Technical Comprehension in the Subject Area of Heat Transfer - Assignment Example

HEAT TRANSFER Introduction Park et al. propose a correlation for the estimation of the Nusselt number in the case of the vibrations-assisted convection emanating from the fins in vertical orientation. Various experimental investigations were carried in various frequencies and amplitudes for the forced vibrations. From the experimental data, the Nusselt number for the different frequencies and amplitude of the forced vibrations were determined; the Nusselt number for the vibrating fin when normalized to the stationary fin is affected by the buoyancy-driven flow velocity and vibration speed ratio. Park et al. proposed a correlation practical velocity of approximately 0-20, while vibration frequencies at 29-59 Hz. Park et al. utilised the auto-power spectrum in the vibrating fins when in the absence of heat supplies were measured via feeding of the random signal into the shaker. The material’s lowest dominant peak frequency for each auto-power spectrum was in the first natural frequency for the fin. The material thermal performance, that is, for the vibrating fins was maximized via transformation the frequency of the forced vibrations into coinciding with the natural frequency, therefore known as the resonant frequency. The experiment utilised different resonant frequencies for the four experimental tests on the fins. The Nusselt number correlation was in good agreement with their experimental or practical data; the data had discrepancies of less than 10%. Their correlation was valid only for frequencies within the range of 29 < f < 59 Hz. Their results indicated good consistency between the experimental and the correlation data when the Rayleigh number was between 20,000 and 8000, and indicated the decrease in normalized Nusselt when the temperature difference is increased. Heris et al. (2014) conducted an experimental study for the investigation the effects emanating from the inclination angle towards the natural convection of nanofluids within a cubic cavity having sides size of approximately 10 cm in length. One of the cubic surfaces for the cavity is maintained in cold temperature while the other side, opposite side, was maintained in hot temperature and the remaining four surfaces were insulated. There existed mixtures of nanoparticles, three different types of the particles were utilised, for example TiO2, CuO, and Al2O3 within the turbine oil (the TO) were utilised as the heat transfer fluids. The experimental heat transfer in the cavity was investigated mainly in the three inclination angles from the horizontal position, for example, 0°, 45° and 90° while the weight fractions of the nanoparticles were approximately 0.2%, 0.5%, and 0.8%. The experimental Nusselt number results were availed for the three varied nanofluids, with their varied angles of inclination, the Rayleigh number, and the weight fraction of the nanoparticles. The experimental results indicated that the turbine oil had the highest Nusselt number at any inclination angle when at the cavity compared with nanofluids. In addition, it was found that at an angle of inclination at 90°, with the weight fraction approximately 0.2%, the application of particles made of TiO2 leads to a maximum Nusselt number, on the other hand, when the weight fraction is approximately 0.8%, the material’s maximum Nusselt number is related to the CuO nanopowders. Titan et al. (2014) conducted an experimental investigations regarding the natural convection heat transfers of the Nanoparticle Enhanced Ionic Liquids (the NEILs) in the rectangular enclosures, that is, of two different sizes in terms of dimensions length x height x width, 50 x 50 x 50 mm while they were heated from below 50 x 50 x 75 mm. The NEILs were manufactured or synthesized via the dispersion different percentage weigth, wt% of 1.0, 2.5, and 0.5 of aluminum oxide (or Al2O3) nanoparticles composed of two varied particle shapes, for instance the whiskers and spherical, into the N-butyl-N-methylpyrrolidinium. The heat transfer that related thermophysical characteristics or properties, for example, viscosity, density, heat capacity, and thermal conductivity of the base of both NEILs and IL were measured and the reported. Their experimental measurement indicated an enhanced thermal conductivity, viscosity, density, and heat capacity for the NEILs when compared to the base IL; the improved increased with the concentration of the nanoparticle. On the other hand, the natural convection heat transfer coefficient indicated deterioration for the NEILs when compared to the base IL, independent of the particles shapes and the aspect ratio for the enclosure, furthermore, the deterioration elevated with an increased nanoparticle concentration. The spherical Al2O3 NEILs show the behaviour of being affected more adversely when compared to the Al2O3 NEILs whiskers. Titan et al. observed the NEILs’ degradation in terms of the heat transfer performance, hence they could not fully explain via the changes of the thermophysical properties; these properties show other factors’ significant played roles in the phenomenon. The thermophysical properties, for example, such as viscosity, density, heat and thermal conductivity capacity were also measured experimentally. The experimental results conclusions were drawn: the thermophysical properties, for all thematerials, increased with the nanoparticles material concentration. The measured NEILs’ effective density correlates very well with the experimental calculated data via the mixing theory. The NEILs’ viscosities are highly temperature dependent, which is usually higher when compared to the base IL. The material enhancement also relied on the shape of the material particles. When looking at the viscosity’s theoretical effective model when under predict the practical measurements; the NEILs’ thermal conductivity is enhanced by approximately 13 to 9% for the 2.5 wt% nanoparticles loading for the whiskers and spherical nanoparticles respectively. The experimentally measured thermal conductivity for the NEILs indicated increased values when compared to Maxwell’s model predictions within the practical or the investigated temperature range. The NEILs’ heat capacity was enhanced by approximately 45% and 62% for the 2.5 wt% nanoparticles loading for whiskers and spherical nanoparticles respectively. The experimental systematic degradation for the natural convection heat transfer for both whiskers and spherical NEILs were obtained using the aspect ratios. The spherical NEILs had slightly lower heat transfer coefficient compared to the whisker NEILs. The experiment’s relative changes of the effective thermophysical properties were not fully responsible towards the degradation of NEILs’ via the natural convection. Furthermore, the material thermophysical properties, clustering of nanoparticles, and particle–fluid interaction also play major role in the degrading the material’s natural convection heat transfer. Question 2 MaxEh= ± [E12 + Ev2 + (-EA)2 + (-)2]1/2 =± 0.0426 E1=±1.54E-3 (-)= ±4.93E-3 EA=±0.014 EV=±0.04 The maximum error for the estimation the heat transfer parameter, Max Eh, can be reduced via the reduction of the error values of EV and EA since they contribute greatly to the maximum error, as compared to the E1 and (-) error values. When Ev=±0.01, then: MaxEh=SQRT ((0.01)^2+(0.00154)^2+(0.014)^2+(0.00493)^2) =±0.0180 (error is significantly reduced) Question 3 Thermal Resistance Rth== Rth =   is the base temperature, while  is the ambient temperature; and q is the heat input.  represents fin efficiency,  is the surface area of the fin, and  is the Nusselt Number. = = h ()  =   =   =  = h ()  =  = Uncertainty   = =2 + 2 2 =  + + +  2 =  + + +  The precision errors, and are calculated as the deviation emanating from the unsteadiness on the observations. Question 4 Show that for ideal gas =1/T. The first equation can also be obtained by, = and the nRT=PV hence V=  = === Question 5 From both equations using their powers; For example n=n for = ; this shows similarity n is always considered be equal to 1/3; this is because with an increased concentration of the nanofluids, the material density, viscosity and thermal conductivity ratios increase with decrease in the thermal expansion coefficient and heat capacity ratios. Question 6 Considering Al2O3 for both cases Figure 1. From journal 3 Nu = 10.2 and Ra=1.1E07 at 0.5% whiskers Figure 2. From journal 1 Ra=5E7 and Nu=54 Journal 1 had increased Ra and Nu when compared to journal 3. Question 7 The normalized Nusselt number, which is the Nusselt number for the vibrating fin divided by the value in stationary mode, is majorly affected by the ratio of the velocity of the buoyancy-driven to the flow vibration speed. The Nusselt number correlation is agreement with their experimental or practical data only for frequencies within the range of 29 < f < 59 Hz. When Rayleigh number is in between 20,000 and 8000, the Nusselt decreases if the temperature difference is increased. Question 8 In journal 3 entailed experimental investigations regarding the natural convection heat transfers of the Nanoparticle Enhanced Ionic Liquids (the NEILs) in the rectangular enclosures, that is, of two different sizes in terms of dimensions length x height x width, 50 x 50 x 50 mm while they were heated from below 50 x 50 x 75 mm. The NEILs were manufactured or synthesized via the dispersion different percentage weigth, wt% of 1.0, 2.5, and 0.5 of aluminum oxide (or Al2O3) nanoparticles composed of two varied particle shapes, i.e the whiskers and spherical, into the N-butyl-N-methylpyrrolidinium. The heat transfer that related thermophysical characteristics or properties, for example, viscosity, density, heat capacity, and thermal conductivity of the base of both NEILs and IL were measured and the reported. In journal 1, the experimental heat transfer in the cavity was investigated mainly in the three inclination angles from the horizontal position, for example, 0°, 45° and 90° while the weight fractions of the nanoparticles were approximately 0.2%, 0.5%, and 0.8%. References Heris, Z., Masoumeh, B.P.O.M. & Somchai, W., 2013. A comparative experimental study on the natural convection heat transfer of different metal oxide nanopowders suspended in turbine oil inside an inclined cavity. International Journal of Heat and Mass Transfer. Park, K., Jin, W.L. & Moon, G.L..H.J.K.D.-K.K., 2013. Nusselt number correlation for vibration-assisted convection from vertically oriented plate fins. International Journal of Heat and Mass Transfer. Titan, C.P. et al., 2014. Experimental investigation of natural convection heat transfer of Al2O3 Nanoparticle Enhanced Ionic Liquids (NEILs). International Journal of Heat and Mass Transfer, p.Elsivier. Read More