This application is based on Japanese Patent Application No. 2014-106783 filed on May 23, 2014, the disclosure of which is incorporated herein by reference.
The present disclosure relates to a heat transfer system that transfers heat using a liquid heat medium.
A heat is generated in an energy exchange in an energy exchange system, for example, in a vehicle. Generally, such system is configured such that the heat generated in the energy exchange is transferred to be dissipated from a heat dissipator to outside the system. A liquid heat medium is used as the heat medium transferring the heat in most cases, and the liquid is required to be antifreeze liquid.
Conventionally, a technique to secure an antifreeze characteristic is disclosed (e.g., refer to Patent Literature 1). According to the technique, a liquid provided by water to which ethylene glycol, as a freezing-point depressant, is added by 50 percent relative to the water is used as the heat medium. Another technique to secure an antifreeze characteristic is disclosed (e.g., refer to Patent Literature 2). According to the technique, a supercooled state of the heat medium is maintained by adding a slight amount of a surfactant agent to the heat medium.
Patent Literature 1: JP 2014-020280 A
Patent Literature 2: JP 2013-032456 A
According to studies by the inventors of the present disclosure, a concentration of ethylene glycol is required to be increased as a target freezing point becomes lower in a case of securing the antifreeze characteristic of the heat medium using a freezing point depression phenomenon as the technique disclosed in Patent Literature 1. However, thermophysical property such as a specific heat and a thermal conductivity deteriorates, and a viscosity of the heat medium increases when the concentration of ethylene glycol is increased. As a result, a size of the heat dissipator or a heat medium pipe may be larger, and power required to flow the heat medium may be greater.
A supercooled state of liquid is a metastable state when the supercooled state is caused in a cooling of the liquid, and thereby there is a high possibility of generating an ice nucleus due to a thermal fluctuation in the system. It is considered that the thermal fluctuation is caused due to a mechanical disturbance or a thermal disturbance in the system.
A freezing of the heat medium therefore may be advanced since the supercooled state is broken due to the disturbance, in a case of securing the antifreeze characteristic of the heat medium by advancing the supercooling as described in Patent Literature 2. The antifreeze characteristic thereby may not be secured sufficiently.
The present disclosure addresses the above-described issues, and thereby it is an objective of the present disclosure to provide a heat transfer system that can suppress a deterioration of a thermophysical property of a heat medium and an increase of a viscosity of the heat medium and that can sufficiently secure an antifreeze characteristic of the heat medium.
A heat transfer system of the present disclosure has (i) a heat source that generates heat, (ii) a heat dissipator that dissipates heat, and (iii) a flow controller that controls a flow of a heat medium in a heat medium passage in which the heat medium in a liquid state flows. The heat from the heat source is transferred to the heat dissipator through the heat medium. The heat medium is configured by a solution that includes a solvent and at least one solute. The at least one solute is configured by a molecule. The molecule has (i) a first portion that selectively approaches a solid-liquid interface of the solvent when a temperature of the heat medium becomes lower than or equal to a predetermined base temperature and (ii) a second portion that is lyophobic and coupled with the first portion.
According to the above-described configuration, the first portion of the solute selectively approaches the solid-liquid interface of the solution and is adsorbed when the temperature of the heat medium falls and becomes lower than or equal to the base temperature. The first portion adsorbing to the solid-liquid interface of the solvent blocks a growth of a solidified nucleus of the solvent, and thereby an advance of a freezing can be suppressed. Moreover, the second portion that is lyophobic prevents the solvent from approaching the solid-liquid interface, and thereby the advance of the freezing can be suppressed more certainly.
As a result, the advance of the freezing of the heat medium can be delayed, i.e., the freezing point of the heat medium can be lower without adding a freezing-point depressant such as ethylene glycol to the heat medium. In addition, it is unnecessary to maintain a supercooled state to decrease the freezing point of the heat medium, and thereby a freezing that is advanced by a disturbance breaking the supercooled state of the heat medium is suppressed.
The deterioration of the thermophysical property and the increase of the viscosity of the heat medium thus can be suppressed, and the antifreeze characteristic of the heat medium can be secured sufficiently.
Embodiments of the present disclosure will be described hereafter referring to drawings. In the embodiments, a part that corresponds to or equivalents to a matter described in a preceding embodiment may be assigned with the same reference number.
A first embodiment will be described hereafter referring to
As shown in
The engine 101 is a heat source that generates heat by an energy exchange. The radiator 102 is a heat exchanger that exchanges heat with an exhaust heat of the engine 101 and cools the cooling water having a high temperature by performing a heat exchange between the cooling water and outside air.
The engine 101 and the radiator 102 are connected to each other by a cooling water passage 100 that configures a closed circuit between the engine 101 and the radiator 102. The cooling water passage 100 is provided with a pump 103, and the pump 103 is mechanically driven by power of the engine 101 and circulates the cooling water in the cooling water passage 100. The cooling water in the cooling water passage 100 flows from a cooling water outlet of the engine 101 to a cooling water inlet of the engine 101 through the radiator 102.
The cooling water passage 100 is a heat medium passage that configures a passage in which the cooling water as the heat medium in the liquid state flows. The pump 103 is a flow controller that controls a flow of the cooling water in the cooling water passage 100.
The following is a description about the cooling water used in the engine cooling system according to the present embodiment. The cooling water of the present embodiment is a solution including a solvent and at least one solute 40.
As shown in
According to the present embodiment, the solvent is water. The head 41 of the solute 40 is one of a quaternary ammonium group, a sulfo group, an ester group, a carboxyl group and a hydroxyl group. The tail 42 of the solute 40 has a main chain configured by carbons. A quantity of hydrophilic groups coupled with the carbons configuring the main chain is less than or equal to four.
Specifically, the solute 40 of the present embodiment is a chemical compound that has a trimethylammonium group as the head 41 and a linear hydrocarbon group, as the tail 42, having less than or equal to sixteen carbons. The solute 40 is a hexadecyltrimethylammonium bromide (i.e., C16TAB).
The solute 40 of the present embodiment is not limited to be C16TAB and may be polyoxyethylene (10) octylphenylether (i.e., Triton (registered trademark) X-100), polyoxyethylene (25) octyldodecylether (i.e., Emulgen (registered trademark) 2025G), polyoxyethylene sorbitan monooleate (i.e., Tween (registered trademark) 80), stearic acid PEG-150, myristyl sulfobetaine, or sodium cholate as shown in
In the solute 40, C16TAB does not have a hydrophilic group, myristyl sulfobetaine has one hydrophilic group, and sodium cholate has three hydrophilic groups. As shown in
A concentration of the solute 40 in the cooling water is smaller than a saturated dissolved concentration of the solute 40 relative to water. A growth of a piece of ice, which is caused when the solute 40 recrystallizes and provides a crystal working as a nucleus of the ice, thereby can be suppressed. Furthermore, a concentration of the solute 40 in the cooling water is smaller than or equal to a critical micelle concentration of the solute 40 relative to water. A growth of a piece of ice, which is caused when the solute 40 becomes micelle and provides a nucleus of the ice, thereby can be suppressed.
As shown in
A relation of a heat transfer coefficient ratio on a liquid side and the freezing temperature relative to the ethylene glycol concentration in the cooling water is shown in
The freezing temperature is required to be lower than or equal to minus 34° C. to secure a property of an antifreeze liquid defined in JIS K 2234. LLC widely used in recent years thus includes ethylene glycol by 50% relative to water.
As shown by the upper graph in
In contrast, the freezing temperature becomes minus 20° C. in a case of using, as the cooling water, C16TAB of which weight percent is 0.1. The concentration of ethylene glycol in the cooling water is 0, and therefore the heat transfer coefficient can be increased.
However, as described above, the freezing temperature is required to be lower than or equal to minus 34° C. to secure a property of an antifreeze liquid defined in JIS K 2234. The present embodiment thus uses a second solute other than C16TAB that is used as a first solute. The second solute is different from C16TAB and depresses a freezing point of water by dissolving in the water. The second solute may be alcohol. The second solute of the present embodiment is ethylene glycol.
As shown in the lower graph of
More specifically, the freezing temperature can be minus 34° C. by designing the weight percent of ethylene glycol to be about 18% in a case of using, as the cooling water, C16TAB of which weight percent is 0.1. At this time, the heat transfer coefficient can be increased by about 40 percent as compared to LLC that is widely used in recent years.
As described above, the solute 40 in the cooling water is configured by a molecule that has the head 41 and the tail 42. The head 41 selectively approaches the solid-liquid interface 50 of the solvent when a temperature of the cooling water becomes lower than or equal to the predetermined base temperature. The tail 42 is a portion that is lyophobic relative to the solvent (i.e., has a lyophobic characteristic) and coupled with the head 41. According to the above-described configuration, the head 41 of the solute 40 selectively approaches to the solid-liquid interface of the solution and is adsorbed when the temperature of the cooling water falls and becomes lower than or equal to the base temperature. The head 41 adsorbing to the solid-liquid interface 50 of the solvent blocks a growth of an ice nucleus (i.e., a solidified nucleus) of the solvent, and thereby an advance of a freezing can be suppressed. Moreover, the tail 42 that is lyophobic relative to the solvent prevents the solvent from approaching the solid-liquid interface 50, and thereby the advance of the freezing can be suppressed more certainly.
As a result, the advance of the freezing of the cooling water can be delayed, i.e., the freezing point of the cooling water can be decreased without adding a freezing-point depressant (e.g., ethylene glycol) to the coolant. Both of a deterioration of thermophysical property and an increase of a viscosity of the cooling water thereby can be suppressed.
In addition, it is unnecessary to maintain a supercooled state to decrease the freezing point of the cooling water. That is, the solute 40 in the cooling water of the present embodiment does not promote a supercooling, but blocks a growth of the ice nucleus as described above. A freezing therefore is not advanced by a disturbance breaking the supercooled state of the cooling water.
As described above, the deterioration of the thermophysical property and the increase of the viscosity of the cooling water thus can be suppressed, and the antifreeze characteristic of the cooling water can be secured sufficiently according to the present embodiment.
In the cooling water of the present embodiment, the tail 42 moves around the head 41 when the head 41 of the solute 40 adsorbs to the solid-liquid interface 50 of the solvent, as shown in
In contrast, the length of the tail 42 can be prevented from being too long by configuring the tail 42 of the solute molecule with the linear hydrocarbon group having less than or equal to sixteen carbons as described above. A distance d between adjacent two of the solute molecules thereby can be shortened, and the advance of the freezing of the cooling water can be suppressed certainly, since it is easy to suppress the growth of the ice nucleus in the solvent.
A second embodiment will be described hereafter referring to
As shown in
The first heat transfer circuit 1 is provided with the engine 101, the radiator 102, and the first pump 103 as described in the first embodiment. The first heat transfer circuit 1 is configured such that heat from the engine 101 is transferred to the radiator 102 through a first cooling water flowing in the first cooling water passage 100.
The second heat transfer circuit 2 is provided with an intercooler 201, a chiller 202, and a second pump 203. The intercooler 201 is a heat exchanger that cools the intake air by performing a heat exchange between the intake air for the engine and a second cooling water flowing in a second cooling water passage 200. The chiller 202 is a heat exchanger that cools the second cooling water by performing a heat exchange between the second cooling water and the outside air. The second pump 203 controls a flow of the second cooling water in the second cooling water passage 200. The second heat transfer circuit 2 is configured such that heat from the intercooler 201 is transferred to the chiller 202 through the second cooling water flowing in the second cooling water passage 200.
The first cooling water and the second cooling water of the present embodiment is “the cooling water” described in the first embodiment. The present embodiment thus can provide the same effects as the first embodiment.
It should be understood that the present disclosure is not limited to the above-described embodiments and intended to cover various modification within a scope of the present disclosure as described hereafter.
(1) The above-described embodiments are an example of using the engine 101 as a heat source, however the heat source is not limited to be the engine. For example, the heat source may be a fuel cell, a battery, or an inverter.
(2) The above-described embodiments are an example of using the radiator 102 as the heat dissipator, however the heat dissipator is not limited to be the radiator. For example, the heat dissipator may be a heater core that heats an air for air conditioning by performing a heat exchange between the cooling water and the air.
Number | Date | Country | Kind |
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2014-106783 | May 2014 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2015/002034 | 4/10/2015 | WO | 00 |