Patent Description:
Aircraft can be equipped with steam ovens for cooking or heating food for passengers of the aircraft. Steam ovens are typically provided as part of a galley insert which enables easy installation and removal of the oven from an aircraft galley. The food is heated in an inner cavity of the oven using steam. The steam can be provided by supplying water to the oven and heating the water within the oven to evaporate it, or by injecting steam into the oven directly.

Factors which affect the cooking process within the steam oven include temperature, pressure and humidity. Whilst temperature and pressure are relatively easy to measure and control, humidity is more challenging. Conventional humidity sensors, e.g. those which use capacitive measurement to determine the amount of moisture in the air, can be fragile and may become easily damaged if used in an oven of an aerospace galley insert. In addition, they may not be suited to the extreme conditions experienced within ovens, such as wide temperature ranges, exposure to cleaning chemicals, corrosion by food spices, etc..

<CIT> discloses a steam oven for an aircraft including cook chamber temperature sensor to measure a temperature of steam discharged from a steam outlet. An amount of water supplied to the cook chamber for steam generation purposes is regulated based on the measured temperature.

The present disclosure aims to provide an improved aerospace galley insert.

According to the invention there is provided an aerospace galley insert comprising: an oven defining therein an oven inner cavity for receiving food to be prepared; a fluid supply for supplying fluid comprising water or water vapour to the oven inner cavity; an exterior space defined outside of the oven inner cavity; a heat pipe extending between the oven inner cavity and the exterior space; a first temperature sensor for detecting a first temperature in the oven inner cavity; a second temperature sensor for detecting a second temperature in the exterior space; a third temperature sensor for detecting a third temperature of the heat pipe where it extends into the exterior space; and a control unit configured to determine an actual water vapour concentration in the oven inner cavity based on the first, second and third temperatures, and configured to control the fluid supply in order to adjust the actual water vapour concentration to a target water vapour concentration.

In an optional example, the target water vapour concentration is a water vapour molar fraction of at least <NUM>%. The target water vapour concentration may be a water vapour molar fraction of at least <NUM>%. The target water vapour concentration may be a water vapour molar fraction of at least <NUM>%. The target water vapour concentration may be a water vapour molar fraction of <NUM>-<NUM>%. The target water vapour concentration may be a water vapour molar fraction of <NUM>-<NUM>% or <NUM>-<NUM>% or <NUM>-<NUM>% or <NUM>-<NUM>%.

In an optional example, the control unit is configured to adjust the actual water vapour concentration based on a measured ambient air pressure. Optionally, the control unit comprises an air pressure sensor for measuring the air pressure in the exterior space and so provide the measured ambient air pressure.

The heat pipe may optionally comprise titanium at least where the heat pipe extends in the oven inner cavity.

In an optional example, the control unit is configured to determine the actual water vapour concentration in the oven inner cavity based on a measured water vapour concentration in the exterior space. The control unit may optionally comprise a water vapour concentration sensor for measuring the water vapour concentration in the exterior space and so provide the measured water vapour concentration.

The heat pipe may optionally comprise a first leg extending between the oven inner cavity and the exterior space, and a second leg extending in the exterior space and joined to the first leg by a bent portion. The second leg may extend at least partly upwardly from the bent portion. The third temperature sensor may optionally be arranged to measure the temperature at the bent portion of the heat pipe.

In an optional example, a minority of the heat pipe is located in the oven inner cavity. In some examples, no more than <NUM>% of the length of the heat pipe is located in the oven inner cavity.

Optionally, the heat pipe comprises a wick.

According to the invention there is provided a method of managing water vapour concentration in an oven of an aerospace galley insert, the oven defining therein an oven inner cavity for receiving food to be prepared, and the aerospace galley insert having a heat pipe extending between the oven inner cavity and an exterior space defined outside of the oven inner cavity, the method comprising: detecting a first temperature in the oven inner cavity; detecting a second temperature in the exterior space; detecting a third temperature of the heat pipe where it extends into the exterior space; determining an actual water vapour concentration in the oven inner cavity based on the first, second and third temperatures; and controlling a fluid supply to the oven inner cavity in order to adjust the actual water vapour concentration to a target water vapour concentration, the fluid comprising water or water vapour.

In an optional example, the method comprises measuring an ambient air pressure and adjusting the actual water vapour concentration based on the measured ambient air pressure. Optionally, the control unit comprises an air pressure sensor for measuring the air pressure in the exterior space and so provide the measured ambient air pressure.

In an optional example, the method comprises measuring a water vapour concentration in the exterior space, and determining the actual water vapour concentration in the oven inner cavity based on the measured water vapour concentration in the exterior space. The control unit may optionally comprise a water vapour concentration sensor for measuring the water vapour concentration in the exterior space and so provide the measured water vapour concentration.

The heat pipe may optionally comprise a first leg extending between the oven inner cavity and the exterior space, and a second leg extending in the exterior space and joined to the first leg by a bent portion. The second leg may extend at least partly upwardly from the bent portion. The third temperature may be the temperature of the bent portion of the heat pipe.

An aspect of the present disclosure provides a method of managing water vapour concentration in a steam oven of an aerospace galley insert as disclosed herein.

Certain embodiments of the disclosure will now be described, by way of example only, and with reference to the accompanying drawings.

<FIG> shows a schematic diagram of an example of an embodiment of the present disclosure. The Figure shows an aerospace galley insert <NUM> comprising an oven <NUM> defining therein an oven inner cavity <NUM> for receiving food for heating or cooking. An exterior space <NUM> is defined outside of the oven inner cavity <NUM> and within the aerospace galley insert <NUM>. The exterior space <NUM> may be at an ambient temperature and pressure of a space in which the aerospace galley insert <NUM> is located. In some examples, the aerospace galley insert <NUM> is located in an aircraft galley, and the exterior space <NUM> is approximately at the cabin air pressure and cabin temperature of the aircraft.

The aerospace galley insert <NUM> comprises a fluid supply <NUM> for providing fluid comprising water or water vapour, i.e. steam, to the oven inner cavity <NUM>. In some examples, the fluid supply <NUM> can provide water vapour directly to the oven inner cavity <NUM> from an exterior water vapour source. In other examples, the fluid supply <NUM> can provide water to a heating element (not shown) located inside the oven inner cavity <NUM>, wherein the water is evaporated using the heating element to create water vapour. The water vapour is used to transfer heat to the food within the oven inner cavity <NUM>. One or more valves <NUM> are provided to control the flow of water or water vapour to the oven inner cavity <NUM> and thereby control the amount of water vapour inside the oven inner cavity <NUM>.

The aerospace galley insert <NUM> further comprises a control unit <NUM>. The control unit <NUM> is configured to control the fluid supply <NUM> to the oven inner cavity <NUM>. In this example, the control unit <NUM> is configured to control the valve <NUM> that regulates the flow of water or water vapour to the oven inner cavity <NUM>. For instance, the control unit <NUM> can increase the amount of water vapour in the oven <NUM> by opening the valve <NUM>, and decrease the amount of water vapour in the oven <NUM> by closing the valve <NUM>. The control unit <NUM> may be configured to control other operations of the oven <NUM> as well, e.g. the internal oven temperature and/or pressure.

A heat pipe <NUM> is partially disposed inside the oven inner cavity <NUM>. The heat pipe <NUM> extends between the oven inner cavity <NUM> and the exterior space <NUM>. The heat pipe <NUM> may be understood as having a first portion 8a located inside the oven inner cavity <NUM>, a second portion 8b extending through a wall <NUM> of the oven inner cavity <NUM>, and a third portion 8c located in the exterior space <NUM>. In this embodiment, the heat pipe <NUM> is substantially straight.

In this example, the heat pipe <NUM> is positioned such that a minority of the heat pipe <NUM> is located in the oven inner cavity <NUM>, i.e. the first portion 8a is a minority of the length of the heat pipe <NUM>. A minority of the heat pipe <NUM> may be less than half of the length of the heat pipe <NUM>. In some examples, no more than <NUM>% of the length of the heat pipe <NUM> is located in the oven inner cavity <NUM>, or no more than <NUM>%, or no more than <NUM>%, or no more than <NUM>%. A smaller proportion of the length of the heat pipe <NUM> being located in the oven inner cavity <NUM> may decrease the likelihood of damage occurring to the heat pipe <NUM> such as during insertion and removal of food, cleaning of the oven inner cavity <NUM>, etc..

When a heat pipe <NUM> is positioned to extend partially into an oven <NUM>, the temperature measured on the heat pipe <NUM> at a particular oven temperature and ambient temperature changes depending on the water vapour concentration inside the oven <NUM>. This is because when the water vapour concentration changes, so does the thermal conductivity of the gas inside the oven <NUM>, thus affecting the ability of the heat pipe to transfer heat from the oven <NUM> along the heat pipe <NUM>. Therefore, the heat pipe <NUM> can be used to estimate the water vapour concentration in the oven <NUM> by measuring the temperature of the heat pipe <NUM> and relating the temperature measurement to the water vapour concentration. The heat pipe can therefore be configured as a water vapour concentration sensor.

The aerospace galley insert <NUM> comprises a plurality of temperature sensors 10n for detecting the temperature of various parts of the aerospace galley insert <NUM>. A first temperature sensor 10a is arranged to detect a first temperature in the oven inner cavity <NUM>. A second temperature sensor 10b is arranged to detect a second temperature in the exterior space <NUM>, which may be an ambient temperature (e.g. a cabin temperature). A third temperature sensor 10c is arranged to detect a third temperature of the heat pipe <NUM> where it extends into the exterior space, i.e. the temperature of the third portion 8c. Other temperature sensors may be provided.

The control unit <NUM> is in electrical communication with the temperature sensors 10n to receive sensor data therefrom. The control unit <NUM> is configured to process the sensor data to determine an actual water vapour concentration inside the oven inner cavity <NUM> based on the temperature data from the three temperature sensors 10a, 10b, 10c.

The water vapour concentration is a measure of the amount or proportion of water vapour in the oven inner cavity <NUM> and is related to the humidity of the oven inner cavity <NUM>. Relative humidity (RH) is the ratio of the partial pressure of water vapour to the equilibrium vapour pressure of water at a given temperature. Relative humidity depends on the temperature and the pressure of the system of interest, i.e. of the oven inner cavity <NUM>. In some examples, the water vapour concentration may be expressed in terms of absolute or relative humidity. The water vapour concentration may alternatively be expressed in terms of molar fractions, which has the benefit that it does not depend on temperature or pressure of the system. The molar fraction is the ratio of the number of moles of one component of a solution or mixture (e.g. water vapour molecules in the oven) to the total number of moles representing all of the components (e.g. water vapour molecules plus air molecules in the oven).

In the example shown in <FIG>, the aerospace galley insert <NUM> further comprises an air pressure sensor <NUM> for measuring the air pressure in the exterior space <NUM>. The air pressure may be an ambient air pressure, e.g. a cabin air pressure. The aerospace galley insert <NUM> further comprises a water vapour concentration sensor <NUM> for measuring the water vapour concentration in the exterior space <NUM>. The air pressure sensor <NUM> and/or the water vapour concentration sensor <NUM> may be of conventional design. Since the water vapour concentration sensor <NUM> is not located inside the oven inner cavity, and hence is not exposed to such harsh conditions and is less likely to be damaged, a conventional humidity sensor may be suitable. The control unit <NUM> is in electrical communication with the air pressure sensor <NUM> and the water vapour concentration sensor <NUM> to receive sensor data therefrom.

In some embodiments, the control unit <NUM> is configured to determine the actual water vapour concentration inside the oven inner cavity <NUM> based on the sensor data from the air pressure sensor <NUM> and/or the water vapour concentration sensor <NUM>. Using these measurements in addition to the temperature measurements may increase the accuracy of the water vapour concentration estimation.

The control unit <NUM> is configured to control the fluid supply <NUM> in order to adjust the actual water vapour concentration to a target water vapour concentration. For instance, if the actual water vapour concentration is lower than the target water vapour concentration, the control unit <NUM> may cause the valve <NUM> to open to allow more water or water vapour to enter the oven inner cavity <NUM>. Conversely, if the actual water vapour concentration is higher than the target water vapour concentration, the control unit <NUM> may cause the valve <NUM> to close to decrease the water or water vapour entering the oven inner cavity <NUM>. The control unit <NUM> may also vent some water vapour from the oven inner cavity <NUM> to decrease the actual water vapour concentration.

In embodiments in which the air pressure and/or the water vapour concentration in the exterior space <NUM> is measured, the control unit <NUM> may be configured to adjust the actual water vapour concentration to the target water vapour concentration based on the measured air pressure and/or the measured water vapour concentration in the exterior space <NUM>.

Achieving or maintaining a target in the oven inner cavity <NUM> may improve the cooking or heating of the food. If the water vapour concentration in the oven inner cavity <NUM> is too low, too much water may transpire out of the food during cooking, leading to a lower food quality. On the other hand, if the water vapour concentration is too high, the ability of the air to transfer heat to the food may decrease because steam cannot transfer heat as well as air, thus increasing cooking time.

In some examples, the target water vapour concentration is at least <NUM>% molar fraction of water vapour (i.e., at least <NUM>% of the total of 'air molecules plus water vapour molecules' are water vapour molecules). In some examples, the target water vapour concentration is at least <NUM>% molar fraction of water vapour. In some examples, the target water vapour concentration is at least <NUM>% molar fraction of water vapour. In some examples, the target water vapour concentration is <NUM>-<NUM>% molar fraction of water vapour. Other target water vapour concentrations may be selected, e.g. depending on the parameters of the system such as cooking temperature and pressure.

The inventors have found that <NUM>% molar fraction of water vapour is the minimum fraction at which no transpiration occurs from food being cooked at <NUM> and <NUM> bar (100000Pa) pressure. Lower cooking pressures have been found to require a higher minimum water vapour molar fraction to prevent transpiration. For instance, at an altitude of <NUM> feet and a corresponding pressure of around 75300Pa, the minimum water vapour fraction at which no transpiration occurs has been found to be around <NUM>%. Thus, a target molar fraction of water vapour of at least <NUM>% or at least <NUM>% may decrease or prevent transpiration when cooking food within an oven of a galley insert on an aircraft at both sea level and high altitudes.

The inventors have also found that an increase in water vapour molar fraction above <NUM>% significantly increases the cooking time due to the negative impact of water vapour on heat transfer. Compromising between the heat transfer and transpiration whilst reducing the impact on both factors, the inventors found an ideal molar fraction for avoiding meal transpiration of <NUM>% or higher at <NUM> feet altitude (i.e. sea level), and of <NUM>% or higher at <NUM> feet altitude; and an ideal molar fraction for limiting the reduction of heat transfer of <NUM>% or lower (largely independently of altitude). Thus, as a balance of these factors, the target water vapour molar fraction may be <NUM>-<NUM>%.

However, in embodiments, water vapour (steam) is not injected for an initial portion of a cooking cycle, and is injected after that initial portion. In embodiments, water vapour (steam) is not injected into the oven for around a quarter of a cooking cycle, in particular the first quarter of a cooking cycle. This is because, for instance, if steam were injected during the first <NUM> minutes of a <NUM> minute cooking cycle before the food has heated sufficiently, the steam would condense on the meals and cause inefficient cooking. Additionally, it takes some time for the oven to reach the set-up temperature. The inventors have found that, as a result of this, the target molar fraction of water vapour can be increased (compared to the theoretical optimum) to further decrease or prevent transpiration from the meals without affecting the cooking time. Thus, the target water vapour molar fraction may be <NUM>-<NUM>%.

The heat pipe <NUM> may optionally comprise metal material which is beneficial to the good thermally conductive properties of metal. For instance, the heat pipe may comprise steel, stainless steel, copper, etc. The first portion 8a of the heat pipe <NUM> may be exposed to more harsh conditions compared to the third portion 8c of the heat pipe <NUM> located in the exterior space <NUM>. The heat pipe <NUM> may therefore include materials which are more robust and/or more resistant to corrosion at least where the heat pipe <NUM> extends into the oven inner cavity <NUM>, i.e. at least at the first portion 8a. In one example, the heat pipe comprises titanium at least where the heat pipe extends in the oven inner cavity. Titanium may be less prone to corrosion and/or more robust than some other materials and hence more suited to enduring the conditions in the oven.

<FIG> shows a conventional heat pipe <NUM>. Heat pipes are commonly used for transferring heat from a region of relatively high temperature to a region of relatively low temperature. Heat pipes utilise the principle of phase changes to transfer heat. The heat pipe <NUM> comprises a wick <NUM> surrounding a vapour cavity <NUM> and disposed inside a casing <NUM>. Inside the heat pipe <NUM> is a working fluid. When a first end 13a of the heat pipe <NUM> is heated, the working fluid in the wick <NUM> will evaporate in the vapour cavity <NUM>, absorbing thermal energy. The working fluid vapour will then migrate along the vapour cavity <NUM> to a second end 13b of the heat pipe <NUM> which is at a relatively low temperature compared to the first end, where the vapour will condense to liquid again. The liquid will flow back to the first end 13a, e.g. by the action of gravity or by the use of a capillary material in the wick <NUM>. This cycle then repeats, causing heat to be transferred from the heated first end 13a to the non-heated second end 13b.

The heat pipe <NUM> may be used in embodiments of the present disclosure for estimating the water vapour concentration inside an oven of an aerospace galley insert. For instance, the heat pipe <NUM> may be used as heat pipe <NUM> in the aerospace galley insert <NUM> of <FIG>. In such examples, the first end 13a is located in the oven inner cavity <NUM>, and the second end 13b is located in the exterior space <NUM> of the aerospace galley insert <NUM>.

In other examples, the heat pipe <NUM> in the aerospace galley insert <NUM> may be another type of heat pipe, such as a wickless heat pipe.

An advantage of using a heat pipe as a water vapour concentration sensor is that heat pipes tend to be more robust than conventional humidity sensors and therefore may be more able to withstand harsh conditions in the oven inner cavity <NUM>, e.g. extreme temperatures, cleaning chemicals, food spices, etc. Therefore, ovens which previously were unsuited for the inclusion of conventional humidity sensors due to the likelihood of damage thereto may be suitable for including a heat pipe humidity sensor. This allows water vapour concentration to be a known variable in the cooking process, which can then be controlled to a desired level. In addition, heat pipes may require less maintenance than traditional humidity sensors, which is particularly beneficial in an aerospace oven context where such maintenance is difficult to perform.

<FIG> shows an example of a second embodiment of the present disclosure. The Figure shows an aerospace galley insert <NUM> which is similar to the aerospace galley insert <NUM> of <FIG>, except that aerospace galley insert <NUM> includes a heat pipe <NUM> comprising a bent portion 28d. Like reference numerals are used to depict like elements between <FIG> and <FIG>.

Similarly to the heat pipe <NUM> in <FIG>, heat pipe <NUM> includes a first portion 28a located in the oven inner cavity <NUM>, a second portion 28b extending through a wall <NUM> of the oven inner cavity <NUM>, and a third portion 28c located in the exterior space <NUM>. The bent portion 28d is part of the third portion 28c of the heat pipe <NUM>. The heat pipe <NUM> comprises a first leg and a second leg which are substantially straight, the first leg and the second leg being joined by the bent portion 28d. The first leg includes the first portion 28a, the second portion 28b, and part of the third portion 28c, and the second leg includes the remainder of the third portion 28c.

The third temperature sensor 10c is arranged to measure the temperature at the bent portion 28d of the heat pipe <NUM>. This is beneficial because at both ends of the heat pipe <NUM> there will be phases changes of the working fluid within the heat pipe <NUM>, while at the bent portion 28d there will always be a liquid phase, and measuring the temperature of the liquid phase is more reliable than measuring at a phase change.

The second leg extends at least partly upwardly from the bent portion 28d, e.g. at least partly upwardly when considering the oven in normal use in an aerospace galley. In this example, the second leg extends substantially vertically upwards from the bent portion 28d at an angle of around <NUM> degrees from the first leg. In some examples the angle between the first leg and the second leg may be a maximum of <NUM> degrees. For instance, the angle may be within the range of <NUM>-<NUM> degrees, <NUM>-<NUM> degrees, <NUM>-<NUM> degrees, <NUM>-<NUM> degrees, <NUM>-<NUM> degrees, <NUM>-<NUM> degrees, or <NUM>-<NUM> degrees. The second leg extending at least partly upwardly allows gravity to assist the flow of liquid working fluid within the heat pipe <NUM> towards the bent portion 28d, and hence towards the temperature sensor 10c to obtain a more reliable temperature reading.

Referring to <FIG> and <FIG>, the relationship between temperature in the aerospace galley insert <NUM>, <NUM> (e.g. temperature of the heat pipe <NUM>, <NUM>, temperature in the oven <NUM>, and ambient temperature) and water vapour concentration in the oven inner cavity <NUM> may be determined e.g. from first principles or empirically. The relationship information may be stored in a look-up table which is accessible by the control unit <NUM>. In such examples, the control unit <NUM> may receive the temperature sensor data from the three temperature sensors 10a, 10b, 10c, and estimate the actual water vapour concentration in the oven inner cavity <NUM> by using the look-up table to associate the temperature measurements with a corresponding estimated water vapour concentration.

<FIG> shows a graph of the results of an experiment to investigate the relationship between temperature of a heat pipe and relative humidity in an oven. In the experiment, a heat pipe was arranged to extend partially inside a climate chamber representing an oven (and heretofore referred to as an oven). The oven was set to a specific temperature and relative humidity. The heat pipe comprised a bent portion located outside the oven, and a thermal sensor was placed at the bent portion to monitor the temperature thereof. The humidity inside the oven was then increased in <NUM>% increments, with the temperature of the heat pipe being measured periodically as the humidity was increased. The temperature of the heat pipe was then plotted as a function of humidity. The experiment was repeated with the oven set at three different temperatures (<NUM>, <NUM> and <NUM> degrees Celsius).

As shown in the graph, at lower humidity (e.g. <NUM>-<NUM>%) there is a small amount of increase in temperature of the heat pipe with increasing humidity. As humidity increases further, the temperature of the heat pipe increases more steeply. Thus, even though the temperature of the oven was approximately constant, the temperature of the heat pipe increased with increasing humidity inside the oven. As mentioned previously, this is thought to be due to the changing thermal conductivity of the gas as humidity changes.

These results demonstrate that there is a correlation between the heat pipe temperature and the relative humidity. Furthermore, the relationship can be quantified using these results so that heat pipe temperature measurements can be used to estimate relative humidity, e.g. in the context of a steam oven in an aerospace galley insert in accordance with the present disclosure.

In this example, a quadratic curve was fitted to the steeper part of the curves shown in <FIG>. A general quadratic relationship can be expressed as: <MAT> where a, b and c are unknown variables, y is the temperature of the heat pipe at the bent portion, and x is the humidity step per <NUM>%: <MAT>.

By using curve fitting of the graph in <FIG>, the parameters a, b and c were determined for each oven temperature setting (i.e. <NUM> degrees, <NUM> degrees and <NUM> degrees). In this example, the following polynomials were found: <MAT>.

Next, two of these equations were combined by subtracting the <NUM> degree equation from the <NUM> degree equation. This resulted in the following equation: <MAT>.

This equation is then the delta for an increase in oven temperature of <NUM> degrees Celsius. In theory, the delta for a <NUM> degrees Celsius increase can be obtained by dividing this formula by <NUM>: <MAT>.

This means that a formula can be created to calculate the temperature of the bent portion of the heat pipe, with reference to e.g. the known <NUM> degree setting. This can be done by applying the following factor for each of the parameters: <MAT> where ParameterToven is the parameter at a particular oven temperature, Parameter<NUM>∘C is the corresponding parameter at the <NUM> degree setting from equation (<NUM>), Toven is the oven temperature, and Parameterdelta is the corresponding parameter in equation (<NUM>).

Thus, inputting the known quantities, expressions for the parameters depending on the oven temperature can be created: <MAT>.

By reversing equations <NUM> and <NUM>, a formula for determining the relative humidity based on measuring the temperature of the heat pipe can be created: <MAT> where a, b and c are given by equations (<NUM>).

Using equations <NUM>, <NUM> and <NUM>, a graph can be plotted which estimates the relative humidity in the oven, based on measurements of the temperature of the heat pipe and the oven. This graph is shown in <FIG>, which depicts the temperature of the oven ("Toven") against the temperature of the heat pipe at the bent portion ("Tcurve") at various relative humidity levels RH <NUM>, RH <NUM>,. , RH <NUM>.

For instance, using the graph of <FIG>, it can be seen that an oven temperature reading of <NUM> degrees Celsius and a heat pipe temperature reading of <NUM> degrees Celsius corresponds to an estimated relative humidity of around <NUM>.

When implemented in an aerospace galley insert comprising an oven, e.g. as shown in <FIG> and <FIG>, the known relationship between heat pipe temperature and oven temperature can be used to estimate the actual water vapour concentration inside the oven inner cavity, and then the fluid supply can be controlled based upon the estimation to achieve a target water vapour concentration. For instance, the data represented in <FIG> can be stored in a look-up table, and the control unit <NUM> can determine the actual humidity of the oven inner cavity <NUM> by receiving the temperature measurements from the temperature sensors 10a, 10c and finding the corresponding humidity in the look-up table. Humidity can then be related to molar fraction of water vapour, which may be a more useful way of representing the level of steam within the steam oven.

The experiment of <FIG> and <FIG> did not take into account ambient temperature, as this was assumed to be constant. However, empirical data can be gathered with ambient temperature as another variable, so that the estimated humidity or water vapour concentration determination is additionally based on the ambient temperature reading. Thus, the control unit <NUM> can determine the actual humidity of the oven inner cavity <NUM> by additionally receiving the temperature measurements from the temperature sensor 10b. This is may be useful in the context of aircraft, where the ambient temperature on board the aircraft at high altitude may not correspond to standard temperature, and may change during the course of the flight.

Claim 1:
An aerospace galley insert (<NUM>; <NUM>) comprising:
an oven (<NUM>) defining therein an oven inner cavity (<NUM>) for receiving food to be prepared;
a fluid supply (<NUM>) for supplying fluid comprising water or water vapour to the oven inner cavity;
an exterior space (<NUM>) defined outside of the oven inner cavity;
a first temperature sensor (10a) for detecting a first temperature in the oven inner cavity; and
a control unit (<NUM>) configured to control the fluid supply;
characterised by:
a second temperature sensor (10b) for detecting a second temperature in the exterior space;
a heat pipe (<NUM>; <NUM>) extending between the oven inner cavity and the exterior space; and
a third temperature sensor (10c) for detecting a third temperature of the heat pipe where it extends into the exterior space;
wherein the control unit (<NUM>) is configured to determine an actual water vapour concentration in the oven inner cavity based on the first, second and third temperatures, and is configured to control the fluid supply in order to adjust the actual water vapour concentration to a target water vapour concentration.