Industrial heat pump using fluid mixture.

High temperature heat pumps are required for industrial usage for energy savings and CO2 emission reduction. A hybrid cycle which uses the principles of absorption and compression was studied. There are two types of absorption/compression hybrid cycles, categorized by their origins. The hybrid cycle studied here is the one developed from the compression cycle, and it has almost the same components as the compression one. Water and glycerol mixture was supposed as a working fluid. The temperature difference between the boiling points of the two fluids is large, so the temperature gradient will be large in the heat exchangers. The systems of the two types were examined in the chart analysis; the system without an internal heat exchanger and the system with an internal heat exchanger. In the usage typical in the conventional compression heat pumps, that the heat is transferred from the low temperature to the high temperature with a certain temperature lift, the system without an internal heat exchanger shows a moderate COP. The system with an internal heat exchanger can realize the large temperature lift with small compression ratio and low working pressure, but the irreversible work at the heat exchanger will be large and the merit superior to the system without an internal heat exchanger will be canceled. This large loss at the internal heat exchanger is caused by the characteristic of the curves of the gas line and the liquid line, resulting in the disagreement of the temperature difference between the inlet and the outlet of the internal heat exchanger. The promising application of the absorption/compression system is for the system in which both the heat source and the heat sink have temperature gradients. One example is the materials heating and products cooling. The second example is a pinch point cancelation. Near the pinch point, both high temperature and low temperature fluids have the temperature gradient and the temperature lift by the heat pump will be relatively small.

为实现节能与二氧化碳减排目标，工业应用场景亟需高温热泵（High temperature heat pumps）。本文针对融合吸收式与压缩式工作原理的混合循环开展研究。按起源可将吸收压缩式混合循环分为两类，本次研究的混合循环源自压缩式循环，其组成部件与压缩式循环基本一致。本次研究选用水甘油混合物作为工质（working fluid）：由于两种流体的沸点温差较大，换热器内的温度梯度也将随之增大。研究人员通过图解分析法对两类系统进行了考察：无内部换热器（internal heat exchanger）的系统，以及搭载内部换热器的系统。在传统压缩式热泵的典型应用场景中，即热量以一定温度升幅从低温侧传递至高温侧时，无内部换热器的系统可获得适中的性能系数（Coefficient of Performance，COP）。搭载内部换热器的系统可在较低压缩比与工作压力下实现较大温度升幅，但换热器内的不可逆功损耗较大，最终其相较于无内部换热器系统的优势将被抵消。内部换热器的此类高损耗源于汽体管路与液体管路的曲线特性，导致内部换热器入口与出口处的温度匹配度不佳。吸收压缩式混合循环的理想应用场景为热源与热沉均存在温度梯度的工况，例如物料加热与产品冷却；其二为夹点（pinch point）消除场景：在夹点附近，高低温流体均存在温度梯度，热泵所需实现的温度升幅相对较小。