Here are some definitions from Hemminger and Hohne, "Calorimetry."
5.1 Isothermal Operation In isothermal operation, the surroundings and the measuring system have the same constant temperature, i.e. TF = TM = constant (Fig. 5-1). In the thought experiment, conducted in phenomenological thermodynamics, the isothermal state is established by having the system exchange heat via an infinitesimally low thermal resistance with surroundings of infinite heat capacity. This is not feasible in calorimetry. Consequently, isothermal operation necessitates a compensation of the heat flux released from the sample. . . . 5.2 Isoperibol Operation The term "isoperibol operation" refers to the use of a calorimeter at constant temperature surroundings with a possibly different temperature of the measuring system. The thermal resistance Rth between the measuring system and the surroundings is infinitesimally small in isothermal calorimeters, of finite magnitude in isoperibol calorimeters (Fig. 5-1) and infinitely large in adiabatic ones . . . Examples of lsoperibol Calorimeters. a classic liquid calorimeter or a heat flux calorimeter, each equipped with a thermostat as surroundings. . . . 5.3 Adiabatic Operation Calorimeters can also be operated in an adiabatic manner. In this case, under ideal circumstances, no heat exchange whatsoever occurs between measuring system and surroundings. There are three ways of meeting this requirement as satisfactorily as possible. I. The sample reaction takes place so rapidly that no appreciable quantity of heat can leave or enter during the measuring interval. 2. The measuring system is separated from the surroundings by an "infinitely large" thermal resistance, i.e. thermally insulated in the best possible way. 3. The temperature of the surroundings is so controlled as to be always equal to that of the measuring system, i.e. TF(t) = TM(t). The various modes of operation of calorimeters will be outlined below. Isothermal (TM = TF = constant) Calorimeters involving compensation of the thermal effect by phase transition or thermoelectric effects. Isoperibol (TF = constant, TM = TM(t)) Calorimeters involving the measurement of a time-dependent temperature difference (liquid calorimeters) or local temperature difference (flow calorimeters, heat flux calorimeters), or involving compensation of the thermal effect by thermoelectric effects in a scanning operation. Adiabatic (TM = TF) Calorimeters for the measurement of a time-dependent temperature difference (liquid calorimeters) or involving a compensation of the thermal effect by thermoelectric effects in a scanning operation.
