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ABSTRACT
In order to solve the problem of overheating of the engine and cooling system of the vehicle in the plateau low-pressure environment, it is necessary to study air-side thermal-hydraulic performance of the vehicle cooling system heat exchanger under low-pressure environment. In this paper, the experimental study on the louvered fin and flat tube heat exchanger of the vehicle is carried out on the low-pressure wind tunnel test bench. The results show that at a gauge pressure of −44 kPa, the air-side convective heat transfer coefficient is reduced by 33.5%~23.3% compared with 0 kPa; the Colburn j-factor is increased by 36.8% on average; the f factor is increased by 51.2% on average. Based on this, numerical simulations are carried out to study the heat transfer and flow characteristics of louvered fins with different structural parameters under low-pressure environment. The empirical correlations of Colburn j-factor and Friction factor f are fitted by multiple linear regression. In the range of gauge pressure from 0 kPa to −44 kPa, the average deviation of the correlation calculation result of Colburn j-factor is 3.4%, and the average deviation of the correlation calculation result of f factor is 5.5%. The research results can provide a basis for the design of louvered fin heat exchangers utilized in the plateau environment.
Nomenclature
| A1 | = | heat exchange area of the fin, [m2] |
| A2 | = | heat exchange area of the flat tube, [m2] |
| Aa | = | air side heat exchange area, [m2] |
| Aw | = | water side heat exchange area, [m2] |
| cp,a | = | constant-pressure specific heat of air, [J/kg·K] |
| cp,w | = | constant-pressure specific heat of water, [J/kg·K] |
| f | = | Fanning friction factor |
| Fb | = | fin flow length, [mm] |
| Fh | = | fin height, [mm] |
| Fp | = | fin pitch, [mm] |
| Ft | = | fin thick, [mm] |
| ha | = | the heat transfer coefficient of the air-side, [W/m2·K] |
| hw | = | the heat transfer coefficient of the water side, [W/m2·K] |
| j | = | Colburn j-factor |
| k | = | heat transfer coefficient, [W/m2·K] |
| Lα | = | louvered angle, [°] |
| Ld | = | length of the fin, [mm] |
| Lh | = | louvered height, [mm] |
| Lp | = | louvered pitch, [mm] |
| ma | = | mass flow rate of air, [kg/s] |
| mw | = | mass flow rate of water, [kg/s] |
| Nu | = | Nusselt number |
| P | = | the ambient pressure, [kPa] |
| P0 | = | the standard atmospheric pressure, [kPa] |
| Qw | = | the heat capacity of the air-side, [W] |
| Qa | = | the heat capacity of the water side, [W] |
| Re | = | Reynolds number |
| Rj | = | the contact thermal resistance, [m2·K/W] |
| Rs | = | fouling thermal resistance, [m2·K/W] |
| Rw | = | the thermal conductivity resistance of the finned tube, [m2·K/W] |
| S1 | = | the non-louvered inlet and exit length |
| S2 | = | redirection length |
| Va | = | velocity of air, [m/s] |
| ηa | = | the total efficiency of rib surface |
| ηf | = | the fin efficiency |
| θ | = | the field synergy angle, [°] |
| θi | = | the field synergy angle of a single node, [°] |
| θm | = | the mean field synergy angle of the computational domain, [°] |
| λ | = | thermal conductivity, [W/m·K] |
| λf | = | thermal conductivity of the fin, [W/m·K] |
| ρ | = | density of air, [kg/m3] |
| ν | = | kinematic viscosity of air, [m2/s] |