• Plate heat exchanger design: a case study for ventilation systems of small residences

    Innovations, Vol. 7 (2019), Issue 2, pg(s) 60-65

    In this study, a plate heat exchanger (PHE) was designed to meet the ventilation requirements in a small dwelling by performing heat recovery. In the Taguchi analysis performed by selecting three-level four effective parameters, L9 orthogonal array was used. In the analysis, the optimal levels of the design variables were determined by using Computational Fluid Dynamics (CFD) results in order to maximize the combined thermal and hydrodynamic effectiveness (CTHE) selected as the performance parameter. The CTHE was defined as the multiply of thermal effectiveness and flow effectiveness of the PHE. The 3-dimesional CFD models of the PHE were designed to include the effects of the local change in the flow cross-section, which will occur at the inlet-outlet of the air flow channels. Thermal and hydrodynamic computation of PHE models were obtained by finite volume software. In Taguchi analysis, design variables and levels that maximize CTHE: sub-channel number-6, channel height-3 mm, average air flow rate-2 m/s and plate material is paper. When the CTHE predicted from Taguchi analysis was compared with that solution of the CFD model generated using the optimized design and operating parameters, the difference was determined to be less than 1%. In addition, in order to calculate the CTHE based on the design variables, a mathematical equation was obtained in a 90% confidence interval.

  • An experimental study for thermal and hydraulic performance of a mini channel shell and tube heat exchanger using low concentration nanofluids prepared with Al2O3 nanomaterials

    Machines. Technologies. Materials., Vol. 13 (2019), Issue 1, pg(s) 29-35

    In this study, tube side thermal and hydraulic performance of a mini channel shell and tube heat exchanger (MC-STHE) designed using Kern method was investigated experimentally for water and α-Al2O3/water nanofluids prepared in two different low volume fractions (0.02% and 0.2%). The average particle diameter of Al2O3 nanomaterial used in the preparation of nanofluids is 50 nm. The copper tubes (L/D=120) with inner diameter of 2 mm and outer diameter of 3 mm and a length of 240 mm were used in the MC-STHE. During the experiments, shell side water flow rate was kept constant at 180 L/h, while the water and nanofluids flow rates on the tube side were changed between 60-600 L/h. The use of nanofluids in the MC-STHE deteriorates tube side convective heat transfer coefficient in the flow rates below 125 L/h, while enhancing convective heat transfer coefficient in the flow rates above 125 L/h, compared to water. The enhancement ratios for convective heat transfer coefficient compared to water were found to be 0.82-1.66 for 0.02% Al2O3/water and 0.9- 1.74 for 0.2% Al2O3/water in the range of 60-600 L/h volume flow rates. However, in the applications in which enhancement of the heat transfer is desired, it was obtained that the increase in pumping power should be taken into consideration depending on the selected nanofluids volume fraction. According to efficiency index in which increase in heat transfer and pressure drop compared to water are evaluated together, it was found that the use of nanofluids was significant in the flow rates above 375 L/h for 0.02% Al2O3/water and in the flow rates above 300 L/h for 0.2% Al2O3/water. The use of mini-channel increased the compactness by decreasing the weight and volume of the heat exchanger, and in addition to this, higher heat transfer coefficients were obtained by using nanofluids instead of water.



    Machines. Technologies. Materials., Vol. 12 (2018), Issue 4, pg(s) 143-148

    This study, considering need of fresh air in the air-conditioning system in a small residence, geometrical dimensions of a flow nozzle and an orifice plate were determined by theoretical equations in the literature. The measurement performances of designed flow meters were compared with numerical method using Computational Fluid Dynamics (CFD). The measured air flow rate is in the range of 80-300 m3/h and Reynolds numbers at the inlet of flow meters are 12,000-46,000. The β ratio of designed flow meters is chosen to be  0.45  in order to avoid excessive increase of pressure drop. Three dimensional numerical models were created to control the accuracy of flow
    meters. The results from numerical solution show that permanent pressure loss in the orifice plate is 2.6 times greater than the flow nozzle. Lower pressure and energy loss occur in the flow nozzle compared to the orifice plate. In a system where continuous measurement for the purpose of velocity control of fans is carried out, it has been found that electric power consumption of the fans will increase by 4.85 W and 12.42 W, respectively, at the flow rates of 150 and 200 m3/h for flow nozzle.