On the steady-state modelling of a two-stage evaporator system

2001 ◽  
Vol 25 (10) ◽  
pp. 859-880 ◽  
Author(s):  
M. N. A. Hawlader ◽  
S. K. Chou ◽  
K. J. Chua ◽  
J. C. Ho ◽  
A. S. Mujumdar
Keyword(s):  
Steady State ◽  
Two Stage

MATHEMATICAL MODELING OF EXISTING TWO STAGE ANAEROBIC DIGESTION PROCESS FOR PALM OIL MILL WASTEWATER

2016 ◽  
Vol 78 (10-4) ◽  
Author(s):  
Nattawut Yingthavorn ◽  
Nirattisai Rakmak ◽  
Prawit Kongjan ◽  
Chairat Siripatana
Keyword(s):  
Steady State ◽  
Palm Oil ◽  
Microbial Growth ◽  
Treatment Plant ◽  
Actual Data ◽  
Water Flooding ◽  
Two Stage ◽  
Future Design ◽  
Palm Oil Mill ◽  
Steady State Simulation

This work is an attempt to describe the dynamics of a two-stage industrial biogas plant using palm oil mill effluent (POME) and the mixture of POME with effluent from rubber factory (LTE), both at steady state and transient peroid before system failure accurred. One incident occurred in POME treatment plant when LFE bypassed its digesters and mixed together with palm-oil-mill wastewater due to no space in the existing latex wastewater ponds under water flooding during heavy raining period. The model was developed based on simplified ADM1 incorporating the effects of ALK/VFA and pH on the microbial growth. The model prediction for such scenario was in agreement with the actual data from the incident which occurred during November 2014. The Steady state simulation estimated that Ss reduced from 74,917 to 2856 mg/l at HRT 15 d which agreed well with the actual data. Dynamic simulation after adding LTE predicted that the Ss reduced to 20,300 at HRT 10.71 d which was the correct trend albeit rather imprecise. That was considered satisfactory for future operational purpose. This discrepancy was due to the difficulty in estimating many process parameters. In general the model demonstrates the usefulness of the ADM1 in describing behavior of an anaerobic wastewater treatment system from palm oil mill industry and can be used for the purpose of future design and operating of the existing plants.

Unsteady Effects in the Heat Load Predictions for a Two-Stage Compressor Turbine

2016 ◽  
Author(s):  
Arman Farhanieh ◽  
Christoph Mau ◽  
Mats Annerfeldt ◽  
Hossein Nadali Najafabadi ◽  
Matts Karlsson
Keyword(s):  
Steady State ◽  
Heat Load ◽  
Leading Edge ◽  
Gas Temperature ◽  
Two Stage ◽  
Mixing Effects ◽  
Transient Simulations ◽  
Load Analysis ◽  
High Level ◽  
Unsteady Effects

Heat load analysis play an important role in the estimation of hot gas components’ lifetime. To achieve a high level of accuracy in heat load analysis, predicting the temperature distribution on the vane and blades is one area where further development is needed. Due to strong flow unsteadiness and mixing effects from blade row interactions and cooling injections, accurate heat load predictions have become an engineering challenge. This study uses both steady and time-accurate computational fluid dynamics (CFD) simulations to investigate the unsteady and mixing effects in a two-stage compressor turbine. The commercial code ANSYS CFX-15 is utilized to evaluate the performance of the steady state, mixing plane (MP) method, versus time-accurate, profile transformation (PT) and time transformation (TT) methods. The presence or absence of the rotor-stator cavities from which purge or cooling air is entering the main flowpath can also play an important role in the unsteadiness and mixing properties. Therefore the unsteady effects have been examined for two cases; a simplified model without any cavity and a detailed geometry with all the cavities included. In the simplified case, the cooling has been implemented as local patches. The results are then compared with gas temperature measurements from the real engine tests using thermo-crystals. The measurements include temperature profiles in front of the leading edge of each stator and rotor for both stages. The findings suggest that including cooling cavities may not improve the results in steady state simulations, however their presence in transient simulations can lead to mixing prediction improvements. Moreover, the results indicate that the transient simulations will improve the mixing predictions mainly in the second stage of the turbine. The results also indicate that in transient simulations, number of passages and pitch ratio between the stators of consecutive stages directly affect the results regardless of which transient method is used.

A Low-Order HCCI Model Extended to Capture SI-HCCI Mode Transition Data With Two-Stage Cam Switching

2014 ◽  
Author(s):  
Patrick Gorzelic ◽  
Prasad Shingne ◽  
Jason Martz ◽  
Anna Stefanopoulou ◽  
Jeff Sterniak ◽  
...  
Keyword(s):  
Steady State ◽  
Extreme Conditions ◽  
Mode Transition ◽  
Two Stage ◽  
Model Based Control ◽  
Model Based ◽  
Hcci Combustion ◽  
Transition Strategies ◽  
Mode Transitions ◽  
Low Order

A low-order homogeneous charge compression ignition (HCCI) combustion model to support model-based control development for spark ignition (SI)/HCCI mode transitions is presented. Emphasis is placed on mode transition strategies wherein SI combustion is abruptly switched to recompression HCCI combustion through a change of the cam lift and opening of the throttle, as is often employed in studies utilizing two-stage cam switching devices. The model is parameterized to a steady-state dataset which considers throttled operation and significant air-fuel ratio variation, which are pertinent conditions to two-stage cam switching mode transition strategies. Inspection and simulation of transient SI to HCCI (SI-HCCI) mode transition data shows that the extreme conditions present when switching from SI to HCCI can cause significant prediction error in the combustion performance outputs even with the model’s adequate steady-state fit. When a correction factor related to residual gas temperature is introduced to account for these extreme conditions, it is shown that the model reproduces transient performance output time histories in SI-HCCI mode transition data. The model is thus able to capture steady-state data as well as transient SI-HCCI mode transition data while maintaining a low-order cycle to cycle structure, making it tractable for model-based control of SI-HCCI mode transitions.

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