Roman letter symbols


V capacitance ratio

for studying heat exchanger transient characterization are introduced, and a detailed analytical, numerical, and experimental study of these models is presented. Mathematical models, analytical and numerical analysis, experimental testing, and validating studies provide a better understanding of the transient effectiveness methodology. It is shown that the transient effectiveness methodology is very useful for thermal dynamic characterization of heat exchangers and the development of compact/CFD transient models. In addition, it is found that methodology is also

The transient effectiveness curves represent both the heat exchanger dynamic behavior and the corresponding boundary conditions on a single curve. It depicts the heat exchanger transient response in a more comprehensive manner, when compared with outlet temperature curves. The transient effectiveness methodology is shown to be useful for characterizing the thermal capacitance effects of the entire system, as well as each component, during transient events. The transient effectiveness curves clearly capture the transient response and the impact of

Two CFD compact modeling methodologies are developed and validated, namely a full transient effectiveness methodology and a partial transient effectiveness methodology. These two compact models are accurate and fast, and can be integrated into large scale models, such as

The authors would like to state that the majority portion of this chapter was taken from

/m

useful for analyzing cooling system transient experimental results.

thermal capacitance on each heat exchanger unit.

216 Heat Exchangers– Design, Experiment and Simulation

previously published work by the same group of authors.

system/building level models.

Acknowledgements

Roman letter symbols

cp fluid specific heat, J/kg�K

Cmin minimum capacity rate fluid Cmax maximum capacity rate fluid

k thermal conductivity, W/m�K L length of heat exchanger, m

m\_ mass flow rate, kg/s

NTU number of transfer units

R conductance ratio, (hA)h/(hA)<sup>c</sup> r mass flow rate variation ratio, r = m<sup>0</sup>

T dimensionless temperature

Cwall specific heat of the wall of HX, J/kg�K

E heat capacity rate ratio, (mcp)h/(mcp)c

M mass of the wall (core) of heat exchanger, kg

NTU<sup>0</sup> time dependent NTU due to mass flow rate variation

Nomenclature

D dimension

