Handbook of air conditioning and refrigeration / Shan K

10.12 CHAPTER TEN
From the psychrometric chart, h ae � 31.6 Btu/lb and the enthalpy of saturated air film at evaporating
temperature T ev � 45°F is 17.65 Btu/lb. Then the total cooling capacity of the DX coil is
The cooling capacity is
� 60 � 5500 � 0.075 � 0.536(31.6 � 17.65) � 185,060 Btu/h (54,223 W)
MBtu/h�ft2 (58.36 kW/m 2 Aa � )
The enthalpy of the conditioned air leaving the DX coil hal is
185,060
� 18.5
10 � 1000
h al � h ae ��h � h ae ��(h ae � h s,r) � 31.6 � 0.536(31.6 � 17.65) � 24.1 Btu/lb (56 kJ/kg)
Draw a cooling and dehumidifying curve from the air entering condition, 80°F (26.7°C) dry-bulb
and 67°F (19.4°C) wet-bulb temperature on the psychrometric chart. Determine the air leaving condition
on the curve since h al � 24.1 Btu/lb (56 kJ/kg). From psychrometric chart, air leaves at
57.6°F (14.2°C) dry-bulb and 56.2°F (13.4°C) wet-bulb temperature with a relative humidity of 93
percent.
10.3 FLOODED LIQUID COOLER
Construction
Q c � 60V˙ s� a �(h ae � h s,r)
Q c
Most medium-size and large liquid coolers are shell-and-tube flooded liquid coolers. In a flooded
liquid cooler, several straight tubes are aligned in a parallel staggered arrangement, usually held in
place at both ends by tube sheets, as shown in Fig. 10.5a. Chilled water circulates inside the tubes,
which are submerged in a refrigerant-filled shell.
Liquid-vapor refrigerant, usually at a quality x around 0.15 in air conditioning applications, is
fed into the bottom of the shell. It is evenly distributed over the entire length of the tubes. As the refrigerant
boils and bubbles rise, the upper part becomes increasingly bubbly. Vapor refrigerant is
discharged from the opening at the top of the cooler. A dropout area, or eliminator, is sometimes installed
to separate the liquid refrigerant from the vapor. The amount of refrigerant fed to the flooded
liquid cooler is controlled by a low-pressure-side float valve, or a multiple-orifice throttling device,
which is discussed in Chaps. 11 and 13.
When halocarbons are used as the refrigerants, copper tubes are always used because they pro-
3 vide higher thermal conductivity and do not react with halocarbons. Tube diameters of �4 and 1 in.
(19 and 25 mm) are often used, such as either internally enhanced copper tubing of 1-in.- (25-mm-)
3 diameter or smooth bore of �4-in.
(19-mm) diameter, and the number of tubes inside the shell varies
from 50 to several thousand. Integral fins are extruded on the outer surface of the tubes to increase
the outer surface area. Other tube geometry on the outside surface is also used to enhance the boiling
heat-transfer coefficient, especially to coupling of a high-voltage and low current electric field
with the fluid field called electrohydrodynamics, and the boiling and condensing heat-transfer coefficient
may be increased in excess of tenfold. Fin spacing ranges from 19 to 40 fins/in. (0.6 to 1.3
fins/mm), typically 26 fins/in. (1 fin/mm) at a height from 0.06 in. (1.5 mm). The outer-to-inner
surface ratio of integral finned tubes ranges from 2.5 to 3.5. Spiral grooves or other enhancements
may be added to the inner surface of the tubes to increase the inner surface heat-transfer coefficient.
By increasing the turbulence, dirt and suspended solids are prevented from settling on the inner surface
during operation.
Possible water flow arrangements in flooded shell-and-tube liquid coolers are shown in
Fig. 10.5b. A one-pass arrangement has the highest chilled water flow rate, two-pass has a lower