Effectiveness Enhancement of the Double Tube Heat Exchanger Using ZnO Nanofluid

In this study, the effect of adding zinc oxide nanoparticles to the reversible effect double tube heat exchanger with a length of 1.5 meters, an outer diameter of 19.0 mm, is made of copper material that is used by Nano water as a cold liquid. Zinc solid nanoparticles with a volume concentration of 3% were used with water as the base liquid. The cold nanoscale water flows into the real tube with a volume of 4 L/min which enters into the heat exchanger at 16°C, where the hot water flows into the separator of the heat exchanger representing a blank volume of 6 L/min. The Reynolds number range and flowrate ranges are 10000 to 20000 and 5 to 15 respectively. The heat exchanger was introduced at a temperature of 65°C. An improvement in the performance of the exchanger was shown in the case of using water with the addition of nanoparticles.


Introduction
The double tube heat exchanger is the significant device of heat transfer between two different types of fluids. Conducted a study to calculate the heat transfer coefficient of nanoscale fluids consisting of aluminum nanoparticles mixed in transformer oil as a base fluid which was stratified in a double-tube heat exchanger and the nanofluid showed significant improvement in effect on friction and heat transfer. The researcher showed a good agreement between experimental and numerical studies.
The effect of the shape of different nanoparticles (cylindrical, plate and spherical) on the performance parameter of a shell-tube type heat exchanger and used (-AlOOH) particles mixed in the mixture of water and ethyl alcohol as the base liquid and the researcher analyzed the performance of the heat exchanger in terms of the heat transfer rate. And the change of entropy in the nanoscale fluid, and the results showed that there was an increase in both the rate of heat transfer and the thermal performance of the exchanger [11]. The results also showed that the cylindrical particles had the best thermal properties on the rate of heat transfer and the largest change in the energy of entropy. The researcher indicated that the entropy increase was less than 1%. Therefore, this increase in entropy energy can be neglected and thus cylindrical particles are considered to be the best for use in heat exchangers to work with nanoscale fluids.
The experimental and numerical study on the thermal transfer of the nanofluid using AL2O3 for two types of heat exchanger, the first type of the double tube and the other type was the shell and tube. The effect of some important factors such as the volumetric flow rates of the hot and cold nanofluid, the temperature of the nanoscale, and the concentration of particles on the heat performance of the exchanger has been considered. The results showed that the thermal performance of these two types increases by increasing the flow rates of the two fluids and increasing the concentration, as well as the temperature of the nanofluid entering the exchanger.
The results also showed that the heat transfer coefficients of the nanoscale fluid in the two exchangers (the first and second) are higher than that of water by (13.2% -21.3%), respectively.
Likewise, the thermal performance coefficient of the nanofluid in the shell and tube type heat exchanger was higher than the thermal performance in the double tube increased by 26.2%. [12] Hussein [13] was studied thermal performance and thermal properties of double pipe heat exchanger under laminar flow by using hybrid nanofluid. It was concluded that the performance of double pipe heat exchanger increases as increase of thermal properties of hybrid nanofluid. This paper is studied the effect of ZnO solid nanoparticles suspended in water on the double tube heat exchanger. The test rig has been fabricated and nanofluid has been prepared.
The friction factor and heat transfer enhancement are measured and compared to pure water.
The effectiveness of the double pipe heat exchanger is evaluated by using nanofluid and

Test rig fabrication
The test rig shown in Figure ( The ZnO solid nanoparticles are suspended in pure water with mechanical mixing to create nanofluid. The ultrasonically device has been applied to break up all agglomerated and ensuring stability of homogenous nanofluid [13]. (a) Image of experimental system.
(b) Schematic of system.

Nanofluid preparation properties
It can be used Eq. (1) to estimate the nanofluid volume concentrations depending on nanoparticles volume (V p ) and water volume (V f ) respectively. (1) The of nanofluids is by; The pH values of nanofluid have been measured using OAKTON device to measure the stability. The pH value before and after tests refers to the stability of nanofluid and the changes of thermophysical properties. ZnO nanopowders suspended in pure water nanofluids undertaken are assumed as a single phase flow, an incompressible, a Newtonian fluid and an isotropic.

Journal of Petroleum Research and Studies
Thermal properties of ZnO nanofluid have been shown in a Table (1).

Calculation of effectiveness
The flow of nanofluid through the double pipe heat exchanger should be under assumptions that the nanofluid is assuming single phase with high stability under the turbulent flow condition.
The hot and cold fluid are assumed to be pure water and nanofluid respectively.
For Counter Flow Arrangement, Logarithmic Mean Difference in temperature.
Based on the inner surface area of the inner pipe, the experimental overall heat transfer coefficient.
Cold Water Flow Rate Heat Capacity Flow Rate of Hot Water Heat Capacity  (7) heat exchanger is well insulated, so the heat transfer from the hot water is equal to that transfer to cold fluid, The heat transfer coefficient at entire surface of the inner tube can be evaluated by the following equation: The overall heat transfer coefficient, U i ,

( )
The friction factor along the test rig can be estimated as the following equation [14].

Uncertainty analysis
The uncertainties of the experimental tests have been evaluated as systematic errors analysis.
The errors were estimated and compared with the maximum errors of parameters and various devices as shown in Table (2).     however, the friction factor also increases [4]. The friction factor due to use the nanofluid is compared with the friction factor when using pure water and the deviation is not more than 4% as shown in Figure ( 21%. The addition of nanoparticles leads to an increase in the value of thermal conductivity and this also leads to an increase in the heat transfer coefficient [14]. concentration. The behavior of Nusselt number is agreed to results of [4] with the maximum deviation equivalent to 17.5%. The reason for the difference in results between research is due to the difference in the shape of the particle, the diameter and the size of the particle, and the accuracy in Readings and volume heat exchanger [16].

Conclusion
This experimental study is included fabrication of double tube heat exchanger and reading