CN102573422A - Method for enhancing heat exchange of free surface array jet system - Google Patents

Abstract

The invention aims at the problems of low heat transfer performance in the existing array jet technology, and provides a method for heat dissipation of electronic devices under the condition of high heat flux, which improves the heat dissipation capacity of the electronic devices and ensures the safe operation of the electronic devices. The invention introduces the nanofluid with high thermal conductivity into the free surface array jet, selects the metal/metal oxide nanofluid with high thermal conductivity, utilizes the high thermal conductivity and enhanced heat transfer effect of the nanofluid, and effectively improves the heat transfer of the array jet system ability, so as to obtain a higher heat transfer effect. Compared with the prior art, the present invention has the remarkable advantages as follows: 1. The experimental working fluid is a nanofluid, which has higher thermal conductivity than the common working fluid; 2. The random movement of nanoparticles in the nanofluid helps heat flow The transfer in the fluid will help to improve the uniformity of the surface temperature of the heating element; 3. The nano-particles in the nano-fluid impact the heat-exchanging surface and improve the heat-exchanging capacity of the free-surface array jet.

Description

A Method of Enhancing Jet Heat Transfer of Free Surface Arrays

technical field

The invention belongs to a heat control method for an electronic device, which introduces a nanofluid with high thermal conductivity into a free surface array jet, thereby effectively enhancing the heat exchange effect of the array jet.

Background technique

The principle of jet impingement cooling is: the fluid is directly sprayed to the surface to be cooled through a nozzle of a certain shape (circular or slit shape). Due to the short flow and high flow rate, a large pressure is formed on the heat exchange surface, and the jet impacts the stagnation point. The boundary layer near the cooling zone becomes very thin, so it has extremely high heat transfer efficiency. Compared with conventional convective heat transfer technology, the impact heat transfer coefficient of jet cooling technology is several times or even an order of magnitude higher. Comparative literature 1 (Fabbri Metteo, Dhir Vijay K., Optimized heat transfer for high power electronic cooling using arrays of microjets, 127(2005): 760-769.) used micro-hole array experiments to study the heat dissipation capability of array jets, proving that array Jets are an extremely effective method of cooling electronics. However, at present, a large amount of working fluids with low thermal conductivity are used in experimental studies. For example, the experimental working medium in Reference 1 is water, and high thermal conductivity working fluids will definitely bring higher heat transfer performance.

Since nanofluids (comparative literature 2 Choi S U S, Enhancing thermal conductivity of fluids with nano-particles . American Society of Mechanical Engineering, 231(1995): 992103.) were proposed, scholars from various countries have conducted research on their thermal conductivity, viscosity, etc. The research has proved that nanofluids contribute to enhanced heat transfer, but no one has combined array jets and nanofluids to enhance the heat transfer performance of array jets and provide effective technical support for the heat dissipation of high-power electrical appliances in the future.

This method introduces the nanofluid into the free surface array jet, combines the high thermal conductivity of the nanofluid and the strengthening effect on heat transfer with the extremely high convective heat transfer performance of the free surface array jet, and effectively improves the impact heat transfer of the array jet ability, so as to more effectively meet the heat dissipation requirements of higher heat flux electronic devices, effectively control the surface temperature of electronic devices, and meet the operating temperature requirements of future high-power electronic devices.

Contents of the invention

The purpose of the present invention is to solve the problems of low heat transfer performance in the existing array jet technology, and provide a method that can be applied to heat dissipation of electronic devices under the condition of high heat flux, which improves the heat dissipation capacity of electronic devices and ensures the stability of electronic devices. safe operation.

Introduce the nanofluid with high thermal conductivity into the free surface array jet, select the metal/metal oxide nanofluid with high thermal conductivity, and use the high thermal conductivity and enhanced heat transfer effect of the nanofluid to effectively improve the heat exchange capacity of the array jet system. Thereby obtaining a higher heat transfer effect.

Realize the technical solution of the present invention is:

A method for strengthening free surface array jet heat transfer, comprising the following specific steps:

(1) Select nanoparticles with high thermal conductivity and high dispersion;

(2) Preparation of nanofluids;

(3) Optimize the free surface array jet system;

(4) Add the prepared nanofluid into the free surface array jet system, adjust the working environment, and perform free surface array jet heat exchange.

The nanoparticles with high thermal conductivity and high dispersion performance described in step (1) are metal/metal oxide nanoparticles, preferably copper, aluminum or their oxides.

The nanofluid in step (2) is prepared by a classic two-step method, and the concentration of the nanofluid is 0.17-1.34Vol.%.

The optimized array jet system described in step (3) is to optimize the body of the heat exchange equipment. The optimization of the heat exchange body requires that the ratio of the distance S between adjacent jet holes to the diameter D of the jet hole be in the range of 3-10, and the impact distance H and the jet hole The diameter ratio is 3.5-15, and the diameter range of the jet hole is 0.5mm-3.0mm; at the same time, the heat exchange surface is grooved to enhance the heat exchange capacity. The groove depth h is selected to be 0.5mm-1.5mm, and the groove width d is selected to be 0.5mm- 2.0mm, the selected value of groove spacing p is 0.5mm-2.0mm.

In step (2), in order to achieve a better dispersion effect, sodium dodecylbenzenesulfonate is used as a dispersant, and the amount of sodium dodecylbenzenesulfonate added is 0-0.1%.

Compared with the prior art, the present invention has the remarkable advantages of:

1. The experimental working medium is nanofluid, which has higher thermal conductivity than ordinary working medium;

2. The irregular movement of nanoparticles in the nanofluid helps to transfer heat in the fluid, which will help to improve the uniformity of the surface temperature of the heating element;

3. The nanoparticles in the nanofluid impact the heat exchange surface, improving the heat exchange capacity of the free surface array jet.

Description of drawings

Fig. 1 is a heat transfer effect diagram of a heat transfer experiment performed on a heat transfer surface with a heat flux density of 50 W/cm ² using nanofluid as a heat dissipation working medium in Example 1 of the present invention.

Fig. 2 is a heat transfer effect diagram of a heat transfer experiment performed on a heat transfer surface with a heat flux density of 50 W/cm ² using the nanofluid of Example 2 of the present invention as a cooling medium.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

The method introduces the nanofluid into the free surface array jet, including the choice of the nanofluid, the free surface array jet environment and working conditions.

The realization of this method is mainly manifested in the selection of nanofluids and the control of working conditions. (1) Select copper, aluminum or their oxide nanoparticles with high thermal conductivity and high dispersion properties; (2) Prepare nanofluids with a concentration of 0.17-1.34Vol.% using a classic two-step method, and investigate the stability of nanofluids (3) Optimize the free surface array jet system to enhance the heat transfer capacity of the system, and the optimization of the heat transfer body requires the spacing S of adjacent jet holes and the diameter of the jet hole D The ratio range is 1.5-10, the ratio of the impact distance H to the jet hole diameter is 3.5-15, and the jet hole diameter range is 0.5mm-3.0mm; at the same time, the heat exchange surface is grooved to enhance the heat transfer capacity, and the groove depth h is selected as 0.5mm -1.5mm, the selected value of groove width d is 0.5mm-2.0mm, and the selected value of groove spacing p is 0.5mm-2.0mm; (4) Add the prepared nanofluid to the free surface array jet system to adjust the working environment and carry out free Surface array jet heat transfer.

Example 1

1. Measure 1.5L each of ethylene glycol and deionized water, and mix them well to make a 1:1 ethylene glycol-water solution;

2. Weigh 120g of metal copper nanoparticles with an average diameter of 50nm, add it to ethylene glycol-water solution, put it into an ultrasonic device for ultrasonication for 4h, and perform mechanical stirring at the same time to prepare copper-ethylene glycol with a volume fraction of 0.56%. Glycol-water nanofluid, which is a two-step method for preparing nanofluid;

3. Optimize the system, heat-preserve the inside of the system tube, adjust the heat exchange equipment, select the diameter of the jet hole to be 1.5mm, the S/D to be 3, and the H/D to be 7; the surface is grooved, the groove depth is 0.5mm, and the groove width is 0.5mm , the groove spacing is 0.5mm, adjust the position of the jet hole to ensure that the array jet hole is facing the center of the heat exchange surface;

4. Add the prepared nanofluid into the experimental system, adjust the experimental temperature to 15°C, the flow rate of the heat exchange working medium is 0.144m3/h, and the simulated heat source is heated to 50W/cm2 to start the heat exchange experiment.

The heat transfer effect is shown in Figure 1. When nanofluids are introduced into the free surface array jet, compared with those without using nanofluids, the heat transfer performance of the system is greatly improved, with the highest improvement rate reaching 18.5%. The superiority of fluid as a working medium. At the same time, Figure 1 also shows that an excessively high proportion of nanoparticles may cause a decrease in heat transfer performance, so selecting the appropriate type and proportion of nanoparticles is a very critical factor.

Example 2

1. Measure 3L of deionized water, weigh 38g of metal copper nanoparticles with an average diameter of 25nm, add it to deionized water, and add sodium dodecylbenzenesulfonate with a mass fraction of 0.05% as a dispersant at the same time, put it in Ultrasonic 4h in ultrasonic equipment, carry out mechanical stirring simultaneously, prepare the copper-water nanofluid that volume fraction is 0.17%;

2. Optimize the system, heat-preserve the inside of the system tube, adjust the heat exchange equipment, select the jet hole diameter as 3.0mm, S/D as 1.5, and H/D as 5; the surface is grooved, the groove depth is 1.0mm, and the groove width is 0.5mm , the groove spacing is 0.5mm, adjust the position of the jet hole to ensure that the array jet hole is facing the center of the heat exchange surface;

3. Add the prepared nanofluid into the experimental system, adjust the experimental temperature to 21°C, the flow rate of the heat exchange working medium to 0.22m ³ /h, and heat the simulated heat source to 49W/cm ² , and start the heat exchange experiment.

The heat transfer effect is shown in Fig. 2. For example, it can be concluded from Fig. 2 that the heat transfer performance of the system is greatly improved when the nanofluid is introduced into the free-surface array jet, and the highest improvement reaches 6.5%, but the effective strengthening effect may not be obtained when the volume fraction is low. Figure 2 also illustrates that dispersants can affect the heat transfer capability of nanofluids.

Example 3

1. Measure 3L of deionized water, weigh 79g of copper oxide nanoparticles with an average diameter of 50nm, add it to deionized water, and add 0.1% sodium dodecylbenzenesulfonate as a dispersant at the same time, put it in Ultrasonic 4h in ultrasonic equipment, carry out mechanical stirring simultaneously, prepare the copper oxide-water nanofluid that volume fraction is 0.33%;

2. Optimize the system, heat-preserve the inside of the system tube, adjust the heat exchange equipment, select the jet hole diameter as 0.5mm, S/D as 10, and H/D as 15; the surface is grooved, the groove depth is 1.5mm, and the groove width is 2.0mm , the groove spacing is 2.0mm, adjust the position of the jet hole to ensure that the array jet hole is facing the center of the heat exchange surface;

3. Add the prepared nanofluid into the experimental system, adjust the experimental temperature to 20°C, the flow rate of the heat exchange working medium is 0.197m3/h, and the simulated heat source is heated to 50W/cm2, and the heat exchange experiment is started.

Using the above method to conduct heat transfer experiments, compared with that without using nanofluids, the maximum increase in heat transfer performance of the system reached 4.3%.

Example 4

1. Measure 3L of deionized water, weigh 240g of metal aluminum nanoparticles with an average diameter of 50nm, add it to deionized water, and add 0.05% sodium dodecylbenzenesulfonate as a dispersant at the same time, put it in Ultrasonic 4h in ultrasonic equipment, carry out mechanical stirring simultaneously, prepare the copper oxide-water nanofluid that volume fraction is 1.343%;

2. Optimize the system, heat-preserve the inside of the system tube, adjust the heat exchange equipment, select the diameter of the jet hole to be 1.5mm, the S/D to be 3, and the H/D to be 7; the surface is grooved, the groove depth is 1.0mm, and the groove width is 1.5mm , the groove spacing is 1.5mm, adjust the position of the jet hole to ensure that the array jet hole is facing the center of the heat exchange surface;

3. Add the prepared nanofluid into the experimental system, adjust the experimental temperature to 20°C, the flow rate of the heat exchange working medium is 0.197m ³ /h, and the simulated heat source is heated to 50W/cm ² to start the heat exchange experiment.

Using the above method to conduct heat transfer experiments, compared with that without using nanofluids, the heat transfer performance of the system can be improved by up to 8.4%.

Example 5

1. Measure 3L of deionized water, weigh 139g of alumina nanoparticles with an average diameter of 50nm, add it to deionized water, and add 0.05% sodium dodecylbenzenesulfonate as a dispersant at the same time, put it in Ultrasonic 4h in ultrasonic equipment, carry out mechanical stirring simultaneously, prepare the copper oxide-water nanofluid that volume fraction is 0.746%;

2. Optimize the system, heat-preserve the inside of the system tube, adjust the heat exchange equipment, select the jet hole diameter as 1.0mm, S/D as 5, H/D as 10, groove on the surface, groove depth 1.5mm, groove width 1.5mm , the groove spacing is 1.5mm, adjust the position of the jet hole to ensure that the array jet hole is facing the center of the heat exchange surface;

3. Add the prepared nanofluid into the experimental system, adjust the experimental temperature to 21°C, the flow rate of the heat exchange working medium is 0.172m3/h, the simulated heat source is heated to 50W/cm2, and the heat exchange experiment is started.

Using the above method to conduct heat transfer experiments, compared with that without using nanofluids, the maximum increase in heat transfer performance of the system reached 5.1%.

Claims (5)

1. A method for strengthening free surface array jet heat transfer, characterized in that said method may further comprise the steps: Step 1, select nanoparticles with high thermal conductivity and high dispersion; Step 2, preparing nanofluid; Step 3, optimize the free surface array jet system; In step 4, the prepared nanofluid is added to the free surface array jet system, the working environment is adjusted, and the free surface array jet heat exchange is performed. 2. The method for strengthening free surface array jet heat exchange according to claim 1, characterized in that the nanoparticles with high thermal conductivity and high dispersion performance described in the first step are metal/metal oxide nanoparticles, preferably copper , aluminum or its oxides. 3. The method for enhancing free surface array jet heat exchange according to claim 1, characterized in that the nanofluid described in the second step is prepared by a classic two-step method, and the concentration of the nanofluid is 0.17-1.34 Vol.%. 4. according to the method for strengthening free surface array jet heat exchange described in claim 1 or 3, it is characterized in that adopting sodium dodecylbenzene sulfonate as dispersant in the 2nd step preparation nanofluid process, described ten The addition amount of sodium dialkylbenzene sulfonate is 0-0.1%. 5. The method for strengthening free-surface array jet heat transfer according to claim 1, characterized in that the optimized array jet system described in the third step is to optimize the heat exchange equipment body, requiring adjacent jet hole spacing S and jet flow The hole diameter D ratio ranges from 3-10, the ratio of the impact distance H to the jet hole diameter is 3.5-15, and the jet hole diameter ranges from 0.5mm to 3.0mm; at the same time, the heat transfer surface is grooved to enhance the heat transfer capacity, and the groove depth h is selected is 0.5mm-1.5mm, the selected value of slot width d is 0.5mm-2.0mm, and the selected value of slot pitch p is 0.5mm-2.0mm.

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