Multiphysics version 5.3a

After the analytical analysis, a model was built-in COMSOL Multiphysics version 5.3a. A 2D-axisymmetrical geometry was built, the material properties were selected from the built-in library, a conjugate heat transfer module was selected in the physics and a stationary study was used. The analysis was done for a single pipe, this was done to assess the absorber performance without the interactions of the header, as the heat transfer in the header may cause stagnation regions [21 (link)]. The analysis, therefore, did not produce a complete schematic diagram and complete flow diagram of the counter-flow absorber connected to the header.
The energy extraction rate of the direct-flow and counter-flow absorber is analyzed with an absorber length of 1.5 m for all simulations. The ETC is required to attain medium temperature (140–200 $°C$ ), therefore analysis is done for an operating temperature range of up to 200 $°C$ . An analysis is made of temperature gain against flow rate at a varied uniform theoretical heat flux of 1000 W/m², 2000 W/m^2, and 3000 W/m².
The following assumptions were made:•

Steady-state conditions.

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There are no convective heat losses between the absorber and surroundings.

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The length of the pipe is long enough to assume a fully developed flow.

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Heat transfer and flow are both stable.

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No header interactions were considered.

For this model, we computationally examined a single fiber of a hepatic HF bioreactor utilizing T‐state PolyhHb as the O₂ carrier, which is shown in Figure 1. Both fluid flow and O₂ mass transport with reactions were computationally modeled using finite element methods in COMSOL Multiphysics version 5.3a (COMSOL Inc., Burlington MA). The model physics are unchanged from a recent publication.17 The HF radius, fiber length, flow rate, inlet O₂ concentration, cell density, and PolyhHb concentration were each varied to evaluate preferred bioreactor operating conditions.