by Hossin Omar, Suliman Alfarawi, Azeldin El-sawi and Mohammed Zeo
Review Article
Flow cross tube banks is an important application of different types of heat exchangers, such as compact heat exchangers, and baffled shell and tube heat exchangers. Baffles are used in shell and tube heat exchangers to allow the flow to become cross the tubes. This ensures the mix and increases the convective heat transfer coefficient. Design models of baffled shell and tube heat exchanger, which ensures the cross flow, relay on convective heat transfer coefficient. Which obtained from empirical correlation available in the literature. This work is a numerical approach to simulate flow cross a single tube and an in-line square tube array to estimate the convective heat transfer coefficient. This approach is an alternative to the experimental approach. In order to calculate the heat transfer coefficient and it’s relation to the Reynolds number for a single tube and for an in-line square tube array, a Computation Fluid Dynamic [CFD] software (ANSYS FLUENT), Which utilizes Reynolds Average Navier Stokes [RANS] method to solve the momentum equation in 3-D, was utilized to conduct the numerical simulations. Each model was simulated at 4 different entry velocities of (10, 15, 20, 25 m/s) for a Reynold’s number ranging between 6000-35000. The turbtulence model used was K-ω sst. The results obtained via the CFD simulations were validated with an empirical correlation for the two models. These results have deviations from the empirical results ranging between 5 to 22%. The numerical simulation and the empirical correlation results have identical trends for the case of a single tube and for the case of in-line square tube array. For further improvement in results validations, further studies should be made.
American Journal of Energy Research. 2021, 9(2), 84-91. DOI: 10.12691/ajer-9-2-2
Pub. Date: October 26, 2021
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by Sahabo Abubakar, Mohammed B. Oumarou, Abubakar M. El Jummah and Alhaji Bukar Abubakar
Original Research
This study presents the design and testing of a waste-to-energy plant by incineration of small scale municipal solid waste to produce steam for electricity production. The average total waste generated within the study area was found to be 55,800kg/day, with an estimated calorific value of 13,958kJ/kg. The waste samples were collected, dried, shredded and weighed in order to reduce the moisture content to the acceptable minimum and decreases the surface area of the sample that will allow easier penetration of heat. The incinerator was designed using CATIA-5 software. The key performance indices of the developed plant are maximum furnace temperature, residence time, mass flow rate, steam pressures and amount of steam generated keeping the mass of waste constant per test but varying the air flow. The moving grate is inclined at an angle of 12° while the volume of the incineration combustion chamber was calculated to be 0.267m3. 150kg of small scale waste was fed into the combustion chamber of the incinerator to produce heat in order to fire the boiler filled to 70 litre capacity level. Tests were carried out with natural air flow and forced air supplied through the primary air nozzles at an air velocity of 6.2m/s. The obtained temperature/pressure results were: 464°C/5 bar and 528°C/7 bar and 542°C/7 bar for tests 1, 2 and 3 respectively. The steam produced in the boiler was able to run a steam turbine used to generate electricity. Preliminary results showed that such a plant could be used to complement the power supplied to the University as a set of 36 - 12V DC bulbs were powered for 15 minutes.
American Journal of Energy Research. 2021, 9(2), 75-83. DOI: 10.12691/ajer-9-2-1
Pub. Date: September 22, 2021
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