RU2624113C2 - Magnetorheologic coolant and method of its application - Google Patents

Abstract

FIELD: heating system.

SUBSTANCE: magnetorheologic coolant consists of a liquid containing a finely dispersed component of a magnetic material the surface of which is treated with a surfactant. The noted liquid is selected from a number of alcohols, polyhydric alcohols, silicone compounds. As a magnetic material, the coolant contains microparticles of carbonyl iron with the size of each microparticle in one plane of not more than 15 mcm with a thickness of no more than 10% of the larger linear dimension in the plane. The amount of said finely dispersed component in the coolant is from 0.05 to 2.5 wt %. The method of using the noted magnetorheological coolant in refrigeration and air-conditioning systems involves impacts on it with a permanent magnetic field with a strength of 2 to 700 Oe.

EFFECT: increased efficiency of heat transfer and control of hydrodynamic flow resistance, for example, volume flow of coolant.

2 cl, 3 tbl

Description

The invention relates to the field of heat transfer and heat transfer technology, namely, heat transfer fluids (coolants) and methods of their use for refrigeration units and systems, as well as for air conditioning, heating and creating a comfortable environment in buildings and structures.

A heat carrier is known in the form of a liquid medium containing dispersed nanoparticles of metals and similar materials [1 and 2], where nickel nanoparticles are dispersed and uniformly distributed in a liquid alkali metal (sodium). Such a coolant is used in heat removal systems of nuclear reactors.

This coolant cannot be used in cold and heat supply systems in refrigeration and air conditioning, where the operating temperature range of the coolant is in the range from plus 20 to minus 40 ° C, and the melting point of the basic alkali metals has limits from plus 180 ° C for lithium, 98 ° C in sodium and 64 ° C in potassium.

Also known is a heat transfer fluid [3] containing nanoparticles and carboxylates, in which aluminum or aluminum oxide nanoparticles coated with a carboxylate film are used to improve its thermal conductivity. This heat carrier has improved thermophysical properties compared to conventional heat carriers without filling with nanoparticles. However, it cannot be used in thermal conductivity and flow control systems, for example, by applying a magnetic field due to the non-magnetic nature of the particle material.

A known class of magnetic fluids (MF) based on the dispersed magnetic phase of nanoparticles of magnetite, gamma-iron oxide, ferrites of manganese, cobalt, zinc and nickel bound by a surfactant to a state of a colloidal solution. [4-6]. These MFs, along with applications in measuring equipment, are used in the purification of oil pollution, as well as in the magnetic separation of fractions of materials, etc.

This class of liquids with magnetic properties has a very complicated manufacturing technology for practical use and is not recommended for use in heat and cold supply and air conditioning systems as a heat carrier, because at significant costs and circulation speeds its corrosive and abrasive properties are manifested in the coolant circuit and amplification is observed the effect of cavitation effects on circuit elements, especially in relation to heat transfer pumps. The flows of such coolants in a cold supply or heating system by known methods of application are regulated and controlled by traditional elements of mechanical or electromechanical valves.

Closest to the proposed invention (prototype) is a magnetorheological fluid (GRM), for example, a suspension based on polyethylsiloxane fluid with microparticles of chromium oxide CrO ₂ or iron Fe ₂ O ₃ coated with a surfactant [7].

Such an MRE possesses magnetic properties when exposed to a constant magnetic field and can be used to control dynamic viscosity and control fluid flow in limited volumes of moving devices.

At the same time, its use as a circulating coolant flow in pipelines and heat exchange equipment of refrigeration and air conditioning systems is inefficient and inappropriate for the following reasons:

- similar GRM, equipped with solid-state particles of metal of chromium oxide or iron of an acute-angled shape and structure, when working in a circulating stream, becomes a source of corrosion-abrasive effects on the material of pipes and refrigeration equipment;

- in addition, it is a source of increased cavitation with a violation of the integrity of the fluid supply channels in the pumps for the transfer of coolant in heat and cold supply systems;

- The GRM of the prototype does not have a sufficiently high thermal conductivity even with magnetic particles of iron oxide and chromium, and hence insufficient efficiency when using refrigeration and air conditioning systems in heat transfer processes.

- The GRM of the prototype does not have sufficiently high magnetic properties to implement a method for efficient and effective control of the fluid flow in the heat and cold supply system using a constant magnetic field due to the insufficiently high level of magnetization of the metal base and its residual magnetism after removing the influence of a constant magnetic field. The initial magnetic permeability of the base is particles, iron oxide Fe ₂ O ₃ ; has a value of about 1000 units, and CrO ₂ about 1500 units. [8-10].

The objective of the new technical solution for the composition of the coolant and the method of its application is to increase the efficiency of heat transfer and control the hydrodynamic resistance of the flow of the coolant by increasing the thermal conductivity and volumetric flow rate of the coolant due to the implementation of the method of processing it with a constant magnetic field.

The problem is solved due to the fact that the proposed new domestic magnetorheological coolant (MRI) is an aqueous solution, for example, based on polyethylsiloxane or organic alcohols with uniformly dispersed flat microparticles of “soft magnetic” carbonyl iron of scaly form, round or obtuse, in size not more than 15 microns of each particle in one plane, with a thickness of not more than 10% of the larger linear size in the plane, coated with surfactants, or their meta organochlorine compounds, and the amount of the dispersed component is 0.05-2.5 wt. %

The way to use this coolant is to regulate its hydrodynamic resistance and directivity in the flow, as well as thermal conductivity by applying exposure to MRI with a constant magnetic field of intensity from 2 to 700 Oersteds.

It should be noted that the most effective MRI according to the prototype and the new MRI, as well as the method of its application, are implemented in heat exchangers made of non-magnetic materials (aluminum, copper, stainless steel, etc.).

A causal relationship between the set of essential features of the claimed objects: the coolant and the method of its application with the technical result is shown in the tables and explanations below.

The advantages of the new MRI in comparison with the prototype:

- the new magnetorheological coolant does not exhibit pronounced corrosion-abrasive properties during operation in the coolant flow in refrigeration and air conditioning systems, because dispersed and coated with surfactant particles are based on “soft magnetic”, flat, rounded or obtuse carbonyl iron particles with less rigidity and abrasiveness compared to the prototype;

- for the same reasons, it is deprived of the pronounced property of enhancing cavitation effects on the pumping group in the heat and cold supply system; moreover, it helps to dampen the cavitation effect and the effects of microhydraulic shock in the system.

These features allow the new magnetorheological coolant to retain thermophysical properties longer than the prototype, because it wears out less in the coated surfactant form;

- magnetically rigid particles of metal oxides coated with a surfactant according to the prototype, have an ellipsoid or spherical shape, and do not change it when implementing the method of regulating the hydrodynamic resistance and thermal conductivity of the flow MRE. As a result, the new MRI versus prototype has a higher efficiency of heat transfer and flow control;

Essential in the method of application of the new coolant is:

- materials based on chromium oxide and iron indicated in the prototype are “magnetically solid”, and carbonyl iron, in the new MRI, is “soft magnetic” material. As a result of magnetization of the MRE - prototype, after removing the magnetic effect, the oxide particles have a residual magnetization, which increases the hydroresistance of the liquid, reduces the volumetric flow rate and thermal conductivity due to the possible formation of conglomerates of magnetic particles. The new MRI takes its initial properties immediately after the removal of the magnetic effect, which allows it to be used to control the flow and thermal conductivity;

- according to the magnetization mechanism, iron and chromium oxides have less pronounced magnetic properties than those of carbonyl iron proposed as metal particles. The initial magnetic permeability of microparticles of iron oxide Fe ₂ O ₃ has a value of about 1000 units and CrO ₂ about 1500 units, and for a new MRI with microparticles of carbonyl iron is about 2500-3000 units [8-10].

A new technical solution allows you to show the above advantages of MRI and the method of its use in comparison with the prototype. The advantages of the new magnetorheological coolant - MRI with dispersed carbonyl iron particles coated with surfactants and the method of its application compared to the prototype, are given in the form of examples and tables below.

The experiments were carried out in the temperature range from (-30 ° С) to (+ 10 ° С) on a bench installation using standard measuring instruments. The tables give the averaged data for the experiments in the range of operating temperatures from (-5 ° С) to (+ 5 ° С), comfortable for organizing technological conditioning and creating moderate cold. Beyond the boundaries of this temperature range, similar ratios of parameters for the prototype and the new MRI are observed both in composition and method of application.

In order to create equal conditions of use, an MRI was taken according to the prototype and in a new MRI version with the same concentration of metal microparticles (iron and chromium oxides and carbonyl iron). The tests were carried out in equal temperature conditions of the environment and MRE - coolant according to the prototype and in a new version. An MRI according to the prototype with microparticles of metals of iron or chromium oxides, and in the second case, MRI with microparticles of carbonyl iron was compared on the basis of the same liquid carrier polyethylsiloxane with its identical characteristics.

Comparison of the MRE according to the prototype and the new MRI version was carried out by comparing the volumetric flow rate and thermal conductivity of the flow depending on the type of microparticles - based on iron oxide or chromium and carbonyl iron of the same volume size with the same concentration in the carrier fluid (polyethylsiloxane).

The implementation of the method of using MRI to control volumetric flow and thermal conductivity was carried out by exposing the MRI and MRI to a constant magnetic field with a strength of 1.0 to 800 Oersted. Data for an optimal concentration of microparticles of 0.70 wt. % are summarized in table 1 and presented below.

Examples of specific implementation.

1. We took an MRE - a prototype with microparticles of iron oxide Fe ₂ O ₃ or chromium CrO ₂ coated with a surfactant in a carrier fluid (polyethylsiloxane) and measured the volumetric flow rate and thermal conductivity when it was treated with a constant magnetic field of 1.0; 2.0; one hundred; 250; 400; 700 and 800 E.

At the same time, a new magnetorheological coolant (MRI) was taken with flake-type Fe carbonyl iron microparticles coated with a surfactant in a liquid (polyethylsiloxane) and thermal conductivity and volumetric flow were measured during treatment with a constant magnetic field of 1.0; 2.0; one hundred; 250; 400; 700 and 800 E.

The volumetric sizes of microparticles according to the prototype and for the new MRI are the same with the same concentration in polyethylsiloxane.

From table 1 it is seen that there is a noticeable increase in volumetric flow rate and thermal conductivity during the processing of MRI and MRI by a constant magnetic field in the range from 2.0 to 700 Oe with a maximum at 250 Oe, moreover, the value of the measured parameters for the new MRI is noticeably higher than for MRI according to the prototype. Outside this range of treatment with a constant magnetic field of less than 2.0 Oe, for example, 1.0 Oe and more than 700 Oe, for example, 800 Oe, the measured values of the prototype and the new MRI are low and the difference between them is insignificant.

As a result, a significant advantage was found in the volumetric flow rate and thermal conductivity of the new MRI with carbonyl iron microparticles compared to the MRI with iron or chromium oxide microparticles when implementing the method of using MRI by processing with a constant magnetic field with a voltage in the range from 2.0 to 700 Oe.

The best characteristics of MRI are explained by both high rates of carbonyl iron microparticles in their magnetic properties, and in optimal size and geometric shape. The latter was established empirically in the course of numerous experiments to select the optimal shape and size of carbonyl iron microparticles in MRI.

The experimental data are summarized in table 2 and presented below. Detailed data are presented for the optimal size of carbonyl iron microparticles. Data outside the optimum are not included in the table due to their large volume, which leads to overloading the tables.

From the data in table 2 it can be seen that the noticeable effectiveness of the new MRI in terms of volumetric flow rate and thermal conductivity is observed when implementing the method of application by processing MRI with carbonyl iron microparticles of linear size in one plane of no more than 15 μm. at a thickness of not more than 10% of the larger linear particle size with a constant magnetic field in the range from 2 to 700 Oe, and the maximum efficiency is observed when processing with a magnetic field of 250 Oe. Outside the range of processing with a constant magnetic field of less than 2.0 Oe, for example , 1.0 Oe and more than 700 Oe, for example, 800 Oe, the value of the measured values of volumetric flow and thermal conductivity, depending on the size of the microparticles, is low and the difference between them is insignificant.

To determine the optimal concentration range of carbonyl iron microparticles of the detected optimal size (not more than 15 μm in one plane with a thickness of not more than 10 percent of the larger linear size in the plane), experiments were carried out in the carrier fluid, which established the best concentration range from 0, 05 to 2.5 wt. % This is confirmed in the method of application by treating a new MRI with a constant magnetic field of 2 to 700 Oe in volumetric flow rate and thermal conductivity of MRI. The data are summarized in table 3 and presented below. The maximum volumetric flow rate and thermal conductivity of MRI was established at a concentration of carbonyl iron microparticles of 0.7 wt. % at a constant magnetic field of 250 E.

Outside this range, for example, microparticle concentration of 0.03 wt. % or 3.0 wt. % and MRI processing with a constant magnetic field of 1.0 or 800 Oe, a low value of the measured values (volume flow and thermal conductivity of MRI) is observed and the difference between them is insignificant.

Examples of the implementation of the MRI composition according to the concentration of carbonyl iron microparticles and the method of its application by treatment with a constant magnetic field to achieve the goal of the invention are to increase the heat transfer efficiency and control the hydrodynamic resistance of the coolant flow by increasing the volumetric flow rate and thermal conductivity of MRI.

We took a new coolant (MRI) with 0.03 wt. % of flat microparticles of carbonyl iron Fe, not exceeding 15 μm in size, in one plane with a thickness of not more than 10% of the larger linear particle size in the plane coated with surfactants, in the liquid - polyethylsiloxane and volumetric flow rate and thermal conductivity were measured during MRI treatment with a constant magnetic field tension 1.0; 2.0; one hundred; 250; 400; 700 and 800 E.

Similarly, a new heat transfer medium (MRI) was taken with a concentration of 0.05.0.10; 0.70; 1.50; 2.50 and 3.0 wt. % of flat microparticles of carbonyl iron Fe, with a size of not more than 15 μm, in one plane with a thickness of not more than 10% of the larger linear size of the particles in the plane coated with surfactants, in the liquid - polyethylsiloxane and measurements of flow and thermal conductivity during MRI processing with a concentration of carbonyl microparticles iron, indicated above, by a constant magnetic field of intensity 1.0; 2.0; one hundred; 250; 400; 700 and 800 E.

The lack of growth in volumetric flow rate and thermal conductivity beyond the lower limit of the declared parameters is explained by the insufficient concentration of magnetic particles in the new magnetorheological coolant. The decrease in volumetric flow rate and thermal conductivity beyond the upper limit of the declared parameters in terms of particle concentration and magnetic field strength is explained by the formation of conglomerates of magnetic particles, which complicates their adjustment in terms of flow rate and thermal conductivity.

Higher values for volumetric flow and thermal conductivity in favor of a new MRI in the claimed concentration range of carbonyl iron microparticles when treated with a constant magnetic field within the declared limits of its intensity are due to better (compared to the beyond the concentration parameters and processing modes) magnetic properties of carbonyl iron microparticles coated Surfactants, their greater thermal conductivity and, accordingly, better controllability by them (adjustment of spatial position) in the heat transfer stream When implementing the method of application by treatment with a constant magnetic field, as well as increased heat transfer efficiency.

A higher role is played by a higher sliding speed and better thermal conductivity in the MRI stream at the boundary of the particle plane — the heat carrier flow — the heat exchanger wall. Flat microparticles of carbonyl iron of the claimed shape and size in the claimed range of concentrations and modes of MRI treatment with a constant magnetic field under the influence of a constant magnetic field are arranged orderly in a horizontal plane in the direction of flow, which improves its flow and heat-conducting characteristics.

The main goal of the development is to obtain and use a new, more effective magnetorheological coolant and its application for heat and cold supply systems, with the possibility of regulating and controlling its flow and thermal conductivity, is revealed and achieved by choosing carbonyl iron microparticles instead of iron or chromium oxide microparticles, and microparticles carbonyl iron are selected a certain shape (scaly form) and size with their optimal concentration in MRI selected.

The method of application is carried out by treating MRI with a constant magnetic field in the established optimal range.

Thus, a new innovative magnetorheological coolant is proposed, consisting of a liquid selected from a series of monohydric alcohols, polyhydric alcohols, organosilicon liquids, water, etc., as well as mixtures of these liquids, including a dispersed metal component coated with a surfactant, and way to use it.

The difference between the new magnetorheological coolant and the method of its application from the known solutions is that in order to increase the efficiency of heat transfer, as well as to regulate and control its hydrodynamic resistance, for example, in terms of volumetric flow rate due to the orientation of the particles of the dispersed component coated with a surfactant, by constant magnetic field, in MRI, as a dispersed component, carbonyl iron particles are used, with a size of not more than 15 microns in one plane with a thickness of not more 10% of the larger particle size in a linear plane, in an amount of 0.05-2.5 wt. %

The implementation of the method of using MRI to regulate thermal conductivity and flow rate and direction of the coolant in the stream is carried out by exposing the magnetorheological coolant to a constant magnetic field with a strength of 2 to 700 Oersteds.

Information sources

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Claims (2)

1. Magnetorheological coolant for refrigeration and air conditioning systems, consisting of a liquid selected from a number of alcohols, polyhydric alcohols, organosilicon substances containing a finely dispersed component of magnetic material, the surface of which is treated with a surfactant, where the finely dispersed component of the magnetic material is carbonyl microparticles iron with the size of each microparticle in one plane of not more than 15 microns with a thickness of not more than 10% of the linear size in the plane, p Thus, the amount of the finely dispersed component in the coolant is from 0.05 to 2.5 wt.%. 2. The method of using the magnetorheological coolant according to claim 1 in refrigeration and air conditioning systems, which consists in the fact that the magnetorheological coolant is exposed to a constant magnetic field of intensity from 2 to 700 E.