MINICHANNEL DEVICES FOR LOW CHARGE REFRIGERATING SYSTEMS

Transcription

1 Webinar Dec 10, 2012 MINICHANNEL DEVICES FOR LOW CHARGE REFRIGERATING SYSTEMS Università degli Studi di Padova Dipartimento di Ingegneria Industriale

2 Why minichannel technology? - The refrigerant charge minimization can be considered one of the most important targets for HVAC&R applications to cope with the new environmental challenges. - Minichannel technology appears to be a very good opportunity to minimize the charge without energy performance loss. - Instead, minichannel technology can help reducing greenhouse gas emissions by improving component and system energy efficiencies.

3 Specific charge for systems using HCs and NH 3 Capacity [kw] Refrigerant Specific charge [g/kw] Cavallini et al. (2010) 100 Propane Fernando et al. (2004) 5 Propane 37 Hrnjak and Litch (2008) 13 Ammonia 20 Corberan (2008) 14 Propane Park and Jung (2009) 3.8 (H) 3.5 (C) R170/R (H) 142 (C) (H): Heating (C): Cooling

4 Specific charge: potential charge reduction Specific charge in the condenser [g/kw] Specific charge in the evaporator [g/kw] Ammonia (R717) Propane (R290) Carbon dioxide (R744) R R134a R410A (Padilla Fuentes Y., Hrnjak P., 2012, Charge reduction potentials of several refrigerants, Int. Refr. Conf. at Purdue, July 16-19; Padilla Fuentes Y., Hrnjak P., 2012, Experimentally validated microchannel heat exchanger performance, 10 th IIR G-L Conf. on Natural Refrigerants, Delft.)

5 Heat exchangers data (KTH) Propane heat pump developed at KTH of Stockholm References: Fernando et al. (2004) 37 g/kw of R290 Heating capacity kw Hydraulic diameter 1.42 mm Number of channels 6 Tube length 651 mm Baffle plates 31 Refrigerant R290 Evaporator Condenser Number of tube Outer area m m 2 Fernando P., Palm B., Lundqvist P., Granryd E., 2004, Propane heat pump with low refrigerant charge: design and laboratory tests, Int. J. of Refrig., 27,

6 Tube sheet of minichannel HX University of Padova

7 Condenser internal volume BPHE 80 plates 8.4 L MINICHANNEL S&T 2 mm i.d. tubes 2.9 L Volume reduction = -65% Charge reduction = -0.8 kg

8 Propane charge Piping length not minimized (around 1 kg of R290) ~0.5 kg of R290 in the liquid receiver ~0.4 kg of R290 in the dehydrating filter Evaporator PHE PHE PHE PHE Condenser PHE MC PHE MC IHX no no yes yes Measured charge ~3.9 kg ~ 3.1 kg ~ 5.1kg ~ 4.3 kg Target charge ~ 3.1 kg ~ 2.3 kg ~ 3.5kg ~ 2.7 kg TARGET CHARGE: 0.5m liquid line, no receiver, with filter

9 Square vs. circular channel SQUARE CIRCULAR

10 Square cross section minichannel (1.18 mm side length) Enlarged picture taken with a micro-endoscope

11 HTC [W m -2 K -1 ] Tsat-Twall [K] Condensation HTC: square vs. circular HEAT TRANSFER COEFFICIENT [W/(m 2 K)] G200 G200 G200 t G200 t T SAT - T WALL [K] VAPOUR QUALITY [/] 0 G = 200 kg/(m 2 s)

12 Liquid-vapour interface during condensation G100 zero-gravity x=0.8 G100 normal gravity x=0.8 G100 zero-gravity x=0.6 G100 normal gravity x=0.6 x = 0.8 G = 100 kg m -2 s -1 x = 0.6 G = 100 kg m -2 s -1

13 HTC [W m -2 K -1 ] Condensation HTC: square vs. circular G790 SQUARE G400 SQUARE xin= G800 CIRCULAR 8000 G400 SQUARE xin=0.68 G400 CIRCULAR G = 800 kg/(m 2 s) 2000 G = 400 kg/(m 2 s) VAPOUR QUALITY [/] VAPOUR QUALITY [/]

14 Thank you for your attention! Università degli Studi di Padova Dipartimento di Ingegneria Industriale