SOLAR ENERGY FOR WATER HEATING BROOKS 



167 



f day 



FiGDBH 5. — Observed temperatures and thermosiphon circulation in a five-pipe absorber 

 connected with a large storage tank, November 13 and 14, 1935, under a clear sky and 

 light wind. 



to the cooling of tlie absorber unit, which contains but little water. 



The rise in temperature of the water in the absorber pipe due to 

 the sun's heating depends primarily upon the length of time the water 

 remains in the absorber pipe. These factors act together so that an 

 automatic balance exists between the pipe friction and the force 

 available from the difference in water density due to heating. If the 

 sunshine suddenly becomes more intense, creating an excess in tem- 

 perature differential, the increased difference in water density pro- 

 vides more force to make the water flow faster ; and then it will be in 

 the absorber for a shorter time and will be warmed to a lower degree, 

 thus balancing any temporary temperature excess. 



Figure 5 shows the observed temperature differentials and rates of 

 circulation for a five-pipe absorber connected to a storage tank with 

 the hot circulation inlet 7i^ feet above the center of the absorbea*. 

 The rate of flow, curve J., was determined by the deflection of a vane 

 suspended in a horizontal glass tube, previously calibrated. 



Circulation begins slowly at 9 o'clock, gradually pushing the cold 

 water in the vertical riser into the tank. Then suddenly, an hour 

 later, a surge occurs when the hot water, too long in the absorber, 

 fills the vertical riser, while the very cold water due to night cooling 

 still fills the vertical part of the pipe from the tank to the bottom of 



