ABSTRACT
Heat exchangers without phase change(s) are sometimes employed as refrigerant desuperheaters, internal heat exchangers (IHEs) and air- or water-cooled refrigerant sub-coolers in mechanical vapor compression heat pump-assisted wood dryers. In industrial processes, heat exchangers without phase change(s) used for cooling and/or heating are usually classified according to their flow arrangement and type of construction. Two basic methods are used to size, analyze, or select heat exchangers: the logarithmic mean temperature difference (LMTD) method, and the effectiveness-number of transfer units (effectiveness-NTU) method. In the most simple concentric (double) tube heat exchangers without phase changes, the hot and cold fluids move in the opposite (counter-flow) directions or in the same (parallel-flow) direction. The mean temperature difference between the two fluids is used because the temperature difference is variable from one place to another in the exchanger.
