Design of a Greenhouse Solar-Assisted Heat Pump Dryer for Kelp (Laminaria japonica): System Performance and Drying Kinetics

Abstract

In order to solve a series of problems with kelp drying including long drying time, high energy consumption, low drying efficiency, and poor quality of dried kelp, this work proposes the design of a novel greenhouse double-evaporator solar-assisted heat pump drying system. Experiments on kelp solar-assisted heat pump drying (S−HP) and heat pump drying (HP) under the condition of irradiance of 100−700 W/m2 and a temperature of 30, 40, or 50 °C were conducted and their results were compared in terms of system performance, drying kinetics, and quality impact. The drying time was reduced with increasing irradiance or temperature. The coefficient of performance (COP) and specific moisture extraction rate (SMER) of S−HP were 3.590−6.810, and 1.660−3.725 kg/kW·h, respectively, roughly double those of HP when the temperatures are identical. The Deff of S-HP and HP were 5.431 × 10−11~11.316 × 10−11 m2/s, and 1.037 × 10−11~1.432 × 10−11 m2/s, respectively; additionally, solar radiation greatly improves Deff. The Page model almost perfectly described the changes in the moisture ratio of kelp by S−HP and HP with an inaccuracy of less than 5%. When the temperature was 40 °C and the irradiance was above 400 W/m2, the drying time of S−HP was only 3 h, and the dried kelp maintained the green color with a strong flavor and richness in mannitol. Meanwhile, the coefficient of performance was 6.810, the specific moisture extraction rate was 3.725 kg/kWh, and the energy consumption was 45.2%, lower than that of HP. It can be concluded that S−HP is highly efficient and energy-saving for macroalgae drying and can serve as an alternate technique for the drying of other aquatic products.

Evaluation of the Performance of the ATESTA Forced Convection Dryer when Drying Pineapples

“…This represents a financial gain of 15% on the energy consumption of 1 kg of pineapple dried by the ATESTA forced convection dryer. The results are in line with those of (24) , who obtained an energy saving of 45.5% by using a heat pump (forced convection) in a solar dryer to dry kelp (Laminariale Japonica).…”

“…Forced convection improves hot air circulation, increases drying speed and improves dryer efficiency. The performance results recorded in Table 9 are in agreement with the work of (24) , who used forced convection to solve kelp drying problems similar to those of the ATESTA dryer with natural convection, including long drying time, high energy consumption, low drying efficiency and poor dried kelp quality. In addition to Kang's works (24) , (19) improved by 30.9%, 15.2% and 8.7%, respectively, the average daily efficiencies of the collector, dryer and photovoltaic panel of the solar drying system when drying tomatoes in forced convection mode.…”

A systematic review of drying in aquatic products

“…Recently, a solar‐assisted heat pump dryer was developed for kelp drying. It demonstrated that the modified HPD system is highly efficient and energy‐saving for macroalgae drying, the moisture content of 1.1 kg kelp reduced from 62.1% to 18% (wet basis) in 3 h at 40°C, and the dried kelp maintained the original colour with acceptable flavour 45 . Considering the production cost and product quality, HPD showed the potential for industrial application in aquatic products.…”

“…It demonstrated that the modified HPD system is highly efficient and energy-saving for macroalgae drying, the moisture content of 1.1 kg kelp reduced from 62.1% to 18% (wet basis) in 3 h at 40 C, and the dried kelp maintained the original colour with acceptable flavour. 45 Considering the production cost and product quality, HPD showed the potential for industrial application in aquatic products. In the meanwhile, hydrocolloid coating and ultrasound are promising pretreatments in improving HPD efficiency and enhancing the quality attributes of dried aquatic products.…”

A Review on Solar Drying Devices: Heat Transfer, Air Movement and Type of Chambers

“…The aim of installing a heat pump is to solve the problem of the intermittent availability of solar radiation. Depending on weather conditions, four working modes can be chosen [163][164][165][166][167][168][169][170][171][172][173][174]: Solar energy heating mode, when solar radiation is sufficient during the daytime; Heat pump heating mode when solar radiation is unavailable; Solar-assisted heat pump heating mode, when solar radiation is insufficient during the daytime; Heat pump dehumidification mode when ambient humidity is high. Beyond all the drying designs associated with heat pump systems, some authors also consider solar systems with chemical heat pumps (CHP) and solar systems with dehumidification systems [13].…”