Convective Heat Transfer and Pumping Power Analysis of MWCNT + Fe3O4/Water Hybrid Nanofluid in a Helical Coiled Heat Exchanger with Orthogonal Rib Turbulators

Utilizing nanofluids in heat exchangers can lead to improved thermal performance. Nanofluids with suspended carbon nanotubes are specifically desirable in thermal systems because of their unique capabilities. In this study, convective heat transfer and required pumping power are studied simultaneously for a helical coiled heat exchanger with laminar water flow while incorporating 0.1 and 0.3 percent volume fraction of the hybrid nanofluid MWCNT + Fe3O4/water. Two different geometries of bare and ribbed tubes are used for the heat exchanger part. The ribs are chosen to be orthogonal, i.e., 90° with respect to the inclined ones. Three different Reynolds numbers are selected for investigation, all in laminar flow regime based on the non-dimensional M number defined in coiled tubes. Computational fluid dynamics is used to study thermal and fluid behavior of the problem. The convective heat transfer coefficient can serve as a criterion to measure the effectiveness of utilizing nanofluids in heat exchangers by taking the pressure drop and pumping power of the system into consideration. Finally, the artificial neural network curve fitting tool of MATLAB is used to make a good fit in the data range of the problem. It is shown that for most cases of the study, the pumping power ratio is less than 1 that can be considered appropriate from energy consumption viewpoint.publishedVersio

Thermo-economic analysis of transcritical CO2 cycles with bounded and unbounded reheats in low-temperature heat recovery applications

Performance of transcritical CO2 Rankine cycles with and without reheat process is investigated thermo-economically in low-grade waste heat recovery applications. Two reheating scenarios are proposed to evaluate the effect of bounded and unbounded reheats on the cycle. In the first method, the constant available heat flow is distributed between the evaporator and the reheater via an optimized ratio, while in the second, the required energy for the reheat process is provided with optimized additional fuel consumption. The proposed cycles are modeled and optimized for source temperatures ranging from 150 to 300 degrees C at fixed flow rate of 1000 kg/s. The results obtained from thermodynamic optimization indicate that reheat cycle with burning additional fuel leads to the largest power generations ranging from 14 to 57 MW depending on the source temperature, while the reheat cycle with heat stream division shows the weakest performance by producing 8-37 MW. In the thermo-economic optimization, the ratio of power output to the cycle total bare module cost has been maximized. Under these conditions, the reheat cycle with burners still shows the highest rate of power production, while economic indicators limit the power generation and introduce the simple Rankine cycle as the best option. (C) 2017 Elsevier Ltd. All rights reserved

Experimental study of a laminar premixed LFG/air flame in a slot burner using Mach-Zehnder interferometry

An experimental study was conducted to investigate the influence of Reynolds number and equivalence ratio on flame temperature field and thermal flame height of laminar premixed LFG fuel. Mach-Zehnder interferometry technique is used to obtain an insight to the overall temperature field. The slot burner with large aspect ratio (L/W), length of L=60 mm and width of W=6 mm was used to eliminate the three- dimensional effect of temperature field. Two kinds of mixed fuels, LFG70 (70%CH4- 30%CO2 on volume basis) and LFG50 (50%CH4- 50%CO2) were used to investigate flame characteristics under the test conditions of 100 ≤ Re ≤ 600 and 0.7 ≤ φ ≤ 1.3. The present measurement reveals that the variation of maximum flame temperature with increment of Reynolds number is mainly due to heat transfer effects and is negligible. On the other hand, the equivalence ratio and fuel composition have a noticeable effect on flame temperature. In addition, the results show that the LFG flames compared to the CH4 ones have a lower flame temperature. With increment of CO2 volume fraction at lean combustion, thermal flame height is augmented while at stoichiometric and rich combustion, its value reduced. Thermal flame height augments linearly by Reynolds number increase, while its increment at rich mixture is higher and the effect of Reynolds number at lean mixtures is insignificant. For validation of experimental results from Mach-Zehnder Interferometry, K-type thermocouples are used at peripherally low and moderate isotherm lines

Numerical Investigation on Slot air Jet impingement Heat Transfer between Horizontal Concentric Circular Cylinders

Numerical study has been carried out for slot air jet impingement cooling of horizontal concentric circular cylinders. The slot air jet is situated at the symmetry line of a horizontal cylinder along the gravity vector and impinges to the bottom of the outer cylinder which is designated as θ=0°. The outer cylinder is partially opened at the top with width of W=30mm and is kept at constant temperature T= 62°C. Inner cylinder which is a part of the slot jet structure is chosen to be insulated. The effects of jet Reynolds number in the range of 100≤ Rej ≤1000 and the ratio of spacing between nozzle and outer cylinder surface to the jet width for H=4.2 and H=12.5 on the local and average Nusselt numbers are examined. In the numerical study, FLUENT CFD package is used and validated by comparing the results with the experimental data at the same Reynolds number. It is observed that the maximum Nusselt number occurs at the stagnation point at (θ=0°) and the local heat transfer coefficient decrease on the circumference of the cylinder with increase of θ as a result of thermal boundary layer thickness growth. Also results show that the local and average heat transfer coefficients are raised by increasing the jet Reynolds number and by decreasing the nozzle-to-surface spacing

On-farm Energy Use (Case of Dire County, Kermanshah Province)

This paper focuses on the amount of diesel consumption as one of the non-renewable energy sources consumed by the agricultural machinery and water pumps in wheat and corn farms in Dire County, Kermanshah Province, Iran. The population of the study was determined by Bartlett et al . (2001) ’stable. Stratified random sampling method and census was used for the selection of respondents. The sample was composed of 247 wheat growers, 235 corn growers, and 57 tractor drivers selected by Bartlett et al .(2001) ’stable. Combine drivers as well as farm irrigation diesel owners were selected by census (n=15, n=48, respectively). The data collection tool was a questionnaire and the data were analyzed by SPSS software package. The findings revealed that in wheat farms, soil preparation had the highest consumption of diesel by 49% and in corn farms inter culturing had the highest diesel consumption by 38%. Moreover, the amount of diesel consumed in 3600 ha wheat and a corn farm in Dire County was 403,852.6 lit/year equivalent to 15,346,399 MJ. Burning this amount of diesel produces about 1, 058,094 kg CO 2 /year. Overall, farm machinery, water pumping and irrigation for two major crops in the county are extremely reliant on nonrenewable fossil fuel resulting in large amount of CO 2 emission. Hence, an aggressive and innovative policy is required to restructure and redesign energy system in agriculture sector at national and local levels. Finally, it seems that paradigm shift to sustainable agriculture and development of clean and renewable energy in Iran's agricultural sector is unavoidable

Experimental studies on the viscosity of Fe nanoparticles dispersed in ethylene glycol and water mixture

In this paper, experimental studies are conducted in order to measure the viscosity of Fe nanoparticles dispersed in various weight concentration (25/75%, 45/55% and 55/45%) of ethylene glycol and water (EG-water) mixture. The experimental measurements are performed at various volume concentrations up to 2% and temperature ranging from 10°C to 60°C. The experimental results disclose that the viscosity of nanofluids increases with increase in Fe particle volume fraction, and decreases with increase in temperature. Maximum enhancement in viscosity of nanofluids is 2.14 times for 55/45% EG-water based nanofluid at 2% volume concentration compared to the base fluid. Moreover, some comparisons between experimental results and theoretical models are drawn. It is also observed that the prior theoretical models do not estimate the viscosity of nanofluid accurately. Finally, a new empirical correlation is proposed to predict the viscosity of nanofluids as a function of volume concentration, temperature, and the viscosity of base fluid