CONCLUTIONS
A bubble expansion valve system has been shown to reduce the temperature difference by more than 50% in comparison with a conventional system with a direct expansion valve.
At the same time the heat transfer effect in the evaporator has improved, which means that the efficiency of the heat transfer, expressed as average heat transfer rate increased from 616Wm2 K to 1579Wm2 K or even to 245 % after the modification to a flooded evaporator system. The improved use of the
CONCLUTIONS
A bubble expansion valve system has been shown to reduce the temperature difference by more than 50% in comparison with a conventional system with a direct expansion valve.
At the same time the heat transfer effect in the evaporator has improved, which means that the efficiency of the heat transfer, expressed as average heat transfer rate increased from 616Wm2 K to 1579Wm2 K or even to 245 % after the modification to a flooded evaporator system. The improved use of the evaporator surface may be attributed to one or more of the following factors:
• The need for overheating has been eliminated, resulting in a significantly higher heat transfer rate and smaller temperature differences in the evaporator. (Prof Dr.-Ing. Michael Kauffeld)
• The need of superheating is eliminated which may reduce the sensitivity of the uneven distribution of refrigerant flow between the parallel refrigerant channels of the plate heat exchanger. Distortion is considered to be a common cause of loss of performance for this type of evaporator. (Stefan S. Jensen)
• The proportions between the refrigerant gas and liquid in the evaporator, is a higher amount of gas in the direct expansion than in the flooded evaporator system. Results reported in the scientific literature show that the heat transfer rate at flooded evaporator in many cases has a maximum for gas/liquid proportion around 70/30. (T.N.Tran , M.W.Wambganss) (Raja Balakrishnan,Mohan Lal Dhasan) (C.K Rice Ph.D)
• Mass flow rate of refrigerant in the flooded evaporator is higher because of the recirculation of the refrigerant. Higher mass flow generally increases the heat transfer rate with flooded evaporator. (T.N.Tran , M.W.Wambganss)
• At parallel flow couple of the evaporator with a small glide medium and with significant pressure drop, a more even temperature profile through the evaporator is obtained. Moreover, the refrigerant is evaporated more effective with increasing temperature-differences at the evaporators inlet and liquid / gas proportion decreases faster (motive see curve fig 2 )
• Positively surface concentration of oil in the evaporator will be changed when switching from a direct expansion system to a flooded evaporation system. This change affects the thermal transition positively, not only in the superheating area of the evaporator. (J. Fei, W. Y. Hu, Z. M. Wang)
Heat exchangers and compressor had original configuration during the tests .The flooded system showed better cooling effect (+16 %) and heating effect (+10%) than the original model.
A completely fair comparison had demanded a smaller electric motor and compressor model for the bubble expansion valve system. This had increased the energy efficiency ratio difference even more in favour of the bubble expansion valve system.
(Ericsson Svenning Palm Björn (measured data) Bilaga 1 ”korrigerad kyleffekt”= cooling effect)
A bubble expansion valve system has been shown to reduce the temperature difference by more than 50% in comparison with a conventional system with a direct expansion valve.
At the same time the heat transfer effect in the evaporator has improved, which means that the efficiency of the heat transfer, expressed as average heat transfer rate increased from 616Wm2 K to 1579Wm2 K or even to 245 % after the modification to a flooded evaporator system. The improved use of the evaporator surface may be attributed to one or more of the following factors:
• The need for overheating has been eliminated, resulting in a significantly higher heat transfer rate and smaller temperature differences in the evaporator. (Prof Dr.-Ing. Michael Kauffeld)
• The need of superheating is eliminated which may reduce the sensitivity of the uneven distribution of refrigerant flow between the parallel refrigerant channels of the plate heat exchanger. Distortion is considered to be a common cause of loss of performance for this type of evaporator. (Stefan S. Jensen)
• The proportions between the refrigerant gas and liquid in the evaporator, is a higher amount of gas in the direct expansion than in the flooded evaporator system. Results reported in the scientific literature show that the heat transfer rate at flooded evaporator in many cases has a maximum for gas/liquid proportion around 70/30. (T.N.Tran , M.W.Wambganss) (Raja Balakrishnan,Mohan Lal Dhasan) (C.K Rice Ph.D)
• Mass flow rate of refrigerant in the flooded evaporator is higher because of the recirculation of the refrigerant. Higher mass flow generally increases the heat transfer rate with flooded evaporator. (T.N.Tran , M.W.Wambganss)
• At parallel flow couple of the evaporator with a small glide medium and with significant pressure drop, a more even temperature profile through the evaporator is obtained. Moreover, the refrigerant is evaporated more effective with increasing temperature-differences at the evaporators inlet and liquid / gas proportion decreases faster (motive see curve fig 2 )
• Positively surface concentration of oil in the evaporator will be changed when switching from a direct expansion system to a flooded evaporation system. This change affects the thermal transition positively, not only in the superheating area of the evaporator. (J. Fei, W. Y. Hu, Z. M. Wang)
Heat exchangers and compressor had original configuration during the tests .The flooded system showed better cooling effect (+16 %) and heating effect (+10%) than the original model.
A completely fair comparison had demanded a smaller electric motor and compressor model for the bubble expansion valve system. This had increased the energy efficiency ratio difference even more in favour of the bubble expansion valve system.
(Ericsson Svenning Palm Björn (measured data) Bilaga 1 ”korrigerad kyleffekt”= cooling effect)
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By shecco , published Nov 04, 2016 - 0 pages
By shecco , published Nov 04, 2016 - 0 pages