This study examines the performance of three heat pump dryers: the original reference design, a modified drying chamber, and an external desiccant wheel design. Unlike most existing studies that normally adopt organic products as the drying materials, in this study we used moist sodium polyacrylate (Orbeez) as the drying material for consistent characterization of the heat pump performance. R-134a was adopted as the refrigerant for the heat pump system. The experiments were performed subject to different weights of Orbeez (drying material) at a constant volumetric flow rate of 100 m³/h. During experimentation, different parameters like the coefficient of performance (COP_HP), drying rate, heat transfer rate by the condenser, moisture extraction rate, and specific moisture extraction rate were calculated. The average COP_HP, mass transfer rate, heat transfer rate, MER, and SMER of the system were calculated as 3.9, 0.30 kg/s, 0.56 kW, 0.495 kg/h, and 1.614 kg/kWh, respectively. The maximum COP for the refrigeration system was achieved at lower test loads with the desiccant wheel. The moisture extraction rate for a lower test loading was higher than that for a higher test load due to the higher penetration of drying air at the lower test load, although the maximum test load showed the maximum relative humidity at the dryer outlet. The desiccant wheel showed good performance in terms of moisture extraction rate and COP_HP, but it showed poor performance in terms of the specific moisture extraction rate due to the high power consumption (around 2.6 kW) of the desiccant dehumidifier. The moisture extraction rate (MER) for all designs increased to a maximum value, followed by consistent decline. However, the maximum MER for the desiccant design exceeded those for the other designs.

In this study, the vertically-oriented pulsating heat pipe (PHP) heat exchangers charged with either water or HFE-7000 in a filling ratio of 35% or 50% were fabricated to exchange the thermal energy between two air streams in a parallel-flow arrangement. Both the effectiveness of the heat exchangers and the thermal resistance of PHP with a size of 132 × 44 × 200 mm, at a specific evaporator temperature ranging from 55 to 100 °C and a specific airflow velocity ranging from 0.5 to 2.0 m/s were estimated. The results show that the heat pipe charged with HFE-7000 in either filling ratio is likely to function as an interconnected array of thermosiphon under all tested conditions because of the unfavorable tube inner diameter, whereas the water-charged PHP possibly creates the pulsating movement of the liquid and vapor slugs once the evaporator temperature is high enough, especially in a filling ratio of 50%. The degradation in the thermal performance of the HFE-7000-charged PHP heat exchanger resulted from the non-condensable gas in the tube became diminished as the evaporator temperature was increased. By examining the effectiveness of the present heat exchangers, it is suggested that water is a suitable working fluid while employing the PHP heat exchanger at an evaporator temperature higher than 70 °C. On the other hand, HFE-7000 is applicable to the PHP used at an evaporator temperature lower than 70 °C.

In order to effectively increase the drying rate and reduce the energy consumption, a dryer which reduces the air humidity at the dryer inlet using desiccant and regenerates the desiccant by recovering waste heat using a heat pipe heat exchanger was developed in this study. Both the adsorption rate and desorption rate of the dryer were measured at several ambient temperatures ranging from 15 °C to 35 °C, relative humidity levels of air ranging from 20% to 85%, and airflow rates ranging from 30 m³/h to 150 m³/h. The results showed that the adsorption rate in an environment of high relative humidity of air was 4.89 times higher than that of low relative humidity of air at 15 °C. Moreover, the difference in adsorption rate between two given relative humidity of air increased as the ambient temperature decreased. The specific energy consumption estimated with both energy consumption during desorption and the desorption rate indicated that the energy consumption was 8.27 kJ/g H₂O without using recovered heat, while the energy consumption was 4.77 kJ/g H₂O using recovered heat at 130 °C.

In this study, a one-dimensional heat transfer measurement device is developed based on the mathematical theory of the Angstrom method. To conform to the mathematical assumption, it is required that the device precisely controls the heat source to generate sinusoidal temperature signal. A thermo-electric module is used as the heat source for the measurement platform. This module is connected to a computer for program control, such that the temperature can be controlled quickly, precisely, and dynamically. In this study, five common heat-conducting materials are tested to verify the proposed one-dimensional heat transfer measurement device. By substituting the experimental results into the mathematical model of the Angstrom method, the thermal diffusion and thermal conductivity of the test material is calculated. The experimental results are compared with the physical properties of the materials, and the accuracy error is extremely low. This study confirmed that the Angstrom method theory applied thermal diffusivity and thermal conductivity measurement, which can be realized by thermo-electric temperature control technology.