module is generally hotter than when entering it (cold=blue).
• Output Connector/Connexion = Red
  Water leaving the module is generally hotter (red=hot) than when entering it.

Example of a M/F convention application and a Power Module realization example

Energy transfer in water uses the well-known formula:
E=m.C.dT (E=Energie [J], m=weight [kg], C=chaleur massique [J/(°C.kg)], dT=Temperature difference [°C])
This formula applied to a flowrate gives the following formula:

Formula-1: Water Flow vs Power vehiculated in water & its temperature rise

To be thermally effective, the water flow shall be moderately turbulent; this condition is met if the so called Reynolds number R_e, representing the ratio between the inertial forces and the viscous forces, is greater than 2000 and smaller than 10E5. Calculation of the Reynolds number is given by the formula:

Formula-2: Reynolds number calculation

Formula which required the calculation of the fluide velocity

Formula-3: fluide velocity calculation

Leading then to the simplified formula (water @ 40°C) for the calculation Reynolds

Formula-4: Reynolds number simplified calculation with 35°C water dynamic viscosity : 0,7.10E-4 Pa.s, and then a fluid viscosity of 7E-7 m²/s

Leading finally to the very handy formula (water @ 40°C) for achieving a efficient thermal cooling

Formula-5: Efficient cooling conditions (water @ 40°C)

On the other hand, excessive water speed my cause erosion corrosion of the cooling pipe: in copper this starts taking place at velocity > 3m/s. This is one of the reasons why efficient cooling in small pipes always produces some erosion.
To find the good combination of diameter and water velocity for a given flow this condition shall be iterated with:

Formula-6: Efficient cooling conditions (water @ 40°C)

A very important parameter is the pressure drop of a water layout, for matching the water network. Some web pages exist (here). For hydraulically smooth pipes of length L and diameter d with inlet as outlet at about the same height, with moderately turbulent flow, the pressure drop is given by the Blasius law which, in practical units, can be written as:

Formula-7: Estimation of a given layout water pressure drop

Another very important parameter is the power level being transmitted through / in water Above a certain level, cavitation will appear, destroying locally the material (whatever it is).
P.transmitted < 8 Watts / cm2 (above 50 Watts / cm2, the conditions are very challenging and would likely lead to material destruction).

Water cooled plates can based on a sandwitch design, giving high flexibility for power design and component placement.

Water Cooled Plate Example and Assembly principles .vsd

Some formulas can be used to better caracterize the thermal environment.

    

Formula-9: Thermal resistance of a given material & case of pipe. (longueur L, diameter external & internal, thermal conductivity)