Eclipse Engineering Guide

II. Spray Washers
Three methods are presented for calculating spray
washer heat requirements. The first is the most accurate,
making use of detailed heat loss factors. The
other two are rule-of-thumb methods. While not as
accurate as method A, they are useful for quickly
estimating burner inputs.
A. Heat Loss Method
1.Data required:
Gpm capacity of spray nozzles
Height & width of washer housing (hood)
Height & width of opening through which
work passes
Liquid pressure head
Liquid temperature
Location of stage in washer
2.Heat Loss factors
From Table 2, find the heat loss factors for
housing height opening width
housing width liquid pressure
opening height liquid temperature
Add all these factors together to get the combined
factor, f.
3.Stage location multiplier, M
Location Multiplier
Entrance Stage 1.75
Intermediate Stage 1.00
After a Cold Rinse 1.25
Exist Stage 1.50
4.Calculation of Gross Burner Input
Btu/hr = Gpm x 500 x f x M
This method yields gross burner input because
an immersion tube efficiency of 70% has
already been assumed in the heat loss factors.
Table 2. Spray Washer Heat Loss Factors
Housing Opening Liquid
Wide High Wide High Press. Temp.
Ft. f Ft. f Ft. f Ft. f PSIG f °F f
2 .7 1 .8 140 .4
3 .8 1 .3 2 .9 1 .5 5 .4 145 .5
4 .9 2 .4 3 1.0 2 .6 7.5 .5 150 .6
5 1.0 3 .5 4 1.1 3 .7 10 .6 155 .7
6 1.1 4 .6 5 1.2 4 .8 12.5 .7 160 .8
7 1.2 5 .7 6 1.3 5 .9 15 .8 165 .9
8 1.3 6 .8 7 1.4 6 1.0 17.5 .9 170 1.0
9 1.4 7 .9 8 1.5 7 1.1 20 1.0 175 1.3
10 1.5 8 1.0 9 1.6 8 1.3 22.5 1.2 180 1.6
11 1.6 9 1.1 10 1.7 9 1.5 30 1.4 185 1.9
12 1.7 10 1.2 11 1.8 10 1.7 32.5 1.6 190 2.2
13 1.8 11 1.3 12 1.9 11 1.9 35 1.8
14 1.9 12 1.4 13 2.0 12 2.1 37.5 2.0
15 2.0 13 1.5 14 2.1 13 2.3 40 2.2
16 2.1 14 1.6 15 2.2 14 2.5 50 2.6
17 2.2 100 3.5
48
B. Temperature Drop Rule of Thumb
1.Data required:
Gpm capacity of spray nozzles
Temperature of liquid
Tube efficiency (usually 70%)
2.Approximate temperature drop of water. Table
3 lists the approximate loss in water temperature
as it is sprayed onto the workload.
Table 3. Water Temperature Drop
Water Temperature
Temperature, °F Drop, °F
150 5
160 6
170 7
180 8
190 9
200 10
3.Calculation of gross burner input.
Btu/hr = Gpm x 500 x Temp Drop x 100
% Efficiency
4.Tank sizing
Tank capacity = 3 x Gpm spray capacity
C. Quick Method Rule of Thumb
Btu/hr gross burner input =
4000 x Gpm sprayed @ 30 psi x 100
% Efficiency
Capacities of spray nozzles are listed in Table 4.
Table 4. Capacities of Spray Nozzles
PSI Ft. Hd.
Gallons per minute of water through
a nozzle diameter of:
Press (Approx.) 1/4" 5/16" 3/8" 7/16" 1/2" 5/8" 3/4"
5 11.5 3.3 5.2 7.4 10.2 13.3 20.8 30.0
10 23.0 4.7 7.3 10.4 14.3 18.7 29.3 42.3
15 35.0 5.8 9.1 12.9 17.7 23.2 36.2 52.3
20 46.5 6.7 10.5 14.8 20.7 26.7 41.8 60.5
25 57.5 7.4 11.7 16.6 22.7 29.7 46.8 67.0
30 68.5 8.1 12.9 18.2 24.8 32.4 50.7 73.0
35 81.0 8.8 13.8 19.7 27.0 35.2 55.1 79.5
40 92.5 9.4 14.8 21.3 28.8 37.7 58.9 85.0
45 104.0 10.0 15.7 22.4 30.6 39.9 65.1 90.0
50 115.0 10.5 16.5 23.5 32.1 42.0 65.7 94.6
55 126.5 11.0 17.3 24.7 33.7 44.1 68.9 99.5
60 138.0 11.0 18.1 25.8 35.2 46.1 72.1 104.0
65 150.0 12.0 18.8 26.9 36.7 48.0 75.0 108.2
70 162.0 12.4 19.6 27.9 38.1 49.7 77.9 112.0
75 172.0 12.9 20.2 28.9 39.4 51.5 80.6 116.0
80 184.5 13.3 20.9 29.9 40.7 53.3 83.1 119.9
85 195.0 13.7 21.5 30.7 41.8 54.7 85.5 123.5
90 205.0 14.0 22.0 31.4 42.9 56.2 87.7 126.7
95 214.5 14.4 22.6 32.1 43.9 57.5 89.8 129.5
100 224.0 14.6 23.1 32.8 44.8 58.7 91.7 132.0
Above values are based on an orifice discharge coefficient of .80
ORIFICE FLOW EQUATION:
Q = 19.65 C D 2 H
WHERE:
Q = Gallons per minute
D = Diameter of orifice in inches
H = Pressure drop across orifice in feet head
C = Orifice discharge coefficient