Abstract
Thermal-sprayed heat exchangers were tested at high temperatures (750 °C), and their performances were compared to the foam heat exchangers made by brazing Inconel sheets to their surface. Nickel foil was brazed to the exterior surface of 10-mm-thick layers of 10 and 40 PPI nickel foam. A plasma torch was used to spray an Inconel coating on the surface of the foil. A burner test rig was built to produce hot combustion gases that flowed over exposed face of the heat exchanger. Cooling air flowed through the foam heat exchanger at rates of up to 200 SLPM. Surface temperature and air inlet/exit temperature were measured. Heat transfer to air flowing through the foam was significantly higher for the thermally sprayed heat exchangers than for the brazed heat exchangers. On an average, thermally sprayed heat exchangers show 36% higher heat transfer than conventionally brazed foam heat exchangers. At low flow rates, the convective resistance is large (~4 × 10−2 m2 K/W), and the effect of thermal contact resistance is negligible. At higher flow rates, the convective resistance decreases (~2 × 10−3 m2 K/W), and the lower contact resistance of the thermally sprayed heat exchanger provides better performance than the brazed heat exchangers.
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Abbreviations
- \(A_{\text{b}}\) :
-
Area of base plate (m2)
- \(\alpha_{\text{sf}}\) :
-
Surface area density (m2/m3)
- \(c_{{{\text{p}}, {\text{air}}}}\) :
-
Specific Heat Capacity of air (J/kg k)
- \(\varepsilon\) :
-
Porosity (%)
- \(h_{\text{c}}\) :
-
Heat-transfer coefficient of air side (W/m2 k)
- H :
-
Height of the channel (m)
- K :
-
Thermal conductivity of air (W/m k)
- L :
-
Length of the channel (m)
- \({\dot{\text{m}}}_{\text{air }}\) :
-
Mass flow rate of air (kg/s)
- Q :
-
Heat transfer between hot and cold sections (Watt)
- \(R^{\prime\prime}_{\text{cont}}\) :
-
Resistance of the interface (m2 K/w)
- \(R^{\prime\prime}_{\text{conv}}\) :
-
Air-side resistance (m2 K/w)
- \(R^{\prime\prime}_{\text{cond}}\) :
-
Resistance of the material (m2 K/w)
- \(\Delta T_{{ {\text{lm}}}}\) :
-
Log mean temperature difference (K)
- \(T_{{ {\text{ai}}}}\) :
-
Temperature of air inlet (K)
- \(T_{{ {\text{ao}}}}\) :
-
Temperature of air outlet (K)
- U O :
-
Overall heat-transfer coefficient (W/m2 k)
- W :
-
Width of the channel (m)
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Hafeez, P., Yugeswaran, S., Chandra, S. et al. Fabrication of High-Temperature Heat Exchangers by Plasma Spraying Exterior Skins on Nickel Foams. J Therm Spray Tech 25, 1056–1067 (2016). https://doi.org/10.1007/s11666-016-0413-9
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DOI: https://doi.org/10.1007/s11666-016-0413-9