Experimental Analysis of Nano Fluid Hydrodynamic Behavior of Al2O3 in Heating Systems of Residential Building

2.1 Preparation of nanofluid

Appropriate mixing and article stabilization is required to prepare nanofluids by spreading nanoparticles in the base fluid. Basically, there are three different methods to achieve the stability and stabilization of nanofluids. These methods are listed as follows:

(1) Acidifying the base fluid, (2) adding lubricant and disperser, (3) using ultrasonic vibrations. The goal of all these techniques is to change the surface properties of a system and prevent settling in order to achieve a stable suspension. In the current study, 20–22nm Al₂O₃ nanoparticles were mixed with distilled water and stabilizers. It then continuously produces 100-watt ultrasonic pulses at 36 ± 3 kHz for 5 hours to break down the masses and accumulate nanoparticles by ultrasonic vibrator (Toshiba, India) before the agent is used in the fluid. The optimum volume concentration in this study was between 0.2 and 1. The pH of the fluids showed that the chemistry of the solutions was almost neutral. A new nanofluid was provided for each test and used immediately. The density of some nanofluid samples was measured before and after laboratory testing to check the stability of nanofluid emissions. No significant differences were observed in the measured density. The distribution of the main nanoparticles Al₂O₃ on a nanoscale can be observed by a transverse electron microscope (TEM) and SEM. Figure 1 (a) shows the SEM images of Al₂O₃ when the flow was set at 75 A.

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Figure 1. (a) SEM image of Al₂O₃ particles (b) TEM image of particles Al₂O₃

The approximate size of the produced Al₂O₃ particle was measured directly from the SEM images by the Protec 2500 Optical Measurement System. In addition, the nanoparticles produced in Figure 1 are well rounded and uniform in size. Figure 1 (b) shows the TEM image of nanoparticle suspension. As shown in Figure 1 (b), the Al₂O₃ nanoparticles prepared by the proposed compound system, represent a good distribution of nanoparticles with an average size of 20–22nm. For this experiment, the relationship of the flow to the nanoparticles can be analyzed by different currents.

2.2 Investigation of pressure loss in piping systems based on ethylene glycol fluid

Power dissipation device from the piping system Resource can be seen in Figure 2.

Determining the flow pressure and flow in a pipe connection system (pipe network) is a general hydraulic issue. A pipe network is a system of pipes that consists of a single pipe or a complex system of pipes of different diameters and lengths. For example, the city's water supply network is a good example of a complex pipeline network. Typically, the network of pipes is designed in series, parallel, and circular in water supply systems. Therefore, it is necessary to measure the rate of energy loss in different places to perform accurate water supply calculations.

The network consists of two circuits (first and second circuits). The first circuit includes a Gate vatve No. 1, standard knee, 90° standard knee, straight pipes. The second circuit includes a ball valve No. 2 with a sudden opening, a sudden narrowing, 90° tee with different radiuses and straight pipes. Piezometer pipes are connected under pressure to measure the pressure loss in the components at the two ends of all components except for the valves.

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Figure 2. Power dissipation device from the piping system Resource

The device has a water tank and a pump for water circulation in the piping system. The inlet water to the system is embedded on the device to measure the flow rate. The measurement unit of discharge is liters per minute.

Hand gauges have been used to measure pressure loss in both valve noses. All air bubbles must be removed from the pipes for testing. To this end, close valve 2 and open valve 1 to turn on the circuit after turning on the flow pump. Close the valve 1 and the flow control valve for a few minutes after the flow was set. Shake the piezometer hoses to direct the air bubbles trapped in different parts into the air-filled space above the piezometers. Close air vent valves (right valves) at the end of the manifold and return the discharge pump valve to a very low value so that the air inside the piezometers is ventilated. After this, close the discharge-regulating valve, turn off the pump, and allow the water level in the piezometers to loss to the desired value by slightly opening the upper and left valves of the piezometers. Then, first close the valve 1 and then the ventilation valve of the piezometers, so that the manometers of the first circuit are ventilated and ready for testing. Close valve 1 and open valve 2 and repeat the last steps to ventilate the second circuit.

2.3 Dimensional specifications of piping system

Some of the test information is:

Internal diameter of pipes: 16mm.

Internal diameter of the pipe after opening and before tightening: 26mm.

Internal diameter of the pipe after opening and before tightening: 16mm.

Distance between pressure gauges for straight pipes and bends: 1mm.

The curvature radius of knees:

G1/G2 knee: 2.5m.

J1/J2 knee: 5cm.

The continuity equation and Bernoulli Energy Relationships are used to calculate water flow in pipes with (1) and (2) relationships:

Continuity equation:

$\mathrm{Q}=\mathrm{A}_{1} \mathrm{~V}_{1}=\mathrm{A}_{2} \mathrm{~V}_{2}$      (1)

$\mathrm{Z} 1+\frac{P_{1}}{\rho g}+\frac{V_{1}^{2}}{2 g}=z_{2}+\frac{P_{2}}{\rho g}+\frac{V_{2}^{2}}{2 g}=h_{2}$     (2)

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Figure 3. Loss due to sudden coefficient of friction

Pressure loss in pipes can be classified as follows:

A) A loss due to viscosity and internal friction of the fluid.

B) A loss caused by local complications or a sudden change in the cross-sectional area.

The loss in water flow pressure in a straight pipe with velocity V, length L, and constant diameter d is proportional to (3):

$\mathrm{h}_{1}=\mathrm{f} \frac{L}{d} \frac{V_{2}}{2 g}$     (3)

In the above equation, the Darcy-Weibach coefficient is the next base factor, which is a function of the Reynolds number and the surface roughness. One of the equations presented for calculating f in smooth pipes provided is Blasius, which is true for Re≤105: 

$\mathrm{f}=\frac{0.3164}{R e^{025}}$     (4)

The f coefficient in the general condition of the pipes is determined by the moody diagram. The Reynolds number is also obtained from Eq. (5):

$\mathrm{Re}=\frac{v d}{u}$      (5)

:V=μ/ρ is systematic, which is equal in water at 25°C. The physical properties of water at different temperatures from 0°C to 100°C are available in the appendix of fluid mechanics books

The cross-section of the flow can suddenly increase or decrease. In pipefittings, the cross-sectional area changes abruptly due to the connection of two pipes with different concavities.

If low cross-section pipes are connected to high cross-section pipes, the localized loss due to sudden opening according is obtained from Eqns. (6) and (7). Loss due to sudden coefficient of friction can be seen in Figure 3.

$\mathrm{h}_{1}=\mathrm{k}_{\mathrm{e}} \frac{V_{1}^{2}}{2 g}=\frac{\left(V_{1}-V_{2}\right)^{2}}{2 g}$     (6)

$\mathrm{Ke}=\left[1-\left(\frac{\mathrm{d}_{1}}{\mathrm{~d}_{2}}\right)^{2}\right]^{2}$     (7)  

In addition, if a pipe with a high cross-section is connected to a pipe with a lower cross-section, a local loss in the ratio (8) and (9).

$\mathrm{h}_{1}=\mathrm{k}_{\mathrm{e}} \frac{v_{2}^{2}}{2 g}=\frac{\left(\mathrm{V}_{1}-\mathrm{V}_{2}\right)^{2}}{2 g}$      (8)

$\mathrm{k}_{\mathrm{e}}=\left(\frac{A_{2}}{A_{1}}-1\right)^{2}=\left[\frac{1}{C_{c}}-1\right]^{2}$      (9)

Ac is the cross-sectional area at the accumulated area and Cc is the contraction coefficient. Approximate values of loss coefficient k for commercial parts in piping can be seen in Table 1.

The difference in balance between the two-piezometer pipes will give the size of the energy difference between the two sections. The value of the difference, or in other words, the measurement loss is displayed with hlw.

hlw=x-(Z2-Z1)=X+Z

Pressure loss can be calculated using these equations using the continuity equation and Bernoulli relations between points 1 and 2 and after simplification.

In the above relation, kc is the dimensionless coefficient of pressure loss in tightness and is obtained from the Table 2.

Local energy loss is caused by the turbulence of the water flow in the pipe knee. The value of this loss for curves is obtained from Eq. (10). Ka is the dimensionless coefficient that depends on the radius of the pipe and the angle of curvature.

$\mathrm{h}_{\mathrm{ln}}=\mathrm{k}_{\mathrm{a}} \frac{V^{2}}{2 g}$      (10)

One of the local connections is the valves, which cause a relatively large loss in flow due to the internal structure. The amount of energy loss in valves is obtained from Eq. (11).

$\mathrm{h}_{1}=\mathrm{k}_{\mathrm{a}} \frac{V^{2}}{2 . g}$      (11)

In the above equation, k1 is the energy coefficient in the valve, which is dimensionless and depends on the type of valve and the degree of its opening. If the valve is completely closed, k = ∞. Table 2 shows the approximate values of the energy coefficient of the valves and other connections.

Table 1. Approximate values of loss coefficient k for commercial parts in piping

Table 2. Pressure loss in tightness

2.4 Obtaining the venture and orifice discharge coefficient

Changes in loss rate depending on current intensity for the components tested (venture meter, orifice, sudden opening, and 90-degree knee) then discharge measurement device can be seen in Figure 4.

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Figure 4. Discharge measurement device

2.5 Device description

The discharge of the flow is measured by several types of flowmeters (venture meters, orifices, and rotameters) by this device. Moreover, the loss rate in flow meters, curves, and parts is measured where there is a sudden change in diameter (diffusion), so that the water flow is pumped into the system by the pump. First, the water enters a horizontal pipe after passing through the valve, which passes through a diffuser (sudden opening) after passing through the venture meter. Along the way, there is an orifice with a diameter of 20mm. After passing through the orifice, the flow enters a 90-degree knee, and finally it goes through a rotameter. The flow is measured by a rotameter. Manometers are used to measure static pressure along the way before and after the flowmeters, as well as before and after the diffuser and knee. The height of the water is measured by the dial behind the manometers.

The test components and their dimensions are as follows then components of flow discharge device can be seen in Figure 5:

1. venture meter with input diameter of 26mm and output diameter of 26mm and throat diameter of 16mm

2. Cone expansion from 26mm diameter to 50mm diameter.

3. Orifice meter with a diameter of 20mm

4. Knee 90 with a diameter of 56mm

5. Rotameter

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Figure 5. Components of flow discharge device

The orifice is a usually round hole through which fluid flows and may have sharp edges or rounded edges. Installing a sharp edge orifice in the pipe causes it to shrink according to (Figure 6) jet passing through it.

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Figure 6. Orifice in the pipe

For the incompressible flow, the Bernoulli equation is written between section 1 and section 2, i.e. the contracted section.

$\frac{V_{U}^{2}}{2 g}+\frac{p_{1}}{y}=\frac{V_{U}^{2}}{2 g}+\frac{p_{2}}{y}$      (12)

qin which, V2 is the theoretical value of contraction velocity. On the other hand, the equation of connection between two sections is expressed as follows:

$V_{2} \frac{\pi D_{1}^{2}}{4}=V_{2} D_{0} \frac{\pi D_{0}^{2}}{4}$      (13)

in which, C0=A2/A0 is the contraction coefficient. By removing V2 in the above equations:

$\frac{V_{21}^{2}}{2 g}\left[1-C_{1}^{2}\left(\frac{D_{0}}{D_{1}}\right)^{4}\right]=\frac{P_{1}-P_{2}}{Y}$      (14)

By solving the above equation, V2 is obtained as follows:

$V_{21}=\sqrt{\frac{2 g\left(P_{1}-P_{2}\right) / y}{1-C_{1}^{2}\left(D_{0} / D_{1}\right)^{4}}}$      (15)

If it is multiplied by C2, the actual velocity at the contraction is obtained:

$V_{21}=\sqrt{\frac{2\left(P_{1}-P_{2}\right) / p}{1-C_{1}^{2}\left(D_{0} / D_{1}\right)^{4}}}$      (16)

Finally, with the real speed hit on the jet level, the actual discharge is achieved:

$\mathrm{Q}=\mathrm{C}_{\mathrm{d}} \mathrm{A}_{0} \sqrt{\frac{2\left(P_{1}-P_{2}\right) / p}{1-C_{1}^{2}\left(D_{0} / D_{1}\right)^{4}}}$       (17)

in which, Cd =C1C2, is the orifice meter discharge coefficient.

The following equation can be used to calculate discharge in venture the help of Bernoulli's equation and by avoiding the loss of energy between the inlet sections in the venture condenser (Proving this equation is similar to proving an orifice relationship).

$\mathrm{Q}=\mathrm{C}_{\mathrm{d}} \mathrm{A}_{0} \sqrt{\frac{2\left(h_{1}-h_{2}\right)}{1-\left(D_{2} / D_{1}\right)^{4}}}$     (18)

A rotameter is a vertical divergent tube in which there is a floating object. The specific gravity of a float is greater than that of a liquid. The fluid in the tube flows upwards and pushes the float upwards. The tube is clear and the float is visible. The pipe is calibrated, from which discharge is read directly.The equation gives calculates the discharge of incompressible flow passing through the venture tube due to the difference in monomeric height. The contraction coefficient is equal to one in venture tube. So, Cd =C1.

The difference in pressure and energy loss between the AB and D.C levels causes the cone to be immersed in equilibrium at altitude Y (Figure 3-7). If the energy loss is between (1) and (2) hH, according to Bernoulli's theorem:

$\frac{p_{1}}{y}=\frac{V_{1}^{2}}{2 g}+\frac{p_{2}}{y}+\frac{V_{2}^{2}}{2 g}+\mathrm{h}_{\mathrm{H}}+\mathrm{H}$     (19)

If the cross-sectional changes between (1) and (2) are ignored, the above equation V1+V2 can be written as follows:

$\frac{P_{1}-P_{2}}{Y}+H+h_{\mathrm{H}}$      (20)

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Figure 7. Cross-sectional changes

Considering the balance of control volume of "ABCD":

$\mathrm{P}_{2} \mathrm{~A}_{2}+\mathrm{W}_{1}+\mathrm{W}_{\mathrm{W}}-\mathrm{P}_{1} \mathrm{~A}_{1}=0$      (21)

In which, W1 is the weight of the cone and WW is the weight of the water inside the control volume. By ignoring the changes in cross section A1= A2 and as a result:

$\left(\mathrm{P}_{1}-\mathrm{P}_{2}\right) \mathrm{A}=\mathrm{W}_{\mathrm{f}}+\mathrm{W}_{\mathrm{W}}$      (22)

After removing (P1 – P2) between the above equations hH = (Wf+ Ww) / YA1 –H, all values to the right of the equation are constant. As a result, hH will be constant for all y values. Given that this loss in energy depends on the rate of flow around the base of the cones. So, the flow rate in the conical base environment will also be constant. If this velocity is shown by V, then the flow intensity is:

$\mathrm{Q}=(\pi D d)^{V}$     (23)

In Figure 2, d = yθ. As a result:

$\mathrm{Q}=(\pi D d V)_{\mathrm{y}}$

The value in the rotameter is directly related to the height of the submerged cone (y).

Energy loss in flowmeters.

Localized lesions are caused by the following reasons:

     Inlet or outlet of the pipe.

     Sudden expansion or contraction.

     The presence of knees, valves, etc.

     Gradual expansion or contraction of the section.

In the orifice, the amount of energy loss is significant, and if it is ignored, a significant error in measurement occurs. In practice, the loss coefficient is used, which can be calculated for each of the devices using the following equation:

$\mathrm{K}=\frac{Q_{m}}{Q_{1}}$      (24)

in which, Q₁ is the calculated discharge from the theatrical discharge and Q_m is the actual calculated discharge. The value of K is generally a function of the shape and specifications of the device and the amount of discharge and fluidity of the fluid specifications.

The energy loss (h1) is obtained during a venture meter, orifice meter, or rotameter from the following equation.

$\mathrm{h}_{1}=\Delta \mathrm{H}=K^{V^{2}} / 2 g$      (25)

V is the speed at the input and deception of the device loss.

The loss factor (K) of each part can be obtained using the following equations by determining the loss in energy and kinetic energy of the input.

Loss in Venturi: ΔH_AC = h_A - h_C.

Loss in Orifice: ΔH_EF = h_E - h_F.

The loss in sudden expansion and according to Figure 8 expansion is considered from section 1 to section 2.

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Figure 8. Loss in sudden expansion

The losses related to the diameter change in the above system are as follows:

$\mathrm{H}_{\mathrm{e}}=K_{e}^{V_{1}^{2}} / 2 g=\frac{\left(V_{1}-V_{2}\right)^{2}}{2 g}$      (26)

$\mathrm{~K}_{\mathrm{e}}=\left(1-\frac{A_{1}}{A_{2}}\right)^{2}=\left[1-\left(\frac{d_{1}}{d_{2}}\right)^{2}\right]^{2}$      (27)

The energy loss between points C and D is calculated from the following equation:

$\Delta \mathrm{H}_{\mathrm{CD}}\left(\mathrm{h}_{\mathrm{C}-} \mathrm{h}_{\mathrm{D}}\right)+\frac{V_{C}^{2}}{2 g}=\left(1-\frac{A_{1}}{A_{2}}\right)^{2}$      (28)

Knee energy loss can be obtained from the following equation with the help of Bernoulli Equation between the inlet and outlet of the knee as well as in the piezometric tubes.

$\Delta \mathrm{H}_{\mathrm{CD}}\left(\mathrm{h}_{\mathrm{C}^{-}} \mathrm{h}_{\mathrm{D}}\right)+\frac{V_{C}^{2}}{2 g}=\left(1-\frac{A_{G}}{A_{H}}\right)^{2}$      (29)

In this test, the pressure loss of aluminum oxide nanoparticles and titanium dioxide in the base fluid of a mixture of ethylene glycol and water was tested as a fluid.

• The results of the experiments due to the addition of nanofluids to the mixture of water and ethylene glycol show the presence of nanoparticles in the test fluid have increased the pressure loss of nanofluid compared to the base fluid. This upward trend increases with increasing nanoparticle concentration. In fact, increasing the volume fraction of nanoparticles and reducing the temperature of the incoming fluid to the radiator are two factors that increase the viscosity of the nanofluid and increase its pressure loss.

• The results of the experiments for the two nanofluids indicate a higher-pressure loss and coefficient of friction of the nanofluid aluminum oxide than the nanofluid titanium dioxide. The reason for this can be expressed in the relatively high dimensions and density of aluminum oxide nanoparticles compared to 20nm titanium dioxide particles.

• The results of the experiment, due to the addition of titanium dioxide nanoparticles and aluminum oxide to the base fluid, indicate a slight difference in pressure loss in the pipelines, as well as the process of non-aggregation of nanoparticles in pipelines and non-correlation in tubular ducts for data obtained by adding titanium dioxide nanoparticles.

• The results show that the fluid tested was ethylene glycol and water in piping systems and closed circuits (such as radiators) to improve the heat transfer process.