Heat Capacity Measurement by Flow Calorimetry: An Exact Analysis

The principal unsolved problem in flow calorimetry for liquid heat capacity measurement accurate accounting for heat loss from the heater lead-in wires as a junction of system properties is analyzed by exact procedures for a five-zone calorimeter model. Temperature distributions in the fluid. and bi-metal wire are obtained from solutions of the governing third-order ODE in the fluid temperature for realistic boundary conditions. Conductive heat losses at the fluid exit q(HL)/(q) over dot are large (up to 20% of energy input), and physical property and flow rate dependent. A new correlating equation for (q(HL)/(q)) over dot gives separately and explicitly, for the first time, its dependence on calorimeter characteristics, flow rates and fluid properties. Experiments on five pure liquids confirmed the predictions of the theoretical model and produced Cp values in close agreement with literature data. Fluid friction and small convection heat losses (U(i)A(i) (Delta T)(lm)) were accounted for experimentally. (C) 2008 American Institute of Chemical Engineers AIChE J, 55: 206-216, 2009