Jacobs_CFD_Fermi_MI65_VaporDispersionStudy_ExhaustSystemSubModel_2022.02.07_excerpt.pdf
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- Attached to
- A/E MI65 Stack Modifications Federal contract opportunity
- Solicitation number
- ISD-351745-SCM
About this file
This document outlines a federal contract opportunity for architectural and engineering services related to modifications for an exhaust stack and condensate storage system at the Fermi National Accelerator Laboratory. The scope of work includes final design and construction documents utilizing previous study results for a ground mounted exhaust system with fan, heater and stack; control strategies; transformer design and placement; an integrated 15,000 gallon condensate storage system; and a separate building enclosure to house the storage system. All design work must adhere to the laboratory's radiological work requirements. The solicitation number is ISD-351745-SCM and responses are due based on the schedule in the solicitation document. The contracting agency is the Department of Energy Fermi National Accelerator Laboratory.
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| Att1 RFP Appendix Detailed Scope description 2024Jan17.pdf | ||
| Jacobs_Fermi_MI-65_ExhaustStackDesignReport_30pct_2021.11.15.pdf | ||
| Jacobs_CFD_Fermi_MI-65_VaporDispersionStudy_2021-12-07.pdf | ||
| AE MI65 Stack Modifications RFP.pdf | ||
| General Terms and Conditions for Services (05.2023).pdf |
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Text version
FDZE7302 Fermi MI-65 Exhaust Stack Design PRELIMINARY 07 February 2022 9
Duct Flow Mixing Study: Methodology and Assumptions
Jacobs proposes that the evaporator exhaust discharge be combined with a constant volume (30,000 cfm) of pre-heated ambient air prior to exiting the stack to enhance the evaporation effect. As this mixing action occurs in the mixing chamber and exhaust stack, potential condensation/evaporation would be contained inside the duct. The proposed design affords greater amounts of moisture uptake than allowed by the current design due to the dilution air volume and pre-heating.
Success of this solution depends on two main factors:
1. Adequate and effective mixing of the two air streams prior to discharge to the atmosphere
2. Pre-heating the supplied outside air to promote evaporation prior to discharge.
This study analyzes the vendor-proposed design including a mixing chamber illustrated to the right where mixing of the pre-conditioned and evaporator airflows mix prior to discharge via a strobic exhaust fan. The strobic exhaust fan includes an additional airflow supply of 12,500 cfm of unconditioned ambient air downstream of the mixing chamber and upstream of the atmospheric discharge. The design is tested for the three ambient meteorological scenarios (warm/humid, moderate, and cold/dry) outlined in this report using computational fluid dynamics (CFD).
This analysis provides a comparison of the effects of increasing per-conditioning heating of the outside air supply into the mixing chamber as well as the effects of the strobic fan additionally entrained air flow of 12,500 cfm of unconditioned outside air. Performance is gauged by the average droplet diameter upon release into the atmosphere.
Inlet from pre-heater
30,000 cfm (conditioned based upon modeled scenario)
Inlet from evaporator
(single unit operational)
• 375 cfm
• 122 ˚F
• 100% relative humidity
• 20 micron droplet diameter
Strobic fan
Entrained air inlet
(strobic feature)
12,500 cfm
(unconditioned)
Stack outlet
42,500 cfm
9’
8.3’
8’
26.7’
8.3’
FDZE7302 Fermi MI-65 Exhaust Stack Design PRELIMINARY 07 February 2022 10
Duct Flow Mixing Study: Evaporation effect scenarios at warm/humid condition
Results of this sensitivity analysis suggest that the evaporation effect in the exhaust stack and mixing chamber are driven primarily by the amount of heat added by the pre-heat system. At the warm/humid condition, +50 degF of pre-heat was required to each full evaporation of the droplets.
Several scenarios considering the pre-heat air temperature and the strobic entrainment airflow rate were studied in order to arrive at this conclusion. Each modeled scenario presented below uses the warm and humid (74 ˚F and 90% relative humidity) case for relative comparison of each of the effects.
No Pre-Heating of Outside Air +25˚F Pre-Heat
+25˚F Pre-Heat
No Entrained from Strobic Fan +50˚F Pre-Heat
+25 ˚F+25 ˚F+0 ˚F +50 ˚F
0 micron
Average particle diameter at outlet
2.5 micron
Average particle diameter at outlet
7.3 micron
Average particle diameter at outlet
17 micron
Average particle diameter at outlet
Additional analysis was performed to determine the effects of the strobic-fan entrained air of
12,500 cfm downstream of the mixing box. When comparing the +25 ˚F pre-heating of the outside air scenario, this additionally entrained air flow hinders the evaporation of the droplet. This is likely due to the strobic fan-entrained air being unconditioned and therefore lowers the bulk airflow temperature and thus hindering the temperature driven evaporation of the droplets.
D ro p le t D ia m e te r (m ic ro n s)
20 µm
Supplied at evaporator
10 µm
0 µm
FDZE7302 Fermi MI-65 Exhaust Stack Design PRELIMINARY 07 February 2022 11
Duct Flow Mixing Study: Evaporation effect at moderate ambient condition
Conclusions derived regarding pre-heat capacity for the warm/humid condition were carried forward for analysis of the moderate ambient condition. Results for this condition suggested that the +50 ˚F pre-heat capacity should be sufficient to achieve full evaporation at the moderate ambient condition.
Illustrated below are the results for +50 ˚F of pre-heating the outside air prior to the mixing chamber.
The last droplet in the path of the exhaust stack shown below very nearly reaches the exit. This result suggests that this moderate ambient temperature of 54 degF may be a lower limit for annual operation if pre-heat capacity is limited to +50 degF. At this temperature pre-heated air enters the mixing chamber at 104 degF which is approximately 18-20 degF less than the evaporator stream temperature.
The evaporation effect of the mixing chamber may be compromised if the differential between pre-heat and evaporator streams is greater than this value.
0.0 micron
Average particle diameter at outlet
+50 ˚F
+50˚F Pre-Heat
D ro p le t D ia m e te r (m ic ro n s)
20 µm
Supplied at evaporator
10 µm
0 µm
FDZE7302 Fermi MI-65 Exhaust Stack Design PRELIMINARY 07 February 2022 12
Duct Flow Mixing Study: Evaporation effect scenarios at cold/dry ambient condition
As described on the previous page, the moderate ambient condition of 54 degF may be a lower limit of allowable operation for the system to produce full evaporation if the pre-heat capacity is limited to +50 degF. For this cold/dry ambient condition of -2 degF, the pre-heat air stream is only at 48 degF when this amount of heating is applied. Results for this condition suggest that full evaporation may not be achieved at the cold\dry ambient condition.
As illustrated below, the evaporation effect associated with pre-heat level of +
50 degF reduces droplet diameter to approximately 5.6 micron. Results suggest that pre-heat up to +70 ˚F may be required for full droplet evaporation.
However, the design does not allow for this level of pre-heat capacity because it cannot be supported by the existing electrical system.
5.6 micron
Average particle diameter at outlet
0.0 micron
Average particle diameter at outlet
+70 ˚F+50 ˚F
+70˚F Pre-Heat*+50˚F Pre-Heat
D ro p le t D ia m e te r (m ic ro n s)
20 µm
Supplied at evaporator
10 µm
0 µm
* Note: This level of pre-heat cannot be supported by the existing electrical system.
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