experimental prediction of evaporation/boiling heat t
Graduate Category: Engineering and Technology Degree Level: Master Abstract ID# 1423
“EXPERIMENTAL PREDICTION OF EVAPORATION/BOILING HEAT TRANSFER COEFFICENT FOR DESIGN OF LOW PRESSURE EVAPORATOR” ABSTRACT
EXPERIMENTAL SET UP
Electric vehicles (EV’s) are the future of clean transportation. In order to increase the marketability of electric vehicles, drive range should be increased dramatically. Vaporcompression refrigeration system employed in EV’s for climate control consumes a significant fraction of battery power, which in turn reduces the drive range considerably. In this project we have developed an Advanced Thermo-Adsorptive Battery (ATB) system to replace the traditional air conditioning system and enhance the drive range of EV’s by almost 30%. One of the essential components of ATB is the evaporator/condenser unit. The thermal design of which predominantly relies on the accurate prediction of evaporation/boiling heat transfer coefficient. The non-homogeneity in the boiling environment at very low pressures (700 to 800 Pa) makes the boiling process really different from those observed at atmospheric pressures. Furthermore, the standard correlations for predicting the heat transfer coefficient are not available at such low pressures. The objective of this presentation is to determine experimentally the average boiling heat transfer coefficient and minimum superheat required for low pressure boiling using commercially available heat exchanger tubes. Results of the experiments are presented and the thermal performance of different types of finned tube surfaces are examined in a well controlled set-up. These results were utilized for designing the evaporator heat exchanger for the ATB system.
• • • • •
Chamber Pressure: 600 - 800 Pa Refrigerant: Distilled Water Water Saturation Temperature: 3- 6◦ c Coolant: 50% Ethylene Glycol Coolant Flow Rate: 4-8 Lit/Min
• ATB’s reliability strongly depends Evaporator/Condenser unit.
on
the
performance
of
• In order to size the heat exchanger properly accurate prediction of average boiling heat transfer coefficient is necessary. • The lack of an experimental correlation for boiling of water at low absolute pressures (600-800 Pa) and the well-known large uncertainty of the Rohsenow’s correlation prompted the need for experimental determination of the variation of the evaporation/boiling heat transfer coefficient.
• Most EV’s today have a range of approximately 100 miles (160 Km) [1] • 77% of customers have concerns about range limitations in EV’s [2] • Reducing HVAC power demands would increase the viability of EV’s by increasing the drive range significantly. • Utilizes evaporation and adsorption of water to regulate cabin temperature. • Heating and cooling capacity of the system is limited by capacity of adsorbent and reservoir • System regeneration is achieved by applying heat to adsorbent bed and forcing desorption of vapor.
SUMMER MODE
TEST CONDITIONS
RESULTS
INTRODUCTION
Arjun Venkataramanan Carlos Rios Perez Carlos Hidrovo Malcolm Leclair
CONCLUSION • •
•
WINTER MODE •
r
At low pressures, Rohsenow correlation for scored copper tube clearly under predicts the performance of evaporator. Tube 2 with larger surface area than tube 1 performs better as the mode of heat transfer at such low superheats was predominantly evaporation rather than boiling. Large fluctuations in heat flux and superheats observed during experiments suggests the need for an improved experimental set up. More accurate assessment of the evaporator thermal performance requires testing the full scale prototype.
r
REFERENCES ATB
REGENERATION MODE Figure 2 Variation of evaporation/boiling heat flux with respect of the wall superheat. Results in this figure correspond to a TURBO-Chill® (Tube 1) and a S/T Trufin® (Tube 2) from Wolverine Tube, Inc. Results from the Rohsenow correlation for a scored tube surface are also included for comparison. Also, best fitting trend line of the Tube 2 results using a third order polynomial approximation are shown as ‘Average Model’. Last, lowest heat flux values for a superheat between 4 and 7 °C were used to determine the ‘worstcondition scenario’ for evaluation of the heat exchanger thermal performance.
[1] Ashley Steven(2013) Adsorption-based thermal batteries could help boost EV range by 40%. Automotive Engineering Magazine http://articles.sae.org/12376/ [2] Barlett,Jeff (2012) Survey: Consumers express concerns about electric, plug-in hybrid cars. Consumer Reports http://www.consumerreports.org/cro/news/2012/01/surveyconsumers-express-concerns-about-electric-plug-in-hybridcars/index.htm
“EXPERIMENTAL PREDICTION OF EVAPORATION/BOILING HEAT TRANSFER COEFFICENT FOR DESIGN OF LOW PRESSURE EVAPORATOR” ABSTRACT
EXPERIMENTAL SET UP
Electric vehicles (EV’s) are the future of clean transportation. In order to increase the marketability of electric vehicles, drive range should be increased dramatically. Vaporcompression refrigeration system employed in EV’s for climate control consumes a significant fraction of battery power, which in turn reduces the drive range considerably. In this project we have developed an Advanced Thermo-Adsorptive Battery (ATB) system to replace the traditional air conditioning system and enhance the drive range of EV’s by almost 30%. One of the essential components of ATB is the evaporator/condenser unit. The thermal design of which predominantly relies on the accurate prediction of evaporation/boiling heat transfer coefficient. The non-homogeneity in the boiling environment at very low pressures (700 to 800 Pa) makes the boiling process really different from those observed at atmospheric pressures. Furthermore, the standard correlations for predicting the heat transfer coefficient are not available at such low pressures. The objective of this presentation is to determine experimentally the average boiling heat transfer coefficient and minimum superheat required for low pressure boiling using commercially available heat exchanger tubes. Results of the experiments are presented and the thermal performance of different types of finned tube surfaces are examined in a well controlled set-up. These results were utilized for designing the evaporator heat exchanger for the ATB system.
• • • • •
Chamber Pressure: 600 - 800 Pa Refrigerant: Distilled Water Water Saturation Temperature: 3- 6◦ c Coolant: 50% Ethylene Glycol Coolant Flow Rate: 4-8 Lit/Min
• ATB’s reliability strongly depends Evaporator/Condenser unit.
on
the
performance
of
• In order to size the heat exchanger properly accurate prediction of average boiling heat transfer coefficient is necessary. • The lack of an experimental correlation for boiling of water at low absolute pressures (600-800 Pa) and the well-known large uncertainty of the Rohsenow’s correlation prompted the need for experimental determination of the variation of the evaporation/boiling heat transfer coefficient.
• Most EV’s today have a range of approximately 100 miles (160 Km) [1] • 77% of customers have concerns about range limitations in EV’s [2] • Reducing HVAC power demands would increase the viability of EV’s by increasing the drive range significantly. • Utilizes evaporation and adsorption of water to regulate cabin temperature. • Heating and cooling capacity of the system is limited by capacity of adsorbent and reservoir • System regeneration is achieved by applying heat to adsorbent bed and forcing desorption of vapor.
SUMMER MODE
TEST CONDITIONS
RESULTS
INTRODUCTION
Arjun Venkataramanan Carlos Rios Perez Carlos Hidrovo Malcolm Leclair
CONCLUSION • •
•
WINTER MODE •
r
At low pressures, Rohsenow correlation for scored copper tube clearly under predicts the performance of evaporator. Tube 2 with larger surface area than tube 1 performs better as the mode of heat transfer at such low superheats was predominantly evaporation rather than boiling. Large fluctuations in heat flux and superheats observed during experiments suggests the need for an improved experimental set up. More accurate assessment of the evaporator thermal performance requires testing the full scale prototype.
r
REFERENCES ATB
REGENERATION MODE Figure 2 Variation of evaporation/boiling heat flux with respect of the wall superheat. Results in this figure correspond to a TURBO-Chill® (Tube 1) and a S/T Trufin® (Tube 2) from Wolverine Tube, Inc. Results from the Rohsenow correlation for a scored tube surface are also included for comparison. Also, best fitting trend line of the Tube 2 results using a third order polynomial approximation are shown as ‘Average Model’. Last, lowest heat flux values for a superheat between 4 and 7 °C were used to determine the ‘worstcondition scenario’ for evaluation of the heat exchanger thermal performance.
[1] Ashley Steven(2013) Adsorption-based thermal batteries could help boost EV range by 40%. Automotive Engineering Magazine http://articles.sae.org/12376/ [2] Barlett,Jeff (2012) Survey: Consumers express concerns about electric, plug-in hybrid cars. Consumer Reports http://www.consumerreports.org/cro/news/2012/01/surveyconsumers-express-concerns-about-electric-plug-in-hybridcars/index.htm
