25
Tw: The cooling liquid temperature at the engine outlet.
Ta: The ambient temperature.
Tia: The cooling air temperature before getting into the inter-cooler and water tank.
Tia=Ta+Δt Δt: Temperature rise of cooling air before getting into the engine and generator. Generally,
Δt equals to 4-7℃.
Herein, ATB=air inlet temperature -Δt; Under standard environment, ATB of diesel engines at power
station is no less than 50℃.
(3) The pressure cap of water tank and expansion water tank
The pressure cap can increase the boiling temperature of cooling liquid, which is especially important
for operation in high-temperature and high-altitude regions. The impact of the pressure of the pressure
cap on the boiling point of cooling liquid is illustrated in the table below.
0
500
1000
2000
3000
4000
101
95
89
79
69
61
100
98
96
93
90
86
112
110
109
107
105
103
115
114
113
111
109
107
Altitude-m
Barometric
pressure-kPa
Boiling point
of water-
℃
Boiling point of 50kPa
pressure cap-
℃
Boiling point of 70kPa
pressure cap-
℃
The expansion water tank can increase the expansion volume of cooling liquid for the cooling system,
separate air from the cooling liquid, maintain a static pressure at the water inlet of the coolant pump and
prevent cavitation erosion for water pump. The expansion water tank can be isolated from the diesel
engine or installed in the upper water chamber of radiator tank.
(4) Design of the cooling system
To improve the cooling efficiency and performance, the design of the cooling system should be carried
out in accordance with the following principles:
① At rated speed, there should be a static pressure at the inlet of the engine water pump. In the case that
a cooler is required in front of the water pump inlet, the negative pressure of the inlet should not exceed
2kPa.
② Ensure that the diameter of the fan is equal to the width or height of the water tank so that the fan can
cover the area of the water tank as much as possible. There needs to be an appropriate distance between
the fan and the water tank, which should not be less than 50mm. The clearance between these two parts
must be within 15-25mm (as small as possible). Excessively large clearance may give rise to backflow
of hot air and reduce the cooling performance.
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