WO2014177150A1

WO2014177150A1 - Free water in scavenge air sensor system and method for monitoring free water in scavenge air

Info

Publication number: WO2014177150A1
Application number: PCT/DK2014/050106
Authority: WO
Inventors: Søren LAUNGAARD; Poul Jessen
Original assignee: Paj Sensor A/S
Priority date: 2013-05-01
Filing date: 2014-04-22
Publication date: 2014-11-06
Also published as: DK201300257A1

Abstract

A sensor system and method for measuring free water in air in an environment, for example the scavenge air intake for an engine, with a sensor unit comprising a heated and non-heated filter or chamber with two separate sensors providing electronic signals indicative of the degree of free water in the air.

Description

FIELD OF THE INVENTION

The present invention relates to a sensor system and method for detecting and measuring free water in air in an environment, specifically the scavenge air intake for an engine. The present invention further relates to use of a sensor system for measuring and regulating air intake cooling, ventilation and moisturising systems and ancillary machinery to lower overall running costs and NO_x emissions, for example in vessels. Other examples of detecting and measuring free water and regulating air intake cooling systems and ancillary machinery are within industrial processing equipment, air or landbased transportation, power generation or for example production of oil and gas.

BACKGROUND OF THE INVENTION

Free water in the scavenging air intakes in marine engines leads to cylinder damages, costly maintenance operations and sometimes vessel downtime. In order to remove the free water in the scavenge air it is necessary to install coolers and ventilation systems, which are both costly and energy demanding. Furthermore, the cooling level required depends on the amount of water and quantity of water to be removed, therefore needs a feedback system to determine the level of humidity so the cooling, ventilation and ancillary systems can be optimized for energy and economically efficient operation. However, as the external climate conditions are constantly changing - pressure, humidity, temperature, etc - or for example by a malfuntioning in the cooler systems one of two problem areas occurs:

1. The coolers do not remove all the free water (droplets), or

2. The coolers run on too high an energy consumption level (compared to the surrounding climate conditions and humidity in the air)

The results are either:

1. Engine damages (for example hydrogen-induced fractures or corrosion) - which frequently occurs, when free water enters into for example engine cylinders, or

2. Waste of energy and excessive NO_x emissions due to unneccasary over-cooling

It would therefore be of great benefit to provide an integrated on-line in-situ free water in scavenging air sensor, actively monitoring the free water levels and informing about it. Such a sensor would, thus, strongly improve the operational efficiency of engine rooms by lowering total running costs including fuel costs, maintenance and downtime costs - as well as it would be lowering NO_x emissions.

Sensors - like hygrometers or dew point sensors - are well known for measuring the moisture content in the environment. Humidity measurement instruments usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. Capacitive relative humidity (RH) sensors, for example, consist of a ceramic substrate on which a thin film of polymer is deposited between two conductive electrodes. The sensing surface is coated with a micropourous metal electrode, allowing the polymer to absorb moisture while protecting it from contamination and exposure to condensation. As the polymer absorbs water, the dielectric constant changes incrementally and is nearly directly proportional to the relative humidity of the surrounding environment. Thus, by monitoring the change in capacitance, relative humidity can be derived. Capacitive sensors are widely used and with calibration, these sensors normally have an accuracy of ±2% RH (Relative Humidity) in the range 5-95% RH - if well calibrated. Capacitive sensors are, however, subject to contamination and aging effects over time. Hygrometers and dew point sensors are, however, only measuring relative or absolute humidity - i.e water in gas form - and neither the hygrometers nor the dew point sensors measure free water (droplets) in air. Relative and absolute humidity sensors measure water vapour - that is, water in its gas phase/form. Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature, calculated as follows:

Relative Humidity = Actual vapour density / saturation vapour density x 100%.

Free water (droplets) is a product of condensation of atmospheric water vapour - also called precipitation. Free water (droplet) in air can, however, occur and exist at less than 100% relative humidity (called the dew point). Scavenge or exhast gas return (EGR) systems are described by a number of patents and applications. EP2112349 relates to a scavenge performance monitoring system. However, the invention relates to optimising a process parameter and the fuel efficiency of the combustion process, by exploiting the termal energy of the exhaust gas- ses. The patent does consequently not address the issues of free water, humidity or regulation of coolers and ancillary systems in relation to this. US patent 5,184,600 deals with regulating the humidity of a heated space by varying the amount of moisture transferred from the combustion gases. The invention is that instead of providing a separate humidifier that operates by evaporating water into the heated air, humidity can be regulated by varying the amount of moisture transferred from combustion gases to the heated space. It is therefore unrelated to the innovation suggested in this document. Despite the widespread use of sensors like hygrometers and dew point sensors and capacitive sensoring, as well as patents on engine scavenge and combustion processes, an on-line in-situ sensor detecting and measuring free water (droplets) in the scavenge air intake for an engine is not mention nor described. Neither is the use of a free water sensor system for measuring and regulating air intake cooling and ventilation systems and ancillary machinery to lower overall running costs and NO_x emissions. Nor is any self-calibration and seal-cleaning property of such sensor system mentioned or described. DESCRIPTION / SUMMARY OF THE INVENTION

It is therefore the object of the invention to detect and measure free water in scavenge air intakes in engines, especially in two and four-stroke marine engines. It is a further object of the invention to provide a self-cleaning, optionally self-calibrating, free water in scavenge air sensor, as well as use the sensor system for measuring and regulating air intake cooling and ventilation systems and ancillary machinery to lower overall running costs and NO_x emissions. These objectives are achieved by embodiments of a sensor system and method for detecting and measuring free water in the scavenge air in an environment as explained in the following. In order to enable a better combustion of fuel oil inside a diesel engine, for example a marine engine, an adequate flow of fresh air is supplied to the combustion engine. The method by which sufficient amount of air is provided to the engine cylinders is known as scavenging. Controlled and regulated scavenging result in better fuel combustion, and therefore power output of the engine. The engines are interfaced with turbochargers which uses the exhaust gases in order to supply a consistent flow of fresh air inside the main engine.

The IMO ship pollution rules (contained in the "International Convention on the Prevention of Pollution from Ships", known as MARPOL 73/78EGR) and commonly referred to as Tier I-III standards sets limits on NO_x and SO_x emissions. Tier III standards coming into effect by 2016 are expected to require dedicated NO_x emission control technologies such as various forms of water induction into the combustion process (with fuel, scavenging air, or in-cylinder), exhaust gas recirculation, or selective catalytic reduction. This will further introduce moisture and free water into the scavenging air intakes for example when the exhaust gas is recirculated. The scavenger air - whether coming from the exhaust gas recirculation or not - must be free of free water (droplets). Failure to ensure water free air will result in a cavitation of the free water inside the combustion cylinder. The water content will further cause increased friction in one or more of the cylinders, leading to irreversible damage, for example frettings in the contact between cylinders and cylinder walls. Today, water from the scavenger air is removed by cooling the air, thus lowering the dew point for saturation to occur, while also directing and changing the flow of air, and the free water is subsequently removed. However, the problem today is that the system is not synchronized with the changes in the outside climate conditions (humidity, pressure, temperature), therefore the amount of water removed is varied and sometime result in partial removal of water which is not enough for either avoiding damages or efficient operation of the engine.

Changes in outside climate conditions, geographical variations in the humidity around the world, day/night variations, etc. all have a major impact on the amount of free water. Described herin is an alert system to detect the amount of free water in the scavenging air before introducing it into the cylinders, as well as automatically regulating the cooler and ancillary systems for optimal running. The sensor will also monitor and regulate the exhaust gas recirculation (EGR) process to optimise this operation also, thus lowering fuel and running costs as well as NO_x emissions. The solution to the above problem involves the use of a sensor to provide continuous data on the free water and humidity levels in the scavenging air with a feed back loop which will be used for efficiently regulating the air cooling. This will not only make the air optimally water free, but also optimises the air cooling for energy and NO_x emission savings. The sensor system is an in situ, and on-line, sensor capable of detecting and measuring the amount of free water in the scavenging air, ensuring that the air consumed by the next combustion cycle is having a sufficiently low level of free water. This process is essential for having a smooth-running internal combustion engine. To ensure that the sensor can measure the content of free water in situ with a sufficient reliability and stability the sensor is based on for example capacitance measurements between two parallel plates sensitive to air humidity - one humidity measure without heating the air (passing through a non-heated fine wire mesh, filter or chamber), and one parallel humidity measure with air passing through a heated filter, fine wire mesh or chamber. Heating the air by passing the heated fine wire mesh, heated filter or heated chamber will transform the free water (droplets) in the air into vapour (water in gas form), which can then be measured by a RH sensor element. Any difference in RH between the two RH sensor element measures (in the heated respectively non-heated filter or chamber measurement) will indicate the presence of free water, and enable calculations of the level of free water in the air.

The advantages of the heated chamber are that is captures and transforms all the water droplets into humidity, depending on the length of the chamber and the heating element, and thus provides a very accurate measure of the free water level. The advantages of heating the fine wire mesh or filter is that the solution is potentially very compact which enables easy installation, maintenance and service. In the below text we have proven and documented two independent systems and principles which both can measure the free water levels based on the above concepts:

System (A) double RH sensor, and

System (B) single RH sensor with reference sensor

System (A) double RH sensor

The sensor is directly placed in the scavenging air.

See Drawings Fig. 1-6 Humidity and power requirement computations, double RH sensor

In order to measure the mass of water that will flow through the main air vent to the engine, as droplets / aerosols, the sensor will be based on measuring Temperature (T), Relative Humidity (RH) and Pressure (P), and will have as output the Specific Humidity (SH). Each of the three measurements will be done in the main air vent (in a high pressure environment), placed in a sensor chamber (at high temperature, the high temperature is meant to force all water in vapor state). We measure the relative humidity, pressure and temperature in the cold chamber and the relative humidity, pressure and temperature in a high temperature chamber were all water has been turned into vapor and compute the difference between these two measures being the amount of free water.

Specific humidity is the ratio of water vapor to dry air in a particular mass, and is sometimes referred to as humidity ratio. Specific humidity ratio is expressed as a ratio of grams of water vapor, m_v, per kilogram of dry air m_a

That ratio is defined as:

SH= ^- ( 1 )

Specific humidity can be expressed in other ways including :

SH= 0,622 H O

P ^* dry air

or:

SH=

The actual vapor pressure P(H₂0) can be computed using the saturated vapor pressure ( p_sat ) and the relative humidity (φ ) :

The Saturated vapor pressure p_sat can be computed using the following formulae:

p_sat 0.61078 * 10' ^{' ;} ' (5)

The dew point temperature can be calculated using different formulae. Which is to be used depends on the needs. A well-known approximation used to calculate the dew point T_d given the relative humidity RH and the actual temperature T of air is: * (T, RH)

a^■■■■ ₇(T, RH) (6)

where

I

\ i iRHJlM)

b + T (7)

Where the temperatures are in degrees Celsius and "In" refers to the natural logarithm. The constants are:

a = 17.271

b = 237.7 °C

This expression is based on the August-Roche-Magnus approximation for the saturation vapor pressure of water in air as a function of temperature. It is considered valid for

0 °C < T < 60 °C

1% < RH < 100%

0 °C < T_d < 50 °C

There is also a very simple approximation that allows conversion between the dew point, the dry-bulb temperature and the relative humidity. This approach will be accurate to within about ± 1 °C as long as the relative humidity is above 50%. The equation is:

T = T - ^{m RH}

a 5 (8)

or

KH = 100 - 5(T - ¾. ₍₉₎

This can be expressed as a simple rule of thumb:

For every 1 °C difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with RH = 100% when the dew point equals the dry bulb temperature, where in this case RH is in percent, and T and T_d are in degrees Celsius.

The derivation of this approach, a discussion of its accuracy, comparisons to other approximations, and more information on the history and applications of the dew point are given in the Bulletin of the American Meteorological Society.

For temperatures in degrees Fahrenheit, * ^" ^5 ( 10)

or

RH = 100 - ¾7)

fj ^{1 Λ}» ( 11)

For example, a relative humidity of 100% means dew point is the same as air temp. For 90% RH, dew point is 3 degrees Fahrenheit lower than air temp. For every 10 percent lower, dew point drops 3 °F.

A calculation used by NOAA:

17.ti77

e_s = G.112 exp

T + 243.5 ,/

17.677^*.,

e„ = 6,112 exp

T - T_w) 0.00066 [1 + (0.001157V)

RH = 100-

Where RH is relative humidity in percentage and 7~_d is dew point in degrees Celsius

T and 7~_w are the dry-bulb and wet-bulb temperatures respectively in degrees Celsius

e_s is the saturated water vapor pressure, in units of millibar, at the dry-bulb temperature e_w is the saturated water vapor pressure, in units of millibar, at the wet-bulb temperature e is the actual water va por pressure, in units of millibar

Psta is "station pressure" (absolute barometric pressure at the site that humid ity is being ca lculated for) in units of millibar (which is also hPa) .

Electrical power to ensure free water is evaporated

A rectangula r electrical wire has cross-sectional area A and length / (Figure 4) . The resistance is then :

R = p{, (37) and the electrical power W becomes W =— =—. (38)

e R pi

Consider next a wrap formed as a cylindrical shell or plate with /, diameter D, and plate thicknesses d varying between 1 and 5 mm. The area A is then

A ~ nDd, (39)

and the resistance becomes

R = p- = p ί^ί^ . (40)

rA ^r n D (meter) d (meter) '

The material resistivity, for the given geometry, that can provide a voltage of 24 V and, simultaneously, a current of 1 A, i.e., a power of 24 W is

A V A 24 A

p ^ = R - l =— I I =— i i . (41) '

The resistivity needed is for example undoped GaAs or Si (silicon) or similar. Thermal power needed - an example

Consider next a situation where the humid air flow speed v into the sensor is 20 m/s and that 10 % of the volume intake is free water. This corresponds to the free water mass flow (units omitted - all values are in SI units) :

The amount of dry air mass flow is

m_dry air = v A^■ 0.9 ^■ 1.2 < < m_wa (43)

and we can therefore safely neglect the power consumption related to heating the dry air!

Next, this amount of free water is converted into steam and heated by, say, ΔΓ= 100 K. The total power required for this is:

W = m_waL + m_wa c_p(steam) ΔΤ = 2257000^■ 2000 ^■ A + 2080 ^■ 100 ^■ 2000 A = 2465000 ^■ A (44)

If one hole of d = 1 mm is made in the sensor wrap, the total hole area is n (0.5 ¹ 10 ^"3)² m^{2 t}he thermal power required is 1.93 W!

Evidently, this is equivalent to a power requirement of

/V-1.93 W (48)

for N holes of d = l mm diameter.

System (B) single RH sensor with reference sensor The sensor is directly placed in the scavenging air.

See Fig. 7 Sensor placed in the application, single RH sensor

See Fig. 8 Sensor outline, single RH sensor

See Fig. 9 The heated chamber, single RH sensor

Fig. 10 The cold chamber, single RH sensor

Fig. 11 assembling drawing, single RH sensor

Humidity and power requirement computations, single RH sensor Measurement of free water content in air intake

The sensor layout is shown in Figure 5. All temperatures are measured in Kelvin in the following and pressures are in millibars. The air intake in the following is dry atmospheric air containing H2O in free water form and steam. The coefficient 0.622 in Equation (1, 2) and the saturation pressure expression obeys the Goff-Gratch relation. Measurement principle

Before the humid air enters the measuring chamber (cold air intake), the temperature is and the pressure is p^. In the measurement chamber, the air is heated to a temperature 7^~ ₂ and the pressure changes to p₂- ^Tne heating is electronically regulated such that the saturated water pressure at 7^~ ₂ ^P^^ ^ ^{is n}'9^{ner tna n tne actua l} water partial pressure at 7^~ ₂ (P_H Q^^)) ^{A NCL} the water is on gas form (no free water). This can always be accommodated by reducing the ratio between the chamber volume and the surface area of the measurement chamber (e.g., by reducing all measurement chamber spatial dimensions proportionally).

References to temperatures (7^ and 7^~ ₂), pressures (p^ and p₂), and relative humidity (φ₂) are the same as in the text in Fig 9.

By measuring the temperature 7^~ ₂, the pressure p₂, and the relative humidity φ₂ in the measurement chamber, the specific humidity SH^ in the measurement chamber becomes

ΡΗ,Ο^

SH₂ = 0.622 , (1)

^(P2-^pH₂0^(T2⁾ where = ^sat^' ⁽²⁾ and (the most-used expression for saturation pressure known as the Goff-Gratch equation) log₁₀P_saf(T₂) = - 7.90298 (373.16/Γ₂ - 1)

+ 5.02808 log₁₀(373.16/J₂)-1.3816- 10^"7( IO¹¹-³⁴⁴^³⁷³-¹⁰' - 1)

+ 8.1328^■ 10^"7( IO^"3-⁴⁹¹⁴⁹^/^{37310 " 1}'- 1)+ log₁₀ (1013.246) . (3)

Here, P_sat. is given in units of millibar and 1 mbar =101.325 Pa (and is in Kelvin). We emphasize that the latter expression applies at other temperatures as well and specifically at T^.

From the specific humidity SH^, we can calculate the amount of water in a volume containing m , . as

s dry air

ATI.. _. = S- -.AT7 , .. (4)

H₂0 2 dry air '

It is now possible to assess whether free water is present in the humid air intake (before the humid air enters the measurement chamber) where the temperature is and the pressure is

P Saturated water at this point would correspond to the following amount of water in a volume containing m . . :

s dry air ^mH₂o,sat⁼ SH_satm_dryair, (5) where

SH₂ = 0.622 ^Psat(Tl) , (6)

and log_joP_satCTJ = - 7.90298 (373.16/1 - 1) + 5.02808 log₁₀(373.16/7 )-1.3816- 10^"7( IO¹¹-³⁴⁴^/³⁷³'¹⁰' - l) + 8.1328^■ 10^"7( IO^"3-⁴⁹¹⁴⁹^/³⁷³-^{10 " 1}) - i)+ log ₁₀ (1013.246) (7)

Evidently, there is free water present before the intake to the measurement chamber only if m_H2o > m_H2o ,sat^■ (8) Furthermore, we can determine the exact amount of supersaturation SUP defined as

mH₂0,sat ' and the amount of free water on the humid air intake side: m_H20 - m_Hz0iSat in a volume containing m , . dry air.

s dry air '

Power needed to heat the humid air

The amount of electrical power W needed to heat the humid air consisting of free water, steam and dry air from a thermodynamic state with temperature and pressure to a state with temperature and pressure p.., we use the following expression

H/-m_dry_air(h_dryair(p₂, T₂) -

+ m_H2o(hsteam(P₂' ^T ₂) ^{_ n}steam(P_l' ^T _l))+ (™H₂0 ~

(10) where ^'m and L are the dry-air mass flow, total hLO mass flow, dry air^{1 171} H-,0' ^hdryair' ^hsteam , steam mass flow [keeping in mind that the total h^O mass flow minus the steam mass flow is the free water mass flow], specific enthalpy of dry air, specific enthalpy of steam, and latent heat of evaporation, respectively. In obtaining this equation, we neglect energy losses to the ambient (such as radiation losses from the metal wrap).

Denoting the relative mass content of dry air x, of steam y, the relative mass content of water is 1 -x-y, and we have the equations

Note that x and y are determined from the expressions in the previous section :

The volumetric flow^'\ is

= Au, (16) where A is the area of the in-flow hole to the sensor and u is the flow velocity. The volumetric flow obviously fulfills

^ ⁼ v + ^ steam + V dry air - (17)

Assuming further that the mass ratios apply equally well to the mass flow ratios, a few manipulations based on Equations (11)-(13) lead to

Vdry air = _a+b+r (18)

where

Pdry air y

b = (20)

Then, we have

V - ^Pdry air 1-x-y ,^

vwa— _n ^v dry air- K*- - )

^wa ^x

1 - ^Pdry air y

"steam _n dry cur > κ'-'-ι

^steam ^x

and the mass flows are

m_Wa = P_wa va- (24) rilsteam ^— Psteam steam · (25)

Dry-air, steam, and water enthalpies are well approximated by the expressions:

hdry air (p₂.T₂) - h_{dry air} (_Pl, Tj = c_p(dry air) (T₂ - T₁ ) , (26)

hsteam (p₂.T₂) - h_steam(_Pl, Tj = c_p(steam) (T₂ - T_x ) . (27)

We now only need material parameters to determine the required power to heat the humid air by use of equation (10). These are approximately (some are rather accurate) :

c_p(dry air) = 1 J/g/K, (28) c_p(steam) = 2.08 J/g/K, (29)

*steam= 0-6 kg/m'. pi)

Q = 1000 kg/m³, (32)

Kwa ^{s y} L = 2257 J/g. (33)

The total in-flow hole area A is small enough to ensure that we can overcome the latent heat by electrical heating as required for the sensor principle.

Sensor output

See Figure 12, a plot of the steam and free water zones in the sensor.

Figure 12 : Schematic plot of the steam and free water zones.

Evidently, the calculations above and especially Equations (4) and (5) allow us to determine uniquely whether we are in the steam or in the free water zone by measuring T ρ^, T^, P₂' and q>2 (refer to Figure 12). The scavenge air is in the steam zone only if mH₂0,sat ^{> m}H₂0 (34) while the scavenge air contains free water if m_H2o > m_H2o ,sat (35)

The sensor will give an alarm if

m_H2o > A m_H2o ,sat> (36) for a number A below 1 but above a specified value. Electrical power given

A rectangular electrical wire has cross-sectional area A and length / (Figure 3). The resistance is then :

R = P-_A, (37) and the electrical power W becomes

A ~ nDd, (39)

and the resistance becomes

L (meter)

^R = ΡΪ = P n D (meter) d (meter) ' (40) The material resistivity, for the given geometry, that can provide a voltage of 24 V and, simultaneously, a current of 1 A, i.e., a power of 24 W is

A V A 24 A

p ^ = R - l =— I I =— i i . (41) '

The amount of dry air mass flow is

m_dry air = v A^■ 0.9 ^■ 1.2 < < m_wa (43)

Evidently, this is equivalent to a power requirement of

/V-1.93 W (48)

for N holes of d = l mm diameter.

Flow principles

Different air flow principles have been reviewed including both seriel and parallel air flows, where the sensors in the seriel flow first passes through the non-heated chamber/filter, and then into the heated chamber/filter. The advantage of the seriel principle, compared to the parallel principle, is that is removes the risk and uncertainty that the air is not comparable in the two chambers. This risk has however been mathematically established to be minimal. The potential risk of the seriel principle is, however, that sensor and filter I (in the unheated chamber) contaminates the airflow and humidity measures for sensor and filter II (in the heated chamber). The parallel airflow principle has thus been estalished as the most precise. Alternative technologies and sensing principles than capacitive sensors and RH could be to use elastic or resistive types of sensoring technologies. The sensor system is alerting via electronic communication, visual or acoustic alarms, or a combination thereof, if free water levels are present or nearing pre-defined critical limits. If the received free water measures indicate that the actual level at the sensor site is higher than the acceptable level, a pre-defined alarm is created. This will allow either manual (for example surveillance personnel) or automatic regulations of the cooling and ancillary system processes in an ongoing and continuous re-calibration flow thus avoiding over- and under-cooling of the scavenge air. The sensor system is further advanced by including further self-cleaning capabilities. This could for example be via titanium dioxide (Ti0₂) coating and UV illumination of the surface of the sensor filter ensuring a cleaner surface of the electrodes for long-term stability in terms of precision and lower running costs. In this way, the sensor system offers unique self-cleaning capabilities, which also improve the lifetime of the sensor system and which avoids the need of frequent transport and external cleaning of the sensor element. Optionally, the sensor elements be easily removed and can be combined with a manual cleaning procedure. The sensor unit comprises electronics for converting the electronic signal indicative of the degree of free water in the scavenge air into sampled data for further data processing . For example, such data processing is performed by the sensor unit. Alternatively, the sensor unit comprises a data transmitter, for example a wireless transceiver, for transmitting the data from the sensor unit to a monitoring station remote from the sensor unit. Such a monitoring station is used for analysing the transmitted data from the sensor unit. The monitoring station is then programmed for evaluating the transmitted data and on the basis thereof determining a parameter indicative of the free water level in the environment. For example, the sensor system comprises a terminal with an indicator configured for indicating whether the actual free water level is below or above a threshold value. Examples of such terminals are computer or control systems, mobile telephones, such as smartphones, displays or monitors. This embodiment has the possibility of providing real-time alerts for critical humidity levels. For example, an alarm is raised by submitting an alarm message to a control terminal with a display for indicating the alarm to surveillance personnel. For example, the sensor comprises a wireless transmitter or transceiver and is transmitting the sensor signal to a monitoring station remote from the sensor. The monitoring station is programmed for evaluating the signal at the monitoring station such that the monitoring station determines whether the actual level of free water corresponds to the threshold characteristics and raises an alarm if the actual level of free water does not correspond to the threshold conditions. Thus, the free water in scavenge air sensor system offers the capability of on-line monitoring at relevant places in a sensor network. Online monitoring provides the end-user with continuous information about the actual free water conditions including warning in case of critical levels, therefore enabling necessary action in time. There are considered a number of free water control levels. The sensor system is able to inform about the free level, the growth rate of the free water, and extrapolations of these data.

Apart from marine engines, other examples of measuring and regulating air intake cooling systems and ancillary machinery are within industrial processing equipment, air or landbased transportation, power generation or for example production of oil and gas.

SHORT DESCRIPTION OF THE DRAWINGS

System (A), double RH sensor

The invention is explained with reference to the drawing, where Fig 13 illustrates a sensor according to the invention in an exploded view;

Fig 14 illustrates a cross sectional view;

Fig 15 illustrates cold and heated chamber

Fig 16 illustrates a RH sensor element with Titanium oxide coating, side view;

Fig 17 illustrates UV light in cold chamber

Communication

Digital output: RS232, RS485 or CANopen (galvanic isolated)

Digital output data transfer: Modbus RTU / Modbus CANopen

Analogue output: 4 - 20 mA (galvanic isolated)

Relays:

Contact arrangement: 2 x NC

Rates voltage: 60V

Rated current(40 C) : 1A

System (B), single RH sensor with reference sensor

The invention is explained with reference to the drawing, where

Fig 18 illustrates single RH sensor in an exploded view; Fig 19 illustrates a cross sectional view for cold chamber, single RH sensor

Fig 20 illustrates a cross sectional view for heated chamber, single RH sensor

Fig 21, Heated chamber, single RH sensor

Fig 22 Cold chamber, single RH sensor

Communication

Digital output: RS232, RS485 or CANopen (galvanic isolated)

Digital output data transfer: Modbus RTU / Modbus CANopen

Analogue output: 4 - 20 mA (galvanic isolated)

Relays:

Contact arrangement: 2 x NC

Rates voltage: 60V

Rated current(40 C) : 1A

DETAILED DESCRIPTION / PREFERRED EMBODIMENT

Systems (A), double RH sensor

Fig 23, complete assembly drawing, double RH sensor

1. Shellmould cast metal housing made of aluminium

2. End cover cast metal housing made of aluminium

3. Foil plate made of polyester with test button built for testing the High alarm and High High alarm functions

4. Sensor element housing made of stainless steel 316

5. Sensor house to cold chamber and hot chamber made of stainless steel 316

6. Sealing ring between the end cap and the sensor house

7. 8 pin connector female for maximum 60 VDC and 2A in plastic and brass

8. 8 pin connector male for maximum 60 VDC and 2A in plastic and brass

9. Nameplate indicating the product number and important product information carried in polyester type 7818

10. 3 pieces screws DIN 7985 made of stainless steel

l l . PCB for heated chamber with an capacitive element detects RH 5 to 95%, T2 temperature transmitter that measures the ambient temperature -40 deg. C to 80 deg. C, T3 tempera- ture transmitter that measures the jacket temperature -40 deg. C to 150 deg. C. Pressure Transmitter PI measuring the pressure in the heated chamber 1 to 6 bar.

PCB for cold chamber with an capacitive element detects RH 5 to 95%, T2 temperature transmitter that measures the ambient temperature -40 deg. C to 80 deg. C, T3 ambient temperature transmitter that measures the jacket temperature -40 deg. C to 150 deg. C. Pressure Transmitter PI measuring the pressure in the heated chamber 1 to 6 bar.

Cold chamber filter as is made of material ceramics and the filter has for example 12 holes, each with a diameter of for example 1 mm, this gives sufficient opening for the free water to pass into the cold chamber.

To ensure against contamination of microorganisms inside of the cold chamber filter it can be coated with titanium dioxide deposited on the inside surface of the cold chamber filter by processes like CVD, PVD, reactive PVD, HiPIMS, lacquer, Sol-Gel, thermal spaying or sintering of a Ti or Ti02 containing powder

In combination with an integrated UV-light source, placed in cold chamber filter, which illuminates the inside surface of the cold chamber filter, the Ti0₂ coated surfaces are able to decompose microorganisms on the surfaces

Teflon isolator between RH Sensor element and the hot filter (red)

Heating chamber filter (11) is made of material ceramics and the filter has for example 12 holes, each with a diameter of example 1 mm, this gives sufficient opening to free water can be heated by allocating for example 24 watt of heating to the chamber filter

Inside the heating chamber filter is a vapour-deposited heater surface with the necessary resistance to heat conduction by using undoped GaAs or Si (silicon) or similar. In the formulas, this is described from 37 to 44. To ensure against contamination of microorganisms there is a built-in functionality that heats the chamber to over for example 85 deg. C

Sensor top housing made of stainless steel 316

Temperature Control relay for heated chamber with integrated UV light

System (B), single RH sensor with reference sensor Fig 24, complete assembly drawing, single RH sensor l . Shellmould Cast metal housing made of aluminium.

2. End cover Cast metal housing made of aluminium.

3. Foil plate made of polyester with test button built for testing the High alarm and High High alarm functions.

4. Sensor element housing made of stainless Steel 316.

5. Sensor house too cold chamber and hot chamber made of stainless steel 316.

6. Sealing ring between the end cap and the sensor house

7.8pins connector female for maximum 60 VDC and 2 Amp.udfort in plastic and brass.

8.8pins connector male for maximum 60 VDC and 2 Amp.udfort in plastic and brass.

9. Nameplate indicating the product number and important product information carried in polyester type 7818.

10. 3 pieces screws DIN 7985 made of stainless steel.

11. PCB for sensor element with a capacitive sensor that detects RH 5 to 95%, T2 temperature transmitter that measures the ambient temperature -40deg. C to 80 deg. C, T3 temperature transmitter that measures the jacket temperature -40 deg. C to 150 deg. C.

Pressure Transmitter which measures the pressure in the heated chamber 1 to 6 bar.

12. Red. Heating chamber filter as indicated by the color red is made of material ceramics and the filter has example 12 holes, each with a diameter of example 1 mm, this gives sufficient opening to free water can be heated by allocating example 24 Watt to the heating chamber filter.

Inside the heating chamber filter is a vapour-deposited heater surface with the necessary resistance to heat conduction by using undoped GaAs or Si (silicon) or similar. In the formulas, this is described from 37 to 44. To ensure against contamination of microorganisms there is a built-in functionality that heats the chamber to over for example 85 deg. C Blue. Cold chamber filter is identical to the hot chamber and the filter is indicated by the color blue, made of ceramic material and the filter has for example 12 holes, each with a diameter of for example 1 mm, this provides sufficient opening for steam and water to freely enter into the cold chamber via the filter. To ensure against contamination of microorganism inside of the cold chamber the filter is coated with titanium dioxide deposited on the inside surface of the cold chamber filter by processes like CVD, PVD, reactive PVD, HiPIMS, lacquer, Sol-Gel, thermal spaying or sintering of a Ti or Ti02 containing powder. The titanium oxide layer thickness is in the range of few nm to microns meter. In combination with an integrated UV-light source, placed in heat control element no. 13, which illumi- nates the inside surface of the cold chamber filter, the Ti0₂ coated surfaces are able to decompose organic material and hence clean themselves to a new steady-state level.

Heat control element with a T3 temperature transmitter placed on the filter wall, measures the hot filter surface Temperature and control the needed power for the heated chamber, with an ambient temperature -40deg. C to 80 deg. C. The T3 temperature transmitter measures the jacket temperature -40 deg. C to 150 deg. C.

Isolator between RH Sensor element and the hot filter (red) material is teflon.

The two Terminal pins connected for example 24VDC voltage named power cables and with example 1 Amp., to heat control element no.13. The needed power (Watt) as defined below, material brass with coated gold. The power cables are connected to the main PCB (16) and in the other end (no. 12 red) and all needed power and all needed two ways communication from PCB (no.16) and to Heat control element (no. 13) are performed by power communication. Power communication and power on the two wires are delivering all functionality information, placed in embedded software on PCB (no. 16.)

The sensor element is no. 11 measures RH and no. H is calibrated against standard salts and, pressure transmitter no. P2 is calibrated against standard pressure transmitter and, temperature transmitter no. T2 is calibrated against standard pressure transmitter

PCB consists of all electronic ad functionality control by embedded software. The power example 24VDC.

Claims

C LAIM S

A double RH sensor system for detecting and measuring free water in a scavenging air intake environment, the sensor system comprising a sensor unit; the sensor unit comprising two sensor elements, wherein each sensor element is a relative humidity based sensor and comprises a sensor element (Fig 15), heated filter or chamber (Fig 16) and non-heated filter or chamber (Fig 17), having two openings (Fig 14) for exposure to the scavenge air from the environment; the sensor being configured for providing and comparing electronic signals indicative of the degree of RH, temperature and pressure from each of the two chambers

A single RH sensor system with reference for detecting and measuring free water in a scavenging air intake environment, the sensor system comprising a sensor unit; the sensor unit comprising two sensor elements, wherein one sensor element is a relative humidity based sensor and comprises a sensor element (Fig 20 and 21), heated filter or chamber (Fig 21) and non-heated filter or chamber (Fig 22), having two openings (Fig 19) for exposure to the scavenge air from the environment; the sensor being configured for providing and comparing electronic signals indicative of the degree of RH, temperature and pressure from each of the two chambers

A sensor system according to claim 1 or 2, wherein the surface in the non- heated chamber (Fig 17 and 22) eliminate the micro organic material by UV light and a photo catalytically active titanium dioxide coating.

A sensor system according to claim 1 or 2, wherein the surface in the heated chamber (Fig 16 and 21) eliminate the micro organic material by increasing the temperature above 85 deg C.

A sensor system according to any preceding claim, wherein the sensor unit comprises electronics (Fig 13 and 24) for analysing and determining the levels of free water in the air, and converting the electronic signals indicative of the degree of free water in the air into sampled data; and wherein the sensor unit comprises a data transmitter for transmitting the data from the sensor unit to a monitoring station remote from the sensor unit. A sensor system according to claim 5, wherein the sensor system comprises a terminal, monitor or display with an indicator configured for indicating whether the actual free water level is below or above a threshold value.

Use of a sensor system according to any one of preceding claims for measuring free water in scavenge air intakes in marine engines, and alerting if levels do not correspond to pre-defined criteria .

Use of a sensor system according to any one of the preceding claims for measuring and regulating air intake cooling systems, exhaust gas return systems and ancillary machinery within vessels.

Use of a sensor system according to any one of the claims 1-7 for measuring and regulating air intake cooling systems and ancillary machinery within i ndustrial processing equipment, air or landbased transportation, power generation or for production of oil and gas.

A sensor system according to any preceding claims wherein the sensor system further comprises a reference sensor as redundancy