314 
y ty) 
0 -40 -30 -20 -10 °C 
Fic. 7—Correlation of the vaporizer tempera- 
ture ¢y with the measuring-section temperature 
ty , at different air speeds vy , and as a function 
of the energy value Qj), added between the 
vaporizer and the measuring section through hu- 
midity or heating 
that the performance of the tunnel decreases as 
the vaporizer temperature goes down, but tends 
toward a higher value as the air-speed falls. For 
this procedure it is tacitly assumed that the 
energy added through humidity is equivalent 
to, and interchangeable with, the energy added 
through heating. 
Although the vaporizer temperature is decisive 
for regulating the system, we are interested here 
rather in the measuring-section temperature ty. 
The conversion of these two values is done ac- 
cording to the expression 
Qvar + Oru 
ty =ty + = = (1) 
= : pi Py-Va-er 
The meaning of the individual symbols is as fol- 
lows: 
tw = the temperature in the measuring sec- 
tion, °C 
ty = the temperature of the vaporizer, °C 
Qian = the energy which is added to the air in 
the tunnel between the vaporizer and 
the measuring section through heating 
and humidity, keal/h 
Onn = cold losses between the vaporizer and 
the measuring section, keal/h 
px = the density of the air, kg/m 
Fy = the sectional area of the tunnel in the 
measuring section, mm? 
vm = the air speed in the measuring section, 
m/h 
cy, = the specific heat of the air, keal/kg® 
ROLAND LIST 
The value Qya can be measured experimen- 
tally, so long as the value Onn is not involved. 
Corresponding values are entered in Figure 7 as 
mean values for the air speeds in question. This 
presentation shows the connections in accordance 
with Eq. (1); it is used especially when the oper- 
ational point for the compressor, that is to say, 
an appropriate vaporizer temperature has to be 
determined on the basis of a desired measuring- 
section temperature ty, a given energy value 
Om present in the tunnel as a result, for example, 
of humidity, and a certain air speed vy . In prac- 
tice, one starts with the energy value (Onn and 
finds the point of intersection with the line rep- 
resenting the chosen speed (Fig. 7). What is then 
given is principally the degree to which the mea- 
suring-section temperature diverges from the va- 
porizer temperature. Additional choice of a ty 
value allows the operational point in the (ty , 
ty) —diagram to be fixed and the vaporizer tem- 
perature ty to be read off which is appropriate to 
the particular experiment. 
Before an experiment calculated in this way 
can be practicably carried out, it is necessary 
to establish whether the assumed amount of 
added energy can in fact be produced for the re- 
sultant vaporizer temperature. This information 
is given in Figure 6. 
Figure 8 shows the maximum performance of 
the tunnel as a function of the air speed with the 
parameter ty, , while Figure 9 gives similar cor- 
relations for the maximum water injection. (It 
was assumed here that the added water has a 
temperature of +10°C.) 
The effect of the heating apparatus provides 
other possibilities beyond improving our control 
over the tunnel. It enables the water content of 
the air in the measuring section to be substan- 
Lid reese ] 
2 mis 
Fig. 8—The maximum effective cold output 
Ly available for the experiment as a function of 
the air speed in the measuring section vy and at 
different measuring-section temperatures fs 
