Patent Description:
A loop heat pipe technology has been traditionally known which uses phase changes of a working fluid to achieve high-density heat transport. A heat transport system employing such a loop heat pipe has been used, for example, to cool an electronic device such as a computer or home electric appliance. In some loop heat pipes, the working fluid is circulated by means of capillary force and/or gravity.

A loop heat pipe includes a closed loop formed by an evaporator, a condenser, a vapor conduit leading from the evaporator to the condenser, and a liquid conduit leading from the condenser to the evaporator. The closed loop is charged with a working fluid. In the evaporator, the working fluid in a liquid phase is heated by heat transferred from a heat generator, and a part of the working fluid changes into a gas phase. The gas-liquid two-phase working fluid moves in the vapor conduit under the action of pressure difference and buoyancy and reaches the condenser. In the condenser, the working fluid is cooled into the liquid phase. The liquid-phase working fluid returns to the evaporator under the action of capillary force and/or gravity. In this manner, the loop heat pipe allows the working fluid to circulate in the two-phase closed loop and transport heat from the evaporator to the condenser, thereby cooling the heat generator thermally connected to the evaporator.

Patent Literature <NUM> proposes an evaporator used in a loop heat pipe as described above, and the evaporator includes a wick located in a lower portion of the evaporator. The pores of the wick are filled with a working fluid, and the liquid-phase working fluid remains in the evaporator while the loop heat pipe is not in operation. Patent Literature <NUM> provides a liquid-cooled cooling device for an electronic equipment, which is capable of removing heat generated from each semiconductor device without being influenced by the dimensional tolerances of the semiconductor devices. Patent Literature <NUM> discloses a thermosiphon cooling assembly which cools an electronic device with a first refrigerant disposed in the lower boiling chamber of a housing for liquid-to-vapor transformation and a second refrigerant disposed in an upper evaporating chamber of a housing for liquid-to-vapor transformation. Patent Literature <NUM> discloses a vehicle control system which includes a function execution unit that executes a function implemented in a vehicle and pre-assigned, a non-function interface unit that provides one or more non-functions for each of the function execution units, the non-function being an operating environment required to realize the function of the function execution unit, and an allocation control unit that allocates the non-function to respective function execution units provided using constraint information including at least one arrangement constraint of the fijnction execution unit and the non-function interface unit.

Electronic devices have become more and more sophisticated and miniaturized, and this has recently led to a growing demand for thermal management in transportation machines such as watercrafts, railcars, automobiles, and aircrafts which are equipped with a large number of electronic devices. Some transportation machines incorporate a loop heat pipe as described above which uses gravity for circulation of a working fluid, and such a transportation machine, the position of the body of which constantly changes, suffers a position change-induced decrease in the drive force for allowing the working fluid to circulate and a corresponding decrease in the heat transport rate.

A type of evaporator includes a heat receiver located at the bottom of a container accommodating a working fluid, and the heat receiver is thermally connected to a heat generator. In case that such an evaporator is tilted, a situation can arise where the liquid-phase working fluid retained at the bottom of the container is not in contact with a part of the heat receiver. This leads to the heat receiver having a dry portion not in contact with the liquid-phase working fluid and a wet portion in contact with the liquid-phase working fluid. As the working fluid does not evaporate in the dry portion, the dry portion absorbs a smaller amount of heat than the wet portion. Thus, the dry portion exhibits a lower ability to cool the heat generator than the wet portion, and consequently the heat generator could be unevenly cooled.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an evaporator and a loop heat pipe including the evaporator, the evaporator including a heat receiver located at the bottom of the evaporator and thermally connected to a heat generator, the evaporator and loop heat pipe being capable of effectively cooling the heat generator in contact with the heat receiver even in case that the position of the evaporator is changed.

An evaporator according to one aspect of the present disclosure is an evaporator for receiving heat from a heat generator to change at least part of a working fluid from a liquid phase to a gas phase, the evaporator including: a housing including an accommodation chamber that accommodates the working fluid; and a heat receiver located on a bottom surface of the housing and thermally connected to the heat generator. The housing includes: a porous plate dividing the accommodation chamber into an upper chamber and a lower chamber and including a large number of pores through which the upper and lower chambers communicate with each other; at least one working fluid inlet opening into the upper chamber; a partition dividing a bottom of the lower chamber into liquid retainers; and at least one working fluid outlet opening into the lower chamber and located above the partition.

A loop heat pipe according to one aspect of the present disclosure includes: the above evaporator that changes at least part of a working fluid from a liquid phase to a gas phase; a condenser that changes the working fluid from the gas phase to the liquid phase; a vapor conduit connecting the working fluid outlet of the evaporator and an inlet of the condenser; and a liquid conduit connecting an outlet of the condenser and the working fluid inlet of the evaporator.

In the evaporator and loop heat pipe configured as described above, the liquid-phase working fluid flowing into the upper chamber of the accommodation chamber of the evaporator enters the lower chamber through the pores of the porous plate and falls into the liquid retainers of the lower chamber. Due to flow resistance accompanying passage through the pores, the working fluid in the upper chamber spreads on the porous plate rather than immediately flowing down into the lower chamber. Thus, the working fluid in the upper chamber is delivered not only to pores directly below the working fluid inlet but also to pores horizontally away from the working fluid inlet, and then falls into the lower chamber. As such, the working fluid is delivered not only to the liquid retainers directly below the working fluid inlet but also to the liquid retainers horizontally away from the working fluid inlet.

In case that the bottom surface of the housing of the evaporator is tilted from the horizontal, the liquid-phase working fluid in the liquid retainers is blocked by the partition from flowing downward along the tilted bottom surface and remains in the liquid retainers. Thus, in case that the position of the evaporator is changed and the bottom surface of the housing is tilted from the horizontal, the working fluid remains at the bottom of the accommodation chamber, and the heat receiver and the working fluid can be kept in thermal contact. Even in case that the heat receiver has dry portions that are not in thermal contact with the working fluid, the dry portions are distributed over different zones of the heat generator with which the heat receiver is in thermal contact, rather than being localized over a particular zone of the heat generator. Thus, despite the change in the position of the evaporator, the entire region of the heat generator that is in contact with the heat receiver can be cooled efficiently.

The present disclosure can provide an evaporator and a loop heat pipe including the evaporator, the evaporator including a heat receiver located at the bottom of the evaporator and thermally connected to a heat generator, the evaporator and loop heat pipe being capable of effectively cooling the heat generator in contact with the heat receiver even in case that the position of the evaporator is changed.

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. <FIG> shows a schematic configuration of an aircraft <NUM> including a loop heat pipe <NUM> according to an exemplary embodiment of the present disclosure.

The loop heat pipe <NUM> of <FIG> includes an evaporator <NUM>, a vapor conduit <NUM>, a condenser <NUM>, and a liquid conduit <NUM>, which are connected to form a closed loop. The closed loop is charged with a working fluid which is a condensable fluid. The working fluid naturally circulates in the loop heat pipe <NUM> by means of phase changes and gravity. The working fluid is not limited to a particular type, and may be a condensable fluid commonly used as a working fluid in heat pipes. Examples of the condensable fluid include water, an alcohol, ammonia, a fluorocarbon, a hydrofluorocarbon, a hydrofluoroether, and a mixture of these fluids.

The evaporator <NUM> is thermally connected to a heat generator <NUM> which is a heat source. In the evaporator <NUM>, the liquid-phase working fluid absorbs heat from the heat generator <NUM>, and part of the working fluid boils into a gas phase. The gas-liquid two-phase working fluid moves in the vapor conduit <NUM> connecting the outlet of the evaporator <NUM> and the inlet of the condenser <NUM> under the action of pressure difference and buoyancy, thereby reaching the condenser <NUM>.

The condenser <NUM> is located above the evaporator <NUM>. The condenser <NUM> includes a cooling path (not shown), and the two-phase working fluid releases heat and is cooled into the liquid phase while passing through the cooling path. The liquid-phase working fluid descends in the liquid conduit <NUM> connecting the outlet of the condenser <NUM> and the inlet of the evaporator <NUM> under the action of gravity, thereby returning to the evaporator <NUM>.

The loop heat pipe <NUM> configured as described above is mounted on a transportation machine. Examples of the transportation machine include watercrafts (including submersibles), railcars, automobiles, and aircrafts. In this exemplary embodiment, the loop heat pipe <NUM> is mounted on the aircraft <NUM> which is an example of the transportation machine. For the aircraft <NUM>, the allowable tilt angle during normal operation is α°. During normal operation, the aircraft <NUM> is tiltable from the horizontal to the allowable tilt angle.

<FIG> partially shows a fuselage <NUM> and main wing <NUM> of the aircraft <NUM>. The fuselage <NUM> has a multilayer structure including an outer panel <NUM> and an interior wall <NUM> closer to the cabin than the outer panel <NUM>. There is a cooling chamber <NUM> between the outer panel <NUM> and the interior wall <NUM>. The temperature inside the cooling chamber <NUM> is low because of cold energy transferred from the outer panel <NUM> which during flight is exposed to outside air having a considerably lower temperature than that near the ground. Alternatively, the outer panel <NUM> may include an air inlet and air outlet communicating with the cooling chamber <NUM>, and outside air may be introduced into the cooling chamber <NUM> during flight.

In the aircraft <NUM>, the condenser <NUM> is located in the cooling chamber <NUM>, while the heat generator <NUM> and the evaporator <NUM> thermally connected to the heat generator <NUM> are located closer to the cabin than the interior wall <NUM>. In the cooling chamber <NUM>, there is a fan <NUM> forcing a gas stream to pass the condenser <NUM>. The condenser <NUM> condenses the working fluid using cold energy of outside air. Examples of the heat generator <NUM> include, but are not limited to: an electronic device including heat-generating parts, such as a control board, an engine control unit (ECU), or a computer; a friction heat-generating mechanical part such as a bearing; and a battery. Instead of the heat generator <NUM>, air inside the cabin may be a heat source.

The following will describe the configuration of the evaporator <NUM> of the loop heat pipe <NUM> configured as described above. <FIG> is a perspective view of the evaporator <NUM> according to this exemplary embodiment. <FIG> is a side view for illustrating the internal structure of the evaporator <NUM>. <FIG> is a plan view showing the interior of the evaporator <NUM> to illustrate liquid retainers <NUM>. <FIG> is a plan view showing the interior of the evaporator <NUM> to illustrate a variant of the liquid retainers <NUM>.

As shown in <FIG>, the evaporator <NUM> according to this exemplary embodiment includes a housing <NUM> and a heat receiver <NUM> located on a bottom surface <NUM> of the housing <NUM>.

The housing <NUM> is in the shape of a rectangular parallelepiped in which the top and bottom surfaces <NUM> and <NUM> have the largest area. The housing <NUM> includes an accommodation chamber <NUM> that accommodates the working fluid. A part or all of the bottom surface <NUM> of the housing <NUM> is formed by the heat receiver <NUM>. The heat receiver <NUM> is a plate made of a metal material with high thermal conductivity such as copper. The heat receiver <NUM> includes a heat-receiving surface <NUM> on the exterior of the housing <NUM> and a boiling surface <NUM> facing the accommodation chamber <NUM> inside the housing <NUM>. The heat-receiving surface <NUM> is thermally connected to the heat generator <NUM> located below the evaporator <NUM> and receives heat from the heat generator <NUM>.

The accommodation chamber <NUM> is divided by a porous plate <NUM> into an upper chamber <NUM> above the porous plate <NUM> and a lower chamber <NUM> below the porous plate <NUM>. The porous plate <NUM> is parallel to the top and bottom surfaces <NUM> and <NUM> of the housing <NUM>. The porous plate <NUM> includes a large number of pores and permits the working fluid to pass through the pores.

At least one working fluid inlet <NUM> opens into the upper chamber <NUM>. The working fluid inlet <NUM> desirably opens at the highest level in the upper chamber <NUM>. The working fluid inlet <NUM> according to this exemplary embodiment opens at the top surface <NUM> of the housing <NUM>. The working fluid inlet <NUM> is connected to the liquid conduit <NUM> extending upward.

At least one working fluid outlet <NUM> opens into the lower chamber <NUM>. The working fluid outlet <NUM> desirably opens at the highest level in the lower chamber <NUM>. The working fluid outlet <NUM> according to this exemplary embodiment opens at the porous plate <NUM> forming the ceiling of the lower chamber <NUM>. Alternatively, the working fluid outlet <NUM> may be located, for example, on a side wall of the housing <NUM> or at a tip of a conduit inserted into the lower chamber <NUM> through the housing <NUM>. The working fluid outlet <NUM> is connected to the vapor conduit <NUM> extending upward.

The bottom of the lower chamber <NUM> is divided into liquid retainers <NUM> by a partition <NUM>. Each liquid retainer <NUM> accommodates the liquid-phase working fluid. The partition <NUM> is made of, for example, a metal material with high thermal conductivity such as copper. The material of the partition <NUM> is not limited to metal materials. The partition <NUM> according to this exemplary embodiment is a plate-like structure extending vertically from the boiling surface <NUM> of the heat receiver <NUM> which is the floor of the accommodation chamber <NUM> (in particular, the lower chamber <NUM>).

The liquid retainers <NUM> are recesses arranged in directions in which the transportation machine is tilted ("tilt directions"). In this exemplary embodiment, as shown in <FIG>, a gridshaped partition <NUM> extending vertically from the bottom surface of the lower chamber <NUM> defines square liquid retainers <NUM> at the bottom of the lower chamber <NUM>. The liquid retainers <NUM> are not limited to this form. For example, as shown in <FIG>, partitions <NUM> parallel to one another and extending vertically from the floor of the lower chamber <NUM> may define the rectangular liquid retainers <NUM> at the bottom of the lower chamber <NUM>.

The partition <NUM> is not limited to the above forms and may be in any form as long as the partition <NUM> defines the liquid retainers <NUM> at the bottom of the lower chamber <NUM>. For example, the partition <NUM> may be a plate extending vertically from the boiling surface <NUM> of the heat receiver <NUM>. For example, the partition <NUM> may be a result of forming the liquid retainers <NUM> by machining a heat-transfer block in contact with the boiling surface <NUM>.

In the evaporator <NUM> configured as described above, the liquid-phase working fluid flows into the upper chamber <NUM> through the liquid conduit <NUM> and the working fluid inlet <NUM>. The working fluid enters the lower chamber <NUM> from the upper chamber <NUM> through the pores of the porous plate <NUM> and falls into the liquid retainers <NUM> of the lower chamber <NUM>. Due to flow resistance accompanying passage through the pores, the working fluid stays temporarily in the upper chamber <NUM> and spreads horizontally on the porous plate <NUM>, rather than immediately flowing down into the lower chamber <NUM>. Consequently, the liquid-phase working fluid staying in the upper chamber <NUM> forms a liquid layer with a vertical thickness in the upper chamber <NUM>. Thus, the working fluid in the upper chamber <NUM> is delivered not only to pores directly below the working fluid inlet <NUM> but also to pores horizontally away from the working fluid inlet <NUM>.

In the manner as described above, the working fluid falls through the large number of pores distributed evenly over the entire porous plate <NUM>. Thus, the working fluid is delivered not only to the liquid retainers <NUM> directly below the working fluid inlet <NUM> but also to the liquid retainers <NUM> horizontally away from the working fluid inlet <NUM>. The liquid surface L of the liquid-phase working fluid accommodated in the liquid retainers <NUM> is at a lower level than the top of the partition <NUM> when the boiling surface <NUM> is in a horizontal position. The liquid surface L may be at the same or a higher level than the top of the partition <NUM>.

The heat that the heat receiver <NUM> receives from the heat generator <NUM> is released to the working fluid through the boiling surface <NUM> and the partition <NUM>. The heat causes at least part of the liquid-phase working fluid in the liquid retainers <NUM> to boil into a gas phase. Consequently, the region above the liquid surface L in the lower chamber <NUM> is filled with the gas-phase working fluid (or the two-phase working fluid including the gas and liquid phases). Strictly speaking, there is no liquid surface L in the two-phase fluid. However, given that in the working fluid located in the lower chamber <NUM>, the volume proportion of the gas present in the liquid increases upward, a boundary plane at which the volume percentage of the gas (void percentage) in the gas-liquid two-phase flow is a given value (e.g., <NUM>%) can be defined as an imaginary liquid surface L.

The porous plate <NUM> includes a large number of pores distributed regularly and evenly over the entire porous plate <NUM>. The pores are not limited to being circular, and the porous plate <NUM> may be, for example, a perforated metal or a metal net. The total area of the porous plate <NUM> depends on the size of the housing <NUM> of the evaporator <NUM>. Thus, selectable parameters of the porous plate <NUM> are the number of pores, the pore size, and the plate thickness. The pore size may be an average size of the pores.

For the porous plate <NUM>, the pressure applied at the pores from the direction of the upper chamber <NUM> is referred to as "first pressure P1", and the pressure applied at the pores from the direction of the lower chamber <NUM> is referred to as "second pressure P2". The first pressure P1 corresponds to a difference calculated by subtracting the following pressure drops from the hydraulic head pressure applied to the porous plate <NUM> by the working fluid present in the upper chamber <NUM> and liquid conduit <NUM>: a pressure drop accompanying passage of the working fluid through the liquid conduit <NUM>; a pressure drop accompanying an abrupt expansion of flow path upon entry of the working fluid from the liquid conduit <NUM> into the upper chamber <NUM>; and a pressure drop caused by the surface tension of the working fluid. The first pressure P1 may be considered approximately equal to the hydraulic head pressure. The second pressure P2 is a pressure applied to the porous plate <NUM> by the working fluid present in the lower chamber <NUM>, and varies according to the amount of evaporation of the working fluid in the lower chamber <NUM>.

For the working fluid to pass from the upper chamber <NUM> to the lower chamber <NUM>, the first pressure P1 must be greater than the sum of the second pressure P2 and the pressure drop Δp of the working fluid passing through the porous plate <NUM> (P1 > P2 + Δp). Thus, the open area ratio ε of the porous plate <NUM> may be set so that the first pressure P1 during rated operation is greater than the sum of the second pressure P2 and the pressure drop Δp during rated operation. However, if the first pressure P1 is significantly greater than the sum of the second pressure P2 and the pressure drop Δp of the working fluid passing through the porous plate <NUM>, the working fluid entering the upper chamber <NUM> flows out into the lower chamber <NUM> without staying in the upper chamber <NUM>. The pressure drop Δp of the working fluid passing through the porous plate <NUM> can be determined by a known equation shown below in Mathematical Formula <NUM>, and the pressure drop for ensuring the working pressure in a desired operation state can be appropriately set.

The parameters defining the pressure drop Δp of the working fluid passing through the pores of the porous plate <NUM> are the density ρ of the working fluid, the average flow velocity u<NUM> of the working fluid, and the coefficient of drag ζ. The parameters defining the coefficient of drag ζ are the open area ratio ε of the porous plate <NUM>, the coefficient of friction drag λ, the equivalent diameter dh of the pores, and the function τ with respect to the ratio between the thickness (l) of the porous plate <NUM> and the pore size. The open area ratio ε of the porous plate <NUM> is chosen based on the pressure drop Δp. The open area ratio ε of the porous plate <NUM> is defined as the ratio of the sum of the areas of the pores to the total area of the porous plate <NUM>. The thickness of the porous plate <NUM> is chosen in view of a plate strength suitable for the open area ratio ε. The thickness l of the porous plate <NUM> is desirably small, but the porous plate <NUM> could lack sufficient strength if the thickness l is less than <NUM>.

The pressure drop Δp across the porous plate <NUM> is sensitive to variations in the open area ratio ε and equivalent diameter dh of the porous plate <NUM>. One of the parameters defining the equivalent diameter dh is the cross-sectional area of flow through the pores, and the equivalent diameter dh is a function of the pore size. The combination of the pore size and the number of the pores can be chosen based on the open area ratio ε. Desirably, the pore size is <NUM> or more. Depending on the type of the working fluid, a pore size of less than <NUM> could cause an excessive pump head leading to interrupted flow of the working fluid.

In the evaporator <NUM>, the use of the porous plate <NUM> with a suitable open area ratio ε allows the working fluid to penetrate through the porous plate <NUM> evenly from the upper chamber <NUM> into the lower chamber <NUM>.

For example, the pressure drop Δp across the porous plate <NUM> can be set so as to prevent passage of the working fluid through the porous plate <NUM> until the liquid layer <NUM> in the upper chamber <NUM> reaches a given thickness. In this case, as shown in <FIG>, the working fluid spreads evenly on the porous plate <NUM> since passage of the working fluid through the porous plate <NUM> is prevented until the working fluid in the upper chamber <NUM> forms a layer with a given thickness. As a result, the working fluid can penetrate through the porous plate <NUM> evenly from the upper chamber <NUM> into the lower chamber <NUM>.

For example, the pressure drop Δp across the porous plate <NUM> can be set so as to prevent the working fluid from flowing back from the lower chamber <NUM> into the upper chamber <NUM>. In this case, the liquid-phase working fluid penetrates through the porous plate <NUM> into the lower chamber <NUM> when the flow rate of the working fluid flowing into the evaporator <NUM> or the amount of evaporation of the working fluid in the evaporator <NUM> is in a given rated range. In case that the pressure of the working fluid in the lower chamber <NUM> sharply increases due to an abrupt increase in the amount of evaporation of the working fluid, the pressure variation (pulsation) is mitigated by the porous plate <NUM> and the working fluid in the upper chamber <NUM>.

As described above, an evaporator <NUM> according to this exemplary embodiment is an evaporator that receives heat from a heat generator <NUM> to change at least part of a working fluid from a liquid phase to a gas phase, the evaporator <NUM> including: a housing <NUM> including an accommodation chamber <NUM> that accommodates the working fluid; and a heat receiver <NUM> located on a bottom surface <NUM> of the housing <NUM> and thermally connected to the heat generator <NUM>. The housing <NUM> includes: a porous plate <NUM> dividing the accommodation chamber <NUM> into an upper chamber <NUM> and a lower chamber <NUM> and including a large number of pores through which the upper and lower chambers <NUM> and <NUM> communicate with each other; at least one working fluid inlet <NUM> opening into the upper chamber <NUM>; a partition <NUM> dividing a bottom of the lower chamber <NUM> into liquid retainers <NUM>; and at least one working fluid outlet <NUM> opening into the lower chamber <NUM> and located above the partition <NUM>.

A loop heat pipe <NUM> according to this exemplary embodiment includes: the above evaporator <NUM> that changes part of a working fluid from a liquid phase to a gas phase; a condenser <NUM> that changes the working fluid from the gas phase to the liquid phase; a vapor conduit <NUM> connecting the working fluid outlet <NUM> of the evaporator <NUM> and an inlet of the condenser <NUM>; and a liquid conduit <NUM> connecting an outlet of the condenser <NUM> and the working fluid inlet <NUM> of the evaporator <NUM>.

In the evaporator <NUM> and loop heat pipe <NUM> configured as described above, the liquid-phase working fluid flowing into the upper chamber <NUM> of the accommodation chamber <NUM> of the evaporator <NUM> enters the lower chamber <NUM> through the pores of the porous plate <NUM> and falls into the liquid retainers <NUM> of the lower chamber <NUM>. Due to flow resistance accompanying passage through the pores, the working fluid in the upper chamber <NUM> spreads on the porous plate <NUM> rather than immediately flowing down into the lower chamber <NUM>. Thus, the working fluid in the upper chamber <NUM> is delivered not only to pores directly below the working fluid inlet <NUM> but also to pores horizontally away from the working fluid inlet <NUM>, and then falls into the lower chamber <NUM>. As such, the working fluid is delivered not only to the liquid retainers <NUM> directly below the working fluid inlet <NUM> but also to the liquid retainers <NUM> horizontally away from the working fluid inlet <NUM>.

In the evaporator <NUM> and loop heat pipe <NUM> configured as described above, in case that the bottom surface <NUM> of the housing <NUM> of the evaporator <NUM> is tilted from the horizontal, the liquid-phase working fluid in the liquid retainers <NUM> is blocked by the partition <NUM> from flowing downward along the tilted bottom surface <NUM> and remains in the liquid retainers <NUM>. Thus, in case that the position of the evaporator <NUM> is changed and the bottom surface <NUM> of the housing <NUM> is tilted from the horizontal, the working fluid remains at the bottom of the accommodation chamber <NUM>, and the heat receiver <NUM> and the working fluid can be kept in thermal contact. Even in case that the heat receiver <NUM> has dry portions that are not in thermal contact with the working fluid, the dry portions are distributed over different zones of the heat generator <NUM> with which the heat receiver <NUM> is in thermal contact, rather than being localized over a particular zone of the heat generator <NUM>. Thus, despite the change in the position of the evaporator <NUM>, the entire region of the heat generator <NUM> that is in contact with the heat receiver <NUM> can be cooled efficiently.

In the evaporator <NUM> and loop heat pipe <NUM> according to this exemplary embodiment, the upper chamber <NUM> includes a liquid layer <NUM> having a given thickness and including the liquid-phase working fluid staying temporarily in the upper chamber <NUM> after flowing into the upper chamber <NUM> through the working fluid inlet <NUM>. To this end, in the evaporator <NUM> and loop heat pipe <NUM> according to this exemplary embodiment, the porous plate <NUM> has an open area ratio ε that allows the working fluid to stay temporarily in the upper chamber <NUM> so that the upper chamber <NUM> includes a liquid layer <NUM> having a given thickness and including the liquid-phase working fluid.

Claim 1:
An evaporator (<NUM>) for receiving heat from a heat generator (<NUM>) to change at least part of a working fluid from a liquid phase to a gas phase, the evaporator (<NUM>) comprising:
a housing (<NUM>) including an accommodation chamber (<NUM>) that accommodates the working fluid; and
a heat receiver (<NUM>) located on a bottom surface (<NUM>) of the housing (<NUM>) and thermally connected to the heat generator (<NUM>), wherein
the housing (<NUM>) includes
a porous plate (<NUM>) dividing the accommodation chamber (<NUM>) into an upper chamber (<NUM>) and a lower chamber (<NUM>) and including a large number of pores through which the upper and lower chambers (<NUM>, <NUM>) communicate with each other,
at least one working fluid inlet (<NUM>) opening into the upper chamber (<NUM>),
a partition (<NUM>) dividing a bottom of the lower chamber (<NUM>) into liquid retainers (<NUM>), and
at least one working fluid outlet (<NUM>) opening into the lower chamber (<NUM>) and located above the partition (<NUM>).