## 2 Experimental Setup
### Integration of the Heat Exchanger into the KSU CSP Test Facility  
In order to evaluate the thermal performance of the heat exchanger, it has been integrated with the particle-based power tower CSP test facility located at the campus of KSU. The facility consists of a heliostat field (66 heliostats with 8 m\({}^{2}\) reflector area and 300 kW peak thermal power), a PHR on top of a tower, a particle lift (Olds Elevator), a PBHX, and a power block; more details about the facility can be found in [4,5]. It is noteworthy that the main purpose of this research facility is to demonstrate the applicability of using solar energy to decrease the dependency on fossil fuels; additionally, it provides an opportunity to evaluate the performance of each component in order to achieve the optimal operation, and to examine their durability as well. Figure 2 shows how the heat exchanger is connected to the components of the facility.  
The power block is a recuperated gas microturbine (air-Brayton cycle) with a nominal electrical power of 100 kW (it is called the T100). It has an external combustion chamber which is modified to admit hot compressed air from the PBHX in addition to burning diesel fuel. The heat exchanger is connected to the T100 through two air/power pipes (8 inch, sch 10) and the first pipe is connected to the recuperator's outlet, while the second is connected to the inlet of the combustion chamber (Figure 3) such that, the air leaving the recuperator enters the heat exchanger from the bottom, exchanges heat with particles flowing inside the tubes, leaves the heat exchanger from the top through the second air pipe, and then enters the combustion chamber. Each air pipe incorporates three expansion joints/bellows to accommodate for thermal expansion and absorb the lateral deflection; a counterweight system is installed to hold the air pipes.  
The particle inlet hopper of the heat exchanger is connected to the outlets of the PHR and the bypass line, such that two particle flow loops are achieved, namely the PHR loop and the bypass loop. The inlets of the PHR and the bypass line are connected to the outlet of the Olds Elevator, so particles can either go to the PHR and then to the heat exchanger or they can bypass the PHR and go directly to the heat exchanger. The process diagram of the particle and air loops is shown in Figure 2. The heat exchanger's particle outlet is connected to the Olds Elevator's inlet through the discharge cone. A 4-inch pipe is used  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Metric** & **Value** & **Unit** \\ \hline Thermal duty & 50 & kW \\ Design pressure & 3 & Barg \\ Particle inlet temperature & 650 & \({}^{\circ}\)C \\ Particle outlet temperature & 582 & \({}^{\circ}\)C \\ Air inlet temperature & 540 & \({}^{\circ}\)C \\ Air outlet temperature & 607 & \({}^{\circ}\)C \\ Air flow rate & 0.707 & kg/s \\ Particle flow rate & 0.7 & kg/s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Heat exchanger design conditions.  
to connect the discharge cone to the bottom hopper of the Olds Elevator. A knife valve is installed on this pipe to isolate the heat exchanger when needed.  
In order to minimize the heat loss, the components of the facility are heavily insulated; ceramic wool (1-inch thick), rock wool (3-inch thick), and glass wool (1-inch thick) have been used as insulation materials. The ceramic wool has a thermal conductivity of 0.152 W/m-K and an operating temperature of 1260 \({}^{\circ}\)C, while the rock wool is of 0.034 W/m-K thermal conductivity and 600 \({}^{\circ}\)C operating temperature. Each component is first wrapped with ceramic wool, and then rock wool and glass wool, respectively. Table 2 shows the number of layers used to insulate the facility components.  
Figure 2: Process diagram of particle and air loops.