![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
The main objective of this work is to present a new modeling approach of thermal performance and design of partially dry–wet cooling coils working under unit or nonunit Lewis number conditions. The innovative model is presented as a new simplified and practical correlation that interrelates the cooling coil effectiveness (ε) with its number of transfer unit, and vice versa. The simplified model was constructed on a basis of solving the heat and mass transfer equation “enthalpy potential method” simultaneously coupled with the thermodynamics equations. The validity of the new correlations was tested through predictions of its thermal performance. The output results of those correlations show satisfactory agreement with those obtained from the referenced data with deviation of less than 10%. The main feature of this novel correlation is its simplicity and easiness in calculation by knowing input Lewis number and some other key parameters. Also, the main benefit of this new model is to provide helpful guidelines for optimization of fully wet or partially dry–wet cooling coils’ performance and developing suitable control strategies to achieve higher thermal behavior of the cooling coil during its operation.
Nomenclature
| A | = | surface area of the cooling coil, m2 |
| Ad | = | surface area of the cooling coil at the end of the dry section, m2 |
| Ai | = | inner surface area of the cooling coil, m2 |
| Ao | = | outer surface area of the cooling coil, m2 |
| b | = | slope of saturation air enthalpy line or fictitious specific heat, kJ/kg K |
| Cpa | = | air specific heat, kJ/kg K |
| Cpw | = | water specific heat, kJ/kg. K |
| Cpraw | = | ratio of specific heat of air and water |
| Cro | = | ratio of fictitious specific heat and water specific heat |
| dbt | = | air dry-bulb temperature,°C |
| dv | = | control volume |
| h | = | specific air enthalpy, kJ/kg |
| ha | = | specific air enthalpy, kJ/kg |
| hs | = | specific saturated air enthalpy, kJ/kg |
| Le | = | Lewis number |
| m | = | mass flow rate, kg/s |
| mraw | = | ratio between mass flow rate of air and water |
| NTU | = | number of transfer unit based on the total surface area |
| NTUd | = | number of transfer unit based on the dry-section surface area |
| Q | = | heat transfer, W |
| SHF | = | sensible heat factor or ratio |
| T | = | temperature,°C |
| Ta | = | air temperature,°C |
| Tw | = | chilled water temperature,°C |
| Ts | = | surface temperature,°C |
| wbt | = | air wet-bulb temperature,°C |
| ε | = | effectiveness |
| α | = | heat transfer coefficient, W/m2 C |
| ηs | = | area-weighted surface fin efficiency |
| Subscripts | = | |
| a | = | air or ambient |
| ai | = | inlet air |
| ad | = | outlet air at the dry section |
| ao | = | outlet air |
| am | = | mean value for air |
| ad | = | air properties at the end of dry section |
| d | = | dry |
| eq | = | equivalent |
| i | = | inner or inlet |
| in | = | inlet |
| J | = | arbitrary control volume |
| m | = | mean |
| o | = | outer or outside |
| out | = | outside |
| s | = | saturated |
| sm | = | mean value for surface |
| swin | = | surface condition at inlet water temperature |
| swd | = | surface condition at water temperature at the end of the dry-section |
| swout | = | surface condition at outlet water temperature |
| w | = | wet or water |
| win | = | inlet water |
| wbti | = | air wet-bulb temperature at the cooling coil inlet |
| wbtd | = | air wet-bulb temperature at the dry-section exit |
| wd | = | outlet water at the dry-section exit |
| wout | = | outlet water at the cooling coil exit |
| wm | = | mean value for chilled water |
Nomenclature
| A | = | surface area of the cooling coil, m2 |
| Ad | = | surface area of the cooling coil at the end of the dry section, m2 |
| Ai | = | inner surface area of the cooling coil, m2 |
| Ao | = | outer surface area of the cooling coil, m2 |
| b | = | slope of saturation air enthalpy line or fictitious specific heat, kJ/kg K |
| Cpa | = | air specific heat, kJ/kg K |
| Cpw | = | water specific heat, kJ/kg. K |
| Cpraw | = | ratio of specific heat of air and water |
| Cro | = | ratio of fictitious specific heat and water specific heat |
| dbt | = | air dry-bulb temperature,°C |
| dv | = | control volume |
| h | = | specific air enthalpy, kJ/kg |
| ha | = | specific air enthalpy, kJ/kg |
| hs | = | specific saturated air enthalpy, kJ/kg |
| Le | = | Lewis number |
| m | = | mass flow rate, kg/s |
| mraw | = | ratio between mass flow rate of air and water |
| NTU | = | number of transfer unit based on the total surface area |
| NTUd | = | number of transfer unit based on the dry-section surface area |
| Q | = | heat transfer, W |
| SHF | = | sensible heat factor or ratio |
| T | = | temperature,°C |
| Ta | = | air temperature,°C |
| Tw | = | chilled water temperature,°C |
| Ts | = | surface temperature,°C |
| wbt | = | air wet-bulb temperature,°C |
| ε | = | effectiveness |
| α | = | heat transfer coefficient, W/m2 C |
| ηs | = | area-weighted surface fin efficiency |
| Subscripts | = | |
| a | = | air or ambient |
| ai | = | inlet air |
| ad | = | outlet air at the dry section |
| ao | = | outlet air |
| am | = | mean value for air |
| ad | = | air properties at the end of dry section |
| d | = | dry |
| eq | = | equivalent |
| i | = | inner or inlet |
| in | = | inlet |
| J | = | arbitrary control volume |
| m | = | mean |
| o | = | outer or outside |
| out | = | outside |
| s | = | saturated |
| sm | = | mean value for surface |
| swin | = | surface condition at inlet water temperature |
| swd | = | surface condition at water temperature at the end of the dry-section |
| swout | = | surface condition at outlet water temperature |
| w | = | wet or water |
| win | = | inlet water |
| wbti | = | air wet-bulb temperature at the cooling coil inlet |
| wbtd | = | air wet-bulb temperature at the dry-section exit |
| wd | = | outlet water at the dry-section exit |
| wout | = | outlet water at the cooling coil exit |
| wm | = | mean value for chilled water |