Thermal hydraulics
Thermal hydraulics (also called thermohydraulics) is the study of
The common adjectives are "thermohydraulic", "thermal-hydraulic" and "thermalhydraulic".
Thermodynamic analysis
In the thermodynamic analysis, all states defined in the system are assumed to be in thermodynamic equilibrium; each state has mechanical, thermal, and phase equilibrium, and there is no macroscopic change with respect to time. For the analysis of the system, the first law and second law of thermodynamics can be applied.[2]
In
Examples of the cycle include the Carnot cycle, Brayton cycle, and Rankine cycle. Based on the simple cycle, modified or combined cycle also exists.
Thermo-Hydraulic Improvement Parameter (THIP)
Authors (Sahu et al.[6]) observed that Thermo-hydraulic Parameter (THP) is less sensitive towards the Friction Factor Improvement Factor (FFER). The deviation between the terms (fR/fS) and (fR/fS)0.33 has been found 48 % to 64 % for the range of roughness and other parameters with (Re) 2900 – 14,000, which has been used for the present study. Therefore, to evaluate in equal proportions of enhancement in heat transfer (Nu) and friction factor (f) in the thermal systems a new parameter has been proposed and introduced using the present work which is more realistic and it is named as Thermo-hydraulic Improvement Parameter (THIP), and it can be evaluated as the ratio of (NNIF) to (FFIF)[6].
Where (NNIF)=Nusselt Number Improvement Factor and (FFIF)=Friction Factor Improvement Factor
Temperature distribution
For steady-state and static case, the heat equation can be written as
where
Applying boundary conditions gives a solution for the temperature distribution.
Single-phase heat transfer
In single-phase heat transfer,
The most convenient way for characterizing the single-phase heat transfer is based on an empirical approach, where the temperature difference between the wall and bulk flow can be obtained from the
Examples of heat transfer correlations are
Multi-phase heat transfer
Compared with single-phase heat transfer, heat transfer with a phase change is an effective way of heat transfer. It generally has high value of heat transfer coefficient due to the large value of latent heat of phase change followed by induced mixing of the flow. Boiling and condensation heat transfers are concerned with wide range of phenomena.
Pool boiling
Pool boiling is boiling at a stagnant fluid. Its behavior is well characterized by Nukiyama boiling curve,[3] which shows the relation between the amount of surface superheat and applied heat flux on the surface. With the varying degrees of the superheat, the curve is composed of natural convection, onset of nucleate boiling, nucleate boiling, critical heat flux, transition boiling, and film boiling. Each regime has a different mechanism of heat transfer and has different correlation for heat transfer coefficient.
Flow boiling
Flow boiling is boiling at a flowing fluid. Compared with pool boiling, flow boiling heat transfer depends on many factors including flow pressure, mass flow rate, fluid type, upstream condition, wall materials, system geometry, and applied heat flux. Characterization of flow boiling requires comprehensive consideration of operating condition.[4] In 2021 a prototype electric vehicle charging cable using flow boiling was able to remove 24.22 kW of heat, allowing the charging current to reach 2,400 amps, far higher than state of the art charging cables that top out at 520 amps.[5]
Critical Heat Flux
Heat transfer coefficient due to nucleate boiling increases with wall superheat until they reach a certain point. When the applied heat flux exceeds the certain limit, heat transfer capability of the flow decreases or significantly drops. Normally, the critical heat flux corresponds to DNB in PWR and dryout in BWR. The reduced heat transfer coefficient seen in post-DNB or post-dryout is likely to result in damaging of the boiling surface. Understanding of the exact point and triggering mechanism related to critical heat flux is a topic of interest.
Post-CHF Heat transfer
For DNB type of boiling crisis, the flow is characterized by creeping vapor fluid between liquid and the wall. On top of the convective heat transfer, radiation heat transfer contributes to the heat transfer. After the dryout, the flow regime is shifted from an inverted annular to mist flow.
Other phenomena
This section is in prose. is available. (November 2022) |
Other thermal hydraulic phenomena are subject of interest:
- Critical discharge
- Countercurrent flowlimitation
- Condensation
- Flow instability
- Rewetting
See also
References
[6] Mukesh Kumar Sahu, Manjeet Kharub, Mahalingam Murugesan Matheswaran. “Nusselt number and friction factor correlation development for arc‑shape apex upstream artificial roughness in solar air heater.” Environmental Science and Pollution Research. Vol. 26, Pages- 65025–65042, 2022.
- ISSN 2195-3708.
- ^ No, Hee Cheon (1989). 핵기계공학. Seoul: Korean Nuclear Society.
- ISSN 0017-9310.
- )
- ^ Lavars, Nick (2021-11-16). "Liquid-to-vapor-cooled cable beats the heat for 5-minute EV charging". New Atlas. Retrieved 2021-11-16.