Precision Temperature Control of High-Throughput Fluid Flows: Theoretical and Experimental Analysis

Abstract

A precision method for attenuating temperature variations in a high-throughput control fluid stream is described and analyzed. In contrast to earlier investigations, the present study emphasizes heat transfer analysis of the constituent control device and derives theoretical descriptions of system responses to time-varying fluid temperatures. Experiments demonstrate that the technique provides: (1) frequency-dependent attenuation which is several orders of magnitude greater than that obtained via a perfect mixing volume; (2) attenuation, over two decades of disturbance frequency, that reduces in-flow temperature variations by factors ranging from 10 to ≈104; (3) asymptotic attenuation greater than three orders of magnitude for spectral components having periods less than the device thermal equilibrium time; and (4) attenuation which is fully consistent with theoretical predictions. The model developed provides design criteria for tailoring system performance. In particular, it is shown that for a given control stream flow rate, the magnitude of maximal attenuation can be adjusted by varying the thermal resistance between the flow and attenuating medium, while the range of frequencies maximally attenuated can be adjusted by varying the product of thermal resistance and attenuating medium heat capacity. The analysis and design are general and should prove useful in the design and analysis of other high-throughput precision temperature control systems.

Direct contact packed bed thermal gradient attenuators: Theoretical analysis and experimental observations

“…As in the earlier investigation, 1 which focused on large, noncontact tube-in-shell attenuators, theoretical heat transfer and system models lead to unambiguous and readily implemented criteria for designing packed bed attenuators. Together, the results of the present and previous 1 investigations should provide a useful basis for designing and analyzing large and small, contacting and noncontacting thermal gradient attenuators.…”

“…Thermal gradient attenuators comprise a key element in precision temperature control systems, [1][2][3] and are designed to attenuate thermal spectral components in fluid control streams that exceed a nominally defined minimum frequency, f min . Temperature oscillations slower than f min pass through for compensation by low-bandwidth heater controllers.…”

“…Recent work 1 has focused on theoretically and experimentally characterizing large tube-in-shell attenuators in which the chilled water control stream passed through a bank of plastic tubes immersed in a large, stagnant volume of water, where the latter served as the attenuating medium. A closed-form, lumped-differential heat transfer model of the system was shown to accurately predict system performance over more than two decades of disturbance frequency and over a wide range of control stream flow rates.…”

“…Techniques for obtaining precision temperature control near room temperature fall into one of three broad classes: methods that employ resistive heaters to maintain a small enclosure near ambient, [3][4][5][6][7][8][9][10] methods that use a stagnant fluid to heat or cool an enclosure, [11][12][13][14] and techniques that rely on a recirculating fluid stream to maintain control of the temperature. 1,[15][16][17][18] See Ref. 1 for a brief overview.…”

“…Surprisingly, little theoretical work has been carried out to support the design and development of precision temperature control devices. 1,19,20 Although formulation of accurate, predictive thermal and system models can be difficult, 5,19 and has led to development of various anecdotal criteria for designing thermal control devices, the potential advantages of formulating such models are significant: ͑i͒ existing devices can be tuned to meet specific performance requirements, ͑ii͒ potential designs can be tested theoretically prior to construction, ͑iii͒ methods for improving device performance can be unambiguously determined and implemented, and ͑iv͒ system behavior can be interpreted and modified or controlled as needed.…”