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The plots in Fig. 3.17 show similar trends, meaning that the cooling COP increases with increase in cooling capacity in each case. However, the values of cooling COP for the simulation are much larger than those for the experimental data. This is because, the heat losses that are not considered are the dead volumes, bypass flow and the likes. Another reason that can be attributed to the high COP is that the thermal conduction term for the solid and fluid in which the temperature has a second-order dependence on distance is not considered in the energy balance. Although, this is justified by the fact that the thermal conductivity of the HTF is low, and that the model complexity increases, it may have an impact in the heat transfer between the solid and the HTF, resulting in a change in COP. The cooling COP is calculated by simply subtracting 1 from the calculated heating COP. Therefore, the work that is considered to be done is only that from the adiabatic magnetization. The work done by the other components of the heat pump like the pump for fluid flow and valve operation is not considered in the model. Therefore, this can also contribute to the high COP obtained in Fig. 3.17.
Therefore, the plots from Fig. 3.13 to Fig. 3.17 suggest that the model that has been developed for the regen- erator is highly optimistic compared to the experimental data. However, since the required trend is achieved in each of the plots, this model is used for the sensitivity analysis discussed in Chapter 4.
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