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ABSTRACT
In order to establish a reliable procedure for estimation of heat transfer coefficient, experiments on plate finned tube heat exchangers have been conducted on five exchangers. Using own and previously published experimental data databank of 969 working regimes, a new correlation was formed. Correlation is based on hydraulic diameter and porous velocity and on the ratio of characteristic surfaces of the finned tube bundle. Statistical parameters of a new correlation for estimation of heat transfer coefficient are very good, and correlation covers a wide range of geometrical and other parameters of heat exchangers that are industrially important.
Nomenclature
| cpA, | = | specific heat capacities of air, J/(kg·K) |
| cpW, | = | specific heat capacities of water, J/(kg·K) |
| dc, | = | collar diameter, m |
| dh, | = | hydraulic diameter, m |
| di, | = | tube inner diameter, m |
| do, | = | tube outer diameter, m |
| F, | = | correction factor that involves the flow pattern of both fluids,/ |
| H, | = | height of a heat exchanger channel, m |
| jH, | = | Colburn heat transfer factor |
| k, | = | overall heat transfer coefficient, W/(m2·K) |
| L, | = | length of the heat exchanger, m |
| LMTD, | = | logarithmic mean temperature difference for counter–current heat exchanger, °C |
| mA, | = | mass flow rate of air, kg/s |
| mW, | = | mass flow rate of water, kg/s |
| Nl, | = | number of tube rows |
| Nt, | = | number of tubes per row |
| Nu, | = | Nusselt number |
| Pr, | = | Prandtl number |
| QW, | = | heat duty (heat power, heat capacity) for water, W |
| QA, | = | heat duty for air, W |
| Qm, | = | mean value of heat duty (i.e. measured heat duty), W |
| Re, | = | Reynolds number based on hydraulic diameter |
| sf, | = | fin pitch, m |
| SHE, | = | air side heat exchange surface (total outside surface), m2 |
| sl, | = | longitudinal tube pitch, m |
| st, | = | transversal tube pitch, m |
| Suf, | = | unfinned surface (surface of bare tubes between fins), m2 |
| sV, | = | specific surface, m2/m3 |
| SW, | = | heat transfer surface for water, m2 |
| tAin, | = | inlet temperature of air, °C |
| tAout, | = | outlet temperature of air, °C |
| tWin, | = | inlet temperature of water, °C |
| tWout, | = | outlet temperature of water, °C |
| = | fluid volume flow rate, m3/s | |
| Vf, | = | heat exchanger free volume, m3 |
| VHE, | = | volume of heat exchanger chamber, m3 |
| W, | = | width of a heat exchanger channel, m |
| wf, | = | air velocity at the front of the heat exchanger, m/s |
| wε, | = | air velocity reduced to the porous cross–section of the exchanger, m/s |
| z, | = | number of experimental regimes (runs) |
Greek
| αA, | = | heat transfer coefficient for air, W/(m2·K) |
| αW, | = | heat transfer coefficients for water, W/(m2·K) |
| δ, | = | fin thickness, m |
| ∆St, | = | unsteadiness,/ |
| ∆tm, | = | corrected mean temperature difference, °C |
| ε, | = | volumetric porosity, m3/m3 |
| η, | = | efficiency of heat transfer surface,/ |
| λA, | = | thermal conductivity of air, W/(m·K) |
| λf, | = | thermal conductivity of fin, W/(m·K) |
| λt, | = | thermal conductivity of tube, W/(m·K) |
| μ, | = | dynamic viscosity, Pa∙s |
| ρ, | = | average fluid density, kg/m3 |