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Abstract
The design and the performance of an innovative shell-and-tube evaporator using round copper microchannels are presented in this article. This prototype has been designed aiming at the minimization of the refrigerant charge, which can be required by safety or environmental restrictions. Experimental data of heat transfer and pressure drop are reported in the present article. The measurements have been obtained with two different evaporator inlet headers and two different working fluids (i.e., R22 and R410A) to investigate the mutual influence of the design of the distribution system and the refrigerant properties on possible maldistribution issues. A computational procedure implementing different correlations has also been developed and validated against experimental data; this procedure allows the prediction of the performance of the same evaporator with a hydrocarbon, such as propane, and comparison of the prototype to a brazed-plate heat exchanger.
Nomenclature
| Co | = | confinement number = [σ/(g(ρl – ρv))]0.5/d (-) |
| cp | = | specific heat (J kg–1 K–1) |
| d | = | diameter (m) |
| Eo | = | Eötvös number = (ρl – ρv)gD2/σ (-) |
| g | = | gravity acceleration (m s–2) |
| G | = | mass velocity (kg m–2 s–1) |
| h | = | specific enthalpy (J kg–1) |
| hlv | = | latent heat (J kg–1) |
| = | mass flow rate (kg s–1) | |
| p | = | pressure (Pa) |
| pRED | = | reduced pressure (-) |
| q | = | heat flow rate (W) |
| t | = | temperature (°C) |
| V | = | volumetric flow rate (m3 s–1) |
| x | = | vapor quality (-) |
Greeks
| Δp | = | pressure difference (kPa) |
| ρ | = | density (kg m–3) |
| σ | = | surface tension (N m–1) |
Subscripts
| evap | = | evaporator |
| HOM | = | homogeneous |
| in | = | inlet |
| l | = | liquid |
| out | = | outlet |
| ref | = | refrigerant |
| v | = | vapor |
| w | = | water |