## 3 Heat Transfer Enhancement
### Experimental Results  
Experimental investigations of forced convective heat transfer of \(Al_{2}O_{3}\)/EG and \(CuO\)/EG nanofluids flowing through double pipe and plate heat exchangers under turbulent flow conditions were conducted by [PERSON] et al. [23]. The results indicated a considerable enhancement in the heat transfer performance with nanofluids compared to pure EG for both heat exchangers and all the operating conditions. For example, in the double pipe heat exchanger, adding 1 vol.% of \(Al_{2}O_{3}\) and \(CuO\) nanoparticles to EG increased the effective heat transfer by about 26% and 37% compared to the base fluid, respectively. They attributed this enhancement to the fact that the chaotic motion of the nanoparticles could accelerate the energy exchange process between the fluid and the wall. [PERSON] et al. [22] studied experimentally the evaluation of the cogeneration and heat exchanger efficiency of a diesel electric generation (DEG) device involving nanofluids. The thermal properties of nanofluids consisting of aluminium oxide nanoparticles dispersed in a 50:50 EG/W mixture were studied for temperatures within the range [25; 26; 270 \({}^{\circ}\)C]. They reported that the nanofluid specific heat decreased by increasing the nanoparticle volume fraction, which means that for higher concentrations of alumina nanoparticles, less heat input was required to increase the temperature of the nanofluid or at the same heat input. They affirmed that by reducing the time required to heat, employing the nanofluid as a jacket water would be very beneficial in the automobile industry especially in Arctic or subarctic regions. They assessed the effect of nanofluids on the cogeneration efficiency, which is defined by the sum of the electrical power reduced and the rate of heat-recovered divided by the energy rate associated with the fuel input to the generator. The results showed that the diesel engine cogeneration efficiency decreased by increasing the \(Al_{2}O_{3}\) nanoparticle concentration. For example, the cogeneration efficiency of the pure EG/W mixture slightly dropped from 79.1% to 76.11% by adding 6 vol.% of \(Al_{2}O_{3}\) nanoparticles. They also examined the effect of the nanoparticles on the efficiency of the heat exchanger connected to the diesel engine. They observed that as the nanoparticle concentration increased, the heat exchanger efficiency was enhanced because of the higher heat transfer coefficient with the nanofluid compared to the base fluid case. For instance, dispersing 6 vol.% of \(Al_{2}O_{3}\) nanoparticles into the EG/W mixture improved the heat exchanger efficiency by up to 81.11% compared to an enhancement of 78.1% for EG/W only. [PERSON] et al. [15] investigated experimentally the influence of using \(CuO\) in a 50:50 EG/W mixture as a coolant on the heat transfer performance of a car radiator over a temperature range between 35 and 54 \({}^{\circ}\)C. The results showed a significant enhancement in the heat transfer rate by adding \(CuO\) nanoparticles to the base fluid. They noted that the overall heat transfer increased when the Reynolds number was increased, as well as the nanoparticle volume concentration. The highest Nusselt number enhancement was found to be about 55% at \(\varphi=0.8\%\) compared to EG/W. An experimental test rig has been recently designed by [PERSON] et al. [17] to evaluate the heat transfer performance of a Perodua Kelisa 1000 cc radiator system (Figure 6a) operating with nanofluids containing multi-walled carbon nanotubes dispersed into a 50:50 EG/W in the laminar flow regime. The results revealed that the thermal performance of the car radiator was improved by adding MWCNTs to the EG/W solution (Figure 6b). As expected, \(h\) is an increasing function of the Reynolds number. The heat transfer coefficient enhancement was found to be 26.8%, 135.3%, and 196.3% for \(\varphi=0.1\), 0.25, and 0.5 vol.% compared to the base fluid, respectively. [PERSON] et al.