Closed fluid system maintains a constant temperature in an insulated region without the use of any moving parts. Within the system, the energy for thermodynamic cycling of two-phase heat transfer fluid and a hydraulic fluid is entirely supplied by the heat generated in the thermally insulated region

Stenger, F. J.

English

NASA Technical Reports Server

Thermal 
Heat 
Control Fluic 
Capsule 
Bellows 
Hydraul 
Fluid C 
November 1965	 Brief 65-10331 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Closed Fluid System Without Moving Parts Controls Temperature 
The problem: To provide a reliable, lightweight 
system that will maintain a constant temperature in 
an insulated region, without requiring the use of 
mechanical pumps, thermostatic control valves, slid-
ing or rotating seals, or a source of electrical power. 
The solution: A closed fluid system in which the 
energy for thermodynamic cycling of two-phase heat 
transfer fluids and a hydraulic (one-phase) fluid is
entirely supplied by the heat generated in a thermally 
insulated region to be maintained at a constant 
temperature. 
How it's done: The system incorporates a capillary 
pumped heat transfer loop containing (I) a fluid 
reservoir with a bellows (expandable bladder) to 
separate working fluid A from hydraulic fluid C, and 
As
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19650000329 2020-03-11T17:21:07+00:00Z
(2) a control fluid B capsule with a bellows to sepa-
rate fluid B from fluid C. The evaporator portion of 
the capillary pumped heat transfer loop (containing 
wick material) is enclosed in the insulated region 
to be maintained at constant temperature. 
The curve representing a plot of the saturated vapor 
pressure of fluid A versus temperature must have a 
sharper slope than the corresponding curve for fluid 
B. The control-temperature band of this system will 
then lie within a few degrees above the crossover 
temperature (the point of intersection between the 
saturated vapor pressure/temperature curves of 
fluids A and B). Water and one of the halogenated 
hydrocarbons are examples of fluids which have cross-
over characteristics required of fluids A and B, re-
spectively. The hydraulic fluid C transfers the volume 
changes between fluids A and B and must have a 
relatively low vapor pressure in the vicinity of the 
crossover point. 
In operation of the system, the evaporator absorbs 
heat generated in the insulated region and vaporizes 
fluid A from the surface of the evaporator wick. The 
resultant vapor passes into an external condenser 
where it gives up its latent heat to the surrounding 
heat sink. The condensate (fluid A liquid) flows from 
the condenser into thç inner feed tube of the evapora-
tor and is pumped by capillary action to the surface 
of the wick, from which it evaporates to begin a 
new heat transfer cycle. 
Under the conditions of dynamic equilibrium within 
the system, the pressure of the fluid at the junction 
of the fluid A reservoir and the liquid feed tube will
tend to be equal to the pressure in the fluid B capsule, 
and the temperature of this capsule will approach the 
temperature of the evaporator walls. These pressure 
and temperature requirements can be simultaneously 
satisfied only when the temperature of the evaporator 
and fluid B capsule is a few degrees above the cross-
over temperature. The system will automatically seek 
and maintain a temperature (within the temperature-
control band at the crossover point) that will satisfy 
both the dynamic heat rejection and internal pres-
sure requirements. 
Notes: 
1. The bellows used to separate the fluids and pro-
vide for volume changes must have a negligible 
pressure resistance to volume change. 
2. The control fluid may be a mixture of two or more 
fluids (used in conjunction with appropriate work-
ing and hydraulic fluids) to permit the system to 
adjust to any desired operating temperature within 
a wide range of temperatures. 
3. Enquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio, 44135 
Reference: B65-10331 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about 
obtaining rights for its commercial use may be made 
to NASA, Code AGP, Washington, D.C., 2054 
Source: Francis James Stenger 
(Lewis-222) 
Brief 65-10331	 Categories 02, 05


Closed fluid system without moving parts controls temperature

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