Discussion: “On the Dynamics of Steam Liquid Heat Exchangers” (Hempel, Arvid, 1961, ASME J. Basic Eng., 83, pp. 244–251)

Results of an experimental study with a support of DRET (France) of two designs of liquid heat exchangers made of multi-channel aluminium tubes are presented with the objective to develop a fuel-oil recuperator, compact and light (less than 3 Kg). It was demonstrated that the application of a combined approach to heat exchange enhancements using three-dimensional turbulators as semi-spherical craters and bulges on channel walls of internal paths allows to increase the specific heat output of the heat exchanger from 10.5 to 13.3 kW/kg.

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On the Dynamics of Steam Liquid Heat Exchangers

Journal of Basic Engineering ◽

10.1115/1.3658935 ◽

1961 ◽

Vol 83 (2) ◽

pp. 244-251 ◽

Cited By ~ 11

Author(s):

Arvid Hempel

Keyword(s):

Frequency Response ◽

Heat Exchangers ◽

Transfer Functions ◽

Liquid Velocity ◽

Amplitude Ratio ◽

Analog Computer ◽

Phase Lag ◽

Liquid Temperature ◽

Response Measurement ◽

Liquid Heat

The aim of the present work has been to present relatively simple transfer functions for steam/liquid heat exchangers, relating outlet liquid temperature to variations in, respectively, the steam temperature, the liquid velocity, and the inlet liquid temperature. The transfer functions are first obtained from the partial differential equations of the system and then simplified. From the simplified expressions the transient response can readily be obtained and, in addition, they are of a form easily simulated on an analog computer. Experimental frequency response data are provided. An analog computer proved useful in analyzing phase lag and amplitude ratio in the frequency response measurement.

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Experimentally Verified Transient Models of Data Center Crossflow Heat Exchangers

Volume 10: Micro- and Nano-Systems Engineering and Packaging ◽

10.1115/imece2014-36022 ◽

2014 ◽

Cited By ~ 5

Author(s):

Tianyi Gao ◽

Bahgat Sammakia ◽

James Geer ◽

Milnes David ◽

Roger Schmidt

Keyword(s):

Heat Exchanger ◽

Data Center ◽

Heat Exchangers ◽

Distribution Systems ◽

Data Centers ◽

Computational Time ◽

Cooling Systems ◽

Rear Door ◽

Compact Models ◽

Liquid Heat

Heat exchangers are key components that are commonly used in data center cooling systems. Rear door heat exchangers, in-row coolers, overhead coolers and fully contained cabinets are some examples of liquid and hybrid cooling systems used in data centers. A liquid to liquid heat exchanger is one of the main components of the Coolant Distribution Unit (CDU), which supplies chilled water to the heat exchangers mentioned above. Computer Room Air Conditioner (CRAC) units also consist of liquid to air cross flow heat exchangers. Optimizing the energy use and the reliability of IT equipment in data centers requires Computational Fluid Dynamics (CFD) tools that can accurately model data centers for both the steady state and dynamic operations. Typically, data centers operate in dynamic conditions due to workload allocations that change both spatially and temporally. Additional dynamic situations may also arise due to failures in the thermal management and electrical distribution systems. In the computational simulation, individual component models, such as transient heat exchanger models, are therefore needed. It is also important to develop simple, yet accurate, compact models for components, such as heat exchangers, to reduce the computational time without decreasing simulation accuracy. In this study, a method for modeling compact transient heat exchangers using CFD code is presented. The method describes an approach for installing thermal dynamic heat exchanger models in CFD codes. The transient effectiveness concept and model are used in the development of the methodology. Heat exchanger CFD compact models are developed and tested by comparing them with full thermal dynamic models, and also with experimental measurements. The transient responses of the CFD model are presented for step and ramp change in flow rates of the hot and cold fluids, as well as step, ramp, and exponential variation in the inlet temperature. Finally, some practical dynamic scenarios involving IBM buffer liquid to liquid heat exchanger, rear door heat exchanger, and CRAC unit, are parametrically modeled to test the developed methodology. It is shown that the compact heat exchanger model can be used to successfully predict dynamic scenarios in typical data centers.

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