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= Absorption heat transformer = An absorption heat transformer (AHT) is a device able to split a heat flow $$\dot Q_1 $$ at an intermediate temperature level $$T_1 $$ in two heat flows, $$\dot Q_2 $$ at a higher (revaluated) temperature level $$T_2 $$ and $$\dot Q_0 $$ at a lower temperature level $$T_0 $$ (rejection heat). Such a device is also denominated type II absorption heat pump or booster heat pump. Absorption heat transformers are especially suitable for heat recovery from industrial processes, its main advantage being the capacity to upgrade to a usable level the temperature of waste heat streams using only negligible quantities of electrical energy and no additional primary energy. The definition of the thermal coefficient of performance is
 * $$COP_{th} = \frac{\dot Q_2}{\dot Q_1}$$

Single effect heat transformers can increase the temperature of approximately 50% of the waste energy by approximately 50 K (depending on the boundary conditions). Single effect heat transformer is effectively a single effect absorption chiller working in reverse. It consists primarily of one condenser, one evaporator one absorber and one generator. The difference with absorption chiller is that the absorber and evaporator now operate at high pressure and the condenser and generator at low pressure. The most common working pairs are water/lithium bromide (refrigerant = water, absorbent = LiBr) and ammonia/water (refrigerant = ammonia, absorbent = water).

Process
In general an absorption heat transformer consists out of the absorber, generator, evaporator and condenser. In addition there are a refrigerant pump, solution pump, solution throttle and mostly included a solution heat exchanger to improve the efficiency. This process description applies to single stage absorption heat transformers using the working pair water/lithium bromide. At the evaporator the refrigerant evaporates driven by the heat flow at intermediated temperature level. The absorbent in the absorber absorbs the refrigerant vapour, while producing heat at high temperature level. This heat is the useful heat. Furthermore the absorbent is diluted while absorbing the refrigerant vapour. That diluted absorbent streams through the throttle in the generator. In the generator the absorbent desorbs the refrigerant also driven by the heat flow at intermediated temperature level. The refrigerant vapour is condensed in the condenser before the liquid refrigerant is pumped by the refrigerant pump into the evaporator. The concentrated absorbent is pump in to the absorber with the solution pump. The occurring heat at the condensore is mostly rejected to the ambient. More detailed information about absorption heat transformer and also absorption devices in general are given here.

Applications
This table shows absorption heat transformer applications in industrial processes. Next to the industrial applications there are some absorption heat transformers in research laboratories.