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Heat transfer

  1. 1. The 9th International Chemical Engineering Congress & Exhibition (IChEC 2015) Shiraz, Iran, 26-28 December, 2015 Heat transfer investigation in a plate heat exchanger by using water-based TiO2 nanofluids Meisam Ansarpour, Ahmad Azari* , Hamed Mohammaddoost Department of Chemical Engineering, Faculty of Oil, Gas and Petrochemical Engineering, Persian Gulf University, Bushehr, Iran *Azari.ahmad@pgu.ac.ir Abstract The prior researches showed enhancement by using various nanofluid in comparison with water or another base fluid. In this study, we experimentally investigated the enhancement of the overall heat transfer coefficient in a plate heat exchanger against Reynolds number for water / TiO2 nanofluids. Two different weight fraction of nanofluids were studied. The results clearly explain that 0.5 %wt nanofluids has significant enhancement at higher Reynolds numbers against water. Keywords: Heat transfer, plate heat exchanger, TiO2 nanofluids Introduction Nanofluids are colloidal suspensions of nanoparticles with range size 1-100 nm in a base fluid that can be water, oil or other conventional base fluid. Nanotechnology are widely used in prior studies such as heat transfer, mass transfer, wastewater treatment and etc. [1-3]. Convective heat transfer development has a significant impact on some industry products such as air conditioner, power generator, chemical products etc. that can enhanced by enhancing flow thermal conductivity [4]. So many researchers focus on this process and try to enhance the heat transfer and conductivity coefficient. Choi and Eastman [5] were the first researchers who did experiment on heat transfer of nanofuids and after them many others investigators conduct some experiments on the nanofluids heat transfer. Among the various heat exchangers Plate heat exchangers (PHEs) are one of most useful heat exchangers due to theirs features in the industries and engineering such as high heat transfer efficiency, ease of maintenance, compactness, durability etc. but the results depend on experiment’s condition, flow arrangement, plate configurations etc. [6]. Compactness is a most useful feature for this type of heat exchangers due to make them energy efficient, cost effective and adaptable for industrial applications [7]. This study investigate the effect of TiO2 nanofluids in heat transfer phenomena by using PHE and the enhancement of that in comparison with water will discussed. Experimentation In this study nanofluids were prepared by sonication of 25 nm TiO2 nanoparticles in deionized water for 20 min processes at 40 W and also 75 W power. 0.1 %wt and 0.5 %wt TiO2 nanofluids were prepared in 40 and 75 W processes, respectively. A circulation process contain the heating section, liquids reservoir and plate heat exchanger were used as shown in
  2. 2. The 9th International Chemical Engineering Congress & Exhibition (IChEC 2015) Shiraz, Iran, 26-28 December, 2015 figure (1). We used hepaco PHE (HP-40 model) and nano particles that purchased from Neotrino Nanotechnology Company. The nanofluids pumped from their reservoir to PHE and after that flows to heating section to increase the temperature. In another side of PHE, cooling water flows from cooling section. Counter current flows used in this study. PHE and nanoparticle specifications were listed in tables 1 & 2.   Table 1. Parameters for PHE Table 2. TiO2 specifications    Plate length 0.194 m Plate width 0.08 m Plate height 0.042 m Number of plates 15 Thermal Power 20000 Kcal/h Chemical formula Average particle size Density Thermal Conductivity Specific Heat TiO2 25 nm 0.4 g/cc 6 W/m.K 0.69 KJ/Kg.K Figure 1: schematic diagram of the experimental rig The overall heat transfer coefficient and properties for nanofluids calculate from following equations: U .∆ 1 ∆ , , , , ln , , , , 2 μ 1 2.5∅ μ 3 ρ ∅ρ 1 ∅ ρ 4
  3. 3. The 9th International Chemical Engineering Congress & Exhibition (IChEC 2015) Shiraz, Iran, 26-28 December, 2015 where A is the total heat transfer area, U is overall heat transfer coefficient (W/m2 .K), is viscosity and ρ referes to density. Also Q equals to ( Qcold + Qhot ) / 2 and ∅ is volume fraction for nanofluid. nf, p and f referes to nanofluid, nanoparticle and fluid, respectively. Re ρuD μ 5 Re is Reynolds number and u is velocity (m/s). D (m) is hydraulic diameter that calculate from the following correlation: D 4 ∗ 6 Results and discussion It’s common for prior studies to determine heat transfer coeffient, Nusslet number and pressure drop against velocity or Reynolds number [8, 9]. However, here we calculate overall heat transfer coeffient and the results were shown in figure (2). In this figure U versus Reynolds numbers of 0.1 %wt nanofluids ploted. Reynold’s number has about ±1 difference for water and 0.5 %wt TiO2 nanofluid due to the alteration of density and viscosity by the addition of nanoarticles according to equations (3) & (4) even at the same velocities for each fluid. The results showed enhancement in overall heat transfer coefficient for 0.5 %wt nanofluids at higher Reynolds numbers. However water has higher overall heat transfer coefficient in comparison with 0.1 %wt nanofluid. The results obviously show that at lower Re number the use of nanofluids can decrease the overall heat transfer coefficient and at higher Re number has the higher performance. This may be due to the heat loss from the PHE. Since the heat loss from the PHE is higher at low Re number with respect to the high Re number. Figure 2: Overall heat transfer coefficient versus Re.
  4. 4. The 9th International Chemical Engineering Congress & Exhibition (IChEC 2015) Shiraz, Iran, 26-28 December, 2015 Conclusions TiO2 nanofluids and deionized water used in this paper to determine overall heat transfer coefficient in the plate heat exchanger. The nanofluids are in 0.1 and 0.5 %wt water-based. We expect by addition nanoparticle to water, the overall heat transfer coefficient increases, but for 0.1 %wt nanofluids, we observed decrease against water. After that for 0.5% wt, at higher Reyolds numbers, enhancement observed and for lower that, water has higher total heat transfer coefficient. References [1] Azari, A. and M. Derakhshandeh,"An experimental comparison of convective heat transfer and friction factor of Al2O3 nanofluids in a tube with and without butterfly tube inserts", Journal of the Taiwan Institute of Chemical Engineers., 52, 31-39 (2015). [2] Kim, J.-K., J.Y. Jung, and Y.T. Kang," The effect of nano-particles on the bubble absorption performance in a binary nanofluid", International journal of refrigeration., 29(1), 22-29 (2006). [3] Sharma, Y., et al.," Nano‐adsorbents for the removal of metallic pollutants from water and wastewater", Environmental technology., 30(6), 583-609 (2009). [4] Ding, Y., et al.," Heat transfer of aqueous suspensions of carbon nanotubes (CNT nanofluids)", International Journal of Heat and Mass Transfer., 49(1), 240-250 (2006). [5] Chol, S.," Enhancing thermal conductivity of fluids with nanoparticles", ASME- Publications-Fed., 231, 99-106 (1995). [6] Nilpueng, K. and S. Wongwises," Experimental study of single phase heat transfer and pressure drop inside a plate heat exchanger with a rough surface", Experimental Thermal and Fluid Science., 68, 268-275 (2015). [7] Khan, M.S., et al.," Evaporation heat transfer and pressure drop of ammonia in a mixed configuration chevron plate heat exchanger", International Journal of Refrigeration., 41, 92-102 (2014). [8] Lee, J. and K.-S. Lee," Friction and Colburn factor correlations and shape optimization of chevron-type plate heat exchangers", Applied Thermal Engineering., 89, 62-69 (2015). [9] Huang, D., Z. Wu, and B. Sunden," Pressure drop and convective heat transfer of Al2O3/water and MWCNT/water nanofluids in a chevron plate heat exchanger", International Journal of Heat and Mass Transfer., 89, 620-626 (2015).

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