Table 3.
Recent work conducted on heat pump drying of selected food products
| Researchers | Application(s) | Conclusions |
|---|---|---|
| Meyer and Greyvenstein (1992) (South Africa) | Grain | There is a minimum operating period that makes the HPD more economical than other dryers |
| Rossi et al. (1992) (Brazil) | Vegetable (onion) | Drying of sliced onions confirmed energy saving of the order of 30% and better product quality due to shorter processing time. |
| Mason and Blarcom (1993) (Australia) | Macadamia nuts | – |
| Strommen and Kramer (1994) (Norway) | Marine products (fish) | The high quality of the dried products was highlighted as the major advantage of HPD and introducing a temperature controllable program to HPD makes it possible to regulate the product properties such as porosity, rehydration rates, strength, texture and colour. |
| Prasertsan and Saen-saby (1998); Prasertsan et al. (1997) (Thailand) | Agricultural food drying (Bananas) | HPD is suitable for drying high moisture materials and the running cost of HPD is cheap making them economically feasible |
| Chou et al. (1998, 2001); Chua et al. (2000) (Singapore) | Agricultural and marine | The quality of the agricultural and marine products can be improved with scheduled drying conditions |
| Products (mushrooms, fruits, sea-cucumber and oyster) | ||
| O’Neill et al. (1998) (New Zealand) | Apple | Produces products with a high level of open pore structure and contributing to the unique physical properties |
| Strommen et al. (1999) | – | HPD with hydrocarbon and natural working fluids can save significant amounts of energy; ammonia was found most favorable refrigerant in the temperatures (30–80 °C). |
| Oktay et al. (2003) (Turkey) | Wool | The SMER was between 0.65 and 1.75 kg/kWh. COP was between 2.47 and 3.95. |
| Teeboonma et al. (2003) (Thailand) | Fruits (papaya and mango glace) | Developed and validated mathematical models; the effects of initial moisture content, cubic size and effective diffusion coefficient of products on the optimum conditions of HPD are also investigated. Exergy and energy analysis was made. |
| Kohayakawa et al. (2004) (Brasil) | Mango | The energy efficiency improved compared with an electrical resistance dryer |
| Hawlader et al. (2006) (Singapore) | Apple, guava and potato | Modified atmosphere heat pump dryer produced better physical properties. |
| Chegini et al. (2007) (Iran) | Plum | Optimum temperature of drying for plums is in vicinity of 70–80 °C; also SMER was notably more than conventional dryers. |
| Aktaş et al. (2009) (Turkey) | Apples | A system which is composed of the combination of both dryers is considered to be more efficient |
Daghigh et al. (2009)